Building tmdEra~lronment, Vol. 26, No. 4, pp. 363-369, 1991. 0360-1323/91 $3.00+0.00 Printed in Great Britain. © 1991 Pergamon Press plc.

An Analysis of Climatic Variables for Thermal Design of Buildings in Khamis Mushayt, Saudi Arabia

S. A. M. SAID* E. T. AL-ZAHARNAH*

In this paper, the microclimatic characteristics of Khamis Mashayt have been identified by analyzing isopleths for the dry bulb air temperature, wet bulb air temperature, relative humidity of air, wind speed and direction, and solar radiation. Comfort temperature ranges have been prepared and a comfort zone chart has been developed by applying these ranges to the dry bulb temperature isopleth. Based on the microclimatic characteristics, recommendations are presented for the design of buildings in the Khamis Mashayt area and may be extended for use in similar climates.

INTRODUCTION

THERMAL COMFORT in buildings can be achieved by the control of the thermal environment by the physical design of buildings. The first stage in this design process is to collect and analyse climatic data for the region of interest. The basic data required is summarized by Evan [1]. The data should relate to a long period since short periods will exhibit variations from the long term average. The predominant physical parameters which determine the thermal characteristics of a climate are: dry bulb air temperature, relative humidity, wind speed and direction, and solar radiation at a particular location.

The ways in which thermal comfort is achieved and the limits within which people are likely to feel comfort- able are given in Evan's study [1]. The diurnal periodic variation of climatic data provides opportunities for creative thermal design of buildings. Methods by which architectural design is developed in response to specific climatic requirements to achieve human thermal comfort in buildings are discussed by many authors [1-4]. One of these methods which provides opportunities for creative thermal design of buildings is the use of isopleth charts. Isopleth charts derived from long-term weather data are a unique means of summarizing the diurnal variation of climatic parameters throughout the year [5]. These charts can be analysed to find what corrective measures or design recommendations are needed to achieve thermal comfort. Many may be achieved by natural means (e.g. landscaping, structure openings, and orientation), where- as, others require mechanical air-conditioning.

The objective of this paper is to promote isopleth chart technique as an efficient and effective way to evaluate climatic design strategies through the presentation and analysis of climatic data for Khamis Mushayt.

* Mechanical Engineering Department, King Fahd University of Petroleum and Minerals, Dhahran-31261, Saudi Arabia.

KHAMIS MUSHAYT

Khamis Mushayt is situated in the geographic center of the southern region of Saudi Arabia. It is about 800 km southwest of Riyadh (capital) and about 500 km southeast of Jeddah in airline distance. It is located at an altitude of just over 2000 meters on a fiat plain. The city is divided by two valleys. The one on the east is Bishah Valley and the other one on the west is Atwood Valley. These two valleys join into one to the north of the city.

The climate of Khamis Mushayt is suitable for hor- ticulture. A number of farm gardens are developed along the valley beds. The Khamis Mushayt area is the sole part of the region where land can be cultivated with flood spread irrigation. It has a good water supply and as much as 300 mm rainfall. Irrigation agriculture has been practised using shallow wells, valley beds, or flood water. The main crops are cereals, fodder crops and vegetables. The total population of the city is estimated to be around 500,000. The activities of the city's population are in transportation, sales, craftsmen, commercial, construc- tion, trade, and manufacturing. Commercial activity in Khamis Mushayt has high potentiality. It is a major trading center serving almost the whole southern region. For more information about the city consult reference [6].

363

DATA BASE

Hourly values of the data were used to construct arith- metic mean hourly averages of the three parameters of interest (dry air bulb temperature, Relative Humidity, and wind speed and direction) for nine years of data recorded by the Meteorological Department [7]. The data tapes were available for the years 1970-74 and 1977-80 giving a nine-year data from which an average year set of hourly values could be constructed by simple arithmetic averages. This average year was used in the construction

364 S. A. M. Said and E. T. AI-Zaharnah

"k \ "19 [ '

3.00 !" ' ~ 5~ i ~ ~ ~ d--

13,00

23.00 ~ ~ J F H A M J J A S 0 N O

MONTH

Fig. 1. Dry bulb temperature (°C) isopleth for Khamis Mushayt : latitude 18°18'N, longitude 42°43'E, and 2066 m elevation.

J F M A H J J A S 0 N D

MONTH

Fig. 3. Relative humidity (%) isopleth for Khamis Mushayt : latitude 18°18'N, longitude 42°43'E, and 2066 m elevation.

1.00

3.00

5.00

7.00

900

110(

13,oc

15.01

170q

19.0'

21.0t

230

J F M A M J J A S O N D

MONTH

Fig. 2. Wet bulb temperature (°C) isopleth for Khamis Mushayt : latitude 18 ° 18'N, longitude 42°43'E, and 2066 m elevation.

100

3.00

5.00

7.00

9.00

11.0¢

13.0C

1S.01

170q

19,0'

21.0q

23.0

J P M A M J J A S 0 N D

MONTH

Fig. 4. Wind speed (knots) with predominant directions isopleth for Khamis Mushayt : latitude 18°18'N, longitude 42°4YE, and

2066 m elevation.

of isopleths of dry bulb air temperature, wet bulb air temperature, relative humidity, and wind speed, Figs 1- 4. These hourly values were then further reduced to yield monthly averages. Monthly average values of the required variables are listed in Table 1. Also monthly average values for dry bulb temperature, wet bulb tem- perature, relative humidity, and wind speed, as a function of hour of the day are shown in Table 2 A-D respectively.

The fifth parameter of interest is the total solar radi- ation. As is typical of many countries, solar radiation data collection and compilation has not received the same attention as other meterorological parameters in Saudi

Arabia. Two independent government agencies are involved in making radiation measurements; The Min- istry of Defence and the Ministry of Agriculture and Water [7,8]. The Ministry of Agriculture [8] has more extensive records of the daily average radiation for Khamis Mushayt in a hard copy form. Measurements have also been made by Saudi Aramco, some of the Universities, consultants etc. but these are seldom avail- able on a long term basis. No reliable recorded hourly solar radiation data were available. The hourly solar radiation data were generated from the daily radiation [8] by using the procedure described by Duffle and Beck-

Thermal Designs of Buildings in Khamis Mushayt

Table 1.Summary of climatic data for Khamis Mushayt, Saudi Arabia

365

Daily total Relative horizontal

Dry bulb temperature Wet bulb temperature humidity Wind speed radiation (°C) (°C) (%) (knots) wh/m2/day

Mean Mean Max Min diurnal Max Min diurnal Max Min

Month mean mean range mean mean range mean mean Max Min Mean

January 19.1 8.2 10.9 11.6 6.2 5.4 78.6 41.5 13.1 3.4 4707 February 20.5 9.3 11.2 12.0 7.4 4.6 75.6 38.6 13.0 3.4 5425 March 21.8 11.7 10.1 13.3 9.0 4.3 74.1 40.9 13.3 3.1 5967 April 24.5 13.1 11.4 14.0 9.8 4.2 70.6 32.7 11.9 1.7 6560 May 26.9 14.7 12.2 14.6 11.3 3.3 70.7 25.7 10.1 1.2 7034 June 29.7 15.8 13.9 14.6 10.6 4.0 58.0 17.0 10.6 0.7 7340 July 29.0 16.8 12.2 15.4 12.5 2.9 65.8 21.7 11.0 0.8 7520 August 29.1 16.9 12.2 16.1 13.2 2.9 70.2 21.7 11.0 1.1 7279 September 27.8 14.3 13.5 13.0 9.2 3.8 55.8 17.5 11.5 1.0 6690 October 24.5 10.9 13.6 12.0 6.3 5.7 55.8 22.5 9.0 1.4 5940 November 22.2 8.7 13.5 12.2 6.6 5.6 76.1 31.0 8.6 1.5 5117 December 20.1 7.0 13.1 11.7 5.8 5.9 84.0 37.5 10.0 1.4 4449

Annual mean 18.4 12.3 11.2 4.4 49.3 7.0 6169

Table 2(A) Monthly average dry bulb temperature as a function of hour of the day

Hour Jan. Feb. Mar. Apr. May Jun. Jul. Aug. Sep. Oct. Nov. Dec.

1 10 .1457 11.5763 13.7419 15.6423 17.2163 18.9062 19.4935 19.3569 18.2114 14.7101 11.6935 9.2398 2 9.5891 11.0424 13.3149 15.0038 16.4461 18.1021 18.8312 18.7575 17.2621 13.8362 11.0168 8.6799 3 9.1630 10.5867 12.8585 14.3470 15.9505 17.5714 18.2455 18.2667 16.4435 13.2034 10.5362 8.2289 4 8.7852 10.1385 12.4060 13.8489 15.5198 16.7987 17.6464 17.7338 15.5809 12.4077 9.8515 7.7111 5 8.4239 9.7247 12.0028 13.4472 15.0071 16.2262 17.0642 17.2426 14.9377 11.6370 9 .2715 7.2505 6 8.2828 9.4262 11.7379 13.1356 14.7746 15.8518 16.8457 16.8862 14.3439 10.9694 8.7359 7.0896 7 8.1773 9.3151 12.0642 14.4767 16.8750 18.4694 18.5121 18.0819 15.7789 11.9812 9 .0707 7.0075 8 10 .0387 11.6218 14.8387 17.6009 20.2506 22.2361 21.7174 21.1663 19.8682 16.1460 12.8282 9.8730 9 13 .0477 14.4046 17.0948 20.0867 22.6827 24.8533 24.1161 23.8496 23.1221 19.0906 15.7991 13.3328

10 15 .5429 16.7464 19.0758 21.9042 24.5150 26.7942 26.1176 25.9513 25.0636 20.9686 18.0882 15.8821 11 17 .2768 18.4775 20.3281 23.1209 25.7196 28.0088 27.5701 27.4217 26.2088 22.2097 19.8552 17.7349 12 18 .3632 19.5225 21.1977 23.9073 26.4697 28.7879 28.4645 28.4425 27.0730 23.1894 20.9030 18.8900 13 18 .9587 20.1868 21.6644 24.3652 26.9293 29.4599 29.0381 29.0663 27.6239 23.9736 21.7809 19.7132 14 19.1477 20.4943 21.7884 24.5158 26.9370 29.7067 28.9029 28.9950 27.8073 24.4456 22.1764 20.0589 15 19 .0210 20.4222 21.5361 24.0870 26.3788 29.5409 28.3622 28.3329 27.8379 24.5499 22.1485 19.9924 16 18 .4600 19.8257 21.1219 23.4282 25.4560 28.8094 27.6673 27.1937 27.2371 24.0098 21.4839 19.2577 17 17 .5249 18.9158 20.3365 22.4982 24.4485 27.9330 26.7516 26.1039 26.2052 22.9040 20.1201 18.0307 18 15 .9830 17.5182 19.0832 21.3433 23.3638 26.7292 25.6815 24.8595 24.8437 21.3887 18.3692 16.1461 19 14 .4602 15.9881 17.5706 19.9890 21.8262 25.2174 24.4047 23.3656 23.4806 20.0744 17.1017 14.8923 20 13 .4032 15.0170 16.6594 18.9937 20.8847 24.0287 23.3877 22.4741 22.5309 19.0840 16.0900 13.8215 21 12 .5090 14.1667 15.9785 18.1933 20.1181 23.1287 22.5736 21.8566 21.7431 18.1796 15.0686 12.6926 22 11 .8048 13.4339 15.3085 17.5815 19.4706 22.0333 21.7993 21.1065 20.9157 17.2229 14.0138 11.7219 23 11 .1992 12.7987 14.8363 16.9718 18.8771 20.8633 21.0036 20.4932 20.1302 16.3702 13.1506 10.8305 24 10 .6496 12.1799 14.2992 16.3931 18.0649 19.8558 20.2487 19.9608 19.1483 15.4230 12.3870 10.0345

man [9]. The hourly solar radiation data were calculated on the average day of each month as recommended in [9]; and these data have been plotted in the isopleth of solar radiation, Fig. 5.

A good summary for the influence of the four major elements o f climatic environment of interest (dry bulb temperature, relative humidity, wind speed, and solar radiation) which affect human comfort is given by Barakat Ullah et al. [5]. Table 3 shows the comfort temperature ranges for Khamis Mushayt obtained for 12 months of the year by comparing the mean monthly maximum and minimum dry bulb temperatures and humidities, given in Table 1, against Evan's comfort tem- perature ranges given in Table 4. It should be pointed out that there are different comfort temperature ranges

for day and night. This should be kept in mind when analysing the comfort zone chart. The comfort zone chart, Fig. 6, is obtained by applying these ranges to the dry bulb temperature isopleth given by Fig. 1. In this paper, zones which meet Evan's [1] scales 'A ' and 'C ' criteria are the modified comfort zones and those ones which satisfy scale 'B' criteria are the comfort zones. Zones of thermal discomfort are the ones which do not meet the criteria of any of these three scales.

DATA ANALYSIS

Evaluation and analysis of Tables 1 and 2, isopleths (Figs 1-5) and comfort chart (Fig. 6) should be the start- ing point for any architectural design aiming at environ-

366 S. A. M. Said and E. T. Al-Zaharnah

Table 2(B) Monthly average wet bulb temperature as a function of hour of the day

Hour Jan. Feb. Mar. Apr. May Jun. Jul. Aug. Sep. Oct. Nov. Dec.

1 7.991 8.766 10 .616 11 .472 13 .114 12 .849 14 .457 14 .905 11.622 9.279 9.083 7.576 2 7.520 8.493 t 0 . 3 2 1 11 .049 12 .675 12 .303 14.031 14 .563 11.164 8.544 8.60I 7.205 3 7.071 8.054 9.826 10 .734 12 .428 11 .883 13 .570 14 .215 10.571 7.623 7.959 6.812 4 6.858 7.792 9.482 10 .379 11 .895 11 .419 13 .148 13 .864 10.070 7.210 7.462 6.442 5 6.584 7.579 9.276 10 .098 11 .510 11 .079 12 .838 13.525 9.579 6.691 6.977 6.122 6 6.439 7.422 9.050 9.873 11 .324 10 .634 12 .534 13.186 9.214 6.252 6.583 5.969 7 6.277 7.401 9.242 10 .715 12 .395 12 .012 13.331 13.779 9.896 6.890 6.803 5.787 8 7.519 8.433 10 .573 ll.899 13 .169 12 .894 13.963 14 .273 11.353 8.838 8.995 7.534 9 8.858 9.405 11.221 12 .383 13 .179 12 .847 13 .877 14 .293 11.885 9.930 9.898 9.046

10 9.692 10.101 11 .769 12 .583 13 .382 13 .010 13 .868 14 .159 12 .018 10 .480 10.458 9.782 11 10.186 10 .646 12.101 12 .837 13 .534 13 .095 13 .952 14 .135 12.141 10 .790 10 .766 10.112 12 10.533 10.941 12 .426 13 .126 13.621 13 .109 14 .093 14 .226 12 .279 11 .058 11 .099 10.417 13 10.894 11 .312 1 2 . 7 5 t 13 .399 13 .800 13 .414 14.251 14 .316 12 .487 11 .330 ll.446 10.825 14 11.197 11 .590 13 .006 13.691 14 .052 13.531 14 .562 14 .618 12 .575 11 .542 11 .656 11.182 15 11.493 11 .880 13 .235 13 .865 14 .352 14.011 14 .793 14 .858 12 .917 11 .634 11 .899 11.484 16 11.610 12 .036 13 .325 lY954 14 .519 14 .193 15 .150 15 .268 13 .055 11 .796 12 .148 11.698 17 11.488 11 .977 13 .275 14 .004 14 .583 14 .253 15 .246 15 .642 13 .006 11.7(13 12 .165 11.707 18 11.088 11 .738 13 .096 13 .833 14 .528 14 .238 15 .328 15 .813 12.781 11 .662 12 .028 11.425 19 10.845 11 .619 12.921 13 .653 14 .198 14 .364 15.453 15 .978 13 .048 12 .073 I2.162 11.469 20 10.421 11 .340 12 .653 13 .375 14 .187 14 .655 15 .397 16 .059 13 .082 11 .960 12 .013 10.942 21 9.910 10 .886 12 .284 13 .139 14 .054 14 .656 15.385 16 .140 12 .974 ll.724 11 .497 10.241 22 9.464 10 .373 11 .948 12 .793 14 .185 14 .395 15 .367 16 .012 12 .737 11.291 10.778 9.438 23 8.851 9.803 11 .545 12 .309 13 .840 13 .914 15.143 15 .660 12 .277 10 .720 10.149 8.725 24 8.385 9.227 11 .139 11 .946 13 .537 13 .430 14.811 15 .184 11 .876 10.018 9.624 8.178

Table 2(C) Monthly average relative humidity a s a function of hour of the day

Hour Jan. Feb. Mar. Apr. May Jun. Jul. Aug. Sep. Oct. Nov. Dec.

I 77 .8259 72.6384 71.8468 65.2885 67.6504 54.9542 62.1630 66.6076 50.7011 54.4981 73.8817 81.0000 2 78 .5263 74.0000 72.6653 66.3962 69.3020 55.8500 63.1268 67.9129 52.7528 54.1128 74.3473 81.7348 3 77 .6033 73.2841 71.8768 68.7048 70.7101 55.8006 63.6777 68.5872 53.1100 50.7600 72.8333 81.8899 4 78 .6852 73.7037 72.4386 69.3877 69.6391 57.0000 64.3808 69.4665 54.6916 52.7454 74.4590 82.8955 5 78 .6918 74.7934 73.9333 70.1135 70.1681 58.0383 65.8742 70.1881 54.9121 53.8043 74.8727 83.7500 6 78 .6494 75.3801 74.1719 70.5714 70.5605 57.0545 65.0295 70.0677 55.8414 54.9169 76.1485 84.0704 7 78 .3269 75.6214 73.1954 67.3970 64.1000 51.0636 60.1799 66.3102 51.7669 52.9941 74.8697 83.1232 8 73 .8129 68.4821 63.5097 55.4970 49.5206 37.8848 46.7324 51.4340 39.2432 41.6129 63.2576 75.2933 9 62 .0290 56.7714 53.9581 45.1667 38.1056 27.4606 35.7449 38.9677 28.4347 34.0557 50.9333 61.0997

10 52 .0419 47.8179 46.9516 38.0697 31.7449 22.1818 28.4018 30.3226 22.5714 29.1324 41.8636 50.3029 II 45 .8355 42.4357 43.0613 34.3121 28.2405 19.2152 24.2493 25.4018 19.7842 26.3842 35.2667 42.4721 12 42 .4000 39.3179 41.1355 32.8394 26.2794 17.5848 22.3900 22.8475 18.0790 24.0676 32.7508 38.7449 13 41 .5484 38.6857 40.9320 32.6758 25.7507 17.0304 21.6891 21.6862 17.5653 22.9267 31.2576 37.5103 14 42 .6613 39.2036 41.8806 33.5697 27.0909 17.1818 23.8798 23.7449 17.6353 22.5206 31.0061 38.1056 15 45 .0419 41.0681 44.4548 36.5061 30.9971 19.5182 26.8182 27.2559 18.9939 22.7273 32.5727 40.2000 16 48 .7475 44.7143 46.5677 39.4970 35.5015 22.4182 30.5208 33.1161 21.5138 25.6341 36.9000 45.1935 17 53 .1016 48.7778 49.9065 43.8485 39.7118 25.3788 34.0567 38.7976 24.6319 29.3659 43.4833 51.8929 18 59 .6852 54.9607 55.2645 48.1939 43.9882 29.3040 38.2827 44.6369 28.4356 35.4116 51.9329 61.0804 19 68.2401 63.5794 62.9032 54.1667 49.3010 35.1937 43.8664 52.1840 34.9965 44.2526 60.6589 70.1355 20 72 .6953 68.1304 66.8561 57.8533 53.7305 41.2917 48.0650 56.6958 38.9756 48.6458 66.1773 73.9486 21 75 .2796 70.7460 68.7885 60.8833 57.0518 45.1708 51.7617 60.3090 41.8014 52.0381 69.3478 76.9935 22 77 .1573 72.1116 71.1169 62.2741 61.3184 48.7458 55.5523 63.5376 44.2884 54.6279 71.2605 77.7885 23 76 .9758 72.2009 71.4113 62.8566 62.7878 51.4292 58.1588 64.8280 45.1760 55.6395 72.5057 78.7742 24 77 .4718 71.9554 72.0726 63.7761 65.4327 53.5042 60.1949 64.8924 47.4815 55.7588 73.4885 80.2302

ment climate balance. This will show the architect what

corrective measures may be achieved by natural means, that is, by adapting architectural design to utilize the climatic elements. Other problems, which fall outside the natural possibilities, will have to be remedied by mechanical means, such as air conditioning.

Konya [10] divided the climates into four main z o n e s - - warm and humid, wet and dry, hot-dry, and sub-trop- ical---each with its major subzones. The comparison of climatic data determines climatic zones for which build- ing design should be coordinated.

The analysis of Tables 1 and 3 shows that the climate of Khamis Mushayy can be identified as sub-tropical

with Mediterraneous subzone mountainous subtype. Recommendat ions for building designs in sub-tropical climate zones are outlined by Konya [10]. The recom- mendat ions are reviewed with the particular charac- teristics and problems of Khamis Mushayt.

The Analysis o f Figs 1-6 and Table 1 show that Khamis Mushayt is blessed with a favourable climate. Temperatures seldom rise above 29.7°C or drop below 7.0°C. The average monthly relative humidity varies between 17.0% and 84.0%. The predominant wind direc- tion is from the south-west. The average annual rainfall amounts to 300 mm. The peak solar radiation is found to be 950 W/m 2 during the month of July. The peak solar

Thermal Desi#ns of Buildinys in Khamis Mushayt

Table 2(D) Monthly average wind speed as a function of hour of the day

367

Hour Jan. Feb. Mar. Apr. May Jun. Jul. Aug. Sep. Oct. Nov. Dec.

1 3.5547 3 .4598 3 .6613 1 .9269 1 .6423 0 .7 6 6 7 1 .4384 1 .6493 2 .2390 2.76265 1.95420 1.4337 2 3.3968 3 .4107 3 .4960 1 .7154 1 .2980 0 .8250 1 .2862 1 .4077 1.7684 2.23346 1.62214 1.3656 3 3.5902 4 .0593 3 .3627 2 .0381 1 .2704 0 .9550 1 .1827 1 .2783 1.5000 2.16308 1.80303 1.8244 4 3.5115 3 .7000 3 .1754 2 .0154 1 .4290 0 .7668 0 .9901 1 .1677 1.3042 1.82515 1.54407 1.6866 5 3.4557 3 .5387 3 .0667 1 .9601 1 .2596 0 .7252 0 .7682 1 .1317 1.0032 1.42202 1.56667 1.7917 6 4.1331 3 .7749 3 .6035 2 .4012 1 .4218 1 .0273 1 .1475 1 .4062 1.0839 1.45697 1.61515 2.5484 7 4.6440 4.0536 4 .1922 2 .9848 1 .8853 1 .1758 1 .1563 1 .4518 1.2844 1.45455 1.56364 2.5513 8 5.0032 4.8500 5 .8097 4 .7303 3 .5647 2 .8636 2 .6324 2 .7214 2.6909 3.10264 2.70909 3.0821 9 7.1581 6.7500 8 .0129 6 .8121 5 .7419 6 .4727 6 .1789 5 .2522 5.9455 5.56305 3.88182 4.9208

10 9.1258 8 .4214 9 .6613 8 .3939 6 .8504 7 .9576 8 .1906 7 .1818 8.6848 6.69795 4.79091 6.4441 11 10 .7065 10.0000 11.0097 9 .3394 7 .3226 8 .2242 8 .4868 7 .9531 9 .9394 7.41642 5.60000 7.7918 12 12 .0129 11.2036 12.1226 10.4970 8 .0676 9 .0606 8 .8739 8 .2610 10.5939 7.68235 6.42249 8.5748 13 12 .8419 12.2179 12.9871 11.1576 8 .6891 9 .0486 9 .1202 8 .7830 10.4545 7.56891 6.99394 9.4194 14 13 .0806 12.9000 13.3065 11.9061 9 .3871 9 .3364 9 .9501 9 .8563 10.2152 7.37059 7.41515 10.0205 15 12 .9387 13.0466 13.3484 11.8970 10.0382 10.1576 10.8065 10.5500 10.7758 8.02346 7.91818 10.0265 16 12 .1770 12.5071 13.1355 11.7061 10.1239 10.5636 10.9673 11.0268 11.4018 8.47561 8.26970 9.8631 17 11 .1738 11.7706 12.0226 11.2152 9 .5500 10.5364 10.7672 10.9643 11.5352 9.00610 8.56839 9.3333 18 9.5770 10.2929 11.1032 10.2152 9 .1529 10.3374 10.4792 9.8988 11.0367 8.66768 7.95427 7.9821 19 7.1971 7.7024 8 .8100 8 .5867 7 .9353 9 .2490 8 .8448 8 .1840 9 .6528 7.85467 6.07692 5.4613 20 5.4229 5 .7945 7 .0360 6 .9633 6 .3896 7 .1250 7 .3141 6 .3902 7.9132 6.61806 4.69231 3.9293 21 4.6846 4.6270 5 .5878 5 .4333 5 .2039 4.8750 5 .5523 4 .8403 6 .3125 5.22491 3.66890 2.9419 22 3.8024 3 .8080 4 .5161 3 .2896 3 .4163 2 .9208 3 .7906 3 .4480 4.7649 4.21705 2.57854 2.3656 23 3.6855 3 .8482 3 .9516 2 .7568 2 .9633 2 .0 3 7 5 2 .4874 2 .5018 3 .7500 3.76744 2.23372 2.0108 24 3.6331 3 .4619 3 .8226 2 .3938 2 .1020 1 .1708 1.8881 2 .1458 2 .9742 3.17121 2.21756 1.6691

1.00

3.00

5.00

7.00

9,00

11.00

13.00

15.00

17.00

10.00

21.00

23.00

J F M A M J J A S 0 N O

Fig. 5. Solar radiation (W/m 2) isopleth for Khamis Mushayt : latitude 18°18'N, longitude 42°43'E, and 2066 m elevation.

radiation in December is around 680 W/m 2 which is minimum for the year. Hence, solar domestic hot water systems may be considered.

The hot period occurs only during the early hours of

night (19:00-23:00) of May through October. The rest of the night time (during these months) falls within the comfort zone. Nights of November through March fall within very cold and cold zones, while nights of March through May fall within the comfort zone. The extremely cold, very cold and cold periods occur during the late hours of night (24 : 00-06 : 00) of September through mid- April. Nights (late hours) of May through September fall within the comfort zone. Every day time falls within modified comfort zones with the exception of the early hours of the day (06 : 00--09 : 00) of October through April and the late hours of the day (17 : 00-19 : 00) of November through January. Also cold zones occur during the early hours of the day (05 : 00-06 : 30) of May through Sep- tember.

From the analysis of the comfort chart (Fig. 6), approximately 16% of the year falls within the comfort zone and 44% falls within the modified comfort zone. Beyond these limits, there exists thermal discomfort. About 6%0 of the time, the thermal discomfort is con- sidered hot, 1% of the time it is very hot, 4% of the time is extremely cold, 14% of the time is very cold, and 15% of the time it is cold.

Table 3. Day and night comfort temperature ranges obtained by Evan's [1]methodforKhamisMushayt, Saudi Arabia

Month

Time Jan. Feb. Mar. Apr. May Jun. Jul. Aug. Sep. Oct. Nov. Dec.

Day 22.5 22.5 22.5 28.5 30 30 30 30 30 30 22.5 22.5 18 18 18 22.5 22.5 22.5 22.5 22.5 22.5 22.5 18 18

20 20 20 20 20 20 20 20 20 20 20 20 Night 16 16 16 16 16 16 16 16 16 16 16 16

BAE 26 :4 -D

368 S. A. M. Said and E. T. Al-Zaharnah

Table 4. Evan's comfort temperature ranges [1]

Scale Conditions

Day Night Humidity temperature temperature

% Cc) ( 'c)

A

C

Upper range of comfort with 1 m/sec movement.

Range of comfort with light summer clothes or one blanket at night.

Lower range of comfort with normal or warm clothes and thick bedding at night.

0-30 32.5--29.5 29.:%27.5 30-50 30.5-28.5 29.0-26.0 50-70 29.5-27.5 28.5-26.0 70-100 29.0-26.0 28.5--25.5

0-30 30.0-22.5 27.5-20.0 30-50 28.5-22.5 26.5-20.0 50-70 27.5-22.5 26.0-20.0 70-100 27.0-22.5 25.5-20.0

0-30 22.5-18.0 20.0-16.0 30-50 22.5 18 .0 20.0-16.0 50-70 22.5-18.0 20.0-16.0 70-100 22.5-18.0 20.0-16.0

RECOMMENDATIONS

Based on the evaluation and analysis of Khamis Mushayt area climatic data, the following recom- mendations are presented for building design.

Cooling Since only 7% of the time the thermal discomfort is

considered hot and very hot, no cooling is required at all. Portable evaporative coolers may be used if needed.

Heating Comfortable conditions can be achieved by using

warm clothing by day and blankets at night. Fixed heat- ing systems are unnecessary. Portable heaters might be desirable during the very cold periods.

J F M A M J J A $ 0 N O

MONTH LEQENO

• ,.,,...,, :o,, • v.,, :0,, [ ] co,, [ ] c..,o.,

Fig. 6. Comfort zone chart for Khamis Mushayt: latitude 18°18'N, longitude 42°43'E, and 2066 m elevation.

Humidification and dehumidification Since the annual mean relative humidity is about 49%,

humidification and dehumidification are not required.

Fans Fans are highly desirable for air movement as natural

ventilation is difficult because of dust, insects, and high outside temperatures during hot periods. Fans have low operating costs.

Ventilation It is important to limit natural ventilation during the

night in the cold months (October to February) because of low outside air temperature.

Windows Must be shielded from direct radiation and glare dur-

ing the hot period; but not excluded during the cold period for solar gain. Awnings or canopies can be used to shield windows from glare.

Wind protection The predominant wind direction being the south-west,

buildings should be protected in this direction.

CONCLUSIONS

In this study, an isopleth chart technique was used in the analysis of climatic variables for the thermal design of buildings. The usefulness of this method is dem- onstrated by applying it to Khamis Mushayt data. The results of this study are summarized as follows:

(1) Isopleths have been prepared for the dry bulb air temperature, wet bulb air temperature, relative humidity of air, wind speed and direction, and total solar radiation.

(2) The microclimatic characteristics of Khamis Mushayt have been identified by analysing these isopleths. The analysis show that the climate of Khamis Mushayt can be identified as sub-tropical with Mediterranean subzone and mountainous subtype.

(3) A comfort zone chart has been prepared to show

Thermal Designs o f Buildings in Khamis Mushayt 369

the combined effect of dry bulb temperature and relative humidity. Comfortable conditions occur in Khamis Mushayt about 60% of the total hours of the year. Thermal discomfort accounts for 40% of the total hours. The 7% of this which is con- sidered hot requires no cooling at all; while the 33% which is considered cold requires the use of

warm clothing by day and blankets at night. Port- able heaters might be desirable during extremely cold periods.

(4) Recommendations are presented for the thermal design of buildings in Khamis Mushayt region and can be used for other regions, in Saudi Arabia and the world, with similar climates.

REFERENCES

I. M. Evan, Housing, Climate and Comfort, The Architectural Press, London (1980). 2. V. Olgyay and A. Olgyay, Design with Climate, Bio-Climatic Approach to Architectural Regionalism,

Princeton University Press, Fourth Printing (1973). 3. D. Watson and K. Labs, Climatic Design, Energy E~cient Building Principles and Practices, McGraw-

Hill, New York (1979). 4. D. Watson, Energy Conservation Through Building Design, McGraw-Hill, New York (1979). 5. Mohammed Barakat Ullah, Wojih Al-Harari and Harold Benson, An Analysis of Climatic Variables

for Thermal Design of Buildings in Dhahran Arabian J. Sci. Engng, 7, (2) (1982). 6. K. Tonge, Khamis-Mushayt, existing conditions, Final Report, Ministry of Municipal and Rural

Affairs, Kingdom of Saudi Arabia. 7. Weather Data, Department of Meteorology, Ministry of Defence, Saudi Arabia, received through

King Fahd University of Petroleum and Minerals, Dhahran, Saudi Arabia. 8. Hydrological Publications, Hydrology Division, Department of Water Resources Development,

Ministry of Agriculture and Water, Riyadh, Saudi Arabia. 9. J.A. Duffle and W. A. Beckman, Solar Thermal Processes, John Wiley, New York (1974).

10. A. Konya, Design Primer for Hot Climates, Architectural Press, London (1980) 11. Koppen, Times Atlas of the World, Comprehensive Edition, Fourth Printing, London (1978).