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Indoor thermal conditions and thermal comfort in air-conditioned domestic buildings in the dry-desert climate of Kuwait
Building and Environment 45 (2010) 704–710
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Indoor thermal conditions and thermal comfort in air-conditioned domestic buildings in the dry-desert climate of Kuwait Farraj F. Al-ajmi a, *, D.L. Loveday b a b
Department of Civil Engineering, College of Technological Studies, P.O. Box 42325, Shuwaikh 70654, Kuwait Department of Civil and Building Engineering, Loughborough University, Loughborough LE11 3TU, UK
a r t i c l e i n f o
a b s t r a c t
Article history: Received 31 March 2009 Received in revised form 30 July 2009 Accepted 16 August 2009
The summer season in the state of Kuwait is long with a mean daily maximum temperature of 45 C. Domestic air conditioning is generally deployed from the beginning of April to the end of October. This accounts for around 75% of Kuwaiti electrical power consumption. In terms of energy conservation, increasing the thermostat temperature by 1 C could save about 10% of space cooling energy [1,2]. However, knowledge of indoor domestic temperatures and thermal comfort sensations is important to aid future advice formulation and policy-making related to domestic energy consumption. A field study was therefore conducted during the summers of 2006 and 2007 to investigate the indoor climate and occupants’ thermal comfort in 25 air-conditioned domestic buildings in Kuwait. The paper presents statistical data about the indoor environmental conditions in Kuwait domestic residences, together with an analysis of domestic-occupant thermal comfort sensations. With respect to the latter, a total of 111 participants provided 111 sets of physical measurements together with subjective information via questionnaires that were used to collect the data. By using linear regression analysis of responses on the ASHRAE-seven-point thermal sensation scale, the neutral operative temperatures based on Actual Mean Vote (AMV) and Predicted Mean Vote (PMV) were found to be 25.2 C and 23.3 C, respectively, in the summer season. Findings from this study provide information about the indoor domestic thermal environment in Kuwait, together with occupant thermal comfort sensations. This knowledge can contribute towards the development of future energy-related design codes for Kuwait. Ó 2009 Elsevier Ltd. All rights reserved.
Keywords: Kuwait domestic buildings Kuwait domestic indoor environments Domestic thermal comfort Dry-desert climates
1. Introduction People in different climates feel comfortable at different indoor air temperatures. Such temperatures can differ considerably from the values adopted by national energy codes, which in turn can impact upon space energy consumption in buildings with airconditioning systems, such as Kuwaiti domestic buildings. Kuwait, as in most countries with a dry-desert climate, has a long summer season with a mean daily maximum temperature of 45 C [3]. Centralized air conditioning, which is generally deployed from the beginning of April to the end of October, accounts for around 75% of national electrical power consumption. Increasing the thermostat temperature setting in the summer season can potentially save significant electrical energy, which would, in turn, decrease energy
* Corresponding author. Tel.: þ965 22314535. E-mail address: [email protected] (F.F. Al-ajmi). 0360-1323/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.buildenv.2009.08.018
expenditure, fossil fuel usage for generating electricity and consequently carbon dioxide emissions. The indoor air temperature (or thermostat temperature) settings for all types of air-conditioned buildings and domestic buildings in particular, are often calculated based on the analytical model developed by Fanger [4]. This model, where comfort sensation is predicted via the Predicted Mean Vote (PMV), has been adopted by the ISO7730 [5] as the standard approach for thermal comfort evaluation. Thermal comfort has been defined by ANSI/ASHRAE-55 [6] and ISO 7730 [5] as ‘‘That condition of mind which expresses satisfaction with the thermal environment’’. In the Fanger-based approach, human thermal comfort depends on the balance between the rate of production of metabolic heat and the rate of heat loss due to exchange with the surrounding environment. The Predicted Mean Vote (PMV) value is a function of a set of environmental conditions that include: air temperature, mean radiant temperature, relative humidity, air velocity, and the personal variables of clothing insulation, and rate of production of metabolic heat. An understanding
F.F. Al-ajmi, D.L. Loveday / Building and Environment 45 (2010) 704–710
2. Context 2.1. The outdoor condition Kuwait is typical of a dry-desert climate with the highest air temperature being recorded in July and August with an afternoon average maximum of 45 C. Summer starts at the beginning of April and continues until the end of October, with a mean air temperature of 37 C [26]. In addition, the air is generally dry with an average relative humidity ranging from 14–42% in the summer to 42–80% in the winter. In winter, the weather is comfortably cool, generally mild, with a monthly mean temperature of 10 C, and a minimum temperature recorded as being occasionally below 5 C. Precipitation is low and dust storms are common [26]. Kuwait is 0 0 located between latitude 29 13 North and longitude 47 58 East at an elevation above mean sea level (m.s.l.) of 45 m. Fig. 1 gives the hourly values of dry and wet bulb temperatures for the summer harshest period, from the beginning of July to the middle of August in the State of Kuwait. 2.2. Buildings surveyed Twenty-five domestic buildings were selected to be surveyed in Kuwait. Buildings were selected evenly over the five provinces of Kuwait (i.e. Capital, Hawalli, Aljahra, Alahamidi and Mobarak Alkabeir). The sizes of the selected buildings ranged from one to three floors with a plot area of 400 m2. Whilst it was impossible to cover all domestic building types in Kuwait in this study, those buildings selected were considered from the perspective of the following specific criteria:
Centralized air conditioning with similar cooling size. Typical type, size and construction materials. Selected buildings are not older than 10 years and distributed evenly amongst the five provinces of Kuwait. In this way, a reasonable sample of housing types from the Kuwaiti domestic building stock is covered by this investigation.
3. Field survey The thermal environment and comfort survey was carried out in 25 domestic buildings across the five provinces of Kuwait. A total of 111 subjects providing 111 sets of physical measurements, and questionnaires were used to collect subjective data. The subjects consisted of 56 (52%) males and 52 (48%) females. The age of the inhabitants ranged from 12 to 65 years, with a mean age of 32.1 years. Their mean height was 159.6 cm and their mean weight was 68.7 kg, (see Table 2). The fieldwork was carried out in the State of Kuwait during the summer season using the following survey procedures. Note that, due to cultural requirements, it was necessary that the survey was conducted by a female experimenter.
3.1. Subjective measurements The subjective study involved collecting data using questionnaires which were given to each subject to complete simultaneously with collection of the physical measurements in each domestic building. The subjective questionnaires and a description of the experimental work procedure had been translated carefully into the Arabic language in order that the occupants could follow and understand. The questionnaire addressed the following areas: (i) background and personal information; (ii) current clothing garments; (iii) subjective thermal sensation vote (the Actual Mean Vote, or AMV) based on the ASHRAE-seven-point scale and consisting of: (3) cold, (2) cool, (1) slightly cool, (0) neutral, (þ1) slightly warm, (þ2) warm, and (þ3) hot; (iv) humidity sensation, scaled as: (3) very humid, (2) humid, (1) slightly humid, (0) neither humid nor dry, (þ1) slightly dry, (þ2) dry, and (þ3) very dry. (v) Air movements’ sensation scaled as: (3) very low, (2) low, (1) slightly low, (0) neither high nor low, (þ1) slightly high, (þ2) high, and (þ3) very high. The subjects were required to make only one choice from the scale for each question.
60.0 dry bulb Wet bulb
Dry/Wet bulb Temperature (C)
of indoor thermal comfort is required to assist building designers in providing an environment that is acceptable to users and that does not impair the health and performance of the occupants of buildings. A large number of thermal comfort studies have been conducted in buildings in all types of climates; most of these were carried out in tropical, subtropical and temperate climate zones [1–17], while other studies were performed in cold climate zones [18,19]. However, investigation of indoor thermal comfort in buildings for countries located in dry-desert climates is limited, although some studies can be mentioned (Baker and Standeven [20]; Cena and de Dear [2]). Their results indicated that the Actual Mean Vote (AMV) of the occupants in air-conditioned buildings is greater than that of the PMV. Saeed [21,22] conducted research in the dry-desert region in Riyadh, Saudi Arabia and measured thermal comfort for classroom students in King Saud University and at Friday prayers during the hot season. The results indicate a fairly good agreement with Fanger’s model in both studies, whilst subjects attending Friday prayer would prefer a cooler climate than the one recorded in his survey. In later studies, clothing insulation (clo values) in both studies was estimated with disregard to the assessment methods of ISO 9920 [23] (i.e. estimation of clothing properties). In the study reported here, however, field experiments were conducted in twenty-five air-conditioned domestic buildings using survey questionnaires and physical measurements to collect data during the summers of 2006 and 2007.This study also takes into account the clothing insulation values that were calculated by Al-ajmi et al. [24,25]. The main objective of this paper is to investigate the indoor climate and thermal conditions in air-conditioned domestic buildings situated in the dry-desert climate of Kuwait. This will provide information that can assist future policy aimed at enhancing energy conservation and reducing carbon emissions.
705
50.0
40.0
30.0
20.0
10.0
0.0 1
67 133 199 265 331 397 463 529 595 661 727 793 859 925 991 1057
hours (July-15 Aug.) Fig. 1. Hourly dry and wet bulb temperature for period between beginning of July to mid August in the state of Kuwait [26].
0.9 0.2 0.65 1.3 .73 .03 .7 .75 .7 .01 .7 .8 1.1 .22 .7 1.3 1.1 .16 .8 1.2 .7 .01 .65 .75 .8 .06 .7 .8 .8 .01 .75 .85 .78 .13 .65 .8 .9 .19 .75 1.1 .7 .01 .65 .75 .8 .01 .75 .85 1
.88 .18 .75 .92 .25 .75 1.2 .78 .38 .7 1.05 .22 .7 1.3
1
.88 .03 .8 1.2 .87 .23 .65 1.1 .93 .15 .8 1.1 .97 .16 .85 1.3 .98 .29 .9 1.1 1.1 .21 .8 1.3 1.2 .44 1 1.3 1.2 .44 1.1 1.3 Clothing insulation Mean 1.1 .72 STD .17 .6 Min .85 .7 Max 1.3 .75
68.7 15.7 20 112 63.6 15.3 40 79 75 15.1 53 93 68.1 18.3 40 90 73.6 11.1 46 93 67.8 14.7 54 91 75.8 12.6 60 89 70.5 7.8 65 76 60.3 35.5 20 87 73.5 19.1 54 96 68.7 4.04 65 73 75.7 13.6 63 90 71.5 3.54 69 74 68.3 20.1 47 87 68.2 4.6 65 75 72.8 24.2 47 112 70 16.1 50 95 57.7 35.3 20 90 57.7 17 38 70 63.3 11.5 51 80 84 12.7 75 93 74.7 79 15.86 22.11 51 60 98 110 44.14 16.56 20 70 70.7 10.1 60 72 61.8 16.7 42 85 Weight Mean STD Min Max
159.6 15 80 183 168.7 151.2 3.62 20 163 123 173 169 153.3 18.5 120 178 165.4 153.6 3.44 16.4 162 119 170 169 162.5 159.5 9.19 5.8 156 152 169 165 166.5 167 173.7 169.3 138.7 6.36 5.57 5.51 5.08 46.8 162 161 168 162 85 171 172 179 173 171 159.8 166.8 160 9.85 8.35 15 148 156 145 177 175 175 140.3 165.5 53.72 9.5 80 157 183 182 164.3 146.7 7.63 36.5 154 105 176 173 165.5 168 10.15 7 158 161 180 175 163.5 7.4 156 174 142.6 22.2 100 170
26.7 4.9 21 29.5 27.5 17.5 12 49.5 44.5 7.1 39.5 49.5 30.5 17.1 12 49.5 27.5 16 12 49.5 21.9 16.1 12 49.5 36.2 5.8 29.5 39.5 22.9 10.1 12 39.5
162 11 151 173
28.1 7.7 21 39.5 37.8 7.5 29.5 49.5 22.3 14.3 12 39.5 32.4 19 12 65 33.8 10.9 21 49.5 32.7 14.2 21 49.5 34.5 7.1 29.5 39.5 30.3 15.9 12 39.5 42 5 39.5 49.5 32.8 5.8 29.5 39.5 43 5.8 39.5 49.5 23.7 10.2 12 29.5
10 9 8 7 6 5 4 3 2 Houses 1
Table 2 Summary of occupants’ personal data.
Kuwaiti male and female clothing ensembles inside domestic buildings are different from those of outdoor ensembles in terms of their appearance, thickness and colours. Traditional Kuwaiti male indoor garments and ensembles are usually a combination of underwear (i.e. pants, long serwal or perhaps short serwal and T-shirt) and gowns or thowb without headdress. Female garments and ensembles are usually a combination of underwear which is most commonly of Western style. Underwear may consist of a bra, underpants and long or short-legged trousers. Trousers differ in terms of their shapes and styles; some are tight while others are slack and loose fitting according to fashion trends. The outermost garment most commonly worn indoors by females is the ‘Daraa’. The Daraa is a traditional gown that falls in a straight line from the shoulder to the ankle, with long sleeves that are tapered toward the wrist. The Daraa may be designed in loosely-fitting or closely-fitting styles, and can vary according to colour, thickness, and decorations. A checklist of Kuwaiti male and female garments shown as photographs and descriptive schemes of ensembles was provided to the occupants at the time of completing the questionnaire survey. A full description of male and female clothing ensembles and clothing insulation values were published in Refs. [24,25], and were coded in ISO 9920 [23]. The overall average clothing insulation values used in this study were estimated to be between 0.65 and 1.3 clo, with a mean value of 0.9 clo, (see Table 2). The clo values of the chair were taken into account in this study [2,6] by adding a value of 0.15 clo to that of the clothing ensemble. The final value obtained was then used in PMV calculations.
11
3.3. Domestic clothing description
Height Mean 155 STD 29.9 Min 102 Max 173
12
13
14
15
16
17
18
19
20
21
In addition to the subjective data collection, physical measurements were carried out in the 25 air-conditioned domestic buildings using a Bruel & Kjaer Indoor Climate Analyser Type 1212. The physical measurements included transducers to measure dry bulb and wet bulb air temperatures, relative humidity, air velocity, and operative temperature. The transducers and data logging system were fitted into a trolley arrangement to collect indoor climatic data at a height of 1.1 m above the floor, as specified by ISO 7730 (2005) [5] for a seated person. This was performed while respondents completed the questionnaires. A period of 15 min was taken prior to the measurements survey to explain and demonstrate the procedure of the field experiments to the subjects in each building. This contributed to allowing the subjects to achieve a steady state thermal balance with their surroundings. The data collection period lasted for 75 min in each building. During this period, occupants were asked to sit in the living room, and were limited to light activity movement, such as body parts movements of hands, feet, neck, etc. The metabolic rate value used in this study was estimated to be 1.2 met as recommended by ISO 7730 [5] for sedentary activity. Five sets of measurements were taken each at 15-min intervals.
39.5 0 39.5 39.5
22
3.2. Physical measurements
30 9.3 21 39.5
11.5% 11.5% 70%
39.5 7.07 29.5 49.5
Cooler
54% 67% 30%
36.3 21.1 12 65
No change
34.6% 22% 0
26 18.5 12 49.5
Warmer 3,2 1,0,þ1 þ3,þ2
24
Thermal preference scales:
23
Sensation vote range
25
All
Table 1 Thermal acceptability of all subjects living in the domestic buildings.
32.1 11 12 65
F.F. Al-ajmi, D.L. Loveday / Building and Environment 45 (2010) 704–710
Age Mean STD D Min. Max.
706
Table 3 Summary of statistical results for indoor environmental parameters in the 25 air-conditioned domestic buildings in Kuwait. Buildings 1
2
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
All
22.7 0.4 22.3 23.1
25.24 0.12 25.1 25.4
20.2 0.23 19.9 20.4
23.1 0.59 22.6 23.8
22.6 0.74 21.8 23.4
24.7 1.5 23.1 27
23.1 0.13 23 23.3
23.1 0.1 23 23.2
22.4 0.37 22.1 23
24.5 0.74 23.9 25.7
24.9 0.34 24.5 25.4
21.8 0.61 20.8 22.4
22.9 1.2 21.5 24.4
21.8 1.21 21.1 23.9
23.3 0.98 22.3 24.8
22.9 2.18 20.8 25.2
20.2 0.27 19.9 20.6
20.9 1.38 19.7 23.2
19.4 0.7 18.8 20.1
24.8 0.48 24.4 25.5
21.6 0.75 20.5 22.3
20.9 0.84 20 22
19.5 0.52 18.9 20.3
22.7 0.8 18.8 28.7
Relative Mean STD Min Max
38.2 0.84 37.2 39.5
35 0.52 34.5 35.6
52.7 0.78 51.9 54
42.2 1.84 40.1 44.1
40.9 0.59 39.6 42.8
39.7 3.1 34.5 42.3
39.2 0.58 38.7 39.9
46.6 0.44 45.9 47.1
50.7 0.4 50.4 51.3
46.7 2.1 44.1 49.2
66.7 1.6 65.1 69.3
40.4 1.8 37.6 43.3
47.4 6 43 56.4
36.5 6.3 33.2 47.6
43.4 2.5 40.2 46.3
41.3 6.8 33.5 50
44.3 1.5 43.4 46.6
44.5 2.8 41.6 49
46 1.9 43.7 47.8
35.1 0.91 33.8 36.8
43.3 0.21 43.1 43.6
43.7 2.1 41.7 47.8
41.6 0.98 40.8 43
43.5 1.97 33.2 69.3
humidity 42.7 38.7 1.81 0.73 40.7 37.4 45.6 39.3
Air velocity Mean 0.09 STD .002 Min .050 Max .10
.29 .004 0.17 .380
.140 .005 .120 0.17
.090 .001 .060 0.13
.130 0.07 .001 .160
.090 .001 .070 0.11
.090 .020 .001 .130
.090 .030 .001 0.17
.080 .020 .001 .150
.130 .020 .080 .140
.080 .020 .001 .110
.190 .110 .001 .30
.150 .001 .110 .230
.090 .010 .050 .130
.260 0.13 .001 0.33
.090 .050 .001 .120
.130 .070 .001 .170
.080 .020 .060 .10
.110 .002 .050 .170
.180 .001 .150 .20
.170 .030 .140 .20
.070 .020 0.05 .090
.140 .040 .070 .180
.120 .060 .060 .170
.180 .10 .001 .230
0.13 0.03 0.001 0.38
Operative temp. Mean 26.3 STD D 0.25 Min. 26 Max. 26.6
(C) 25.8 23.6 25.4 .830 .320 0.05 24.8 23.2 25.4 26.6 24 25.5
21 0.35 20.6 21.4
23.9 0.35 23.3 24.2
23.9 0.46 23.1 24.2
25 0.91 24.3 26.3
24.1 0.32 23.8 24.6
23.9 0.1 23.8 24
23.5 0.7 23 24.7
25.2 0.19 25 25.5
26 0.94 25.3 27.6
22.3 0.17 21.9 22.9
23.9 0.96 22.7 25.3
23.5 0.8 22.9 24.9
24.5 0.7 23.8 25.6
23.9 1.33 22.4 25
21.5 0.28 21.2 21.8
22.3 0.78 21.3 23.6
21.4 0.58 20.9 22.2
25.9 0.48 25.5 26.6
22.9 0.57 22.1 23.5
22.2 0.42 21.6 22.6
20.9 0.72 20.2 22.1
23.71 0.54 20.2 27.6
AMV Mean STD D Min. Max. P P D (%)
0.32 0.18 0.2 0.6 7.1
0.07 0.5 0.4 0.6 5.1
0.3 0.52 1.2 .4 6.9
0.2 0.54 0.6 1 5.8
1.7 0.44 1 2 61.8
0.2 0.28 0.4 0 5.8
v0.07 0.41 0.8 0.4 5.1
0.1 0.5 0.6 0.4 5.2
0 0.4 0.4 0.4 5
0.1 0.31 0.6 0.2 5.2
0.4 0.34 0.8 0 8.3
0.2 0.75 0.8 0.6 5.8
0.6 0.35 0.2 0.8 12.5
0.2 0.28 0.4 0 5.8
0.2 0.2 0.4 0 5.8
0.6 0.35 0.8 0.2 12.5
0.3 0.18 0.4 0 6.9
0.2 0.14 0.25 0 5.8
0.7 0.14 0.8 0.6 15.3
0.8 0.29 1 0.4 18.5
0.44 0.38 1 0 9
0.1 0.75 1 1.5 5.2
0.75 0.33 1.2 0.2 16.8
0.25 0.22 0.5 0 6.3
0.84 0.23 1 0.6 19.9
0.28 0.33 1.2 1.5 10.7
PMV Mean 0.7 STD D 0.09 Min. 0.58 Max. 0.84 P P D (%) 15.3
0.3 0.04 0.25 0.34 6.9
0.56 0.04 0.5 0.62 11.6
0.5 0.05 0.42 0.56 10.2
0.08 0.05 0.02 0.14 5.1
0.16 0.06 0.09 0.22 5.5
0.3 0.04 0.26 0.35 6.9
0.3 0.03 0.27 0.34 6.9
0.25 0.05 0.21 0.31 6.3
0.45 0.04 0.39 0.48 9.2
0.8 0.09 0.7 0.91 18.5
.04 0.07 .01 0.07 5
.13 0.24 .14 0.3 5.4
0.25 0.5 0.21 0.32 6.3
0.19 0.39 .07 0.55 5.7
.81 0.14 1 .61 18.8
.43 0.28 .71 0.03 8.9
.75 0.14 .87 .54 16.8
1.04 0.1 0.94 1.19 27.8
0.23 0.16 0.01 0.39 6.1
.43 0.22 0.7 0.2 8.9
.94 0.09 1.1 .87 23.7
0.13 0.13 1.1 1.19 10.21
0.3 0.05 0.23 0.35 6.9
0.35 0.03 0.3 0.38 7.5
.05 0.33 .07 0.44 5.1
F.F. Al-ajmi, D.L. Loveday / Building and Environment 45 (2010) 704–710
3
Air temperature Mean 25.3 26.3 STD D 1.6 2.4 Min. 25.1 23.1 Max. 25.5 28.7
707
708
F.F. Al-ajmi, D.L. Loveday / Building and Environment 45 (2010) 704–710 45
4.1. Domestic indoor thermal conditions Table 2 provides a summary of the personal data from the 111 occupants in the survey, together with their clothing insulation values. Data are presented as the mean of the family occupants in each of the 25 households. Indoor climate measurements for the 25 domestic buildings are presented in Table 3. Indoor air temperature values ranged between 18.8 and 28.7 C with a mean value of 22.7 C, and standard deviation of 0.8, whilst recorded indoor relative humidities ranged from 33.2 to 69.7% with a mean value of 43.5% and standard deviation of 1.97. Fig. 2(a,b) shows these data in histogram forms. Average indoor air movements varied between 0.01 and 0.38 m/s with mean value of 0.13 m/s and standard deviation of 0.03, whilst operative temperatures were in the range of 20.2–27.6 C, with a mean of 23.7 C and standard deviation of 0.54, see Fig. 2(a). Table 3 also provide statistical summaries of thermal environments and thermal indices of occupants, with actual mean votes (AMVs) ranging from 1.2 to þ1.5 with a mean of 0.28 and standard deviation of 0.33.
4.2. Actual mean vote of subjects The fieldwork was carried out during the two summer seasons (May–October) of 2006 and 2007, in the State of Kuwait. Fig. 3 shows the occupants’ overall Actual Mean Vote (AMV) for the surveyed domestic buildings. It can be seen that 37.6% of the respondents feel neutral (0), whilst 38.4% feel slightly cool. In addition, 9.9% of occupants feel cool (2), while 5.4% feel warm (þ2). Furthermore, the thermal preference scale showed that 67%
Percentage of frequency (%)
4. Results and analyses
40 35 30 25 20 15 10 5 0
3
2
1
0
-1
-2
-3
AMV Fig. 3. Distribution of overall actual mean vote of selected buildings.
of occupants did not want a change to their indoor environments, while 22% wanted to be warmer, (see Table 1). The actual mean vote (AMV) of the occupants (male and female) in air-conditioned domestic buildings on the ASHRAE-seven-point scale were found to be marginally slightly cool (i.e. 0.28), which corresponds to a predicted percentage dissatisfaction (PPD) equal to 10.7%, while that for predicted mean vote (PMV) were marginally slightly warm (i.e. þ0.13), which corresponds to a PPD value equal to 10.2%. Findings for both AMV and PMV are very close to the neutral vote (see Table 3). Further analysis was conducted to find the indoor neutral temperature for the domestic buildings, as follows: Operative temperatures of the 25 air-conditioned domestic buildings were binned into 0.5 C intervals and analyzed to find the bin’s mean thermal sensation of the occupants. Linear regression analysis was then applied to determine the actual mean vote (AMV) and predicted mean vote (PMV) as a function of operative temperature (to) The linear regression equations obtained were then solved for neutrality (actual mean vote ¼ 0) to determine the neutral operative temperature. The linear regression equations for occupants’ reported thermal sensation (AMV) and for their Predicted Mean Vote (PMV) were thus found to be:
AMV ¼ 0:2318to 5:8444
ðr ¼ 0:848Þ
(1)
ðr ¼ 0:864Þ
(2)
and
PMV ¼ 0:2409to 5:6162
Fig. 2. (a) Indoor mean air temperature and operative temperature, and (b) Relative humidity, for all 25 domestic buildings.
The linear regression coefficient for the actual mean vote (AMV) as a function of operative temperature (to) (equation (1)) is 0.848, whilst that for the predicted mean vote (PMV) as a function of operative temperature (equation (2)) is 0.864. The gradient of the regression lines represents the sensitivity of the occupants with respect to the operative temperature index, and is found to be 0.2318/ C, for both equations, see Fig. 4. In Fig. 4, when the regression lines of AMV and PMV are plotted, the mean neutral operative temperature is the point where the regression line crosses the x-axis. Furthermore, Eqs. (1) and (2) were solved for neutrality to derive values for the neutral operative temperature. The neutral operative temperatures for AMV and PMV were thus determined to be 25.2 C and 23.3 C, respectively. PMV predictions underestimated observed neutrality by about 1.9 C less than that of AMV. This may indicate that the ISO 7730
F.F. Al-ajmi, D.L. Loveday / Building and Environment 45 (2010) 704–710 1 AMV
PMV
AMV / PMV
0.5
0 20
21
22
23
24
25
26
27
-0.5
-1
-1.5
Operative Temperature (C) Fig. 4. Linear regression calculation based on binned AMV and PMV versus operative temperature.
standard for calculating PMV underestimates the individual’s actual thermal sensation in a dry-desert climate. One explanation might be that occupants in air-conditioned buildings located in extremely hot and arid climates like that of Kuwait in fact find their indoor environments to be thermally comfortable even if they are being overcooled. However, a more extensive study is necessary to further investigate this possibility. It is interesting to note that similar findings were obtained in tests carried out in Kalgoorlie-Boulder, a hot, arid region of Western Australia, by Cena and de Dear [2]. Here, it was found that the AMV of the occupants in air-conditioned buildings is higher than that of the PMV. One possible explanation being put forward was that occupants adapt to their indoor air-conditioned environments (Cena and de Dear [2]). However, interpretation of the differences between actual mean vote (AMV) and predicted mean vote (PMV) is not straightforward. This can be due to the nature of calculation from the averaged estimation of variables, i.e. the activity rates or clothing insulation values, as well as the possibility of adaptation effects. According to Parsons [27] and Olesen and Parsons [28], use of the PMV method has been criticized and improvements are required to the PMV formula. An alternative use of the adaptive approach to account for a range of adaptation effects. Thus, further research is needed to fully investigate the use of the PMV technique for predicting the thermal sensation of individuals in air-conditioned domestic buildings located in extreme hot dry-desert climates. 5. Thermal acceptability The thermal acceptability of indoor environments is considered in ASHRAE standard 55(2004) [6] and ISO7730 (2005) [5] to be defined on the seven-point scale as being within the limits of either 1, 0, 1 (which accounts for 80% or more), or 0.5, 0, þ0.5 which accounts for 90%, or a predicted percentage of dissatisfaction (PPD) of 10%. Both limits are applicable due to the physiological variances of occupants. However, the most widely accepted thermal comfort range is for subjects who vote inside the limit (0.5, 0, þ0.5) of the ASHRAE-seven-point scale. Applying the latter limit corresponds to an operative temperature range of 23–27 C for thermal acceptability.
709
harsh summer seasons. Reduction of energy consumption in buildings is a major aim worldwide and is a particular challenge in a desert climate. In Kuwait, the Ministry of Electricity and Water (MEW) issued an energy conservation code in 1983 [29], which is still in force and has not been modified, despite the fact that more effective energy-efficient products and techniques have been developed since then. In addition, electrical energy costs in Kuwait are highly subsidized by the government, and without any updating of the energy code to date. Thus, a better-defined energy conservation code with more effective and energy-efficient design could offer both economic and environmental benefits for the Kuwaiti government. Furthermore, the energy code in Kuwait contains some rules and regulations for designing air-conditioning systems in Kuwait conditions. This code represents a set of regulations that guides the energy performance of new buildings. The energy code of Kuwait aims to guide local architects and airconditioning engineers to achieve energy-efficient design of modern buildings. For example, the code recommends the operative temperature of the indoor environment and outdoor design dry-bulb temperature for the Kuwait summer season to be 24 C and 46 C, respectively, for the purpose of designing the HVAC systems for air-conditioned buildings. However, reducing the indoor–outdoor temperature differences can potentially reduce energy consumption of HVAC systems, and in addition an electrical energy saving of 10% can be achieved by raising the thermostat temperature setting by 1 C [1,2] (for cooling). A neutral operative temperature value for the sample (25) of airconditioned domestic buildings in Kuwait was found in this study to be 25.2 C. With this finding, as the recommended and widely adopted indoor operative temperature by Kuwaiti energy code,then energy saving of over 10% could be achieved [29]. Adjustment of 1 C to the outdoor design temperature could yield further energy savings. This latter statement is based on the following. The existing outdoor summer design condition (or cooling design temperature) for Kuwait, as recorded in the Kuwaiti energy code (1983) is given as 46 C [29]. This finding (i.e. current outdoor design condition) was revised by analyzing the collected Kuwait climatological data summaries from 1962 to 2006, leading to a value of outdoor summer design temperature equal to 45 C [3,26]. Consequently, this may lead to more relevant design of HVAC systems for Kuwaiti buildings. Clearly more research is needed before firm recommendations of this nature can be made, but this discussion serves to illustrate the potential for energy saving by adjustment of recommended design temperatures. 7. Conclusions The main objective of this study was to investigate the indoor climate, thermal conditions and occupant thermal comfort sensations in air-conditioned domestic buildings in the State of Kuwait. A total of 111 occupants in twenty-five air-conditioned domestic buildings located in the dry-desert climate of Kuwait were surveyed during the summers of 2006 and 2007. The survey involved the recording of environmental parameters and human thermal comfort responses. The domestic buildings were evenly distributed across the five provinces of Kuwait. The main results of the study were as follows:
6. Potential for energy conservation Economic and industrial development in the dry-desert climate of Kuwait has led to an increasing demand for electricity, much of which is consumed in air conditioning systems that are used extensively to overcome indoor thermal discomfort during the
Across all domestic buildings the mean indoor dry-bulb air temperature was found to be 22.7 C with standard deviation of 0.8 and mean relative humidity of 43.5% with standard deviation of 1.97 and a mean air movement of 0.13 ms1, with standard deviation of 0.03.
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The neutral operative temperature for occupants was found to be 25.2 C. This was obtained by linear regression analysis of actual mean vote on operative temperature. The Actual Mean Vote (AMV) was within the range of 1.2 to þ1.5 with the occupants’ mean thermal sensation being 0.28, whilst for Predicted Mean Vote (PMV) the range was 1.1 to þ1.19, with a PMV equal to þ0.13. The neutral operative temperatures based upon AMV and PMV were determined to be 25.2 C and 23.3 C, respectively. PMV predictions underestimated observed neutrality by about 1.9 C less than that of AMV. This finding is similar to that reported by Cena and de Dear [2] and may indicate that the ISO 7730 standard for calculating PMV underestimates the individual’s actual sensation in a dry-desert climate due to possible adaptive effects, though further research is needed to confirm this. The widely accepted criterion for thermal acceptability, namely the central three values of 0.5 to 0 to þ0.5 of the 7-point scale (which accounts for predicted percentage of dissatisfaction (PPD) of 10%) corresponds to an operative temperature range of 23–27 C for thermal acceptability in the domestic residences. Were adjustments to be made to the indoor/outdoor design temperatures in the energy code of the Ministry of Electricity and Water in the State of Kuwait, the effect on national energy consumption could be considerable. However, more extensive research is needed before such a recommendation can be made. Acknowledgments This work was financially supported by the Kuwait Foundation for the Advancement of Sciences (KFAS) under research grant (2004-1508-02), this support being gratefully acknowledged. The authors also are grateful to the Department of Civil Engineering at the College of Technological Studies, State of Kuwait, and to the Department of Civil and Building Engineering, Loughborough University, UK. The authors express their gratitude to all volunteer subjects who took part in this work. They are also thankful to Mr. Mohammed Ali and Mrs. Nadia Alayoub for their assistance during the fieldwork. References [1] Sekhar SC, Ching CS. Indoor air quality and thermal comfort studies of an under-floor air-conditioning system in the tropics. Energy and Buildings 2002;34(5):431–44. [2] Cena K, de Dear R. Thermal comfort and behavioural strategies in office buildings located in a hot-arid climate. Journal of Thermal Biology 2001;26(4– 5):409–14. [3] Al-ajmi F, Hanby VI. Simulation of energy consumption for Kuwaiti domestic buildings. Energy and Buildings 2008;40:1101–9.
[4] Fanger PO. Thermal comfort: analysis and applications in environmental engineering. Copenhagen: Danish Technical Press; 1972. [5] ISO 7730:2005. Moderate thermal environments. Determination of the PMV and PPD indices and specification of the conditions for thermal comfort. 2nd ed. Gevena, Switzerland: International Organisation for Standardisation; 2005. [6] ANSI/ASHRAE. Standard 55-2004. Thermal environmental conditions for human occupancy. American Society of Heating, Refrigerating and Air-conditioning Engineers, Inc., Atlanta, Georgia. [7] de Dear RJ, Brager GS. Developing an adaptive model of thermal comfort and preference. ASHRAE Transactions 1998;104(1):145–67. [8] Schiller GE. A comparison of measured and predicted comfort in office buildings. ASHRAE Transactions 1990;96(1):609–22. [9] Benton C, Bauman F, Fountain M. A field measurement system for the study of thermal comfort. ASHRAE Transactions 1990;96(1):623–33. [10] de Dear RJ, Fountain ME. Field experiments on occupant comfort and office thermal environments in a hot-humid climate. ASHRAE Transactions 1994;100(2):457–75. [11] Mallick FH. Thermal comfort and building design in the tropical climates. Energy and Buildings 1996;23(3):161–7. [12] Howell WC, Kennedy PA. Field validation of the Fanger thermal comfort model. Human Factors 1979;21(2):229–39. [13] Busch JF. Thermal responses to the THAI office environment. ASHRAE Transactions 1990;96(1):859–72. [14] Xia YZ, Zhao RY, Jiang Y. Thermal comfort in naturally ventilated houses in Beijing. Heating, Ventilation, Air-conditioning and Refrigeration 1999;29(2):1–5. [15] Cena K, de Dear RJ. Field study of occupant comfort and office thermal environments in a hot, arid climate. ASHRAE Transactions 1999;105(2):204–17. [16] Hwang RL, Lin TP, Kuo NJ. Field experiments on thermal comfort in campus classrooms in Taiwan. Energy and Buildings 2006;38:53–62. [17] Mui KW, Wong LT. Neutral temperature in subtropical climatesdA field survey in air-conditioned offices. Building and Environment 2007;42(2): 699–706. [18] Wang ZA. Field study of the thermal comfort in residential buildings in Harbin. Building and Environment 2006;41(8):1034–9. [19] Donnini G, Molina J, Martello C, Lai DHC, Lai HK, Chang CY, et al. Field study of occupant comfort and office thermal environments in a cold climate. ASHRAE Transactions 1996;103(2):795–802. [20] Baker N, Standeven M. Comfort criteria for passively cooled buildings. APASCOOL task. Renewable Energy 1994;5(5–8):977–84. [21] Saeed RAS. Thermal comfort requirements in hot dry region reference to Riyadh: Part 1: for university students. International Journal of Ambient Energy 1993;14(3):147–54. [22] Saeed RAS. Thermal comfort requirements in hot dry region with special reference to Riyadh: part 1: for Friday prayers. International Journal of Ambient Energy 1996;17(1):17–21. [23] ISO 9920:2006. Ergonomics of the thermal environment-Estimation of the thermal insulation and evaporative resistance of clothing. International Standard Organization for Standardization (ISO). [24] Al-ajmi F, Loveday DL, Bedwell KH, Havenith G. Thermal insulation and clothing area factors of typical Arabian Gulf clothing ensembles for males and females: measurements using thermal manikins. Applied Ergonomics 2008;39(3):407–14. [25] Al-Ajmi F, Loveday DL, Havenith G. Thermal insulation of Arabian Gulf male clothing: measurements using a thermal manikin. ASHRAE Transactions 2006;112(2). [26] Kuwait International Airport. Meteorological summaries year 1962–2006. State of Kuwait: Meteorological Department Climatological Division; 2006. [27] Parsons KC. The effects of gender, acclimation state, the opportunity to adjust clothing and physical disability on requirements for thermal comfort. Energy and Buildings 2001;34(6):593–9. [28] Olesen BW, Parsons KC. Introduction to thermal comfort standards and to the proposed new version of EN ISO 7730. Energy and Buildings 2002;34:537–48. [29] Kuwait, the Ministry of Electricity and Water (MEW) issued an energy conservation code in 1983.
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Building and Environment journal homepage: www.elsevier.com/locate/buildenv
Indoor thermal conditions and thermal comfort in air-conditioned domestic buildings in the dry-desert climate of Kuwait Farraj F. Al-ajmi a, *, D.L. Loveday b a b
Department of Civil Engineering, College of Technological Studies, P.O. Box 42325, Shuwaikh 70654, Kuwait Department of Civil and Building Engineering, Loughborough University, Loughborough LE11 3TU, UK
a r t i c l e i n f o
a b s t r a c t
Article history: Received 31 March 2009 Received in revised form 30 July 2009 Accepted 16 August 2009
The summer season in the state of Kuwait is long with a mean daily maximum temperature of 45 C. Domestic air conditioning is generally deployed from the beginning of April to the end of October. This accounts for around 75% of Kuwaiti electrical power consumption. In terms of energy conservation, increasing the thermostat temperature by 1 C could save about 10% of space cooling energy [1,2]. However, knowledge of indoor domestic temperatures and thermal comfort sensations is important to aid future advice formulation and policy-making related to domestic energy consumption. A field study was therefore conducted during the summers of 2006 and 2007 to investigate the indoor climate and occupants’ thermal comfort in 25 air-conditioned domestic buildings in Kuwait. The paper presents statistical data about the indoor environmental conditions in Kuwait domestic residences, together with an analysis of domestic-occupant thermal comfort sensations. With respect to the latter, a total of 111 participants provided 111 sets of physical measurements together with subjective information via questionnaires that were used to collect the data. By using linear regression analysis of responses on the ASHRAE-seven-point thermal sensation scale, the neutral operative temperatures based on Actual Mean Vote (AMV) and Predicted Mean Vote (PMV) were found to be 25.2 C and 23.3 C, respectively, in the summer season. Findings from this study provide information about the indoor domestic thermal environment in Kuwait, together with occupant thermal comfort sensations. This knowledge can contribute towards the development of future energy-related design codes for Kuwait. Ó 2009 Elsevier Ltd. All rights reserved.
Keywords: Kuwait domestic buildings Kuwait domestic indoor environments Domestic thermal comfort Dry-desert climates
1. Introduction People in different climates feel comfortable at different indoor air temperatures. Such temperatures can differ considerably from the values adopted by national energy codes, which in turn can impact upon space energy consumption in buildings with airconditioning systems, such as Kuwaiti domestic buildings. Kuwait, as in most countries with a dry-desert climate, has a long summer season with a mean daily maximum temperature of 45 C [3]. Centralized air conditioning, which is generally deployed from the beginning of April to the end of October, accounts for around 75% of national electrical power consumption. Increasing the thermostat temperature setting in the summer season can potentially save significant electrical energy, which would, in turn, decrease energy
* Corresponding author. Tel.: þ965 22314535. E-mail address: [email protected] (F.F. Al-ajmi). 0360-1323/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.buildenv.2009.08.018
expenditure, fossil fuel usage for generating electricity and consequently carbon dioxide emissions. The indoor air temperature (or thermostat temperature) settings for all types of air-conditioned buildings and domestic buildings in particular, are often calculated based on the analytical model developed by Fanger [4]. This model, where comfort sensation is predicted via the Predicted Mean Vote (PMV), has been adopted by the ISO7730 [5] as the standard approach for thermal comfort evaluation. Thermal comfort has been defined by ANSI/ASHRAE-55 [6] and ISO 7730 [5] as ‘‘That condition of mind which expresses satisfaction with the thermal environment’’. In the Fanger-based approach, human thermal comfort depends on the balance between the rate of production of metabolic heat and the rate of heat loss due to exchange with the surrounding environment. The Predicted Mean Vote (PMV) value is a function of a set of environmental conditions that include: air temperature, mean radiant temperature, relative humidity, air velocity, and the personal variables of clothing insulation, and rate of production of metabolic heat. An understanding
F.F. Al-ajmi, D.L. Loveday / Building and Environment 45 (2010) 704–710
2. Context 2.1. The outdoor condition Kuwait is typical of a dry-desert climate with the highest air temperature being recorded in July and August with an afternoon average maximum of 45 C. Summer starts at the beginning of April and continues until the end of October, with a mean air temperature of 37 C [26]. In addition, the air is generally dry with an average relative humidity ranging from 14–42% in the summer to 42–80% in the winter. In winter, the weather is comfortably cool, generally mild, with a monthly mean temperature of 10 C, and a minimum temperature recorded as being occasionally below 5 C. Precipitation is low and dust storms are common [26]. Kuwait is 0 0 located between latitude 29 13 North and longitude 47 58 East at an elevation above mean sea level (m.s.l.) of 45 m. Fig. 1 gives the hourly values of dry and wet bulb temperatures for the summer harshest period, from the beginning of July to the middle of August in the State of Kuwait. 2.2. Buildings surveyed Twenty-five domestic buildings were selected to be surveyed in Kuwait. Buildings were selected evenly over the five provinces of Kuwait (i.e. Capital, Hawalli, Aljahra, Alahamidi and Mobarak Alkabeir). The sizes of the selected buildings ranged from one to three floors with a plot area of 400 m2. Whilst it was impossible to cover all domestic building types in Kuwait in this study, those buildings selected were considered from the perspective of the following specific criteria:
Centralized air conditioning with similar cooling size. Typical type, size and construction materials. Selected buildings are not older than 10 years and distributed evenly amongst the five provinces of Kuwait. In this way, a reasonable sample of housing types from the Kuwaiti domestic building stock is covered by this investigation.
3. Field survey The thermal environment and comfort survey was carried out in 25 domestic buildings across the five provinces of Kuwait. A total of 111 subjects providing 111 sets of physical measurements, and questionnaires were used to collect subjective data. The subjects consisted of 56 (52%) males and 52 (48%) females. The age of the inhabitants ranged from 12 to 65 years, with a mean age of 32.1 years. Their mean height was 159.6 cm and their mean weight was 68.7 kg, (see Table 2). The fieldwork was carried out in the State of Kuwait during the summer season using the following survey procedures. Note that, due to cultural requirements, it was necessary that the survey was conducted by a female experimenter.
3.1. Subjective measurements The subjective study involved collecting data using questionnaires which were given to each subject to complete simultaneously with collection of the physical measurements in each domestic building. The subjective questionnaires and a description of the experimental work procedure had been translated carefully into the Arabic language in order that the occupants could follow and understand. The questionnaire addressed the following areas: (i) background and personal information; (ii) current clothing garments; (iii) subjective thermal sensation vote (the Actual Mean Vote, or AMV) based on the ASHRAE-seven-point scale and consisting of: (3) cold, (2) cool, (1) slightly cool, (0) neutral, (þ1) slightly warm, (þ2) warm, and (þ3) hot; (iv) humidity sensation, scaled as: (3) very humid, (2) humid, (1) slightly humid, (0) neither humid nor dry, (þ1) slightly dry, (þ2) dry, and (þ3) very dry. (v) Air movements’ sensation scaled as: (3) very low, (2) low, (1) slightly low, (0) neither high nor low, (þ1) slightly high, (þ2) high, and (þ3) very high. The subjects were required to make only one choice from the scale for each question.
60.0 dry bulb Wet bulb
Dry/Wet bulb Temperature (C)
of indoor thermal comfort is required to assist building designers in providing an environment that is acceptable to users and that does not impair the health and performance of the occupants of buildings. A large number of thermal comfort studies have been conducted in buildings in all types of climates; most of these were carried out in tropical, subtropical and temperate climate zones [1–17], while other studies were performed in cold climate zones [18,19]. However, investigation of indoor thermal comfort in buildings for countries located in dry-desert climates is limited, although some studies can be mentioned (Baker and Standeven [20]; Cena and de Dear [2]). Their results indicated that the Actual Mean Vote (AMV) of the occupants in air-conditioned buildings is greater than that of the PMV. Saeed [21,22] conducted research in the dry-desert region in Riyadh, Saudi Arabia and measured thermal comfort for classroom students in King Saud University and at Friday prayers during the hot season. The results indicate a fairly good agreement with Fanger’s model in both studies, whilst subjects attending Friday prayer would prefer a cooler climate than the one recorded in his survey. In later studies, clothing insulation (clo values) in both studies was estimated with disregard to the assessment methods of ISO 9920 [23] (i.e. estimation of clothing properties). In the study reported here, however, field experiments were conducted in twenty-five air-conditioned domestic buildings using survey questionnaires and physical measurements to collect data during the summers of 2006 and 2007.This study also takes into account the clothing insulation values that were calculated by Al-ajmi et al. [24,25]. The main objective of this paper is to investigate the indoor climate and thermal conditions in air-conditioned domestic buildings situated in the dry-desert climate of Kuwait. This will provide information that can assist future policy aimed at enhancing energy conservation and reducing carbon emissions.
705
50.0
40.0
30.0
20.0
10.0
0.0 1
67 133 199 265 331 397 463 529 595 661 727 793 859 925 991 1057
hours (July-15 Aug.) Fig. 1. Hourly dry and wet bulb temperature for period between beginning of July to mid August in the state of Kuwait [26].
0.9 0.2 0.65 1.3 .73 .03 .7 .75 .7 .01 .7 .8 1.1 .22 .7 1.3 1.1 .16 .8 1.2 .7 .01 .65 .75 .8 .06 .7 .8 .8 .01 .75 .85 .78 .13 .65 .8 .9 .19 .75 1.1 .7 .01 .65 .75 .8 .01 .75 .85 1
.88 .18 .75 .92 .25 .75 1.2 .78 .38 .7 1.05 .22 .7 1.3
1
.88 .03 .8 1.2 .87 .23 .65 1.1 .93 .15 .8 1.1 .97 .16 .85 1.3 .98 .29 .9 1.1 1.1 .21 .8 1.3 1.2 .44 1 1.3 1.2 .44 1.1 1.3 Clothing insulation Mean 1.1 .72 STD .17 .6 Min .85 .7 Max 1.3 .75
68.7 15.7 20 112 63.6 15.3 40 79 75 15.1 53 93 68.1 18.3 40 90 73.6 11.1 46 93 67.8 14.7 54 91 75.8 12.6 60 89 70.5 7.8 65 76 60.3 35.5 20 87 73.5 19.1 54 96 68.7 4.04 65 73 75.7 13.6 63 90 71.5 3.54 69 74 68.3 20.1 47 87 68.2 4.6 65 75 72.8 24.2 47 112 70 16.1 50 95 57.7 35.3 20 90 57.7 17 38 70 63.3 11.5 51 80 84 12.7 75 93 74.7 79 15.86 22.11 51 60 98 110 44.14 16.56 20 70 70.7 10.1 60 72 61.8 16.7 42 85 Weight Mean STD Min Max
159.6 15 80 183 168.7 151.2 3.62 20 163 123 173 169 153.3 18.5 120 178 165.4 153.6 3.44 16.4 162 119 170 169 162.5 159.5 9.19 5.8 156 152 169 165 166.5 167 173.7 169.3 138.7 6.36 5.57 5.51 5.08 46.8 162 161 168 162 85 171 172 179 173 171 159.8 166.8 160 9.85 8.35 15 148 156 145 177 175 175 140.3 165.5 53.72 9.5 80 157 183 182 164.3 146.7 7.63 36.5 154 105 176 173 165.5 168 10.15 7 158 161 180 175 163.5 7.4 156 174 142.6 22.2 100 170
26.7 4.9 21 29.5 27.5 17.5 12 49.5 44.5 7.1 39.5 49.5 30.5 17.1 12 49.5 27.5 16 12 49.5 21.9 16.1 12 49.5 36.2 5.8 29.5 39.5 22.9 10.1 12 39.5
162 11 151 173
28.1 7.7 21 39.5 37.8 7.5 29.5 49.5 22.3 14.3 12 39.5 32.4 19 12 65 33.8 10.9 21 49.5 32.7 14.2 21 49.5 34.5 7.1 29.5 39.5 30.3 15.9 12 39.5 42 5 39.5 49.5 32.8 5.8 29.5 39.5 43 5.8 39.5 49.5 23.7 10.2 12 29.5
10 9 8 7 6 5 4 3 2 Houses 1
Table 2 Summary of occupants’ personal data.
Kuwaiti male and female clothing ensembles inside domestic buildings are different from those of outdoor ensembles in terms of their appearance, thickness and colours. Traditional Kuwaiti male indoor garments and ensembles are usually a combination of underwear (i.e. pants, long serwal or perhaps short serwal and T-shirt) and gowns or thowb without headdress. Female garments and ensembles are usually a combination of underwear which is most commonly of Western style. Underwear may consist of a bra, underpants and long or short-legged trousers. Trousers differ in terms of their shapes and styles; some are tight while others are slack and loose fitting according to fashion trends. The outermost garment most commonly worn indoors by females is the ‘Daraa’. The Daraa is a traditional gown that falls in a straight line from the shoulder to the ankle, with long sleeves that are tapered toward the wrist. The Daraa may be designed in loosely-fitting or closely-fitting styles, and can vary according to colour, thickness, and decorations. A checklist of Kuwaiti male and female garments shown as photographs and descriptive schemes of ensembles was provided to the occupants at the time of completing the questionnaire survey. A full description of male and female clothing ensembles and clothing insulation values were published in Refs. [24,25], and were coded in ISO 9920 [23]. The overall average clothing insulation values used in this study were estimated to be between 0.65 and 1.3 clo, with a mean value of 0.9 clo, (see Table 2). The clo values of the chair were taken into account in this study [2,6] by adding a value of 0.15 clo to that of the clothing ensemble. The final value obtained was then used in PMV calculations.
11
3.3. Domestic clothing description
Height Mean 155 STD 29.9 Min 102 Max 173
12
13
14
15
16
17
18
19
20
21
In addition to the subjective data collection, physical measurements were carried out in the 25 air-conditioned domestic buildings using a Bruel & Kjaer Indoor Climate Analyser Type 1212. The physical measurements included transducers to measure dry bulb and wet bulb air temperatures, relative humidity, air velocity, and operative temperature. The transducers and data logging system were fitted into a trolley arrangement to collect indoor climatic data at a height of 1.1 m above the floor, as specified by ISO 7730 (2005) [5] for a seated person. This was performed while respondents completed the questionnaires. A period of 15 min was taken prior to the measurements survey to explain and demonstrate the procedure of the field experiments to the subjects in each building. This contributed to allowing the subjects to achieve a steady state thermal balance with their surroundings. The data collection period lasted for 75 min in each building. During this period, occupants were asked to sit in the living room, and were limited to light activity movement, such as body parts movements of hands, feet, neck, etc. The metabolic rate value used in this study was estimated to be 1.2 met as recommended by ISO 7730 [5] for sedentary activity. Five sets of measurements were taken each at 15-min intervals.
39.5 0 39.5 39.5
22
3.2. Physical measurements
30 9.3 21 39.5
11.5% 11.5% 70%
39.5 7.07 29.5 49.5
Cooler
54% 67% 30%
36.3 21.1 12 65
No change
34.6% 22% 0
26 18.5 12 49.5
Warmer 3,2 1,0,þ1 þ3,þ2
24
Thermal preference scales:
23
Sensation vote range
25
All
Table 1 Thermal acceptability of all subjects living in the domestic buildings.
32.1 11 12 65
F.F. Al-ajmi, D.L. Loveday / Building and Environment 45 (2010) 704–710
Age Mean STD D Min. Max.
706
Table 3 Summary of statistical results for indoor environmental parameters in the 25 air-conditioned domestic buildings in Kuwait. Buildings 1
2
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
All
22.7 0.4 22.3 23.1
25.24 0.12 25.1 25.4
20.2 0.23 19.9 20.4
23.1 0.59 22.6 23.8
22.6 0.74 21.8 23.4
24.7 1.5 23.1 27
23.1 0.13 23 23.3
23.1 0.1 23 23.2
22.4 0.37 22.1 23
24.5 0.74 23.9 25.7
24.9 0.34 24.5 25.4
21.8 0.61 20.8 22.4
22.9 1.2 21.5 24.4
21.8 1.21 21.1 23.9
23.3 0.98 22.3 24.8
22.9 2.18 20.8 25.2
20.2 0.27 19.9 20.6
20.9 1.38 19.7 23.2
19.4 0.7 18.8 20.1
24.8 0.48 24.4 25.5
21.6 0.75 20.5 22.3
20.9 0.84 20 22
19.5 0.52 18.9 20.3
22.7 0.8 18.8 28.7
Relative Mean STD Min Max
38.2 0.84 37.2 39.5
35 0.52 34.5 35.6
52.7 0.78 51.9 54
42.2 1.84 40.1 44.1
40.9 0.59 39.6 42.8
39.7 3.1 34.5 42.3
39.2 0.58 38.7 39.9
46.6 0.44 45.9 47.1
50.7 0.4 50.4 51.3
46.7 2.1 44.1 49.2
66.7 1.6 65.1 69.3
40.4 1.8 37.6 43.3
47.4 6 43 56.4
36.5 6.3 33.2 47.6
43.4 2.5 40.2 46.3
41.3 6.8 33.5 50
44.3 1.5 43.4 46.6
44.5 2.8 41.6 49
46 1.9 43.7 47.8
35.1 0.91 33.8 36.8
43.3 0.21 43.1 43.6
43.7 2.1 41.7 47.8
41.6 0.98 40.8 43
43.5 1.97 33.2 69.3
humidity 42.7 38.7 1.81 0.73 40.7 37.4 45.6 39.3
Air velocity Mean 0.09 STD .002 Min .050 Max .10
.29 .004 0.17 .380
.140 .005 .120 0.17
.090 .001 .060 0.13
.130 0.07 .001 .160
.090 .001 .070 0.11
.090 .020 .001 .130
.090 .030 .001 0.17
.080 .020 .001 .150
.130 .020 .080 .140
.080 .020 .001 .110
.190 .110 .001 .30
.150 .001 .110 .230
.090 .010 .050 .130
.260 0.13 .001 0.33
.090 .050 .001 .120
.130 .070 .001 .170
.080 .020 .060 .10
.110 .002 .050 .170
.180 .001 .150 .20
.170 .030 .140 .20
.070 .020 0.05 .090
.140 .040 .070 .180
.120 .060 .060 .170
.180 .10 .001 .230
0.13 0.03 0.001 0.38
Operative temp. Mean 26.3 STD D 0.25 Min. 26 Max. 26.6
(C) 25.8 23.6 25.4 .830 .320 0.05 24.8 23.2 25.4 26.6 24 25.5
21 0.35 20.6 21.4
23.9 0.35 23.3 24.2
23.9 0.46 23.1 24.2
25 0.91 24.3 26.3
24.1 0.32 23.8 24.6
23.9 0.1 23.8 24
23.5 0.7 23 24.7
25.2 0.19 25 25.5
26 0.94 25.3 27.6
22.3 0.17 21.9 22.9
23.9 0.96 22.7 25.3
23.5 0.8 22.9 24.9
24.5 0.7 23.8 25.6
23.9 1.33 22.4 25
21.5 0.28 21.2 21.8
22.3 0.78 21.3 23.6
21.4 0.58 20.9 22.2
25.9 0.48 25.5 26.6
22.9 0.57 22.1 23.5
22.2 0.42 21.6 22.6
20.9 0.72 20.2 22.1
23.71 0.54 20.2 27.6
AMV Mean STD D Min. Max. P P D (%)
0.32 0.18 0.2 0.6 7.1
0.07 0.5 0.4 0.6 5.1
0.3 0.52 1.2 .4 6.9
0.2 0.54 0.6 1 5.8
1.7 0.44 1 2 61.8
0.2 0.28 0.4 0 5.8
v0.07 0.41 0.8 0.4 5.1
0.1 0.5 0.6 0.4 5.2
0 0.4 0.4 0.4 5
0.1 0.31 0.6 0.2 5.2
0.4 0.34 0.8 0 8.3
0.2 0.75 0.8 0.6 5.8
0.6 0.35 0.2 0.8 12.5
0.2 0.28 0.4 0 5.8
0.2 0.2 0.4 0 5.8
0.6 0.35 0.8 0.2 12.5
0.3 0.18 0.4 0 6.9
0.2 0.14 0.25 0 5.8
0.7 0.14 0.8 0.6 15.3
0.8 0.29 1 0.4 18.5
0.44 0.38 1 0 9
0.1 0.75 1 1.5 5.2
0.75 0.33 1.2 0.2 16.8
0.25 0.22 0.5 0 6.3
0.84 0.23 1 0.6 19.9
0.28 0.33 1.2 1.5 10.7
PMV Mean 0.7 STD D 0.09 Min. 0.58 Max. 0.84 P P D (%) 15.3
0.3 0.04 0.25 0.34 6.9
0.56 0.04 0.5 0.62 11.6
0.5 0.05 0.42 0.56 10.2
0.08 0.05 0.02 0.14 5.1
0.16 0.06 0.09 0.22 5.5
0.3 0.04 0.26 0.35 6.9
0.3 0.03 0.27 0.34 6.9
0.25 0.05 0.21 0.31 6.3
0.45 0.04 0.39 0.48 9.2
0.8 0.09 0.7 0.91 18.5
.04 0.07 .01 0.07 5
.13 0.24 .14 0.3 5.4
0.25 0.5 0.21 0.32 6.3
0.19 0.39 .07 0.55 5.7
.81 0.14 1 .61 18.8
.43 0.28 .71 0.03 8.9
.75 0.14 .87 .54 16.8
1.04 0.1 0.94 1.19 27.8
0.23 0.16 0.01 0.39 6.1
.43 0.22 0.7 0.2 8.9
.94 0.09 1.1 .87 23.7
0.13 0.13 1.1 1.19 10.21
0.3 0.05 0.23 0.35 6.9
0.35 0.03 0.3 0.38 7.5
.05 0.33 .07 0.44 5.1
F.F. Al-ajmi, D.L. Loveday / Building and Environment 45 (2010) 704–710
3
Air temperature Mean 25.3 26.3 STD D 1.6 2.4 Min. 25.1 23.1 Max. 25.5 28.7
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F.F. Al-ajmi, D.L. Loveday / Building and Environment 45 (2010) 704–710 45
4.1. Domestic indoor thermal conditions Table 2 provides a summary of the personal data from the 111 occupants in the survey, together with their clothing insulation values. Data are presented as the mean of the family occupants in each of the 25 households. Indoor climate measurements for the 25 domestic buildings are presented in Table 3. Indoor air temperature values ranged between 18.8 and 28.7 C with a mean value of 22.7 C, and standard deviation of 0.8, whilst recorded indoor relative humidities ranged from 33.2 to 69.7% with a mean value of 43.5% and standard deviation of 1.97. Fig. 2(a,b) shows these data in histogram forms. Average indoor air movements varied between 0.01 and 0.38 m/s with mean value of 0.13 m/s and standard deviation of 0.03, whilst operative temperatures were in the range of 20.2–27.6 C, with a mean of 23.7 C and standard deviation of 0.54, see Fig. 2(a). Table 3 also provide statistical summaries of thermal environments and thermal indices of occupants, with actual mean votes (AMVs) ranging from 1.2 to þ1.5 with a mean of 0.28 and standard deviation of 0.33.
4.2. Actual mean vote of subjects The fieldwork was carried out during the two summer seasons (May–October) of 2006 and 2007, in the State of Kuwait. Fig. 3 shows the occupants’ overall Actual Mean Vote (AMV) for the surveyed domestic buildings. It can be seen that 37.6% of the respondents feel neutral (0), whilst 38.4% feel slightly cool. In addition, 9.9% of occupants feel cool (2), while 5.4% feel warm (þ2). Furthermore, the thermal preference scale showed that 67%
Percentage of frequency (%)
4. Results and analyses
40 35 30 25 20 15 10 5 0
3
2
1
0
-1
-2
-3
AMV Fig. 3. Distribution of overall actual mean vote of selected buildings.
of occupants did not want a change to their indoor environments, while 22% wanted to be warmer, (see Table 1). The actual mean vote (AMV) of the occupants (male and female) in air-conditioned domestic buildings on the ASHRAE-seven-point scale were found to be marginally slightly cool (i.e. 0.28), which corresponds to a predicted percentage dissatisfaction (PPD) equal to 10.7%, while that for predicted mean vote (PMV) were marginally slightly warm (i.e. þ0.13), which corresponds to a PPD value equal to 10.2%. Findings for both AMV and PMV are very close to the neutral vote (see Table 3). Further analysis was conducted to find the indoor neutral temperature for the domestic buildings, as follows: Operative temperatures of the 25 air-conditioned domestic buildings were binned into 0.5 C intervals and analyzed to find the bin’s mean thermal sensation of the occupants. Linear regression analysis was then applied to determine the actual mean vote (AMV) and predicted mean vote (PMV) as a function of operative temperature (to) The linear regression equations obtained were then solved for neutrality (actual mean vote ¼ 0) to determine the neutral operative temperature. The linear regression equations for occupants’ reported thermal sensation (AMV) and for their Predicted Mean Vote (PMV) were thus found to be:
AMV ¼ 0:2318to 5:8444
ðr ¼ 0:848Þ
(1)
ðr ¼ 0:864Þ
(2)
and
PMV ¼ 0:2409to 5:6162
Fig. 2. (a) Indoor mean air temperature and operative temperature, and (b) Relative humidity, for all 25 domestic buildings.
The linear regression coefficient for the actual mean vote (AMV) as a function of operative temperature (to) (equation (1)) is 0.848, whilst that for the predicted mean vote (PMV) as a function of operative temperature (equation (2)) is 0.864. The gradient of the regression lines represents the sensitivity of the occupants with respect to the operative temperature index, and is found to be 0.2318/ C, for both equations, see Fig. 4. In Fig. 4, when the regression lines of AMV and PMV are plotted, the mean neutral operative temperature is the point where the regression line crosses the x-axis. Furthermore, Eqs. (1) and (2) were solved for neutrality to derive values for the neutral operative temperature. The neutral operative temperatures for AMV and PMV were thus determined to be 25.2 C and 23.3 C, respectively. PMV predictions underestimated observed neutrality by about 1.9 C less than that of AMV. This may indicate that the ISO 7730
F.F. Al-ajmi, D.L. Loveday / Building and Environment 45 (2010) 704–710 1 AMV
PMV
AMV / PMV
0.5
0 20
21
22
23
24
25
26
27
-0.5
-1
-1.5
Operative Temperature (C) Fig. 4. Linear regression calculation based on binned AMV and PMV versus operative temperature.
standard for calculating PMV underestimates the individual’s actual thermal sensation in a dry-desert climate. One explanation might be that occupants in air-conditioned buildings located in extremely hot and arid climates like that of Kuwait in fact find their indoor environments to be thermally comfortable even if they are being overcooled. However, a more extensive study is necessary to further investigate this possibility. It is interesting to note that similar findings were obtained in tests carried out in Kalgoorlie-Boulder, a hot, arid region of Western Australia, by Cena and de Dear [2]. Here, it was found that the AMV of the occupants in air-conditioned buildings is higher than that of the PMV. One possible explanation being put forward was that occupants adapt to their indoor air-conditioned environments (Cena and de Dear [2]). However, interpretation of the differences between actual mean vote (AMV) and predicted mean vote (PMV) is not straightforward. This can be due to the nature of calculation from the averaged estimation of variables, i.e. the activity rates or clothing insulation values, as well as the possibility of adaptation effects. According to Parsons [27] and Olesen and Parsons [28], use of the PMV method has been criticized and improvements are required to the PMV formula. An alternative use of the adaptive approach to account for a range of adaptation effects. Thus, further research is needed to fully investigate the use of the PMV technique for predicting the thermal sensation of individuals in air-conditioned domestic buildings located in extreme hot dry-desert climates. 5. Thermal acceptability The thermal acceptability of indoor environments is considered in ASHRAE standard 55(2004) [6] and ISO7730 (2005) [5] to be defined on the seven-point scale as being within the limits of either 1, 0, 1 (which accounts for 80% or more), or 0.5, 0, þ0.5 which accounts for 90%, or a predicted percentage of dissatisfaction (PPD) of 10%. Both limits are applicable due to the physiological variances of occupants. However, the most widely accepted thermal comfort range is for subjects who vote inside the limit (0.5, 0, þ0.5) of the ASHRAE-seven-point scale. Applying the latter limit corresponds to an operative temperature range of 23–27 C for thermal acceptability.
709
harsh summer seasons. Reduction of energy consumption in buildings is a major aim worldwide and is a particular challenge in a desert climate. In Kuwait, the Ministry of Electricity and Water (MEW) issued an energy conservation code in 1983 [29], which is still in force and has not been modified, despite the fact that more effective energy-efficient products and techniques have been developed since then. In addition, electrical energy costs in Kuwait are highly subsidized by the government, and without any updating of the energy code to date. Thus, a better-defined energy conservation code with more effective and energy-efficient design could offer both economic and environmental benefits for the Kuwaiti government. Furthermore, the energy code in Kuwait contains some rules and regulations for designing air-conditioning systems in Kuwait conditions. This code represents a set of regulations that guides the energy performance of new buildings. The energy code of Kuwait aims to guide local architects and airconditioning engineers to achieve energy-efficient design of modern buildings. For example, the code recommends the operative temperature of the indoor environment and outdoor design dry-bulb temperature for the Kuwait summer season to be 24 C and 46 C, respectively, for the purpose of designing the HVAC systems for air-conditioned buildings. However, reducing the indoor–outdoor temperature differences can potentially reduce energy consumption of HVAC systems, and in addition an electrical energy saving of 10% can be achieved by raising the thermostat temperature setting by 1 C [1,2] (for cooling). A neutral operative temperature value for the sample (25) of airconditioned domestic buildings in Kuwait was found in this study to be 25.2 C. With this finding, as the recommended and widely adopted indoor operative temperature by Kuwaiti energy code,then energy saving of over 10% could be achieved [29]. Adjustment of 1 C to the outdoor design temperature could yield further energy savings. This latter statement is based on the following. The existing outdoor summer design condition (or cooling design temperature) for Kuwait, as recorded in the Kuwaiti energy code (1983) is given as 46 C [29]. This finding (i.e. current outdoor design condition) was revised by analyzing the collected Kuwait climatological data summaries from 1962 to 2006, leading to a value of outdoor summer design temperature equal to 45 C [3,26]. Consequently, this may lead to more relevant design of HVAC systems for Kuwaiti buildings. Clearly more research is needed before firm recommendations of this nature can be made, but this discussion serves to illustrate the potential for energy saving by adjustment of recommended design temperatures. 7. Conclusions The main objective of this study was to investigate the indoor climate, thermal conditions and occupant thermal comfort sensations in air-conditioned domestic buildings in the State of Kuwait. A total of 111 occupants in twenty-five air-conditioned domestic buildings located in the dry-desert climate of Kuwait were surveyed during the summers of 2006 and 2007. The survey involved the recording of environmental parameters and human thermal comfort responses. The domestic buildings were evenly distributed across the five provinces of Kuwait. The main results of the study were as follows:
6. Potential for energy conservation Economic and industrial development in the dry-desert climate of Kuwait has led to an increasing demand for electricity, much of which is consumed in air conditioning systems that are used extensively to overcome indoor thermal discomfort during the
Across all domestic buildings the mean indoor dry-bulb air temperature was found to be 22.7 C with standard deviation of 0.8 and mean relative humidity of 43.5% with standard deviation of 1.97 and a mean air movement of 0.13 ms1, with standard deviation of 0.03.
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The neutral operative temperature for occupants was found to be 25.2 C. This was obtained by linear regression analysis of actual mean vote on operative temperature. The Actual Mean Vote (AMV) was within the range of 1.2 to þ1.5 with the occupants’ mean thermal sensation being 0.28, whilst for Predicted Mean Vote (PMV) the range was 1.1 to þ1.19, with a PMV equal to þ0.13. The neutral operative temperatures based upon AMV and PMV were determined to be 25.2 C and 23.3 C, respectively. PMV predictions underestimated observed neutrality by about 1.9 C less than that of AMV. This finding is similar to that reported by Cena and de Dear [2] and may indicate that the ISO 7730 standard for calculating PMV underestimates the individual’s actual sensation in a dry-desert climate due to possible adaptive effects, though further research is needed to confirm this. The widely accepted criterion for thermal acceptability, namely the central three values of 0.5 to 0 to þ0.5 of the 7-point scale (which accounts for predicted percentage of dissatisfaction (PPD) of 10%) corresponds to an operative temperature range of 23–27 C for thermal acceptability in the domestic residences. Were adjustments to be made to the indoor/outdoor design temperatures in the energy code of the Ministry of Electricity and Water in the State of Kuwait, the effect on national energy consumption could be considerable. However, more extensive research is needed before such a recommendation can be made. Acknowledgments This work was financially supported by the Kuwait Foundation for the Advancement of Sciences (KFAS) under research grant (2004-1508-02), this support being gratefully acknowledged. The authors also are grateful to the Department of Civil Engineering at the College of Technological Studies, State of Kuwait, and to the Department of Civil and Building Engineering, Loughborough University, UK. The authors express their gratitude to all volunteer subjects who took part in this work. They are also thankful to Mr. Mohammed Ali and Mrs. Nadia Alayoub for their assistance during the fieldwork. References [1] Sekhar SC, Ching CS. Indoor air quality and thermal comfort studies of an under-floor air-conditioning system in the tropics. Energy and Buildings 2002;34(5):431–44. [2] Cena K, de Dear R. Thermal comfort and behavioural strategies in office buildings located in a hot-arid climate. Journal of Thermal Biology 2001;26(4– 5):409–14. [3] Al-ajmi F, Hanby VI. Simulation of energy consumption for Kuwaiti domestic buildings. Energy and Buildings 2008;40:1101–9.
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