Prediction of the hourly temperature in a Kuwaiti house

Solar & Wind TectmologyVol. 2, No. 3/4, pp. 183--189, 1985 Printed in Great Britain.

0741-983X/85 $3.00+ .00 Pergamon Press Ltd.

P R E D I C T I O N OF T H E H O U R L Y T E M P E R A T U R E HOUSE ADNAN M. WAKED* and N~REm~ K.

IN A K U W A I T I

GHADDAR

Mechanical Engineering Department, Kuwait University, Kuwait

(Received 27 April 1985; accepted 7 July 1985) Abslract--The bihourly room temperature inside a passively designed house in Kuwait, without backup heating and cooling, is studied, for both the original design and with the addition of thermal insulation to the house walls and roof. The calculations were performed using the Goldstein-Lokmanhekim method to find the floating temperature inside the house and to see the effectofthermal insulation on this temperature and also on the energy requirement when mechanical cooling is used. Results show that adding insulation will reduce the cooling energy requirement, but insulation is found to be unnecessary when no mechanical cooling is used.

INTRODUCTION

Passive solar buildings frequently operate in the floating temperature mode, in which heat gains and losses result in changes in room temperature rather than heating or cooling loads. Actually a building can be designed such that its temperature always floats in the comfort region with as low energy requirements for heating and cooling as possible. This is an important aspect for a builder in Kuwait where the weather is characterized by hot, dry summers and cool winters. For 7 months of the year, April through October, the temperatures are substantially above comfort levels and intense solar radiation occurs. This requires continuous and intensive mechanical cooling to bring down the indoor temperature, whereas the weather in winter is fairly cool and energy demand is not as severe as in summer. The floating temperature on a design day is one of the most important measures of the building performance. Changes can be made in building design so as to affect different aspects of floating behaviour, such as increasing the thermal mass of walls or adding more insulation. The prediction of floating temperature inside the building is done using the GoldsteinLokmanhekim method on a TI-59 hand calculator. The inputs to the program are: (a) Building design parameters such as thermal conductances, specific heats and densities of the building materials.

(b) Weather parameters which include daily solar heat gain for design days, average ambient temperature, day length from sunrise to sunset and typical diurnal temperature fluctuations. The calculations will describe the building's response to design days, i.e., days with idealized sinusoidal weather. The mathematical model employed [1, 2] describes the thermal behaviour of buildings using Fourier Response Functions, incorporating the effects of thermal storage of the massive walls and insulation. Although the model used has some limitations, still by studying the room temperature response to solar and temperature input, one can learn much about heating and cooling needs of the building. For each month of the year an average design day is considered for the caiculaton of the floating room temperatures. The calculations are first performed without backup heating or cooling in the house. Then the supplementary heating or cooling required to bring room temperature to comfort level are computed for each month of the year and compared for the two design modes, i.e., before and after adding insulation--to the building envelope. The house shown in Fig. 1, is a two-storey residential structure of conventional Kuwaiti construction, with its main entrance facing east. THE HOUSE PARAMETERS

Case I : the original design The house was divided into a number of different types of construction sections. Each section is associated" with a surface facing the inside of the

*Mechanical Engineering Department, Kuwait University. Kuwait. 183

184

ADNAN M. WAKED and NESREEN K. GHADDAR

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building. Once the surfaces have been established, the fraction of solar radiation entering the house and absorbed by each surface ~ is estimated. Since the number of sections or surfaces is limited to three, the number of materials can be reduced with good approximation, by combining materials of similar properties into a single material with averaged properties [3, 4]. Thus the house was divided into three delayed heat transfer construction surfaces. These surfaces and their thermal properties and the necessary design parameters are given in Table 1.

It was also calculated that the fraction of solar energy entering the house and absorbed on light surfaces is ~ = 0.15. Using the appropriate values for the heat transfer coefficient U for the different parts of the house the design heat loss values per degree temperature difference were calculated and shown in Table 2.

Case II : the original design with added insulation To see the effect of insulation on the floating temperature inside the house, an alternative design with insulation added to the house walls and roof was

Table 1. The construction surfaces with their design parameters Construction surface design parameter d(m) R (m2 C W-t) h ( W m - 2 C -1) K (W m--t C-t) pC (kJ m - D C - i) A (mz)

Envelope walls

Partition wall with floor

Roof with partition walls

Case 1" Case II** Case I* Case II** Case I* Case II** 0'22 0-3l 8.12 0.92 1600"6 0"1 545

0-22 0'13 0-13 0.16 0-16 1-36 4.52 4.52 1.63 3-49 8-12 8-60 8.60 9-3 9.3 0-92 1-05 1.50 1.21 1.21 1600"6 1817"7 1817"7 1698-1 1698.1 0"1 0"425 0-425 0"325 0"325 545 570 570 418.57 418.47

* The original design. ** The design with added insulation.

187

Prediction of the hourly temperature in a Kuwaiti house Table 2. Design heat loss values {q) per degree temperature difference U (W m-2°C -I) House component Stairway roof House roof Floor House enveope walls Attic walls Glass windows Wooden doors

A (m 2)

q = UA

(W C -1)

Case I

CaseII

Case1

CaseII

CaseI

CaseII

1.19 1'01 0'5 1'51 1.1 4"9 1.93

0.522 0.522 0"5 0.582 0.581 4-9 1-93

22.5 209.3 231.8 507-1 37.9 48'27 3.4

22.5 209.3 231.8 507.1 37.9 48.27 3.4

26"8 23ff2 115.9 765.7 41.7 236"5 6.6

11.75 109-3 115.9 295-1 22"0 236-5 6-6

considered. In the walls an insulation material of resistance R = 1.2 m 2 C W - 1 is to be filled in place of the air space. The same insulation material will replace the vermoculite in the roof. The design parameters in this case are given in Table 1, and the design loss values per degree,temperature difference are given in Table 2.

To study the house performance over the year an average design day for each month of the year is considered. The weather data taken from references [5, 6] was used to calculate the period of solar gain (td), the amplitude of daily solar gain through glass (S), the average ambient temperature for the design day (Ta), the amplitude of diurnal temperature fluctuations (ATA), the time from midnight to time of maximum temperature (q51) and the time from midnight to sunrise (~b2).The values of these parameters are shown in Table 3.

minimum temperature of 13-1°C in January. The temperature swing, which is the difference between the maximum and minimum temperature for the month, lies between 1.8 and 3.7°C. The temperatures shown in Table 5 show the bihourly temperature inside the house after applying insulation to the house, envelope walls and roof. In this case the maximum yearly temperature of 39.5°C occurs in July and the minimum is 13-8°C in January. The temperature swing lies between 1.6 and 2.6°C. The comparison between the temperatures inside the house in both considered cases is shown in Fig. 2. Though adding insulation to the house has reduced the temperature swing, the average inside temperature is higher for the insulated house. On the other hand adding insulationto the house will reduce the house's cooling and heating loads by a significant factor. Table 6 shows that the saving in the cooling load would average out to about 34%.

RESULTS

SUMMARY AND CONCLUSION

Table 4 shows the bihourly temperature inside the house in its original design. The maximum yearly room-temperature of 30°C occurs in July, and the

Passive solar design is one of the promising conservation strategies which can reduce spaceheating and cooling needs significantly. The original

Weather parameter

Table 3. Weather design parameters for a typical year in Kuwait Paramater Month

S(W)

~l (h)

O2 (h)

td (h)

n/td

January February March April May June July August September October November December

9836 9798 9504 9802 9261 9124 9021 10294 11116 11212 10776 10180

- 15'5 - 15.5 - 15 - 15 --14.7 - 14.8 - 15.5 - 15.5 - 15"5 - 15-5 - 15'5 - 15'5

-6.75 -6.5 -6"0 - 5"35 --5.0 -4"8 --5"0 -5-26 - 5"15 - 5.6 -6'25 -6'35

10-38 11.15 12.48 12.86 13.62 13.98 13.83 13.16 12.33 11.46 10-7 10.28

0"3 0-282 0'252 0-244 0-230 0-225 0-227 0"239 0"255 ff274 0-293 0'305

T~ (63 13 15 18"5 23 " 31.8 32.4 36.7 34"5 32"3 • 31 21.5 20

ATA (63 4'2 5.1 3.4 6'3 6.9 6.9 5.4 6.4 6.9 7.7 4-4 4.4

188

ADNAN M. WAKED and NESREEN K. GHADDAR

Table 4. The bihourly temperature inside the house (:C) Time

Jan

Feb

Mar

Apr

May

June

July

Aug

Sept

Oct

Nov

Dec

M 2 4 6 8 10 N 14 16 18 20 22

13.9 13.5 13.1 13.1 13.2 14.7 14.3 14.8 14.9 14.9 14.8 14.3

16 15-5 15.1 15-1 15"4 16.0 16-7 17.2 17-4 17.3 16.9 16'5

19.4 18"9 18.6 18.6 19 19.7 20.4 20.9 21 20.9 20.5 20

23.8 23-2 22.9 23 23.5 24.2 25 25.5 25.8 25.6 25.1 24.5

32.3 31.8 31-4 31.5 31.7 32.9 33.7 34-3 34.5 34.2 33.7 33

34 33.6 33 33.1 33.6 34.4 35.2 35.8 36 35.9 35.4 34.7

37.4 36.9 36-6 36-5 36.9 37.3 38.2 38.7 39 38.9 38.5 38

35.4 34.7 34.3 34.3 34.7 35-4 36.2 36.8 37-I 36-8 36.6 36

33 32.4 32 32.1 32.7 33.5 34-3 34-9 35-1 34.9 34.4 33-7

31.9 31.1 306 30.4 30.8 316 32'5 333 33.6 33.6 33.3 32-7

22.4 21-9 21-6 21.6 21.9 22-5 23-1 23.5 23.6 23.6 23.5 23.2

20.8 20.4 20-1 20 20.3 20-9 21.5 21.9 22 21-9 21.6 21.2

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14

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19-8

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Table 5. The bihourly temperature inside the insulated fiouse {~C) Time

Jan

Feb

Mar

Apr

May

June

July

Aug

Sept

Oct

Nov

Dec

M 2 4 6 8 I0 N 14 16 18 20 22

14.5 14-1 13.9 13.8 14 14.6 15 15.3 15.4 15.2 15.1 14.8

16.6 16.2 16 15.9 16-2 16.2 17-3 17.17 17.8 17.7 17.4 17

20-1 19.7 19.5 19.6 19.9 20.5 20-9 21-4 21.5 21.3 21 20-5

24.6 24.1 23.9 24 24.4 25 25.7 26-1 26.2 26 25.6 25.1

33-1 32.6 32.4 32"5 33 33.7 34.3 34.8 34.9 34.7 34-2 33.6

34.7 34.3 34 34.2 34.6 35.3 35.9 36.4 36.6 36.3 35.8 35.3

38.2 37.7 37.5 37-5 37.8 37.8 38.9 39'3 39-5 39.4 39 38.6

36.1 35-6 35.3 35.4 35.7 36.4 37 37.5 37.7 37-5 37-1 36.6

33.8 33.3 33.1 33.2 33.7 34.4 35.1 35.5 35.6 35.3 34.9 34.4

32.4 31,9 31.5 31.5 32 32.7 33-5 34 34-1 34 33.0 33.~

23 22.7 22.5 22.4 22.7 23.3 23.8 24.1 24.l 24 23-7 23-4

21.4 21.1 20-9 20.8 21.1 21 6 22-I 22-4 22,4 222 21.1 2!.8

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Time, Fig. 2. Comparison between the inside temperatures for the original design and the design with added insulation.

design of the house did include some insulation in the root, and an air space was left between the sand cement block on tile interior side and the exterior side of the wall which is the sandlime brick. In the case when no backup heating or cooling is provided, it is noticed that the a d d e d insulation to the house has p r o d u c e d higher mean t e m p e r a t u r e o~.er all the design days. These results show that the adding of insulation does not necessarily contribute to the comfort of passively designed houses in hot climates. O n the other hand, it will definitely reduce the energy required to cool these houses if they are mechanica!13 cooled. The levels of insulation for different types e:" buildings in Kuwait are listed in the Kuwaiti Ener(ly Conservation Program: Code of Practice [771 (see Appendix I). O t h e r factors which can be effective in passive design, but not considered here are, the house's shape, color and orientation, windows and shading devices, etc. These factors are considered in m o r e detail in [5] and [871.

Prediction of the hourly temperature in a Kuwaiti house Table 6. The coolingload (kW) and the expected saving due to insulation Month

Case I

January February March April May June July August September October November December

- 19.33" - 12-15" . . 10.45 38.67 43-63 54 47.43 49.45 35.73 4.94 --

Case 11

% Saving

- 10.94" -6.35* . . 8"04 25"63 28"96 35.47 31.43 27-05 23.99 4.47 --

43 48 23 34 34 34 34 33 33 10 --

* Heating requirement.

The method used here for analyzing the building's thermal behaviour can be used as a good design tool for passive solar architects and also as a guide for adding passive solar modifications for existing buildings. NOMENCLATURE K p

C d h R % A q

thermal conductivity (W m - 1°C- 1) density (kg m - 3) specific heat capacity (kJ kg- ~°C- 1) thickness of massive construction (m) interior heat transfer film eoet~cient coupling surface to room air (W m-2°C -~) thermal resistance (m- 2oc- i W - 1) fraction of solar energy entering the house and absorbed by the surface fraction of solar energy which is absorbed by light surfaces total area of the surface facing the room (m 2) design heat loss of building per degree temperature difference through all quick heat transfer mechanisms (W°C- 1)

189

te S TA ATA O1

the length of day in hours from sunrise to sunset amplitude of daily solar gain through glass (W) average ambient temperature for the design day (°C) amplitude of diurnal temperature fluctuations (°C) (no. of h, from midnight to the time of maximum temperature) 02 no. of h from midnight to sunrise TR room temperature (°C). Tm mean room temperature for the design day (°C)

REFERENCES

1. D.B. Goldstein, M. Lokmanhekin and R. D. Clear, Desion Calculations for Passive Solar Buildinqs Usin# a Programmeable Hand Calculator. LBL-9371, EEB-W-79-09, U ni versity of California, Berkeley, California 94720 (1979). 2. D. B. Goldstein, Some Analytic Models of Passive Solar Building Performance.LBL-7811, University of California, Berkeley, California 94720 (1978). 3. T. R. Allison, The Buildino Materials of Kuwait. KISR/PPI081/ENB-PT-G-7902. Kuwait Institute for Scientific Research,. Kuwait (1979). 4. Building Division, Thermal Properties of Buildin0 in Arid Zones. KISR, Bldg. 2, VII, 74, Kuwait (1974). 5. S. M. Fereig, A. Waked, M. Shukry and S. Al-Sibakhi, The Effect of Insulation, Windows and Infiltration Rates on the Energy Consumption of a KuwaJti Villa. Journal of the University of Kuwait (Science), Vol. 10, No. 2. 6. Climatoloaical Data, Meterological Department, Directorate General of Civil Aviation, Kuwait (1980). 7. Ministry of Electricity and Water, Kuwait. Pub. MEW/R-6 Eneroy Conservation Proorara: Code of Practice (1983). 8. A. Waked, Energy conservation measures in Kuwaiti buildings. Proceedinos of First Regional Symposium on Thermal Insulation in the Gulf States, Kuwait Institute for Scientific Research (1979). APPENDIX 1

The recommended levels of insulation for ditIcrent buildings' construction are given in Table 7. The maximum overall U-value allowed for various types of walls is 0-1 and 0.07 (Btu h - ~ ft-2°F - 1) for roofs. Note that: 1Btu/h- aft- 2°F- 1 = 5.675 W/m- 2°C- a.

Table 7. Recommended U value in Btu/h- 1 ft - 2°F- 1for wails and roofs Description 1. Heavy construction, external color 2. Medium construction, medium/light external color 3. Medium construction, external color 4. Light construction, medium/light external color 5. Light construction, external color

Wall

Roof

0.075

0-045

0-085 0-075

0-06 0-035

0-075 0"065

0-05 0'03