Eur J Appl Physiol (2008) 102:471–480 DOI 10.1007/s00421-007-0609-2
ORIGINAL ARTICLE
Investigation of gender difference in thermal comfort for Chinese people Li Lan Æ Zhiwei Lian Æ Weiwei Liu Æ Yuanmou Liu
Accepted: 26 October 2007 / Published online: 9 November 2007 Springer-Verlag 2007
Abstract Gender difference in thermal comfort for Chinese people was investigated through two laboratory experiments. Both subjective assessment and objective measurement were taken during the experiment. Skin temperature (17 points) and heart rate variability (HRV) were measured in one of the experiment. Our results show that there are gender differences in thermal comfort for Chinese people. Correlation of thermal sensation votes and air temperature and vapor pressure shows that females are more sensitive to temperature and less sensitive to humidity than males. Subjective assessment, skin temperature and HRV analysis suggest that females prefer neutral or slightly warmer condition, due to their constantly lower skin temperature and the fact that mean skin temperature is a good predictor of sensation and discomfort below neutrality. Female comfortable operative temperature (26.3C) is higher than male comfortable operative temperature (25.3C), although males and females have almost the
L. Lan Z. Lian (&) W. Liu Institution of Refrigeration and Cryogenics, Shanghai Jiao Tong University, Shanghai 200240, China e-mail:
[email protected] L. Lan e-mail:
[email protected] W. Liu e-mail:
[email protected] Y. Liu College of Basic Medicine, Shanghai Jiao Tong University, Shanghai 200025, China e-mail:
[email protected]
same neutral temperature and that there is no gender difference in thermal sensation near neutral conditions. Keywords Gender difference Thermal comfort Skin temperature Heart rate variability (HRV)
Introduction The issue of whether there are differences between males and females in perception of thermal comfort has evoked many researches, which were carried out in laboratory or in field investigation, with the specific purpose of ascertaining any biases in thermal comfort conditions due to sex, age, nationality, etc. The individual differences in thermal comfort responses are well known, but the differences between males and females are considered to be small (Ellis 1953; McIntyre 1980; de Dear and Fountain 1994; Donnini et al. 1997). The skin temperature and evaporative heat loss variations for males and females in thermal comfort were analyzed based on the previously published data (Modera 1993), while no difference in optimal skin temperatures was found for sedentary males and females. Usually, the differences, if they have been found, have been explained in terms of clothing differences. But gender differences were also found in several studies: •
•
Earlier field studies of thermal comfort in office buildings have noted differences in thermal requirements of sexes (Fishman and Pimbert 1979). Gender differences in terms of thermal sensation complaints were found in a field investigation, females complaining that it is cold at a higher temperature than males (Federspiel 1998).
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Only small differences in the thermal comfort between male and female subjects were found in a laboratory study (Parsons 2002), but in cool conditions females tended to be cooler than males. Preferred ambient temperature differed markedly between males and females according to a laboratory investigation for European (Grivel 1991). A field survey carried out in an office (Junta Nakano et al. 2002) showed that the neutral temperature of a Japanese-female group was 3.1C higher that of a nonJapanese male group. A successive ASHRAE projects (RP-702,821 and 921) investigated office environments in temperate, hothumid, cold and hot-acid regions (de Dear and Fountain 1994; Donnini et al. 1997; Cane and de Dear 1999). The former two surveys found no differences between genders in terms of thermal neutrality, while the last investigation indicated that abnormally males felt a little cooler than females; all three investigations found that females were more prone to express thermal dissatisfaction. A field investigation carried out more recently (Hwang et al. 2006) also found that there was significant difference between sexes in thermal sensation. Real lift studies carried out in Finland (Karjalainen 2007) found that, females were less satisfied with room temperatures than males, preferred higher room temperature than males, and felt both uncomfortably cold and uncomfortably hot more than males.
However gender differences were more usually found in field studies in the literature. In this study two laboratory experiments were performed, applying a new investigation methodology based on both objective and subjective surveys, to investigate whether there is gender difference in thermal comfort for Chinese people in air-conditioned room.
three groups of 6 each. Subjects were asked to have a good rest and avoid alcohol and intense physical activity at least 12 h prior to each experimental session.
Questionnaire survey The subjects were asked to assess their thermal environment for thermal comfort, humidity sensation, draught sensation, and fatigue etc. Only assessments of thermal comfort were analyzed in this study. Thermal sensation votes (TSV) were cast on the ASHRAE/ISO seven-point thermal sensation scale, which was defined hot (+3), warm (+2), slightly warm (+1), neutral (0), slightly cool (-1), cool (-2) and cold (-3). Thermal comfort (TC) was cast on a nine-point thermal comfort scale––comfortable (0), slightly uncomfortable (1), uncomfortable (2), very uncomfortable (3), and limited tolerance (4), recognizing the same positive/negative convention for warm/cold discomfort.
Thermal environment measurement All measurements were taken at the height of 1.0 m above the floor, which represents the height of the occupant at seated level. Measurement devices were shown in Table 1 and Fig. 1. The indoor air temperature was measured with standard mercury thermometer (Shanghai Huoer Co, China). The relative humidity was measured with D-W (dry-bulb and wet-bulb) stand psychrometer (Shanghai Huachen Medical Instruments Co, China). Air velocity was measured with compact anemometer (Testo 425, KRIJON Ltd, Germany). The mean radiant temperature was estimated from the globe temperature, which was measured using a 150 mm diameter black globe thermometer.
Experiment procedure Methodologies Experiment I Subjects Eighteen healthy college students (9 males and 9 females), aged 20–26 years (l = 23, r = ±3) were recruited for this experiment. Age groups could not be considered since the subjects were all in their twenties. Males and females wore almost identical light clothing (long sleeved shirt and long trousers) and their own underwear, socks and shoes (an estimated clothing insulation value of 0.8 Clo, including the insulation of the chair). Subjects occupied the office in
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The experiment was carried out in an climate chamber, 3 ml 9 4.7 mW 9 2.85 mH, equipped with an air-conditioner that could adjust temperature from 18 to 32C, at Shanghai Jiao tong university. Five step-up temperature levels (21, 24, 26, 29, and 32C respectively) were investigated. The experiment lasted for 15 days (each group were test for 5 days), with only one temperature being performed each day for 1 h in the morning, from 10:00 to 11:00. After subjects entered the air-conditioned room, they were asked to seat and rest for about 40 min. Then questionnaires written in Chinese were handed out to all the subjects. Until all subjects had finished the questionnaire,
Eur J Appl Physiol (2008) 102:471–480 Table 1 Measurement devices of this experiment
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Name
Type
Accuracy
Purpose
Thermocouple
–
±0.2C
Measure skin temperature
Anemometer
Testo 425
0.05 m/s (full scale:10 m/s)
Measure air velocity
Multi-channel data collector
KEITHLEY 2700
–
Collect data of thermocouple
Stand thermometer
–
±0.1C
Air temperature
D-W stand psychrometer
–
±0.5C
Relative humidity
Black globe thermometer
–
±0.1C
Measure radiant temperature
Bio signal meter
PowerLab
–
Measure HRV
they could not leave the room. Physical environment were measured when the subjects filled out questionnaires.
exposed to four step-down temperature conditions, nominally 29, 26, 24 and 21C. The anthropometric data of subjects is shown in Table 2. Age groups could not be considered since the subjects were all in their twenties.
Experiment II Subjective assessment, physical environment measurement and physiological measurement (skin temperature and HRV-heart rate variability) were taken in the second experiment.
Subjects A different set of 20 subjects (10 males and 10 males) were recruited for the second experiment. All subjects were healthy, non-smokers and had no history of cardiovascular disease. All protocols were approved by the university’s ethics committee and conformed to the guidelines contained within the Declaration of Helsinki. Verbal and written informed consent was obtained from each subject prior to the participation of each protocol. Subjects were asked to avoid caffeine, alcohol, smoking, and intense physical activity at least 12 h prior to each experimental session. All subjects were required to wear short-sleeved Tshirt and walking shorts (an estimated clothing insulation value of 0.5 Clo, including the insulation of the bed). Twenty subjects were divided into two groups: one group with 5 females and 5 males, were exposed to four step-up temperature conditions, nominally 21, 24, 26 and 29C; another group with 5 females and 5 males, were
Subjective assessment and thermal environment measurement Subjects were asked to assess their thermal sensation votes (TSV) and thermal comfort (TC) based on the same scales utilized in preceding experiment. Objective physical measurements were carried out at the height of bed near the subjects. The indoor air temperature, relative humidity, air velocity and mean radiant temperature were also measured with the same devices as preceding experiment.
Skin temperature Skin temperatures changes in response to changes of external environmental temperature, and is one of the most important objective indices to judge thermal comfort at present. Skin temperatures at seventeen points (Ouyang 1985) were measured with thermocouples (as shown in Fig. 2). The skin temperatures were collected by the KEITHLEY data acquisition system. Mean skin temperature can be calculated with the sum of products of local skin temperatures Tsi and respective weight factors fi (as shown in Table 3):
Fig. 1 Equipments and appurtenances of this experiment
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Table 2 Anthropometric data of subjects Group
1
2
Gender
Females
Males
Total
Females
Males
Total
Numbers
5
5
10
5
5
10
Age (years)
22.8 ± 1.8
24.0 ± 2.0
23.5 ± 2.5
22.2 ± 1.8
22.3 ± 2.7
22.3 ± 2.7
Height (m)
1.646 ± 0.066
1.718 ± 0.058
1.685 ± 0.105
1.668 ± 0.048
1.760 ± 0.040
1.718 ± 0.098
Weight (kg)
51.6 ± 11.6
60.3 ± 9.7
56.4 ± 16.4
55.4 ± 4.6
68.2 ± 13.2
62.4 ± 15.6
Ts ¼
17 X
fi Tsi
ð1Þ
i¼1
Heart rate variability Power spectral analysis of heart rate variation (HRV) has been widely used for assessing the autonomic nervous
system function. Heart rate variation is measured by determining the constantly temporal distance between succeeding heartbeats (R-R intervals). It is essentially based on the antagonistic oscillatory influences of the sympathetic and parasympathetic (vagal) nervous system on the nodus sinuatrialis of the heart (Hainsworth 1995). Thus HRV is an integrating measurement variable that reflects the prevailing balance of vagal and sympathetic tone, especially under resting conditions (Mohr et al. 2002). Generally the power spectra of HRV is divided into very low frequency (VLF,\0.04 Hz), low frequency (LF, 0.04– 0.15 Hz) and high frequency (HF, 0.15–0.4 Hz) components. Studies indicate that the LF power is modulated mainly by sympathetic nerve, while the HF power mainly reflects the activity of the vagal nerve (Pomeranz et al. 1985; Pagani et al. 1986; Malliani et al. 1991). However, the origin of the very low frequency (VLF) is not clear yet. Therefore the ratio of absolute powers in low frequency and high frequency bands (LF/HF ratio) is often considered as an indicator of sympathetic/vagal nerve balance (Malliani et al. 1991). Subjects’ electrocardiogram (ECG) was recorded by a Powerlab 8/30 system (AD Instruments, Australia), in which, standard bipolar limb leads (ML-1340, AD Instruments, Australia) and adhesive ECG pads (MLA-1010, AD Instruments, Australia) were linked to data acquisition system (Powerlab 8/30, AD Instruments, Australia) through a bioamplifier (ML-132, AD Instruments, Australia). The arrangement of three electrodes on the subject’s body is illustrated in Fig. 3. Based on a 5-min record of ECG, the value of LF/HF ratio was calculated by the software of Chart for Windows (ChartTM 5, AD Instruments, Australia). The calculation method was depicted in its user’s guide 24. Experiment procedure
Fig. 2 Locations of skin temperature measurement (total 17). A forehead, B left neck, C right upper arm, D left chest, E left back, F left abdomen, G left lumbar, H left forearm, I left hand, J right hand, K left buttocks, L anterior thigh, M posterior thigh, N anterior calf, O posterior calf, P left foot, Q right foot
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This experiment lasted for 20 days, each day for 5 h in the afternoon, from 13:30 to 18:30. Only one subject was exposed to the four temperatures each day. The experiment was performed in the same climate chamber as preceding experiment.
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Table 3 Weighting factors of each position as to calculation of mean skin temperature Positions
Forehead
Left neck
Right upper arm
Left chest
Left back
Left abdomen
Weighting
0.037
0.037
0.075
0.063
0.063
0.063
Positions
Left lumbar
Left forearm
Left hand
Right hand
Left buttocks
Anterior thigh
Weighting
0.063
0.075
0.025
0.025
0.063
0.0875
Positions
Posterior thigh
Anterior calf
Posterior calf
Left foot
Right foot
Weighting
0.0875
0.0875
0.0875
0.0305
0.0305
Detailed schedule for each experimental session is described following. Subjects were asked to complete questionnaires (written in Chinese) about thermal sensation and thermal comfort after entering and resting in the chamber for about 40 min. Following the evaluation, physiological parameters, including skin temperatures and ECG, were recorded for 10 min. Then the temperature shift to next level. During each temperature change interval, 40 min were left to allow subjects accommodate to the new thermal environment. Questionnaires, physic environment parameters and physiological parameters were taken under each temperature condition.
Fig. 3 Locations of ECG measurement. 1 White Lead (Negative); 2 Red Lead (Positive); 3 Black Lead (Ground)
Results Results of physic measurement The measured environment parameters were list in Table 4. They did not deviate from the intended levels.
Results of questionnaire survey Table 5 lists the correlations of thermal sensation, temperature, humidity for males and females (P \ 0.05 for both four equations). The equations in Table 5 indicate that females in this study were more sensitive to temperature and less sensitive to humidity than the males. The results are coordinate with the results derived from European college students (ASHRAE, 2005). The different coefficients between the two experiments may attribute to different clothing insulation. Equations in Table 5 also indicate that subjects are less sensitive to air temperature and more sensitive to humidity when less body area is exposed to environment. The linear regression of thermal sensations versus operative temperature for males and females are shown in Fig. 4. It can be seen that males and females have almost the same neutral temperature. In Experiment I, neutral temperatures were 23.1 and 23.5C for males and females respectively, females having slightly higher neutral temperature. In Experiment II, males and females has exactly the same neutral temperature (26.3C). The larger regression coefficients also show that females are more sensitive to changes of ambient temperature than males. So it is predictable that females are more tend to express dissatisfaction to their thermal environment. It suggests that the fraction of people dissatisfied could be reduced by choosing the ambient temperature to be closer to thermal comfort temperature of females. Figure 5 illustrates the correlation of thermal comfort and thermal sensation for males and females. The positive/ negative of thermal comfort was not considered to simply the correlation trend. It can be seen from Fig. 5 that females are more prone to show thermal dissatisfaction below neutral, while males are more prone to feel thermal
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Table 4 Statistic data for experimental conditions
Nominal value (C)
I
II
* Measured values are means ± SD
Measured values Air temperature (C)
Air velocity (m/s)
Relative humidity (%)
Mean radiant temperature (C)
20
20.20 ± 0.08
0.10 ± 0.005
45.82 ± 1.39
21.16 ± 0.10
23
22.92 ± 0.05
0.08 ± 0.004
47.28 ± 2.00
23.58 ± 0.10
26
25.83 ± 0.06
0.09 ± 0.002
58.11 ± 2.00
26.65 ± 0.10
29
29.00 ± 0.04
0.12 ± 0.005
74.17 ± 2.31
30.07 ± 0.07
32
32.02 ± 0.04
0.08 ± 0.003
76.00 ± 2.12
32.49 ± 0.09
21
21.18 ± 0.06
0.02 ± 0.001
42.61 ± 1.18
21.75 ± 0.09
24 26
24.03 ± 0.04 26.00 ± 0.05
0.02 ± 0.002 0.02 ± 0.002
50.64 ± 1.27 56.27 ± 1.23
24.65 ± 0.07 26.47 ± 0.10
29
29.02 ± 0.04
0.02 ± 0.001
56.91 ± 1.01
29.54 ± 0.10
Table 5 Correlations of thermal sensation with temperature and humidity for males and females Experiment I II a
Subjects
Regression equationsa
Males
Y = 0.111t + 0.714p - 3.552
Females
Y = 0.180t + 0.537p - 5.179
Males
Y = 0.476t + 0.627p - 13.491
Females
Y = 0.543t + 0.405p - 14.841
Y values refer to the ASHRAE thermal sensation scale
t dry-bulb temperature (C), p vapor pressure (kpa)
discomfort from slightly warm to warm. It means that females prefer neutral or slightly warmer condition; males prefer neutral or slightly cooler condition. The steeper curve also suggests that females are more likely to show dissatisfaction to their environment.
Results of physiological measurements Skin temperature The mean skin temperatures for males and females are plotted as a function of operative temperature in Fig. 6 and Table 6. Female mean skin temperatures are lower than male mean skin temperature at different operative temperature. It is clear that mean skin temperature increases with increased operative temperature, decreases with decreased operative temperature. Regression equations shown in Table 6 indicate that female mean skin temperature varied more rapidly with operative temperature than that of males. Correlation of mean skin temperature and thermal comfort for males and females is illustrated in Fig. 7. Comfortable mean skin temperature for males and females are 33.25 and 32.95C respectively. Casting on Fig. 6, comfortable operative temperature for males and females are 25.3 and 26.3C respectively. The results indicate that
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Fig. 4 Operative temperature and thermal sensation votes. a Experiment I; b Experiment II
females prefer warmer conditions than males. Females show more discomfort below neutral may due to their low skin temperature.
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477
Fig. 6 Mean skin temperature versus operative temperature for males and females
variability (Stein et al. 1997; Bigger et al. 1995). It should be noted that, the mean LF/HF ratio and variations for males at uncomfortable warm level is larger than that at uncomfortable cool, but the mean LF/HF ratio and variations for females at uncomfortable warm level is smaller than that at uncomfortable cool level.
Discussions
Fig. 5 Thermal sensation votes and corresponding mean comfort votes (thermal comfort level: 0 comfortable, 1 slightly uncomfortable, 2 uncomfortable, 3 very uncomfortable, 4 limited tolerance). a Experiment I; b Experiment II
Heart rate variability (HRV) Figure 8 shows the comparison of mean LF/HF ratio under different thermal comfort state. The comparison was done among three comfort levels: uncomfortable cool, comfortable, uncomfortable warm. It can be seen from the figure that the LF/HF ratio in comfortable environment is lower than that in uncomfortable environment for males and females. Paired t-tests show that the effect of comfort level on LF/HF ratio is significant for both males and females (P \ 0.01), comfortable level having the smallest LF/HF ratio. The figure also shows that female LF/HF ratio is lower than that of male at different comfort levels. Analysis of variance shows that males have significantly higher LF/HF ratio (P \ 0.05) than females. The result agrees with the study of gender effects on heart rate
Our results show that there are gender differences on thermal comfort for Chinese people: females prefer slightly warmer environment, but males prefer slightly cooler environment, although there are no significant differences on neutral temperature. We find that female comfortable operative temperature (26.2C) is higher than male comfortable operative temperature (25.3C) based on skin temperature and thermal comfort vote. This gender preference can be derived from subjective assessment and objective measurement. The correlation of thermal comfort and thermal sensation shown in Fig. 5 suggests that females prefer neutral or slightly warmer condition, and males prefer neutral or slightly cooler condition. The LF/ HF ratio for males and females at three comfort level also support this preference. Studies (Lu 2000; Iwasea et al. 1997; Sawasaki et al. 2001) show that LF/HF ratio can reflect human thermoregulation and state of thermal comfort. When people feel thermal uncomfortable (warm or cool), the sympathetic nerve will be activated (LF/HF ratio increase) to regulate body temperature, with the efferent responses of vasodilatation and sweating, vasoconstriction and shivering. So LF/HF ratio increases with the extent of discomfort, with lower value when people feel comfortable. Figure 8 shows
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Hot : Cold :
tb ¼ 0:9tcr þ 0:1tsk
ð2Þ
tb ¼ 0:67tcr þ 033tsk
Mean Skin Temperature (°C)
(a)
34.50
34.00
33.50
33.00
32.50
32.00
-1 ( Error bars: +/- 2.00 SD)
0
1
Thermal Comfort Males
(b) Mean Skin Temperature (°C)
that female mean LF/HF ratio at uncomfortable cool level is larger than that at uncomfortable warm, but the situation is totally opposite for males. It suggests that the activation of sympathetic nerve is stronger below neutral for females, and under this condition they feel more uncomfortable than above neutral; the activation of sympathetic nerve is stronger above neutral for males, and they feel more uncomfortable under this environment. Regression equations (shown in Table 5) show that females are more sensitive to temperature and less sensitive to humidity than males. Measurement results of skin temperature can explain the reason why females are more sensitive to temperature variation, and why females show more discomfort in cool environment. Figure 6 and Table 6 show that female skin temperature is constantly lower than that of male, and especially female skin temperature is more sensitive to air temperature. The relationship between bodily state and sensation is different above and below thermal neutrality (McIntyre 1980): below neutrality, mean skin temperature is a good predictor of sensation and discomfort, and the relation between sensation and physiological state above thermal neutrality is affected by the sweating response. In the cold, warm blood is withdrawn from the outer layers of the body, effectively reducing the volume of the warm core. As skin temperature falls below the comfortable level of 33.5C, cold sensation increases rapidly (Gagge et al. 1967). The mean body temperature, tb, estimated from a weighted average of core temperature, tcr and skin temperature, tsk, also illustrate that mean skin temperature is a good predictor of sensation and discomfort below neutral:
34.00
33.00
32.00
31.00 -1 ( Error bars: +/- 2.00 SD)
0
1
Thermal Comfort Females
Fig. 7 Correlations of mean skin temperature and thermal comfort for males and females. -1 uncomfortable cool; 0 comfortable; +1 uncomfortable warm
ð3Þ
In addition, the surface to volume difference (Modera 1993) made it logical that females should be inherently more sensitive to skin temperature effects. So females are more sensitive to cool environment, and show more discomfort in cool environment. Above neutrality, people regulate body temperature by vasodilatation and sweating. Studies show that females had lower sweating than males under either dry or humid
conditions when being exposed to heat stress (Modera 1993; Avellini and Kamon 1980). So it is reasonably that males are more sensitive to humidity. Interestingly, we found that female trunk temperatures (including abdomen, back, buttock and thigh) other than extreme temperatures decreased far more quickly with environment temperature after comparing the variation of 17 points skin temperatures. Whether there are different sensitive local points between females and males to cold and hot stress needs further investigation.
Table 6 Correlation of mean skin temperature and operative temperature for males and females Gender
Regression equations
Conclusions
Males
tsk = 0.238top + 27.235
Females
tsk = 0.248top + 26.440
Gender difference on thermal comfort for Chinese people was investigated based on both objective and subjective surveys. It can be concluded that:
tsk mean skin temperature (C), top operative temperature (C)
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(a)
479
4.
2.5000
LF/HF Ratio
2.0000
5.
1.5000
1.0000
Female skin temperature is constantly lower than that of male, especially female skin temperature is more sensitive to air temperature. It is logical that females are more sensitive to cool environment according to analysis of skin temperature and the relationship between bodily state and sensation.
It should be noted that, the temperature investigated in this study was not deviated very much from neutral environment, as to the very hot and very cold environment, further investigation is needed.
0.5000
0.0000 -1
0
1
( Error bars: +/- 2.00 SD) Thermal Comfort
Males
(b)
Acknowledgments This work was supported by National Natural Science Foundation of China under the contract of No.50478018. The authors also would like to thank the occupants for their excellent cooperate in this survey and experiment.
2.5000
References
LF/HF Ratio
2.0000
1.5000
1.0000
0.5000
0.0000 -1
( Error bars: +/- 2.00 SD)
0
1
Thermal Comfort
Females
Fig. 8 Correlations of mean LF/HF ratio and thermal comfort. -1 uncomfortable cool; 0 comfortable; +1 uncomfortable warm
1.
2.
3.
The LF/HF ratio and variations for males at uncomfortable warm level is higher than that at uncomfortable cool; but the mean LF/HF ratio and variations for females at uncomfortable warm level is lower than that at uncomfortable cool level. Subjective assessment, skin temperature and HRV analysis suggest that females prefer neutral or slightly warmer condition, while males prefer neutral or slightly cooler condition. Female comfortable operative temperature (26.3C) is higher than male comfortable operative temperature (25.3C), although males and females have almost the same neutral temperature and that there is no gender difference in thermal sensation near neutral conditions. Females are more sensitive to temperature and less sensitive to humidity than the males.
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