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Thermal comfort studies in hawker centres in Singapore
Buihling and Em,ironmem. Vol. 13, pp. 161 166 © Pergamon Press Ltd. I978. Printed in Great Britain
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0360,1323/78/0901 0161 $02.00/0
Thermal Comfort Studies in Hawker Centres in Singapore K. R. RAO* J. C. H O t
This study deals with a programme of experimental studies on thermal comfort levels inside hawker centres in Singapore. Hawker centres in Singapore are large metal-roof structures having typical floor areas of 2000m 2 and roof heights of about 5 m, and within which varieties of cooked food are sold. The experimental studies were conducted during typically hot days when the dry-bulb temperature was close to the daily maximum value of 30"4 C. Continuous measurements of the dry-bulb temperature, relative humidity, air movement, radiation from the metal roof and the thermal corn]brt index were carried out. Based upon the experimental results, measures for improving the comfort levels were recommended. An Equatorial Comfort Index was derived and an optimum value relevant to the environment of the hawker centres was established.
Hawker centres, as they are known locally, are covered structures within which are stalls serving cooked food and beverages to customers numbering is many as a few hundred during peak hours. As such these hawker centres are a common feature of life in this equatorial island. Architecturally, the hawker centres are fairly large single-storey structures with a typical floor area of 2000 m: and roof height of about 5 m. Walls are not provided in order to allow maximum cross-ventilation. Roof material is in the form of uninsulated galvanized steel sheets available commercially as Spandek sheets. It can be readily realized that due to the nature of the roofing material used, the thermal comfort environment within the hawker centre are most susceptible to changes of the local weather conditions. The objectives of this study are to determine and define the comfort levels within the hawker centre under typically hot weather conditions, and to propose on the basis of the experimental results, recommendations for achieving improved comfort levels in the environment of the hawker centre. It needs to be pointed out here that because of the nature of the construction of the hawker centres, completely neutral comfort conditions cannot be obtained in such a relatively uncontrolled environment. Furthermore, comfort levels deemed to be acceptable are applicable to local people, that is, subjects acclimatised to an equatorial climate.
1. I N T R O D U C T I O N THE PROVISION for indoor thermal comfort is among the important objectives in the design and construction of non-airconditioned buildings in the tropics and equatorial regions where high daytime temperatures and relative humidity prevailed over the greater part of each day. These adverse thermal comfort conditions are especially true in Singapore where temperatures exceeding the daily maximum value of 30.4°C and the accompanying relative humidity values are about 70-80 %, are often encountered. To date, various studies have been carried out on the thermal comfort conditions and the establishment of comfort indices in Singapore and elsewhere with similar climatic conditions. Among these studies are those of Webb[1] and Ellis[2]. The thermal comfort charts prepared by ASHRAEI-3] are also applicable and have been used to determine thermal comfort levels. The index of thermal comfort is the effective temperature which is a function of the dry bulb temperature, relative humidity and air movement. For equatorial climates like that of Singapore, an equivalent comfort index called the Equatorial Comfort Index (ECI) was proposed by Webb. Webb's ECI is based on experimental studies carried out on Singapore people under indoor conditions. Webb's study indicates that an optimum value for thermal comfort in Singapore is 25-6°C. Within a range of deviation of _ 1.1°C from the optimum value 95% of the subjects experienced satisfactory thermal comfort level. This paper deals with a programme of experimental studies on thermal comfort conditions in the uncontrolled environment of hawker centres in Singapore.
2. D E S C R I P T I O N OF THE HAWKER CENTRE A brief description of some of the common features of the hawker centres is given here so as to provide a better picture 6f their environment and surroundings. More often than not, the shape of the hawker centre is that of a rectangle measuring 60 × 40m; hawker centres exist with a larger length to width ratios but covering approximately the same area. The roofing
*Department of Building Science, University of Singapore. tDepartment of Mechanical Engineering, University of Singapore. 161
162
K. R. Rao aml .I, ( . 11o
material used is in the form of Spandek sheets with the under surface left unpainted while a dark green paint is provided for the surface exposed to solar radiation. Maximum roof height for economical cost of construction, is kept to about 5"8m and the roof slope is about 5 . Fascias, also constructed out of Spandek sheets, of height 3 m, serve as means for sun shading and for reducing rain penetration. Steel or concrete is the material for structural beams and columns. The hawker stalls where cooked food is sold are located in rows running parallel to the width of the hawker centre and are spaced approx 10m apart. In the area between rows of cooked food stalls, small tables and chairs are provided for the customers. In the case of long rectangular hawker centres, a row of cooked food stalls is located centrally and parallel to the length of the hawker centre. Sitting spaces on either side of the row of food stalls are provided along the entire length. Directly above the cooked food stalls at the roof, are ventilation fans. These fans are provided for the purpose of exhausting cooking fumes and smoke from the hawker centre. The hawker centres studied are located within Singapore's low cost housing estates in which blocks of high-rise fiats are located relatively close to one another. As such, some obstruction by the blocks of flats to the ventilation of the hawker centre inevitably occurs. This, however, does not pose a serious problem except for the large-square type of hawker centres where air movement in the central regions is greatly reduced.
3. DESCRIPTION OF THE EXPERIMENTAL STUDIES In order to determine the comfort levels in the hawker centres during typically hot days, the following data were collected in each hawker centre at 2 3 rain intervals over periods varying from 2 to 3 h: 1. dry bulb and wet bulb temperature: 2. air velocity; 3. thermal radiation from the roof. Wet bulb and dry bulb temperature measurements were carried out using a sling psychrometer. Air velocities in the hawker centres were measured using a hot-wire type anemometer. The hot wire anemometer is a portable instrument, the probe of which has also been calibrated to measure static air temperature. Vertical temperature distributions from the roof of the hawker centre to the sitting level (1.25m from the floor) were recorded once or twice during the course of the experimental study at each hawker centre. Tim amount of thermal radiation from the roof of the hawker centre to a point 1.25 m from the floor was measured using a net radiometer. This is an instrument development developed by the Commonwealth Scientific and Industrial Research Organization (CS1RO) of Victoria, Australia. The amount of radiation measured at 1-25m is thus assumed to be that incident upon a subject sitting inside the hawker centre.
In addition, two indices of thcrrnal comfort sensations, the Predited Mean Vote {PMV) and the Equilibrium Temperature (ET) were simultaneously recorded. Measurements of these two indices were carried out using a 'Comfy-Test' meter developed by Fanger[4]. The 'Comfy-Test" meter is a thermal sensation recording instrument which essentially integrates the effects of air temperature, air movement and radiation incident on a sensor and displays a numerical value in the range - 3 to + 3. These numerical values have the following meanings: 3: Very cold - 2 : Cold - 1: Cool 0: Neutral 1: Warm 2: Hot 3: Very hot. The effects of clothing, activity (metabolism rate) and relative humidity need to be taken into consideration. For the experimental studies conducted, mean values h)r the relative humidity and clothing and activity levels corresponding to light tropical wear and sedentary activity were prescribed to the 'Comfy-Test' meter. The abovementioned factors affecting comfort levels were integrated by the 'Comfy-Test' meter to produce in addition to the PMV, an equivalent temperature called the Equilibrium Temperature experienced by a subject under similar conditions. in an attempt to obtain a direct evaluation of the comfort levels within the hawker centre and to provide a basis for the correlation of the experimental data, a thermal comfort survey was conducted among the customers and hawkers of the centre. Interviewers were provided with questionnaires and were required to elicit from the users of the hawker centre, information on thermal sensations such as the degree of hotness, presence of perspiration, the radiant heat from the roof, and length of stay in the hawker centre. These thermal sensation surveys were conducted simultaneously with the experimental measurements described previously. On each questionnaire, the time of the interview was recorded and hence the results of this survey could be correlated with the measurements of the factors affecting comfort levels.
4. RESULTS OF EXPERIMENTAL STUDIES Experimental studies of the nature described in the preceding section were carried out at six hawker centres. One of the six hawker centres is a concreteroof structure, the rest being Spandek-roof structures. In one of the five Spandek-roof hawker centres, insulation against thermal radiation was available in the f o r m of aluminium installed on the under-surface of the roof. The objectives of this section is to present some of the results of the experimental studies and from these results, attempts will be carried out to compare the comfort levels at each of the hawker centres and to identify those factors adverse or favourable to thermal comfort. Another objective is to establish equatorial comfort indices relevant to the environment of the hawker centres.
Thermal comfort studies in hawker centres in Singapore 4.1 Summary of experimental results A large amount of data was obtained during the experimental studies and thermal comfort surveys carried out at the six hawker centres. A set of measurements comprising dry and wet bulb temperatures, air velocity roof thermal radiation, under surface temperature of the roof and the comfort index (PMV) were obtained at 2 - 3 m i n intervals. A summary of the results from four hawker centres is presented here.
Henderson Road Hawker Centre Size of hawker centre: 105 x 16.4m Roof material: Spandek sheets M a x i m u m height of hawker centre: 4.8 m Date of experiment: 22-8-75 Time of experiment: 12:55 p.m.-2:07 p.m., 2:37 p.m.3:00 p.m. N u m b e r of sets of readings taken: 53
Average: Maximum: Minimum:
Ta
Rh
fC)
(%)
V (m/s)
(°C) (W/m 2) PMV
T,
Q,
28-6 29.5 27.8
77-2 83.0 60.0
1-42 3-48 0.14
40.9 47.8 35.0
47-0 72.0 19.5
0.43 1-55 -0.5
Total number of interviews taken: 66 Percentage of interviews with thermal response corresponding to P M V 0 = 56.7 ~o Percentage of interviews with thermal response corresponding to P M V 3 = 0 Percentage of interviews with thermal response corresponding to P M V - 1 to + 1 = 100~o Td = dry bulb temperature, Rh = relative humidity, V = air velocity, T~ = roof underside surface temperature, Q, = thermal radiation from roof and P M V = predicted mean vote.
163
M a x i m u m height of hawker centre: 4.5 m Date of experiment: 20-6-75 Time of experiment: 2:21 p.m.-2:41 p.m. N u m b e r of sets of readings taken: 20
Average: Maximum: Minimum:
Td ("C)
Rh (%)
V (m/s)
T, Q, (~C) ,(W/m 2) PMV
32.2 32.8 31.7
54.7 59 53
0.16 0.40 0.05
30 31.1 29.6
- 8 - 6 -9*
1.9 2.0 1.7
*Negative readings show that the roof temperature is lower than the air temperature inside hawker centre. Total number of interviews taken: 20 Percentage of interviews with thermal response corresponding to P M V 0 = 35 ~o Percentage of interviews with thermal response corresponding to P M V 3 = 0 Percentage of interviews with thermal response corresponding to P M V - 1 to + 1 = 85 %.
Holland Drive Hawker Centre Size of hawker centre: 44'7 x 13 m Roof material: Spandek sheets with aluminium reflective foil attached to under surface Maximum height of hawker centre: 12'7 m Date of experiment: 26-6-75 Time of experiment: 12:11 p.m.-12:49 p.m., 2:24 p.m.2:40 p.m. N u m b e r of sets of readings taken : 30
Average: Maximum: Minimum:
7~ (°C)
Rh (%)
V (m/s)
T, Q, (°C) (W/m 2) PMV
31-5 32.1 31.1
71 78 62
0.56 1.80 0-15
34.4 35.6 33-6
20.0 27.0 14-0
1-4 1.8 1.02
Bendemeer Road Hawker Centre Size of hawker centre: 104 × 34m Roof material: Spandek sheets M a x i m u m height of hawker centre: 5"8m Date of experiment: 27-8-75 Time of experiment: 1:15 p.m.-3:00 p.m. N u m b e r of sets of readings taken: 46
Average: Maximum: Minimum:
Td Cc)
Rh (%)
V (m/s)
Tr Q, (°C) (W/m 2) PMV
30.2 32.8 27-8
75.7 88.0 59.0
0.48 2-0 0.22
39.4 53.3 25
33.0 85.0 3.5
1-5 3 0.1
Total number of interviews taken: 63 Percentage of interviews with thermal response corresponding to P M V 0 = 19-6 ~o Percentage of interviews with thermal response corresponding to P M V 3 = 10"9 ~o Percentage of interviews with thermal response corresponding to P M V - 1 to + 1 = 60.9 %.
Toa Payoh Central Hawker Centre Size of hawker centre: 37.8 x 50 m Roof material: concrete
Total number of interviews taken: 30 Percentage of interviews with thermal response corresponding to P M V 0 = 30 % Percentage of interviews with thermal response corresponding to P M V 3 = 0 Percentage of interviews with thermal response corresponding to - 1 to + 1 = 83-3 ~o. The summary of the experimental results for the four hawker centres indicates clearly that conditions adverse to thermal comfort were commonly encountered inside the hawker centres. These adverse thermal conditions which are characterised by high dry bulb temperature (the average being more than 3if'C) and high relative humidity of about 75 %. Such conditions prevail almost throughout the year for daily periods of about 5h (from 11:00 a.m. to 4:00 p.m.). F r o m the time variation graphs of the air temperature, roof thermal radiation, air velocity and the P M V shown in Figs. 1 4 , relief from thermal discomfort is present only in those instances where the air velocity exceeds 1 m/s. The results of Figs. 1~, further indicate that when the thermal radiation from the roof is reduced to about 20 W / m 2, significant improvement in the comfort level can be obtained in spite of high dry bulb
164
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251
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2D5
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Fig. 3. Variation of comfort level factors with time. Location:
Fig. 1. Variation of comfort level factors with time. Location: Henderson hawker centre. Date 22-8-1975.
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241
Time,
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Toa Payoh central hawker-market centre. Date 2t)-6-1975.
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t235
12 45
Time,
p.m.
Fig. 2. Variation of comfort level factors with time. Location: Bendemeer Road hawker centre. Date 27-8-1975.
Fig. 4. Variation of comfort level factors with time. Location: Holland Drive hawker centre. Date 26-6-1975.
t e m p e r a t u r e of a b o u t 31°C and for air velocity near or less t h a n 1 m/s. Finally the results of Fig. 3, which were obtained from a concrete-roof hawker centre, show that in the absence of roof radiation, satisfactory comfort levels were not existing when conditions of high air temperatures and low air velocities prevailed.
A sample of the vertical air t e m p e r a t u r e distribution in the hawker centre is provided in Fig. 5. Figure 5 shows clearly that the t e m p e r a t u r e gradient is largest in a region of a b o u t 2 5 c m from the roof. Increasing the roof height would reduce the a m o u n t of thermal radiation received at the sitting level but would not
165
Thermal confort studies in hawker centres in Singapore Temperature, 025
35
°C
45
n55
50
I
Bright sun condition o
2 Cloudy condition
•
I00
200
300
400
500
Fig. 5. Vertical temperature distributions for Henderson Road hawker centre.
produce any significant reduction in the air temperature at the sitting level. Altogether, 435 thermal comfort interviews were collected from the six hawker centres and of these, 69 % indicated thermal comfort levels corresponding to PMV values in the range - 1 to + 1. In other words, according to this 69?/o of the users of the hawker centres, favourable comfort level prevailed inside the hawker centres. Such a high percentage of users indicating favourable comfort levels is quite unexpected, and it contradicts somewhat the results obtained from the 'Comfy-Test' meter. The cause of this larger than expected percentage is the general tendency of the hawker centre users to under-rate, knowingly or otherwise, the actual degree of thermal discomfort. In the absence of a mathematical model which would have to incorporate the effects of air temperature, roof radiation, air velocity, relative humidity and architectural details of the hawker centres, recommendations for the improvement of comfort levels are based on the results thus obtained. Satisfactory comfort levels relevant to the environment of the hawker centres in Singapore, that is, predicted mean vote values of about 1.0, can be obtained by a combination of roof thermal radiation reduced by the installation of aluminium foil to about 20W/m 2, and air velocities near or exceeding 1.0m/s. The latter requirement is readily brought about through the installation of ceiling or oscillating wall-mounted fans.
5. D E T E R M I N A T I O N O F ACCEPTABLE COMFORT LEVELS FOR HAWKER CENTRES A final section of this paper is devoted to the determination and definition of acceptable comfort levels in the environment of the hawker centre. One of the widely used comfort indices for defining comfort levels is that proposed by the American Society for Heating, Refrigeration and Air Conditioning Engineers (ASHRAE). For equatorial eli-
mate like that of Singapore, a similar index called the Equatorial Comfort Index (ECI) is that proposed by Webb, Webb's Equatorial Comfort Index was derived based on experimental studies on subjects under indoor conditions, which were different from those of the present study. The regression equation expressing the ECI was found to be ECI = 0.447ta + 0.553t w- 0-231 V 1/2 where td = dry bulb temperature, ' F t., = wet bulb temperature, =F V = air velocity, ft/min. The optimum value found in such an environment was 78-1°F (25,6°C). For the environment under which this study was carried out, the effects of thermal radiation need to be considered. Accordingly, in order to compare the results of the present study with those of Webb's, the mean radiation temperature Tm,, is given by: T,,,, = (.L E, T 4 + fz T~) ~'4
where f~ and f2 are the view factors of the roof and the surroundings of the hawker centre, T~ and Td are the absolute values of the roof and air temperatures, and E, is the emissivity of the roof, was first calculated. In order to correct the ECI for radiation, the globe temperature was calculated using t9 =
0.353 td+ (tm,t--ta)~
,/v
•
Finally by substituting tg for td in Webb's regression equation, the radi~ition corrected ECI can be obtained for each of the sets of data obtained from the hawker centres. The optimum value for the corrected ECI, that is, the value corresponding to a PMV value of l'0
166
K . R . Rao and J. ('. Ho
(warml, was found to be 26.4 C. "['his is about 1 C higher than Webb's EC1. The higher value for the optimum value for the corrected ECI is expected since conditions inside the hawker centre, although subject to higher air velocities, are more adversely affected by the presence of roof thermal radiation.
6. C O N C L U S I O N S On the basis of the experimental studies on comfort level carried out at the hawker centres the following conclusions may be stated:
(1) Adverse thermal comfort levels prevailing tn the environment of the hawker centres are brought about by the combined effects of air temperatures, exceeding 3 0 C , relative humidity values of about 75",,, poor air movement (less than 1 m/sl and roof thermal radiation exceeding 50 W/m-'. (2) Acceptable comfort levels can be achieved by the installation of fans to increase air movement and the use of reflective aluminium foil to reduce the roof thermal radiation to about 20 W/m 2. (3) The optimum corrected value of the Equatorial Comfort Index relevant to the environment of the hawker centres is found to be 264 C.
7. REFERENCES 1. F. P. Ellis, Thermal comfort in warm and humid atmosphere: observations on groups and individuals in Singapore, J. Hyg, Camb. 51,386 (1953). 2. C.G. Webb, An analysis of some observations of thermal comfort in an equatorial climate, Br. J. Ind. Med. 16, 297 (1959). 3. C. G. Webb, American Society of Heating, Refrigeration and Air Conditioning Engineers. Handbook of Fundamentals, New York {1967}. 4. P.O. Fanger, Thermal ComJbrt-Analysi.s and Application m Environmental Engineering. McgrawHill, New York (1972).
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0360,1323/78/0901 0161 $02.00/0
Thermal Comfort Studies in Hawker Centres in Singapore K. R. RAO* J. C. H O t
This study deals with a programme of experimental studies on thermal comfort levels inside hawker centres in Singapore. Hawker centres in Singapore are large metal-roof structures having typical floor areas of 2000m 2 and roof heights of about 5 m, and within which varieties of cooked food are sold. The experimental studies were conducted during typically hot days when the dry-bulb temperature was close to the daily maximum value of 30"4 C. Continuous measurements of the dry-bulb temperature, relative humidity, air movement, radiation from the metal roof and the thermal corn]brt index were carried out. Based upon the experimental results, measures for improving the comfort levels were recommended. An Equatorial Comfort Index was derived and an optimum value relevant to the environment of the hawker centres was established.
Hawker centres, as they are known locally, are covered structures within which are stalls serving cooked food and beverages to customers numbering is many as a few hundred during peak hours. As such these hawker centres are a common feature of life in this equatorial island. Architecturally, the hawker centres are fairly large single-storey structures with a typical floor area of 2000 m: and roof height of about 5 m. Walls are not provided in order to allow maximum cross-ventilation. Roof material is in the form of uninsulated galvanized steel sheets available commercially as Spandek sheets. It can be readily realized that due to the nature of the roofing material used, the thermal comfort environment within the hawker centre are most susceptible to changes of the local weather conditions. The objectives of this study are to determine and define the comfort levels within the hawker centre under typically hot weather conditions, and to propose on the basis of the experimental results, recommendations for achieving improved comfort levels in the environment of the hawker centre. It needs to be pointed out here that because of the nature of the construction of the hawker centres, completely neutral comfort conditions cannot be obtained in such a relatively uncontrolled environment. Furthermore, comfort levels deemed to be acceptable are applicable to local people, that is, subjects acclimatised to an equatorial climate.
1. I N T R O D U C T I O N THE PROVISION for indoor thermal comfort is among the important objectives in the design and construction of non-airconditioned buildings in the tropics and equatorial regions where high daytime temperatures and relative humidity prevailed over the greater part of each day. These adverse thermal comfort conditions are especially true in Singapore where temperatures exceeding the daily maximum value of 30.4°C and the accompanying relative humidity values are about 70-80 %, are often encountered. To date, various studies have been carried out on the thermal comfort conditions and the establishment of comfort indices in Singapore and elsewhere with similar climatic conditions. Among these studies are those of Webb[1] and Ellis[2]. The thermal comfort charts prepared by ASHRAEI-3] are also applicable and have been used to determine thermal comfort levels. The index of thermal comfort is the effective temperature which is a function of the dry bulb temperature, relative humidity and air movement. For equatorial climates like that of Singapore, an equivalent comfort index called the Equatorial Comfort Index (ECI) was proposed by Webb. Webb's ECI is based on experimental studies carried out on Singapore people under indoor conditions. Webb's study indicates that an optimum value for thermal comfort in Singapore is 25-6°C. Within a range of deviation of _ 1.1°C from the optimum value 95% of the subjects experienced satisfactory thermal comfort level. This paper deals with a programme of experimental studies on thermal comfort conditions in the uncontrolled environment of hawker centres in Singapore.
2. D E S C R I P T I O N OF THE HAWKER CENTRE A brief description of some of the common features of the hawker centres is given here so as to provide a better picture 6f their environment and surroundings. More often than not, the shape of the hawker centre is that of a rectangle measuring 60 × 40m; hawker centres exist with a larger length to width ratios but covering approximately the same area. The roofing
*Department of Building Science, University of Singapore. tDepartment of Mechanical Engineering, University of Singapore. 161
162
K. R. Rao aml .I, ( . 11o
material used is in the form of Spandek sheets with the under surface left unpainted while a dark green paint is provided for the surface exposed to solar radiation. Maximum roof height for economical cost of construction, is kept to about 5"8m and the roof slope is about 5 . Fascias, also constructed out of Spandek sheets, of height 3 m, serve as means for sun shading and for reducing rain penetration. Steel or concrete is the material for structural beams and columns. The hawker stalls where cooked food is sold are located in rows running parallel to the width of the hawker centre and are spaced approx 10m apart. In the area between rows of cooked food stalls, small tables and chairs are provided for the customers. In the case of long rectangular hawker centres, a row of cooked food stalls is located centrally and parallel to the length of the hawker centre. Sitting spaces on either side of the row of food stalls are provided along the entire length. Directly above the cooked food stalls at the roof, are ventilation fans. These fans are provided for the purpose of exhausting cooking fumes and smoke from the hawker centre. The hawker centres studied are located within Singapore's low cost housing estates in which blocks of high-rise fiats are located relatively close to one another. As such, some obstruction by the blocks of flats to the ventilation of the hawker centre inevitably occurs. This, however, does not pose a serious problem except for the large-square type of hawker centres where air movement in the central regions is greatly reduced.
3. DESCRIPTION OF THE EXPERIMENTAL STUDIES In order to determine the comfort levels in the hawker centres during typically hot days, the following data were collected in each hawker centre at 2 3 rain intervals over periods varying from 2 to 3 h: 1. dry bulb and wet bulb temperature: 2. air velocity; 3. thermal radiation from the roof. Wet bulb and dry bulb temperature measurements were carried out using a sling psychrometer. Air velocities in the hawker centres were measured using a hot-wire type anemometer. The hot wire anemometer is a portable instrument, the probe of which has also been calibrated to measure static air temperature. Vertical temperature distributions from the roof of the hawker centre to the sitting level (1.25m from the floor) were recorded once or twice during the course of the experimental study at each hawker centre. Tim amount of thermal radiation from the roof of the hawker centre to a point 1.25 m from the floor was measured using a net radiometer. This is an instrument development developed by the Commonwealth Scientific and Industrial Research Organization (CS1RO) of Victoria, Australia. The amount of radiation measured at 1-25m is thus assumed to be that incident upon a subject sitting inside the hawker centre.
In addition, two indices of thcrrnal comfort sensations, the Predited Mean Vote {PMV) and the Equilibrium Temperature (ET) were simultaneously recorded. Measurements of these two indices were carried out using a 'Comfy-Test' meter developed by Fanger[4]. The 'Comfy-Test" meter is a thermal sensation recording instrument which essentially integrates the effects of air temperature, air movement and radiation incident on a sensor and displays a numerical value in the range - 3 to + 3. These numerical values have the following meanings: 3: Very cold - 2 : Cold - 1: Cool 0: Neutral 1: Warm 2: Hot 3: Very hot. The effects of clothing, activity (metabolism rate) and relative humidity need to be taken into consideration. For the experimental studies conducted, mean values h)r the relative humidity and clothing and activity levels corresponding to light tropical wear and sedentary activity were prescribed to the 'Comfy-Test' meter. The abovementioned factors affecting comfort levels were integrated by the 'Comfy-Test' meter to produce in addition to the PMV, an equivalent temperature called the Equilibrium Temperature experienced by a subject under similar conditions. in an attempt to obtain a direct evaluation of the comfort levels within the hawker centre and to provide a basis for the correlation of the experimental data, a thermal comfort survey was conducted among the customers and hawkers of the centre. Interviewers were provided with questionnaires and were required to elicit from the users of the hawker centre, information on thermal sensations such as the degree of hotness, presence of perspiration, the radiant heat from the roof, and length of stay in the hawker centre. These thermal sensation surveys were conducted simultaneously with the experimental measurements described previously. On each questionnaire, the time of the interview was recorded and hence the results of this survey could be correlated with the measurements of the factors affecting comfort levels.
4. RESULTS OF EXPERIMENTAL STUDIES Experimental studies of the nature described in the preceding section were carried out at six hawker centres. One of the six hawker centres is a concreteroof structure, the rest being Spandek-roof structures. In one of the five Spandek-roof hawker centres, insulation against thermal radiation was available in the f o r m of aluminium installed on the under-surface of the roof. The objectives of this section is to present some of the results of the experimental studies and from these results, attempts will be carried out to compare the comfort levels at each of the hawker centres and to identify those factors adverse or favourable to thermal comfort. Another objective is to establish equatorial comfort indices relevant to the environment of the hawker centres.
Thermal comfort studies in hawker centres in Singapore 4.1 Summary of experimental results A large amount of data was obtained during the experimental studies and thermal comfort surveys carried out at the six hawker centres. A set of measurements comprising dry and wet bulb temperatures, air velocity roof thermal radiation, under surface temperature of the roof and the comfort index (PMV) were obtained at 2 - 3 m i n intervals. A summary of the results from four hawker centres is presented here.
Henderson Road Hawker Centre Size of hawker centre: 105 x 16.4m Roof material: Spandek sheets M a x i m u m height of hawker centre: 4.8 m Date of experiment: 22-8-75 Time of experiment: 12:55 p.m.-2:07 p.m., 2:37 p.m.3:00 p.m. N u m b e r of sets of readings taken: 53
Average: Maximum: Minimum:
Ta
Rh
fC)
(%)
V (m/s)
(°C) (W/m 2) PMV
T,
Q,
28-6 29.5 27.8
77-2 83.0 60.0
1-42 3-48 0.14
40.9 47.8 35.0
47-0 72.0 19.5
0.43 1-55 -0.5
Total number of interviews taken: 66 Percentage of interviews with thermal response corresponding to P M V 0 = 56.7 ~o Percentage of interviews with thermal response corresponding to P M V 3 = 0 Percentage of interviews with thermal response corresponding to P M V - 1 to + 1 = 100~o Td = dry bulb temperature, Rh = relative humidity, V = air velocity, T~ = roof underside surface temperature, Q, = thermal radiation from roof and P M V = predicted mean vote.
163
M a x i m u m height of hawker centre: 4.5 m Date of experiment: 20-6-75 Time of experiment: 2:21 p.m.-2:41 p.m. N u m b e r of sets of readings taken: 20
Average: Maximum: Minimum:
Td ("C)
Rh (%)
V (m/s)
T, Q, (~C) ,(W/m 2) PMV
32.2 32.8 31.7
54.7 59 53
0.16 0.40 0.05
30 31.1 29.6
- 8 - 6 -9*
1.9 2.0 1.7
*Negative readings show that the roof temperature is lower than the air temperature inside hawker centre. Total number of interviews taken: 20 Percentage of interviews with thermal response corresponding to P M V 0 = 35 ~o Percentage of interviews with thermal response corresponding to P M V 3 = 0 Percentage of interviews with thermal response corresponding to P M V - 1 to + 1 = 85 %.
Holland Drive Hawker Centre Size of hawker centre: 44'7 x 13 m Roof material: Spandek sheets with aluminium reflective foil attached to under surface Maximum height of hawker centre: 12'7 m Date of experiment: 26-6-75 Time of experiment: 12:11 p.m.-12:49 p.m., 2:24 p.m.2:40 p.m. N u m b e r of sets of readings taken : 30
Average: Maximum: Minimum:
7~ (°C)
Rh (%)
V (m/s)
T, Q, (°C) (W/m 2) PMV
31-5 32.1 31.1
71 78 62
0.56 1.80 0-15
34.4 35.6 33-6
20.0 27.0 14-0
1-4 1.8 1.02
Bendemeer Road Hawker Centre Size of hawker centre: 104 × 34m Roof material: Spandek sheets M a x i m u m height of hawker centre: 5"8m Date of experiment: 27-8-75 Time of experiment: 1:15 p.m.-3:00 p.m. N u m b e r of sets of readings taken: 46
Average: Maximum: Minimum:
Td Cc)
Rh (%)
V (m/s)
Tr Q, (°C) (W/m 2) PMV
30.2 32.8 27-8
75.7 88.0 59.0
0.48 2-0 0.22
39.4 53.3 25
33.0 85.0 3.5
1-5 3 0.1
Total number of interviews taken: 63 Percentage of interviews with thermal response corresponding to P M V 0 = 19-6 ~o Percentage of interviews with thermal response corresponding to P M V 3 = 10"9 ~o Percentage of interviews with thermal response corresponding to P M V - 1 to + 1 = 60.9 %.
Toa Payoh Central Hawker Centre Size of hawker centre: 37.8 x 50 m Roof material: concrete
Total number of interviews taken: 30 Percentage of interviews with thermal response corresponding to P M V 0 = 30 % Percentage of interviews with thermal response corresponding to P M V 3 = 0 Percentage of interviews with thermal response corresponding to - 1 to + 1 = 83-3 ~o. The summary of the experimental results for the four hawker centres indicates clearly that conditions adverse to thermal comfort were commonly encountered inside the hawker centres. These adverse thermal conditions which are characterised by high dry bulb temperature (the average being more than 3if'C) and high relative humidity of about 75 %. Such conditions prevail almost throughout the year for daily periods of about 5h (from 11:00 a.m. to 4:00 p.m.). F r o m the time variation graphs of the air temperature, roof thermal radiation, air velocity and the P M V shown in Figs. 1 4 , relief from thermal discomfort is present only in those instances where the air velocity exceeds 1 m/s. The results of Figs. 1~, further indicate that when the thermal radiation from the roof is reduced to about 20 W / m 2, significant improvement in the comfort level can be obtained in spite of high dry bulb
164
K. R. Rao and J. ('. f t o
30 i 20
~o
05 i0 (
0
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~
34 33
~:
29 28
f
32
o
27 E ~
80
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~
nO
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I
I
2
o
o
1 2 21
I I 35
I 55
I 45
Time,
251
p.m.
2D5
p.m.
Fig. 3. Variation of comfort level factors with time. Location:
Fig. 1. Variation of comfort level factors with time. Location: Henderson hawker centre. Date 22-8-1975.
E
241
Time,
J
I
k
2 ~,1
Toa Payoh central hawker-market centre. Date 2t)-6-1975.
b5
~,o
'~
0
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t
=5
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L
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2.25
235
Time,
2.45
p.m
12 15
L
1
L
12.25
t235
12 45
Time,
p.m.
Fig. 2. Variation of comfort level factors with time. Location: Bendemeer Road hawker centre. Date 27-8-1975.
Fig. 4. Variation of comfort level factors with time. Location: Holland Drive hawker centre. Date 26-6-1975.
t e m p e r a t u r e of a b o u t 31°C and for air velocity near or less t h a n 1 m/s. Finally the results of Fig. 3, which were obtained from a concrete-roof hawker centre, show that in the absence of roof radiation, satisfactory comfort levels were not existing when conditions of high air temperatures and low air velocities prevailed.
A sample of the vertical air t e m p e r a t u r e distribution in the hawker centre is provided in Fig. 5. Figure 5 shows clearly that the t e m p e r a t u r e gradient is largest in a region of a b o u t 2 5 c m from the roof. Increasing the roof height would reduce the a m o u n t of thermal radiation received at the sitting level but would not
165
Thermal confort studies in hawker centres in Singapore Temperature, 025
35
°C
45
n55
50
I
Bright sun condition o
2 Cloudy condition
•
I00
200
300
400
500
Fig. 5. Vertical temperature distributions for Henderson Road hawker centre.
produce any significant reduction in the air temperature at the sitting level. Altogether, 435 thermal comfort interviews were collected from the six hawker centres and of these, 69 % indicated thermal comfort levels corresponding to PMV values in the range - 1 to + 1. In other words, according to this 69?/o of the users of the hawker centres, favourable comfort level prevailed inside the hawker centres. Such a high percentage of users indicating favourable comfort levels is quite unexpected, and it contradicts somewhat the results obtained from the 'Comfy-Test' meter. The cause of this larger than expected percentage is the general tendency of the hawker centre users to under-rate, knowingly or otherwise, the actual degree of thermal discomfort. In the absence of a mathematical model which would have to incorporate the effects of air temperature, roof radiation, air velocity, relative humidity and architectural details of the hawker centres, recommendations for the improvement of comfort levels are based on the results thus obtained. Satisfactory comfort levels relevant to the environment of the hawker centres in Singapore, that is, predicted mean vote values of about 1.0, can be obtained by a combination of roof thermal radiation reduced by the installation of aluminium foil to about 20W/m 2, and air velocities near or exceeding 1.0m/s. The latter requirement is readily brought about through the installation of ceiling or oscillating wall-mounted fans.
5. D E T E R M I N A T I O N O F ACCEPTABLE COMFORT LEVELS FOR HAWKER CENTRES A final section of this paper is devoted to the determination and definition of acceptable comfort levels in the environment of the hawker centre. One of the widely used comfort indices for defining comfort levels is that proposed by the American Society for Heating, Refrigeration and Air Conditioning Engineers (ASHRAE). For equatorial eli-
mate like that of Singapore, a similar index called the Equatorial Comfort Index (ECI) is that proposed by Webb, Webb's Equatorial Comfort Index was derived based on experimental studies on subjects under indoor conditions, which were different from those of the present study. The regression equation expressing the ECI was found to be ECI = 0.447ta + 0.553t w- 0-231 V 1/2 where td = dry bulb temperature, ' F t., = wet bulb temperature, =F V = air velocity, ft/min. The optimum value found in such an environment was 78-1°F (25,6°C). For the environment under which this study was carried out, the effects of thermal radiation need to be considered. Accordingly, in order to compare the results of the present study with those of Webb's, the mean radiation temperature Tm,, is given by: T,,,, = (.L E, T 4 + fz T~) ~'4
where f~ and f2 are the view factors of the roof and the surroundings of the hawker centre, T~ and Td are the absolute values of the roof and air temperatures, and E, is the emissivity of the roof, was first calculated. In order to correct the ECI for radiation, the globe temperature was calculated using t9 =
0.353 td+ (tm,t--ta)~
,/v
•
Finally by substituting tg for td in Webb's regression equation, the radi~ition corrected ECI can be obtained for each of the sets of data obtained from the hawker centres. The optimum value for the corrected ECI, that is, the value corresponding to a PMV value of l'0
166
K . R . Rao and J. ('. Ho
(warml, was found to be 26.4 C. "['his is about 1 C higher than Webb's EC1. The higher value for the optimum value for the corrected ECI is expected since conditions inside the hawker centre, although subject to higher air velocities, are more adversely affected by the presence of roof thermal radiation.
6. C O N C L U S I O N S On the basis of the experimental studies on comfort level carried out at the hawker centres the following conclusions may be stated:
(1) Adverse thermal comfort levels prevailing tn the environment of the hawker centres are brought about by the combined effects of air temperatures, exceeding 3 0 C , relative humidity values of about 75",,, poor air movement (less than 1 m/sl and roof thermal radiation exceeding 50 W/m-'. (2) Acceptable comfort levels can be achieved by the installation of fans to increase air movement and the use of reflective aluminium foil to reduce the roof thermal radiation to about 20 W/m 2. (3) The optimum corrected value of the Equatorial Comfort Index relevant to the environment of the hawker centres is found to be 264 C.
7. REFERENCES 1. F. P. Ellis, Thermal comfort in warm and humid atmosphere: observations on groups and individuals in Singapore, J. Hyg, Camb. 51,386 (1953). 2. C.G. Webb, An analysis of some observations of thermal comfort in an equatorial climate, Br. J. Ind. Med. 16, 297 (1959). 3. C. G. Webb, American Society of Heating, Refrigeration and Air Conditioning Engineers. Handbook of Fundamentals, New York {1967}. 4. P.O. Fanger, Thermal ComJbrt-Analysi.s and Application m Environmental Engineering. McgrawHill, New York (1972).