the influence of building envelope design towards internal heat gain, thermal comfort and ac system

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The Influence of Building Envelope Design Towards Internal Heat Gain, Thermal Comfort and AC System

THE INFLUENCE OF BUILDING ENVELOPE DESIGNTOWARDS INTERNAL HEAT GAIN, THERMALCOMFORT AND AC SYSTEM

Khotijah Lahji, Yasseri D. Apritasari and Eka Sediadi Rasyad

Departement of Architecture, Faculty of Civil Engineering and Planning, Trisakti University, Jakarta,[email protected]

ABSTRACT: The room thermal comfort can be realized through building envelope design relatedto tropical architecture and/or green building design concepts. The design concept aims toreduce the heat gain and minimize the cooling load for the mechanical air conditioning; it is one ofthe primary focuses in the building energy policy nowadays. This paper discusses the use of airconditioning system on the 8th & 9th floor of a building which used as an Auditorium. The studywas aimed to find the relationship between (1) the influences of building envelope design towardsinternal heat gain, internal thermal comfort of the occupants and (2) the efficiency of air conditioningsystem. The research steps were: (1) Measuring the internal temperature and its humidity, (2)Administering data of the existing building envelope (orientation of the opening and buildingmaterials), room volume, occupants activities and the micro climate analysis using archipacsoftware to find out the internal heat gain, the profile of temperature and humidity in the coolestand hotest month every day of the year (3) Mapping the internal and the average thermal comfortof the occupants. The result of the study shows that there is a different profiles of temperature inthe building which affecting the efficiency of the mechanical air conditioning. In the coolestmonth, the daily period of comfort could merely covers the building for two hours long while inthe hottest month, 90 to almost 100 % of the building is overheated.Keywords: building envelope, heat gain, thermal comfort, air conditioning system

1. INTRODUCTION

The Indonesian climatic condition is tropical humid, with high temperature and high humidity. Thiscondition entails overheating/uncomfortable for the occupants of any building. High sun radiationthrough building envelope reates internal heatgain, resulted in a high load air conditioner (AC). Thispaper discusses the use of material, the orientation, and design of the building envelope which caninfluence internal heatgain in the building. The object of the research was an auditorium located onthe 8th & 9th floors of D building which consists of nine floors at Trisakti University in Jakarta. Theresearch steps were conducted in several ways e.g. : (1) by measuring the internal temperature andits humidity, (2) by measuring comfort of the occupants, (3) by gathering data the existing load andAC system, (4) by mapping the internal and the average thermal comfort of the occupants, (5) bygathering data of the existing building envelope (orientation of the opening and building materials),the room volume, the occupants activities and the micro climate analysis by using archipac softwareto find out the internal heat gain, the profile of temperature and humidity in the coolest and hottestmonth every day of the year.

According to Santamouris (1996) thermal performance can be understood as indoor controlledmethod through the design of building envelope (orientation of the opening, characteristic and

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physical of the building materials: massive/tranparants and the use of construction). Moreover, thethermal performance is considered successful if indoor condition of the building is psycologicallyfelt comfortable by the occupants (occupants sensation).

The use of AC system is an effort to reach the termal comfort. The empirical study done atBPD building in Jakarta states that the percentage load of AC heatgain in that office building consistsof 10-15% human heatgain, 40-50% of sun radiation through the window glasses, 15-20% of heattransmission through the massive envelope of the building, 7-8% of heat ventilation, and 8-10% ofheat equipment and lighting (Simbolon, 1981). These measurements are applicable in gettingappropriate temperature and humidity of the AC system.

2. CLIMATIC CONDITION

The climatic condition in a year in Jakarta as it is shown in Table 1 that the average air temperatureis 24.1ºC-32.1°C, and the humidity rate (RH) is 52%-95%. The previous outdoor temperaturerepresents the rate score of thermal comfort.

Table 1: The yearly climatic condition in Jakarta

Jan Feb Mar Apr Mei Jun Jul Agt Sep Okt Nop Des

T Max 30 30.6 31.8 32.5 32.9 32.8 32.9 32.6 32.9 32.6 32.2 31.2T av max 32.1 32.1 32.1 32.1 32.1 32.1 32.1 32.1 32.1 32.1 32.1 32.1Sd max 1.5 1.1 0.2 0.3 0.6 0.5 0.6 0.4 0.6 0.4 0.1 0.6T Min 23.7 23.7 24.1 24.9 24.5 24.5 23.9 23.5 24 24 24.5 24.3Sd Min 0.3 0.3 0 0.6 0.3 0.3 0.1 0.4 0.1 0.1 0.3 0.1T av Min 24.1 24.1 24.1 24.1 24.1 24.1 24.1 24.1 24.1 24.1 24.1 24.1RH am 95 95 94 92 91.3 90 88 87.3 87.6 89.6 92.3 93.3RH pm 69 66.3 63 60.3 58 56.3 52 52.3 52 58 58.6 64Rain 309 280 348 297 147 146 3 36 97 47 201 271

Source: BMG-Indonesia 2006

The climatic analysis employs psycometric chart method shows that indoor temperature everymounth of a year is uncomfortable for the occupants (overheating occupants sensation), or thiscondition is at above the comfort zone. The Szocolay’s theory (1987) describes about the methodpassive control, and this method is appropriate for humid tropical climate through indoor airmovement. The air movement is important to decrease the temperature and humidity in order toreach indoor comfort zone. If the air/wind flows at the speed of 1 until 1,5 m/sec, the room will becomfort, as it is shown in Figure 1.

The specific problem of humid tropical climate is overheating almost 8 until 10 hours everyday (33,3%-50%), it is usually happened from 10.00 until 15.00. This uncomfortable condition canonly be reduced by the use of AC system and the air/wind movement. In this study, the thermalcomfort and energy efficiency can be reached through the use of AC system by considering thehottest (May) and coolest months (January) as it appears in Table 1. The outdoor climatic condition


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influences the internal temperature and humidity in which in the coolest month the load of ACsystem is least regarding the less heat radiation. As such in the hottest month, the load of AC systemwill be much more because the load of heat radiation through the building envelope is also consideredhottest.

3. OBJECT DESCRIPTION

The explanation in this section will cover measuring of the internal temperature and its humidity,gathering data of the existing building envelope, the room volume, the occupants activities and themicro climate analysis by using archipac software to find out the internal heat gain, the profile oftemperature and humidity in the coolest and hottest month every day of the year, mapping thetemperatura, humidity and the occupants sensation.

Figure 1: The Analysis of micro climate by psychrometric chartSource: Analisis ARCHIPAK, Szocolay2002


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3.1 The Existing condition

Trisakti University auditorium is the part of Trisakti University building complex (campus A) on the8th & 9th floors of D building in Jakarta which is located in the urban area. The D building consists ofnine floors, each floor is 1071 m², the auditorium is 791 m², and the heigt ceeling is 8,4 m. Thebuilding is quadrangle (see Figure 2 and 3).

The material of the buiding envelope at the auditirium are:

1. The floor is made of concrete finished by carpet and vinyl.2. The ceeling/plafond is made of accoustic gypsum tile of 6 mm thick.3. The walls are double: external and internal walls, the external wall is made of brick panel in

ceramic tile, and the internal wall is made of double teakwood of 4 mm thick with glasswool asaccoustic tile in beetwen.

4. The top/roof floors are made of concrete with screed and waterproofing tile.

3.2 The Building Envelope

The front and back sides (south-north) of the building envelope at the auditorium have the samefasades, however, the material of the building envelope used 60% of massive wall/brick panel and40% of transparants wall/window glasses with 1 m sun-shading. The east and west sides design ofthe building envelope used 70% massive wall/brick panel and 30% of transparants wall/windowglasses with 1 m sun-shading (see Figure 2 and 3).

The D building uses centralize AC system to decrease the indoor temperature and humidity. Inthe auditorium 2 package units are added each of which consists of 5 TR AC at the front of the room(stage area) and at the back of room as well because the state condition of the stage are is hot.

Figure 2: The elevations and sections of the building in 2006

The righ and left elevation The section of building


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3.3 Occupants Activities

The auditorium has the average capacity of 380 people which can accommodate formal activitiessuch as seminars and workshops. The following Figure 4 shows the measuring result of the occupantssensation.

Figure 3: The D building as object of the research

Figure 4: The percentage of occupants’ sensation


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In the morning (at 10.00-12.00) that 55% of the respondents state that they feel comfort, 35%feel cool, 5% feel hot uncomfortable, and 5% feel cold uncomfortable. In the afternoon (at 12.00 –15.00) the occupants sensation significantly decrease to 38% feel comfort, 43% feel cool, 0% hotuncomfortable, 19% feel cool uncomfortable. These different conditions are resulted by high externalheat gain (the sun radiation) through the building envelope, so the load of the AC system is bigger.

3.4. Measuring the Temperature and Humidity in the Auditorium

The measuring of indoor/outdoor temperature and humidity was carried out at the same time, twicea day every day in a week at 24 points for seeting and standing positions. The 24 points of measuringcan be seen in the following Figure 5.

.

Figure 5: The points of measuring of the temperature and humidity in the auditorium

Table 2: Outdoor temperature

No Room Time : 10.00-12.00 Time : 12.00-15.00

Temperature Humidity Temperature Humidity

18 I 29.5 59.0 30.0 56.119 II 29.5 56.6 30.3 56.320 III 29 59.5 30.7 53.821 IV 29.1 57.3 30.4 57.3

Source: The existing temperature in Dec 2007


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4. THE ANALYSIS OF THERMAL PERFORMENCE

4.1 Mapping of the Thermal Comfort

The mapping activity was done to acquire information regarding the thermal comfort zone or thethermal uncomfort zone. The mapping variables are: temperature, humidity and occupants sensationin the auditorium while the AC system was being operation. The average of thermal comfort inJakarta is between 24,9ºC-27,9ºC (Karyono, 2003) and the average humidity is between 50-70%(Purbo,1996). The results of measuring temperature and humidity at the 24 points at the two timesmeasurements (morning and afternoon) as is shown in Figure 6 and 7 which describe the temperaturemappings of seating and standing positions.

a. The temperature variable

For the mappings, the researchers use yellow, blue, and red colors in which the red color is anuncomfortable zone, the yellow color is a comfort rather hot/warm zone, and the blue color iscomfort zone. The red zone represents high temperature between 10.00-12.00 and 12.00-15.00 thisis because at this side, the door is always open and of heat transmission through the building envelopefrom west side. Because the heat radiation of the west side is bigger from the other sides, the westzone is uncomfortable zone (hot). To create thermal comfort at this position, it needs additional aircool distribution of AC system accordingly (load/install AC).

Figure 6: Mapping of the morning temperature (10.00-12.00)

Figure 7: Mapping of the afternoon temperature (12.00-15.00)


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b. The humidity variable

The result of measuring temperature and humidity at 24 points as is shown in Figure 8 and 9 in whichthe red color represents 10.00-12.00 and 12.00-15.00 which is uncomfortable zone therefore itneeds additional humidity of AC system to the room condition appropriately.

c. The occupants’ sensation variable

Based on the result of the questionnaire, mapping situation of the occupant sensation is shown inFigure 10 and 11.

The violet colour represents uncomfortable rather hot zone at points 1, 2, 3 which is the stagearea and is usualy used as presentation area with quite formal clothes. The same condition appearsat point 23 because the air cool distribution of AC system cannot be gained through the backceeling. The point 6 is uncomfortable zone because of the door is always open. Because of theuncomfortable conditions of these several points, it is suggested to add air cool distribution from theAC system as necessary. The green colour is comfortable zone which is mostly located at east,front and middle sides. The blue colour represents comfortable rather cool zone at middle and westsides.

Figure 9: Mapping of the humidity at 12.00-15.00

Figure 8: Mapping of the humidity at 10.00-12.00


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4.2 Analysis of Thermal Performance

The simulation of ARCHIPAK program is used to analyze the thermal performance of the auditoriumon May and January as the hottest and coolest months of the year. To gather the result of temperatureprofile (thermal performance), we supply data on room volume, percentage of heat gain material ofthe building envelope (massive and transparent), and heat orientation.

Figure 10: Mapping the occupant sensation at 10.00-12.00

Figure 11: Mapping the occupant sensation at 12.00-15.00


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Table 3: Heatgain percentage of the building material and orientation

Element Orientation% Heatgain

Hottest month Coolest month

Floor wall 0 (north) 1.1% 1.3%wall 90 (east) 0.6% 0.7%.window 90 (east) 43.4% 42.9%wall 180 (south) 2.2% 2.7%wall 270 (west) 0.5% 0.7%window 270 (west) 43.6% 43.1%roof 8.6% 8.6%

Source: Simulasi ARCHIPAK

The windows are made of clear glass with west-east orientations which provide highest heatgaincontributions in bulding, but because the glasses have the high u-value, the east-west sides hashead-cooeficient value twice bigger than north-south sides.

a. The hottest month (May)

Figure 12: The temperature profile in the hottest monthNote: To: outdoor temperature, Ti: indoor temperature, Tb: lowest thermal comfort,

Ta: highest thermal comfort l, violet zone: indoor time of activity.Source: the result of simulation analysis by using ARCHIPAK program


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The result of archipak simulation shows the following auditorium’s temperature profile: indoortemperature profile is higher than outdoor temperature at 22.00 until 17.00, and at 17.00- 22.00 theindoor temperature is lower than outdoor temperature. The outdoor condition is overheating at09.00-23.00, and the indoor condition is overheating at 24.00-08.00. The comfort period is at 24.00-08.00. This analysis shows that when the room is in use, it is overheating. The overheating conditionis caused by transparent design of building envelope (windows made by glasses) and west-eastorientations. The auditorium is located on the 8th and 9th floors of the building (top floors), so the heatgain from the top roof contributes heat in the building. This simulation emphasizes that maximumtemperature of the auditorium in the afternoon (14.00) is 33.8°C.

b. The coolest month (January)

In the coolest month overheating periode is 10 hours (09.00-18.00), and the comfort periodeis 14 hours (18.00-09.00), and the maximum temperature at 15.00 is 31.7°C. The comfort periodein the auditorium is only for 2 hours (08.00-09.00). This condition is the same with the hottestmonth that the internal temperature is higher than external temperature. The average internaltemperature increaces to 0,52K in the coolest month and 0.95K in hottest month, as it shown inTable 4.

Figure 13: Temperature profile in the coolest month

To: outdoor temperature, Ti: indoor temperature, Tb: lowest of thermal comfort,Ta: highest thermal comfort l, violet zone: indoor time of activity.

Source: the result of simulation analysis by using ARCHIPAK program


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Table 4: Analysis of comfort period and overheating

Hotest month (Mei) Coolest month (January)

Comfort Overheating Ti Max Comfort Overheating Ti Maxperiods periods periode periode

Auditorium 0 (-) 10 jam 33.8°C. 2 jam 8 jam 31.7°C(08.00-17.00) (14.00) (jam 08.00-09.00) (08.00-17.00) (15.00)

5. CONCLUSION

The comfort condition is constantly decreased from morning until afternon. The different positionscan provide different comfort of the occupants sensation. This condition is caused by the unbalancedair cool distribution of AC system in the room. The starting of high radiation at daytime is notfollowed by appropriate indoor temperature of AC system. The different comfort zones at everyposition in the auditorium is caused by external heatgain of the building materials at west side, andheat ventilation from the opening entrance. In addition, formal clothes required to be wear at thestage area contribute uncomfortable sensation to the occupants because of the lack of air cooldistribution from the AC system. To minimize the heat condition and to use the energy efficiently inthe auditorium, it is advisable to install additional AC system by balancing and arranging the distributionof air cool each time of the day accordingly.

The highest temperature in the building is caused by heat sun radiation through glass wall atwest/east sides, heat conduction of building envelope material and internal heatgain (occupant,equipment and lighting). The indoor temperature in the coolest month has two hours of comfortwhile at the hottest month there is no comfort period. This situation represents that there is 90-100%overheating when the auditorium is being occupied. The maximum indoor temperature at 14.00-15.00, therefore, the temperature of AC system can be reduced accordingly in order to reachthermal comfortable or the load of AC system need to be increased.

REFERENCES

Badan Meteorologi dan Geofisika, Departemen Perhubungan (2006). The climate data in Indonesia, Jakarta.Evans, Martin (1980). Housing, Climate, and Comfort, The Architectural Press Limited, London.Karyono, Tri Harso (2001). Teori dan Acuan Kenyamanan Termis Dalam Arsitektur, Jakarta: Catur Libra

Optima.Poerba Hartono ( 1996 ). Utilitas bangunan, Jakarta : Penerbit Djambatan, Jakarta.Santamouris, M. et al., (1996). Passive cooling, London. Applied Science Publishers Ltd.Santosa, Mas (1986). Energy Conservation Through Urban Settlement Pattern. Adelaide Proceeding World

Planning and Housing CongressSimbolon,T. B. (1981). Fisika Bangunan, Jakarta: Penerbit Instasi Pemda DKI, Penerangan Jalan Umum.Szokolay, S. V. (1987). Thermal Design of Building, Australia. RAIA Education Division.Van Straaten, J. F. (1980). Passive Cooling and Heating Through Building Design, University of Miami,

Florida. Proceeding Seminar Passive and Low Energy Cooling, Heating and Dehumidification.


the influence of building envelope design towards internal heat gain, thermal comfort and ac system

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