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American Institute of Aeronautics and Astronautics

IMPROVING ENERGY EFFICIENCY OF AIR CONDITIONED BUILDINGS

THROUGH SUMMER ELUSIVE CLIMATE

Ahmed A. Medhat (1) and Essam E.Khalil (2)

(1) HVAC Consultant, Dept. Of Building Physics & Environment, Housing & Building Research Center, Egypt P.O.Box 1770 Cairo, Egypt Email: aamf30@hotmail.com & a.medhat@hbrc.edu.eg

(2) Professor of Mechanical Engineering, Faculty of Engineering, Cairo University, Cairo, Egypt. Cairo University, Egypt, Fellow ASME, AIAA, Member ASHRAE ,ISIAQ Email: khalile1@asme.org

ABSTRACT Human thermal comfort is affected by several thermal and non-thermal variables, such as temperatures, humidity, local air speed, health, age, activity, clothing, sex, food, location, season,etc., and acclimatization for any particular person. This paper is a part of long-term, (3-years) field case-study investigations to establish compatible tropical comfort chart suitable and appropriately applicable to Egyptian citizens from different governorates (states). Such investigations were based on the same concepts and methodologies used and applied to establish the well known ASHRAE 1, comfort chart, but all statistical data were directed to field studies not laboratory tests. This study dealt with only men over 45-years old with the same metabolic rate during the summer season and were dressed with clothing that ranged from 0.5 Clo To 0.65 clo, which ASHRAE 1 clarified as cloth unit, weighted from 70-to-90 kg and subjected to air conditions treated for long periods (over two hours) inside public buildings in Cairo and Alexandria. Most of the citizens after being subjected to treated air become acclimated to the indoor conditions in their original environment; then they were moved into another pre-adjusted zone such as theatre waiting lobbies, lecture hall salons, patient or laboratory rooms, conference dining halls or offices. All of them had immediately expressed their vote and reactions to the new indoor climatic conditions,( warm, cool, fair, and same). The questionnaire vote level was based on a minimum of 10 persons covering each Egyptian governorate. A large volume of data were collected and stored to apply the related Operative Temperature (O.T) to the psychrometric chart. One of the main conclusions was that the analysis of obtained results could greatly enhance our understanding, and explain the causes of many abnormal human characteristics due to the human stress mode. These results indicate the need to include human stress modes to the human comfort variables.

INTRODUCTION Great experience was gained over the past fifty years in Egypt concerning how Egyptian Citizens thermal comfort and sensations are related to indoor environmental parameters, references [2-11]. While most international codes and standards are based mainly on laboratory studies for thermal factors, surely in the field, there are other non-thermal factors that may affect directly both human thermal comfort and sensations. The indoor environment is complex and responds to the interactions among its affected factors. This paper focused directly on the effects of both thermal and non-thermal factors when their criteria are applied together. Field investigations were carried out for selected air conditioned and new public buildings in Cairo and Alexandria, which are considered the first and second capitals of Egypt and most of the citizens commute from different governorates daily to and from major cities to perform their jobs and missions. As Cairo is considered the most crowded, dusty city and highly venerable to pollution in Egypt, while Alexandria has small low population and minimal dust and pollutant weather. As shown on Fig.1, Egypt’s densely populated area can be divided to seven zones covering the majority of governorates. Cairo is located at zone-6 and Alexandria located at zone-1. Field investigations were based on the proper selection of the air conditioned buildings to be tested, which should satisfy the following conditions and requirements: 1…Seven-Day operation projects for minimum 14-working hours. 2…Occupancy rate should be over 75 healthy persons. 3…Test objects should be available for three hours or more having same activity level.

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4…Projects should include two chambers at which dry-bulb and wet-bulb temperatures were adjusted to give the same thermal feeling. 5… Independent air-conditioning systems for each test chambers. Allow for individual control of air parameters. 6…Full coordination with the projects engineers. To facilitate the control of indoor conditions and collecting questionnaires

FIELD TEST METHODOLOGY Investigations were based, nearly, on the same concepts applied by ASHRAE and using modified and developed methodologies. The current research is concerned with the following configurations: 1. Only men over 45-years old. They should have the same (activity level) metabolic rates for occupancies during tests. 2. Tests were carried out during summer season and at atmospheric pressure. 3. Citizens under tests should be dressed with clothing that ranges from [0.5-to-0.65] clo (one clo = 0.155 m2.0C/W with weights ranged from [70-to-90] kg. 4. Citizens shall be subjected to treated air for long periods (about two hours) to assure acclimatization and with minimum periods of thirty minutes. 5. Measurements periods ranged from [2-to-4] minutes. 6. Mean radiant temperatures ranged from [20-to-25] 0 C at indoors local air speed ranged from [0.1-to-0.35] m/s. 7. Temperature differences applied on chambers ranges from [8-to-14] 0C; floor temperatures being kept near the space temperatures. 8. Non-uniformity of temperature and humidity (fluctuations, cycling, drifts & ramps) and radiant temperature asymmetry are neglected. 9. Homogenous vertical air temperature gradients are considered; the indoor temperature ranged from [12-to-35] 0C. 10. Indoor relative humidity ranged from [30-to- 85] % for the test duration carried out between [9.00am –to- 10.00pm].

When applying the previous concerns and considerations in the form of questionnaires for different applications and with the aid of state-of-the-art instrumentations, the distributions of the local air velocity and turbulence intensity were obtained utilizing heated-thermocouple anemometer air velocity sensors. The distributions of the local mean temperature were obtained by means of thermal positive coefficient thermistor and resistant-temperature-differential (RTD). Finally the local mean humidity distributions were obtained by capacitive sensing elements. Experimental investigations were carried out in a systematic, pre-programmed sequence and precise manner by evaluating thermal comfort and sensations during the presence of subjects inside the first chamber every twenty minutes until they achieved acclimatization in the chamber environment then subjects moved into the other chamber which had different and/or the same operative temperature and immediately recorded their reaction to the new condition. Every twenty minutes in the new conditions their responses were collected until acclimatization took place. Using several subjects and changing the conditions of the test chamber many times, a large volume of data was gathered. Results of experimental work were collected and tabulated in a convenient way, and compared with the ASHRAE data and previous investigations, as indicated in the results and discussion section.

RESULTS AND DISCUSSION These long-term, field case-study investigations have, no doubt, furnished the basis of all available data and materials that establish compatible tropical comfort levels and comfort chart characteristics covering most of thermal and non-thermal criteria. Previous laboratory investigations results were valid for specific case studies while for local Egyptian applications these either largely deviated from reality or gave accurate patterns with odd results. One of the main conclusions clearly outlined from the present analysis is that the obtained Operative Temperature (OT) scale was different from that of the ASHRAE1.At optimum OT; the maximum acceptable comfort level did not exceed 78% according to the type of application. Figure 2 shows that these samples of acceptable ranges of operative temperatures during summer season are deviated from that introduced by ASHRAE comfort charts. As those were related for maximum percentage of occupant thermal satisfaction by not more than 78%, while the actually presented contours [A] & [B] are not straight lines but were curve fits with large deviations among the responses. Moreover at zone [B] in the same figure, which was determined many times at different indoor local air velocities, shows that the [B] contours seem to be located in the range of 0.12 m/s to 0.30 m/s; no change in the thermal feeling within this band was observed. Citizens related to zone [A] are very sensitive to the local air

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velocities, as the presented contour can be shifted 1-degree of the ET lines to the left and change the inclination of the OT lines slightly every 0.1m/s step. Figures 3 & 4 indicate that there are major changes in the environmental classifications among Egyptian citizens from Upper Egypt to North Egypt compared with the commonly used international criteria. While it was shown that both classifications can be changed to be nearly the same as ASHRAE based results when all tests were carried out in Alexandria (with non polluted and non dusty weather) and without any stresses on the human nerves system. Analysis of obtained results can enhance our understanding and explain the causes and reasons of many abnormal human characteristics due to the human stress mode.

RECOMMENDATIONS It is strongly recommended to include human stress modes to the human comfort variables. It can also be concluded that all men over 55-years of age prefer an effective temperature one degree higher than persons below this age. While psychological problems has a great effects on the selection of effective temperatures specially when persons feels that they are in a dark ,tight glass window rooms and they cannot see outside or the individuals who are not comfortable unless they have open windows . Finally, the contrast between indoor and outdoor conditions plays a vital role in the acclimatization of citizens as most of them prefer a low contrast gradient.

REFERENCES [1] ANSI / ASHRAE 55-1992, Thermal Environmental Conditions for Human Occupancy. [2] International Standard ISO 7730 Second edition 1994-12-15, Moderate thermal environments-Determination of PMV & PPD indices as Specifications of the conditions for thermal comfort [3] Khalil, E.E. Energy Efficiency in Air conditioned Spaces, Proceedings of 5th Jordanian Mechanical Engineering Conference, Keynote paper, April2004. [4] Kameel, R., 2002, Computer aided design of flow regimes in air-conditioned operating theatres, Ph.D. Thesis work, Cairo University. [5] Kameel, R., 2003, Assessment of airflow characteristics in air-conditioned spaces using 3D time-dependent CFD model, IECEC 2003-5960, Portsmouth. [6] Kameel, R., and Khalil, E. E., 2002, Generation of the grid node distribution using modified hyperbolic equations, 40th Aerospace Sciences Meeting & Exhibit, Reno, Nevada, AIAA-2002-656, 12-15 January 2002. [7] Patankar, S. V. 1980, Numerical heat transfer and fluid flow, Hemisphere Publishing Corporation, WDC. [8] Sorensen, D. N., and Nielsen, P. V., 2003, Quality control of computational fluid dynamics in indoor environments, Indoor Air, Volume 12 No.1, page 2. [9] Leonard, B. P., and Drummond, J. E., 1995, Why you should not use ‘hybrid’, ‘power-law’ or related exponential schemes for connective modelling – there are much better alternatives, International Journal for Numerical Methods in Fluids, 20, 421-442, 1995. [10] Anderson, D. A., Tannehill, J. C., and Pletdher, R. H., 1980, Computational fluid mechanics and heat transfer, Hemisphere 1980. [11] Nielsen, P. V., Restivo, A. and Whitelaw, J. H., 1978, The velocity characteristics of ventilated rooms, J. Fluids Eng., 100, 291–298.

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Figure 1: Map of Egypt showing main population climatic zones.

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Figure 2: Adopted Acceptable Ranges of Operative Temperatures and Relative Humidities.

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Figure 3: Sample of Environmental Classification for Southern Egyptian Citizens

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Figure 4: Sample of Environmental Classification for Northern Egyptian Citizens