Design Strategies for Personalized Ventilation

Ph.D. Thesis

by Radim Čermák

International Centre for Indoor Environment and Energy Department of Mechanical Engineering

Technical University of Denmark

ISBN: 87–7475–318–5

MEK-I-Ph.D. 04-02 July 2004 International Centre for Indoor Environment and Energy Department of Mechanical Engineering Technical University of Denmark Building 402, 2800 Kgs. Lyngby Denmark

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Table of content

Table of content .................................................................................................................................iii Preface .................................................................................................................................................. v Summary............................................................................................................................................vii Resumé ................................................................................................................................................ ix Nomenclature..................................................................................................................................... xi 1. Introduction..................................................................................................................................1

1.1 Background ...........................................................................................................................1 1.2 Principles of personalized ventilation ...............................................................................1 1.3 Design, installation, performance ......................................................................................3 1.4 Contaminants indoors .........................................................................................................7 1.5 Room air distribution...........................................................................................................9

1.5.1 Mixing ventilation ........................................................................................................9 1.5.2 Displacement ventilation...........................................................................................10 1.5.3 Underfloor air distribution........................................................................................14 1.5.4 Control strategies........................................................................................................16

1.6 Interaction of airflows........................................................................................................16

2. Objectives ...................................................................................................................................19 3. Method ........................................................................................................................................21

3.1 Experimental design ..........................................................................................................21 3.2 Air movement room...........................................................................................................24 3.3 Ventilation systems ............................................................................................................25

3.3.1 Personalized ventilation ............................................................................................25 3.3.2 Total-volume ventilation...........................................................................................26

3.4 Heat and contaminant sources simulation .....................................................................28 3.4.1 Heat sources ................................................................................................................28 3.4.2 Contaminant sources .................................................................................................28

3.5 Measuring Instruments .....................................................................................................30 3.5.1 Breathing thermal manikin .......................................................................................30 3.5.2 Artificial lung ..............................................................................................................31 3.5.3 Tracer-gas analyzer ....................................................................................................32 3.5.4 Low velocity anemometers .......................................................................................33

3.6 Procedure.............................................................................................................................33 3.6.1 Concentration measurement.....................................................................................33 3.6.2 Temperature and velocity measurements...............................................................35

3.7 Criteria for evaluation........................................................................................................36 3.7.1 Contaminant concentration.......................................................................................37 3.7.2 Temperature ................................................................................................................38 3.7.3 Velocity ........................................................................................................................39

3.8 Uncertainty of measurement ............................................................................................39

4. Personalized, mixing and displacement ventilation ..........................................................41 4.1 Objectives.............................................................................................................................41 4.2 Experimental conditions....................................................................................................41 4.3 Visualization of personalized airflow..............................................................................41 4.4 Inhaled air concentration...................................................................................................42

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4.5 Inhaled air temperature.....................................................................................................45 4.6 Thermal comfort of seated occupants..............................................................................47 4.7 Contaminant distribution..................................................................................................50

4.7.1 Contaminant concentration profiles ........................................................................50 4.7.2 Inhaled air quality of walking occupants................................................................53

4.8 Temperature distribution ..................................................................................................54 4.9 Velocity distribution ..........................................................................................................55 4.10 Discussion............................................................................................................................56 4.11 Conclusions .........................................................................................................................61

5. Personalized and underfloor ventilation..............................................................................63 5.1 Experiment 1 .......................................................................................................................63

5.1.1 Objectives.....................................................................................................................63 5.1.2 Experimental conditions............................................................................................63 5.1.3 Aerodynamic data of floor diffusers........................................................................63 5.1.4 Inhaled air concentration...........................................................................................66 5.1.5 Inhaled air temperature.............................................................................................67 5.1.6 Contaminant distribution..........................................................................................68 5.1.7 Temperature distribution ..........................................................................................71 5.1.8 Velocity distribution ..................................................................................................72

5.2 Experiment 2 .......................................................................................................................74 5.2.1 Objectives.....................................................................................................................74 5.2.2 Experimental conditions............................................................................................74 5.2.3 Inhaled air concentration...........................................................................................75 5.2.4 Inhaled air temperature.............................................................................................76 5.2.5 Contaminant distribution..........................................................................................77 5.2.6 Temperature distribution ..........................................................................................79 5.2.7 Velocity distribution ..................................................................................................80

5.3 Experiment 3 .......................................................................................................................81 5.3.1 Objectives.....................................................................................................................81 5.3.2 Experimental conditions............................................................................................81 5.3.3 Upward airflow direction..........................................................................................81 5.3.4 Horizontal or downward airflow direction............................................................82

5.4 Discussion............................................................................................................................84 5.5 Conclusions .........................................................................................................................92

6. General discussion....................................................................................................................93 7. Recommendations...................................................................................................................103 8. Conclusions ..............................................................................................................................105 References.........................................................................................................................................107 Appendix A Expression of uncertainty ......................................................................................115 Appendix B Inhaled air concentration with PV, mixing and displacement ventilation ..119 Appendix C Inhaled air temperature with PV, mixing and displacement ventilation.....121 Appendix D Whole-body manikin-based equivalent temperature......................................123 Appendix E Inhaled air concentration with personalized and underfloor ventilation....125 Appendix F Vertical distribution of active contaminants with underfloor ventilation ...127 Appendix G Risk of airborne infection transmission.............................................................131 Appendix H Intake fraction .........................................................................................................135

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Preface

This thesis is the result of a study carried out at the International Centre for Indoor Environment and Energy, Department of Mechanical Engineering, Technical University of Denmark from August 2001 to July 2004. The principal supervisor of the study has been Assoc. Professor Arsen K. Melikov, Ph.D. I would like to express my gratitude to Professor P. Ole Fanger for inviting me to join the Centre in 1999, first to carry out my M.Sc. project and later for supporting me to continue research as a Ph.D. student. I appreciate his encouragement. I am most grateful to Arsen K. Melikov. It was a great experience being his student. I wish to thank him for support, numerous discussions, constructive criticism, as well as for sharing with me his rich experience and inexhaustible optimism. I owe him a great deal. I would like to thank my colleagues with whom I had the pleasure to cooperate: Luboš Forejt and Oldřich Kovář for teamwork during the first stage of the experiments and for carrying out measurements and data analyses; Gabriella Stefanova and Tsvetelina Ivanova for help during the second stage of the experiments; and Quinfan Zeng for developing a control system for supplying air for personalized ventilation. I am grateful to Jan Kaczmarczyk for many discussions on personalized ventilation, and for his advice during the final stage of writing this thesis. I would like to extend my gratitude to the scientific, technical and administrative staff at the Centre. I would like to thank Gunnar Langkilde for help on administrative issues and Andreas Szekacz for help and advice with experimental facilities. My thanks are due to Judith Ørting for proofreading this thesis, and to Peter Strøm-Tejsen for translating the summary of this thesis to Danish. Last, but certainly not least, I would like to thank my parents and Eva for their support over the years. The study has been supported by the Danish Technical Research Council (STVF) as a part of the research programme of the International Centre for Indoor Environment and Energy established at the Technical University of Denmark for the period 1998-2007. The Technical University of Denmark has granted my scholarship.

Kgs. Lyngby, 31. July 2004 Radim Čermák

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Summary

Personalized ventilation (PV) provides clean air at each workplace. Each occupant is given an opportunity to improve substantially the quality of inhaled air, and to generate and control his/her preferred thermal environment. Because occupants may use PV at small airflow rates and close to isothermal temperatures, a supplementary total-volume ventilation and air-conditioning system has to be applied in rooms with high heat and/or pollution load. In the present study, two types of air terminal device for PV were combined with the most common total-volume ventilation systems – mixing ventilation, displacement ventilation and underfloor ventilation. The performance of the combined systems was examined in full-scale experiments. The criteria for evaluation were air quality and thermal comfort. A mock-up of a typical office with two identical workplaces was built in a climate chamber. Two breathing thermal manikins simulating occupants were seated behind each other facing in the same direction. The air terminal devices tested were a round diffuser mounted on a movable arm duct, positioned above a computer monitor, and a narrow grill positioned at the front edge of a desk. Both terminals were adjusted according to the positioning most often preferred by people. The major difference between the terminals was the direction of personalized airflow – horizontal/downward in the case of the movable panel and upward in the case of the desk grill. The arrangement of workplaces did not change during the whole study, allowing for a direct comparison of the combined systems. Different tracer-gases were used to simulate the most common contaminant sources indoors. Floor covering, human bioeffluents and exhaled air were selected. The exposure of occupants was estimated from the gas concentration measured in the inhalation of the manikins. Temperature of inhaled air, which is important for the perception of air quality, was measured as well. The thermal comfort of seated occupants was evaluated based on the heat loss from the manikins. Furthermore, the distribution of contaminants, temperature and velocity were measured in order to reveal the airflow pattern in the room. The performance of the PV was tested at different combinations of personalized airflow rates (0, 7 and 15 L/s). This covered the range of possible individual patterns of PV use. The total-volume ventilation system was controlled so that the total cooling capacity of personalized air plus total-volume ventilation air was constant. The exhaust air temperature was maintained at 26°C. Results on air quality showed that in rooms with mixing ventilation, PV will always be able to protect occupants from pollution and thus increase the quality of inhaled air. The mixing air distribution principle implies that the type of contaminant source (active or passive, localized or plane) and its location is unimportant. The inhaled air quality of occupants protected with PV is determined to a large extent by the efficiency of an air terminal device, and the direction and the rate of personalized airflow. In inhaled air, the temperature was well correlated with the concentration of the contaminants distributed uniformly in the room. In a room with displacement ventilation, PV was shown to improve the inhaled air quality in regard to a passive and plane contaminant located on the floor. This is the case for carpet, PVC or linoleum. The use of PV was shown, however, to increase mixing of contaminants located in the vicinity of the personalized airflow, such as exhaled air and bioeffluents. The

Summary

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personalized flow generated large non-uniformities and differences in the distribution of human-produced contaminants near the workplace. Further from the workplace the non-uniformities disappeared; however, the concentration of the human-produced contaminants increased compared to the case without PV. This may decrease the inhaled air quality for occupants unprotected with PV. The distribution of the human-produced contaminants was affected by the direction and rate of personalized airflow. Upward personalized flow (desk grill) was observed to cause a lower transmission of the human-produced contaminants between workplaces than horizontal/downward flow (movable panel). Personalized airflow may also affect the distribution of contaminants generated at another workplace. In that respect, the impact of upward personalized airflow (desk grill) was greater than the impact of horizontal/downward airflow (movable panel), most probably due to its higher velocity. The performance of PV in combination with an underfloor air distribution (UFAD) system with a short throw (up to 0.3 m) was comparable with the performance of PV in combination with displacement ventilation. UFAD, however, decreased non-uniformities of contaminants and vertical temperature gradients. Also with UFAD, the use of PV increased mixing of contaminants located in its vicinity. The experiments confirmed that personalized airflow directed upward (desk grill) provides a lower transmission of contaminants between workplaces than personalized airflow directed downward (movable panel). An increase in the throw diminished gradually the impact of the direction of personalized airflow on the transmission of contaminants. The impact of the PV direction on the transmission disappeared when the throw was comparable to the height of the breathing zone. The analyses indicate that the use of PV in combination with any total-volume ventilation system could be efficient in protecting occupants even from highly infectious diseases, and therefore become an alternative or supplement to traditional methods of occupant protection. The impact of PV on the thermal environment was very localized, even at high rates of personalized air (15 L/s). The use of PV at one workplace did not affect the thermal comfort of the occupant at another workplace. The cooling performance of PV was independent of the room air distribution generated by a total-volume ventilation system. The cooling provided by PV was equivalent to decreasing room air temperature by 1-2°C, depending on the actual combination of PV air terminal, total-volume ventilation principle and workplace. The ability of PV to affect the air movement in the lower occupied zone was small. In rooms with thermal stratification (displacement or underfloor ventilation), PV was shown not to contribute to the removal of heat from the lower zone. This may cause an increase in temperature in the occupied zone and thus increase the energy consumption of a total-volume ventilation system. On the other hand, a higher temperature may decrease the risk of draught and high vertical air temperature difference. The present study identified that each combination of PV and total-volume ventilation tested could be applied in practice. Because of an excellent air quality performance and a low risk of thermal discomfort, a combination of PV and underfloor ventilation with a short vertical throw, controlled according to a constant air volume strategy, is recommended. If the control of an airborne transmission of contaminants between occupants has highest priority, personalized air terminals supplying air upward are preferable. Development of air terminal devices with a high efficiency and a low ability to promote mixing of contaminants located in its vicinity is recommended.

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Resumé

Personlig ventilation (PV) tilvejebringer ren luft til den enkelte arbejdsplads. Hver bruger bliver tilbudt en mulighed for at forbedre kvaliteten af indåndingsluften væsentligt, og at frembringe og kontrollere hans/hendes termiske omgivelser til det foretrukne. Da den en- kelte bruger muligvis anvender PV med kun en beskeden luftstrøm og tæt ved isotermiske temperaturer, skal der i rum med en høj varme og/eller forureningsbelastning anvendes et supplerende ventilations og luftkonditionerings system for rummet. I nærværende studie blev to forskellige PV indblæsningsterminaler undersøgt i kombination med de hyppigst anvendte ventilationssystemer hhv. opblandingsventilation, fortræng- ningsventilation og »underfloor« ventilation. Virkningen af de kombinerede systemer blev undersøgt ved fuld skala forsøg. Vurderingskriterierne var luftkvalitet og termisk komfort. En fuld-skala model af et typisk kontor med to identiske arbejdspladser blev opført i et kli- makammer. To vejrtrækkende termiske mannequiner, simulerende tilstedeværende perso- ner, blev anbragt siddende bag hinanden med ansigtet vendt i den samme retning. De ind- blæsningsterminaler, som blev undersøgt, omfattede en rund luftfordeler monteret på en bevægelig arm placeret over en computer skærm, og en smal rist placeret i arbejdsbordets forkant. Begge blev justeret i overensstemmelse med den hyppigst foretrukne placering. Den væsentligste forskel mellem terminalerne var luftstrømningen – horisontalt/nedadrettet i tilfældet med den bevægelige luftfordeler, og opadrettet i tilfældet med bordristen. Ar- bejdspladsernes udformning blev ikke ændret under hele undersøgelsen, hvilket gav mulig- hed for en direkte sammenligning mellem kombinationen af de undersøgte ventilationssy- stemer. Forskellige sporgasser blev anvendt for at simulere de mest almindelige indendørs forureningskilder. Der blev valgt gulvbelægning, menneskelig emitterede bioeffluenter og udåndingsluft. Personers eksponering blev vurderet på grundlag af den koncentration af gasser, som blev målt i mannequinernes indåndingsluft. Indåndingsluftens temperatur, som er vigtig for oplevelsen af luftkvalitet, blev ligeledes målt. Den termiske komfort af siddende individer blev evalueret på basis af varmetabet fra mannequinerne. Yderligere blev forde- lingen af forurening, temperatur og lufthastighed målt med henblik på at afsløre luftens strømningsmønstre i rummet. Virkningen af PV systemet blev undersøgt ved forskellige kombinationer af de personkontrollerede luftstrømme (0, 7 og 15 L/s). Dette svarer til mu- lige individuelle former for brugen af PV. Ventilationssystemet for rummet som helhed blev reguleret således, at den totale kølekapacitet af personkontrolleret luft plus luft fra rum ven- tilationen forblev konstant. Udsugningsluftens temperatur blev fastholdt ved 26°C. Resultater vedrørende luftkvalitet viste, at i lokaler med opblandingsventilation vil PV altid være i stand til at beskytte de tilstedeværende personer mod forurening og således forbedre kvaliteten af indåndingsluften. Princippet for opblandingsventilation indebærer, at typen af forureningskilde (aktiv eller passiv, lokal eller jævnt fordelt) og dens placering er uden be- tydning. Kvaliteten af indåndingsluften for personer, der har PV til rådighed, er i stort om- fang bestemt ved effektiviteten af indblæsningsterminalen, samt retning og omfang af den personkontrollerede luftstrøm. Indåndingsluftens temperatur var velkorreleret med den i lokalet jævnt fordelte forureningskoncentration. I et lokale med fortrængningsventilation viste PV at forbedre kvaliteten af indåndingsluft i relation til en passiv og jævnt fordelt forurening placeret på gulvet. Dette er tilfældet med gulvtæppe, PVC og linoleum. Anvendelsen af PV viste sig imidlertid at forøge opblandin-

Resumé

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gen af forurening, der befandt sig i nærheden af den personkontrollerede luftstrøm, såsom udåndingsluft og bioeffluenter. Den personkontrollerede luftstrøm skabte store uensarted- heder og forskelle i fordelingen af menneskelig forurening tæt ved arbejdspladsen. Længere væk fra arbejdspladsen forsvandt uregelmæssighederne, men koncentrationen af menneske- lig forurening blev forøget i sammenligning med tilfældet uden PV. Dette kan om muligt reducere kvaliteten af indåndingsluften for personer, der ikke har PV til rådighed. Fordelin- gen af den menneskelige forurening var påvirket af retning og omfang af den personkon- trollerede luft. Den opadrettede luftstrøm (bordristen) viste sig at medføre en mindre trans- mission af menneskelig forurening mellem arbejdspladserne end den horisonta- le/nedadrettete strømning (bevægelige luftfordeler). En personkontrolleret luftstrøm kan også påvirke fordelingen af forurening frembragt ved en anden arbejdsplads. I så henseende var indvirkningen af den opadrettede luftstrøm (bordristen) større end indvirkningen af den horisontale/nedadrettede luftstrømning (bevægelig luftfordeler), mest sandsynligt på grund af den større strømningshastighed. Virkningen af PV i kombination med et »underfloor« ventilationssystem med begrænset ka- stelængde (op til 0.3 m) var sammenlignelig med virkningen af PV i kombination med for- trængningsventilation. »Underfloor« ventilationssystemet reducerede imidlertid ujævnhe- der af forurening og temperaturgradienter. Og medførte endvidere, at anvendelse af PV for- øgede opblandingen af forurening i dens nærhed. Undersøgelserne bekræftede, at en opadrettet luftstrøm (bordristen) medfører en mindre transmission mellem arbejdspladserne end den nedadrettede luftstrøm (bevægelige luftfordeler). En forøgelse af systemets kaste- længde reducerer gradvis effekten af den personkontrollerede luftstrøms retning på overfø- ring af forurening. Indvirkningen af PV retningen på transmission forsvandt, når kaste- længden var sammenlignelig med højden af indåndingszonen. Analysen peger på, at PV, i kombination med et hvilket som helst ventilationssystem, kan være effektivt til at beskytte personer selv mod meget smitsomme sygdomme, og derfor bli- ve et alternativ eller supplement til traditionelt anvendte metoder for personbeskyttelse. Indvirkningen af PV på det termiske indeklima var meget lokalt, selvom endog meget eks- treme individuelle anvendelsesformer for PV systemet blev undersøgt. Anvendelsen af PV ved en arbejdsplads havde ikke indvirkning på den termiske komfort for en person ved en anden arbejdsplads. Den kølende virkning af PV var uafhængig af luftfordelingen frembragt af ventilationssystemet. Kølingen, som blev frembragt af PV, var ækvivalent med en reduk- tion af rummets lufttemperatur på 1-2°C, afhængig af den aktuelle kombination af PV ind- blæsningsterminal, ventilationsprincip og termisk mannequin (arbejdsplads). Muligheden for, at PV indvirker på luftbevægelser i den nedre opholdszone, var begrænset. I lokaler med termisk lagdeling (fortrængnings- eller »underfloor« ventilation) viste det sig, at PV ikke bidrager til at fjerne varme fra den nedre zone. Dette kan medføre en temperaturfor- øgelse i opholdszonen og herved forøge ventilationssystems energiforbrug. Dog kan en hø- jere temperatur måske reducere risikoen for træk og betydelige lodrette temperaturforskelle. Nærværende studie har påvist de kombinationer af PV og rum ventilation, som blev under- søgt, vil kunne anvendes i praksis. På grund af en fortrinlig virkning på luftkvaliteten og en lav risiko for termisk ubehag anbefales en kombination af PV og »underfloor« ventilation med begrænset lodret kastelængde, kontrolleret i overensstemmelse med en strategi for konstant lufttilførsel. Såfremt kontrol med luftbåren transmission af forurening mellem in- divider har den højeste prioritet, vil indblæsningsterminaler, der tilfører en opadrettet luft- strøm, være at foretrække. Udvikling af indblæsningsterminaler med en høj virkningsgrad og begrænset opblanding af omkringliggende forurening, er anbefalelsesværdig.

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Nomenclature

Abbreviations ATD Air terminal device CAV Constant air volume CFD Computer fluid dynamics DR Draught rating DV Displacement ventilation MV Mixing ventilation PV Personalized ventilation RMP Round movable panel SBS Sick building syndrome TV Total-volume ventilation UFAD Underfloor air distribution VAV Variable air volume VDG Vertical desk grill VOC Volatile organic compound Symbols

c Contaminant concentration, mg/m3 C Constant c(-) Normalized contaminant concentration, dimensionless CRP Contribution ratio of pollution source, dimensionless ET Manikin-based equivalent temperature, °C iF Intake fraction, dimensionless PRE Pollutant removal efficiency, dimensionless Qt Sensible heat loss, W/m2 RA0 Reproductive number for an infectious disease in indoor environment,

dimensionless T Air temperature, °C T(-) Normalized air temperature, dimensionless Tu Turbulence intensity, % U Uncertainty v Mean air velocity, m/s ∆ET Difference between ET with PV and ET without PV; cooling effect, K εP Personal exposure effectiveness, dimensionless εV Ventilation effectiveness, dimensionless Subscripts 0 Without personalized ventilation; reference case E Exhaust I Inhaled PV With personalized ventilation S Supply

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1. Introduction

1.1 Background Numerous field studies (Bluyssen et al., 1996; Mendell, 1993) have documented substantial rates of dissatisfaction with the indoor environment in many buildings. A recent review of the scientific literature by a multidisciplinary group of European scientists showed a strong association between the level of ventilation and comfort (perceived air quality), health (sick building syndrome (SBS) symptoms, inflammation, infections, asthma, allergy, short-term sick leave) and productivity (Wargocki et al., 2002). It has been shown that better air quality increases satisfaction and productivity and decreases health problems. The studies show at the same time, that meeting today’s standards does not prevent widespread complaints of poor air quality and frequent building-related symptoms. Ventilation rates have been given as a required supply of outdoor air per person in order to dilute human bioeffluents to an acceptable odour level (Fanger, 1998). The fact that many other sources indoors (new building materials, electronic equipment, etc.) can contribute to the pollution of air was not considered. Systematic selection of low-polluting materials is certainly the most efficient way to improve the indoor air quality. However, at present, there are limits to which the pollution sources can be reduced. Another way to improve the indoor air quality is to provide larger amounts of outdoor air, but this method poses a risk of thermal discomfort and may increase energy consumption substantially. In practice, rooms are used by occupants with different physiological and psychological responses, clothing, activity, individual preferences to the air temperature and movement, etc. It is consequently difficult to create an environment that would satisfy everyone when many people occupy the same space. Various studies have demonstrated that on average, 5-10% of subjects are always dissatisfied with the thermal environment that is considered acceptable by the majority of the population. The total-volume ventilation and air-conditioning, at present the method most used in practice, aims at providing uniform environmental conditions throughout rooms. The ability of occupants to create and control their preferred environment is limited.

1.2 Principles of personalized ventilation Personalized ventilation (PV) provides clean air at each workplace. Its primary aim is to improve the quality of air inhaled by each occupant, and thus reduce complaints, increase satisfaction and performance and ensure health. Protecting occupants from inhaling airborne contaminants, whether they are airborne infectious agents produced by other occupants or chemicals from building materials, is an important quality of PV systems. Specifically designed air terminal devices supply clean air direct to the breathing zone (face) of each occupant. The interaction of personalized airflow with the flow in the human boundary layer, room airflow and the flow of respiration determines the ability of PV to

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ensure high air quality. Low velocity and turbulence intensity of the supply airflow is required in order to (1) reduce the mixing of the fresh personalized air and the ambient polluted air and (2) to reduce draught discomfort. However, an airflow that is too weak may not penetrate the human boundary layer, and it is also susceptible to the impact of buoyancy forces. The highest air quality is achieved when an occupant inhales air direct from a potential core region of a personalized air jet. Because of a wide and long concentration core, the PV terminals developed recently by Bolashikov et al. (2003) are able to provide inhaled air consisting of nearly 100% clean air from PV at a supply rate of 10 L/s per person. Fang et al. (1998a, b) confirmed earlier studies and showed that although the odour intensity of air does not change significantly with temperature and humidity, air is perceived more acceptable with decreasing temperature and humidity. Because of the positive influence of low air temperature on the perception of air quality, it is advantageous to supply cool air. The positive impact of a low air temperature has been confirmed in recent laboratory studies with human subjects (Kaczmarczyk et al., 2002a, accepted; Zeng et al., 2002; Yang et al., 2003; Kaczmarczyk, 2003). Cooling of personalized air is not intended to provide space conditioning. The presence of air movement in the vicinity of an occupant inevitably affects his or her thermal sensation. Hence, PV is potentially successful in improving thermal comfort if individual differences and preferences can be accommodated. The control of thermal comfort is usually realized by changing velocity, temperature and direction of the supply air stream. Studies show that PV is able to affect thermal comfort equivalent to decreasing room air temperature by several degrees (Tsuzuki et al., 1999). This is sufficient for most occupants. The mechanism of cooling is equivalent to using a desk fan. Analyses indicate that occupants may have to prioritize between excellent air quality and preferred thermal comfort. While strong airflow may be desirable in warm climates to provide cooling, it may at the same time increase the entrainment of polluted room air and thus decrease the inhaled air quality. In contrast, in a cold environment, sensitive occupants may prefer not to use PV and thus would not benefit from the high air quality. Kaczmarczyk et al. (accepted) and Kaczmarczyk (2003) showed that occupants might not perceive the differences in the air quality between two terminals, which otherwise look similar. He suggests that thermal comfort is an important parameter for occupant’s preferences. The provision of individual control is the third advantage of PV systems. Research by Bauman et al. (1998) suggests that it is more important for workers to have the ability to control their local environment than it is for them to exactly make a large number of control adjustments. The ability to consume less energy in comparison with conventional systems may be the fourth advantage of PV systems. Although important for application of PV in practice, this issue has been studied the least. At present, no quantitative proof has been given. The potential to save energy has been associated with providing smaller volumes of air (less conditioning), and shutting the PV system off when a workplace is not occupied. As pointed out by Fanger (2001), the actual breathing requirement of sedentary occupants is as low as 0.1 L/s, while a hundred times more air is typically provided by conventional systems. In conclusion, personalized ventilation aims to improve perceived air quality and protect occupants from airborne contaminants, to make each occupant thermally comfortable, to satisfy his or her individual preferences and to be environmentally responsible in saving

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energy. Occupants, in order to avoid draught discomfort, may use PV at small flow rates and temperatures only a few degrees cooler than the room air temperature. Therefore, total-volume ventilation and air-conditioning have to be applied in combination with PV in rooms with high heat and/or pollution loads.

1.3 Design, installation, performance Individual ventilation and air-conditioning systems have been used in vehicle and airplane cabins for many years. Air supply nozzles and slots are designed to produce high momentum jets that promote intensive mixing of the clean air with the surrounding air and are efficient mainly in improving passengers’ thermal comfort. In buildings, air terminals incorporated in furniture have been used to deliver conditioned air close to the occupants in some auditoria and theatres. Applications of PV in offices and non-industrial working premises have been limited. At present, individually controlled systems providing an improved level of air quality, referred to also as the task/ambient conditioning systems, can be grouped in the following three categories: • Underfloor ventilation systems • Workplace (furniture) integrated systems • Air terminals in the breathing zone. Underfloor ventilation systems Several researchers investigated the performance of individually adjustable floor-based terminals named Task Air Modules (TAM), manufactured by Tate Architectural Products. Air was discharged through four adjustable grills mounted on an access floor panel. A rotary knob recessed to one grill allowed occupants to control the quantity of supply air. Fisk et al. (1991) showed that inhaled air quality improved only when the air was directed in a manner that yielded an upward vertical displacement flow. The thermal comfort performance of TAM was comparable with other underfloor air ventilation systems (Arens et al., 1991). Tsuzuki et al. (1999) reported on the ability of TAM to increase the heat loss from a thermal manikin. The development of another system with the local control of air velocity and temperature was described by Spoormarker (1990). Workplace (furniture) integrated systems Sodec and Craig (1990) reported on desk outlets for office applications designed as linear slots or round swirl diffusers. The airflow rate was limited to 14 L/s per person in order to prevent excessive velocities, which could be adjusted in the range from 0 to 0.6 m/s at the head level of seated occupants. The systems were installed typically in conjunction with an underfloor air distribution system, which was operated in order to remove the total heat gain. The improvement of the inhaled air quality was considered but not studied. The outlets had not seen widespread use due to their cost, and the installations of underfloor ventilation systems alone prevailed. Personal Environments Module (PEM) from Johnson Controls has affected a great deal of research interest. It consists of two adjustable nozzles located at the rear corners of the desk. From a desktop control unit, the occupant can select his or her own settings for air temperature, airflow rate and direction. The system is accomplished with a radiant heating panel at the knee space, task lighting and a background noise generator.

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Faulkner et al. (1999) studied the efficiency of PEM to ventilate the breathing zone of seated occupants. Although the systems could provide re-circulated and filtered air, only the outdoor air was provided. The system was operated in conjunction with an overhead mixing ventilation system, which provided additional space cooling but no outside air. The efficiency was assessed based on the Air Change Effectiveness index (ACE), which was defined as the ratio of the age of air of the exhaust air and the age of air in the breathing zone (Etheridge and Sandberg, 1996). The maximum ACE reported for PEM was 1.6, which indicated 60% improvement in comparison to mixing ventilation. The efficiency was also studied in regard to the contaminants emitted from the floor covering and the body odours from other occupants using several point sources of perfluorocarbon tracer gases. The inhaled air quality was assessed using the Pollutant Removal Efficiency index (PRE), which is equivalent to the Ventilation Effectiveness index (CEN, 1998). The highest value of PRE was 1.5 in regard to the body source, and 1.3 in regard to the floor source. The room distribution of the contaminants was not reported. In the earlier research by Faulkner et al. (1993), the PEM terminals were operated alone without an additional system. The supply airflow and temperature were adjusted to balance the heat load of the office in order to provide a comfortable environment. This was made possible because of large airflows (up to 40 L/s per person). The inhaled air quality improved only when the highest rates of outdoor air were directed at the breathing zone. The conditions were described as unlikely comfortable due to the high velocities in the face. Measurements throughout the room indicated mixing of indoor air. Arens et al. (1991) and Bauman et al. (1993) studied the thermal performance of PEM in a simulated office space. During some tests, a ceiling supply diffuser was used to provide supplemental space conditioning. The units were shown to be able to maintain close to comfortable conditions in workstations with different heat load levels. Cho et al. (2001) measured the air velocity and temperature distribution of PEM installed in combination with an underfloor air distribution system. The study showed that the temperatures became more uniform when the supply rate of PEM increased while the airflow from the floor decreased. The ability of PEM to affect the heat loss from a thermal manikin under various conditions was studied by Tsuzuki et al. (1999). Another system available on the market, named Climadesk (manufactured by Mikroklimat Sweden AB), provides the air from outlets at the front edge of the desk. Two adjustable slots supply the air horizontally towards the occupant and the third slot, on the top of the desk, supplies the air upward to the breathing zone. The maximum airflow is about 7 L/s. The system also provides radiant heating at the thighs. The efficiency of Climadesk to ventilate the breathing zone of a seated thermal manikin was examined by Faulkner et al. (1999), and compared to the efficiency of PEM. The maximum values of ACE and PRE in regard to both a body source and a floor source were 1.9 and 1.6, respectively. The performance of the Climadesk was a little better than the performance of PEM. The high values were, however, achieved only when the system supplied outdoor air, and the manikin’s head was located precisely within the vertical jet of air. Recently, Faulkner et al. (2002) investigated experimentally the effectiveness of an air supply nozzle located underneath the front edge of the desk. The supply airflow rates ranged from 3.5 to 6.5 L/s. The measured values of ACE in the breathing zone ranged from 1.4 to 2.7, which converted to PRE (using the correlation between ACE and PRE for a floor source presented in Faulkner et al., 1999) correspond to 1.2 and 2. The efficiency was higher than

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typically reported for previously tested outlets (Faulkner et al., 1999) or displacement ventilation systems. The system was tested in a room with mixing ventilation. Loomans (1998) proposed a desk displacement ventilation system. The supply terminal was situated below the desktop (against the back of the desk) and supplied air at a low velocity, 0.1 to 0.2 m/s, towards the occupant. The concept was tested experimentally and numerically. The inhaled air quality reportedly did not improve in comparison to rooms with traditional displacement ventilation. Izuhara et al. (2002) tested a similar concept. A fan-equipped partition was used to deliver clean air from the floor level under the desktop. A traditional displacement ventilation system was installed in the room. The measurements using the age of air concept did not show large differences between the displacement ventilation alone and in combination with the partition. Studies on PV and task/ambient conditioning systems reported in the literature recently include a ventilation tower system (Hiwatashi et al., 2000) and a partition integrated fan-coil unit (Chiang et al., 2002). An improvement of air quality and/or thermal comfort for occupants was indicated; however, the studies did not reveal exceptional characteristics or outstanding performance of the designs tested. Recently, Melikov et al. (2002) investigated five different designs of supply air terminal devices. The designs are schematically shown in Figure 1.1. They comprised: Movable Panel placed above occupant’s head, Computer Monitor Panel located above the monitor, two desk grills supplying air vertically upward and horizontally towards the torso from the front edge of the desk, and pair of PEM terminals tested previously by Faulkner et al. (1999). The terminals were adjusted in order to provide clean air directly to the breathing zone. The idea of the movable panel was that due to its construction it is possible to change the location of the terminal in relation to the occupant.

Figure 1.1. Air terminal devices studied by Melikov et al. (2002): movable panel (MP), computer monitor panel (CMP), vertical desk grill (VDG), horizontal desk grill (HDG) and personal environments module (PEM). The terminals were compared in terms of the inhaled air quality and thermal comfort of a seated occupant, using a breathing thermal manikin in a climate chamber. The room distribution principle was upward piston flow with a mean velocity of less than 0.06 m/s. An isothermal and 6 K lower than the ambient chamber air was supplied from the terminals at an airflow rate ranging from 3 to 23 L/s. A new index, Personal Exposure Effectiveness, was proposed. The efficiency of personalized ventilation is expressed as the portion of clean

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personalized air in inhalation. Furthermore, the temperature of inhaled air was measured. Results showed that the performance of PV in terms of both the indices depends to a large extent on the supply air terminal type and the airflow rate. Increasing the airflow rate through the PV increased the amount of personalized air inhaled. The highest personal exposure effectiveness was about 0.7 (PRE of 3.3) measured with the panel above the computer screen (CMP). The supply airflow was 23 L/s and isothermal. The best performing outlet for both an isothermal and a non-isothermal air supply was the vertical desk grill (VDG), which provided a personal exposure effectiveness of about 0.5 (PRE of 2.0) already at an airflow rate of 10 L/s. The next best outlet was the movable panel (MP), which for isothermal conditions performed similarly to the VDG. The study also reports on the portion of exhaled air that was re-inhaled. It was generally low and did not exceed 1% for any of the conditions or terminals tested. The cooling ability of the terminals was reported as well. Kaczmarczyk et al. (2002a, b) modified the Movable Panel in order to provide better flexibility and appearance of the system (later referred as the 2nd generation MP). The human response to the terminal was examined (see below). The personal exposure effectiveness (measured additionally) was 0.3, which is, however, rather mediocre. This, together with somewhat encouraging results from the experiments with human subjects, initiated a development of a new terminal (Bolashikov et al., 2003), named Round Movable Panel (RMP). It was made in a circular shape and fitted with a flow straightener in order to provide low turbulent flow with a long concentration core. The RMP was mounted on a movable arm-duct attached to the desk, which allowed for its positioning in respect to the occupant. Physical measurements revealed that for the typical positioning, as used by occupants, the inhaled air consisted of 100% of clean personalized air at a supply rate of 15 L/s. At lower rates, the performance was influenced by the temperature difference between the supply air and ambient air. Air terminals in the breathing zone The effort to reduce the mixing of clean personalized air and ambient air led to a development of terminal devices positioned direct in the breathing zone of a person. Zuo et al. (2002) studied the concept of a facial air supply outlet. Nozzles of different shapes and sizes were placed on the chest of a manikin and provided with air at a rate of up to 2 L/s. At the highest rate, the ratio of the personalized air in inhalation was calculated to be 0.61. The results are compromised by the fact that the manikin was not heated. It is known that the inhaled air quality depends on the complex interaction of airflows around a human body, of which the free convection along the body is one of the most important. Bolashikov et al. (2003) developed an air terminal incorporated in a commercially available set of headphones. The microphone piece was replaced with a small rectangular nozzle, providing clean air of up to 0.5 L/s from a short distance direct to the mouth/nose of a person. The design was tested by means of both physical measurements with a breathing thermal manikin and experiments with human subjects (see below). The physical measurements revealed that the inhaled air consisted of up to 80% of clean air from the PV. The ability of the Headset to affect the heat loss from a thermal manikin was very small. Human response to personalized ventilation Knowledge about the human response to PV is limited. Kaczmarczyk et al. (2002a, b, accepted), Zeng (2002) and Kaczmarczyk (2003) examined the response of 60 human subjects to the 2nd generation Movable Panel (MP) and mixing ventilation at several combinations of room air temperature and PV air temperature. A series of 4-hour experiments was carried out in a controlled laboratory environment. They showed that MP providing cool outdoor

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air was able to improve the perceived air quality and decrease the intensity of some SBS symptoms compared to mixing ventilation. The acceptability of the thermal environment with PV compared to the situation without PV was improved at the higher temperature in the office. Improved self-estimated performance was indicated. Most recently, Kaczmarczyk (2003) and Kaczmarczyk et al. (2004) examined perceived air quality, thermal sensation and individual preferences with five different air terminal devices for PV and mixing ventilation. The devices used were the Round Movable Panel (RMP), the Headset, the 2nd generation MP, the Vertical Desk Grill (VDG) combined with the Horizontal Desk Grill (HDG), and the Round Movable Panel combined with the Horizontal Desk Grill. The subjects experienced each system in 25-minute sessions under different combinations of the pollution level and temperature of ambient air. Results showed that all the terminals improved the perceived air quality compared to the office (mixing ventilation). The system with the highest rating in terms of the perceived air quality and thermal conditions was the RMP. It was also the system most frequently selected by subjects. The subjective evaluation of the MP was fairly similar to the RMP, despite the differences in their ventilation performance identified by objective physical measurements. The combination of VDG and HDG caused unpleasant cooling of the pelvis, legs and chest, which was due to HDG. The analyses showed that most subjects used the VDG to achieve high air quality, and closed the HDG. The least rated terminal was the Headset. The subjects reported an unpleasant sensation due to very localized and high velocity, impractical and uncomfortable design (air was supplied to the headset through tubing), and lack of cooling for larger body areas at elevated temperatures. At present, the movable panels, namely the RMP, and front-desk-edge mounted grills have the highest potential to ensure excellent air quality and preferred thermal environment for occupants. The performance of PV in regard to the distribution of different contaminants has been studied only recently (Cermak and Melikov, 2003; Faulkner et al., 1999).

1.4 Contaminants indoors All people emit a complex mixture of effluents, which produce an unpleasant odour in sufficient concentration. The odour levels are typically controlled by ventilation to a level that is acceptable by most occupants. The percentage dissatisfied with air polluted by human bioeffluents as a function of the ventilation rate per person is available (CEN, 1998). Although the bioeffluents are not the strongest pollutant in today’s buildings, they are still important because they will ultimately be present in buildings after other contaminants have been removed. Carbon dioxide (CO2) produced in the human lung proportionally to the metabolic rate is a good indicator of human bioeffluents. CO2 is not toxic, except at high concentrations. Exhaled air contains about 3.6% CO2, which is, however, diluted in indoor air by ventilation. The first effects are noticeable at a concentration of about 1% (McIntyre, 1980). This is rather high and reached typically only in crowded and under-ventilated spaces. The symptoms include increase in the depth of breathing, frequency of breathing and headache, which may reduce performance. Environmental tobacco smoke is an unprecedented source of odour and irritation. It has been shown to increase the risk of a variety of diseases and no safe levels of exposure can be recommended. Despite its adverse health effect, tobacco smoke continues to be one of the

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most important contaminants indoors, especially in underdeveloped parts of the world. Its emission is a combination of the smoke exhaled by the smoker and the smoke released directly from the burning cigarette. Air exhaled by people is the vehicle for release of respiratory infectious agents. Both viruses, which range in size from 0.003 to 0.06 µm, and bacteria, which mostly range between 0.4 and 0.5 µm, do not occur alone but in colonies or attached to other particles. The agents can be dispersed from the respiratory tract during sneezing, coughing or talking.

Figure 1.2. Predicted total respiratory depositions at three levels of exercise based on the International Commission on Radiological Protection deposition model. Average data for males and females. Reprinted from Hinds (1999). Most airborne viral and bacterial aerosols originate from human-produced droplet nuclei. Very little information is, however, available on the size of these droplets. The distribution reported in the literature differs according to the measurement techniques applied. Duguid (1945), who measured stain marks found on slides exposed to exhaled air, reported that most droplets were between 4 and 8 µm in diameter. Fairchild and Stamper (1987) concluded, using an optical particle counter, that a great majority of particles are less than 0.3 µm and a few greater than 1 µm. Papineni and Rosenthal (1997) demonstrated the existence of droplets in the exhaled breath using an optical particle counter and measurements of dried droplets collected upon electron microscopy grids. The droplet size ranged from the lower limits of detection of the methods used (0.3 µm with the optical counter) to approx. 8 µm. After expulsion, the large droplets either settle out of the air or they evaporate to droplet nuclei that approach the size of the individual agent. Brosseau et al. (1994) reported, based on a literature review, that the diameter of droplet nuclei ranges from 0.5 to 5 µm. ASHRAE Systems and Equipment Handbook (2000) states that the droplet nuclei average about 3 µm in diameter. The exhaled air may also contain particles that were previously inhaled and did not deposit in the respiratory tract. The respiratory deposition for a wide range of particle sizes presented in Figure 1.2 indicates that the most respirable particles range from 0.1 to 1 µm.

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Infectious particles behave physically in the same way as any other aerosol-containing particles with similar size, density, electrostatic charge, etc. Particles less than 0.1 µm in diameter behave similarly to gas molecules. They travel with Brownian movement and with no predictable or measuring settling velocity. Particles from 0.1 to 1 µm have settling velocities that can be calculated but that are very low. Although particles in the 1 to 10 µm range settle in still air, normal air currents may still keep them in suspension for appreciable periods. Thus airborne infectious agents can be transported by airflow from person to person. The successful transmission of an infection depends on susceptibility of the individuals (immunity), duration of exposure, concentration of agent, virulence of agent, etc. Volatile Organic Compounds (VOCs) have been associated with poor air quality, eye and airway irritation and consequently the prevalence of SBS symptoms (Wargocki et al., 1999; Pejtersen et al., 2001). Building products, which represent the largest surfaces indoors, are considered the major VOC sources (Wolkoff, 1995). Most studies associated the building-related complaints with the presence of carpeting, PVC and linoleum (Mendell, 1993; Jaakkola at al., 1999, 2000; Wolkoff et al., 1995). Despite availability of low-polluting materials, such as polyolefin, carpets are still being used frequently in many buildings. Recently, some personal computers (PC) have been identified as a strong pollution source having a negative effect on perceived air quality and productivity in offices (Bakó-Biró et al., 2004). Sensory evaluation showed that the classical cathode-ray tube displays were the major polluting elements. Polluting load of the flat Thin Film Transistor (TFT) displays as well as computer towers was small (Wargocki et al., 2003). The significance of PCs as contaminant sources is expected to decrease due to an increase of the market share of the TFT displays. Other office equipment such as printers and copy machines producing ozone are typically fitted with active charcoal filters, which reduce the ozone emission. Besides, they are often placed in sparsely occupied areas (e.g. corridors) where the exposure of occupants is limited. The exposure of occupants to a contaminant depends on the distribution of the contaminant in a room. The distribution is influenced by the principle of ventilation, type of a contaminant source and its location in respect to the occupant, airflow generated by the activity of occupants, distribution of heat sources (thermal plumes), weather conditions, etc.

1.5 Room air distribution Total-volume ventilation and air-conditioning of rooms is at present the method most used in practice. Mixing and displacement room air distribution are the main principles applied. Underfloor air distribution, which combines the characteristics of mixing and displacement distributions, has become popular for ventilation of offices in recent yeas.

1.5.1 Mixing ventilation Mixing air distribution aims at creating relatively uniform air velocity, temperature, humidity, and air quality conditions in the occupied zone. Air quality is maintained by dilution of the released contaminants. Conditioned air is normally supplied from air terminal devices at relatively high velocities, much greater than those acceptable by building occupants. Supply air temperature may be above, below or equal to the air temperature in the occupied zone. The diffuser jets mix with the ambient room air by entrainment and reduce the air velocity and equalize the air temperature. With ceiling-based devices, a region of discomfort is contained above the head level and does not typically affect the occupants.

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However, the quality of air inhaled by occupants is necessarily lowered, allowing the supply air to mix with the contaminants that collect near the ceiling. Studies show that ideal mixing may not be and is often not achieved. Fisk et al. (1997) provided evidence of short-cutting of air between supply diffusers and exhaust grills located on the ceiling when the supply air was heated, especially when ventilation rates were low. The short-cut did not occur when the supply air was cooled. Heiselberg (1996) showed that the supply airflow rate, location of the return opening, location of the contaminant source and density of the contaminant influences the contaminant distribution. Large differences in distribution were found especially when the airflow rate was low. On the other hand, the activity of occupants (walking, opening and closing of doors) contributes to mixing and diminishes the large differences in air quality that are often found in the test rooms. CEN Report 1752 (1998) acknowledges an inhomogeneity of the air quality in mixing-ventilated rooms. The typical values of ventilation effectiveness range from 0.4 to 1. The lower values are achieved when the temperature of supply air is higher than the temperature of air in the breathing zone. The low values of ventilation effectiveness are associated with heating. In cooling application, the ventilation effectiveness typically ranges from 0.9 to 1.

1.5.2 Displacement ventilation Nielsen (1993) and most recently REHVA (2002) provide comprehensive overviews of displacement ventilation (DV). Ventilation air is introduced direct to the occupied zone at a temperate slightly (3-6°C) below the room temperature by floor- or wall-mounted diffusers. Due to the gravity forces, it spreads along the floor in an almost horizontal layer. The thermal plumes generated by warm surfaces (people, equipment, etc.) entrain and transport the air as well as heat and contaminants from the lower levels of the space upward, where they are exhausted at or close to the ceiling. The fraction of air that is not exhausted (the exhaust rate is usually smaller than the flow generated by the plumes) is forced to flow downwards and mix with the ambient air. A level that is said to separate the clean and polluted parts of the room is called a neutral or stratification height. Displacement air distribution has the ability to provide occupants with better air quality, as compared with traditional mixing systems, especially when the contaminant sources are also heat sources (Brohus and Nielsen, 1996). Energy can be used more efficiently, because air is exhausted at temperatures that are several degrees above the temperature in the occupied zone. However, vertical air temperature differences always exist in displacement-ventilated rooms, with low air temperatures and high air velocities often near the floor. Therefore, if not well designed, the risk of local discomfort due to draught (Pitchurov et al., 2002) and vertical air temperature difference is high (Melikov and Nielsen, 1989). Contaminant distribution The undisturbed flow pattern gives a gradient in both temperature and contamination within the room. The gradients are not necessarily of the same form. The characteristic two-zonal contaminant distribution is generated when the contaminant sources are associated with heat sources (Brohus and Nielsen, 1996). This is the case of e.g. electronic equipment or human bioeffluents emitted from a still person. The interface layer between the lower clean and upper polluted zone is formed where the net flow rate of plumes equals the supply airflow rate. The thickness of the layer is typically about 0.5 m (Etheridge and Sandberg, 1996). The amount of air transported in the convection flows, and the height to which the

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plume rises, depend on the shape, surface temperature and distribution of the heat sources. Furthermore, the high to which the plume rises is strongly influenced by the temperature gradient in a room. If the convection current from the contaminant source, in a room with several heat sources, is not the warmest, the contaminant may settle in a layer where the concentration locally exceeds the exhaust concentration (Skistad, 1994). Data on the volume flux in the plumes above different sources can be found e.g. in Nielsen (1993), Mundt (1995) or Aksenov et al. (1998). In a calm environment a free convection flow exists around warm or cold surfaces. Around people, the free convection flow is able to a great extent to entrain and transport air from the lower part of the space to the breathing zone. Brohus and Nielsen (1994, 1996) proposed a quantity named the effectiveness of entrainment in the human boundary layer, which expresses the ability of the free convection flow to supply (fresh) air from the floor area to the breathing zone. An almost linear relationship between the effectiveness and the ratio of the stratification height to the breathing zone height was identified. However, the inhaled air quality in displacement ventilated rooms may not be high when contaminants are passive, i.e. without any significant initial momentum or buoyancy, and/or positioned close to a person (Brohus and Nielsen, 1995, 1996). Murakami et al. (1998) introduced a modified effective entrainment ratio, which takes into account the ability of the rising stream to carry not only clean air but also contaminants, which decrease the inhaled air quality. Hayashi et al. (2002) performed CFD analyses showing the spatial distribution of the portion of air to be inhaled by a standing, sitting and sleeping occupant. Unless the source is located on the floor or close to an occupant, the values of ventilation effectiveness typically exceed 1. Examples of ventilation effectiveness in the breathing zone as reported in CEN Report 1752 (1998) range from 1.2 to 1.4, assuming that the contaminant sources are distributed uniformly in the space. The results of various full-scale measurements reported in the literature are summarized in Brohus and Nielsen (1996). The values of ventilation effectiveness ranged from 1 to 8 (referred to as the personal exposure index). Activity of occupants The activity of occupants in a displacement-ventilated room is generally detrimental to the inhaled air quality. Movements of a person can disturb the boundary layer around his/her body, which prevents the breathing zone from being supplied with usually clean air from the lower space when the person is still. A person moving/walking in the room may also disturb the overall temperature and contaminant distribution and affects thus the inhaled air quality of other people in the room indirectly. Hyldgaard (1994) and Brohus and Nielsen (1995) studied the concentration of contaminants inhaled by a thermal manikin exposed to uniform horizontal flow of different velocities in a wind channel. The effect of movements of the manikin was assumed to be equivalent to the impact of the uniform velocity field. They showed that the boundary layer and hence the inhaled air quality was affected considerably already at a velocity of 0.1 m/s. Mattsson (1999) and Bjørn et al. (1997) carried out a study with a person simulator moving continuously back and forth in a displacement-ventilated room. The inhaled air quality decreased at around 0.2 m/s, at which speed the convection flow reportedly seemed to be deflected away from the breathing zone. All the studies generally agree that the air quality in the breathing zone of a fast walking person (> 1.0 m/s) can be considered the same as in the ambient air.

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The ambient air quality in the occupied zone depends strongly on the physical activity of the people in the room. Brohus and Nielsen (1994) measured the concentration profiles with four persons, two of whom were either seated or walked normally around the room. They showed that although the concentration profile changed between the two conditions, the moving people were not able to destroy the stratification completely. Mattsson (1999) showed that a rather high activity, such as a sports activity, is needed to completely abolish the displacement effect. Physical measurements with the back and forth moving human simulator reported by Mattsson (1999) and Bjørn et al. (1997) showed that already at a speed of 1.0 m/s the distribution was close to the completely mixed situation. Exhaled air The distribution of exhaled air deserves special attention because of its importance with respect to the transmission of infectious agents, and in situations with passive smoking. Air is exhaled with positive buoyancy and initial momentum. It typically penetrates the free convection boundary layer around the body and becomes free of it. Observation shows that both the buoyancy and momentum are diffused quickly after the exhalation. In a calm environment the exhaled air may stratify in the breathing zone height. If it does so, the local concentration may exceed several times the concentration around the person at the same height. Different authors disagree about the impact of a breathing opening. Bjørn et al. (1997) observed stratification of air exhaled through the mouth. Exhalation through the nose did not stratify and the contaminant distribution was similar to the case when the contaminant was released in the plume above the manikin. To the contrary, exhalation through the nose reportedly stratified in experiments of Hyldgaard (1994). Bjørn (2002) showed that the pulmonary ventilation rate is more important for the flow pattern in front of a person than the exhaled air temperature. According to Bjørn (2002), the stratification is affected by the steepness of the vertical temperature gradient in the immediate surroundings of the respiration zone. The critical limit for the stratification to develop is approx. 0.5 °C/m. Bjørn et al. (1997) showed that movement of a manikin in the room at a very low speed (0.2 m/s) dissolved the stratification layer of exhaled air. Bjørn and Nielsen (1996) studied personal exposure to air exhaled by another person using two breathing thermal manikins standing in a displacement-ventilated room. They showed that the inhaled air concentration was significantly greater than in the exhaust when the manikins exhaled directly towards each other. As the distance between the manikins increased, the exposure decreased. The concentrations inhaled were comparable to the exhaust concentration when the distance exceeded 1.2 m for exhalation though the mouth, and 0.8 m for exhalation through the nose. When exhalation was directed towards the back of the manikin, larger exposures did not occur. A CFD simulation by Bjørn and Nielsen (1998) showed that the personal exposure was very sensitive to variations in the convective heat output of both the exposed person and the exhaling person, and in the cross-sectional exhalation area (mouth) and the pulmonary ventilation rate of the exhaling person. Particles Only the distribution of contaminants that follow air currents, such as gases, vapours and small particles, has been considered so far. The ability of DV to displace the contaminants that do not follow the currents, namely larger particles, to the upper part of the room and create a fairly clean lower zone may be limited. Mattsson (2002) studied the vertical distribution of particles generated through office-like activity of people ranging from 0.3 to > 25 µm. The distribution was measured in a displacement-ventilated room at moderate to high ventilation rates. He showed that the displacement effect started to decline for particles in the range 5-10 µm. Slightly negative concentration gradients were observed for particles >

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10 µm at the lowest ventilation rate (1.5 air changes per hour), suggesting a significant influence of gravity. Mundt (2001) obtained similar results. Thermal environment A vertical temperature gradient will rise in a room due to the vertical flow of heat to the ceiling region. The gradient is always positive, increasing temperature up to the ceiling. Its magnitude and shape depend strongly on the geometrical extension, surface temperature and vertical location of the heat sources, supply airflow rate (Mundt, 1995) and the emissivity of the surfaces in a room (Nielsen, 1995; Li et al., 1993). Temperature gradients for different rooms and heat source arrangements are presented elsewhere. It is a general experience that the vertical temperature gradients are identical at any location in the room outside areas with thermal plumes. Nielsen (1995) summarized five temperature distribution models with varying levels of complexity. The temperature gradient is often assumed to vary linearly with the height from a minimum temperature near the floor to a maximum temperature near the ceiling. Mundt (1995) showed that the linear model is a good approximation in rooms of moderate heights. The thermal stratification in the room air is much less influenced by physical activity than the contaminant stratification, apparently due to the accumulation of heat in materials (Mattsson, 1999; Brohus and Nielsen, 1994). The stratification is usually quite stable, even if people are moving around in a room. A stronger gradient is less sensitive to the disturbances. Even if the room air is temporarily mixed, the stratification is re-established after cessation of the activity. Air distribution in the vicinity of terminals In order to avoid thermal discomfort it is necessary to be aware of the adjacent zone close to the air terminal device, so-called near zone. Several definitions are nowadays used in practice. Originally, the near zone was considered as a zone around the outlet within which the mean velocity is higher than 0.2 m/s. In some cases the near zone was restricted only for heights 0.1 m above the floor level. Melikov et al. (1990) proposed a more reasonable definition of the near zone based on the percentage dissatisfied due to draught (Fanger et al., 1988; ISO, 1994). Melikov and Langkilde (1990) showed that the zone for 15% dissatisfied penetrates almost twice as deep into the room as the zone defined by the mean air velocity of 0.2 m/s. The size and the shape of the near zone are a characteristic of each air terminal. The information is usually available from a manufacturer. Practical considerations There are several disadvantages associated with the DV concept for offices. • The lowest permissible supply air temperatures restrict the cooling capacity of DV to 30-

60 W/m2, depending on the air terminal design. In contrast, overhead mixing ventilation systems can remove loads of up to 100 W/m2 comfortably.

• Displacement ventilation is not suitable for heating. • Large airflow rates of clean air are required in order to maintain a high level of

stratification, which is necessary to ensure a high quality of inhaled air. • There are large space requirements in respect to the near zone. The areas can neither be

occupied nor furnished. • The principle ensures horizontal uniformity and limits individual control over the

environment. • The principle may be inefficient in regard to passive pollution sources.

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1.5.3 Underfloor air distribution UFAD systems use an open space between the structural slab and the underside of a raised floor to deliver ventilation air direct to the occupied zone. The air is delivered to the space through floor diffusers or grills and returned at or close to the ceiling. An UFAD system may offer improved air quality levels in the occupied zone due to the stratification of contaminants and reduced energy. Moreover, UFAD systems may better address the individual differences in regard to thermal comfort as well as provide flexibility of relocation and reconfiguration of workplaces. Loudermilk (2003) states, however, that cases that involve justification of a raised floor system solely based on the integration of an underfloor air delivery system are few. Instead, economic justification (in contrast to overhead mixing systems) is usually achieved upon the flexibility the platform offers to the relocation of incorporated power, voice and data services for the space. Several factors affect the design and thus the typical air distribution pattern of underfloor ventilation systems. First, there is an increased possibility of extensive draught as well as vertical temperature difference due to the close proximity of supply outlets to occupants. The requirement for a small near zone facilitates high induction air terminals, which discharge air most efficiently by means of turbulent jets. The jets are often designed to develop in the vertical direction in order to reduce the extent of the near zone. The thermal comfort issues practically limit the supply air temperatures to 15-18°C, and the quality of supply air up to 50 L/s per diffuser. This increases the number of diffusers that need to be used as compared to the number of ceiling-based diffusers used in room with overhead mixing ventilation. Consequently, numerous diffusers providing turbulent jets reportedly create mixing conditions in the lower part of a room (Loudermilk, 1999). The height above the floor where supply air stream velocity decreases to 0.25 m/s is referred to as the throw height or a maximum penetration height of supply air jets. It is a common assumption that the mixing effect is then minimized. Above the mixing zone, air is entrained into the heat sources and drawn upward in the form of thermal plumes, as in the case of displacement ventilation. The plumes then transport heat and contaminants to the upper space of the room where a mixed zone is typically established. A relation between the throw height and the stratification height is crucial for the air quality performance of UFAD systems. Figure 1.3 or illustrates two scenarios that may happen. Assuming there is a step change of concentration from the supply air level to the exhaust level, and the interface between the lower clean and the upper polluting zone is higher than the breathing zone height, the inhaled air quality would equal the supply air quality (Figure 1.3, left). The contaminants are assumed to be associated with heat sources (e.g. human bioeffluents). If the interface height is below the breathing zone height, but still higher than the throw, the inhaled air quality could be predicted using the model of Brohus and Nielsen (1996) for displacement ventilation. Yamanaka et al. (2002) proposed a model to calculate the vertical distribution of contaminants, when the maximum throw is greater than the height of the interface. The model was verified experimentally in a scaled room. Providing that the supply airflow does not affect the thermal plumes around occupants (i.e. they can transport air upward), it interacts with the interface and forces the contaminants from the upper polluted zone to flow downward (Figure 1.3, right). The model allows for predicting the contaminant concentration in the lower occupied zone and the thickness of the interface layer. Occupants were considered the only sources of heat and contaminants.

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Figure 1.3. Air distribution models for underfloor air distribution. The vertical throw and the extent of the near zone depend on the characteristics of a diffuser (geometry), the supply air volume and the temperature difference between supply air and room air. Several types of floor diffusers are recognized. Swirl diffusers supply air with high-turbulence flow and a large induction effect; they are the diffusers most often available commercially. Constant air velocity (active) diffusers are designed for VAV operation. An internal automatic damper maintains a constant discharge velocity, even at reduced supply air volumes. The throw is relatively constant as the discharge area is throttled. The diffuser may also consist of a slotted square floor grill supplying the air in a jet-type pattern. Displacement floor outlets generate low-turbulence, radial horizontal flow for displacement ventilation. For many years, linear floor grills have been used, particularly in computer room applications. Air is supplied in a jet-type planar sheet making them suitable for placement in perimeter zones adjacent to exterior windows. The selection of floor diffusers should be based on the depth of the diffuser’s mixing zone and the radius of the near zone. Bauman and Webster (2001) recommend designing the floor diffuser systems to allow mixing only in the occupied zone, i.e. up to 1.2-1.8 m. Loudermilk (2003) argues that the mixing must be limited to just below the respiration level in order to transmit the exhaled air to the exhaust and thus prevent cross-respiration to other occupants. The mixing zone depth is also critical for creating the upper level stratification necessary to efficiently isolate space convective loads (Loudermilk, 1999). Consideration must be taken to ensure that outlets are not located so close to stationary occupants because uncomfortable conditions around the outlets are likely to bother them. There are not many studies on the thermal performance of UFAD systems either. A similarity of underfloor ventilation with displacement ventilation is often anticipated. No particular attention was paid to the impact of the vertical throw on the thermal environment. Webster et al. (2002a, b) studied the thermal stratification with variable area and swirl diffusers in a test room. They showed that as the total room airflow increases at a constant heat load, room air stratification decreases and vice versa, particularly for the swirl diffusers. The reason might be the change of the diffusers throw. The temperature near the floor remained relatively constant unless the supply air temperature changed. Variations of the supply air temperature increased or decreased the temperature profiles, but it did not affect their shape. The variable area diffusers were less sensitive to diffuser flow rate, because they maintained a constant throw estimated at 1.8 to 2 m. Bauman and Daly (2003) state that the normalized temperature near the floor increases from 0.5 with displacement ventilation to 0.7 with UFAD because of mixing in the occupied zone.

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Despite the lack of deeper understanding of the room air distribution with UFAD systems, mixing and displacement air distributions are the extreme cases. The literature (e.g. Arens et al., 1991; Bauman et al., 1991; Fisk et al., 1991; Loudermilk, 1999; REHVA, 2003; Bauman and Daly, 2003) indicates that the airflow pattern of UFAD resembles displacement ventilation when a discharged strategy with a short vertical throw is employed. On the other hand, high airflow rates supplied vertically may reach the ceiling and produce mixing, which is comparable to overhead systems. The most recent overview of an underfloor air distribution (UFAD) can be found in Bauman and Daly (2003), who address also many practical issues such as the design of the supply plenums, UFAD equipment, energy use, etc.

1.5.4 Control strategies There are two basic strategies to maintain a comfortable environment in response to changing heat load by supply air. A Constant Air Volume (CAV) system changes the supply air temperature in response to the space load, while maintaining a constant airflow. The indoor air quality remains the same unless the contaminant emission varies. With a Variable Air Volume (VAV) system, a terminal unit at the zone varies the quantity of supply air to the space. The supply air temperature is held relatively constant. Supply air temperature must always be low enough to meet the cooling load in the most demanding zone, and to maintain appropriate humidity. The ability to reduce the supply air quantity allows for energy savings on the one hand, and on the other it reduces the air changes per hour and thus decreases the indoor air quality. The VAV strategy can also be operated on the basis of contaminant concentration, such as CO2. The airflow rate is then varied in order to maintain air quality, while changes in temperature maintain the thermal environment.

1.6 Interaction of airflows Airflows of a different nature exist in the vicinity of an occupant. The free convection flow around a human body, the flow of respiration and the flows generated by PV, and the total-volume ventilation systems are the most important. The complex interaction of these airflows determines both the inhaled air quality and thermal comfort. Section 1.5 presented the airflow patterns with the most common ventilation principles. Transient flow of respiration The respiration depends primarily on the activity level and the body weight. At light work a seated person of an average size has a respiration frequency of 10 per minute. Each cycle of the breathing function consists of inhalation, exhalation and pause. The pulmonary ventilation (airflow rate) is 0.6 L per inhalation and the typical breathing pattern is through the nose. The exhaled air has a temperature of approximately 34°C (influenced by room air temperature) and a relative humidity close to 100% (Höppe, 1981). The inhaled air quality is affected mostly by the flow of inhalation. The flow has only a small impact on the airflow around the human body due to the rapid velocity decay near the opening. Hyldgaard (1994) calculated that assuming the air is taken from half a sphere, the velocity already at a distance of 0.05 m from the mouth decreases to 0.015 m/s. Hence, the impact of inhalation through the mouth or through the nose on the inhaled air quality is negligible. The flow of exhalation affects the air movements around the human body much stronger than the flow of inhalation. Hyldgaard (1994) performed velocity measurements along the

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axis of the exhaled air from the nose air jet with the head in upright position. He reported that the mean velocity of the exhaled air from each nostril is 1.85 m/s. The direction of the exhalation is approximately 45° below the horizon. The two nostrils create two independent jets 30° apart which do not collapse but diffuse in the room. Section 1.5.2 described the distribution of exhaled air in a room with displacement ventilation. Free convection flow around a human body Upward free convection air movement around the human body exists due to differences between the temperature of the body surface and the room air temperature. The airflow is slow and laminar with a thin boundary layer at the lower parts of the body and becomes faster and turbulent with a thick boundary layer at the height of the head. The velocity profile is similar to a wall jet. Homma and Yakiyama (1988) measured a maximum velocity and the boundary layer thickness at the ankle and beside the head of a standing naked subject. The maximum velocity and the boundary layer thickness were 0.1 m/s and 8 mm for the ankle level and 0.25 m/s and 150-200 for the head level, respectively. The room air temperature was 20°C. Melikov and Zhou (1996) measured the velocity and temperature distribution at the neck of a seated and clothed thermal manikin using a highly accurate Laser Doppler Anemometer. The maximum velocity was 0.18 m/s at a distance of 5-8 mm from the surface. The velocity boundary layer thickness was 80-90 mm. The thickness of the temperature boundary layer was 30-35 mm. The air movement caused by the free convection flow is important for people’s thermal comfort and air quality. As described earlier in Section 1.5.2, the flow in the human boundary layer is able to entrain and transport air (polluted or clean) from the lower levels to the breathing zone, from where it is inhaled. Furthermore, the air is heated, humidified and polluted by bioeffluents generated by the body and it is distributed to the room in the form of a thermal plume. Personalized airflow Airflow generated by personalized ventilation can be very different. There is primary airflow supplied from an air terminal device, but also secondary airflows generated by entrainment in a confined workstation space. As stated earlier, the personalized airflow should be of low velocity and low turbulence intensity in order to reduce the mixing of clean and polluted air. The primary air stream should be directed at the breathing zone, where it needs to penetrate the free convection flow as well as the flow of exhalation in order to achieve high quality of inhaled air. Interaction of airflows Brohus (1997) investigated the inhaled air quality in regard to a point contaminant source in a unidirectional flow field generated in a wind channel. He found that the personal exposure depends highly on the source location as well as the flow direction relative to the person. Measurements and smoke tests confirm that the thermal boundary layer that entrains and transports air from below to the breathing zone in a calm environment is considerably affected at uniform velocities above 0.05 – 0.10 m/s. Melikov and Zhou (1996) showed that an invading flow with a mean velocity of only 0.1 m/s and a turbulence intensity of 10% is able to destroy the free convection flow at the neck of a person. The velocity boundary layer decreased to approx. 40 mm and the temperature boundary layer to less than 10 mm. The air temperature near the skin surface was decreased by 4°C, which lead to an increase in the heat flux by 22%.

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Cermak et al. (2002) used a two-dimensional particle image velocimeter (PIV) to identify the complex flow at the breathing zone of a seated person exposed to airflow from a PV system. A thermal manikin with a realistic breathing function was used to simulate a human being. The air terminal was the 2nd generation Movable Panel tested by Kaczmarczyk et al. (2002a, b, accepted) and described in Section 1.3. The panel was positioned in front and above the breathing zone at a distance of 0.45 m from the manikin’s nose. The PIV system allowed instantaneous measurements of the velocity field to be taken corresponding to exhalation, inhalation and pause. Figure 1.4 presents the mean air velocity contours during exhalation through the mouth when the personalized airflow rate was 5 L/s. The results showed that the personalized airflow penetrated the free convection flow even at a very low airflow rate. As documented in the plot, the flow of exhalation was deflected downward and the free convection flow at the chin destroyed.

Figure 1.4. Distribution of the mean air velocity (m/s). PV airflow rate 5 L/s. Exhalation through the mouth. Reprinted from Cermak et al. (2002). Recently, prior to the present study, Cermak and Melikov (2003) examined the interaction of PV airflow and the room airflow in a mock-up of a 2-person office. The 2nd generation Movable Panel was combined with an underfloor air distribution system and tested in regard to the transmission of exhaled air between occupants. Two breathing thermal manikins facing each other were used. One manikin was polluting and the other one exposed. They showed that the PV of the polluting manikin increased the concentration of exhaled air in the room as compared to the reference case of underfloor ventilation alone. As a result of mediocre efficiency, the PV was not able to protect the exposed manikin from inhaling contaminants. The inhaled air concentration increased up to 3.6 times when both the manikins were using their PV systems at 20 L/s per workplace. The study revealed a possible drawback of the PV concept, but due to the small number of experimental conditions it was impossible to draw a general conclusion. The interaction between the airflow generated by PV, occupants (free convection flow around the body and respiration) and the airflow pattern outside the workplaces has not been studied in detail. The design of PV as well as the parameters of the supply airflow may have an impact on the distribution of contaminants at workplaces and in a room. The use of PV systems by occupants, i.e. their preferred rates, temperatures and directions of supply airflow that differ at each workplace, may affect the distribution as well.

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2. Objectives

The objective of the present study is to identify the performance of personalized ventilation in combination with total-volume ventilation in regard to air quality (including transmission of contaminants between occupants) and thermal comfort in the occupied zone of rooms. The personalized ventilation design, total-volume ventilation principle and their control are of main interest. An additional objective of the study is to recommend a strategy for application of personalized ventilation in practice.

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3. Method

The performance of personalized ventilation combined with total-volume ventilation was examined in full-scale experiments. The experiments were divided into two stages according to the total-volume ventilation system applied (Table 3.1). In the second stage, three sets of experiments were performed. The method was identical for all experiments with only minor changes in between the stages. Table 3.1. Experimental stages.

Stage Total-volume ventilation Aim 1 Mixing, displacement Overall performance 2-1 Underfloor Overall performance 2-2 Underfloor Impact of the throw of UFAD 2-3 Underfloor Impact of the airflow rate of PV

3.1 Experimental design A mock-up of a typical office with two identical workplaces was built in a climate chamber (length x width x height = 4.8 x 5.4 x 2.6 m3). Two breathing thermal manikins were used to simulate occupants (Section 3.5.1). Each workstation consisted of a desk with an air terminal device for personalized ventilation, a personal computer and a desk lamp (Section 3.4.1). The workplaces were arranged behind each other with the manikins facing in the same direction. The layout aimed at creating the worst possible scenario with PV transmitting large portions of human-produced contaminants from the front manikin to the back manikin. Figures 3.1 and 3.2 show respectively the layout of the office and its photo. Air temperature outside the chamber was controlled at 25°C in order to reduce the heat transfer through the walls. The office thus simulates an interior section of an open-plan office, if the blocking effect of the walls is disregarded. The manikins were dressed with underwear, short-sleeved T-shirt, pants, socks and shoes, giving a total clothing insulation of 0.45 clo (estimated). The upholstered office chairs on which the manikins were seated had an additional thermal insulation of 0.15 clo. Floor covering and occupants with their bioeffluents and exhaled air were selected as the most common contaminant sources in offices. Three different tracer-gases were used (Section 3.4.2). The floor covering was simulated by means of a rectangular grid of tubing, from which carbon dioxide (CO2) was released over the entire floor area. The tubing was perforated every 0.6 m creating an array of 8x8 dosing points. Air exhaled from the front manikin was marked with sulphur hexafluoride (SF6). The bioeffluents were simulated with nitrogen dioxide (N2O). The gas was released at three locations under the clothing of the front manikin. Both the floor covering and the exhaled air from the front manikin were present in all the experiments (both stages). The bioeffluents were studied only in stages 1 and 2-1. In the stage 2-2, N2O was used to mark the air exhaled from the back manikin (such as SF6 for the front manikin). This allowed for the evaluation of the transmission of exhaled

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air between the two manikins. In stage 2-3 different contaminant sources were used (see Table 5.3). Two types of air terminal device for PV were tested. They were the Round Movable Panel (RMP) mounted on a movable arm duct and the Vertical Desk Grill (VDG) positioned at the front edge of a desk (Section 3.3.1). Both types currently represent the most promising solutions for providing excellent air quality and preferred thermal comfort for occupants. The major difference is the direction of personalized airflow in respect to a person. The flow from the RMP and the VDG is respectively transversal and assisting to the flow in the human boundary layer. Only one type of terminal was tested at a time. The positioning was adjusted in order to comply with the positioning most often preferred by people (Kaczmarczyk et al., 2002b; Kaczmarczyk, 2003). The positioning did not change during the study.

Figure 3.1 Office plan: (1) front thermal manikin – 23 sections, (2) back thermal manikin – 16 sections, (3) Personalized ventilation – RMP, (4) Personalized ventilation – VDG, (5) Displacement ventilation supply, (6) Mixing ventilation supply, (7) Underfloor ventilation supply, (8) Exhaust, (9) 17” computer monitor – 70 W, (10) Computer tower – 75 W, (11) Desk lamp – 55 W, (12) Ceiling light fixture – 6 W, (A)-(E) Measurement positions. Four scenarios were examined: (1) both manikins using PV, (2) front manikin using PV while back manikin did not or (3) vice versa, (4) neither of the manikins using PV, i.e. total-volume ventilation alone (reference case). In most cases the personalized airflow rate was either 7 L/s or 15 L/s per person. In one experiment 30 L/s per person was supplied. The supply air temperature was 20°C in all experiments (all stages). The combinations tested are presented in detail at the beginning of each result section. The performance of PV was studied in combination with mixing, displacement and underfloor ventilation (Table 3.1). Mixing and displacement ventilation systems are well understood, besides the fact that they are the most common air distribution principles used today. The underfloor ventilation system was studied more extensively. An installation of PV in conjunction with a raised floor is easy, allowing both PV and total-volume systems to benefit from the same platform. For all combinations air was exhausted at the ceiling level.

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Figure 3.2. Photo of the office. The arrangement is identical to that used in the study except: (1) the manikins did not have wigs and were dressed in short-sleeved T-shirts and (2) there were two racks holding low velocity anemometers and tracer-gas sampling tubes in the room. The number and distribution of the heat sources corresponded to a typical office. The total sensible heat gain was 580 W (22.5 W/m2) and constant during all experiments. Studies showed (Kaczmarczyk et al., accepted; Zeng, 2002; Yang, 2003) that the improvement of inhaled air quality and thermal comfort with PV is greater at elevated room air temperature. The exhaust air temperature was designed at 26°C. The temperature in the occupied zone was intended to fulfil the requirements of present standards for summer conditions (ISO, 1994; CEN, 1998 – category B). Both PV and total-volume ventilation supplied outdoor air. The amount of outdoor air per person was 40 L/s in most experiments, and down to 25 L/s in some experiments in stage 2-2 (see below). The ventilation rate fulfilled the requirements for removal of sensory pollution load when 40-100% tobacco smokers are present, according to CR 1752 (1998), category B, and ensured high elevation of interfacial layer (stratification height) when displacement ventilation was used. The recirculation of exhaust air to the supply air was not utilized in order to increase sensitivity of the tracer-gas measurements. The supply air temperature and airflow rates were set in order to allow for comparison of the combined systems. In stages 1 and 2-1 the supply air temperature was 20°C. Assuming ideal mixing, the total airflow rate was calculated at 80 L/s (= 4.3 air changes per hour). The total amount of air supplied to the office was kept constant. The use of PV thus led to a decrease in the total-volume ventilation rate (i.e. VAV control). In the stage 2-2 experiments the impact of the throw of UFAD on the performance of the combined systems was examined. Two throw heights were achieved by providing different airflow rates. The first airflow rate was 80 L/s, i.e. identical to the previous stages. The second rate was 50 L/s (= 2.7 air changes per hour). In the reference cases without PV, the supply air temperatures of UFAD were respectively 20 and 16.4°C. Contrary to stages 1 and 2-1, the underfloor airflow rate was kept constant (i.e. CAV control), 80 L/s or 50 L/s, regardless of the PV use. When PV was used, the supply air temperature of underfloor ventilation was increased in order to ensure a constant cooling capacity of ventilation air (PV combined with UFAD). The system was not under thermostatic control and the supply air temperature set point was determined from a calculation. A detailed overview of the supply air conditions is given in Table 5.2, page 74. The performance of the combined systems was studied in regard to inhaled air quality and thermal comfort. Section 3.7 describes the criteria for evaluation. The breathing thermal

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manikins were used for the assessment of inhaled air quality (contaminant concentration, inhaled air temperature) and thermal environment in the workplaces. The assessment of the environment for standing and/or walking occupants was based on the measurement of contaminant concentration, air temperature and air velocity at five positions throughout the room (Figure 3.1). At positions A and B the measurement of air velocity and temperature were performed at several heights. The supply and exhaust air temperatures and the surface temperatures of walls were monitored as well.

3.2 Air movement room Figure 3.3 shows a sketch of the climate chamber. The chamber has a modular structure based on a load-bearing steel construction with a module of 1.2 m. Its maximum size is 7.2 x 4.8 x 5.0 m3 (length x width x height). The walls surrounding the perimeter are made of insulated chipboard. One of the walls is single glazed up to a height of 2.4 m. The floor is made of 0.6 x 0.6 m2 chipboard tiles raised 0.7 m above a structural concrete slab. The surface of the floor is finished with a low-polluting material. The ceiling is made of 0.6 x 0.6 m2 gypsum tiles suspended 0.4 m from the ceiling steel construction. The ceiling is divided into 3 parts (2.4 x 4.8 m2) and can be adjusted to different heights, each part separately or as a whole. A height of 2.6 m was used in the present study. The chamber size was also modified with a floor-to-ceiling partition, which splits the chamber into two sections. The larger section, sized 5.4 x 4.8 m2, was used in the experiments, while the other part was empty and not used. Neither the ceiling nor the floor was thermally insulated. There were six fluorescent light fixtures evenly distributed along the ceiling in order to provide overall lighting. The chamber, including the light fixtures and the door, was carefully sealed prior to the experiment.

Figure 3.3 Sketch of climate chamber. The section framed bold sized 5.4 x 4.8 x 2.6 m3 (length x width x height) was used for the experiment. The climate chamber was situated in a laboratory hall sized 11 x 10 x 8 m3. The floor and the ceiling of the hall were made of concrete, the walls of bricks. The hall was ventilated and air-conditioned by mixing ventilation. The temperature in the laboratory hall was controlled at 25°C, i.e. similar to the mean air temperature inside the chamber.

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3.3 Ventilation systems

3.3.1 Personalized ventilation Round movable panel (RMP) The RMP was an air terminal device with a round front panel with a diameter of 215 mm. The face (free) area was 0.027 m2. The RMP was designed so as to provide a low-turbulent flow with a long potential core in order to reduce mixing of the outdoor air and ambient room air. The RMP was mounted on a movable arm-duct attached to the desktop. The construction of the movable arm-duct allowed for changing the position of the ATD and the angle of the supply jet. Figure 3.4 shows the positioning of the RMP used in the present study. The figure shows also the posture of a manikin and its distances from the desk and the computer monitor. The layout was identical for the two manikins and maintained during the whole study.

Figure 3.4 Details of the positioning of the Round Movable Panel Vertical desk grill (VDG) The air terminal device consisted of a plenum box with two air discharge openings. The plenum box was attached underneath the desktop. The supply air entered the plenum at the back of the desk. The two discharge openings were located in the horizontal and the vertical plane at the front edge of the desk. The opening on the horizontal plane (20 x 220 mm2) supplied air vertically to the breathing zone. The opening in the vertical plane (15 x 245 mm2), which was aimed at the horizontal supply toward a torso, was closed. The openings were equipped with vanes for directing the airflows. Figure 3.5 shows the construction and positioning of the vanes as used in the experiments.

Figure 3.5. Vertical desk grill. Construction and positioning of the vanes.

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Personalized air temperature and airflow rate The air terminal devices were provided with conditioned outdoor air. The connection was made with a flexible duct using the plenum beneath the floor. The supply air was first cooled in the main air-conditioning units and then heated separately for each workstation to a temperature of 20°C. The reference temperature sensor was mounted direct in the air terminal. The on/off control used caused fluctuations of the supply air temperature by approx. ±0.1°C around the mean. The air humidity was not controlled. A differential pressure sensor (Micatrone, type MFS-C-080) was used to measure the airflow rate. The airflow rate was proportional to the pressure difference measured before and after the body of the sensor. The sensor was calibrated against an orifice plate and with a tracer-gas constant emission method prior to the experiments. The construction and characteristics of the sensor ensured that it was possible to measure flows down to 3 L/s with high accuracy and low drop of pressure. The measurement error as specified by the sensor manufacturer was < 3% of the actual airflow. The pressure differential was measured with a high precision micromanometer (Furness, type FCO510). The accuracy was 0.025% of reading up to 20 Pa, ± 0.01 Pa; and 0.25% of reading between 20 and 200 Pa, ± 0.01 Pa. The measured pressure was roughly 4, 17 and 70 Pa at a rate of respectively 7, 15 and 30 L/s.

3.3.2 Total-volume ventilation Commercially available supply and exhaust air terminals were used. The terminals were sized based on the manufacturers’ guidelines. The positioning of the air terminals in the room is shown in Figure 3.1. Mixing air terminal device A swirl type diffuser (TROX, type RFD-R-D-US/250), shown schematically in Figure 3.6, was used for its ability to ensure a high level of induction and rapid reduction in temperature differential. The diffuser was suitable for the VAV application. Its performance was reportedly optimal between 30 and 110 L/s (i.e. 25 to 100% of the max. airflow rate). Displacement air terminal device A semicircular unit (Lindab, type COMDIF-CBA 2010) with a radius of planar projection of 250 mm and a height of 1000 mm was used for displacement ventilation (Figure 3.8). The unit was fitted with nozzles, which made it possible to change the geometry of the near zone. The adjustment ensured that the supply airflow spread mainly along the walls and only minimally perpendicular to the room. The near zone, defined as a horizontal distance from the wall to the place in a room where the maximum velocity decreases to 0.2 m/s, was predicted and experimentally verified not to be longer than 0.7 m. Underfloor air terminal device Four swirl diffusers (TROX, type FBM-3-EU-K/200-SM) were used for underfloor ventilation (Figure 3.7). The supply ductwork was balanced in order to provide an equal amount of air through each diffuser. The airflow rate through each diffuser was measured with a flow capture hood meter. Each diffuser was fitted with a swirl element, which allowed for adjustments of the swirl in a vertical or a horizontal (radial) direction. The diffuser core had a diameter of 200 mm. The size of the diffusers and their number were selected according to a predicted throw height. Section 5.1.3 presents the results of the air velocity measurement and smoke visualization of the air discharge pattern. The prediction agreed with the measurement.

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Figure 3.6 Swirl diffuser for mixing ventilation. Dimensions in mm.

Figure 3.7. Floor diffuser installed in a floor panel: (1) diffuser core, (2) swirl element for adjustment of air discharge direction, (3) dirt trap, (4) plenum box.

Figure 3.8. Semicircular air distribution unit for displacement ventilation.

Exhaust air terminal device The exhaust air terminals were four circular ceiling diffusers (∅D = 160 mm) with a perforated front plate (Lindab, type PCA-160). The exhaust airflow rate was also balanced between the diffusers. Supply and exhaust air temperature and airflow rate The supply and exhaust air temperatures were measured with a thick film thermistor mounted direct in the terminal device. The thermistors were not radiation shielded; however, they were mounted with care in order to prevent the influence of radiation from the room. Only one sensor was used for the four floor diffusers. The exhaust air temperature was measured with two sensors on the diagonal (the difference was small). The sensors were calibrated against a precision mercury thermometer with a scale division of 0.1°C prior to the experiments. The uncertainty of temperature measurement was estimated to ±0.3°C with a high level of confidence. The supply and exhaust airflow rate were determined by means of an orifice plate measuring section. The installation complied with ISO (1991). Two sizes of an orifice plate were used to cover the range from 50 to 110 L/s. An industrial transducer (Halstrup-Walcher, type PU-0.5-S-230-X-L-02) with an accuracy of 0.5% of reading (0-500 Pa) was used to measure the pressure differential. The accuracy was estimated based on manufacturer’s data and checked with a reference manometer, which was used for the measurement of a personalized airflow rate (Section 3.3.1). The accuracy of the airflow rate measurement was better than 2% (safe estimate).

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3.4 Heat and contaminant sources simulation

3.4.1 Heat sources Table 3.2 shows the total sensible heat gain of the equipment used in the simulated office mock-up. The electrical power consumption was measured and assumed to be equal to the total heat gain (radiant plus convective). The accuracy of the consumption meter as reported by a manufacturer was 0.4 W. The layout of the sources is shown in Figure 3.1. Table 3.2. Total sensible heat gain of the heat sources.

Source Sensible heat gain (W) Breathing thermal manikin 2x 75 Computer tower 2x 74 Computer monitor (CRT, 17") 2x 70 Desk lamp 2x 55 Ceiling light fixtures 6x 6 Total 584 (= 22.5 W/m2)

3.4.2 Contaminant sources Three contaminant sources were simulated by means of a constant emission of different tracer-gases. The emission rate was determined considering the density (impact of buoyancy), safe health exposure, measurement range and accuracy of the gas analyzer and consumption of the gas in respect to its price. Table 3.3 provides a summary of the sources, characteristics of the gases and the amounts used. The doses as well as the exhaust air concentration are given in their typical ranges, because the doses differed between the experimental stages. The dosing set-up was identical for the three gases. It consisted of a gas cylinder, 2-step reduction valve, a needle valve (to adjust the resistance of the distribution tubing) and a glass tube flowmeter (rotameter). The flowmeter was used to monitor the flow stability (not for measurement). The flow rate (dose) was determined from a mass balance of the tracer-gas (i.e. supply rate of outdoor air multiplied by the concentration differential between the exhaust and the supply). The whole arrangement was placed outside the chamber. Practical experience showed that the dosing was constant during the experiments. Table 3.3.Summary of the contaminant sources.

Source Tracer-gas Density* Dose** Supply air Exhaust air (kg/m3) (mL/s) (ppm) (ppm) Floor covering CO2 1.83 24 - 40 400 700 - 900 Exhaled air (front m.) SF6 6.07 0.14 - 0.18 0.01 1.8 - 2.2 Exhaled air (back m.) & Bioeffluents

N2O 1.83 0.12 - 0.15 0.3 1.8 - 2.2

* at 20°C and 101325 Pa ** at 80 L/s (= 4.3 air change per hour)

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Floor covering In order to achieve a uniform distribution over the entire floor a 4-quadrant symmetrical grid of PVC tubing was arranged on the floor of the chamber (Figure 3.9). Very small holes were pierced into the tubing forming a grid of dosing points with distance between the points of 0.6 m. The tubing was placed in metal U-profile beds mounted in between 16 mm thick chipboard plates. A distribution box was arranged in the intersection of the quadrants (i.e. in the centre of the room) and connected with the flowmeter outside the chamber. The CO2 temperature in the distribution box was monitored in order to make sure that the gas was discharged at the room temperature. The discharge temperature was not controlled. Any impact of the expansion of the tracer-gas (after pressure reduction) on the gas temperature was not observed.

Figure 3.9. Simulation of floor contaminant source. Left: one quarter of the floor area with a distribution box in the centre of the room. Right: details of the chipboard and positioning of the tubing in a U-profile spacer. Dimensions in mm. High resistance of the tubing perforation (and therefore a high overpressure in the system), in contrast to a low flow resistance of the tubing, is believed to have ensured the uniformity of the gas distribution. The testing of the uniformity could be troublesome. In the present study it was examined based on the concentrations measured at numerous locations throughout the chamber. The chamber was ventilated with 50 L/s using either the mixing or the displacement principle. The distribution was considered uniform because the concentrations measured at several locations were identical. Exhaled air Two different tracer-gases were used to mark the air exhaled from the two manikins. SF6 was used for the front manikin in all experiments, while in stage 2-2 experiments N2O was switched from simulating bioeffluents generated from the front manikin (see below) to mark the air exhaled from the back manikin. The dosing set-up was identical. After the flowmeter

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there was a 3-way solenoid valve mounted inside each lung. The valve was synchronized with breathing so that the gas was released to the exhalation airway only when the exhalation took place. Providing the pulmonary ventilation (breathing rate) was 6 L/min, the exhaled air contained 1400 – 1800 ppm of SF6 or 1200 – 1500 ppm of N2O (Table 3.3). The exhaled air was heated to respectively 36 and 34.3°C in order to have a density similar to that of air exhaled by people (Section 3.5.1). The heating compensated also low water content in the exhaled air (~ 15% RH exhaled). Human bioeffluents The front manikin was also used as a source of human bioeffluents. A constant dose of N2O was released at three points under the clothing of the manikin: two points were located at armpits and one at a pelvis region. The dosing set-up was identical to the set-up for the exhaled air, except for the 3-way valve (inside each lung). The discharge temperature of N2O was similar to the surface temperature of the manikin, as it was heated when circulated under the clothing.

3.5 Measuring Instruments

3.5.1 Breathing thermal manikin Two breathing thermal manikins were used to simulate occupants. The manikins were identical, except the number of segments their surface was divided into: the front manikin consisted of 23 sections and the back manikin consisted of 16 sections. The second, less important difference, was the location of the connectors for supply and exhaust of respiration air. The connectors were placed at the waist and on the top of the head for the front manikin and the back manikin, respectively. Table 3.4 lists the manikins’ body segments and their surface area. The manikins are shaped as a 1.7 m tall average woman. Their body is made of a 3 mm fiberglass armed polystyrene shell. The junctions at neck, shoulders, hips and knees allow the body to be adjusted in a variety of postures. The surface of the manikins is divided into several sections, each independently heated by means of electric resistance wires. A 0.5 mm thick cover of a glass fiber shield protects the wiring from mechanical damage. The distance between the wires is less than 2 mm in order to ensure uniform temperature distribution on the surface. Thermal control The surface temperature of each body segment was controlled to be equal to the skin temperature of an average person under thermal neutrality. The control is based on the correlation between the skin temperature and the dry heat loss of an average human body according to Fanger’s comfort equation (Tanabe et al., 1994):

tsk QT 054.04.36 −= (3.1) where Tsk is the skin surface temperature, °C,

Qt is the sensible heat loss, W/m2, 36.4 is the deep body temperature, °C, 0.054 is thermal resistance offset of the skin temperature control system, °C.m2/W.

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31

The control system adjusts the power (power consumption is equal to the sensible heat loss) in order to fulfil Equation 3.1. The surface temperature for each body segment is determined from the resistance of the wires. The temperature-resistance relationship was calibrated prior to the experiments. Table 3.4. Surface area of manikins’ body segments (m3).

Body segment Front manikin Body segment Back manikin Left foot 0.043 Left foot 0.043 Right foot 0.043 Right foot 0.041 Left lower leg 0.090 Left lower leg 0.089 Right lower leg 0.090 Right lower leg 0.089 Left front thigh 0.080 Left front thigh 0.16 Left back thigh 0.080 Left back thigh 0.165 Right front thigh 0.083 Right back thigh 0.083 Pelvis 0.055 Pelvis 0.182 Back side 0.110 Scull 0.050 Head 0.1 Left face 0.026 Right face 0.026 Back of neck 0.025 Left hand 0.038 Left hand 0.038 Right hand 0.037 Right hand 0.037 Left forearm 0.050 Left forearm 0.052 Right forearm 0.050 Right forearm 0.052 Left upper arm 0.073 Left upper arm 0.073 Right upper arm 0.078 Right upper arm 0.078 Left chest 0.070 Chest 0.144 Right chest 0.070 Back 0.130 Back 0.133 All 1.480 All 1.476

3.5.2 Artificial lung Each manikin was equipped with an artificial lung that simulates the human breathing function (Melikov et al., 2000). The lung is placed outside the manikins and the respiration air is delivered to and from the manikins with flexible tubing. The breathing cycle (inhalation, exhalation and pause) and the amount of respiration air as well as the temperature and humidity of the exhaled air could be controlled. In the present study the lung was adjusted to simulate breathing of an average sedentary person performing work of light physical activity. The breathing cycle consisted of 2.5 s inhalation, 2.5 s exhalation and pause. The pause of the front manikins and the back manikin was set to last for 0.9 s and 1.1 s, respectively, in order to prevent their synchronization. The breathing frequency was 10 per minute and the pulmonary ventilation was 6 L/min, or 0.6 L per breath. The instantaneous rate was higher, however, because both inhalation and exhalation took 2.5 s of the 6 s breathing cycle, hence: 0.6 L / 2.5 s = 0.24 L/s = 14.4 L/min. The pulmonary ventilation was monitored by means of a glass tube flowmeter (rotameter). The measurement accuracy was ±1.1 L/min (corresponds to ±5% of full scale).

Chapter 3

32

The exhaled air was not humidified in the present study, but heated to a density that is close to the density of air exhaled by people. The density was calculated to be 1.144 kg/m3 based on the following exhaled air properties: air exhaled from a person consists of 78.1 vol.% N20, 17.3 vol.% O2, 3.6 vol.% CO2 and 0.9 vol.% of Ar, its temperature is approximately 34°C at room air temperatures between 20 and 26°C (Höppe, 1981), the relative humidity is close to 95%. However, in the experiments, the actual temperature of air exhaled from the two manikins was different and not identical, due to the different tracer-gas contents (see Section 3.4.2). The breathing openings are shaped so as to mimic a real person. Providing the manikin sits upright, the two jets emerging from the nose are declined 45° from the horizontal plane, and 30° from each other. Each of the nostrils has a diameter of 8 mm. The oval shaped mouth distributes the exhaled air horizontally. The width and the height of the mouth opening are 25 and 5 mm, respectively. Although both the nose and the mouth can be used for exhalation and inhalation, the air was exhaled through the nose (most typical breathing pattern) and inhaled through the mouth. The reason for using the different openings is that there would be a shortcut of exhaled air containing a tracer-gas to the inhaled air (where the gas concentration is analysed) if the same opening were used.

Figure 3.10. Temperature sensor mounted in the mouth of a manikin. Inhaled air temperature The temperature of air inhaled to the manikins was measured with a fast response Thermobead sensor Series B07, with a time constant of 0.12 s in still air. The sensors were mounted in the mouth of the manikins (Figure 3.10) and connected by a transducer to a A/D card (personal computer). Both sensors were calibrated simultaneously against a precision mercury thermometer with a scale division of 0.1°C prior to the experiments. The uncertainty of the measurement was estimated at ±0.2°C with a high level of confidence.

3.5.3 Tracer-gas analyzer The concentration of the three tracer-gases, used to simulate pollution in the present study, was measured continuously with a multi-gas monitor (Brüel & Kjær, type 1302) based on the photo-acoustic infrared detection method of measurement. The measurement range was 1.5 - 150000, 0.004 - 400 and 0.03 – 3000 ppm for CO2, SF6 and N2O, respectively. The analyzer was calibrated for all gases in a certified laboratory prior to the experiments. A multipoint sampler unit (Brüel & Kjær, type 1303) was used to deliver samples of air from up to 6 locations at a time to the analyzer. The samples of air were exhausted outside the laboratory in order to prevent contamination. Both the analyzer and the sampler were controlled with a personal computer, which was also used to store the measured data.

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33

3.5.4 Low velocity anemometers Instantaneous values of velocity and temperature were measured simultaneously at several locations throughout the room. The system (Sensor, type HT400) consists of 16 omni-directional thermal anemometers (Figure 3.11) connected to a measurement station. The velocity sensor was spherical with a diameter of 2 mm, ensuring a fast response. The temperature sensor was shielded against radiation. The temperature compensation of the velocity measurement was utilized. Table 3.5 presents the technical specification.

Figure 3.11. Low velocity thermal anemometer.

Table 3.5. Technical specification of low velocity anemometers.

Measurement velocity range 0.05 to 5 m/s Repeatability range of 0.05 to 1 m/s ±0.02 m/s, ±1 % of reading range of 1 to 5 m/s ±3 % of reading Accuracy of temp. compensation better than ±0.2 %/K Upper frequency* min. 1 Hz, typ. 1.5 Hz Temperature range -10 to +50 °C Accuracy of temp. measurement 0.3 °C * The upper frequency is defined as the highest frequency up to which the standard deviation ratio remains in the limits of 0.9 to 1.1 (Melikov et al., 1998)

3.6 Procedure All experiments were performed under steady-state conditions. Each experiment lasted for 1 day. The procedure as well as data analyses were designed in order to reduce the impact of possible instability of the process in time.

3.6.1 Concentration measurement The tracer-gas concentration was measured in the air inhaled by the two manikins, at 5 positions throughout the room as shown in Figure 3.1, in the supply and exhaust of the chamber, and in the laboratory hall where the test room was located. The concentrations were measured at heights of 0.1, 0.6, 1.1, 1.4, 1.7 and 2.2 m at positions A and B, and at a height of 1.7 m at positions C, D and E. The positions were selected in order to characterize the room airflow pattern. The A and B positions aimed at describing the environment in the vicinity of the workplaces in terms of concentration gradients. The C, D and E positions represented the inhaled air quality for a walking person. In total, there were 20 locations measured. The supply and exhaust airflow rates and the supply air temperature of both personalized and total-volume (TV) ventilation were adjusted in the evening prior to an experiment. This allowed for creating a steady-state condition in the chamber overnight. The dosing of the

Chapter 3

34

tracer-gases started in the morning next day. The tracer-gas distribution was allowed to reach steady-state conditions in approx. 3 hours. The measurement locations were grouped and measured in sequences of 6 (Table 3.6 and Table 3.7). The samples in each sequence were analysed one after another in a loop. The time required to analyse a sequence of 6 channels was about 10 minutes, i.e. the concentration readings from a given location were available in 10 minute intervals. Each location was sampled at least 10, but usually 12 times (~ 2 hours) in order to make reliable statistical analyses possible. In each A1 sequence (see below) 3 readings were typically acquired from each channel (~ 30 minutes). The dosing system was turned off at the end of the experiment and the conditions were set for another day. All heat sources in the chamber including the thermal manikins were running all the time. Table 3.6. Measurement sequences during stage 1 and 2-1 experiments.

Channel Seq.A1 Seq.A2 Seq.A3 Seq.A4 1 Laboratory Lung manikin 1 Pos. A (0.1 m) Pos. B (0.1 m) 2 Laboratory Lung manikin 2 Pos. A (0.6 m) Pos. B (0.6 m) 3 Supply air (PV) Position C Pos. A (1.1 m) Pos. B (1.1 m) 4 Supply air (PV) Position D Pos. A (1.4 m) Pos. B (1.4 m) 5 Supply air (TV) Position E Pos. A (1.7 m) Pos. B (1.7 m) 6 Exhaust air Exhaust air Pos. A (2.2 m) Pos. B (2.2 m) Table 3.7. Measurement sequences during stage 2-2 and 2-3 experiments.

Channel Seq.A1 Seq.A2 Seq.A3 Seq.A4 Seq.A5 1 Lung manikin 1 Lung manikin 1 Pos. A - 0.1 m Pos. A - 1.1 m Pos. B - 0.1 m 2 Lung manikin 2 Lung manikin 2 Pos. A - 0.6 m Pos. A - 2.2 m Pos. B - 0.6 m 3 Supply air (PV) Position C Pos. A - 1.1 m Pos. B - 1.1 m Pos. B - 1.1 m 4 Laboratory Position D Pos. A - 1.7 m Pos. B - 2.2 m Pos. B - 1.4 m 5 Supply air (TV) Supply air (TV) Supply air (TV) Supply air (TV) Supply air (TV)6 Exhaust air Exhaust air Exhaust air Exhaust air Exhaust air Table 3.8. Order of measurement during stage 1 and 2-1 experiments.

Hours 0 1 2 3 4 5 6 7 8 9 10Seq.A1 Supply, Exh, LabSeq.A2 Inhaled air + C,D,ESeq.A3 Position ASeq.A4 Position BTemperature and velocity Table 3.9. Order of measurements during stage 2-2 and 2-3 experiments.

Hours 0 1 2 3 4 5 6 7 8 9 10Seq.B1 Supply, Exh, LabSeq.B2 Inhaled air + C,DSeq.B3 Position ASeq.B4 Position A-BSeq.B5 Position BTemperature and velocity

11

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35

Order of sampling locations It was desirable to monitor simultaneously the gas concentrations in 8 locations: the supply, the exhaust and 6 locations at positions A or B. However, the sampling had to be split into sequences because of the limited number of channels from which the gas analyzer was able to sample at a time. The order of the sampling locations in sequences (and hence also the order of the sequences) was different in the two stages. In stages 1 and 2-1, the integrity of the concentration profiles was prioritized (Table 3.6). The supply and exhaust air concentrations were measured separately as part of A1 sequence, i.e. in between the other sequences. At the same time, the laboratory environment was monitored making it possible to abort the experiment in the case of gas leaking to or from the chamber. The day averages of the supply and exhaust concentrations were used to calculate the ventilation indexes for all locations. The order of the sequences is shown in Table 3.8. The design was improved in stages 2-2 to 2-3. The supply and the exhaust concentration were monitored continuously during the day (Table 3.7). This was possible because the measurement of positions A and B was split in 3 sequences. Table 3.9 presents the order of the sequences. The indexes were calculated using the data corresponding to the same measurement sequence, thus improving the uncertainty. The process instability evaluation had also improved because data from a whole day were available. Detailed analyses performed after the experiments showed that the only source of instability was the fluctuation of CO2 concentration in the supply air during a day, and that the uncertainty was practically comparable with the two designs (i.e. orders of sequences and sampling points).

3.6.2 Temperature and velocity measurements The room air temperature and velocity, the inhaled air temperature and the heat loss from the thermal manikins (manikin-based equivalent temperature) were measured several times during a day at the same occasion. The occasions are indicated in Tables 3.8 and 3.9. Results showed that the all temperatures were extremely stable during an experiment. Table 3.10 summarizes the sampling frequency and duration of the data acquisition used. Table 3.10.Sampling frequency and duration of the data acquisition.

Quantity

Frequency of data acquisition

Duration of measurement stage 1&2-1/stage 2-2&2-3

Inhaled air temperature 20 Hz 1.5 min Heat loss from the manikins 3 per minute 3 min/5 min Room air temperature 5 Hz 3 min/5 min Room air velocity 5 Hz 3 min/5 min Boundary conditions 3 per minute 10 min Inhaled air temperature The temperature was recorded continuously for 1.5 minutes during the transient breathing. Only the data corresponding to a period of 2 s during inhalation were selected using a computer program and analysed. Figure 3.12 shows the typical recording of inhaled air temperature. The diamonds indicate the samples selected for analyses.

Chapter 3

36

25

26

27

28

29

30

0 5 10 15 20 25 30Time (s)

Tem

pera

ture

(°C

)

Inhalation

Exhalation Pause

Figure 3.12. Inhaled air temperature measurement. The mean inhaled air temperature is 26.1°C. Heat loss from the manikins The heat loss from the manikins (Section 3.5.1) was acquired with a personal computer, which was also used to control the surface temperature of the manikins. Data for all body segments were stored together with a whole-body average, which was weighted by the surface area of the segments. Room air temperature and velocity The air temperature and air velocity were measured at position A and B using a system of 16 omnidirectional thermal anemometers (Section 3.5.4). The heights of the measurements were 0.05, 0.1, 0.2, 0.6, 1.1, 1.4, 1.7 and 2.2 m in the cases of displacement and underfloor ventilation and 0.1, 0.35, 0.6, 0.85, 1.1, 1.4, 1.7 and 2.2 m in the case of mixing ventilation. Boundary conditions The boundary conditions measurement involved the measurement of the supply and exhaust air temperatures of PV and total-volume ventilation, laboratory temperature and surface temperatures of internal chamber walls. The same type of a temperature sensor (thick film thermistor, described in Section 3.3.2) and a data acquisition unit were used. There were 4-5 temperature sensors taped on each of the walls, the floor and the ceiling in a cross-like layout. Results showed that the wall temperature was similar to the air temperature at a given height, and the results are thus not reported. As regards the supply air temperature (and total-volume ventilation supply airflow rate), each quantity was monitored by means of the control system of the air-handling unit continuously during an experiment. The supply air temperature and rate of personalized air were checked at regular intervals, corresponding to the other temperature and velocity measurements. Both quantities were very stable during the experiments.

3.7 Criteria for evaluation The performance of PV in combination with different total-volume ventilation principles was examined in regard to the inhaled air quality and thermal comfort. Both seated and standing/moving occupants were considered in the present study. The air quality was evaluated based on tracer-gas concentration and air temperature (Melikov et al., 2000, submitted). Both quantities were measured in the air inhaled by the breathing thermal manikins and at numerous locations throughout the room. No attempt was made to derive a combined index, which would e.g. predict the percentage dissatisfied with the air quality, due to both concentration and temperature. The two quantities were

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37

evaluated separately. Humidity of air, which also affects human perception of air quality, was not analysed. The measurement of heat loss from the thermal manikins was used to assess the thermal comfort of seated occupants. Air temperature and velocity recorded throughout the room were used for evaluation of thermal comfort outside the workplaces. The criteria for evaluation included the draught rating and the vertical air temperature difference between the head and the ankles (ISO, 1994; CEN, 1998).

3.7.1 Contaminant concentration Normalized concentration The concentration of contaminants has most often been expressed in term of normalized concentration, c(–). The concentration was defined as:

SE

S

ccccc

−−

=−)( (3.2)

where c is the contaminant concentration in a point; cS is the contaminant concentration in the supply air; cE is the contaminant concentration in the exhaust air. The normalized concentration is equal to 1 if there is complete mixing of air and contaminants. If the air quality is better than in the exhaust, the normalized concentration is lower than 1 and vice versa. The supply air has a normalized concentration of 0. The reciprocal value of the normalized concentration has been referred to as the ventilation effectiveness, εV (e.g. CEN, 1998). Personal exposure effectiveness A personal exposure effectiveness index, εP, was proposed by Melikov et al. (2002) and used for the evaluation of air terminal devices for personalized ventilation. It was defined as:

PVSI

IIP cc

cc

,0,

0,

−−

=ε (3.3)

where cI,0 is the contaminant concentration in the inhaled air without PV;

cI is the contaminant concentration in the inhaled air with PV; cS,PV is the contaminant concentration in the air supplied from PV.

The personal exposure effectiveness can be interpreted as the portion of clean air from PV in the inhaled air. It is equal to 1 when 100% of personalized air is inhaled and equal to 0 when no personalized air is inhaled. The effectiveness of zero thus does not mean that a person does not inhale any clean air, but only that the person does not inhale any air from PV. The concept of the index is identical to that of the effectiveness of entrainment in the human boundary layer introduced by Brohus and Nielsen (1996). The personal exposure effectiveness can be expressed in terms of the ventilation effectiveness. The relationship is independent of the contaminant distribution:

Chapter 3

38

V

V

VSI

SEP cc

ccε

εε

ε 0,

0,

111 −=−−

−= (3.4)

Where εV is the ventilation effectiveness in the inhaled air without PV. In case of mixing (cI,0 = cE) it can be is simplified to:

VP ε

ε 11−= and )(1 −−= cPε (3.5)

Unlike with ventilation effectiveness, data from two different experiments (with and without PV) are needed for the calculation of εP in a room where the distribution of a contaminant is non-uniform. The normalized concentrations were used in order to avoid error due to a possible difference in the tracer-gas emissions between the experiments. On the other hand, the uncertainty increased due to the propagation of error.

3.7.2 Temperature Inhaled air temperature The inhaled air temperature has been expressed in terms of either absolute temperature (i.e. as measured) or the normalized temperature TI(–). The normalized temperature was defined as:

PVSI

PVSII TT

TTT

,0,

,)(−

−=− (3.6)

where TI is the inhaled air temperature (with or without PV); TS,PV is the supply air temperature of PV; TI,0 is the inhaled air temperature without PV. The normalized temperature is equal to 1 when PV does not have any impact on the inhaled air temperature. When the inhaled air temperature equals the supply temperature of PV, the index becomes 0. Room temperature distribution The temperature distribution has been expressed in a similar way, i.e. either in terms of the absolute temperature or the normalized temperature T(–). The normalized temperature was defined as:

SE

S

TTTT

T−−

=−)( (3.7)

where T is the air temperature in a point; TS is the air temperature in the total-volume ventilation supply; TE is the air temperature in the room exhaust. So as for the normalized concentration, the normalized temperature is equal to 1 when the room air temperature equals the exhaust temperature. The normalized temperature of the supply air is 0.

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39

Manikin-based equivalent temperature The manikin-based equivalent temperature, ET, has been used to evaluate the thermal comfort of seated occupants (Nilsson et al., 1999; Holmér et al., 1999). The manikin-based equivalent temperature is defined as the temperature of a uniform enclosure in which a thermal manikin with realistic skin surface temperatures would lose heat at the same rate as it would in the actual environment (Tanabe et al., 1994). It can be interpreted as a temperature that a person senses in the actual environment. The relationship between the equivalent temperature and heat loss for each individual body segment (or the manikin as whole) can be expressed as:

tCQET −= 4.36 (3.8) where ET is the manikin-based equivalent temperature, °C;

C is constant depending on clothing, body posture, chamber characteristics and thermal resistance offset of the skin surface temperature control system, °C.m2/W, determined experimentally;

Qt is the sensible heat loss, W/m2. The constants were determined experimentally. The manikins were exposed to several level of equivalent temperature in a uniform reference environment (air temperature = mean radiant temperature, velocity close to zero). The manikins’ clothing and posture were as in the experiments. The heat loss was measured and the constants calculated. The constants were then used to determine the equivalent temperature of the actual non-homogenous environment. Various analyses were carried out: • The impact of PV on occupants’ thermal comfort was assessed from the change of the

equivalent temperature from the reference condition without PV (∆ET). The segmental and the whole-body equivalent temperatures were evaluated.

• The vertical temperature difference and the horizontal temperature asymmetry between (1) front and back of a person and (2) left and right side of a person were used to indicate the severity of the local thermal discomfort.

3.7.3 Velocity The velocity distribution was expressed in terms of the mean velocity, v , and the turbulence intensity, Tu. The turbulence intensity is defined as the standard deviation of the velocity fluctuations divided by the mean velocity. The velocity and temperature data were used in the calculation of the draught rating (DR), which was expressed by means of the following equation (ISO, 1994; CEN, 1998):

( )( ) ( )14.337.005.034 62.0 +⋅⋅−−= TuvvTDR (3.9)

3.8 Uncertainty of measurement Table 3.11 summarizes the typical values of absolute uncertainty based on the analyses of measurements. The values are given for each uncertainty component together with the sample uncertainty U and the uncertainty of a derived quantity Uc. The uncertainty components are described in detail in Appendix A. Because the uncertainty of the concentration measurements was largely influenced by the component Umeas, a single typical

Chapter 3

40

value cannot be given. The instrument uncertainty Uinstr was the strongest component in the case of other quantities, and the uncertainty of a measured quantity U can be thus considered a constant for practical purposes. Except for the concentration measurement, which varies among the measured locations, the uncertainty of the temperature and velocity measurement is generally not presented together with the mean value in the result sections. When presented, the uncertainty is indicated by means of error bars. The level of confidence is 95%. Table 3.11. Typical values of absolute uncertainty with a level of confidence of 95%. The component having the largest impact on the combined uncertainty is printed in bold.

Quantity Umeas Ustab Uinstr U Uc

Concentration (inhaled and room)

Fluctuations due to nature, 10-12 readings Stable*

1% of reading** See results See results

Inhaled air temperature

<0.03°C, 560 readings <0.05°C 0.2°C 0.23°C

TI(-): < 0.07***

Manikin-based equivalent temp.

< 0.05°C, 15 readings < 0.01°C 0.2°C 0.23°C ∆ET: 0.33°C

Surface temperature

< 0.03°C, 30 readings < 0.01°C 0.3°C 0.31°C −

Room air temperature −

< 0.01°C 0.3°C 0.3°C T(-): < 0.1***

Room air velocity Standard deviation or Tu < 0.005 m/s < 0.025 m/s < 0.025 m/s −

* ca. ±3% fluctuations of supply CO2 due to weather, otherwise very stable ** rectangular distribution *** uncertainty decreases as the derived index decreases

41

4. Personalized, mixing and displacement ventilation

4.1 Objectives The objective of the work presented in this chapter is to investigate the performance of PV in combination with the total-volume ventilation principles most used in practice: mixing and displacement ventilation.

4.2 Experimental conditions The two types of ATDs for a personalized ventilation system, namely Round Movable Panel (RMP) and vertical desk grill (VDG), were combined with an overhead mixing ventilation system and a displacement ventilation system. A variable air volume strategy was used for the control of the total-volume ventilation. The contaminant sources examined were a floor covering, and bioeffluents and exhaled air produced by the front manikin. In the following, the front manikin and the back manikin are referred to as the polluting manikin and the exposed manikin, respectively. Several scenarios of PV use in terms of the PV supply airflow rates were tested. They are summarized in Table 4.1. The supply temperature for both PV and total-volume ventilation was 20°C and constant in all experiments, aiming at an exhaust air temperature of 26°C. The experimental design is described in detail in Chapter 3. Table 4.1. Combinations of personalized airflow rate (L/s) tested.

PV type Mixing ventilation Displacement ventilation

Polluting manikin

Exposed manikin

Polluting manikin

Exposed manikin

- 0 0 0 0 RMP 0 7 0 7 RMP 0 15 0 15 RMP 15 0 15 0 RMP 15 7 15 7 RMP 15 15 15 15 VDG 0 7 0 7 VDG 0 15 0 15 VDG 15 0 15 0 VDG 15 7 15 7 VDG 15 15 15 15

4.3 Visualization of personalized airflow A smoke visualization was used to reveal the local airflow pattern in front of the thermal manikins exposed to personalized air. Figure 4.1 presents a smoke visualization at airflow

4

Chapter 4

42

rates of 7 L/s and 15 L/s per person. At the rate of 15 L/s, the clean personalized air reached the face of the manikin directly with both the terminals. At the lower rate the buoyancy forces affected easily the weak airflow from the RMP terminal – the supplied air dropped on the desk and mixed with the surrounding polluted air. The face velocity (airflow rate divided by the free area of the outlet) was 0.26 m/s at the rate of 7 L/s. Reynolds and Archimedes numbers were 3200 and 0.43, respectively. It is possible that personalized airflow could accelerate, due to its negative buoyancy, and penetrate the free convection flow even at a lower rate, if rearranged (Bolashikov et al., 2003). Supplying personalized air along the free convection flow around the body should make it easier for the VDG to achieve high air quality in the breathing zone. However, the flow from the VDG was relatively strong and turbulent even at a lower rate, entraining large quantities of the surrounding air. The face velocity was as high as 1.6 m/s (rate of 7 L/s). The free convection flow with a maximum velocity at the breathing zone height of about 0.25 m/s (Section 1.6) was most probably destroyed and did not affect the performance of the VDG.

Figure 4.1. Smoke visualization. The RMP terminal (top) and the VDG terminal (bottom). Personalized airflow rate was 7 L/s per person (left) and 15 L/s per person (right).

4.4 Inhaled air concentration Figure 4.2 presents the normalized concentration of the three simulated contaminants in air inhaled by the exposed manikin. The total-volume ventilation principle is mixing. The concentrations are presented at different PV airflow rates of the exposed manikin, while the polluting manikin did not use its PV. The concentrations of the three contaminants were averaged because (due to the mixing) the exposure of the manikin to the three contaminants was comparable. This is documented in Appendix B. The data in Appendix B also show that

Chapter 4

43

the use of PV at the polluting manikin’s workplace did not affect the inhaled air quality of the exposed manikin.

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 L/s 7 L/s 15 L/s

Personalized ventilation

Con

cent

ratio

n (C

-CS/C

E-C

S)

Mixing + RMPMixing + VDG

Figure 4.2. Concentration of contaminants in air inhaled by the exposed manikin versus PV airflow rate. The concentration of the floor contaminant, bioeffluents and exhaled air are averaged. The error bars indicate the maximum uncertainty from the three contaminants with a level of confidence of 95%. The results in Figure 4.2 show that the use of PV decreased the concentration of contaminants in the air inhaled by the exposed manikin considerably. The largest improvement was achieved with the RMP at a rate of 15 L/s. When compared to the mixing ventilation alone, inhaled air concentration decreased (i.e. the inhaled air quality increased) as many as 6.9 times. This was comparable to the efficiency of the displacement ventilation alone measured in this study, which is, however, seldom achieved in practice due to disturbance to the airflow patter (e.g. activity of occupants). The VDG (at a rate of 15 L/s) did not decrease the inhaled air concentration as much as the RMP; however, the inhaled air concentration was still 2.7 times lower than in the case of mixing ventilation alone. At a rate of 7 L/s the efficiency of the RMP decreased as a result of the interaction of flows in front of the manikin (cold supply air did not penetrate the free convection flow, dropped on the desk and mixed with the surrounding polluted air). The inhaled air concentration was lower with the VDG than with the RMP (at 7 L/s), because the impact of buoyancy forces on the stronger airflow from the VDG was smaller. Even at a rate of 7 L/s, however, the inhaled air concentrations provided with both types of PV were lower than the inhaled air concentrations with mixing ventilation alone. With PV and displacement ventilation, the exposures to the three contaminants were not comparable. The details of exposures at different PV airflow rates are documented in Appendix B. Figure 4.3 presents the concentration of the floor contaminant in the air inhaled by the exposed manikin with PV and displacement ventilation. The airflow rate of the exposed manikin’s PV was 7 L/s and 15 L/s. The PV of the polluting manikin was not used. It is shown that the inhaled air concentration with PV and displacement ventilation was very similar to the inhaled air concentration with PV and mixing ventilation (Figure 4.2). The reason was the uniformity of the distribution of the floor contaminant, described in Section 4.7.1. So as with mixing ventilation, the performance of the two terminals was different due to their efficiency as well as the interaction of flows around the manikin (discussed previously).

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44

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 L/s 7 L/s 15 L/s

Personalized ventilation

Con

cent

ratio

n (C

-CS/C

E-C

S)

Displ. + RMPDispl. + VDG

Figure 4.3. Concentration of floor contaminant inhaled by the exposed manikin with PV coupled with displacement ventilation. The inhaled air concentration of exhaled air and bioeffluents was similar in all but one case (i.e. front manikin using VDG at 15 L/s while back manikin does not, see Appendix B). The similarities made it possible to average the concentrations of the two contaminants and consider them as a single contaminant produced by a person. Figure 4.4 plots the averaged concentrations in the air inhaled by the exposed manikin versus the airflow rate of PV. The cases when the polluting manikin used and did not use its PV are shown separately.

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 L/s 7 L/s 15 L/s

Personalized ventilation (Exposed manikin)

Con

cent

ratio

n (C

-CS/C

E-C

S)

RMP 0 L/sVDG 0 L/sRMP 15 L/sVDG 15 L/s

Polluting manikin

Figure 4.4. Concentration of exhaled air and bioeffluents (averaged) inhaled by the exposed manikin with PV coupled with displacement ventilation. The inhaled air quality of the exposed manikin was fairly high with the displacement ventilation alone (Figure 4.4, PV airflow rate 0 L/s). The reason was the free convection flow around the human body, which could transport clean air from the lower levels upward to the breathing zone. The concentration of the human-produced contaminants inhaled was 6 times lower with the displacement ventilation than with the mixing ventilation. The measurements showed, however, that the use of PV increased mixing of the human-produced contaminants generated in its vicinity and thus decreased the inhaled air quality in the occupied zone. The concentration of the contaminants inhaled by the exposed manikin, when unprotected by PV, increased 3-4 times compared to the displacement ventilation alone. Comparison of the terminals shows that the exposure of the unprotected exposed manikin was about 20% lower with the VDG terminal than with the RMP terminal. The use of PV by the exposed manikin (PV used for protection) decreased the concentration of the human-produced contaminants inhaled in a similar way to the decrease of the concentration of the floor contaminant. The comparison of the total-volume ventilation systems (Figures 4.2 and 4.4) shows that the inhaled air concentrations were lower with PV

Chapter 4

45

coupled with displacement ventilation than with PV coupled with mixing ventilation. The differences between the two cases could have been due to the differences in adjustments of the terminals, which were rearranged between the measurements with mixing and displacement ventilation. The lowest inhaled air concentration was 0.02, which corresponds to a ventilation effectiveness of 50 (provided with RMP at a rate of 15 L/s). This was the highest performance of PV identified in the present study (observed also in some experiments with PV and underfloor ventilation, Chapter 5). The inhaled air quality of the exposed manikin was very high as long as PV in the vicinity of the polluting manikin was not used. Figure 4.4 shows that both types of PV had difficulty in decreasing the concentration inhaled at a rate of 7 L/s further from the reference case of displacement ventilation alone. The inhaled air concentration decreased substantially only with the RMP at a rate of 15 L/s (6 times compared to the displacement ventilation alone). The use of VDG did not decrease the inhaled air concentration compared to the reference case due to its low efficiency.

4.5 Inhaled air temperature The inhaled air temperature was measured in the mouth cavity of each manikin. The analyses of the results (presented in Appendix C in detail) showed that the operation of the PV system of one manikin did not change the inhaled air temperature of the other manikin by more than 0.3°C, regardless of the total-volume ventilation.

20

21

22

23

24

25

26

27

28

0 L/s 7 L/s 15 L/s

Personalized ventilation (Exposed manikin)

Tem

pera

ture

(°C

)

Mixing + RMPMixing + VDGDispl. + RMPDispl. + VDG

Figure 4.5. Inhaled air temperature of the exposed manikin as a function of the personalized airflow rate. The pollution manikin did not use its PV. Figure 4.5 presents the inhaled air temperature of the exposed manikin with the mixing ventilation and the displacement ventilation, alone and in combination with PV. The PV unit of the polluting manikin was not used. The inhaled air temperature was 26.6°C with the mixing ventilation alone, and 25.6°C with the displacement alone. The use of PV decreased the inhaled air temperature from the reference. The lowest inhaled temperature was 20.7°C with the RMP at a rate of 15 L/s, when combined with the displacement ventilation. The combination of PV with displacement ventilation consistently provided lower temperatures of the inhaled air that the combination with mixing ventilation. This is due to the generally lower temperatures in the occupied zone when the displacement ventilation was applied. It is more interesting to realize than the relationship between the inhaled air temperature and personalized airflow rate is similar to the relationship between the inhaled air concentration and the personalized airflow rate (compare with Figures 4.2 and 4.3). A better air quality,

Chapter 4

46

associated with a lower temperature, was achieved with the RMP at the high airflow rate, while the VDG terminal performed better at the lower rate.

y = 1.07xR2 = 0.96

0

0.2

0.4

0.6

0.8

1

1.2

0 0.2 0.4 0.6 0.8 1 1.2

Concentration (CI-CS/CE-CS)

Tem

pera

ture

(TI-T

S/T

I,max

-TS)

MixingDisplacement

Figure 4.6. Inhaled air temperature versus concentration of a floor contaminant with personalized, mixing and displacement ventilation. The maximum inhaled air temperature (TI,max) was different for mixing and displacement ventilation. Figure 4.6 plots the normalized inhaled air temperature of the exposed manikin versus the normalized concentration of the floor contaminant with mixing ventilation and displacement ventilation. It is shown that the two properties are very well correlated. The relationship presented is independent of the total-volume ventilation principle, because the floor contaminant concentration was almost uniform with both the displacement and mixing ventilation (discussed below). The differences in the inhaled air temperature between the two ventilation principles (temperature was lower with the displacement ventilation than with the mixing ventilation, Figure 4.5) were eliminated when the maximum inhaled air temperatures (TI,max) measured for each ventilation principle were used to determine the normalized air temperature. The correlation between the inhaled air temperature and the three contaminants with only personalized and mixing ventilation was identical (y = 1.07x, R2 = 0.96).

y = 1.12xR2 = 0.96

0

0.2

0.4

0.6

0.8

1

1.2

0 0.2 0.4 0.6 0.8 1 1.2

Concentration (CI-CS/CE-CS)

Tem

pera

ture

(TI-T

S/T

I,max

-TS)

MixingDisplacementLinear (Mixing)

Figure 4.7. Inhaled air temperature versus concentration of exhaled air with personalized, mixing and displacement ventilation. The maximum inhaled air temperature (TI,max) was different for mixing and displacement ventilation. Figure 4.7 presents the relationship between the inhaled air temperature and the concentration of the exhaled air contaminant with mixing ventilation and displacement ventilation. The experimental conditions are identical with Figure 4.6. It is shown that the two properties are well correlated in the case of mixing ventilation, while with displacement

Chapter 4

47

ventilation they are not. The reason was the non-uniformity of the exhaled air concentration in the room, which was also influenced by the use of PV. The relationship between the inhaled air temperature and the concentration of bioeffluents was comparable (y = 1.12x, R2 = 0.95). The correlations presented are not related to the type of contaminant source so much as to the distribution of the contaminant in a room. A good correlation is obtained when the distribution is uniform and vice-versa. In rooms with displacement ventilation most contaminants are distributed non-uniformly. Also the concentrations of the floor contaminant were literally non-uniform near the floor (Figure 4.16); however, uniformity was achieved further from the floor in the occupied zone. Therefore, in rooms with displacement ventilation, the distribution of contaminants must be considered. In rooms with mixing ventilation, on the other hand, the type and location of the contaminant source is unimportant.

4.6 Thermal comfort of seated occupants Equivalent temperature (ET) measured by means of two thermal manikins was used to evaluate the thermal comfort of seated occupants. As expected, an increase in the PV airflow rate increased cooling and hence decreased the ET for the exposed body segments and consequently the ET for the whole body. Figure 4.8 compares the whole-body cooling performance of PV combined with the mixing ventilation and the displacement ventilation for the two manikins. PV was used at 15 L/s (both manikins) and 7 L/s (exposed manikin only). Despite the differences between the ET measured with the two manikins (see below), the combinations of PV with displacement ventilation are consistently shown to provide a lower ET that the combination of PV and mixing ventilation. The reason was a lower air temperature in the occupied zone in the former case (documented in Figure 4.19). On average, the use of PV at a rate of 15 L/s decreased the ET by 1-2°C. At a rate 7 L/s, the whole body ET decreased by as little as 0.5°C. The details of the whole-body ET are presented in Appendix D. The data in Appendix D document that the use of PV by one manikin did not affect the ET of the other manikin, whether or not its PV unit was used.

22

23

24

25

26

27

RMP VDG no PV RMP VDG no PV

Polluting manikin Exposed manikin

ET (°

C)

15 L/s

22

23

24

25

26

27

RMP VDG no PV

Exposed manikin

ET (°

C)

MixingDispl.

7 L/s

Figure 4.8. Whole-body manikin-based equivalent temperature. Left: both PV units used at 15 L/s per workplace. Right: polluting manikin using PV at 15 L/s, and exposed manikin using PV at 7 L/s. It is not certain from the present data which air terminal for PV is able to decrease the whole-body equivalent temperature the most. The results for the polluting manikin showed that the RMP terminal provided higher cooling than the VDG, while with the exposed manikin the classification was opposite. The most likely reason is that the environment

Chapter 4

48

evaluated was not identical, especially with PV. It is assumed that even a slight misalignment of the PV airflow and/or the difference in the thermal resistance of the clothing caused by air pockets and folds could have affected the heat loss greatly. The impact of PV on the segmental ET was analysed in order to reveal possible sources of local thermal discomfort. Figure 4.9 presents the distribution of ET over the body of the exposed manikin in the reference cases without PV. It is shown that the distribution of the ET was different for the mixing ventilation and for the displacement ventilation. The difference was pronounced most for feet and lower legs (1°C) and less for thighs and pelvis (0.5°C). The total-volume ventilation principles did not affect the rest of the body.

23

24

25

26

27

28

L.Fo

ot

R.F

oot

L.Lo

w.L

eg

R.L

ow.L

eg

L.Th

igh

R.T

high

Pel

vis

Hea

d

L.H

and

R.H

and

L.Fo

rear

m

R.F

orea

rm

L.U

pper

Arm

R.U

pper

Arm

Che

st

Bac

k

Who

le B

ody

ET (°

C)

MixingDisplacement

Figure 4.9. Distribution of manikin-based equivalent temperature on body segments with mixing and displacement ventilation alone (without PV). The cooling effect of PV was expressed in terms of the decrease of the ET measured with PV from the ET measured without PV in a corresponding reference case. Figures 4.10 and 4.11 present the cooling effect of respectively RMP and VDG on the manikin’s body segments. The exposed manikin (reported) was using PV at 7 L/s and 15 L/s while the polluting manikin was using PV at 15 L/s. It is shown that the impact of PV on the body cooling was very localized (only a few body parts were affected) and strong in comparison with the impact of total-volume ventilation. The cooling effect of PV was independent of the background environment, i.e. the decrease of ET from the reference conditions was comparable for PV in combination with mixing ventilation and for PV in combination with displacement ventilation. Furthermore, the fact that the ET for most body parts did not change to any great extent when PV was used indicates that an increase in the ambient air temperature (recorded near the two workplaces, Figure 4.19) did not have a large impact on thermal comfort.

Chapter 4

49

-10

-8

-6

-4

-2

0

2

L.Fo

ot

R.F

oot

L.Lo

w.L

eg

R.L

ow.L

eg

L.Th

igh

R.T

high

Pel

vis

Hea

d

L.H

and

R.H

and

L.Fo

rear

m

R.F

orea

rm

L.U

pper

Arm

R.U

pper

Arm

Che

st

Back

Who

le B

ody

∆ ET

(K)

Mix. + RMP, 7 L/sMix. + RMP, 15 L/sDispl. + RMP, 7 L/sDispl. + RMP, 15 L/s

Figure 4.10. Cooling effect on manikin’s body segments caused by RMP terminal combined with mixing and displacement ventilation.

-10

-8

-6

-4

-2

0

2

L.Fo

ot

R.F

oot

L.Lo

w.L

eg

R.L

ow.L

eg

L.Th

igh

R.T

high

Pel

vis

Hea

d

L.H

and

R.H

and

L.Fo

rear

m

R.F

orea

rm

L.U

pper

Arm

R.U

pper

Arm

Che

st

Bac

k

Who

le B

ody

∆ ET

(K)

Mix. + VDG, 7 L/sMix. + VDG, 15 L/sDispl. + VDG, 7 L/sDispl. + VDG, 15 L/s

Figure 4.11. Cooling effect on manikin’s body segments caused by VDG terminal combined with mixing and displacement ventilation. The parts most affected by PV were the head and chest of the manikin. The greatest cooling effect was achieved with the VDG, which decreased the ET of the head to as low as 18°C. This result means that the system may be able to cover large individual differences between occupants. The gentle cooling of the manikin’s thighs and upper arms indicates that the cooling of the RMP was distributed more uniformly over the body surface. The distribution of the ET was similar for the front manikin, which was exposed to only one condition of personalized airflow rate. The cooling was more uniform at a lower rate of 7 L/s with both the terminals. With the VDG, however, the cooling still affected hands and chest of the manikin. It is precisely the cooling of the lower chest that was identified as the major source of complaint by occupants with VDG (Kaczmarczyk, 2003; Kaczmarczyk et al., 2004).

Chapter 4

50

4.7 Contaminant distribution

4.7.1 Contaminant concentration profiles In the experiments with mixing ventilation, the concentrations of the floor contaminant, exhaled air and bioeffluents were uniform along the room height and equal to the exhaust air concentration. The use of RMP or VDG did not have an impact on the contaminant distribution. Although uniformity was expected also in the horizontal direction, differences in magnitude were observed along the length of the room for the exhaled air and bioeffluents consistently in most experiments. The higher concentrations were measured in the polluting manikin’s part of the room, i.e. closer to the source, and vice versa. The normalized concentrations ranged from 1.0 to 1.3 closer to the source (position A), and from 0.8 to 1.0 further form the source (position B). The concentration of the floor contaminant was horizontally uniform. With displacement ventilation the contaminant concentrations were stratified. The distribution of the contaminants was influenced by the personalized air terminal used, its airflow rate, and the type and location of the contaminant source. Personalized airflow in the vicinity of the source The distribution of the exhaled air and bioeffluents changed substantially when the PV of the polluting manikin was used. Figures 4.12 and 4.13 show the concentration profiles of bioeffluents and exhaled air measured near the polluting and the exposed manikin, respectively. The impact of the PV airflow rate on the distribution is compared.

0

0.5

1

1.5

2

2.5

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

Bioeffluents (C-CS/CE-CS)

Hei

ght a

bove

floo

r (m

) Displacement aloneDispl. + RMP (1)Displ. + RMP (2)Displ. + VDG (1)Displ. + VDG (2)

0

0.5

1

1.5

2

2.5

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

Exhaled air (C-CS/CE-CS)

Hei

ght a

bove

floo

r (m

) Displacement aloneDispl. + RMP (1)Displ. + RMP (2)Displ. + VDG (1)Displ. + VDG (2)

Figure 4.12. Concentration profiles of human bioeffluents (top) and exhaled air (bottom) near the polluting manikin. Legend: (1) polluting manikin using PV at 15 L/s while exposed manikin does not; (2) both manikins using PV at 15 L/s.

Chapter 4

51

0

0.5

1

1.5

2

2.5

0 0.5 1 1.5 2

Bioeffluents (C-CS/CE-CS)

Hei

ght a

bove

floo

r (m

)

0

0.5

1

1.5

2

2.5

0 0.5 1 1.5 2

Exhaled air (C-CS/CE-CS)

Hei

ght a

bove

floo

r (m

) Displacement aloneDispl. + RMP (1)Displ. + RMP (2)Displ. + VDG (1)Displ. + VDG (2)

Figure 4.13. Concentration profiles of human bioeffluents (left) and exhaled air (right) near the exposed manikin. Legend: (1) polluting manikin using PV at 15 L/s while exposed manikin does not; (2) both manikins using PV at 15 L/s. The contaminant concentration in the occupied zone increased substantially. The profiles measured in front of the polluting manikin (Figure 4.12) revealed concentration peaks at a height of 0.6 m. With the RMP the peaks were observed for both the bioeffluents and the exhaled air. With the VDG a peak was found only for the bioeffluents. The distribution of the exhaled air had a linear profile without a peak. The peaks can be explained considering the local airflow pattern, especially the direction of personalized airflow in respect to the human body. The downward airflow from the RMP transported the contaminants from both the breathing zone and around the body under the table, in front of which the peaks were measured (see the smoke visualization presented in Figure 4.1). The airflow from the VDG allowed the bioeffluents from the pelvis region to spread under the table so that they could stratify in the lower occupied zone. Therefore, the peak of the bioeffluents with the VDG is much lower than the peaks with the RMP. The concentration of the human-produced contaminants increased also next to the exposed manikin, although there were no peaks detected there (Figure 4.13). The distribution of the bioeffluents and exhaled air were comparable. In the upper occupied zone the concentrations increased more with the VDG than with the RMP. This may lead to the conclusion that VDG causes higher transmission of contaminants between workplaces. The inhaled air concentration presented in Figure 4.4 showed, however, that the exposure of the exposed manikin was larger with RMP. The reason must have been a low concentration of contaminants near the floor, which was transported to the breathing zone by means of the free convection flow around the body. The differences in the distribution due to RMP and VDG are less clear from the concentration profiles presented. The comparison of Figures 4.12 and 4.13 illustrates huge spatial differences between the contaminant concentrations. This suggests that the personal exposures may vary considerably depending on the position of the person in a room. Moreover, as discussed previously, the inhaled concentration will not be correlated with the inhaled air temperature. Personalized airflow not directed towards the source The ability of PV to affect the distribution of an active contaminant generated from a localized source located far from a workplace was studied. This was the case of the exhaled air and bioeffluents released from the polluting manikin. The case is represented with the exposed manikin using PV while the polluting manikin’s PV was switched off. The analyses showed (not presented) that unless the polluting manikin used its PV, the distributions of

Chapter 4

52

the bioeffluents and the exhaled air were very similar. The two contaminants were thus averaged and are presented together as a single contaminant.

0

0.5

1

1.5

2

2.5

0 0.5 1 1.5 2

Concentration (C-CS/CE-CS)

Hei

ght a

bove

floo

r (m

)

PV: 7 L/s

0

0.5

1

1.5

2

2.5

0 0.5 1 1.5 2

Concentration (C-CS/CE-CS)H

eigh

t abo

ve fl

oor (

m)

Displacement aloneDispl. + RMPDispl. + VDG

PV: 15 L/s

Close to exposed manikin

Figure 4.14. Distribution of human-produced contaminants close to the exposed manikin (position B) using PV at 7 L/s (left) and 15 L/s (right). PV of the polluting manikin not used. Figure 4.14 presents the distribution of the exhaled air and bioeffluents with PV and displacement ventilation measured near the exposed manikin (position B) at two PV airflow rates. At a rate of 7 L/s, the weak airflow from the PV did not affect substantially the contaminant distribution in comparison with the displacement ventilation alone, regardless of the air terminal device used. At a rate of 15 L/s, both the RMP and the VDG caused mixing in the occupied zone. The profile with the VDG remained linear, but it tilted towards a higher concentration near the ceiling. The shape of the profile with the RMP may suggest that there was a two-zonal distribution (characteristic of displacement ventilation). It is more likely, however, that the profile was influenced by the flow conditions at position B, considering that the RMP provided clean air to the vicinity of the manikin.

0

0.5

1

1.5

2

2.5

0 0.5 1 1.5 2

Concentration (C-CS/CE-CS)

Hei

ght a

bove

floo

r (m

)

Displacement aloneDispl. + PV: 7 L/sDispl. + PV: 15 L/s

Close to polluting manikin

Figure 4.15. Distribution of human-produced contaminants close to the polluting manikin (position A), when its PV was not used. Exposed manikin using PV at 7 L/s and 15 L/s. The analyses showed (not presented) that the type of PV used by the exposed manikin did not affect the distribution of the human bioeffluents and exhaled air near the other workplace, where the contaminants were generated. Instead, as documented in Figure 4.15, the profiles were influenced by the supply airflow rate. Two distinct vertical zones typical for a displacement ventilation pattern could be identified: a cleaner zone in the lower levels and a contaminated zone below the ceiling. It may be suggested, however, that the profiles

Chapter 4

53

reflect the presence of the thermal plumes above the polluting manikin’s workplace rather then the overall airflow pattern. Figure 4.15 shows that the thermal plume carrying contaminants dissolved higher above the floor when the PV was used, most probably due to the decrease in the vertical temperature gradient in the room (Figure 4.19). Figure 4.16 presents the average concentration profiles of a floor contaminant based on the profiles measured near the two workplaces (positions A and B). The distribution is compared at different patterns of use of PV. In either case, the personalized airflow did not encroach directly onto the surface of the floor, i.e. the contaminant source was not affected.

0

0.5

1

1.5

2

2.5

0 0.5 1 1.5 2

Floor contam. (C-CS/CE-CS)

Hei

ght a

bove

floo

r (m

) Displacement aloneDispl. + RMP (1)Displ. + RMP (2)Displ. + VDG (1)Displ. + VDG (2)

Figure 4.16. Average concentration profiles of a floor contaminant based on the profiles measured near the two manikins. Legend: (1) polluting manikin using PV at 15 L/s while exposed manikin does not; (2) both manikins using PV at 15 L/s. The type of PV did not have a substantial impact on the distribution. The distribution was uniform (~1) above a height of 0.6 m. Despite the contaminant release at the floor level, the concentration was low near the floor (as compared to the exhaust concentration) because of the clean air current from displacement ventilation. The free convection flow along a human body thus transported the clean air upward to the breathing zone. However, substantial improvement of the inhaled air quality did not materialize due to the entrainment of contaminated room air from the free convection flow. The results presented in Figure 4.3 showed that the normalized concentration in the inhaled air to the exposed manikin did not differ by more than 5-10% from unity.

4.7.2 Inhaled air quality of walking occupants The concentration of a contaminant inhaled by a walking occupant is the same as the concentration of the contaminant in the ambient air at the breathing zone height at a given position in the room (Brohus and Nielsen, 1996; Mattsson, 1999). Figures 4.17 and 4.18 present the concentrations of the exhaled air contaminant measured at five positions in the room at a height of 1.7 m in the case of PV combined with displacement ventilation. The figures document two scenarios of PV use: the polluting manikin alone using PV at 15 L/s, and both manikins using PV at 15 L/s. The measurement positions are sorted so as to represent the exposure of an occupant walking around the desks (Figure 3.1).

Chapter 4

54

0

0.2

0.4

0.6

0.8

1

1.2

A C D E B

Con

cent

ratio

n (C

-CS/C

E-C

S)

Displ. + RMPDispl. + VDGDisplacement alone

Position:

Figure 4.17. Concentration of exhaled air at 5 locations across the room at the breathing zone height (1.7 m). Only polluting manikin is using PV at 15 L/s.

0

0.2

0.4

0.6

0.8

1

1.2

A C D E B

Con

cent

ratio

n (C

-CS/C

E-C

S)

Displ. + RMPDispl. + VDGDisplacement alone

Position:

Figure 4.18. Concentration of exhaled air at 5 locations across the room at the breathing zone height (1.7 m). Both PV units are used at 15 L/s per workplace. With the displacement ventilation alone, the concentrations were generally high in front of the polluting manikin (position A). Behind the polluting manikin (positions D, E and B) the concentrations decreased and remained low. The use PV decreased the concentrations in front of the polluting manikin. However, behind the polluting manikin, the concentration increased, compared to the displacement ventilation alone. There was a difference between the two terminals: although the VDG terminal seemed to evacuate the exhaled air contaminants from the occupied zone, it promoted mixing and increased the concentration at the breathing zone height more than the RMP. This implies that the use of VDG increases the exposure of walking occupants to active contaminants. The difference between the terminals is, however, not large. Figure 4.18 documents that the use of RMP at the exposed manikin’s workplace increased the concentration in its vicinity to a mixing ventilation level, and the two terminals became comparable. Moreover, continuous activity of occupants would destroy the stratification of contaminants and create mixing conditions, as demonstrated by Mattsson (1999).

4.8 Temperature distribution The results on the thermal environment measurement showed that the PV did not contribute substantially to the temperature (and velocity) distribution in the occupied zone. Unlike the concentration, the temperature was fairly uniform horizontally. Figure 4.19 presents the vertical air temperature profiles with the mixing ventilation and the displacement

Chapter 4

55

ventilation, alone and in combination with PV used at both workplaces at 15 L/s. The results of the tests with lower personalized airflow rates, or only a single PV unit, lay between the profiles of the two cases. The profiles are based on the measurements near the two workplaces. The repeatability of the temperature measurements was very high.

0

0.5

1

1.5

2

2.5

0.2 0.4 0.6 0.8 1 1.2

Temperature (T-TS/TE-TS)

Hei

ght a

bove

floo

r (m

) Displ. aloneDispl. + RMPDispl. + VDGMixing aloneMixing + RMPMixing + VDG

Figure 4.19. Average air temperature profiles based on the profiles measured near the two manikins. Personalized ventilation airflow rate 15 L/s per workplace. The use of PV increased the normalized temperature by less than 0.1 near the floor. No differences between the two terminal types were observed. This suggests that the reason was rather the decrease in the displacement ventilation airflow rate to 50 L/s than the direct impact of the PV. The temperatures differentiated for the two terminals between the heights of 0.6 and 1.4 m. The VDG terminal increased the temperatures more than the RMP. The largest increase in the dimensionless temperature of about 0.2 was equivalent to an absolute temperature of 1°C. The differences almost vanished above the occupied zone. With the VDG and displacement ventilation, the small decrease of the temperature was caused by the upward direction of the VDG airflow, which affected the upper sensors near the exposed manikin. The PV combined with the mixing ventilation did not affect the temperature distribution at any location measured. The distribution was fairly uniform both horizontally and vertically. The presence of the supply air diffuser on the ceiling caused the decrease of the temperature above the occupied zone.

4.9 Velocity distribution The velocity profiles measured near the two manikins were averaged in order to generalize the results, despite the fact that the two profiles were not absolutely identical. The differences between the positions were due to the velocity field and not to poor repeatability or high uncertainty. Figure 4.20 presents the mean air velocity profiles with and without PV. When applied, both the PV units were used at 15 L/s. The cases with both displacement ventilation and mixing ventilation are documented in the figure. With the displacement ventilation, the highest velocity was identified in the vicinity of the floor due to the horizontal flow emerging from the diffuser mounted on the wall. The velocities decreased gradually from the floor up to a height of 1 m, above which they remained low and constant. Only with the VDG, which supplied air upward, did the velocities increase near the ceiling. The velocities near the floor decreased a little when the PV was used. This is most probably caused by the decrease in the displacement ventilation airflow rate from 80 L/s to 50 L/s. However, the uncertainty of measurement should be

Chapter 4

56

considered. The measurement range of the thermal anemometers used starts from 0.05 m/s with a typical level of uncertainty of the mean of 0.025 m/s (Section 3.8).

0

0.5

1

1.5

2

2.5

0 0.05 0.1 0.15 0.2

Velocity (m/s)

Hei

ght a

bove

floo

r (m

) Displ. aloneDispl. + RMPDispl. + VDGMixing aloneMixing + RMPMixing + VDG

Figure 4.20. Average profiles of mean air velocity based on the profiles measured near the two manikins. Personalized ventilation airflow rate 15 L/s per workplace. The velocity levels were higher with the mixing ventilation than with the displacement ventilation. The highest velocities were measured near the floor. The velocity decreased gradually from the floor, but it increased again near the ceiling. The profile reflects the airflow pattern. The airflow from the ceiling-based diffuser was deflected from the walls, directed downward and after being deflected for the second time from the floor it emerged to the lower occupied zone. The velocities did not decrease below a level of 0.1 m/s in the reference case. When the PV was used, the velocities decreased down to 0.05 m/s, but most probably again due to the total-volume ventilation rather than the PV. This is supported by the fact that the velocities with the personalized and mixing ventilation were always higher than with the personalized and displacement ventilation, although the PV obviously contributed to the mixing of the air in both cases.

4.10 Discussion The two most promising but very different air terminals for PV were combined with the total-volume ventilation principles most used in practice: mixing and displacement ventilation. The performance of the combined systems was examined under the most extreme occupants’ patterns of use. The tested combinations of PV airflow rates reflected the fact that some occupants may choose not to use the PV system, while others would exploit the system at its maximum capacity. The results for the mixing ventilation showed that the distribution of the three contaminants was very homogenous across the room, although the types and locations of the contaminant sources were very different. Because of mixing, the concentrations of the contaminants in the air inhaled by the exposed manikin were comparable and similar to the exhaust air concentrations (Melikov et al., 2003). As expected, the use of PV improved the inhaled air quality (i.e. decreased the inhaled air concentration) of the exposed manikin considerably. As compared to the mixing ventilation alone, the inhaled air concentration decreased 6.8 and 2.6 times in the case of RMP and VDG, respectively. The improvement was similar in regard to the three contaminants. Hence, PV will always be able to protect occupants from pollution and thus increase the quality of inhaled air in rooms with mixing air distribution. The mixing air distribution principle implies that the inhaled air quality does not depend on

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the type of contaminant source and its location. The performance of PV tested in the present study was comparable to the performance of similar air terminal devices reported in the literature (Bolashikov et al., 2003; Melikov et al., 2002; Faulkner et al., 1999). The inhaled air concentration and temperature were measured at two rates of personalized air (7 and 15 L/s). Bolashikov et al. (2003) and Melikov et al. (2002) presented the performance characteristics of respectively RMP and VDG (similar terminal) over a range of airflow rates. The direction of personalized airflow in respect to the occupant’s head may affect the inhaled air quality to a great extent. The air terminals tested in the present study complied with the positioning most often preferred by people in previous experiments (Kaczmarczyk et al., 2002b) and were not rearranged at different airflow rates. The smoke visualization demonstrated that cold personalized air may not reach directly the face of an occupant and thus may not always ensure excellent air quality. In addition, the inhaled air quality might either increase or decrease if the occupant moves. Hence, unless PV airflow reaches the face of an occupant directly, the concentration of contaminants in the surrounding ambient air will affect the inhaled air quality and thus will have to be considered. In rooms with displacement ventilation the distribution of contaminants is typically non-uniform, depending on the type and location of the contaminant source. A passive plane contaminant located on the floor, representing pollution from carpet, PVC or linoleum, was exposed direct to the clean air current from the wall-based displacement unit. The clean air was polluted at a very short height (ca. <0.2 m) and the concentration of the floor contaminant became uniform further from the floor. Although the free convection flow along a human body transported the clean air upward to the breathing zone, substantial improvement of the inhaled air quality did not materialize due to the entrainment of contaminated room air to the free convection flow. The results showed that the normalized concentration in the air inhaled by the exposed manikin did not differ from unity by more than 5-10%. The inhaled air concentration was thus not higher than the concentration in the ambient air, as suggested by Murakami et al. (1998) based on a CFD simulation. The use of PV did not affect the distribution of the floor contaminant in the room, while the inhaled air quality of the manikin protected with PV improved several times (Figure 4.3). The improvement with PV in combination with displacement ventilation (in regard to the floor contaminant) was comparable to the improvement with PV in combination with mixing ventilation, i.e. it was independent of the room air distribution principle. Displacement air distribution is typically associated with a low exposure of occupants to active contaminants. Also in the present study, the inhaled air quality provided in regard to the human-produced contaminants was relatively high, equivalent to a ventilation effectiveness of 6 (Melikov et al., 2003). The measurements showed that it was difficult for PV providing low airflow rates (i.e. mediocre performance) to improve the already high air quality. Such high values of air quality may not be typical in rooms with displacement ventilation in practice. The activity of occupants and flow obstacles may disturb the buoyancy driven airflow pattern. The typical values of ventilation effectiveness reported in CEN Report 1752 (CEN, 1998) range between 1.2 and 1.4. If this is the case, the improvement of the inhaled air quality with PV is likely to be significant, even at lower supply rates of personalized air. The mixing of contaminants in the occupied zone may also increase when the personalized airflow is located in the vicinity of the contaminant source. The results documented that the use of PV in a room with displacement ventilation increased the concentration of human

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bioeffluents and exhaled air in the occupied zone as compared to the case without PV. This may result in an increased transmission of contaminants between workplaces, and an increased likelihood of infections for occupants if infectious agents and exhaled air are associated. Detailed analyses of the risk of infections are performed in Chapter 6. If the impact of PV on the mixing of contaminants were comparable with the impact of the activity of occupants, the increase in the exposure of occupants due to the use of PV would be practically unimportant. Such a comparison, however, remains to be made. The measurements showed that, although PV promoted mixing, the exposure of the exposed manikin was always lower than in a room with mixing ventilation. The ability of PV to increase the transmission of contaminants between workplaces is associated with the strength and direction of personalized airflow. Because the personalized airflow from RMP was weaker than the personalized airflow from VDG, the primary cause for the increased transmission seems to be the airflow direction rather than the strength of the airflow. Furthermore, the impact of PV on the concentration of contaminants in the occupied zone may be confounded with the decrease of the stratification height of the contaminants. It is assumed that the use of PV with an upward airflow direction (VDG) decreases the stratification height, because the personalized airflow entrains surrounding air and acts like a thermal plume. The stratification also decreases with the airflow rate from displacement ventilation (when PV is used). None of these factors (direction and strengths of PV airflow, height of stratification), however, were studied in detail. The distribution of human bioeffluents in the room was similar to the distribution of exhaled air. However, the two contaminants are of a different nature. Human bioeffluents are carried upward by means of a free convection flow around the body. The airflow of exhalation penetrates the free convection flow due to its momentum and interacts with the room airflow. The distributions were similar most probably because of the presence of the heated office equipment in the workplaces. The thermal flow generated around the equipment entrained the exhaled air, so that it was carried upward and distributed in the room in the same way as the bioeffluents. The use of PV caused large non-uniformities and spatial difference in the distribution of exhaled air and bioeffluents in front of the workplace where the contaminants were generated. The distribution of the two contaminants, described in detail in Section 4.6 (reported also in Cermak et al., 2004), was different with the two types of PV. In the rest of the room the differences between the two contaminants diminished, and the non-uniformities disappeared. The concentrations of the human-produced contaminants in front of the polluting workplace were higher than the concentrations in the rest of the room. This suggests that if there was an occupant seated in front of the polluting workplace, his or her exposure to the contaminants might have been greater than the exposure of an occupant seated behind the polluting workplace (i.e. exposed manikin measured in this study). Therefore, the arrangement of workplaces may be important for the inhaled air quality of occupants. Because different occupants may produce contaminants (e.g. virulent agents) at one and the same time, it is difficult to recommend an office layout that would ensure a low exposure of all occupants at any time. A barrier placed in front of a desk (e.g. a partition) should in principle prevent the spread of contaminants into the room. This, however, remains to be studied. A weak personalized airflow (at a rate of 7 L/s) supplied at the workplace of the exposed manikin was not able to affect the room distribution of contaminants generated at the workplace of the polluting manikin. At high flow rates, however, personalized airflow may

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cause mixing. At a rate of 15 L/s, the impact of PV on the room air distribution was very localized. The airflow from VDG was able to cause more mixing than the airflow from RMP. Because the two terminals supplied air in opposite directions and at different velocities, it is not certain whether the airflow direction or the velocity was the reason. In the opposite side of the room, the distribution was affected only slightly and no differences were found between the two terminals. It is likely that a stronger personalized airflow would promote mixing of all contaminants in the whole occupied zone, as demonstrated in the study on PEM (described in Section 1.3) by Faulkner et al. (1993). Not only the level of air pollution but also air temperature and air humidity influences the perception of air quality. Fang et al. (1998a, b) confirmed earlier studies and showed that air is perceived more acceptable with decreasing temperature and humidity. Therefore, the inhaled air temperature was measured in the present study as well. Without PV, the temperature was 1°C lower with the displacement ventilation than with the mixing ventilation. This may cause an improvement of the perceived air quality, depending on the pollution level. The impact will be more pronounced if the air is clean. The use of PV providing air 6°C colder than the room air caused the inhaled air temperature to decrease by up to 5°C (with RMP at 15 L/s). This is in agreement with the results by Melikov et al. (2002) for CMP and MP, described in Section 1.3. The inhaled air temperature with PV and displacement ventilation was consistently lower than the inhaled air temperature with PV and mixing ventilation. The reason was a lower temperature in the occupied zone in the case of displacement ventilation. The ability of PV to decrease in the inhaled air temperature as compared to the reference inhaled air temperature did not depend on the total-volume ventilation system. The analyses presented in Section 4.5 showed that the inhaled air concentrations are very well correlated with the inhaled air temperatures. The correlation applies, however, only on the contaminants distributed uniformly (see Section 4.5 for more details). The correlation allows for a simplification of the perceived air quality analyses as well as measurements, because information about only one quantity is needed. The inhaled air quality is assumed to be the most important criterion for the performance assessment of PV systems. However, the ability of PV to provide cooling at high temperatures and not to affect thermal sensation at comfortable temperatures is also important. The present results showed that the whole-body cooling ability of the two types of PV was about the same. At a rate of 15 L/s, the cooling was equivalent to decreasing the room air temperature by 1-2°C. The values varied depending on the actual combination of PV, a total-volume ventilation principle and a thermal manikin (workplace). Such cooling, even though small, may be sufficient for many occupants who need only minor adjustment of the local thermal environment. The whole-body cooling ability of PV is influenced by the strength and direction of personalized airflow. The air terminals tested in the present study were adjusted according to people’s preferences identified by Kaczmarczyk et al. (2002b), which may not correspond to the adjustment providing the greatest cooling. The cooling ability of VDG agreed with the maximum cooling ability of Climadesk (similar terminal, described in Section 1.3) of 1°C, reported by Tsuzuki et al. (1999). The maximum cooling ability of another terminal tested by Tsuzuki et al. (1999), Personal Environment Module (PEM), was equivalent to decreasing the room temperature by 7°C. The airflow from PEM was, however, much stronger than airflows examined in the present study. The measurements by Melikov et al. (2002) showed that the ventilation performance of a strong airflow from PEM is very mediocre (see below).

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The thermal comfort of occupants may be affected by the distribution of cooling over the body. The measurements showed that the cooling impact of both PV types was very localized (Forejt et al., 2004). The body parts most cooled were those exposed direct to personalized air, i.e. the head and the chest. The human response to localized cooling is difficult to predict, because the sensitivity of body parts to air movement, clothing, activity and preferences of occupants differs in rooms in practice. Nevertheless, the distribution of cooling provided by PV may not be important so long as the occupants can change the strength and direction of personalized airflow. Unfortunately, the distribution of cooling preferred by an occupant may not always ensure an optimum quality of inhaled air. Therefore, it may be necessary for an occupant to prioritize between a high air quality and preferred thermal comfort. The thermal environment provided with both mixing ventilation alone and displacement ventilation alone was comfortable according to the present standards and guidelines (ISO, 1994; CEN, 1998). The temperatures in the occupied zone were lower with displacement ventilation than with mixing ventilation due to thermal stratification. The combination of PV and displacement ventilation increased the air temperature in the occupied zone by approx. 1°C. The measurements with the thermal manikins showed that the changes in the ambient air temperature did not affect the heat loss from the manikins considerably. This indicates that the use of PV by some occupants will not stimulate other occupants to adjust their PV. This would cause a chain reaction with subsequent and continuous changes in thermal environment, leading to disturbances of occupants and a loss of productivity. The temperature in the occupied zone increased because of two reasons. The measurements of velocity identified that PV used at a rate of 15 L/s did not cause mixing of personalized air and ambient air in the lower occupied zone. Because the airflow rate of displacement ventilation decreased when PV was used, a smaller volume of conditioned air was involved in the removal of heat from the lower occupied zone. This caused the increase in temperature near the floor. The second reason was the ability of PV to increase mixing in the upper levels of the room (warm air was brought to the occupied zone). This was the case of VDG, where the ability to cause mixing was greater than that of RMP (at a supply rate of 15 L/s). Therefore, VDG caused the temperature in the occupied zone to increase more than RMP (Figure 4.19). The consequence of the increase in temperature could be an increase in the energy consumption for additional conditioning of air, if the temperature in the occupied zone should be maintained constant. The normalized (dimensionless) temperature near the floor was 0.4 with displacement ventilation alone, and it increased to 0.5 when PV was used (Figure 4.19). The value of 0.4 agrees very well with the model by Mundt (1990). According to the model, the temperature near the floor rises due to the radiation between the ceiling and the walls to the floor and the following convective transport to the supply air in the floor area. Because the use of PV did not increase the temperature near the floor substantially, the model by Mundt (1990) can also be used for rooms with PV and displacement ventilation when a rough estimate is needed. One should consider that the predicted temperature might underestimate the actual temperature with the combined system. More measurements at different airflow rates are needed in order to adjust the model by Mundt (1990) for the combined system. An increase in the convective heat transfer coefficient might be an option. A coefficient of 6 W/m2 (instead of 3 or 5 W/m2 as used in the original model) provided a better estimate in the present study.

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In the present study, the profiles were not linear (steeper in the lower part of the room, Figure 4.19). The shape of the profiles reflected the fact that most heat sources were located in the lower part of the room. In practice, a linear profile is usually used as a first approximation of the temperature distribution. The analyses of the present results indicate that the linear profile would underestimate the actual vertical air temperature difference between head and ankles by roughly 50% (the actual temperature difference was larger), with or without PV. The assumption of the linear profile is thus questionable in this case.

4.11 Conclusions • PV will always be able to protect occupants from pollution and thus increase the quality

of inhaled air in rooms with mixing air distribution. The type of a contaminant source (active or passive, localized or plane) and its location is unimportant. The positioning of an air terminal device in respect to the occupant and it design influences the quality of inhaled air to a great extent.

• In rooms with displacement ventilation, the PV will improve the inhaled air quality in

regard to a passive and plane contaminant located on the floor, such as carpet, PVC or linoleum. The use of PV may, however, increase mixing of contaminants located in the vicinity of the personalized airflow, such as exhaled air and bioeffluents. This may increase the transmission of contaminants between workplaces as compared to the case without PV.

• The inhaled air temperature is well correlated with the inhaled air concentration of

contaminants distributed uniformly. The temperature and concentration are not correlated if the distribution of the contaminant is non-uniform.

• The impact of a room air distribution principle on the thermal comfort of occupants is

small and insignificant compared to the impact of PV when its maximum cooling capacity is used. The cooling of the human body provided by PV is rather independent of the room air distribution generated by a total-volume ventilation system.

• The direction and rate of personalized airflow determine the distribution of active

contaminants generated at workplaces in rooms with displacement ventilation. The use of PV creates large non-uniformities and spatial difference in the distribution of human-produced contaminants in the vicinity of a workplace. The distributions of exhaled air and bioeffluents may be different, depending on the flow direction of personalized air.

• In rooms with displacement ventilation, PV does not affect the distribution of active

contaminants generated in another workplace when the supply airflow rate is low. At a high rate the type of supply air terminal and its airflow direction may be important.

• The impact of PV on the distribution of temperature and velocity is very localized. PV

does not contribute to the removal of heat from the lower occupied zone in rooms with displacement ventilation. This increases temperature and consequently the cooling requirements if the thermal environment should be maintained constant.

63

5. Personalized and underfloor ventilation

5.1 Experiment 1

5.1.1 Objectives The objective of the work presented in this chapter is to investigate the performance of PV in combination with underfloor air distribution (UFAD).

5.1.2 Experimental conditions Four passive swirl diffusers (Section 3.3.2) were tested in the present study. A swirl element mounted in each diffuser allowed for adjustment of air discharge to either a horizontal or a vertical direction. Both the discharge directions were studied. The experimental design in terms of an office layout, furniture, manikins, contaminant sources, positions and methods of measurement were identical with the experiments with mixing and displacement ventilation, presented in Chapter 4. The supply air temperatures of both PV and UFAD were 20°C. The total airflow rate supplied was 80 L/s. These conditions were identical in all experiments. The UFAD system was controlled according to a VAV strategy, i.e. the amount of air supplied from the floor decreased proportionally to the increase in the personalized airflow. The conditions tested (Table 5.1) were designed to allow for a comparison between the mixing ventilation, displacement ventilation and underfloor ventilation. Table 5.1. Combinations of personalized airflow rate (L/s) tested.

PV type UFAD vertical discharge UFAD horizontal discharge

Polluting manikin

Exposed manikin

Polluting manikin

Exposed manikin

- 0 0 0 0 RMP 0 15 0 15 RMP 15 0 15 0 RMP 15 15 15 15 VDG 0 15 0 15 VDG 15 0 15 0 VDG 15 15 15 15

5.1.3 Aerodynamic data of floor diffusers The evaluations of the throw height and the near zone of the diffusers were based on a distribution of velocity. The throw height and the near zone were defined as respectively a horizontal distance and a vertical distance from the centre of the diffuser where the supply air stream velocity decreases to 0.25 m/s. The supply airflow rates examined were 20 L/s (case 1, Table 5.1) and 12.5 L/s (cases 4 and 7, Table 5.1) per diffuser. The supply air

5

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temperature was 20°C in both cases. The former condition corresponds to the reference case without PV (80 L/s through UFAD). The latter condition represents the discharge pattern when both PV units were used (50 L/s through UFAD + 2 times 15 L/s from PV); however, PV was not used during the velocity measurements in order not to affect the flow field.

Figure 5.1. Mean air velocity contours for the vertical discharge. Supply airflow rate 20 L/s per diffuser (left) and 12.5 L/s per diffuser (right).

Figure 5.2. Mean air velocity contours for the horizontal discharge. Supply airflow rate 20 L/s per diffuser (top) and 12.5 L/s per diffuser (bottom). Figure 5.1 shows the mean air velocity contours of the airflow provided with the vertical discharge of UFAD. Only one half of the flow field is presented with the centre of the diffuser positioned in the origin of the plot. The figure shows that the air spreads in a V-shape pattern. As expected, the flow dissolved at a lower height when the supply airflow

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was weaker. The throw was about 1.0 m and 0.3 m for an airflow rate of 20 and 12.5 L/s per diffuser, respectively. The contours show that the radius of the near zone was about 0.5 m and 0.2 m for the two airflow rates. The velocity distribution with the horizontal discharge is presented in Figure 5.2. The throw was limited to a very short height, regardless of the airflow conditions. On the other hand, the near zone radius was much longer compared to the vertical discharge: 0.5 m and 0.2 m at airflow rates of respectively 20 and 12.5 L/s per diffuser. The area of velocities above 0.1 m/s (where there is a risk of draught) was greater than 1 m.

Figure 5.3. Top: airflow rate 80 L/s, vertical discharger (left) and horizontal discharge (right). Bottom: Airflow rate 50 L/s, vertical discharge (left) and horizontal discharge (right). Figure 5.3 shows the smoke visualization for the two discharge patterns. The conditions of the visualization and of the measurement (Figures 5.1 and 5.2) are identical. Each photo was taken approx. 10 s after introducing the smoke. The white square grid at the back of the scene had a module of 0.3 m. Similar to the velocity measurement, the visualization reveals obvious differences between the vertical and the horizontal discharge and the supply air conditions. In the case of the horizontal discharge a certain amount of mixing was created above a height of 0.1 m when the supply airflow reached the walls at a distance of 0.85 m from the centre of the diffuser as well as when the flows from two diffusers collided (not shown). The reflection from the walls was not apparent from the velocity contours, which were measured in the direction parallel to the walls. The visualization was influenced by a systematic error due to the fact that the smoke was essentially warmer than the supply air. The supply air temperature was estimated to rise by 1°C to 3°C during the short period the smoke was introduced to the room.

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5.1.4 Inhaled air concentration Exhaled air and bioeffluents Figure 5.4 presents the inhaled air concentrations of bioeffluents and exhaled air with different total-volume ventilation systems alone and in combination with PV. Because the differences between the two concentrations were much smaller than the differences between the conditions tested, the concentrations of the bioeffluents and exhaled air were averaged. The results for mixing ventilation and displacement ventilation (as discussed in Chapter 4) are presented for comparison.

0

0.2

0.4

0.6

0.8

1

no PV RMP (1) RMP (2) VDG (1) VDG (2)

Con

cent

ratio

n (C

I-CS/C

E-C

S)

MixingUFAD verticalUFAD horiz.Displacement

Figure 5.4. Concentration of exhaled air and bioeffluents (averaged) in the air inhaled by the exposed manikin with RMP terminal and VDG terminal in combination with different total-volume ventilation principles. The error bars indicate the maximum uncertainty from the two contaminants with a level of confidence of 95%. Legend: (1) Exposed manikin using PV at 15 L/s while polluting manikin does not; (2) both manikins using PV at 15 L/s. The concentration of human-produced contaminants provided with the horizontal discharge of UFAD alone was comparable to the concentration provided with the displacement ventilation alone. With the vertical discharge the concentration in the inhaled air increased due to mixing in the lower occupied zone. The concentrations provided with the vertical and the horizontal discharge of UFAD alone were 1.6 and 8.2 times lower than in the case of the mixing ventilation alone. The use of PV caused the differences between the discharge patterns to disappear. The comparison of the terminals shows that the RMP terminal achieved a lower inhaled air concentration of the contaminants than the VDG terminal, regardless of the total-volume ventilation principle and the pattern of use. The performance of the terminals was influenced by the interaction of airflows in front of a human body (discussed in detail in Chapter 4.3). The inhaled air concentrations provided with RMP were between 0.04 and 0.02. This corresponds to a ventilation effectiveness of 25 to 50. With the VDG, the concentrations of human-produced contaminants were higher due to the entrainment of contaminated room air in its very turbulent jet. The values of ventilation effectiveness ranged between 3 and 6. Comparison with the horizontal discharge of UFAD (ventilation effectiveness of 8.7) shows that the VDG was not able to decrease the inhaled air concentration below its reference level. Figure 5.5 examines the transmission of the human-produced contaminants between the workplaces. The inhaled air concentration to the exposed manikin with underfloor, mixing and displacement ventilation is compared. The polluting manikin was using PV at 15 L/s while the PV of the exposed manikin was not used. With the UFAD system, the transmission increased with both types of air terminal device. The transmission was lower with the VDG

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than with the RMP for the combinations tested. The concentration of contaminants was somewhat lower with the horizontal discharge of UFAD than with the displacement ventilation.

0

0.2

0.4

0.6

0.8

1

no PV RMP VDG

Con

cent

ratio

n (C

I-CS/C

E-C

S)

*)

MixingUFAD verticalUFAD horiz.Displacement

Figure 5.5. Concentration of exhaled air and bioeffluents (averaged) in the air inhaled by the exposed manikin with PV in combination with different total-volume ventilation principles. Polluting manikin using PV at 15 L/s while exposed manikin does not. The error bars indicate the maximum uncertainty from the two contaminants with a level of confidence of 95%. *) There was a difference between exhaled air and bioeffluents – see Appendix B. Floor contaminant The analyses showed that there were no differences in the inhaled air concentration of the floor contaminant between the four total-volume ventilation systems. No differences were identified between the two manikins either. The normalized concentration in the inhaled air of both the manikins did not differ by more than 5-10% from unity. The use of PV did not have any adverse effects on the inhaled air quality of an unprotected manikin. This was to be expected, because the concentration of the floor contaminant was largely uniform. Lower concentrations were recorded with both the UFAD and the displacement ventilation near the floor. However, the entrainment of room air in the upward boundary layer flow increased the concentration almost to the room air level before it was inhaled. The use of PV decreased the inhaled air concentration several times, depending on the personalized air terminal used. Appendix E presents the details of the floor contaminant concentration in the inhaled air.

5.1.5 Inhaled air temperature Figure 5.6 compares the inhaled air temperature of the polluting manikin with the different ventilation systems tested, with and without PV. The PV airflow rate of the polluting manikin was 15 L/s, while the exposed manikin did not use PV. The inhaled air temperatures with both the discharge patterns of UFAD alone were between the temperatures of the mixing and displacement ventilation. The figure shows that the RMP provided a lower inhaled air temperature than the VDG. The results are well correlated with the inhaled air concentration of the floor contaminant (Section 4.5). Regardless of the total-volume ventilation system, the temperatures were about the same for each terminal type, except for the RMP combined with the mixing ventilation. The reason can be the airflow direction of RMP, which was re-adjusted between the experimental stages 1 and 2.

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20

21

22

23

24

25

26

27

28

no PV RMP VDG

Tem

pera

ture

(°C

)MixingUFAD verticalUFAD horiz.Displacement

Figure 5.6. Inhaled air temperature of the polluting manikin with different total-volume ventilation principles. Polluting manikin using PV at 15 L/s while exposed manikin does not. The error bars indicate the maximum uncertainty from the two contaminants with a level of confidence of 95%.

5.1.6 Contaminant distribution The distribution of the floor contaminant was generally uniform under all scenarios tested, except for near the floor, where non-uniformities were identified due to the close proximity of the supply air terminals and a coarse grid of the tracer-gas dosing points on the floor. The distribution was very similar to the distribution with displacement ventilation. Therefore, only the distribution of the human-produced contaminants is presented in this section. There were no differences found between the concentrations of bioeffluents and exhaled air for any combination of PV with underfloor ventilation. The concentrations of the two contaminants were thus averaged in most of the following figures in order to provide generalization. Total-volume ventilation alone Figure 5.7 compares the distribution of the human-produced contaminants (average of bioeffluents and exhaled air) with the underfloor, mixing and displacement ventilation alone. The concentrations recorded in front of the polluting manikin and next to the exposed manikin were averaged in order to provide a more general picture of the distribution. The distribution for the horizontal discharge of UFAD was identical with the distribution for the displacement ventilation. The concentrations are very low near the floor, and they increased with the room height. The exact horizontal position of the interface layer between the lower cleaner zone and the upper more contaminated zone is difficult to identify. The concentrations begin to stratify between the heights of 0.6 and 1.1 m. With the vertical discharge the concentrations in the occupied zone were higher compared to the horizontal discharge. The vertical swirl flow penetrated the upper contaminated zone and brought contaminants to the occupied zone. The interface layer stretched between the heights of 1.1 and 1.7 m. With all the systems, the concentrations exceeded a value of 1 above the occupied zone (i.e. exhaust air concentration). Analyses showed that the profiles measured in front of the polluting manikin overestimated the average contaminant distribution in the room, apparently because of the proximity of the source.

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0

0.5

1

1.5

2

2.5

0 0.5 1 1.5 2

Concentration (C-CS/CE-CS)

Hei

ght a

bove

floo

r (m

)

MixingUFAD verticalUFAD horizontalDisplacement

Figure 5.7. Concentration profiles of human bioeffluents and exhaled air (averaged) near the two workplaces (positions A and B, averaged) with total-volume ventilation systems alone. Personalized airflow close to a source The distribution of the contaminant varied considerably depending on the relation between personalized airflow and the location of a contaminant source. The situation was similar to the combination of PV and displacement ventilation. Figure 5.8 presents separately the concentration of human bioeffluents and exhaled air measured in front of the polluting manikin (position A). The polluting manikin was using PV at 15 L/s, while the exposed manikin did not use PV. Figure 5.9 presents the concentration of the human-produced contaminants measured next to the exposed manikin (position B) under the same condition. The use of PV increased the concentration of both the human-produced contaminants in the occupied zone. In all cases the VDG terminal achieved lower concentration levels in the occupied zone. The concentrations were higher with the vertical discharge than the horizontal discharge. The distributions with the vertical discharge were similar for the two positions, while with the horizontal discharge they were not similar. Less mixing in the lower occupied zone with the horizontal discharge allowed for stratification of the contaminants in a horizontal layer at a height of 0.6 m. Although lower in magnitude, a similar concentration peak was observed also in experiments with displacement ventilation. Personalized airflow far from a source Figure 5.10 documents the impact of the RMP on the distribution of human bioeffluents and exhaled air that was generated at another workplace. The exposed manikin used PV and the polluting manikin did not. The profiles recorded near the two manikins (positions A and B) were averaged. The concentration in the occupied zone decreased when the RMP was used, most probably as a result of decreasing the throw of UFAD. The distribution of the contaminants was not affected with the combination of the RMP and the horizontal discharge. The concentration remained very low near the floor. Figure 5.11 shows the distribution for the VDG terminal. When the horizontal discharge was employed, the mixing introduced by the VDG caused an increase of the concentrations near the floor (compared with the RMP that did not change the concentration). At the same time, the concentration decreased near the ceiling. With the VDG and the vertical discharge the concentrations decreased near the floor. It is impossible, however, to conclude with any certainty, whether the decrease in the throw or the use of PV was the cause.

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0

0.5

1

1.5

2

2.5

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

Bioeffluents (C-CS/CE-CS)

Hei

ght a

bove

floo

r (m

) Vertical aloneVert. + VDGVert. + RMPHorizontal aloneHor. + VDGHor. + RMP

0

0.5

1

1.5

2

2.5

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

Exhaled air (C-CS/CE-CS)

Hei

ght a

bove

floo

r (m

) Vertical aloneVert. + VDGVert. + RMPHorizontal aloneHor. + VDGHor. + RMP

Figure 5.8. Concentration profiles of bioeffluents (top) and exhaled air (both) in front of the polluting manikin (position A) with PV and two discharge patterns of UFAD. Polluting manikin using PV at 15 L/s while exposed manikin does not.

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Vertical aloneVert. + VDGVert. + RMPHorizontal aloneHor. + VDGHor. + RMP

Figure 5.9. Concentration profiles of exhaled air and bioeffluents (averaged) next to the exposed manikin (position B) with PV and two discharge patterns of UFAD. Polluting manikin using PV at 15 L/s while exposed manikin does not.

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)

Vertical aloneHorizontal aloneRMP + verticalRMP + horizontall

Figure 5.10. Concentration profiles of exhaled air and bioeffluents (averaged) near the two workplaces (positions A and B, averaged) with RMP and both discharge patterns of UFAD. Exposed manikin using PV at 15 L/s while polluting manikin does not.

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Vertical aloneHorizontal aloneVDG + verticalVDG + horizontal

Figure 5.11. Concentration profiles of exhaled air and bioeffluents (averaged) near the two workplaces (positions A and B, averaged) with VDG and both discharge patterns of UFAD. Exposed manikin using PV at 15 L/s while polluting manikin does not.

5.1.7 Temperature distribution The temperature distribution was assessed using the vertical air temperature profiles measured in front of the polluting manikin and next to the exposed manikin. Analyses showed that the temperature profiles were very similar at the two positions. Figure 5.12 compares the normalized temperature profiles of underfloor ventilation with the profiles measured for mixing and displacement ventilation. Personalized ventilation was not used in any of the cases presented. It is shown that the temperatures near the floor were equal to approx. 0.6 and 0.7 with the horizontal and the vertical discharge of underfloor ventilation, respectively. The normalized temperature with the displacement ventilation was 0.4, as discussed in Chapter 4. However, already at a height of 0.6 m the differences between the discharge patterns had vanished and the distribution with UFAD became similar to the distribution with displacement ventilation.

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r (m

) DisplacementUFAD verticalUFAD horizontalMixing

Figure 5.12. Mean air temperature profiles next to the two workplaces (positions A and B, averaged) with different ventilation principles without PV. Figure 5.13 documents the impact of PV and underfloor ventilation on the temperature distribution when both PV units supplied air at 15 L/s. The use of the VDG increased the temperature in the occupied zone compared to the reference case by 0.15 (0.9°C) and 0.25 (1.5°C) when it was combined respectively with the vertical and the horizontal discharge. The RMP combined with the horizontal discharge increased the temperature by as little as 0.1 (0.5°C) and it did not increase the temperature to any degree when combined with the vertical discharge. The increase of temperature was pronounced most at a height of 0.6 m. Above a height of 1.4 m the temperatures were generally unaffected. Air temperature decreased below the ceiling when the VDG terminal was used. The analysis of the individual profiles identifies that this was the case only near the exposed manikin, where the upward airflow from the VDG had a direct influence on the temperature measurement. The same effect was identified also with the displacement ventilation (Figure 4.19).

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) Vertical aloneVertical + RMPVertical + VDG

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Hei

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r (m

) Horizontal aloneHorizontal + RMPHorizontal + VDG

Figure 5.13. Mean air temperature profiles next to the two workplaces (positions A and B, averaged) with the vertical discharge (left) and the horizontal discharge (right). Both manikins using PV at 15 L/s.

5.1.8 Velocity distribution Figure 5.14 presents the average profiles of mean velocity at the two locations with the four total-volume ventilation systems tested. The profiles measured near the floor for the displacement ventilation and the horizontal discharge of UFAD are similar due to the air current that spreads in a thin layer along the floor. The highest velocity of around 0.16 m/s was measured at a height of 0.05 m, and it decreased rapidly to a level of 0.05 m/s already at

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a height of 0.2 m. The velocities are lower with the vertical discharge of UFAD. Above a height of 1 m the differences between the displacement ventilation and both the discharge patterns of UFAD vanished. The highest velocities among the tested systems were identified for the mixing ventilation. Section 4.9 offers an explanation based on the airflow pattern.

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r (m

) DisplacementUFAD verticalUFAD horizontalMixing

Figure 5.14. Mean air velocity profiles next to the two workplaces (positions A and B, averaged) with different total-volume ventilation principles without PV.

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ght a

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r (m

) Vert. aloneVert. + RMPVert. + VDGHor. aloneHor. + RMPHor. + VDG

Figure 5.15. Mean air velocity profiles next to the two workplaces (positions A and B, averaged) with PV and underfloor ventilation. Both manikins using PV at 15 L/s. Figure 5.15 presents the velocity distribution with the UFAD system alone and in combination with PV. The previously high velocity near the floor decreased when PV was used due to the decrease in the underfloor ventilation rate. The VDG terminal is shown to increase the velocities in the upper zone, regardless of the discharge direction of UFAD (also identified with the displacement ventilation, Figure 4.20). The velocities did not exceed a level of 0.05 m/s above a height of 0.2 m (incl.) with the RMP or any of the discharge patterns of UFAD.

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5.2 Experiment 2 The results presented in the previous chapter indicated that the throw height of UFAD had an impact on the distribution of contaminants, temperature and velocity in the room. In order to ensure a comfortable thermal environment, the volume of air supplied from the floor decreased proportionally with an increase in the PV airflow rate. The basic problem was that the operation of the two systems was related, and hence their impact on the distribution confounded with each other, which made the evaluation of the impact of the throw height difficult.

5.2.1 Objectives The objective of this part of the study is to identify the impact of the throw height of UFAD on the performance of PV in rooms with UFAD.

5.2.2 Experimental conditions Two levels of the throw provided with a vertical discharge of UFAD were investigated. Unlike in the previous chapter, the throw was maintained constant regardless of the use of PV. This was achieved by supplying a constant amount of air from the floor. In order to ensure a comfortable thermal environment, however, the temperature of air supplied from the floor had to be increased with an increase in the PV airflow rate. The changes in the supply air temperature did not have a large impact on the throw height (see below). The supply airflow rate of the floor diffusers was 80 L/s (identical with the previous experiments) and 50 L/s. The throw heights, as reported in Section 5.1.3, were 1.0 m and 0.3 m respectively in the two cases. Both RMP and VDG were tested at a supply rate of 15 L/s. The combinations of PV airflow rates tested (patterns of PV use) were identical with those tested in the previous stage (see Table 5.1, substitute the vertical discharge and the horizontal discharge with respectively a long throw and a short throw). Table 5.2. Combinations of airflow rates and temperatures of PV and UFAD.

PV supply UFAD supply Exhaust Airflow rate Temperature Airflow rate Temperature Airflow rate Temperature

(L/s) (°C) (L/s) (°C) (L/s) (°C) 0 - 80 20 80 26

15 20 80 21.1 95 26 15 + 15 20 80 22.2 110 26

0 - 50 16.4 50 26 15 20 50 18.2 65 26

15 + 15 20 50 20 80 26 Table 5.2 presents the combinations of the supply air volume and temperature of personalized and underfloor ventilation systems arising from the constant air volume control strategy applied. The UFAD system was not under thermostatic control. The supply air temperature was determined from a calculation in order to provide the same cooling capacity of the supply air. The impact of the supply air temperature on the vertical throw was examined at a rate of 50 L/s (12.5 L/s per diffuser). Figure 5.16 shows the mean air velocity contours at a supply air temperature of 20°C and 16.4°C. The centre of the diffuser is located in the origin of the plot. It is shown that the supply air temperature did not have a

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substantial impact on the throw height. It should be noted, however, that the room air temperature was approx. 1°C higher when the supply air temperature was 20°C than when it was 16.4°C. The reason was a lower cooling ability of the supply air, because PV was not used in either of the cases in order to avoid its impact on the distribution.

Figure 5.16. Mean air velocity contours for the vertical discharge at a supply airflow rate 12.5 L/s per diffuser. Supply air temperature 20°C (left) and 16.4°C (right). A consistent similarity between the distribution of bioeffluents and exhaled air was identified in most cases presented in the previous chapter. The experimental design was modified in that the tracer-gas used to simulate the bioeffluents of the polluting manikin was applied to mark the air exhaled from the exposed manikin. Human bioeffluents were thus not simulated in this part of the study. Therefore, because both manikins acted as a source of contaminants, the manikins referred previously to as the polluting manikin and the exposed manikin are referred to in the following as respectively the front manikin and the back manikin. The experimental design in terms of an office layout, furniture, positions and methods of measurement was not changed.

5.2.3 Inhaled air concentration The inhaled air concentrations of the floor contaminant and exhaled air are presented in detail in Appendix E. Figure 5.17 shows the concentration of exhaled air produced by one manikin in the air inhaled by the other manikin at the two throw heights of UFAD. The manikin presented was using PV at 15 L/s, while the other (polluting) manikin did not use PV. It is shown that the throw height of UFAD did not have an impact on the inhaled air concentration, although different levels of concentration were provided with the two terminals. RMP is shown to achieve a very low contaminant concentration (corresponding to a ventilation effectiveness of 50). The concentration provided with VDG was higher due to its low efficiency.

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cent

ratio

n (C

-CS/C

E-C

S)

0

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RMP VDG no PV

Con

cent

ratio

n (C

-CS/C

E-C

S)

1.0 m (80 L/s)0.3 m (50 L/s)

UFAD throw height

Figure 5.17. Concentration of exhaled air in the air inhaled by the front manikin (left) and the back manikin (right). The manikin presented is using PV at 15 L/s, while the other manikin (producing contaminants) does not. The only drawback of PV identified in the previous chapters was associated with the ability of PV to increase mixing of indoor air, and thus to increase the transport of human-produced contaminants between occupants. Figure 5.18 compares the inhaled air concentration of exhaled air at two different throw heights of UFAD. The exposure of both the manikins to a contaminant generated by the other manikin is presented. The manikin presented did not use its PV while the other (polluting) manikin used PV at 15 L/s. It is shown that the throw height of UFAD affects the transmission of contaminants between occupants. With the long throw there was almost no difference between the two terminals, while the VDG terminal performed better than the RMP terminal when the throw was short. The results were very similar for the two manikins. This means that the transmission of exhaled air from the front manikin to the back manikin is comparable with the transmission of exhaled air from the back manikin to the front manikin.

0

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RMP VDG no PV

Con

cent

ratio

n (C

-CS/C

E-C

S)

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Con

cent

ratio

n (C

-CS/C

E-C

S)

1.0 m (80 L/s)0.3 m (50 L/s)

UFAD throw height

Figure 5.18. Concentration of exhaled air in the air inhaled by the front manikin (left) and the back manikin (right). The manikin presented does not use PV, while the other manikin (producing contaminants) uses PV at 15 L/s.

5.2.4 Inhaled air temperature The inhaled air temperatures of the manikins were identical with the two throw heights, although the supply air temperature UFAD was different for the two discharge patterns (Table 5.2). Analyses showed that neither the supply conditions of UFAD nor the use of PV by the other manikin were able to affect the inhaled air temperatures substantially. The use of PV decreased the inhaled air temperature of a manikin exposed to PV. The temperatures were comparable with the temperatures measured in the previous chapter. No impact of the throw height or temperature of UFAD on the inhaled air temperature was found.

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5.2.5 Contaminant distribution The distribution of the floor contaminant was similar to the distribution of the floor contaminant identified in the previous section, and hence similar to the distribution with the displacement ventilation. Therefore, only the distribution of exhaled air is reported in the following. Both manikins acting as a source of exhaled air made it possible to use two experiments to evaluate the distribution of the exhaled air under an analogous setting but in an opposite layout. For example, the distribution of the contaminant exhaled from the front manikin using PV while the back manikin did not use PV was supplemented with the distribution of the contaminants exhaled from the back manikin using PV while the front manikin did not use PV. The contaminant profiles measured next to the two manikins in the two cases were similar and therefore averaged in order to provide a more general picture of the distribution. Personalized airflow close to a source Figures 5.19 and 5.20 present the vertical concentration profiles of exhaled air for UFAD alone and in combination with respectively the RMP and the VDG terminal. The manikin generating contaminants was using PV at 15 L/s, while the other manikin did not use PV. The contaminant distribution was clearly stratified with the UFAD alone. When the throw was short, the concentrations were very low in the lower occupied zone. A long throw obviously affected the contaminants collected above the occupied zone and brought them to the lower zone. The concentration near the floor increased to about 50% of the concentration in the exhaust. The use of the RMP promoted diffusion of the exhaled air in the room air and thus destroyed the stratification (Figure 5.19). The concentration profiles did not depend on the throw height. The use of VDG also increased the concentration in the occupied zone. However, the stratification was not destroyed completely. Lower concentrations were measured near the floor for the combination of the VDG and the short throw, as compared to the long throw. Figure 5.21 presents the vertical contaminant profiles of exhaled air with the VDG terminal combined with UFAD. Both VDG units were used at 15 L/s. The throw height of UFAD was again constant, whether or not PV was used. The use of both the VDG units achieved a uniform distribution when the throw of UFAD was long; however, the stratification decreased but remained when the throw was short. Comparison of Figures 5.20 and 5.21 shows that the use of both VDG units at a rate of 15 L/s increased the concentration in the occupied zone as compared to the case when only one VDG unit was used.

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r (m

) UFAD alone throw 0.3 m (50 L/s)

UFAD alone throw 1.0 m (80 L/s)

UFAD + RMP throw 0.3 m (50 L/s)

UFAD + RMP throw 1.0 m (80 L/s)

Figure 5.19. Concentration profiles of exhaled air. RMP terminal directed towards the source in combination with the vertical discharge of UFAD. Personalized airflow rate 15 L/s.

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Hei

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r (m

) UFAD alone throw 0.3 m (50 L/s)

UFAD alone throw 1.0 m (80 L/s)

UFAD + VDG throw 0.3 m (50 L/s)

UFAD + VDG throw 1.0 m (80 L/s)

Figure 5.20. Concentration profiles of exhaled air. VDG terminal directed towards the source in combination with the vertical discharge of UFAD. Personalized airflow rate 15 L/s.

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Concentration (C-CS/CE-CS)

Hei

ght a

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r (m

) UFAD alone throw 0.3 m (50 L/s)

UFAD alone throw 1.0 m (80 L/s)

UFAD + VDG throw 0.3 m (50 L/s)

UFAD + VDG throw 1.0 m (80 L/s)

Figure 5.21. Concentration profiles of exhaled air. VDG terminal directed towards the source in combination with the vertical discharge of UFAD. Both VDG units used at 15 L/s. Personalized airflow far from a source Figure 5.22 presents the vertical concentration profiles of exhaled air with the RMP and UFAD. The manikin generating contaminants did not use PV, while the other manikin used PV at 15 L/s. It is shown that the use of the RMP (not directed towards the source) did not affect the contaminant distribution in the occupied zone substantially at any throw height of UFAD. The differences between the contaminant profiles are caused due to small local non-uniformities. The exhaled air concentration profiles of the VDG and UFAD are shown in Figure 5.23. The conditions are identical with the previous figure for RMP. Unlike the RMP terminal, the VDG terminal created mixing both in the occupied zone and below the ceiling in comparison with the UFAD system alone. The concentration in the lower occupied zone increased in the case of the short throw, but it did not change from the reference when the throw was long. This indicates that the long throw dominated the airflow pattern in the lower occupied zone.

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r (m

) UFAD alone throw 0.3 m (50 L/s)

UFAD alone throw 1.0 m (80 L/s)

UFAD + RMP throw 0.3 m (50 L/s)

UFAD + RMP throw 1.0 m (80 L/s)

Figure 5.22. Concentration profiles of exhaled air. RMP terminal not directed towards the source in combination with the vertical discharge of UFAD. Personalized airflow rate 15 L/s.

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r (m

) UFAD alone throw 0.3 m (50 L/s)

UFAD alone throw 1.0 m (80 L/s)

UFAD + VDG throw 0.3 m (50 L/s)

UFAD + VDG throw 1.0 m (80 L/s)

Figure 5.23. Concentration profiles of exhaled air. VDG terminal not directed towards the source in combination with the vertical discharge of UFAD. Personalized airflow rate 15 L/s.

5.2.6 Temperature distribution The temperature in the occupied zone was affected by the fact that the supply air temperature of UFAD was varied in order to provide a constant cooling ability for the room (Table 5.2). As in the previous chapter, the temperature distribution was assessed based on the vertical profiles of the mean air temperature recorded near the two workplaces. The profiles from the two positions were averaged because they were similar. Figure 5.24 presents the dimensionless temperature profiles with PV and UFAD for the two different throw heights. Both PV units were used at 15 L/s. The situation represents the case when the impact of PV was the greatest. The comparison of the reference cases showed that the larger throw height increased mixing in the occupied zone and provided higher temperatures near the floor compared to the lower throw height. The temperature profile was steeper (larger stratification) when the throw was lower. The use of PV increased the temperature in the occupied zone due to the increase in the airflow rate and temperature of UFAD as well as to the mixing generated by PV. With the RMP the temperatures did not increase significantly. The largest increase in the normalized temperature with RMP was 0.1 when combined with the vertical discharge providing a throw of 1.0 m (Figure 5.24, left). The temperatures increased more with the VDG than with the RMP. In the case of the long throw the normalized temperature increased by as much as 0.2, so that the stratification was almost destroyed. The differences between the air terminals and the throw heights vanished above a height of 1.4 m. The temperature below the ceiling decreased with the VDG

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regardless of a combination of the discharge direction and the airflow rate. The same characteristic, caused by the upward direction of personalized airflow, was identified also in the previous section.

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Vertical discharge - 50 L/s

Figure 5.24. Mean air temperature profiles next to the two workplaces (positions A and B, averaged) with the vertical discharge of UFAD providing a throw of 1.0 m (left) and a throw of 0.3 m (right). Both manikins using PV at 15 L/s.

5.2.7 Velocity distribution The distribution of velocity is not reported in detail because it was similar to the distribution with the vertical discharge identified in the previous experiment. The highest velocities were again measured in the lower occupied zone; however, they did not exceed a value of 0.07 m/s at any height.

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5.3 Experiment 3 The results presented in the previous chapters showed that PV supplying 15 L/s towards a contaminant source was able to promote mixing of the contaminant in the occupied zone and thus increase the transmission of the contaminant between workplaces.

5.3.1 Objectives The objective of this section is to investigate the impact of the strength of PV airflow on mixing in the occupied zone.

5.3.2 Experimental conditions The ability of PV to decrease mixing in the occupied zone was studied with both RMP and VDG supplying air at a rate of 7 L/s. The experiments are summarized in Table 5.3. Although different discharge patterns were used (experiments were not performed in the same period of time), they both provided a short throw and were thus not supposed to affect mixing in the occupied zone significantly. The ability of RMP to increase mixing of the contaminants generated at another workplace at a high supply rate of 30 L/s was tested as well. The supply air temperature of PV was 20°C in all cases. The experimental design in terms of an office layout, furniture, positions and methods of measurement was identical with those of the previous experiments. Table 5.3. Experimental conditions. Impact of the strength of PV airflow on mixing in the occupied zone. PV UFAD ContaminantTerminal Airflow rate (L/s) Discharge Airflow rate Temperature source

Front

manikin Back

manikin (L/s) (°C)

VDG 7 0 vertical 50 17.2 as in 5.2 VDG 0 7 vertical 50 17.2 as in 5.2 RMP 7 0 horizontal 73 20 as in 5.1 RMP 0 30 horizontal 50 20 as in 5.1

5.3.3 Upward airflow direction Figure 5.25 examines the impact of the VDG airflow rate (7 L/s and 15 L/s) on the transmission of exhaled air between occupants. Similar results were obtained for the two manikins. It is shown that the transmission of contaminants increase even at a rate of 7 L/s, but not as much as at a rate of 15 L/s. Figure 5.26 presents the vertical concentration profiles of the exhaled air with the VDG under the same conditions. The distribution with the VDG directed towards the manikin generating contaminants while the other manikin did not use PV is presented. So as in Experiment 2 (Section 5.2.5), the figure is based on two experiments with an analogous setting but an opposite layout (Table 5.3). It is shown that the VDG providing 7 L/s increased the concentration in the occupied zone compared to the reference case of UFAD alone; the increase was not as large as at a rate of 15 L/s. Although the concentrations increased, the stratification was preserved in all cases.

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no PV VDG: 7 L/s VDG: 15 L/s

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cent

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-CS/C

E-C

S)

front manikinback manikin

Inhaled to

Figure 5.25. Concentration of exhaled air in the air inhaled by both manikins. VDG combined with a vertical discharge of UFAD, short throw. The manikin presented did not use PV, while the other used PV at 7 L/s or 15 L/s.

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) UFAD aloneUFAD + VDG 7 L/sUFAD + VDG 15 L/s

Figure 5.26. Concentration profiles of exhaled air. VDG terminal directed towards the source in combination with the vertical discharge of UFAD, short throw. Personalized airflow rate of 7 L/s and 15 L/s.

5.3.4 Horizontal or downward airflow direction Figure 5.27 documents the impact of RMP airflow rate on the transmission of bioeffluents and exhaled air from the front manikin to the back manikin. The measurements showed that the transmission of the contaminants was comparable for the airflow rates of 7 L/s and 15 L/s. Although the airflow did not reach the face of the manikin directly at 7 L/s (see smoke visualization, Figure 4.1), the mixing was apparently high enough to promote diffusion of the contaminants to the room. The figure also documents the similarity between the human bioeffluents and exhaled air. Figure 5.28 compares the distribution of the human-produced contaminant at the two airflow rates of RMP directed towards the front manikin. The profiles were very different at the two positions. At a lower rate of 7 L/s the RMP did not support the stratification of the contaminants in the form of a peak in front of the polluting manikin. The concentrations were uniform and due to the proximity of the source, higher than 1. Further from the source, i.e. next to the back manikin, the contaminant profiles were similar. This reveals the reason for the almost identical inhaled air concentrations presented in Figure 5.27.

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no PV RMP: 7 L/s RMP: 15 L/s

Con

cent

ratio

n (C

-CS/C

E-C

S)

BioeffluentsExhaled air

Figure 5.27. Concentration of bioeffluents and exhaled air in the air inhaled by the exposed manikin with RMP and horizontal discharge of UFAD. Polluting manikin using PV at 7 L/s and 15 L/s while back (exposed) manikin does not.

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r (m

)

Horizontal alone, ARMP 7 L/s, ARMP 15 L/s, AHorizontal alone, BRMP 7 L/s, BRMP 15 L/s, B

Figure 5.28. Concentration profiles of exhaled air and bioeffluents (averaged) next to the two workplaces (positions A and B) with RMP and the horizontal discharge of UFAD. Front manikin using PV at 7 L/s and 15 L/s while back manikin does not. Figure 5.29 presents the vertical concentration profiles of the human-produced contaminants produced by the front manikin while the back manikin used PV at a rate of 15 L/s and 30 L/s. The front manikin did not use PV. The distributions measured near the two workplaces were very similar, despite the different distance from the source and the PV, and are thus averaged. It is shown that the airflow rate had little impact on the contaminant distribution.

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Hei

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r (m

)

Horizontal aloneRMP 15 L/sRMP 30 L/s

Figure 5.29. Concentration profiles of exhaled air and bioeffluents (averaged) recorded next to the two workplaces (positions A and B, averaged) with RMP and the horizontal discharge of UFAD. Exposed manikin using PV at 15 L/s and 30 L/s while front (polluting) manikin does not.

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5.4 Discussion Two types of air terminal device for PV were combined with UFAD discharging air in a vertical and a horizontal direction. The impact of the vertical throw height of UFAD and the airflow rate of PV were studied. Knowledge concerning the distribution of different contaminants in rooms with UFAD systems (without PV) is limited. The literature (Arens et al., 1991; Bauman et al., 1991; Fisk et al., 1991; Loudermilk, 1999; REHVA, 2003; Bauman and Daly, 2003) indicates that on the one hand the performance of UFAD providing a short throw resembles displacement ventilation. On the other hand, the ventilation performance of UFAD with a long throw was associated with mixing ventilation. The impact of different throw heights of UFAD on the inhaled air quality was not, however, studied in detail. The analyses of the contaminant distribution measured in the present study showed that the performance of UFAD with a horizontal discharge of air (throw of 0.1 m) was similar with the performance of displacement ventilation. In both cases the supply air spread along the floor in a thin layer, which made it possible for the free convection flow around the body to entrain and transport clean air upward to the breathing zone (performance in regard to thermal comfort was different, see below). UFAD with a short vertical throw (0.3 m) provided a similar pattern, although both the distribution of velocity (Figure 5.14) and the smoke visualization (Figure 5.3) indicated more mixing in the lower occupied zone. As expected, UFAD with a longer vertical throw penetrated into the occupied zone and brought polluted air from the higher levels towards the floor. The results showed that the throw height just comparable to the height of the breathing zone (1.0 m) increased the concentration of human-produced contaminants in the lower zone to about 50% of the concentration in the exhaust air. Mixing conditions were not created, apparently because the throw was still too short. The results of measurements were used in order to verify two physical models of UFAD systems suggested recently. Lin and Linden (2002) discussed a situation with one heat source and one supply opening. However, the model could not be applied in the present, more complex case due to the large number of simplifications it contained. Yamanaka et al. (2002) proposed a model that aims at predicting the vertical distribution of human-produced contaminants. The model was verified in a scaled experimental room. The distribution predicted for the conditions tested was in a good agreement with the distribution obtained from the measurement. This is documented in Appendix F. Although more experimental data are needed for further verification, the model by Yamanaka et al. (2002) could become an efficient tool for predicting the distribution of active contaminant in rooms with UFAD. With the throw comparable to the height of the breathing zone, the inhaled air quality of seated occupants was similar to the air quality in the lower occupied zone. The ventilation effectiveness (personal exposure index, pollutant removal efficiency) measured in the inhaled air was around 2. Loudermilk (2003) stated that mixing (promoted by underfloor ventilation) must be limited to just below the respiration level of seated occupants in order to prevent transmission of contaminants between occupants. The present results indicate that although such stratification decreases the exposures of occupants to one half the exposure with mixing ventilation, a shorter throw is required in order to reduce the transmission significantly. Finding the relationship between the inhaled air quality and the throw height is, however, not easy. The stratification of contaminants as well as mixing of air in the lower occupied zone (due to UFAD) makes it difficult to assess the ability of the

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upward free convection flow around the body to provide clean to the breathing zone (based on data measured and published so far). Therefore, more research in this area is needed. The concentration of human-produced contaminants inhaled with different ventilation systems (without PV) was presented in Figure 5.4.

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0.1 m (65 L/s,horiz.)

0.3 m (50 L/s) 0.6 m (65 L/s) 1.0 m (80 L/s)

Throw height of UFAD (airflow rate)

Con

cent

ratio

n (C

-CS/C

E-C

S)

UFAD + RMPUFAD + VDG

Figure 5.30. Concentration of exhaled air from the front manikin inhaled by the back manikin. Back manikin using PV at 15 L/s while front manikin does not. The data for a throw height of 0.1 m (i.e. horizontal discharge) and 0.6 m were obtained in stage 2-1. The data for a throw height of 0.3 m and 1.0 m were obtained in stage 2-2. The throw height of 0.6 m, corresponding to the airflow rate of 65 L/s, was not measured but it was estimated as half way between the throw at 50 and 80 L/s. The inhaled air quality increases substantially when PV is used. The largest improvement is realized when an occupant inhales air direct from the potential core region of a personalized air jet. The air quality outside of the core is a product of mixing between clean personalized air and polluted surrounding air. Figure 5.30 compares the concentration of contaminants exhaled from the front manikin in the air inhaled by the back manikin at different vertical throws of UFAD. The back manikin was protected with PV. It is shown that the throw height of UFAD did not have a substantial impact on the contaminant concentration in the inhaled air, although the manikin did not inhale direct from the clean core region (if so the concentration would be zero). Furthermore, the concentrations with PV and UFAD (all throw heights) were comparable with the concentrations provided by PV and displacement ventilation (Figure 5.4). The reason is not clear. It is possible that the local concentration surrounding the air terminals did not change substantially, although the concentration levels near the floor varied with the throw. The uncertainty of measurements should be considered as well. In practice, both a high air quality experienced close to the personalized airflow, and a lower air quality inhaled at the workstation (when PV is not used) will certainly contribute to the exposures of occupants over a period of time. Hence, a short throw of UFAD, which decreases the exposures of unprotected occupants (Figure 5.4), should be prioritized. In the room with UFAD as well as in the room with displacement ventilation, the use of PV increased mixing of the contaminants located in its vicinity and thus decreased the inhaled air quality of other occupants. Cermak and Melikov (2003) observed the same phenomenon previously; however, only one PV system was studied and the throw height of UFAD was not considered as a parameter. Figure 5.31 compares the transmission of exhaled air from the front manikin to the back manikin at different throw heights of UFAD. The front manikin used PV at 15 L/s, while the back manikin was unprotected. The results for the RMP showed that the level of transmission did not change with the throw height, unless the throw was very short. The VDG is shown to cause a lower transmission of contaminants than the RMP (Cermak and Melikov, 2004). Moreover, the transmission with the VDG

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decreases proportionally to the decrease in the throw (discussed below). The direction of personalized airflow and not its strength is supposed to be the reason, because the airflow provided upward (VDG) had a greater momentum (and it caused lower transmission) than the airflow provided downward (RMP). The transmission was somewhat lower with PV and the horizontal discharge of UFAD than with PV and the displacement ventilation (Figure 5.5). The ability of UFAD to reduce non-uniformities and thus prevent the vertical spread of contaminants (discussed below) might be the reason.

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0.3 m (50 L/s) 0.6 m (65 L/s) 1.0 m (80 L/s)

Throw height of UFAD (airflow rate)

Con

cent

ratio

n (C

-CS/C

E-C

S)

UFAD + RMPUFAD + VDG

Figure 5.31. Concentration of exhaled air from the front manikin inhaled by the back manikin. Front manikin using PV at 15 L/s, while back manikin does not. The data for a throw height of 0.1 m (horizontal discharge) and 0.6 m were obtained in stage 2-1. The data for a throw height of 0.3 m and 1.0 m were obtained in stage 2-2. The extent of mixing and thus the transmission of human-produced contaminants was expected to decrease with the decrease in the air velocity impinging the source. The ability of RMP to affect the transmission was examined at a rate of 7 L/s, where its efficiency to provide clean air to the breathing zone starts to decline (Bolashikov et al., 2003). This corresponds to a supply air velocity of 0.26 m/s and a Reynolds number of 3200. The measurements showed, however, that even such a weak airflow was not able to maintain the transmission low near the reference level without PV (Figure 5.27). Although the non-uniformities of the human-produced contaminants decreased in the vicinity of the polluting manikin’s workplace (Figure 5.28), the distribution of the contaminants next to the exposed manikin did not differ from the case where the supply air velocity was twice as high (at 15 L/s). Contrary to RMP, VDG supplying air at a rate of 7 L/s did not increase significantly the transmission of contaminants between workplaces as compared to the reference level without PV. The supply air velocity and the Reynolds number (based on a hydraulic diameter) were respectively 1.6 m/s and 3900. The analyses showed that the centreline velocity of the upward airflow from VDG decreases to approx. 0.3 m/s at the ceiling level (Awbi, 1998), which is still high enough to encourage mixing. Therefore, the ability of PV to cause mixing of contaminants generated in its vicinity depends more likely on the direction of PV airflow than on its velocity. The measurements with UFAD showed that the transmission of exhaled air from the front manikin to the back manikin and vice versa are comparable, even when the throw of UFAD is short. The reason can be the ability of UFAD to provide a more uniform contaminant distribution across the room, which was demonstrated by the reduction of the concentration peaks in front of the polluting manikin (discussed below). This implies that in rooms with UFAD, the layout of workplaces will not have an impact on the transmission of contaminants between occupants (discussed in more detail in Chapter 6).

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The ability of PV to affect the distribution of contaminants generated at another workplace is difficult to generalize. The reason is that the direction, strength, airflow rate and the construction of supply air terminal were confounded. Table 5.4 summarizes the ability of PV in combination with UFAD to affect the distribution of contaminants. The physical properties of personalized air jets are included in the table. It is shown that neither terminal type affects the distribution of contaminants at a rate of 7 L/s. At higher airflow rates, however, the ability of the two types of PV to affect room air distribution differs. The RMP terminal was not able to affect the distribution even at a rate of 30 L/s, while the VDG caused mixing already at a rate of 15 L/s. The comparison of the physical properties may suggest that PV does not affect the distribution of the contaminants generated at another workplace for momentum flux lower than ca. 0.015 N and velocities lower than 1-1.5 m/s, regardless of the direction of the PV airflow. However, more measurements are needed in order to identify the threshold values with certainty. The experimental design should involve several terminals with different dimensions. Each terminal should be tested when providing air from different directions in order to prevent confounding of terminal construction and airflow direction (the case in the present study). Table 5.4. Impact of PV on the distribution of contaminants generated at another workplace.

RMP VDG Airflow

rate (L/s)

Impact on distribution

Momentum flux (N)

Supply velocity (m/s)

Impact on distribution

Momentum flux (N)

Supply velocity (m/s)

7 No 0.002 0.26 No* 0.013 1.59 15 No 0.010 0.56 Mixing 0.061 3.41 30 No 0.040 1.12 - - -

* Not presented in detail, observed also with PV and displacement ventilation (Chapter 4) Room air distribution In the experiments with displacement ventilation, the use of PV created large non-uniformities and differences between the distribution of human-bioeffluents and the distribution of exhaled air in the vicinity of the contaminant source. With UFAD, the distributions of the two contaminants were similar. The concentration peaks were more than 50% lower in magnitude with the RMP combined with the horizontal discharge of UFAD (Figure 5.8) than with the RMP combined with the displacement ventilation (Figure 4.12). With the vertical discharge of UFAD, the peaks vanished completely. The mixing generated by UFAD, although limited to a relatively short height, reduces thus the contaminant non-uniformities and the horizontal spread of contaminants in the occupied zone as compared to displacement ventilation. It is possible that non-uniformities and differences between the distribution of human bioeffluents and the distribution of exhaled air still exist in the immediate vicinity of an occupant. In rooms with PV and UFAD, the distribution of an active contaminant depends on the interaction between the mixing zone height (throw) and the stratification height. The stratification height decreases when the airflow rate of UFAD decreases (as with displacement ventilation). Personalized airflow directed upward entrains surrounding air and acts like a thermal plume, thus decreasing the stratification height as well. The volume of air entrained to different PV airflows in a confined office workplace was, however, not studied. Personalized airflow directed horizontally or downward may not affect the stratification height; however, it affects the concentration of contaminants in the lower occupied zone when directed towards the source.

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Figure 5.32 illustrates the vertical concentration profiles of active contaminants for three possible scenarios of a combined performance of PV providing air upward and UFAD utilizing passive floor diffusers. The concentration profiles are supported by the measurements (see Figures 5.20-5.23). UFAD alone (without PV) providing a long throw will reach the height of the stratification and bring contaminants from the upper mixed zone to the lower zone (Figure 5.32, left). The use of PV will decrease the stratification. If the airflow rate of UFAD is kept constant when PV is used, the throw and thus the mixing created by UFAD in the lower zone will not change. The upward airflow from the floor diffusers may then interact with the decreased stratification, increasing thus the contaminant concentration in the occupied zone (Figure 5.32, middle). A decrease in the airflow rate of UFAD will decrease the stratification height even further. At the same time, however, the mixing in the lower zone may decrease and provide a fairly low concentration level in the lower zone (Figure 5.32, right). The flow in a human boundary layer may then transport air from the lower levels upward to the breathing zone, providing a lower exposure of occupants compared to the former two cases. However, a further decrease in the stratification height would decrease the inhaled air quality due to the entrainment of polluted surrounding air by the free convection flow around the body. Because of the complex interaction of stratification height, throw height and PV airflow, it is premature to elaborate a physical model that would describe the vertical distribution (and inhaled air concentration) of active contaminants in rooms with PV and UFAD.

Figure 5.32. Examples of concentration profiles of active contaminants with PV supplying air upward and UFAD with a vertical discharge. Left: PV is not used - throw is comparable to the height of the breathing zone. Middle: PV is used - throw height did not change. Right: PV is used – airflow rate of UFAD and throw height decreased. The analyses suggest that a design strategy ensuring a low transmission of contaminants between workplaces should involve a short throw of UFAD and a personalized air terminal supplying air upward. As long as the throw is short, the control strategy of UFAD is less important. However, a constant air volume strategy will not decrease the stratification height (with passive floor diffusers) and will also result in a higher ventilation rate when PV is used. The airflow rate of UFAD should be chosen to determine a stratification height according to criteria for displacement ventilation, e.g. comparable to the height of the breathing zone. The inhaled air quality will not deteriorate due to PV if its airflow rate (supply velocity) is low, as discussed previously. The worst strategy, on the other hand, would maintain a long throw, and decrease the airflow rate of UFAD when PV is used. The throw height of UFAD seems unimportant from the viewpoint of transmission of contaminants between occupants when a personalized air terminal device generating horizontal/downward flow is used. However, a shorter throw would provide a lower

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exposure of unprotected occupants to other active contaminants present in the room. Depending on the design of the floor diffusers (discharge pattern), the use of a shorter throw may be associated with a draught risk and a larger vertical temperature difference between head and ankles. Thermal environment Temperature stratification plays an important role in determining occupants’ thermal comfort as well as energy performance of the combined systems. With UFAD alone, the air temperature near the floor increases due to the ability of swirl flows to entrain larger amounts of surrounding air, as compared to a unidirectional flow of displacement ventilation. A normalized temperature near the floor measured for the long vertical throw was 0.7. This corresponds to the temperatures reported in the UFAD design guide by Bauman and Daly (2003), based on Webster et al. (2002a, b). The normalized temperature with the vertical discharge providing a short throw and the horizontal discharge was about 0.6. This is much higher than the normalized temperature of 0.4 recorded in the experiments with displacement ventilation and implies that the risk of thermal discomfort is smaller in rooms with UFAD. The differences between the temperature stratification with UFAD and the temperature stratification with displacement ventilation decrease with the distance from the floor. The shape of the temperature profiles reflects the fact that the majority of the heat sources are located in the lower occupied zone (e.g. REHVA, 2003). If the heat sources are located in the upper level of the space, the temperature may not increase sharply near the floor and the differences between the temperature profiles for the different systems will probably disappear.

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pera

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E-T

S)

PV + UFADPV + DisplacementDisplacement (Mundt, 1990)

Figure 5.33. Normalized temperature near the floor (0.1 m) as a function of the room airflow rate per m2 floor area. Results for displacement ventilation according to Mundt (1990). The use of PV promoted mixing, disturbed the thermal stratification and thus increased the temperature in the occupied zone. The temperature in the occupied zone may not, however, increase if it is already high due to the mixing generated by UFAD. This was the case for the RMP terminal and UFAD with the vertical discharge. Regardless of the discharge pattern of UFAD, the temperature increased more with the VDG terminal than with the RMP terminal. The differences between the terminals, and their impact on the thermal comfort of seated occupants, are discussed in Chapter 4. Figure 5.33 plots the normalized temperature near the floor for PV and UFAD (all experiments performed in phase 2-1 and 2-2) versus the overall room airflow rate. The normalized temperatures for PV and displacement ventilation (all experiments performed in phase 1) are presented as well. The measurements were taken at a height of 0.1 m. The curve for displacement ventilation was suggested and verified with a large number of experimental data by Mundt (1990). It can be seen that the normalized

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temperatures with PV and UFAD range between 0.7 and 0.8 over a range of airflow rates. The values correspond to the highest values of normalized concentration reported by Bauman and Daly (2003) for underfloor ventilation alone. In their case, however, the vertical throw of the floor diffusers was generally longer than in the present study (0.6 m to 2 m). This indicates that the increase in temperature caused by a long throw of UFAD is comparable to the increase in temperature caused by PV in combination with a shorter throw. The temperatures with PV and UFAD were higher than the temperatures measured in rooms with PV and displacement ventilation. The temperature measured with the displacement ventilation (the lowest diamond in the figure) agrees well with the model of Mundt (1990). As discussed in Chapter 4, the model of Mundt (1990) could be used to predict the normalized temperature near the floor in rooms with PV and displacement ventilation. However, the model cannot be applied in the case of underfloor ventilation, neither alone nor in combination with PV. The results presented by Bauman and Daly (2003) for a wide range of airflow rates suggest that the relationship between the normalized temperature and the airflow rate does not follow the theoretical relationship as derived by Mundt (1990). Therefore, more research is needed before any model for practical purposes can be recommended. In rooms with displacement ventilation, a linear vertical temperature profile is often assumed as a first approximation. The result for displacement ventilation (discussed in Chapter 4) showed that the vertical air temperature difference between head and ankles predicted on the assumption of profile linearity could be very different from the difference actually measured. An increase in temperature near the floor in rooms with UFAD caused the linear profile to agree better with the measurement, especially in the case of UFAD providing a long vertical throw. Therefore, in rooms with UFAD providing a long vertical throw, the use of a linear profile can be justified. It should be noted, however, that the temperature profiles measured in the present study were very steep in the lower zone due to the presence of most heat sources. A good agreement between a linear profile and measurements can be expected in rooms where the distribution of heat sources is vertically uniform, regardless of the distribution system.

02468

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no PV with RMP with VDG

Dra

ught

ratin

g (%

)

A

B MixingDisplacementUFAD horizontal (VAV)UFAD vertical (VAV)UFAD vertical short (CAV)UFAD vertical long (CAV)

Figure 5.34. Draught rating at a height of 0.1m based on the measurement of temperature and velocity in the room. Categories of thermal environment (A and B) according to CEN (1998) are indicated. Draught has been identified as the major local discomfort factor for the occupants in rooms with displacement ventilation (Pitchurov et al., 2002). Figure 5.34 presents a comparison of the draught rating with the different ventilation systems tested, with and without PV. The rating is based on the measurement of mean air temperature, mean air velocity and

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turbulence intensity at a height of 0.1 m. The larger value of the rating obtained at positions A and B (Figure 3.1) is presented. It is shown that in general the use of PV decreased the draught rating as compared to the reference cases without PV. The highest rating of about 12% was identified for mixing ventilation (due to elevated velocities near the floor, Figure 5.14). Although the rating with displacement ventilation and UFAD providing air horizontally decreased as compared to mixing ventilation, only UFAD with a vertical air discharge was able to decrease the draught rating substantially. All values corresponded to a thermal environment of category A according to CEN Report 1752 (CEN, 1998), as indicated on the right-hand side of the figure.

0123456789

10

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ver

t. ∆T

(%)

A

B

C

MixingDisplacementUFAD horizontal (VAV)UFAD vertical (VAV)UFAD vertical short (CAV)UFAD vertical long (CAV)

Figure 5.35. Percentage dissatisfied with a vertical air temperature difference between head and ankles (1.1 and 0.1 m above the floor). Categories of thermal environment (A, B and C) according to CEN (1998) are indicated. The predicted percentage dissatisfied with vertical air temperature difference between head and ankles is documented in Figure 5.35. The larger value of the vertical temperature difference obtained at positions A and B (Figure 3.1) was used and converted to the percentage dissatisfied by means of the relationship presented in CR Report 1752 (CEN, 1998). The lowest percentage dissatisfied was predicted for mixing ventilation and UFAD providing a long vertical throw. The percentage dissatisfied was low also with all the UFAD systems. In one case, with UFAD alone (no PV) providing a short vertical throw, the percentage dissatisfied increased due to the low temperature of supplied air (16.4°C). As expected, the largest risk of discomfort was identified for displacement ventilation, even though the supply air temperature was 20°C. The measurement position is an important factor that determines the prediction of local thermal discomfort. The measurement positions used in the present study and the thermal manikins were both located approximately at the same distance from the displacement diffuser (Figure 3.1). In the case of underfloor ventilation, the distance between the measurement positions and the floor-based outlets was shorter than the distance between the manikins and the outlets. Therefore, the results for underfloor ventilation overestimate the local thermal discomfort of occupants (as compared to displacement ventilation). The results (Figures 5.34 and 5.35) indicate that UFAD systems with a vertical discharge pattern have a greater potential to provide a lower risk of local thermal discomfort than displacement ventilation or UFAD systems with a horizontal discharge pattern, both with and without PV. On the other hand, displacement ventilation and UFAD with a horizontal discharge are advantageous in providing a better air quality. Because PV makes it possible for occupants to increase their inhaled air quality substantially, the ability of a total-volume

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ventilation system to provide high air quality may not be important. Therefore, an air distribution system ensuring a comfortable thermal environment, i.e. UFAD system with a vertical discharge pattern, should be preferred. Chapter 7 outlines the recommendations for practical application.

5.5 Conclusions • The performance of PV in combination with UFAD is affected by the throw height of

UFAD, and the direction and the strength of PV airflow. • The performance of PV in combination with UFAD providing a short throw is

comparable to the performance of PV in combination with displacement ventilation in regard to inhaled air quality. However, UFAD is advantageous in decreasing the non-uniformities of contaminants and the vertical air temperature gradients.

• In the occupied zone of rooms with UFAD providing a short throw, personalized airflow

directed upward will provide a lower concentration of an active contaminant located in its vicinity than the personalized air directed horizontally/downward. Therefore, the use of PV with an upward airflow direction may result in a better air quality for other occupants who are unprotected with PV.

• An increase in the throw height of UFAD decreases the inhaled air quality of occupants,

both with and without PV. The impact of the direction of personalized airflow on the mixing of contaminants in the occupied zone decreases gradually with the increase in the throw, and it disappears when the throw is comparable to the height of the breathing zone.

• The transmission of active contaminants between two workplaces arranged in a row behind each other is independent of the location of the workplace where the contaminants are generated. This suggests that the layout and arrangement of an office may not have a significant impact on the transmission in rooms with UFAD.

93

6. General discussion

A series of physical measurements was carried out in order to examine the performance of personalized ventilation (PV) in combination with different total-volume ventilation systems. Two types of air terminal device for PV were examined. At present, they represent the concepts with the highest potential to ensure excellent air quality and preferred thermal environment for occupants. The major difference between the terminals was the direction of personalized airflow in relation to the occupant. The total-volume ventilation systems were mixing ventilation, displacement ventilation and underfloor ventilation. The impact of the total-volume ventilation principle on the performance of PV, and vice versa, was examined under well-defined conditions. The methods, the experimental design and the conditions tested were identical. This is important, because it allows for a credible comparison of the performance of the combined systems. The criteria for evaluation were the air quality, assessed on the basis of the distribution of three simulated contaminants (floor covering, human bioeffluents and exhaled air) and inhaled air temperature, and thermal comfort of occupants. The results for each combined system are discussed in detail in the corresponding chapters. The most important findings and their possible implications in practice are discussed in the following. Air quality Ventilation by mixing represents the most common air distribution principle in practice. In the present study, the mixing ventilation system acted as a reference case for all other distribution systems. The measurements showed that the mean air velocity in the occupied zone was high enough to affect buoyancy-generated primary airflows such as a free convection flow around occupants, thermal plumes above electronic equipment, etc. Therefore, the distribution of the three contaminants, temperature and velocity were close to uniform. The use of PV provided a substantial improvement of the inhaled air quality. The amount of clean personalized air inhaled was influenced by the efficiency of the air terminal devices and their positioning in respect to the occupant (discussed in Chapter 4). The results generally agree with the results of the previous studies reported in the literature (Bolashikov et al., 2003; Melikov et al., 2002; Faulkner et al., 1999). The use of PV in combination with mixing ventilation did not have an impact on the room ambient environment in any way, although rather extreme patterns of PV use were tested (PV was used at high airflow rates by different occupants at a time). Neither did the room airflow affect the performance of PV. Therefore, as compared to the performance of a mixing ventilation system alone, the application of PV in rooms with mixing ventilation can only be beneficial. The present study, the first of its kind, examined the performance of PV in a room with a controlled non-uniform distribution of contaminants. The non-uniform distribution was provided with a displacement ventilation system and an underfloor ventilation system. With the displacement ventilation system alone, the room air distribution followed the expected pattern. The distribution of the active contaminant (human bioeffluents) was stratified with a low concentration near the floor and a high concentration near the ceiling. The interface layer between the two zones was formed at a height of about 1 m. This ensured

6

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a high air quality for seated occupants, whose breathing zone was served with clean air by means of a free convection flow around the body. No differences were found between the distribution of bioeffluents and the distribution of exhaled air (exhaled air is heated and discharged with an initial momentum while bioeffluents are carried by the convection flow around the body). The distribution of the floor contaminant was generally uniform, except near the floor. The entrainment of air in the human boundary layer caused the inhaled air quality, in regard to the floor contaminant, to be comparable to the air quality in the ambient air at the height of the breathing zone. The vertical throw of supply airflows determines the distribution of active contaminants in rooms with underfloor ventilation. The present results showed that the distribution of contaminants with UFAD providing a short throw was comparable to the distribution of contaminants with displacement ventilation. This is in agreement with Fisk et al. (1991). An increase in the throw provided a more intensive mixing, which increased the concentration of active contaminants in the occupied zone. Analyses showed that a room air distribution model proposed recently by Yamanaka et al. (2002) agreed rather well with the measurements obtained in the present study (Appendix F). The use of PV provided a substantial improvement in the quality of inhaled air. With the most efficient air terminal device tested, the inhaled air concentration of contaminants decreased as much as 50 times compared to the concentration of the contaminants in the exhaust air. However, in a room with displacement or underfloor ventilation, the use of PV was shown to promote mixing of contaminants located in its vicinity. This is the case of human bioeffluents, exhaled air (both studied) and possibly also contaminants located on occupants’ desks. The results indicate that the mixing due to PV may increase the transport of contaminants between workplaces and decrease the air quality of occupants unprotected with PV, as compared to the case where PV was not used. This may be of concern in cases with tobacco smoking, or when occupants are sources of contagious diseases and the control of their transmission is desirable. However, the air quality of occupants unprotected with PV was still higher than in a room with mixing ventilation. As discussed in Chapter 4, the mixing caused by PV could be comparable to mixing caused by an activity of occupants, and therefore it might not be considered as a drawback of PV systems in real life. Such comparison, however, remains to be made. It was identified that the inhaled air quality of unprotected occupants depends on the direction and strength of the personalized airflow used by other occupants. Personalized air directed upward was shown to ensure a better air quality than personalized air directed downward or horizontally. The phenomenon was observed with both displacement and underfloor ventilation (regardless of its throw height). The differences between the systems, in particular the impact of the throw height of UFAD, were discussed in detail in Chapter 5. The use of PV in a room with displacement ventilation or underfloor ventilation may or may not affect the distribution of active contaminants generated further from the personalized airflow. Such contaminants can be human bioeffluents and exhaled air generated elsewhere in a room, contaminants from office equipment or even passive contaminants carried by means of thermal plumes above various heated objects. The ability of PV not to affect the distribution of human-produced contaminants may be of interest in e.g. admission areas in hospitals, where a possible infector (unprotected with PV) frequently comes into contact with hospital personnel (possibly protected with PV). Analyses discussed in detail in Chapter 5 suggest that PV may not affect the mixing of contaminants generated at another workplace at velocities below 1-1.5 m/s. However, because of a limited number of experiments, the threshold values could not be determined with certainty. If available, such

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information would allow designers to restrict the supply airflow rate or optimize the dimensions of an air terminal device so that the impact of PV on the room air distribution is negligible. The discussion presented so far concerned only the distribution of active (heated) contaminants generated from localized sources. However, many more contaminant sources are present in indoor environments. In the present study, the distribution of passive contaminants emitted from a plane source located on the floor was examined as well. This represents pollution (VOCs) from carpet, PVC or linoleum, which has been associated with a prevalence of SBS symptoms (Section 1.4). The results showed that the distribution of the floor contaminant was generally uniform with all the total-volume ventilation systems. With displacement ventilation and underfloor ventilation, non-uniformities were observed in a region close to the floor where the supply air current diluted the contaminants to a lower concentration (discussed in Chapter 4). However, the lower concentrations near the floor did not have an impact on the inhaled air quality of unprotected occupants. The use of PV improved the inhaled air quality of occupants substantially, while the room distribution of the floor contaminants was not affected. This is important, because the use PV will thus always protect occupants from the contaminants emitted from floors. Risk of indoor airborne transmission of infectious diseases The Wells-Riley equation is commonly used to model the risk of indoor airborne transmission of infectious diseases. Rudnick and Milton (2003) derived an alternative equation that determines the risk of transmission of infectious diseases using CO2 concentration as a marker for exhaled-breath exposure. This is possible because air exhaled by people is the vehicle for release of respiratory infectious agents (Section 1.4). Analogous analyses were performed in the present study (air exhaled from the manikins was marked with tracer-gases). The concept of the normalized concentration was introduced in the model in order to quantify the impact of various ventilation systems on the risk of infections. Instead of the probability of infections, as used in the original Wells-Riley equations, the reproductive number for an infectious disease in a building environment (RA0) was calculated. The reproductive number is the number of secondary infections that arise when a single infectious case is introduced into a population where everyone is susceptible. An infectious agent can spread in a given population, if RA0 > 1. The greater the value of RA0 the more likely is the infection to reproduce rapidly. The equations used as well as examples of application are presented in Appendix G. The typical values of a normalized concentration of exhaled air contaminants in the air inhaled by the thermal manikins were used to calculate the basic reproductive number for a typical infectious disease such as influenza. The normalized concentration of 1, 0.2, 0.05 and 0.7 was taken for respectively mixing ventilation alone, UFAD alone, UFAD plus RMP protecting the occupant, and UFAD plus RMP not protecting the occupant. A quantum generation rate of 100 quanta/hour estimated by Rudnick and Milton (2003) was used. Figure 6.1 presents the basic reproductive number at two ventilation rates of outdoor air, of which one corresponds to the ventilation rate of outdoor air required by present standards (CEN, 1998; ASHRAE, 1992). It may be assumed that the recirculation of exhaust air to supply air is utilized in cases with PV and UFAD, where it would be unrealistic to supply an airflow rate of as low as 10 L/s per person simultaneously with both systems. The chart is constructed assuming a presence of 30 persons in the room (chosen arbitrarily) and a time of exposure of 8 hours.

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0

1

2

3

4

5

6

7

8

Mixing UFAD RMP+UFAD(protected)

RMP+UFAD(unprotected)

Rep

rodu

ctiv

e nu

mbe

r, R

A0 10 L/s per person

40 L/s per person

Figure 6.1. Reproductive number for selected ventilation systems (typical values) at different outdoor air ventilation rates for influenza (generation rate = 100 quanta/hour). In the case of mixing ventilation and a supply rate of 10 L/s per person, there is a likelihood that 7 out of 30 occupants contract influenza after an 8-hour exposure. The number of possibly infected person decreases to just 2 (1 already and 1 secondary infected) if either the ventilation rate is increased to 40 L/s per person or an underfloor ventilation system is employed. It is shown that the use of PV enables the occupants to protect themselves efficiently from infections. However, the use of PV by other occupants increases the risk of infections for an occupant unprotected with PV. As shown in Figure 6.1, there is a probability of as many as 3 new cases of influenza if the infected occupant uses PV while the other occupants do not use PV for protection, as compared to a still environment with underfloor ventilation alone. Nevertheless, the risk is always lower than in a mixing ventilated room, and perhaps comparable to the case when an activity of occupants causes mixing of indoor air. In the model presented it has been assumed that the loss of viability, filtration, settling and other mechanisms are small compared with removal by ventilation (discussed by Rudnick and Milton, 2003). An additional assumption is that the transmission of infectious agents due to the use of PV is independent of the room size and the space distribution of occupants. The CFD simulation by Murakami et al. (1992) indicated that in large open-plan offices with underfloor ventilation, a horizontal spread of contaminants could be reduced when the supply and exhaust airflow rates of underfloor ventilation are balanced locally in the small place allocated to each supply opening. The resulting floor-to-ceiling pattern could remove heat (studied by Murakami et al., 1992) and possibly contaminants near the workstation where they are generated. This would reduce the horizontal transport of contaminants in rooms. The infectiousness of a disease (i.e. estimation of the generation rate of infectious doses) is crucial for the risk of transmission analyses. With a less infectious agent such as rhinovirus, the infection would not spread in any of the cases presented in Figure 6.1. This implies that the ability of PV to increase the transmission of contaminants between occupants does not pose a problem. On the other hand, it is very difficult to prevent the spread of a highly infectious disease such as measles. It was calculated for the given conditions (30 occupants, 10 L/s per person) that the spread of measles would cease at a normalized concentration of 0.02 (ventilation effectiveness of 50). This is comparable to the top performance of the RMP terminals tested. This suggests that PV could be effective in protecting occupants even in environments with a high risk of infections, and it could become an alternative or supplement to traditional methods of occupant protection such as high-efficiency filtration

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or ultraviolet disinfection of air. In the present study, the highest performance of RMP was measured in the rooms with displacement and underfloor ventilation. The performance of RMP in combination with mixing ventilation was somewhat lower. However, as documented by Bolashikov et al. (2002), the performance of RMP in combination with mixing ventilation can be extremely high as well (normalized concentration in inhaled air of 0.1, i.e. almost 100% clean air). Therefore, the ability of PV to protect occupants from infectious diseases can be considered independent of a total-volume ventilation principle. In the present study, the airborne transmission of respiratory infections associated with exhaled breath was simulated by means of tracer-gases. In real life, not all droplets generated in the respiratory tract by talking, sneezing or coughing are airborne immediately after expulsion. As reviewed in Section 1.4, the size distribution of exhaled droplets may vary between 0.01 µm to 100 µm or more. After expulsion, the larger droplets either settle out or evaporate to droplet nuclei (droplets contain impurities) that approach the size of the individual agent (viruses range between 0.003 and 0.06 µm). The distribution of particle size is difficult to measure because the droplet size changes in space and time due to evaporation and coagulation. It is reasonable to assume that most exhaled air droplets smaller than ca. 10 µm (larger droplets are likely to settle out after expulsion) will become airborne and can be transported by air routes over long distances (see Section 1.4). Therefore, the use of tracer-gases for the simulation of airborne infection transmission is justified. However, tracer-gases may not simulate properly the transport of larger droplets, which do not follow air currents due to momentum (after expulsion) and/or forces of gravity. In real life, both large droplets and smaller droplet nuclei contribute to the exposure of occupants to infectious agents. Thermal comfort The thermal environments evaluated in the present study were not under thermostatic control. The supply air was conditioned in order to provide a constant cooling capacity sufficient for the removal of internal heat gains of 580 W (22.5 W/m2). The room air temperature was 26°C and uniform with the mixing ventilation. With the displacement ventilation and the underfloor ventilation the temperature distributions were stratified. Although the inhaled air quality was similar with the two principles (UFAD providing a short throw), the normalized (dimensionless) temperatures near the floor increased from about 0.4 with displacement ventilation to 0.6-0.7 with underfloor ventilation. The normalized temperatures with underfloor ventilation agree well with the previous studies (Bauman and Daly, 2003; Webster et al., 2002a, b). As discussed in Chapter 5, the increase in the temperature decreased the risk of draught and a high vertical air temperature difference. A recent study dealing with a human response to PV systems (Kaczmarczyk, 2003; Kaczmarczyk et al., accepted) suggested that thermal comfort is an important parameter for people’s preferences. They showed that occupants take into account both air quality and thermal comfort when adjusting PV upon arrival at a workplace. With the time elapse, as occupants became adapted to air quality, thermal comfort started to play a more important role in determining the individual adjustments of PV. Two thermal manikins were used in the present study to identify the impact of PV on thermal comfort of seated occupants. Because the performance of PV is influenced to a large extent by the direction and airflow rate of personalized air, which are both under occupants’ control, only a general overview of the topic was given in Chapter 4. The cooling effect of PV was shown to be independent of the room air distribution principle, i.e. PV affected the thermal comfort the same way when combined with e.g. mixing ventilation or displacement ventilation. The equivalent temperature was lower with PV and displacement ventilation than with PV and mixing

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ventilation due to the thermal stratification (and identical conditions of supply air). In rooms with a thermostatic control of the ambient environment the differences would, however, vanish. PV did not have an impact on the air temperature field in the room with mixing ventilation. Although the manikin-based equivalent temperature decreased when PV was used, the distribution of air temperature measured near the workplaces did not change. The mixing ensured that the heat removal capacity of both personalized and total-volume ventilation air spread uniformly. The situation was different in a room with displacement and underfloor ventilation, where the heat is removed by means of thermal plumes. As documented by the measurement of velocity, personalized airflow did not affect the air pattern in the lower occupied zone, and hence it did not contribute to the removal of heat from the sources located near the floor. This led to an increase in the temperature in the present study, because either the airflow rate of total-volume ventilation decreased (VAV control) or the supply air temperature of total-volume ventilation increased (CAV control) when PV was used. The ability of PV to promote mixing also contributed to the increase in temperature in the occupied zone. In practice, a constant air temperature is usually maintained in the occupied zone. Because the temperature is likely to increase in rooms with thermal stratification when PV is used, more energy will be needed if a constant room air temperature should be ensured. A higher airflow rate or a lower supply air temperature will be required if a total-volume ventilation system is controlled according to a VAV strategy or a CAV strategy, respectively. The room air temperature and thus the energy consumption may not, however, increase substantially. The measurements showed that the largest increase in the air temperature was about 1°C at a height of 0.6 m, and around 0.5°C at another heights, when all PV units were used at a high airflow rate. When the personalized airflow rate decreased or only one unit was used, the increase in the temperature was small, comparable to the uncertainty of measurement. The increase in the temperature does not pose a problem for the thermal comfort of occupants either, because the cooling effect of PV is large compared to the change of the ambient environment. Because the increase in the temperature was small, a chain adjustment of PV by individuals (in order to compensate for continuous environmental changes) is not likely to occur. To the contrary, an increase in the temperature near the floor is advantageous in decreasing the risk of draught and vertical temperature difference. Office arrangement The layout and furnishing of an office may have a great influence on the airflow pattern and thus the distribution of contaminants. Nonetheless, considering the large number of possible arrangements, evaluation of the impact of office arrangement is problematic and difficult to generalize. In the present study, the workplaces were arranged behind each other with the occupants facing in the same direction. An active contaminant was generated in the front workplace in most experiments, while the exposure of an occupant seated at the back workplace was evaluated. It was assumed that the use of PV would, due to its airflow direction, carry contaminants from the front workplace to the back workplace, and thus provide unfavourable conditions (high ambient concentration) for the PV. Several experiments with underfloor ventilation (stage 2-2) showed that the transmission of active contaminants between the two workplaces was independent of the location of the workplace where the contaminants were generated. This suggested that the layout and arrangement of an office might not have a large impact on the transmission in rooms with UFAD. In rooms with displacement ventilation, contaminants may spread horizontally over relatively long distances, and the impact of the office arrangement should therefore be considered. The

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workplaces were not partitioned in the present study. The use of partitions is expected to be beneficial, because they may restrict the horizontal movement of air and thus decrease the transport of contaminants between workplaces. It is also possible that partitions will restrict the movement of clean personalized air from workplaces. This may improve the exposures of occupants when they do not inhale clean air direct from PV airflow. Air quality in terms of different quantities Different quantities have been used and reported in the literature to evaluate the exposure of occupants to contaminants. In the present study the normalized concentration of the contaminant, defined as the concentration of a contaminant at a point divided by the concentration of a contaminant in the exhaust (Section 3.7.1), was used for its simplicity. The calculation of two other indices used frequently – ventilation effectiveness and personal exposure effectiveness – is straightforward using the normalized concentration. The reciprocal value of the normalized concentration has been referred to as the ventilation effectiveness, εV, (CEN, 1998) or the pollutant removal efficiency, PRE (e.g. Faulkner et al., 1999). With the aim of differentiating between the mean ventilation effectiveness in the occupied zone and the ventilation effectiveness at different locations, Brohus and Nielsen (1996) introduced indexes named the ventilation effectiveness in the occupied zone, the local ventilation effectiveness (for a point in the room) and the personal exposure index (for inhaled air). Despite the different definitions, the value of a ventilation effectiveness indicates how many times the concentration at a point or an area of interest is lower that the concentration in the exhaust. Moreover, the value of ventilation effectiveness shows how many times more clean air would be needed for a mixing ventilation system alone to achieve the same concentration of contaminants as the ventilation system in question. For example, in order to achieve the same level of air quality as RMP (ventilation effectiveness of 50), a mixing ventilation system alone would have to supply a 50 times higher airflow rate than RMP in combination with mixing ventilation. However, such airflow rates (provided with mixing ventilation) would obviously cause draught and increase the consumption of energy. The problem of ventilation effectiveness is the fact that it converges towards infinity when the concentration at the point approaches the supply air concentration. The index is thus not suitable for PV applications, where high amounts of clean air (i.e. very low concentrations) are expected in occupant’s inhalation, as demonstrated by Melikov et al. (2002). On the other hand, the ventilation effectiveness is equivalent to the dilution factor as used by Haghighat et al. (2001). They showed that the acceptability of air is proportional to the logarithm of the dilution factor (ventilation effectiveness). If extended with the impact of enthalpy on the acceptability of air (Fang et al., 1998a, b), as suggested by Melikov et al. (submitted), the transformation could be used for the assessment of perceived air quality with PV. The logarithm relation between the acceptability and the ventilation effectiveness suggests that an order of magnitude increase of the ventilation effectiveness is needed in order to yield an improvement of the perceived air quality. The largest values of ventilation effectiveness identified in the present study were 50 (normalized concentration of 0.02). This indicates that a substantial improvement of the perceived air quality, and hence a decrease in the prevalence of SBS symptoms, may be possible with PV. This was already indicated in the example of selected SBS symptoms in the experiments with human subject (Kaczmarczyk et al., 2002a, accepted; Kaczmarczyk, 2003). The concept of the personal exposure effectiveness index, proposed by Melikov et al. (2002), was described in detail in Section 3.7.1. The index expresses the portion of clean air from a ventilation system in the inhaled air, as compared to a reference case. The index makes it

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possible to evaluate the contribution of different combined systems to the inhaled air quality. This is demonstrated in Table 6.1. The normalized concentrations, which were used for the calculation of the personal exposure effectiveness by means of Equation 3.5, are presented in the table as well (taken from Figure 5.4). With mixing ventilation alone the inhaled air consisted entirely of room air (i.e. personal exposure effectiveness of 0). The inhaled air consisted of 85% clean personalized air when PV was used in combination with mixing ventilation. The use of PV in combination with UFAD increases the portion of clean air inhaled from both PV and UFAD to 98%, which is close to the aim of 100% clean air in inhaled air. Table 6.1. Personal exposure effectiveness with different ventilation systems. Ventilation principle Normalized conc. (-) Personal Exp. Effect. (%) Mixing 0.94 0 PV + mixing 0.14 86 PV + UFAD 0.02 98 In outdoor environmental health literature, the concept of intake fraction (iF) has been used for comparative risk assessment. The index expresses the fraction of a pollutant release that is inhaled by a receptor (Bennett et al., 2002; Marshall et al., 2002). In indoor environments, iF depends on the ventilation rate, the effectiveness of ventilation (normalized concentration), the breathing rate of occupants, the number of occupants and the duration of exposure (Appendix H). Figure 6.2 presents the individual intake fraction (single occupant) with different ventilation systems. The data are based on the results obtained in the present study for a human-produced contaminant (bioeffluents). The normalized concentrations of 1, 0.2, 0.05 and 0.7 were used respectively for the four cases presented. In the first approach (relative comparison of systems) it was assumed that an occupant spends 100% of time indoors. The breathing rate of an occupant was assumed to be 6 L/min.

0

2000

4000

6000

8000

10000

12000

Mixing UFAD RMP+UFAD(protected)

RMP+UFAD(unprotected)

iF (p

er m

illion

)

10 L/s per person40 L/s per person

Figure 6.2. Intake fraction for indoor environments with different ventilation systems. Figure 6.2 shows that the intake fraction may range between 125 and 10000 per million depending on the ventilation system and the ventilation rate of outdoor air. The largest value corresponds to a room with mixing ventilation providing a ventilation rate of 10 L/s per person, which is required by standards nowadays (CEN, 1998; ASHRAE, 1989). Providing that occupants are exposed to an office environment 23% of the time annually (8 hours x 5 days x 50 weeks), the annual average intake fraction with mixing ventilation decreases to 2300 per million. This is, however, about one order of magnitude the exposure to outdoor sources in urban areas, which ranges between 1-100 per million (for summary of different studies see Marshall et al., 2002). This underlines the importance of occupants’

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exposures to indoor sources, which may be much larger than the exposures to outdoor source (e.g. tobacco smoking vs. emission of motor vehicles). Furthermore, the wide spread of the values of the intake fraction for indoor environments documents the importance of outdoor ventilation rates as well as the efficiency of ventilation systems. The impact of various contaminants is included in the normalized concentration, which evaluates the non-uniformity of their distribution. The analyses indicate that the exposure levels provided with PV can be comparable to the exposure levels outdoors. The potential adverse effect from a pollutant release depends not only on the intake of individuals, as expressed by the intake fraction, but also on the likelihood of adverse effects with increasing intake. The likelihood of adverse effects, such as a spread of contagious diseases, was demonstrated and discussed previously. As described in Appendix G, the concept of intake fraction was actually used in the model by Rudnick and Milton (2003), referred to as the “volume fraction of inhaled air that is exhaled breath”. Murakami et al. (2000) proposed two indices that express the Contribution Ratio of a Pollution (CRP) source. The CRP 1 indicates the percentage of a pollutant (e.g. VOC) inhaled after being released from the source. The concepts of the CRP 1 and the intake fraction are thus identical. Murakami et al. (2000) documented the concept of the CRP in a case study. Computer simulation was performed in a room in order to determine the distribution of contaminants emitted from the walls, floor and ceiling. Exposure of an occupant standing in the centre of the room was determined. The room was ventilated by a displacement principle. The CRP 1 was about 2.6-2.8% (or 26000-28000 per million) for the floor area, while for the ceiling it was 0-0.09% (0-900 per million). Because the CRP 1 depends on the ventilation rate, the breathing rate and the efficiency of air distribution, it is difficult to make a comparison with the present results without analyzing the airflow patterns in detail. The CRP 2 indicates the portion of pollution from a source with the total amount of pollution inhaled taken as 100%. In the case study by Murakami et al. (2000), 65% of all contaminants inhaled were the contaminants emitted from the floor, and 10% were the contaminants emitted from the ceiling. This implies that the pollution emitted from the floor is more important than the pollution emitted from the ceiling. Such analyses may be an effective tool for the evaluation of personal exposures; however, measurements with numerous sources or complex CFD analyses are required. Applicability The ratio of personalized airflow rate to total-volume ventilation airflow rate may be important for the ability of PV to affect the distribution of contaminants and the thermal stratification. It might be expected that the impact of PV on the room air distribution will increase when the ratio of the airflow rates increases, i.e. the personalized airflow rate is relatively large as compared to the total-volume ventilation airflow rate. However, no correlation between the ratio of the airflow rates and e.g. the transport of contaminants between occupants was found. The direction and strength of personalized airflow was found to be more important. For example, a personalized airflow from VDG terminals was able to affect the distribution of contaminants generated at another workplace when the ratio was small (e.g. 15/80 = 0.19), while airflows from RMP terminals did not affect the distribution when the ratio was high (e.g. 30/50 = 0.6). The limit case is a room with PV alone (total-volume ventilation may be natural). The impact of one type of PV (PEM, see Section 1.3) on the distribution of temperature and velocity, operated in a room without any other ventilation system except PV, was reported in Bauman et al. (1993); however, no generalization was attempted.

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Studies by Kaczmarczyk et al. (2002b, accepted) showed that occupants used efficiently the delegated control of the airflow rate and the positioning of the air terminal devices. Some occupants may choose not to use the PV system, while others would exploit the system to its maximum capacity. Such extreme conditions in terms of a PV supply rate have been considered in this study. The impact of factors such as the distribution of heat sources, total heat gain, air change rate, etc. has not been studied. It is assumed that the present findings will apply for various situations in typical offices, where total-volume ventilation provides a recognizable and well-defined airflow pattern in the room.

103

7. Recommendations

The ability of occupants to generate and control their preferred environment is an important feature of PV systems. Because occupants may choose not to use PV, or they may use PV in a way that does not provide a substantially better air quality but preferred thermal comfort, the quality of the background environment must be considered. The present results identified that each combination of PV and total-volume ventilation tested can be applied in practice. This is an important result, because many other factors, such as an architectural concept, energy saving requirements or preferences of the building owner, may affect the selection of a total-volume ventilation system in real life. The use of PV in rooms with mixing ventilation may only be beneficial for both air quality and thermal comfort of occupants. The inhaled air quality improves in rooms with displacement ventilation or underfloor ventilation. Although the use of PV promotes mixing of contaminants generated in its vicinity, the inhaled air quality in rooms with displacement ventilation and underfloor ventilation can be better (depending on the extent of mixing) than in a room with mixing ventilation. The inhaled air quality in regard to a plane contaminant located on the floor does not differ with the different ventilation systems. The inhaled air quality in regard to active contaminants is higher with displacement ventilation and UFAD providing a horizontal discharge pattern than with UFAD providing a long throw. The ranking of the systems in terms of the risk of local thermal comfort is, however, opposite. Both displacement ventilation and UFAD with a horizontal discharge provide low temperatures and high velocities near the floor. An increase in the throw height of UFAD increases temperatures and decreases the velocities, which decreases the risk of draught. The present study identified that UFAD with a vertical throw of about 0.3 m provides as high air quality as displacement ventilation, but provides almost as a low risk of draught as UFAD with a long throw (Figures 5.34). The use of UFAD providing a short throw is thus recommended. The control of supply air conditions is less important as long as the throw is short. A constant air volume (CAV) strategy may be preferable in combination with passive floor diffusers, because variations in airflow rate (VAV strategy) may increase the throw height and thus decrease the air quality. Moreover, the use of PV will increase the total amount of ventilation air provided when a CAV strategy is utilized. The ventilation systems tested in the present study provided 100% outdoor air. The primary reason was to increase the sensitivity of tracer-gas measurements. In practice, recirculation of exhaust air to supply air is often used, because it is desirable to keep the quantity of outdoor air to a minimum for economic reasons and to conserve energy. A certain economic benefit could be achieved if only a PV system provided outdoor air (in accordance with the present standards), while another (total-volume air distribution) system would provide conditioning of room air. If the recirculation were utilized, the shape of normalized concentration profiles would not change from the situation when 100% outdoor air is supplied; however, the absolute concentration of contaminants in a room would increase proportionally to the dilution of contaminants. A cross-sectional questionnaire and field study (Sundell et al., 1994) showed no increased risk of SBS associated with recirculation of

7

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air; however, they found an elevated prevalence of general SBS symptoms with outdoor air supply rates lower than 13.6 L/s per person. Another study (Milton et al., 2000) found a consistent association of increased sick leave with lower levels of outdoor air supply and indoor air quality complaints. Therefore, the use of recirculation may be acceptable (ambient air quality), so long as the outdoor air ventilation rate is high. The use of PV will provide benefits in terms of the improvement of air quality and thermal comfort of seated occupants. Air terminal devices representing the most promising solutions for providing excellent air quality and preferred thermal comfort for occupants were examined in the present study. However, new air terminal devices are being constantly developed, tested and optimized. It was shown that the impact of PV on the air quality and thermal comfort of occupants is in general very localized. As indicated by this and other studies (e.g. Faulkner et al., 1993), PV discharging air at high velocities causes mixing. This affects the upward air movement in rooms with displacement ventilation and underfloor ventilation and increases temperature in the lower occupied zone. Providing personalized air at lower velocities, e.g. less than 1-1.5 m/s, is thus desirable and recommended. Such velocities still provide occupants with the ability to adjust their thermal comfort according to their preferences. The airflow direction is important when personalized air is directed towards a contaminant source. If so, the upward direction is preferable to the horizontal/downward direction, regardless of the personalized airflow rate. The preferable air terminal device should be highly efficient while not increasing the transmission of contaminants between workplaces. However, none of the air terminal devices tested in the present study had such qualities. The RMP terminal was extremely efficient (providing almost 100% clean air in inhalation), but it caused an increase in the transmission of human-produced contaminants between workplaces. The VDG terminal, on the other hand, did not increase the transmission, but its efficiency was lower. Therefore, the development of a new air terminal device is desirable. Because indoor air is polluted from a large number of sources, and not only by human bioeffluents and exhaled air, the efficiency of air terminal devices should be preferred to the their ability to cause mixing. At present, the use of the RMP terminal devices can be recommended. Table 7.1. Comparison of air quality and thermal comfort performance of the ventilation systems tested. Scale: 1 to 5 (1-worst, 5-best).

No PV VDG / RMP Air quality

Total-volume ventilation Air quality Thermal

comfort Protected occupant

Unprotected occupant

Thermal comfort

Mixing 1 3 3 / 4 1 / 1 4 / 5 Displacement 3 1 4 / 5 3 / 2 2 / 3 Underfloor horizontal 3 1-2 4 / 5 4 / 3 3 / 4 Underfloor vertical short 3 2-3 4 / 5 3 / 2 4 / 5 Underfloor vertical long 2 3 4 / 5 2 / 1 4 / 5 Table 7.1 provides a comparison of total-volume ventilation systems alone and in combination with PV tested in the present study. Air quality and thermal comfort of occupants were the criteria. With PV, air quality of occupants protected and unprotected with PV is considered. Air quality of occupants unprotected with PV is associated with the ability of PV used by other occupants in the room to cause transmission of contaminants between workplaces.

105

8. Conclusions

The performance of personalized ventilation in combination with total-volume ventilation comprising mixing, displacement and underfloor air distribution was studied in regard to the air quality and thermal comfort of occupants. The main findings are as follows: • Personalized ventilation is able to protect occupants from pollution and thus increase the

quality of inhaled air in comparison with total-volume ventilation principles. The positioning of an air terminal device in respect to the occupant and its design influences the quality of inhaled air to a large extent.

• The use of PV promotes mixing of contaminants located in its vicinity. In rooms with

displacement or underfloor air distribution, this may cause an increase in the transmission of contaminants between workplaces and thus decrease the air quality of occupants as compared to the case without PV. Personalized air directed upward ensures a better air quality than personalized air directed horizontally/downward.

• In rooms with displacement or underfloor air distribution, the use of PV does not affect

the distribution of active contaminants generated in another workplace when the supply airflow rate is low. At a high rate the type of air terminal device and its airflow direction may be important.

• The cooling of occupants provided with PV is rather independent of the room air

distribution generated by a total-volume ventilation system. The impact of PV on the distribution of temperature and velocity in the room is very localized.

• PV does not contribute to the removal of heat from the lower occupied zone in rooms

with displacement or underfloor air distribution. This may increase the temperature in the occupied zone and consequently the consumption of energy, if the temperature should be maintained constant.

• The analyses indicate that PV in combination with any total-volume ventilation principle

could be efficient in protecting occupants even from highly infectious diseases, and therefore become an alternative or supplement to traditional methods of occupant protection.

The following recommendations can be outlined: • A combination of PV and underfloor air distribution with a vertical discharge direction

providing a short throw, controlled according to a CAV strategy, is recommended. If the control of an airborne transmission of contaminants between occupants is desirable, air terminal devices supplying air upward are preferable.

• Development of air terminal devices with a high efficiency and a low ability to promote

mixing of contaminants located in its vicinity is recommended.

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113

115

Appendix A Expression of uncertainty Well-established basic statistical techniques were used for the treatment and analyses of data. The methods applied have been described elsewhere. In the present study, the underlying references were Montgomery (2001) and ISO (1993). Generally, the result of each measurement was characterized by the arithmetic mean of the observations y accompanied by a statement of the uncertainty of the mean U. The mean y was the best available estimate of the measured quantity, assuming that the samples were drawn from an independent population. Violations of the independence (correlation, trends, etc.) were identified visually using the plot of residuals in time order. At first, a sample standard uncertainty (level of confidence of 68%) has been calculated for each quantity. In cases of derived quantities (indexes), the uncertainty was further propagated. Finally, the uncertainty was expanded in order to increase the level of confidence to estimated 95%. Section 3.8 summarizes the typical values of uncertainty and discusses most important sources of uncertainty for each quantity.

Sample standard uncertainty Each quantity, except for the tracer-gas concentration (see Section 3.6.1), was recorded in periods several times during each experiment. The periods were identical and adequate in terms of duration and sampling frequency to estimate the quantity with high accuracy. The tracer-gas measurement determined the length of an experiment and hence the need for several measurement periods. The tracer-gas concentrations were recorded continuously in sequences. The sample standard uncertainty of the mean Ust typically consisted of 3 components:

222max, instrstabmeasst UUUU ++= (A.1)

where Umeas,max is the maximum uncertainty of measurement (random error);

Ustab is the uncertainty of process stability; Uinstr is the uncertainty of instrument (calibration).

Table A-1. Standard uncertainty components of measured quantities.

Quantity Umeas Ustab Uinstr

Concentration (inhaled and room) � −−−−

�

Inhaled air temperature � � �

Manikin-based equivalent temp. � � �

Surface temperature � � �

Room air temperature − � �

Room air velocity − � �

Appendix A

116

Table A-1 summarizes the measured quantities and the components of uncertainty used. In the case of the concentration measurements, the stability of the process was not evaluated because each measurement was performed in a single sequence (except for the supply and exhaust air concentration in stages 1 and 2-1, when the whole day measurement was used). The uncertainty of room air temperature did not include the uncertainty of measurement in each period, because the information was not available from the instrument. The uncertainty of velocity measurement was covered by the uncertainty of instrument, provided by the manufacturer. Uncertainty of measurement (during each period or sequence) On the assumption of normality, uncertainty of the mean Umeas,i was expressed using the standard deviation of the mean. The sample standard deviation is was computed as a measure of dispersion of the observed values around their mean jy .

ms

mm

yyU i

m

jiji

imeas =−

−=

∑=

)1(

)(1

,

, (A.2)

where jiy , is the j-th observed value in the i-th period or sequence;

iy is the mean of the observed values in the i-th period or sequence;

is is the sample standard deviation; m is the number of samples taken during each period or sequence.

The uncertainty of the mean Umeas,i defines an interval having a 68% level of confidence. The maximum value of uncertainty from the periods (4 or 9 in the case of respectively stages 1 and 2-1 and stage 2-2) was used to calculate the sample standard uncertainty. Uncertainly of process stability Each quantity might have changed a little during the whole experiment lasting for 1 day. The evaluation of process instability was based on the repeated periods of measurements. The standard deviation of the mean was used:

ns

nn

yyU

n

ii

stab =−

−=

∑=

)1(

)(1 (A.3)

where y is the grand mean of the observed values;

s is the period standard deviation; n is the number of measurement periods.

Uncertainty of instrument Table A-2 presents the uncertainty associated with the instruments used. Three different approaches were applied: 1. Repeatability of concentration measurement was available from the manufacturer of a

gas analyzer (Section 3.5.3). The repeatability was assumed to have a rectangular probability distribution, i.e. the measured value lay with equal probability in the interval

Appendix A

117

of ±a. If the differential between the bounds is denoted by 2a, the uncertainty is calculated as:

3

2aUinstr = (A.4)

2. The uncertainty of the instrument was estimated based on experience in the case of the

inhaled air temperature, manikin-based equivalent temperature and wall surface temperature. It was assumed that the uncertainty defines an interval having a 95% level of confidence. Assuming a normal distribution was used, the standard uncertainty (level of confidence of 68%) was taken as:

295,instr

instr

UU = (A.5)

where 2 is the factor corresponding to the 95% level of confidence.

3. Equation provided by the manufacturer was applied for each measurement period in the

case of velocity. The maximum value of uncertainty was taken. Table A-2. Uncertainty of instrument.

Quantity Uncertainty Comment Concentration (inhaled and room) 1% of reading* repeatability Inhaled air temperature 0.2°C** 95% confidence Manikin-based equivalent temp. 0.2°C** 95% confidence Wall surface temperature 0.3°C** 95% confidence Room air temperature 0.3°C* 95% confidence Room air velocity (0.02· v )+0.022* 95% confidence * Manufacturer's specification ** Estimate

Uncertainty of derived quantities In cases of indexes, where a quantity Y was not measured, but was determined from other quantities through a functional relationship ),...,,( 21 NXXXfY = , the combined standard uncertainty Uc,st was estimated. It was given by:

)(22

1, ist

N

i icst xU

xfU ∑

=

∂∂= (A.6)

where xi is the i-th measured quantity; Ust(xi) is the standard uncertainty of the quantity.

Appendix A

118

Expanded uncertainty Expanded uncertainty U is obtained by multiplying the standard uncertainty Ust (or combined standard uncertainty Ust,c) by a coverage factor k. The value of the coverage factor k is chosen on the basis of the level of confidence required of the interval covered. If the probability distribution characterized by y and Ust is normal and the effective degree of freedom of Ust is of significant size (say greater than 10), the coverage factor k = 2 will produce an interval stkUy ± corresponding to the level of confidence 95%.

Testing for normal distribution In order to see if a given set of data followed a normal distribution, a visual examination using a residual-quantile plot and the numerical Shapiro-Wilk’s w-test was applied. The residual-quantile plot is a plot of the ordered residuals against the quantiles of a normal distribution function. If the normal distribution adequately describes the data, the plotted points fall approximately along a straight line. The plots were constructed using statistical package S-PLUS 6.

119

Appendix B Inhaled air concentration with PV, mixing and displacement ventilation Figures B-1 and B-2 present the concentration of the floor contaminant, bioeffluents and exhaled air inhaled by the exposed back manikin with respectively mixing ventilation and displacement ventilation. The concentrations are compared for the two types of PV and different scenarios of PV use. It is shown that the use of PV decreased the concentration of contaminants in the inhaled air as compared to the reference case without PV. The improvements were different for the two types of terminal, but only small differences were observed among the three contaminants within the same condition when mixing ventilation was used. Furthermore, the use of PV at the polluting manikin’s workplace did not affect the inhaled air quality of the exposed manikin.

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0-0 0-7 0-15 15-0 15-7 15-15 0-7 0-15 15-0 15-7 15-15

RMP VDG

Con

cent

ratio

n (C

-CS/C

E-C

S)

Floor cont.

Bioeffluents

Exhaled air

Figure B-1. Mixing ventilation. Concentration of contaminants inhaled by the back manikin. Different patterns of use are compared: the X-Y labels on the x-axis indicate the PV airflow rates of the front manikin and the back manikin in L/s per workplace.

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0-0 0-7 0-15 15-0 15-7 15-15 0-7 0-15 15-0 15-7 15-15

RMP VDG

Con

cent

ratio

n (C

-CS/C

E-C

S)

Floor cont.

Bioeffluents

Exhaled air

Figure B-2. Displacement ventilation. Concentration of contaminants inhaled by the back manikin. Different patterns of use are compared: the X-Y labels on the x-axis indicate the PV airflow rates of the front manikin and the back manikin in L/s per workplace.

121

Appendix C Inhaled air temperature with PV, mixing and displacement ventilation Figures C-1 and C-2 present the inhaled air temperature for the front manikin and the back manikin, respectively. The temperatures are compared for the two types of PV coupled with mixing ventilation and displacement ventilation at different combinations of PV supply rates. It is shown that the use of PV at one workplace did not affect the inhaled air temperature of the occupant at another workplace by more than 0.3°C, regardless of the total-volume ventilation system. The impact of the PV airflow rate on the inhaled air temperature is apparent, as is the ability of the displacement ventilation to provide a lower inhaled air temperature than mixing ventilation (both with and without PV).

20

21

22

23

24

25

26

27

28

0-0 0-7 0-15 15-0 15-7 15-15 0-7 0-15 15-0 15-7 15-15

RMP VDG

Tem

pera

ture

(°C

)

Mixing

Displacement

Figure C-1. Inhaled air temperature of the front manikin. Different patterns of use are compared: the X-Y labels on the x-axis indicate the PV airflow rates of the front manikin and the back manikin in L/s per workplace.

20

21

22

23

24

25

26

27

28

0-0 0-7 0-15 15-0 15-7 15-15 0-7 0-15 15-0 15-7 15-15

RMP VDG

Tem

pera

ture

(°C

)

Mixing

Displacement

Figure C-2. Inhaled air temperature of the back manikin. Different patterns of use are compared: the X-Y labels on the x-axis indicate the PV airflow rates of the front manikin and the back manikin in L/s per workplace.

123

Appendix D Whole-body manikin-based equivalent temperature Figures D-1 and D-2 present the whole-body manikin-based equivalent temperatures (ET) for PV combined with respectively mixing and displacement ventilation at different rates of personalized air. Although different in magnitude (due to difference between the workplaces), the temperature characteristics are similar in the two figures. As expected, an increase in the PV airflow rate increased cooling and hence decreased the ET. It is shown that the use of PV by one manikin did not affect the ET of the other manikin.

22

23

24

25

26

27

0-0 0-7 0-15 15-0 15-7 15-15 0-7 0-15 15-0 15-7 15-15

RMP VDG

ET (°

C)

Frontmanikin

Backmanikin

Figure D-1. Mixing ventilation. Whole body manikin-based equivalent temperature. Different patterns of use are compared: the X-Y labels on the x-axis indicate the PV airflow rates of the front manikin and the back manikin in L/s per workplace.

22

23

24

25

26

27

0-0 0-7 0-15 15-0 15-7 15-15 0-7 0-15 15-0 15-7 15-15

RMP VDG

ET (°

C)

Frontmanikin

Backmanikin

Figure D-2. Displacement ventilation. Whole body manikin-based equivalent temperature. Different patterns of use are compared: the X-Y labels on the x-axis indicate the PV airflow rates of the front manikin and the back manikin in L/s per workplace.

125

Appendix E Inhaled air concentration with personalized and underfloor ventilation Figures E-1 to E-4 present the inhaled air concentration of the floor contaminant, human bioeffluents and exhaled air with underfloor air distribution for different discharge patterns and different supply airflow rates. The concentrations are compared for the two types of PV performing under different patterns of use. The X-Y labels on the x-axis indicate the PV airflow rates of the front manikin and the back manikin in L/s per workplace.

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0-0 0-15 15-15 15-0 0-15 15-15 15-0

RMP VDG

Con

cent

ratio

n (C

-CS/

CE-

CS)

Floor cont. inh.to front man.

Floor cont. inh.to back man.

Bioeffluents inh.to back man.

Exhaled air inh.to back man.

Figure E-1. Vertical discharge of UFAD, stage 2-1 (VAV strategy). Concentration of contaminants inhaled by the front manikin and the back manikin.

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0-0 0-15 15-15 15-0 0-15 15-15 15-0

RMP VDG

Con

cent

ratio

n (C

-CS/

CE-

CS)

Floor cont. inh.to front man.

Floor cont. inh.to back man.

Bioeffluents inh.to back man.

Exhaled air inh.to back man.

Figure E-2. Horizontal discharge of UFAD, stage 2-1 (VAV strategy). Concentration of contaminants inhaled by the front manikin and the back manikin.

Appendix E

126

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0-0 0-15 15-15 15-0 0-15 15-15 15-0

RMP VDG

Con

cent

ratio

n (C

-CS/

CE-

CS)

NA

Floor cont. inh.to front man.

Floor cont. inh.to back man.

Exhaled air inh.to front man.

Exhaled air inh.to back man.

Figure E-3. Vertical discharge of UFAD, long throw (80 L/s), stage 2-2 (CAV strategy). Concentration of contaminants inhaled by the front manikin and the back manikin.

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0-0 0-15 15-15 15-0 0-15 15-15 15-0

RMP VDG

Con

cent

ratio

n (C

-CS/

CE-

CS)

Floor cont. inh.to front man.

Floor cont. inh.to back man.

Exhaled air inh.to front man.

Exhaled air inh.to back man.

Figure E-4. Vertical discharge of UFAD, short throw (50 L/s), stage 2-2 (CAV strategy). Concentration of contaminants inhaled by the front manikin and the back manikin.

127

Appendix F Vertical distribution of active contaminants with underfloor ventilation Yamanaka et al. (2002) proposed a model that aims at predicting the vertical distribution of active contaminants in rooms with underfloor ventilation. The distribution is three-zonal (Figure F-1). The model makes it possible to predict the concentration of contaminants in the lower zone as well as the concentration of contaminants in the interface layer.

Figure F-1. Air distribution model for underfloor ventilation. Although not explained in detail in their article, the model is obviously based on a mass balance for the interface layer. If the vertical flow from underfloor ventilation penetrates the height of stratification (see Figure 1.3), air and contaminants from the upper zone are forced to flow downward. Part of the down flow is entrained by the plumes above occupants and heated objects. The rest of the down flow brings contaminants to the lower zone. The mass balance for the interface layer can be written as:

LLPEPEUU cVcVcV += (F.1) where VU is the down airflow rate from the upper zone, cU is the concentration of contaminants in the upper zone,

VPE is the airflow rate entrained by thermal plumes, cPE is the concentration of contaminants in the interface layer, entrained by

thermal plumes, VL is the down airflow rate to the lower zone,

cL is the concentration of contaminants in the lower zone. According to Yamanaka et al. (2002), the top of the interface layer is located at the same height as maximum throw of vertical flow from underfloor ventilation. They defined the maximum throw height as the height where velocity decreases to zero (instead of the height where velocity decreases to 0.25 m/s, as used in Chapter 5). Moreover, they defined the down flow rate as the surplus flow rate of the plume flow at the top of the interface layer:

VU cU

VPE cPE

VMT

VINT

V

cL

cU

VL cL

Maximum throw

Interface height

Height above floor

Concentration

VUE

Appendix F

128

VVV MTU −= (F.2) where VMT is the airflow rate in the thermal plume at the height of maximum throw, V is the airflow rate of underfloor ventilation, The airflow rate entrained by thermal plumes (VPE) is equal to the airflow rate in the thermal plumes at the height of maximum throw (VMT) minus the airflow rate in the thermal plumes at the height of interface (VINT). The down airflow rate to the lower zone was assumed to be equal to the airflow rate in the thermal plume at the height of the interface, i.e. VL = VINT. Entrainment of air by the vertical flow of underfloor ventilation (VUE) was not considered in the original model. The concentration of contaminants in the upper zone was assumed to be 1 (normalized for the exhaust concentration), i.e. cU = 1. Yamanaka et al. (2002) assumed that the concentration of the airflow from the interface layer to thermal plumes is equal to the average value of the upper zone concentration and the lower zone concentration. Hence, the concentration of contaminants in the lower zone can be expressed from Equation F.1 as:

( )INTMT

INTMTMTL VV

VVVVc

++−−

=2

(F.3)

Yamanaka et al. (2002) validated the model using a scaled experimental room. The ventilation air was supplied from the floor by means of 16 round openings. Two ventilation airflow rates and three throw heights (achieved by changing the diameter of the openings) were studied. Four person simulators were arranged on the floor and a tracer-gas was released at the top of the simulators. The vertical distribution of the contaminants was measured. The widths of the interface layer (W, in metres), which is needed for the definitions of the interface height, were determined experimentally:

UVW 000956.0= (F.4) where VU is the down airflow rate from the upper zone in m3/h. Application The model by Yamanaka et al. (2002) was applied in the present study in order to determine the vertical distribution of human-produced contaminants in the case of underfloor ventilation alone. The comparison was made for two airflow rates of underfloor ventilation (vertical discharge direction), namely 80 and 50 L/s. The maximum throw at the two rates was estimated respectively at 1.5 m and 0.8 m, based on Figure 5.1. Table F-3 presents the volumetric flows in thermal plumes at the height of maximum throw and the height of the interface. The flows were estimated based on charts presented by Nielsen (1993), reprinted also in REHVA (2003) guidebook. Equation F.4 was used to calculate the width of the interface: 0.35 and 0 m for the two cases, respectively. Figure F-2 compares the predicted contaminant concentration with the contaminant concentration of exhaled air (both manikins, averaged) measured near the two workplaces (positions A and B, averaged) in the present study. The two distributions are in good agreement. However, more full-scale measurements are needed in order to validate the model by Yamanaka et al. (2002) in real settings with certainty.

Appendix F

129

Table F-3. Convection volume flow above occupants and heated objects per workplace in L/s. Elevation of the objects above floor is indicated in parenthesis. Heat source Long vertical throw Short vertical throw

Maximum

throw height Interface

height Maximum

throw heightInterface

height (1.5 m) (1.15 m) (0.8 m) (0.8 m) Person 30 20 15 15 PC tower (0.3 m) 30 20 15 15 PC monitor (0.8 m) 25 10 0 0 Desk lamp (1 m) 5 0 0 0 Total 90 50 30 30

0

0.5

1

1.5

2

2.5

0 0.5 1 1.5Concentration (C-CS/CE-CS)

Hei

ght a

bove

floo

r (m

) MeasuredCalculated

Long throw0

0.5

1

1.5

2

2.5

0 0.5 1 1.5Concentration (C-CS/CE-CS)

Hei

ght a

bove

floo

r (m

) MeasuredCalculated

Short throw

Figure F-2. Comparison of concentration profiles measured (see Figure 5.7) and calculated based on Yamanaka et al. (2002). The model can be improved by considering the ability of the vertical flows of underfloor ventilation to transport air from the lower zone to the interface layer. If included, the down airflow rate to the lower zone can be assumed to be equal to the airflow rate in the thermal plume at the height of the interface plus the airflow rate entrained by the vertical flow of underfloor ventilation in the lower zone, i.e. VL = VINT + VUE . However, the predictions using the original model (airflow from underfloor ventilation not considered) agreed well with the results of measurement in the present study. The reason may be the fact that relatively small amounts of air were transported by the vertical flows of underfloor ventilation from the lower zone to the interface layer, as indicated by low air velocity at the interface height (Figure 5.3). In other situations, especially when the vertical throw is long, the impact of the vertical flows of underfloor ventilation on the contaminant distribution may be important.

131

Appendix G Risk of airborne infection transmission The Wells-Riley equation is commonly used to model the risk of airborne transmission of infectious diseases. Because air exhaled by people is associated with a release of infectious agents, Rudnick and Milton (2003) derived an alternative equation that determines the risk of transmission by using CO2 concentration as a marker for exhaled-breath exposure. The normalized concentration of exhaled air contaminants (= 1/ventilation effectiveness) was introduced in the model of Rudnick and Milton (2003) in order to quantify the impact of various ventilation systems on the risk of infections. The volume fraction of inhaled air that is exhaled breath is determined as:

( )a

Se

CCC

CVV

f−

=−= (G.1)

where Ve is the equivalent volume of exhaled breath contained in indoor air, m3; V is the volume of the shared air space, m3; C(-) is the normalized concentration, see Section 3.7.1; C is the volume fraction of the exhaled air tracer in inhaled air; CS is the volume fraction of the tracer in supply air, Ca is the volume fraction of the tracer added to the exhaled breath during

breathing. Rudnick and Milton (2003) used CO2 produced by people as a marker of exhaled breath. In the present study the exhaled air was marked with a constant dose of SF6 for the front manikin and N2O for the back manikin (stage 2-2). Because every person in a shared space produces CO2, the volumetric fraction of inhaled air that was exhaled by infectors had to be determined:

nfIf =′ (G.2)

where I is the number of infectors; n is the number of persons in a ventilated space. In the present study there was only a single infector (the manikins used different tracers), and nobody in the room contributed to the tracer-gas concentration in the room, hence

ff =′ . Example: A room with mixing air distribution (i.e. normalized concentration in inhaled air equal to 1) is ventilated with 80 L/s of clean air. The pulmonary ventilation of occupants is 6 L/min (0.1 L/s). Alternatively, exhaled air from the front manikin contains about 1600 ppm SF6, while the concentration of SF6 inhaled by the back manikin is 2 ppm (measured).

Appendix G

132

00125.01600

02180

1.0 =−==′= ff (G.3)

The calculation reveals that the air inhaled by the back manikin contains 0.125% of air exhaled from the front manikin. The basic reproductive number (R0) is the number of secondary infections that arise when a single infectious case is introduced into a population where everyone is susceptible. An infectious agent can spread in a given population, if R0 > 1. The larger the value of R0 the more likely is the infection to reproduce rapidly in the form of an epidemic. The reproductive number in a building environment (RA0) can be derived (see Rudnick and Milton, 2003) as:

( ) ( )[ ]qtfnRA ′−−−= exp110 (G.4)

where q is the quantum generation rate by an infected person, quanta/hour; t is the total exposure time, hour. Rudnick and Milton (2003) stress that q represents the generation rate of infectious doses, not organisms or infectious particles; hence, it is the average infectious source strengths of infected individuals. The quantum generation rate depends on the infectious agent. Rudnick and Milton (2003) assessed the risk of 3 infections with a different q value: measles: q = 570 quanta/hour, influenza: q = 100 quanta/hour, rhinovirus: q = 4 quanta/hour. The same estimates are used in the following analyses. There are several factors that determine the reproductive number: outdoor ventilation rate, effectiveness of the ventilation system, quantum generation rate (infection), number of occupants in a shared space and total exposure time. Figure G-1 demonstrates the risk of infections in a typical open plan office. It shows the reproductive number as a function of the normalized concentration of an agent in inhaled air (= 1/ventilation effectiveness) for 3 different infections. There are 30 persons in the room (chosen arbitrarily) and the outdoor ventilation rate is 10 L/s per person, which corresponds to the typical requirements of present standards (CEN, 1998; ASHRAE, 1994). The time of exposure is 8 hours. The figure shows that in the case of mixing ventilation (i.e. normalized concentration of 1) there is a likelihood that 23 out of 30 persons contract measles, if a single infector were present. In the same setting 7 out of 30 persons may contract influenza. Rhinovirus would not spread (RA0 < 1). The risk of infections decreases with the decrease in the normalized concentration, i.e. as the efficiency of ventilation increases. It is obvious that the number of secondary infections depends on the ventilation rate, i.e. on the diluting of the infectious dose generated. Figure G-2 compares the reproductive number for three supply rates of outdoor air in an example of influenza. The number of occupants is again 30 and the exposure time is 8 hours. It is shown that a ventilation effectiveness as high as 10 would be required in order to prevent the spread of influenza at a ventilation rate of 10 L/s per person, while at a rate of 40 L/s per person a ventilation effectiveness of just 2 would be sufficient. Wargocki et al. (2002) concluded, based on scientific data, that outdoor air supply rates above 25 L/s per person are likely to decrease the risk of health and comfort problems (SBS symptoms) and increase productivity. Figure G-2 demonstrates that a ventilation effectiveness of 3 would be needed in order to prevent the spread of influenza in such a case.

Appendix G

133

0

5

10

15

20

25

0 0.2 0.4 0.6 0.8 1

Concentration (C-CS/CE-CS)

Rep

rodu

ctiv

e nu

mbe

r, R

A0

MeaslesInfluenzaRhinovirus

Figure G-1. Reproductive number vs. dimensionless concentration of measles, influenza or rhinovirus.

0

1

2

3

4

5

6

7

8

0 0.2 0.4 0.6 0.8 1

Concentration (C-CS/CE-CS)

Rep

rodu

ctiv

e nu

mbe

r, R

A0 10 L/s per person25 L/s per person40 L/s per person

Figure G-2. Reproductive number vs. dimensionless concentration of influenza at three levels of outdoor ventilation rate for influenza.

135

Appendix H Intake fraction Intake fraction (iF) has been used in the environmental health literature to express the source-to-intake relationship. The intake fraction is defined as the integrated incremental intake of a pollutant, summed over all exposed individuals, and occurring at any time, released from a specific source, per unit of pollutant emitted (Bennett et al., 2002). iF can be expressed as:

( )

( )∫

∫∞

=2

1

1

T

T

T

dttE

dttnQCiF (H.1)

where T1, T2 are the starting and ending time of the emission, s,

n is the number of occupants exposed, Q is the breathing rate of an occupant, m3/s, C is the inhaled air concentration from a specific source, g/m3, E is the emission of the source, g/s. For indoor environments, the inhaled air concentration from a specific source (C) can be determined based on the ventilation rate and the emission of the source. In rooms with a non-uniform distribution of contaminants, the ventilation effectiveness (or the normalized concentration) must be considered. Equation G.1 became:

( ) ( )V

nQCE

CVEnQ

iF −=−

= (H.2)

where V is the room ventilation rate, m3/s, C(-) is the normalized concentration (= 1/ventilation effectiveness). It is shown that iF became independent of the emission source and its strengths. Assuming a constant breathing rate, the intake fraction depends entirely on the ventilation rate, the ventilation effectiveness (i.e. normalized concentration) and the number of occupants in a room. In addition, a whole-day exposure under a steady-state condition was assumed in Equation H.2 for simplification. In the present study (Figure 7.2), the breathing rate (Q) of an occupant performing light office work was assumed to be 6 L/min (8.6 m3/day). This is lower than 20 m3/day, typically used in environmental health literature.