International Journal on Architectural Science, Volume 7, Number 2, p.47-52, 2006

47

STUDY ON INDOOR THERMAL SENSATION OF YOUNG COLLEGE STUDENTS IN THE AREA WHICH IS HOT IN SUMMER AND COLD IN WINTER P.F. Hu﹡, W. Liu＋ and Z.N. Jiang﹡ ﹡ School of Environmental Science and Engineering, Huazhong University of Science and Technology Wuhan, Hubei, 430074, P.R. China ＋ School of Energy and Power Engineering, Huazhong University of Science and Technology Wuhan, Hubei, 430074, P.R. China (Received 29 August 2006; Accepted 17 May 2007) ABSTRACT This paper analyzes the thermal sensation of Chinese in the area which is hot in summer and cold in winter. We investigated young college student respondents both in an air conditioned indoor space (a laboratory) in hot and cold season and a naturally ventilated indoor space (a classroom) from September to January. The neutral temperatures in laboratory in summer and winter season are 27.1 and 17.2 oC respectively while the predicted neutral temperature is 22oC in classroom. The range that the acceptability is over 80% in laboratory is 26.6 to 28.6oC in summer or 15.7 to 18.3oC in winter, and it is 18.4 to 26.1oC in classroom. The methods adopted by respondents to achieve comfort are different when the respondents have different thermal sensation. 1. INTRODUCTION There are a lot of studies around the world about thermal comfort. deDear and Fountain [1] made a field investigation of indoor climate and occupant comfort in 12 air conditioned buildings in Townsville, a city in Australia’s tropical north. Xia et al. [2] performed a field study in Beijing, north of China. deDear et al. [3-4] conducted series of climate chamber experiments on temperature preferences and thermal acceptability in Singapore. Jitkhajornwanich et al. [5] carried out a field survey of 593 subjects occupying both indoor (air conditioned and naturally ventilated) and outdoor environments, dealing with experience of transitional spaces of buildings in the cool seasons in Bangkok, Thailand. But most of these studies were in tropical, temperate or cold climate zones. This paper conducted investigations about the thermal sensation of the respondents in the area which is hot in summer and cold in winter in China. The area which is hot in summer and cold in winter in China is about the middle and lower reaches of the Chang Jiang river, and the latitude of the area is about 23° to 34° north of the equator. It includes all area of Shanghai and Chongqing cities and Hubei, Jiangxi, Anhui, and Zhejiang Provinces and parts of Sichuan, Guizhou, Jiangshu, Henan, Fujian, Shanxi, Gansu, Guangdong and Guangxi provinces. The total population in this area is about 550 million and the GDP (gross domestic products)

accounts for 45% of that of the country. With a very important economic status, it is the most densely populated and economic and cultural developed area. The notable climatic characteristics in this area are that it is hot in summer and cold in winter with a high humidity. Its climatic condition is relatively poor among the area with same latitude in the world. In summer (June ~ September), subsidiary tropical high pressure goes to west along the Chang Jiang river and the cool wind from the Pacific Ocean was obstructed by the southeast hills. In winter (December ~ February), the cold wave from Siberia and North Pole often invades and the cold air stays for the resistance of the south mountains and southeast hills. There is a 15 to 30 days period in which the maximum temperature is higher than 35oC. The average temperature at 14:00 in the hottest month reaches 32 to 33oC and there is not any cool time in the whole day. The period in which the lowest temperature is lower than 5oC lasts more than two months. The average temperature in January in the area is about 8 to 10oC lower than that in other area which has the same latitude in the world. Also this area is water net region. It is very humid with relative humidity of 80 to 85% in summer and 73 to 83% in winter. It is significant to study the thermal comfort in this area.

International Journal on Architectural Science

48

2. METHODS Respondents and Buildings

Wuhan is located in the area which is hot in summer and cold in winter in China. We carried out the research measurement both in an air conditioned indoor space (a laboratory) and a naturally ventilated indoor space (a classroom) in Wuhan. The laboratory is 6 m in length, 4 m in width and 3 m in height. Conditioned air is supplied to the occupied zone from the front wall. The workstation is a classroom in a university. The dimensions of it are 25.1 m (length) × 15.6 m (width) × 4.1 m (height). There are eight windows in the room with four of them on a wall. The dimensions of the windows are 2.38 m × 2.37 m. The wall is 240 mm thick brick wall and the heat transfer coefficient of the bricks is 2.3 Wm-2.K-1. The windows are made of single glass and aluminum alloy frame. The classroom is on the 2nd floor. All the respondents are from the area which is hot in summer and cold in winter and acclimatized to the thermal environment in the area. The respondents in our research are university students. 10 respondents were in the laboratory (winter and summer) and 186 were in the classroom. The 10 respondents also participated in the classroom measurements. The profile of the respondents is summarized in Table 1. Measurement and Questionnaires Process

In the laboratory, we carried out the measurement and questionnaires in summer (June ~ September) and winter (December ~ February) respectively. There are 39 experimental conditions in summer and 26 in winter. And in classroom, the measurement and questionnaires lasted for half a year, from September to January, once or twice a week. The measurements were made in 31 conditions. All of the measurements and questionnaires are on the morning or afternoon.

The environmental parameters we measured are air temperature (Ta), relative humidity (RH), air velocity (v) and mean radiant temperature (Tr). The clothing insulation value is determined by the clothing status. The effect of chair to clothing insulation was added according to the previous study [6]. The metabolic rate was determined by the activity of the respondents. Then we calculated new effective temperature (ET*). In laboratory we adjusted temperature to different values. The contents of the questionnaires included: 1 Background

Personal information. Clothing Activity

2 Responses to the thermal environment

Thermal sensation (using the seven-point ASHRAE scale)

Adaptation Satisfaction acceptance

3. RESULTS Study in the Laboratory

Thermal sensation vs. new effective temperature The respondents wore a uniform with mean cloth insulation 1.8 clo in winter and 0.3 clo in summer according to the general clothing habit of the inhabitants in the area. The mean air velocity is set at 0.13 ms-1 (± 0.03 ms-1) in December (winter) and 0.12 ms-1 (± 0.02 ms-1) in September (summer). The relative humidity is set at 50.4 ± 1.1%. All the respondents were asked to seat for a minimum of 15 minutes period, so the metabolic rate was assumed to be 1.1 met [7].

Table 1: Profile of the respondents in the laboratory Male Female Age 18 ~ 22 (Mean = 20.3) 18 ~ 22 (Mean = 20.5) Weight (kg) 56 ~ 70 (Mean = 62.8) 55 ~ 60 (Mean = 57.4) Height (cm) 165 ~ 175 (Mean = 170.4) 156 ~ 168 (Mean = 160.9) Table 2: Profile of the respondents in the classroom Male Female Age 18 ~ 24 18 ~ 23 Number 141 45 Weight (kg) 52 ~ 73 (Mean = 63.2) 48 ~ 61 (Mean = 55.3) Height (cm) 164 ~ 178 (Mean = 170.2) 155 ~ 170 (Mean = 161.5)

International Journal on Architectural Science

49

In the range of the new effective temperature (ET*) in the laboratory we measured, the value of mean thermal sensation increased as the ET* increased. The thermal sensation results of the respondents and the regression are shown in Fig. 1 (December) and Fig. 2 (September). The data are binned into 0.5oC intervals. The predicated neutral temperature (Tn, corresponding to TSV = 0) estimated from the regression is 17.2oC in winter and 27.1oC in summer. As for the thermal acceptability, we adopted the means established by ISO 7730 [8] and asked the respondents a direct acceptability question. Fig. 3 and Fig. 4 show the results of thermal acceptability. In December, the range in which the percentage of acceptability is over 80% is 15.7 to 18.3oC. In September, the range of acceptability over 80% is 26.6 to 28.6 oC. Study in the Classroom

At first, we surveyed the clothing habit of the respondents in different seasons (summer, autumn

and winter). Fig. 5 shows the mean insulation of clothing related to ET* in the room. As the ET* increased, the insulation of clothing people wearing decreased. When the ET* was 6oC, the mean insulation of clothing is 2.01 clo. When the ET* achieved 36oC, the mean insulation of clothing is only 0.31 clo. The fitted equation is: Clothing clo. value = 2.4107 - 0.0684ET*(r = -0.94) (1) In order to understand the respondent’s thermal sensations in the natural ventilated space, survey was conducted and the results are shown in Fig. 6. As the indoor air temperature varied, the respondents’ thermal sensation varied consequently although their clothing varied. Not all the thermal sensation values fell within the thermal comfort zone. The fitted equation is: Thermal sensation value = -2.9304+0.1335 ET* (r = 0.98) (2) The neutral ET* in the situation is 22.0oC.

ET* / ℃

ET* / oC

Ther

mal

sens

atio

n vo

tes

Fig. 1: Mean thermal sensation votes (Lab., Winter)

Fig. 2: Mean thermal sensation votes (Lab., Summer)

ET* / oC ET* / oC

Ther

mal

acc

epta

bilit

y / %

Ther

mal

acc

epta

bilit

y / %

Fig. 3: Thermal acceptability (Lab., Winter) Fig. 4: Thermal acceptability (Lab., Summer)

ET* / oC

Ther

mal

sens

atio

n vo

tes

International Journal on Architectural Science

50

Fig. 7 shows the thermal acceptability related to mean indoor air temperature. The thermal acceptability varied rapidly when ET* is less than 14oC and increased slowly when ET* is 14 to 19oC. And it decreased rapidly when ET* is more than 28

oC. The range in which the percentage of acceptability is over 80% is 18.4oC ≤ ET* ≤ 26.1oC.

Table 3 shows the McIntyre Scale results while respondents’ thermal votes within the central three categories in the seven-point scale (from -1 to +1). No obvious cool or warm bias was seen. We investigated the methods adopted by the respondents to achieve thermal comfort when they feel too warm or too cool in the classroom. The results are shown in Table 4.

Table 3: McIntyre Scale (Preference) for -1 to +1 of the sensation

McIntyre Scale (Preference) for -1 to +1 of the sensation scale (percentage)

Sensation scale Cooler No Change Warmer

-1 11.8 41.2 47.0 0 22.2 63.9 13.9

+1 38.9 44.4 16.7

Ther

mal

sens

atio

n vo

tes

Fig. 6: Mean thermal sensation votes (Classroom) Fig. 5: Mean clothing insulation (Classroom)

Mea

n cl

othi

ng in

sula

tion

valu

e/cl

o.

ET* / oC ET* / oC

Fig. 7: Thermal acceptability (Classroom)

Ther

mal

acc

epta

bilit

y /%

ET* / oC

International Journal on Architectural Science

51

Table 4: The methods adopted by the respondents to achieve thermal comfort when they feel too warm or too cool

Methods adopted The number of respondents when they have different thermal sensation

_______________________________ -3 -2 -1 0 +1 +2 +3

Turn on heating equipment 129 30 18 Increase clothing 90 124 70

When too cool Increase activity 33 38 57 Close window 66 81 54 Have hot drink or food 71 52 24

Turn on AC equipment 2 27 111

Use fan or electric fan 19 94 57 When too warm Decrease clothing 24 85 73

Have cool drink 63 109 42 Open window 75 81 63 Take a cool water bath 6 15 48

The methods adopted by respondents to achieve comfort are different when the respondents have different thermal sensation. When respondents feel cold (thermal sensation = -3), the foremost method is to turn on heating equipment. And to increase clothing become the foremost way when they feel cool (thermal sensation = -2) and slightly cool (thermal sensation = -1). It is noticeable that to turn on heating equipment is the least choice at this situation. We observed that increasing clothing is a common method when people feel too cool. Similarly turning on AC (air conditioning) equipment is the foremost method when respondents feel hot. To have cool drink, use fan or electric fan, open window and decrease clothing are the most frequent choice when respondents feel hot or warm. Decreasing clothing and providing ventilation (including use fan or electric fan and open window) are important means though clothing is not important as that in the situation when people feel too cool. 4. DISCUSSION Comparison of study results in the laboratory

and in the classroom The neutral temperature in classroom is different from that in laboratory. Because we made the measurement continuously from September to January, there is only a neutral temperature in the range of measuring temperature. The value of the neutral temperature in classroom (22.0oC) is between that in winter (17.2oC) and in summer (27.1oC) in laboratory. The range that the acceptability is over 80% in classroom (18.4 to

26.1oC) is wider than the sum of the range of that in winter (15.7 to 18.3oC) and in summer (26.6 to 28.6oC) in laboratory. The respondents were more sensitive to temperature variation in laboratory than that in the classroom. A gradient of about one sensation unit per 3 to 4oC was found in the laboratory (3oC in summer and 4oC in winter) while the figure was nearly 6oC in the classroom. The reason for the above phenomenon is that respondents have more choice to wear suitable cloth to meet their desirable thermal comfort condition in the classroom while respondents were set to wear a fixed uniform in the laboratory. In the laboratory study, the slope of regression of thermal sensation in winter (0.24) is lower than that in summer (0.35). It seems that respondents in the area are more sensitive to hot climate than to cold climate. Comparison with previous studies

In the laboratory which is air conditioned, the neutral temperature (27.1oC, in September) in this study is a little higher than that in Singapore (25.4oC, preferred operative temperature) [3]. The difference of clothing insulation between this study (0.3 clo) and that in Singapore (0.6 clo) may be the main reason. The range that the acceptability is over 80% in laboratory in September is similar to the results in Singapore [4]. The gradient of 0.24/oC and 0.35/oC were found here in winter and summer respectively. The result

International Journal on Architectural Science

52

in summer is similar to that of Schiller’s field study in San Francisco (0.308/oC) [11]. There is no similar situation in previous study with this study in laboratory in winter where respondents’ clothing insulation value is 1.8. So the result here is particular. Nevertheless after omitting the effect of clothing, we found no significant difference between this study and previous study. In the classroom study which is natural ventilated, though the neutral temperature (22.0oC) is occurred in undefined season we may conclude that the clothing insulation value is about 0.91 clo according to Fig. 5. The results is similar to that of the Montreal study (22.6oC in winter/cold season) [10] while the clothing insulation in both areas approximately equal (0.91 clo in Wuhan and 1.06 clo in Montreal), and it shows the neutral temperature in this study occurred in the same season as that in Montreal study. 5. CONCLUSION The study of thermal sensation in air conditioned indoor space (a laboratory) and naturally ventilated indoor space (a classroom) in the area which is hot in summer and cold in winter was conducted. And the results are summarized as follows: The insulation clo value of the clothing

people in the area wear habitually is about 0.3 in summer and 1.8 in winter. At this situation, the neutral temperature is about 27.1oC in summer and 17.2oC in winter. The range in which the percentage of acceptability is over 80% is 26.6 to 28.6oC in summer or 15.7 to 18.3oC in winter in laboratory while it is 18.4 to 26.1oC in classroom.

There are much wider temperature ranges of

thermal comfort for people wearing clothing according to thermal condition in natural ventilated classroom than that for people wearing certain clothing in air conditioned laboratory. Many respondents would not turn on heating or AC equipment until the temperature is relatively low and they feel cold or hot respectively. The effect of clothing for thermal comfort is very important especially in winter. We should attach great importance to it and take full advantage of it to conserve energy of air conditioning.

For the thermal condition in this area, the

emphasis is the thermal comfort in summer/hot season.

REFERENCES 1. R.J. de Dear and M.E. Fountain, “Field

experiments on occupant comfort and office thermal environment in a hot-humid climate”, ASHRAE Transactions, Vol. 100, No. 2, pp. 457-475 (1994).

2. Y.Z. Xia, R.Y. Zhao and Y. Jiang, “Thermal comfort in naturally ventilated houses in Beijing”, HV & AC, Vol. 29, No. 2, pp. 1-5 (1999).

3. R.J. de Dear, K.G. Leow and A. Ameen, “Thermal Comfort in the humid tropics - Part I: Climate chamber experiments on thermal preference in Singapore”, ASHRAE Transactions, Vol. 97, No. 1, pp. 874-879 (1991).

4. R.J. de Dear, K.G. Leow and A. Ameen, “Thermal Comfort in the humid tropics - Part II: Climate chamber experiments on thermal acceptability in Singapore”, ASHRAE Transactions, Vol. 97, No. 1, pp. 880-886 (1991).

5. K. Jitkhajornwanich, A.C. Pitts, A. Malama and S. Sharples, “Thermal comfort in transitional spaces in the cool season of Bangkok”, ASHRAE Transactions 104, No. 2, pp. 1181-1193 (1998).

6. E.A. McCullough, B.W. Olesen, and S. Hong. “Thermal insulation provided by chair”, ASHRAE Transactions, Vol. 100, No. 1, pp. 795-802 (1994).

7. ASHRAE Handbook – Fundamentals, Atlanta: American Society of Heating, Refrigerating, and Air-Conditioning Engineers, Inc. (1989).

8. ISO, International Standard 7730, Moderate thermal environments determinations of the PMV and PPD indices and specification of the conditions for thermal comfort, Geneva: International Organization for Standardization (1984).

9. J.F. Busch, “Thermal response to the Thai office environment”, ASHRAE Transactions, Vol. 96, No. 1, pp. 859-872 (1992).

10. G. Donnini, J. Molina, C. Martello, D.H.C. Lai, H.K. Lai, C.Y. Chang, M. Laflamme, V.H. Nguyen and F. Haghighat, “Field study of occupant comfort and office thermal environments in a cold climate”, ASHRAE Transactions, Vol. 103, No. 20, pp. 795-802 (1996).

11. G.E. Schiller, E.A. Arens, F.S. Bauman and C.Benton, “A field study of thermal environments and comfort in office buildings”, ASHRAE Transactions, Vol. 94, No. 2, pp. 280-308 (1988).