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Received 14 Nov. 2008; Revised 15 Oct. 2009; Accepted 25 Oct. 2009

*Corresponding author E-mail: mazran79@hotmail.com

Comparison of Different Hybrid Turbine Ventilator (HTV)Application Strategies to Improve the Indoor Thermal Comfort

Ismail, M.* and Abdul Rahman, A. M.

School of Housing, Building & Planning (HBP), Universiti Sains Malaysia (USM), 11800Penang, Malaysia

ABSTRACT: This paper discusses the results of the full-scale field measurement study to investigatethe most efficient application strategy of the Hybrid Turbine Ventilator (HTV) in improving theindoor thermal comfort in hot-humid tropics. The effects of three different HTV application strategiesperformance on improving the levels of indoor air temperature, relative humidity (RH) and air velocitywere evaluated for a three-clear day period. The results were analyzed and compared based on twothermal comfort indices i.e. Operative Temperature (OT) and Standard Effective Temperature (SET*).The study shows that the HTV for the occupied space with extractor fan at ceiling level is the mostefficient strategy when it succeeded to reduce indoor air temperature and relative humidity of up to0.7°C and 1.7%RH, respectively. It also succeeded to induce air velocity in the occupied level up to0.38m/s in average and reduced the level of OT by 60% and SET* by 90% compared to the existingcondition. The overall results also indicated that the performance of the HTV could be enhanced byapplying the device for both occupied space and attic space at the same time and ensure thatopenings are kept opened.

Key words: Stack ventilation, Turbine ventilator, Solar energy, Thermal Comfort, Hot-humid climate

INTRODUCTIONGenerally, building sector consumes about 30-

40% of the world’s energy demand and it isexpected to increase rapidly in the near future(Santamouris, 2005). In South-East Asian countries,example of the hot and humid tropical region, theaverage energy consumption of building is 233kWh/m²/yr, of which about 60% is for air-conditioning.This scenario of high energy consumption due tothe extensive use of air-conditioning system is quitefrustrating since various studies indicated thatpeople in hot-humid tropical climate are moretolerable to higher temperature due to theacclimatization factor (Givoni, 1992).

Concerning this issue, various studies havebeen done in order to find out possible alternativesto air-conditioning without compromising theenvironment and people’s thermal comfort. Oneof the ventilation strategies that is considerablecheap and technologically simple to operate is the

use of wind-driven turbine ventilator (AbdulRahman, 2004). According to Dale andAckerman (1993), the conventional Ø305mmturbine ventilator was helpful to increase atticventilation rates by approximately 15% from 5.3to 6.1 air changes per hour (ACH) on average ascompared to the existing condition of the roofequipped with soffit vents in the test house underthe windy condition of USA. On the other hand,Lai (2003) showed that the installation of thedevice in building or factory in Taiwan high-outdoor wind condition of between 10 m/s to 30m/s is significantly capable to increase ventilationrate from 60m³/h (with no ventilator) to 140m³/hfor a Ø500mm turbine ventilator.

However, since its function is totally dependson the outdoor wind condition, its applicability andeffectiveness in erratic and low-wind velocityregion is always questionable. These weaknesseshave been revealed by Lai (2003) who found that

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in the low wind-velocity condition, the fins of theturbine actually blocked the airflow in theconnecting duct, resulting in much lower extractionrate of air compared to open stub. This limiteduse of the turbine ventilator has prompted someresearchers worldwide to investigate the possibleimprovements of the device. West (2001) carriedout an experimental study on the effect of turbineheight on its ventilation performance and foundthat 13.5% improvement in flow rates can beachieved by increasing 50% of the blade height.Meanwhile, Khan et al. (2008) investigated theeffect of different forms of turbine blades andshowed that the curved vane ventilator couldproduce 25% larger flow rate compared to thestraight vane ventilator of the same size.

On the other hand, several studies attemptedto investigate the possibility of combining theturbine ventilator with electrical extractor fan inan effort to improve its ventilation performance,especially in the low-wind velocity condition. Thisincludes the study by Kuo and Lai (2005) on thecombination of the roof turbine ventilator withbathroom ventilation system equipped withextractor fan in subtropical climate of Taiwan. Thestudy found that such combination is effective toachieve sufficient air change rate required forhygienic need with the ventilation incrementcreated by the ventilator with outdoor airflow(ventilation increment induced by per-unit outerwind speed) was 53.26 CMH/(m/s). Following thisstudy, Lai (2006) conducted a prototypedevelopment study of the hybrid turbine ventilatorthat integrated the wind-force turbine ventilatorwith PV-powered inner fan and found that theprototype is successful to increase ventilation rate,especially with a rate rotation speed of 1500 rpmand a battery. However, the result showed that itsoptimal operation could only be achieved in lowoutdoor wind speed up to 5 m/s. This illustratedthe problems of having a turbine itself which couldpossibly be a major resistance for much higherrate of extraction air that could be produced bythe inner fan below. In a more recent study, Zain-Ahmed et al. (2007) investigated the potential ofthe prototype hybrid ventilator that combinedconventional turbine ventilator with lightpipe andfound that such combination is significant toimprove both indoor ventilation and daylightingconditions.

Following these studies, the authors intend toinvestigate the actual performance of the hybridsolar-wind turbine ventilator (HTV) in the realbuilding and under real weather conditions byconducting full-scale field measurement study. Forthis purpose, a new configuration of the HTV with20cm inner duct in the turbine and larger free outletarea on the upper part was developed in order toallow more extraction rate of air. To evaluate thesignificance effect of this HTV in improvingthermal comfort condition in hot-humid tropicalbuilding, three different application strategies i.e.HTV for attic space and 2 HTVs for Indoor(occupied space) with different locations of theextractor fan were studied. This is to find out themost effective strategy in reducing internal airtemperature along with relative humidity and atthe same time increasing air velocity in the occupiedzone. Using simplified comparisons of OperativeTemperature (OT) and Standard EffectiveTemperature (SET*) indices, the results then willlead to reveal the best application strategy forimproving indoor thermal environment in thisregion, and consequently suggests its possibilityto be used in the low-wind velocity areaworldwide.

MATERIALS & METHODSThe field study was conducted in the

rectangular room (in the top floor of an institutionalbuilding in Malaysia) with a dimension of 27.5m x12m and 2.85 m height. The total floor area isapproximately 330.0 m² and the volume of theoccupied space and attic is 940.5 m³ and 330.0m³, respectively. To ensure the conducive indoorenvironment, insulation barrier in the roof and largeopenings of 330.0 m² which is equivalent to 17%of the openings to floor area ratio was applied.However, from the observation, the room stillsuffered a hot indoor air problem which is mainlydue to relatively wide area of its roof exposed tothe sun. This problem is worsen by the presenceof large vegetations and newly built buildingsadjacent to it which limit the effectiveness ofnatural cross ventilation to ventilate the most areaof the room (Fig. 1).

As a response to the findings from theprevious studies which illustrated that the turbineitself could possibly be a major constraint toachieve higher rate of extraction air, a new

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configuration of the device with larger free outletarea on the upper part has been developed usingconventional 18" turbine ventilator Fig.2(a).Integrated with solar-powered extractor fan withØ30cm fan blade and Ø35cm aluminum ventilationduct, three complete sets of the HTVs wereinstalled on the roof along with 6 panels ofpolycrystalline photovoltaic (20 watt each) Fig.2(b).In order to investigate the most efficient useof the device in improving thermal environment,three different application strategies and theexisting condition without it were studied. Table 1below summarizes all the HTV applicationstrategies studied.

Since the studies have been done on thedifferent days which represent different outdoorclimatic conditions, the measurements for bothoutdoor and indoor conditions were taken. Theambient temperature and relative humidity weremeasured at a height of 1 meter above the (third)floor level and were protected from the sun. The

VRI Building

Attic

Occupied SpaceThird Floor Level

Second Floor Level

THE ROOM STUDIED

VETOR RESEARCH INSTITUTE

COURTYARD

MAIN ENTRANCE

(a) (b)Fig. 1. The test-bed (a) third floor plan of the building (b) graphic cross sectional view

Fig. 2. Configuration of the HTV (a) before installation (b) three complete sets of the HTV installed on the roof

global solar radiation was measured by apyranometer located on the parapet wall near theroof. At the same time, all sensors for indoortemperature, relative humidity and air velocitywere located in the middle of the room with adistance of 1.0 m above the floor (occupied level)and 6 m from both side walls. Data from allsensors were recorded continuously at fifteenminute intervals for three clear days onto aBABUC data logger for each case. However, thedata analyzed in this paper was based only on theperiod of 9.00am to 10.00pm as this period of timeis considered to be among the most critical timeto achieve indoor comfort condition under this hot-humid climate.

The main aim of the study is to investigate theeffectiveness of each application strategy of HTVin improving indoor thermal environment. Althoughthe results could demonstrate the pros and consof each strategy, the comparison analysis betweenall the strategies should be made to reveal the most

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Hybrid Turbine Ventilator

Table 1. Conceptual designs of the different types of HTV strategies

efficient application strategy under the hot humidclimate of this region. Therefore, two simplifiedcomparisons were made;In comparing theventilation performance of each strategy that wasdone in different days which represents variousclimatic conditions, the authors realized that it isnot easy and almost impossible to produce theaccurate and objective answer. However, asimplified comparison using Relativeness Index(RI) was used as an indicator to formulate generaland subjective conclusions (Khedari et al., 2000).This index count on the value of differencebetween average indoor temperature and outdoor

temperature, dT (°C) as a comparison tool. Inaddition to the air temperature, evaluation of theventilation performance also involved the reductionlevel of relative humidity in both attic and occupiedspaces and air velocity at the occupied level.

From the literature review, it was found thatgenerally neutral temperature for people’s thermalcomfort in the hot-humid tropics ranges from 24°Cto 29°C for natural ventilated building. Howeverfor this study which is done in Malaysia, the neutraltemperature was chosen as 26.5°C, which is0.2°C higher than Zain-Ahmed et al. (1997) and0.2°C lower than neutral temperature proposed

S trategies Configuration Extractor fan location

1.

Hybrid Turbine Ventilator (HTV) for Indoor (f an at ce iling leve l)

2.

Hybrid Turbine Ventilator (HTV) for Indoor (fan near roof leve l)

3.

Hybrid Turbine Ventilator (HTV) for Attic

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by Abdul Rahman (1999) based on Model YearClimate Data. To validate this value, it was testedby the two main thermal comfort theories i.e. thePredicted Mean Vote (PMV) and the AdaptiveModel. The PMV theory represents the ‘predictedmean vote’ (on the thermal sensation scale) of alarge population of people exposed to a certaincontrolled environment (Fanger, 1970). On the otherhand, the adaptive approach is based on empiricalobservation of the results from field surveys whichinclude the variations in outdoor climate fordetermining thermal preferences indoor (De Dearand Brager, 1998, Nicol and Humphreys, 2002).

To validate the thermal neutrality using thePMV theory, the Software ASHRAE ThermalComfort Program V1.0 was used to make thecalculations with several assumptions:♦ The Mean Radiant Temperature (MRT) was assumed to be the same as the air temperature (26.5°C),♦ The relative humidity is 80% (the mean value for this climate),♦ The metabolic rate is 1.0 met to indicate seating and writing activity and♦ The clothes were assumed to be 0.5 Clo

Moreover, the air movement was taken as0.1m/s to represent the condition with still air. Fromthe analysis, it was found that the value for thePMV and Predicted Percent Dissatisfied (PPD)were 0.4 and 9%, respectively. Based on ISO7730,these values were obviously within the comfortzone when that standard stated that an acceptablePPD should be <10% which corresponds to aPMV between -0.5 and 0.5.On the other hand,the expression by de Dear and Brager (2002)based on Auliciems (1981) correlation was usedto validate the thermal neutrality of 26.5°C usingthe Adaptive Model.

Tcomf = 0.31Ta,out + 17.8

Where Tcomf = optimum comfort temperature andTa,out = mean outdoor dry bulb temperature of themonth.

However, since the study was done during thetwo months period of May and June 2008, wherethe mean temperatures were recorded as 27.8°Cand 28.2°C respectively by Bayan Lepas (Penang,Malaysia) Meteorological Station, the averagevalue of 28.0°C was chosen for the calculation.

Based on the equation, the thermal neutrality wasfound to be equal to 26.5°C. However, accordingto this theory, the comfort zone can be taken as±2.0°C about the neutrality temperature. Thus, thevalue of 28.5°C was used as the upper limit ofcomfort in this study, considering also theacclimatization of people to hot humid conditionsand living in naturally ventilated building.

RESULTS & DISCUSSIONThe analyzed data of indoor thermal condition

without the use of HTV indicated that usually theindoor air temperature was lower than ambientduring 11.00am to 4.00pm. However, with the useof HTV, the lower indoor air temperature relativeto ambient could be earlier by one hour andextended by one hour compared the existingcondition. This is due to the HTV installed on theroof begun to effectively operate from 9.00am to5.00pm. This observed condition illustrated theperiod of time when adequate incident solarradiation is received by the crystalline photovoltaicto generate solar electricity to run the device.

As a simplified comparison of theeffectiveness of different extractor fan locationsalong with existing condition without the use ofHTV, Fig. 3 below shows the air temperaturedifference between indoor and outdoor of thehottest days of each strategy.The lowertemperature difference means the higher airchange rate (ach) and consequently the lowertemperature of the indoor air. From the graph, itcan be said that the reduction of air temperatureis not very much influenced by the location of theextractor fan since the lower values of airtemperature achieved by both HTV compared toexisting condition are almost the same, which theup and down differences that occurred sometimeswere mainly because of the different level of solarradiation it received. However, it can be seen thatthe effect of HTV for both strategies in reducinginternal peak temperature is not significant after5.00pm due to the end of solar radiation.

On the other hand, Fig. 4 below shows theimpact of both HTVs for Indoor strategies inreducing the level of temperature for the averagethree-day period. The lower value achieved byeach strategy means that more indoor airtemperature is reduced and more significant the

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Fig. 3. Comparison of the difference between indoor and outdoor temperature for different ventilationstrategies (windows and doors closed)

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strategy would be. By the graphs, it can be seenthat both HTV strategies show almost the samereduction of 0.7°C lower than existingcondition(without HTV). However, it still can beobserved that the mean minimum air temperatureof HTV for Indoor (fan near roof level) is slightlylower than HTV for Indoor (fan at ceiling level).This is mainly due to the higher solar radiation andsolar intensity it received at that time which meansthe higher rate of the extractor fan it has andconsequently, the lower temperature it produced.

On the other hand, the results regardingmean maximum temperature shows acontradiction when the HTV with fan at ceilinglevel shows a better result which is mainlybecause of the same solar radiation factor. Thus,it can be concluded that the reduction level ofindoor air temperature is not verymuch influencedby the extractor fan location since the ACH andventilation rate that matters most, which arehugely determined by the the rotation rate of thesolar-powered extractor fan.

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Fig. 4. Comparison of the mean maximum and mean minimum indoor-outdoor air temperature differences fordifferent ventilation strategies when windows and doors closed

Ismail, M. and Abdul Rahman, A. M.

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Fig. 5. Comparison of the temperature differences in the closed case for different ventilation strategies (a)attic-outdoor difference (b) indoor-outdoor difference

(b)

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Regarding the profile of air velocity in the closedcase, as expected, the application of HTV with fanat ceiling level shows the best result in highest airvelocity produced, where the mean maximum airvelocity for three days study achieved is 0.10m/s,the value of 0.04m/s higher than when the fan wasnear roof level. However, the advantage of havingextractor fan placed at the ceiling level which meansnearer to the occupied zone is not very helpful tocreate ample air movement of 0.25 - 1.0m/s neededto improve thermal condition.To investigate the

effect of applying HTV for attic ventilation, themeasurements of air temperature and relativehumidity were also taken in the attic space. Fromthe results, it was found that HTV for Attic strategysucceeded to reduce attic air temperature byapproximately 0.9°C and 1.0°C compared to HTVfor Indoor (fan at ceiling level) and the case withoutHTV, respectively. Fig. 5(a) below shows theexample of the temperature reduction whichrepresents the attic-outdoor temperature differencefor the hottest day of each strategy.

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However, although its effect in reducing indoor(occupied space) air temperature is slightly betterthan existing condition in the afternoon, the moresignificant effect of this strategy is quite obviousfrom 4.00pm to 7.00pm when solar radiation getsweak Fig. 5(b). The positive results during thisperiod compared to HTV for Indoor strategyclearly shows the importance of this strategy tolower down the level of heat radiated from theceiling to indoor spaces, which at these timescannot be forced out effectively with HTV forIndoor due to weak solar radiation. In addition,the study also shows that this HTV for Atticstrategy is quite significant to reduce relativehumidity level in the occupied space, as shown inthe Fig. 6.

Investigating the effect of openings isimportant since some studies on the ventilationstrategies in this climate found that the openedwindows and doors could bring in hot and humidoutdoor air to interior spaces, thus worsen theindoor thermal condition (Ahmed et al., 2005). Theadverse impact of having the openings openedseems to be true when Fig. 7(a) illustrates thatthe Indoor-outdoor relative humidity difference islower when the windows and doors are openedcompared to when it are closed. This means thatthe closed windows are helpful to ensure the indoorrelative humidity remained lower although thehumidity ambient is getting higher. From the

graphs, it can also be observed that in this openingsclosed case, the HTV for indoor with fan at ceilinglevel shows the best performance in terms ofhumidity reduction when it succeeded to reducerelative humidity level by 1.7%RH as comparedto the existing condition without any HTV installed.

However, the results of the studies regardingthe profiles of air temperature (Fig. 7 (b) and airvelocity (Fig. 7(c) show some contradictions whenall the HTV application strategies were found toperform better when the windows and doors wereopened. Moreover, the effect of openings is moreobvious in the reduction of temperature using HTVfor Attic strategy when its application in the openedcase shows much more promising resultscompared to when openings were closed.Thisresult demonstrates that if the application of theHTV for Attic strategy is simultaneouslyaccompanied by the HTV for Indoor strategy toextract the hot indoor air out, the best indoorthermal condition could possibly be achieved (Fig.7(a). This will indicate the most efficient applicationstrategy of the HTV under this hot and humidclimate region.

In this study, the mean value of the OperativeTemperature, (OT) and Standard EffectiveTemperature (SET*) achieved by the differentHTV application strategies were compared toevaluate the thermal comfort improvement. The

Mean Min Temperature Dif (°C) Mean Max R. Humidity Dif (%)

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Natura l Ventilation HTV for Indoor (fan a t ceiling level) HTV for Attic

Fig. 6. Comparison of the mean minimum value of indoor-outdoor temperature difference and mean maximumvalue of indoor-outdoor relative humidity difference for different ventilation strategies

(windows and doors closed)

Hybrid Turbine Ventilator

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temperature difference c) mean maximum indoor air velocity

Ventilation Strategies

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value of OT was taken as the average temperatureof Indoor Temperature and Mean RadiantTemperature (MRT), since air velocity is found tobe <0.2m/s and MRT is within 4°C at all the timefor the closed case. As for the opened case, theexpression below was used since there weresometimes air velocities exceeded 0.2m/s.

to = Ata + (1-A) tr

where to = operative temperature (°C), A = 0.6for air velocity between 0.2 and 0.6m/s, ta = airtemperature (°C) and tr = MRT (°C).

On the other hand, the Software ASHRAEThermal Comfort Program V1.0 was used tocalculate the SET* with metabolic rate wasassumed to be 1.0 met and clothes to be 0.5 clo.Forthe purpose of comparison, the value of differencesbetween the mean OT and mean SET* of theroom compared to mean outdoor temperaturewere used as comparison tools. In this case, thevalues achieved by the existing condition wereacted as base cases and the percentage ofreduction achieved by each strategy wereevaluated to find out the most efficient strategy.In addition, the number of hours of OT and SET*achieved by each strategy which were above the

Table 2. Comparison of the difference between mean OT and mean SET* compared to mean outdoortemperature and reductions achieved by different ventilation strategies (a) Closed Case (b) Opened Case

Operative Temperature (OT) (°C)

Standard Effective Temperature (SET*) (°C)

(Closed Case) Mean OT–Mean Outdoor, dT (ºC)

Reduct ion (%)

Mean SET*–Mean Outdoor,

dT (ºC)

Reduction (%)

Without HTV 0.7 - 1.2 - HTV for Indoor (fan a t ceiling level) 0.5 28.6 1.0 16.7 HTV for Indoor (fan near roof level) 0.3 57.1 0.8 33.3

HTV for Attic 0.6 14.3 1.1 8.3

(a)Operative Temperature (OT)

(°C) Standard Effective Temperature

(SET*) (°C) (Opened Case) Mean OT–Mean Outdoor, dT (ºC)

Reduction (%)

Mean SET*–Mean Outdoor, dT (ºC)

Reduction (%)

Without HTV -0.2 - -0.1 - HTV for Indoor (fan at ceiling level) -0.5 60.0 -1.0 90.0

HTV for Indoor (fan near roof level) -0.4 50.0 -0.3 66.7

HTV for Attic -0.6 66.7 -0.5 80.0

(b)

upper comfort limit of 28.5°C were also countedin order to make a subjective conclusion of theeffectiveness of the HTV in satisfying people’sthermal comfort in this region.

From the findings that are summarized inTable 2, it can be concluded that the comparisonresults of thermal comfort improvement is almostin line with the finding from ventila tionperformance comparison. For the closed case, thehigher reduction of OT and SET* when the fanwas at roof level strategy compared to when thefan at ceiling level strategy is the same like inprevious comparison. A detailed analysis thenrevealed that the lower OT and SET* achieved ismainly due to the higher 3 days average of solarradiation received by the first strategy, which is378.5w/m² compared to only 324w/m² for the laterstrategy. This condition illustrates that the higheraverage of solar radiation received means that thehigher rate of the extractor fan produced and moreconstant its operation would be.

However, in general both HTV for Indoorstrategies showed better performances comparedto HTV for Attic strategy, especially in the closedcase when it succeed to reduce OT by 28.6% to57.1% and SET* by 16.7% to 33.3%. But, the

Ismail, M. and Abdul Rahman, A. M.

W ithout HTV HTV for Indoor(fan-ceiling)

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HTV Applica tion Stra tegiesOutdoor DBT Operative Temperature (OT) SET*

Fig. 8. Frequencies of number of hours above the upper comfort limits for different ventilation strategies whenwindows and doors are opened

relatively higher reduction of OT and SET*achieved by the HTV for Attic strategy in theopened case, which is 66.7% for OT and 80% forSET* show that this strategy is also significant ifthere is an avenue for the heat radiated from theceiling to be expelled out.

The results from the study regarding thefrequencies of temperatures above the comfortlimits confirmed the potential of this attic ventilationstrategy when the percentage of OT and SET*achieved in the range of comfort level is almostas efficient as with HTV for indoor strategies, ifoutdoor condition is taken into account. By thegraph of this opened case Fig. 8. it can be concludedthat although all the HTV application strategiesshow better performances than the existingcondition, the fact that 75% to 90% of the OTand 75% to 95% of the SET* were above theupper comfort limits of 28.5°C revealed thatsignificant enhancement should be made to thedevice and its application strategy. One possiblesolution derived from the results is by applyingthe HTV for both occupied space and attic spaceat the same time and ensure that openings arekept opened.

CONCLUSIONA study to investigate the most efficient HTV

application strategy in improving thermal comfortcondition was carried out in a medium size roomwithin an institutional building. Using simplifiedcomparisons of thermal comfort indices, the pros

and cons of each strategy were identified. Theresults show that:1)The strategy of the HTV for Indoor (fan atceiling level) with windows and doors are keptopened is the most effective HTV applicationstrategy, especially in terms of inducing higher airvelocity in the occupied level. The ability to induceair velocity of up to 0.38m/s and to decrease theair temperature and relative humidity by up to0.7°C and 1.7%RH in average have resulted inreducing the levels of OT by 60% and SET* by90% compared to the existing condition.2)However, a lthough the mean indoor airtemperature and relative humidity produced by twoHTV for Indoor Strategies i.e. fan at ceiling leveland fan near roof level are lower than existingcondition and HTV for Attic strategy, theperformance between both strategies is not verymuch different in terms of those profiles. Thisindicates that the reduction of air temperature andrelative humidity levels are more influenced byAir Change Rate (ACH) and ventilation ratewhich in this context is mainly determined by thecorrelation between the rotation rate of the solar-powered extractor fan and the level of solarradiation it received.3)From the results, it was also found that commonapplication of the turbine ventilator which is forattic space alone is not very efficient strategy sincethe air temperature and relative humidity producedin the occupied space was higher compared toboth HTV for Indoor strategies, except during theevening when it showed better performance.

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However, it was observed that the HTV for atticstrategy was able to reduce the attic airtemperature by approximately 1.0°C in averagecompared to the existing condition of the atticspace, and was also helpful to improve theoccupied space conditions by reducing the SET*level by 80% in the opened case. These resultsshow that this strategy is also significant if it issimultaneously accompanied by another strategyto extract hot occupied space air which is radiatedfrom the ceiling out to the outside.4)Generally, it can be concluded that although allthe HTV application strategies achieved toproduce relatively lower air temperature andhumidity compared to existing condition of theroom, its effectiveness in satisfying people’sthermal comfort condition in this hot and humidtropical region is far from acceptable. The meanOperative Temperature (OT) and StandardEffective Temperature (SET*) of around 29.0°Cto 30.0°C which were equivalent to 70% -90% ofthe time i.e. from 9.00am to 10.00pm were outfrom acceptable upper limit of comfort conditionshows that a significant enhancement should bemade to improve the device. Thus, since the studyclearly shows that reducing an air temperatureand humidity in the attic is equally important as inthe occupied space, so the applications of the HTVfor attic and occupied space at the same time couldbe a possible answer.

ACKNOWLEDGEMENTThe authors would like to thank the Research

Creative Management Office (RCMO), UniversitiSains Malaysia (USM) for the financial supportprovided for this research project.

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