Temperature Oman

TJER 2013, Vol. 10, No. 2, 52-68

Selection and Assessment of Passive Cooling Techniquesfor Residential Buildings in Oman Using a Bioclimatic

Approach N Al-Azri*a, YH Zurigatb and N Al-Rawahia

aMechanical and Industrial Engineering Department, College of Engineering, Sultan Qaboos University, PO Box 33, PC123, Al-Khoud, Muscat - Sultanate of Oman

bMechanical Engineering Department, American Universty of Sharjah, PO Box 26666, UAE

Received 9 July 2011; accepted 29 January 2013

Abstract: Passive cooling is an ancient technique used in air reconditioning and ventilation. Despite itshistorical use, its relevance in building design has never ceased. To be sure, with the increasing interestin saving energy and preserving the environment, passive cooling stands out as a sustainable possibility.However, this is not always a viable option, and its practicality is determined mainly by the system'sfunctionality, the type of activities involved in the space to be cooled, and the surrounding area's biocli-matic variables (i.e. temperature, humidity, and diurnal temperature differences). In areas under consid-eration for passive cooling systems, bioclimatic charts are helpful. Comprehensive charts, in which year-long hourly meteorological data are projected on a psychrometric chart, help to determine the fitsrequired by a particular location. In this paper, psychrometric charts were developed for eight locationsin Oman, and a systematic procedure on the selection and viability of using passive cooling techniquesis provided through meteorological data. Givoni's passive cooling zones are used and the applicability ofeach technique is quantified. The eight study locations are widely scattered around and Oman, and pos-sess great geographical diversity. The presented results can help delineate the applicability of each pas-sive cooling technique for residential buildings at each of the study locations and their proximities.

Keywords: Thermal comfort zone, Bioclimatic chart, Evaporative cooling, Ventilation, High mass

_______________________________________*Corresponding authors e-mail: [email protected]

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N Al-Azri, YH Zurigat and N Al-Rawahi

1. Introduction

According to the International Energy Agency(IEA), world electricity demand will double by 2030as compared to the demand of 2006, with an averagegrowing rate of 2.6%. This increase will be accompa-nied by a 75% increase in CO2 emissions. The hugeincrease is mainly attributable to manufacturing devel-opment in the third world, in addition to the increasein population (IEA 2006). Climate change and soaringfossil fuel prices, in addition to the uncontrollablegrowth of energy demand, are putting renewableresources in more demand than ever. The world invest-ment in renewable energy is increasing rapidly. It wasUS$ 211 billion in 2010 compared to only US$ 33 bil-lion in 2006, with an average growth rate of 39%. Therenewable energies sectors with the highest growthrates are wind and solar (UNEP 2011).

In Oman, air conditioning consumes more energythan any other electrical appliance. In the hottest sixmonths (April to September), energy consumption isdouble that of October to March. Unfortunately,drought and the dry nature of the country pose anintractable constraint towards using solar cooling.Passive cooling techniques can offer good energy-sav-ing opportunities at low or no additional cost.

2. Passive Cooling Strategies

Passive cooling techniques have been used on theArabian Peninsula since antiquity. Intuitively, the def-inition of a passive cooling process is simply anyprocess in which cooling takes place without the inter-action of any externally powered system. A more tech-nical definition is the use of renewable sources ofenergy to increase heat loss (Givoni 2009). Passivetechniques are based on three basic strategies: masseffect, air movement, and evaporative cooling(Szokolay 2004). These strategies include a widespectrum of applications.

2.1 High Mass with Night Ventilation In hot climates, heavy external walls can retard the

flow of heat by as many as 12 hours, especially whenthere is a difference between night and daytime tem-peratures, or diurnal range, which exceeds 6oC(Reardon 2010). The day-to-night temperature differ-ence requirement makes thermal mass more effectivein hot dry climates. When this temperature differenceis beyond 10oC, thermal mass can be an indispensablestrategy.

Thermal mass can have a positive effect on thermalcomfort. High-mass structures can limit a high interiortemperature and sustain a steadier thermal environ-ment. A material with a high mass increases comfort,

especially during considerable air temperaturechanges where there is a significant differencebetween day and nighttime temperatures. The per-formance of the high mass materials is also influencedby the thermophysiccal properties of the constructionmaterial (Santamouris and Asimakopoulos 1996). Foran effective storage of heat, density (U thermal heatcapacity (Cp), and thermal conductivity (O) should beselected properly. The increase in the value of the threeparameters promotes a higher heat storage capacity.Porous materials with low specific heat exhibit a lowthermal mass. Good thermal conductivity and lowreflectivity are also required for effective passive cool-ing when thermal mass is used (Reardon 2010). Thus,with this in mind, reinforced concrete has a high ther-mal mass (2060 kJ/m3K) while earth adobe has a lowthermal mass (1300 kJ/m3K).

Thermal diffusivity (O / U CP) decides the depthdiurnal heat waves reach within the storage material,where Cp is the specific heat capacity of the material(Santamouris and Asimakopoulos 1996). For cooling,a proper tradeoff should be decided between thermaldiffusivity and wall thickness. If the wall is too thick,this will delay the penetration of heat to the interioruntil the next day.

The thermal mass effectiveness depends on the con-struction material as well as the thickness of its con-struction. Thermal mass is basically the density timesthe specific heat (Cp.U) measured in units of kilojoules(kJ/m3K) or British thermal units (Btu/ft3R). Hence,the construction thickness (L) is the second factor thatcomes in to play. When high thermal mass is desirable,the thickness has to be economically justified; hence,one should consider calculating (L.Cp.U) and selectingthe optimal tradeoff when capitalizing on thick con-struction while saving energy.

In regions where there is a significant differencebetween day and nighttime temperatures, night venti-lation is used to cool the building so that it can toler-ate the daytime heat gain. The ventilation process canbe carried out naturally or forced using fans. Nightcooling allows the thermal mass to absorb the heatgain of the next day. During the daytime, when theexterior is hotter than the interior, the thermal massdecelerates the penetration of the heat to the interior.The nighttime ventilation gets rid of that daytime heatgain (Shaviv et al. 2001).

The use of air movement as a cooling means is anintuitive and essential passive cooling strategy. Windprovides cooling through air circulation and evapora-tive cooling. It is applicable in all types of climates butis less effective in tropical climates at high humidity.At moderate temperature values, a wind blowing at a

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Selection and Assessment of Passive Cooling Techniques for Residential Buildings in Oman Using a Bioclimatic Approach

fraction of a meter per second can have a coolingeffect equivalent to a few degrees centigrade at 50%humidity (Reardon 2010). At higher humilities, thespeed has to be more in order to have the same coolingeffect.

Ventilation is basically the process in which indoorair is refined by circulation or replacement with out-door air. The ventilation process can be either mechan-ically operated or natural. In natural ventilation, air isallowed to circulate through open windows or by trick-le vents. The American Society of Heating,Refrigerating and Air Conditioning Engineers(ASHRAE 2009) define ventilation air as the air usedfor providing quality indoor air. In night ventilation,the accumulated heat during the day is decreased,allowing cold air to enter the building. The cold airreplaces the hot air naturally with the help of wind andthe stack effect (thermal buoyancy). This coolingprocess is based on convective heat transfer from theexposed building surfaces (Breesch and Janssens2007; 2010). Night ventilation is most effective inmoderate to hot climates with a significant diurnaltemperature difference and low humidity(Kolokotroni 1995).

2.2 Evaporative Cooling As its name suggests, evaporative cooing is based

on eliminating heat through the evaporation of water.Evaporative cooling can either be direct or indirect. Inthe direct method, the hot air stream passes through awet structure where it loses some of its heat throughthe evaporation of moisture and also increases itsmoisture content. The discharged cold stream willhave a lower dry bulb temperature than the hot stream,but the same wet bulb temperature.

In the indirect method, the purpose is only todecrease the air dry bulb temperature without increas-ing the moisture content. In this method, the hotstream will first be cooled using the direct evaporativemethod and then it will be used to cool the room air ina heat exchanger. Because evaporative cooling isbased on saturating air with moisture, it is mostlyeffective in dry climates where there is enough roommoisture to be absorbed by air. In this way, evapora-tion takes place.

3. Thermal Comfort

Human thermal comfort is relative and is almostimpossible to define with high accuracy due to indi-vidual, climatic, and cultural differences. For instance,people living in naturally ventilated, unconditionedbuildings usually have more tolerance to wide changesin the temperature of a summer day (Givoni 1992).

Macpherson (1973) specified six factors that canimpact the sensation of comfort: air speed, mean radi-

ant temperature (MRT), metabolic rate, temperature,and humidity, in addition to the individual's clothinglevel. Fanger (1972), however, suggested a model thattakes into consideration of human factors. In additionto the environmental variables, he considered people'sactivity and clothing levels. His predicted mean vote(PMV) model was experimentally derived from theresponses of college-age subjects set in a uniformenvironment with conditions held steady. The group'sPMV was defined as the predicted mean of votesraised by any large population expressing their thermalsensation in any given environment.

Because of the diversity in the governing variablesthat affect comfort, there has not been an exact defini-tion of a comfort zone (CZ). In the PMV model, com-fort was graded qualitatively using a seven-point scaleranked the same as the (ASHRAE 2009) scale: cold,cool, slightly cool, neutral, slightly warm, warm, andhot. However, the quantitative scaling of this methodascends from -3 to 3 instead of going from 1 to 7 as inthe case of ASHRAE's scale. Macpherson (1973) sug-gested a 19-grade index that is a function of one ormore of the six factors impacting the level of comfort.

In spite of these differences, there is a range ofhumidity and temperature values within which the vastmajority of people will feel thermally comfortable.Different authors might vary slightly their delineationof the boundaries of a thermal zone, but they all agreeon a vast common portion. The CZ set by (ASHRAE2009) assumes no consideration to people's acclimati-zation to different climates.

According to ASHRAE Standard 55, thermal neu-trality is defined as the indoor thermal index value cor-responding with a mean vote of neutral on the thermalsensation scale. Earlier works defined temperatures atwhich thermal neutrality is achieved and is correlatedto the external air temperature. Comfort is achieved atthese temperature values provided that other factorssuch as humidity and clothing are satisfied.Humphreys (1978) carried out lab and field experi-ments in order to estimate thermal neutrality. Hedefined neutral temperature as a function of outdoortemperature using the correlation

Tneutrality = 11.9 + 0.534 Toutdoor (1)

Similar to that of Humphreys, Auliciems (1981)approach considers thermal neutrality as a function ofthe mean outdoor temperature using the correlation

Tneutrality = 17.6 + 0.31 Toutdoor (2)

The operative temperature ranges between 17.8 and29.5oC. The validity of the neutrality is also dictatedby ASHRAE standard 55-81, which bounds the mois-ture content within 4-12 5/kg DA, and also relative

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humidity not exceeding 90%. Another method thatdeals with heating and cooling loads in relation to theoutdoor conditions is the degree day method. Thismethod can be defined as the annual cumulative time-weighted temperature (Sayigh et al. 1998).

In this method, a reference indoor temperature is setand the difference between the reference temperatureand the mean daily outdoor temperature is calculatedfor the whole year to obtain heating degree-days andcooling-degree days. This method is very useful whenthe order of the yearly cooling load is to be comparedfrom one year to another for the same location (Sayighet al. 1998).

4. Building Bioclimatic Charts

Building bioclimatic charts offers a convenient wayto predict whether or not a passive cooling techniqueis likely to improve the level of comfort in a building.The selection of a building's possible passive thermaldesign strategies is based heavily on the local climaticconditions. Identifying a suitable strategy for anygiven location can be done using bioclimatic charts.Building bioclimatic charts offers a convenient way topredict whether or not a passive cooling technique islikely to improve the level of comfort in a building.

Olgyay's bioclimatic chart (Fig. 1), developed in the1950's, was one of the earliest attempts to specify dif-ferent strategies at different combinations of relativehumidity (as abscissa) and dry bulb temperatures (asordinate). Oglyay's chart sets the CZ between 20 and30oC. The level of comfort is applicable to indoorspaces where occupants are wearing indoor clothing.The CZ is shown at the center of Olgyay's chart. The

chart shows the effect of climatic factors such as themean radiant temperature, wind speed, and solar radi-ation on thermal comfort. Above the lower boundaryof the zone, shading is necessary to maintain a reason-able level of comfort. Up to 10oC below the CZ, com-fort can be retained provided that there is enough solarradiation to offset the decrease in temperature.Likewise, to retain comfort up to around 10oC abovethe zone, wind speed can offset the increase in temper-ature. Evaporative cooling according to this chart isanother means to retain comfort at high temperaturevalues but at low humidity.

Since Olgyay's chart only considers the outdoorconditions and disregards the indoor physiologicalconsiderations, it is only applicable for hot humid cli-mates where there is minimal fluctuation between theindoor and outdoor temperatures. This limits its appli-cation to low-mass ventilated buildings (Sayigh et al.1998).

Another approach that disregards building parame-ters and is based on calculating degree-hours withvariable building temperature is the climatic coolingpotential (CCP) (Artmann et al. 2007). The building-specific parameters are disregarded so as to enhancethe generality of the method. CCP is defined as themean of the products of the temperature differencebetween building and external air by the time intervalfor N nights. To be considered in the mean calculation,the temperature difference has to achieve a thresholdvalue when night ventilation is applied. This value wasset at 3K in Artmann's study. The building temperatureis assumed to oscillate harmonically within the rangeof 24.5 + 2.5oC. This range reflects the recommenda-tion for thermal comfort in offices. The variation in the

Figure 1. Olgyays bioclimatic chart (Olgyay, 1963)

Relative Humidity (%)

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CCP model is represented by a cosine-function of thedifference in hours between a given hour and the ini-tial hour for time ventilation.

Figure 2 shows the application of the method toZurich, Switzerland. The shaded areas represent pas-sive cooling opportunities which happened to occur attimes when the difference between the building tem-perature (Tb) and external air temperature (Te) exceed-ed the threshold.

Another graphical method based on the psychro-metric chart is the control potential zone (CPZ) by(Szokolay 1986). This method applied Auliciems'(1981) approach of the adaptive thermal comfort dis-cussed above. The CPZ approach depends on the loca-tion and people's thermal sensation at that particularlocation.

A simplified method for anticipating cooling load isbased on the hourly difference between the air temper-

Time of day

Figure 2. Climate cooling potential (CCP) for Zurich, Switzerland during one week in summer 2003 (Artmannet al. 2007)

Figure 3. Typical building bioclimatic charge (Givoni 1992)

CZ: Conform ZoneNV: Natural VentilationHM: High MassHMV: High Mass/Night VentilationEC: Evaporative Cooling

Psychrometric Chart

Patm = 101.325 kPa

Dry Bulb Teperature, oC

TbTc

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ature and a base temperature-the cooling degree hoursand days (Hasse and Amato 2009). The degree daysare obtained by summing up the degree hours fromone day. The number of cooling degree days in a givenperiod represent the cooling load required.

Other popular bioclimatic approaches are those of(Givoni 1992, 1994 and Lomas et al. 2004). The chartwas based on the linear relationship between the tem-perature amplitude and vapor pressure of the outdoorair (Sayigh et al. 1998). Unlike other bioclimaticcharts, this chart is laid on the familiar psychrometricchart and preserves the relevant psycrometric parame-ters which are essential to the selection of passive

cooling strategies. The development of the Givonichart was based on experimental research on buildingsin Europe and the USA. These buildings were charac-terized by their low heat gain; therefore, the reliabilityof the charts for thermally heavyweight buildings isquestionable (Givoni 1994; Lomat et al. 2004).

Givoni's chart (Fig. 3) is mainly applicable to resi-dential and office buildings where heat gain is minimal(Watson 1981). Modifications to Givoni's chart thatsuit nondomestic buildings can also be found in the lit-erature (Lomas et al. 2004). The natural ventilationzone on Givoni's chart assumes that the indoor meanradiant temperature and the vapor pressure are the

Figure 4. The map of Oman and the studied locations on the map

Table 1. The geographic location of the studied locations

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same of those at outdoor conditions. This assumptionlimits the application to buildings with medium to highthermal mass (Watson 1981).

At high temperatures, mechanical air conditioningis necessary to maintain a habitable environment with-in buildings. On the left of the CZ, heating is neededto restore comfort using either solar or mechanicalheating. The high thermal mass effect is provided byheavy construction material that helps absorb heat andcan be reversed in direction overnight (Szokolay2004). If the climate is hot and dry, night ventilation

will help by releasing heat through windows, assistedby fans if necessary.

Due to their simplicity and preservation of all psy-chrometric parameters, Givoni's charts can be used instudying the application of passive cooling techniquesin Oman.

5. Application of Passive Cooling in Oman

Oman is located in the tropical zone, in the north-eastern Arabian Peninsula. Its mainland is bounded

Figure 5. Thermal mass in the old building structures in Oman

Month

Figure 6. The average monthly dry-bulb temperature of the eight locations

between 63o 40' and 57o 0' to the north and liesbetween 19o 0' and 22o 30' to the east (Fig. 4). Themainland has a coastline exceeding 1,700 kilometersand a diverse interior topography of arid desert, moun-tainous regions, and cultivable plains. In this study, the

hourly climatic data of eight locations were analyzedin order to evaluate prospective passive cooling oppor-tunities in these locations. The eight locations are scat-tered throughout the country, and this variability oflocation is one of the reasons that they were chosen.

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Month


Psychrometric Chart

Patm = 97.786 kPa

CZ: Comfort ZoneNV: Natural VentilationHM: High MassHMV: High Mass/Night VentilationEC: Evaporative Cooling

Figure 8. Givonis bioclimatic chart for location (1), Buraimi

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Table 2. Average monthly temperatures and humidity

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Table 3. Average maximum and minimum temperatures and relative humidity

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Moreover, while hourly weather data in Oman arevery scarce, these eight locations benefit from consid-erable hourly weather data due to the fact that they allhappen to be the bases for oilfields, refineries, and air-ports. Their coordinates and altitudes are shown inTable 1. Location 1 is a relatively heavily populatedtown surrounded by a typical Arabian desert and isabout 75 km from the coastline. Locations 2, 3, and 4are major population centers characterized by hightemperatures and high humidity and are located on thecoastline. Locations 5 and 7 are oil fields located inthe Arabian Desert of the Empty Quarter and are about250 and 70 km, respectively, away from the coastline.Location 6 is an island in the Indian Ocean. It is about640 square kilometers and is about 20 km away fromthe mainland. Location 8 is a town with a moderate cli-mate throughout the year and is famous as a summerresort in the region.

In the summer time, electrical power consumptionis significantly higher than that in the winter timebecause of the high demand for air conditioning. In2007, the demand went from 1,000 MW in January to2,773 MW in July. This figure has been increasing atan annual growth rate of 9% and was expected to reach4,634 MW in 2013 (AER-Oman, 2008). Currently, thegovernment is launching long-term initiatives for theuse of renewable energies in the country. Passive cool-ing was practiced in the past using empirical method-ologies. Historically, high mass (Fig. 5) with ventila-tion was quite commonly practiced in the interior ofthe country, which has a climate characterized bylower humidity and a reasonably significant day-to-night temperature difference.

This study will allow a systematic approach to thedetermination of effective passive cooling strategies inthe country using bioclimatic charts. As mentionedabove, Givoni's charts were used in the study, and aquantitative measure is presented below based on theprojection of the psychrometric parameters on the dif-ferent zones in the chart. The weather data wasprocessed and analyzed using MATLAB (MathWorks,Inc, Nattick, Massachusetts). The charts were alsodeveloped using the same software.

6. Results and Discussions

Table 2 shows the monthly mean dry bulb temper-ature and humidity for each location. The meteorolog-ical data were taken from a study by (Zurigat et al.2003) in which the hourly reading for several yearswere statistically analyzed. As mentioned above, dayand night temperature differences, humidity, and tem-perature were the variables used to decide a suitabletechnique for a given location.

Figure 6 shows the average temperature of eachmonth for the eight locations. The non-coastal loca-tions (1, 5 and 7) exhibited high temperatures consis-

tent with the time of year. July and August seemed tobe the hottest months of the year. The rest of the coast-line locations had slightly lower average temperatures,except for Locations 6 and 8, which are affected by theIndian monsoon from June to September.

Another equally important criterion for the selec-tion of passive cooling techniques is the day-to-nighttemperature difference. If this difference is small, ther-mal mass and night ventilation will not be effectiveenough to allow adequate cooling. Figure 7 shows thisdifference for the eight locations. For each location ina given month, a point represents the average day-to-night temperature difference. Non-costal locations haddifferences greater than 10oC, which justifies usingthermal mass as a passive cooling strategy in theselocations.

Figures 8 to 15 show the Givoni charts for the eightlocations based on the average minimum and maxi-mum hourly temperature and humidity values shownin Table 3. Givoni charts are more qualitative. Theinclusion of the line segment for each month in a givenzone gives an approximate idea if the application ofthat method would be appropriate. One should alsocare about the diurnal temperature difference andwhether the placement of the line segment within thezone is promising enough by checking the dry bulbtemperature and humidity values.

Table 4a&b shows the fractions of the projectionof the hourly readings in each of the five zones foreach month with the bold face figures indicating day-to-night temperature differences exceeding 10oC. Forinstance, 0.8 means that for 80% of the hours, the tem-

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perature and humidity readings would be containedwithin the zone of conditions appropriate for passivecooling mechanisms. Since the different zones over-lap, the sum of the different zone does not have to addup to unity. The calculations of these figures couldhave been done to more decimal places. Such an

effort, however, would have been superfluous sincethe yearly deviation of readings can be greater than theapproximate figure used here.

From Fig. 8 and Table 4a&b, one can see that,except for the months from June to September, passivecooling techniques would be quite effective in

Figure 10. Givonis bioclimatic chart for location (3), Seeb

CZ: Comfort ZoneNV: Natural VentilationHM: High MassHMV: High mass/Night VentilationEC: Evaporative Cooling

Psychrometric Chart

Patm = 101.281 kPa

Psychrometric Chart

Patm = 101.224 kPa




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Buraimi. In the months of December throughFebruary, solar heating would be needed but in March,May, October, and November, passive cooling wouldbe a promising method for more than 70% of the time.

Location 2, Majis, proved itself a less desirable

location for passive cooling (Fig. 9; Table 3). Exceptfor April and May, the diurnal temperature differenceis low and high humidity prevents the use of passivecooling and night ventilation. Air conditioning is nec-essary for most of the year in this location.

Figure 12. Givonis bioclimatic chart for location (5), Fahud

Psychrometric Chart

Patm = 101.160 kPa



Psychrometric Chart

Patm = 99.299 kPa



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Location 3, Seeb, which is on the coastline, exhib-ited a similar result to Location 2 (Fig. 10; Table4a&b). However, the weather data showed that Seebfalls within the CZ for a longer and more reassuring

period from November to March. Location 4, Sur, fol-lowed somewhat the same trend as Location 2 (Fig. 11,Table 4a&b). The climate was quite comfortable fromDecember to February, and passive cooling would be

Figure 14. Givonis bioclimatic chart for location (7), Marmul

Psychrometric Chart

Patm = 101.099 kPa



Psychrometric Chart

Patm = 98.135 kPa

CZ: Comfort ZoneNV: Natural VentilationHM: High MassHMV: High Mass/Night VentilationEC: Evaporative Cooling


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feasible only in April. The diurnal temperature differ-ence was greater than 10oC in some months, but thelower end of the temperature range was still too high,necessitating air conditioning.

Locations 5 and 7 (Figs. 12 and 14, Table 4a&b)depicted similar trends to one another. The diurnaltemperature difference was always greater than 10oCand passive cooling techniques would be quite effec-tive for most of the year. The broadness of the differ-ence in diurnal temperature can be extrapolated fromthe long segments on the Givoni chart. Location 6,Masirah, proved less acceptable as a locationamenable to passive cooling as a substitute formechanical cooling (Fig. 13, Table 4a&b). The humid-ity in Masirah is quite high (60%) and, althoughDecember to February have temperatures in the CZ,they experience high humidity.

In Location 8, the temperatures from November toMarch were within the range acceptable for a passivecooling zone, but the low diurnal temperature differ-ence may discourage its application (Fig. 15; Table4a&b).

7. Conclusions

The applicability of the different passive coolingtechniques is controlled by a spectrum of factors relat-ed not only to climatic changes but also to cultural andsituational factors. It is far from realistic to dictatefirm prerequisites and provide distinctive instructionson when the mechanisms should be applied and whatpassive technique to use. However, climatic factors arealways the most relevant. Early design tools can pro-vide deeper insight into the robustness of a given strat-

Table 4a. The projection of weather data in the different zones for passive cooling Strategies (Buraimi, Majis,Seeb and Sur)

*CZ: Conform Zone, NV: Night Ventilation, HM: High Mass, HMV: High Mass with Night VentilationEC: Evaporative CoolingBold Figures: Diurnal temperature difference greater than 10oC

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Table 4b. The projection of weather data in the different zones for passive cooling strategies (Fahid, Masirah,Marmul and Salalah)

*CZ: Conform Zone, NV: Night Ventilation, HM: High Mass, HMV: High Mass with Night Ventilation

Psychrometric Chart

Patm = 101.085 kPa

CZ: Comfort ZoneNV: Natural VentilationHM: High MassHMV: High mass/NightVentilationEC: Evaporative Cooling

Dry Bulb Teperature, oCFigure 15. Givonis bioclimatic chart for location (8), Salalah

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egy and its required tradeoffs. This study considersthat aspect in the application of passive cooling. Foreach of the eight locations widely scattered aroundOman, 8,760 hourly readings were used (Zurigat et al.2003). MATLAB codes were developed to perform thecalculations, and data were plotted on Givoni's charts.This graphical representation was quantified by calcu-lating the portion of inclusion in each of the zones. Theaverage diurnal temperature difference was also calcu-lated and is shown on the tabulated representation. Itcan be concluded that passive cooling strategies pres-ent energy saving opportunities, especially in the inte-rior of the country (eg. Buraimi, Fahud, and Marmul).The slight swing in day-to-night temperatures wouldpresent an obstacle to the implementation of high masswith night ventilation in some coastal locations (eg.Majis, Seeb, and Sur). Salalah and Masirah enjoy rel-atively more comfortable weather and exhibit lessvariation throughout the day because of the presenceof the Indian monsoon.

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