Investigation of Subjectively Assessed Health Symptoms and Human Thermal Perceptions in Transient Thermal Environments

Jing Xiong; Zhiwei Lian; Xin Zhou

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Procedía Engineering 121 (2015) 212 - 216

Procedía Engineering

www.elsevier.com/locate/procedia

9th International Symposium on Heating, Ventilation and Air Conditioning (ISHVAC) and the 3rd International Conference on Building Energy and Environment (COBEE)

Investigation of Subjectively Assessed Health Symptoms and Human Thermal Perceptions in Transient Thermal Environments

Jing Xionga, Zhiwei Liana*, Xin Zhoua

aDepartment of Architecture, School of Naval Architecture, Ocean & Civil Engineering, Shanghai Jiao Tong University, Shanghai 200240,

Abstract

People are often likely to expose themselves to sudden temperature change in daily life and they may suffer from not only thermal discomfort but also even some health symptoms. In this study, the influence of different air temperature steps (S5:32°C-37°C-32°C, S11:26°C-37°C-26°C, and S15:22°C-37°C-22°C) on subjective health symptoms and thermal perceptions was studied with 24 volunteered participants in the laboratory experiment. Several subjective rating scales were used to assess participant's subjective feelings imposed by temperature steps. Our results show that perspiration, eyestrain, dizziness, accelerated respiration and heart rate are found to be sensitive self-reported symptoms in response to temperature step changes. Thermal sensation and comfort just before temperature step are significantly distinguished from that immediately after step change except for thermal comfort under up step situation of S15 (22oC-37oC). Moreover, temperature step amplitude and direction have significant impact on subjective perceptions.

Peer-review under responsibility of the organizing committee of ISHVAC-COBEE 2015 Keywords: Temperature steps; health symptoms; thermal comfort

1. Introduction

Human beings are often likely to expose themselves to sudden temperature changes in daily life. For example,

* Corresponding author. Tel.: +86-213-420-4263; fax: +86-213-420-4263. E-mail address: zwlian@sjtu.edu.cn

Peer-review under responsibility of the organizing committee of ISHVAC-COBEE 2015 doi:10.1016/j.proeng.2015.08.1056

people will encounter temperature steps when entering or existing air-conditioned buildings, getting on or off planes, etc. Many studies have been performed to exam influence of temperature steps on human. Overshooting in thermal sensation was always observed under sudden cooling conditions [1-4] while such phenomenon is not often observed in temperature up-step situation. Both temperature step magnitude and precious experienced temperature affect thermal comfort at the following point in the consequence [5, 6]. However, most studies mainly focus on thermal comfort while little attention is paid to the change of self-reported symptoms over time after step changes. Besides, only few studies have investigated the effect of temperature steps being to equal magnitude but opposite direction transients. In this study, we carried out an experiment to investigate human subjective feelings in response to both temperature up-steps and down-steps, aiming to lay scientific foundations for the understanding of human responses to step changes.

2. Methodologies

We recruited 24 healthy college students (12 males and 12 females) with an average age of 21±1 years. All subjects' BMI lies in the normal range [7]. All of them were not currently taking prescription medication and were asked to avoid caffeine, alcohol, and intense physical activity at least 12 hours prior to the experiment. Participants were required to wear short-sleeved T-shirts, short trousers and slippers.

The experiment was carried out in a climate chamber which contains two adjacent rooms (Room A: 3.8m*3.6m*2.65m, Room B: 3.8m*3.8m*2.65m) connected by an interior door. Room A was set at 37oC while Room B was set at 22/26/32oC. The relative humidity in all rooms was controlled in range of 30%-70%. Air speed was kept under 0.1m/s. After arrival, subjects first stayed in room A and have a rest for about 15 min. Then the experiment began. Each test lasted for 135 min. First, subjects stayed in Room A for 30min (phase 1). Next, they moved to Room B for 60 min (phase 2). Finally, subjects returned to Room A remaining for 45 min (phase 3). During the experiment, occupants' subjective perceptions were evaluated at 15, 31, 33, 36, 53, 63, 85, 91, 93, 96, 110, 126, 135min. Subjective measurements included self-reported symptoms and thermal perceptions. On the one hand, subjects were asked to answer whether or not they were suffering from health symptoms like perspiration, nausea, dizziness, accelerated respiration, itchy throat, sneezing, eyestrain, accelerated heart rate and nasal congestion at present time. One the other hand, subjects were also required to access their subjective thermal feelings. Specifically, thermal comfort was cast on ASHRAE continuous seven-point scale; thermal comfort and acceptability were also rated using split continuous scales (thermal comfort — very comfortable (+2), comfortable (+1), slightly comfortable (+0.1), slightly uncomfortable (-0.1), uncomfortable (-1), very uncomfortable (-2); thermal acceptability — clearly acceptable (+1), just acceptable (+0.1), just unacceptable (-0.1), clearly unacceptable (-1)).

3. Results and discussion

The varying percentages of self-reported symptoms under three temperature step change conditions are described in Figure 1. After sudden heating, the percentages of self-reported symptoms including perspiration, eyestrain, dizziness, accelerated respiration and accelerated heart rate mount to their climax and then witness a drop when encountering a sudden cooling. Self-reported symptoms just before and after temperature steps were compared using McNemar's test. For temperature up-step, the ratio of perspiration after sudden heating is significantly higher than that before change in S5 and S11. Additionally, the percentage of eyestrain after up-step of S5 also increases significantly. For temperature down-step, significant decrease of perspiration is detected in S11 and S15. When the environmental temperatures increase, thermoregulatory centre dictates vasodilatation to speed up the blood flow and hence strengthen the heat dissipation from skin. Meanwhile, body circulation like heart rate, respiration rate improves with air temperature to help heat diffusion to the environment. If ambient temperature continues to rise, people will excrete sweat. Because of the large amount of energy consumption, people are inclined to have fatigue symptoms like dizziness and eyestrain. On the contrary, when encountering down-step, thermoregulatory centre will execute vasoconstriction, and also the body circulation will slow down to conserve energy and prevent heat loss.

Fig. 1. The change of self-reported symptoms over time response to temp step change.

Subjects' thermal sensation changed swiftly with thermal environments (Figure 2(a)). When entering room B, people perceived different thermal sensations because of diverse temperature step intensities, and their thermal sensations became nearly the same at the end of phase 2, followed by an immediately sharp decrease in thermal sensation when returning to room A. Paired comparisons between thermal sensations before and after temperature steps show statistical significance in both up-steps and down-steps of all three conditions. Cooling overshot was widely reported by many researchers [1, 3-4], however, no obvious thermal sensation overshoot was observed in this study. The fact that in this study subjects were not immediately asked to fill out the questionnaire after temperature step change may partly explain such discrepancy.

(a) Thermal sensation vote

(b) thermal dissatisfaction

Fig. 2. Changes of thermal perception over time in response to temperature steps.

Figure 2(b) displayed the dissatisfaction percentages over time in response to temperature steps. The percentage of dissatisfaction was calculated by counting thermal acceptability votes within the range of -1 to -0.01 as "dissatisfied", and divided by the total number of the subjects. It can be seen in Figure 2(b) that all people are satisfied with the thermal environment in S11 and S15 while more than 20 % subjects express dissatisfaction in phase 1, then the ratios witness sharp increases and at the end of phase 2, the percentages are about 66%, 54% and 50% for S5, S11 and S15 respectively, followed by prompt decreases immediately after corresponding down-steps separately. Table 1 illustrates the comparison between values just before and after temperature steps for thermal comfort. There are significances under all conditions except for up-step condition of S15. One explanation is that the previous low ambient temperature can influence people's feeling even ambient temperature change, which would alleviate thermal discomfort to some extent at the initial time.

Table 1. Changes of thermal comfort over time in response to temperature steps.

Time 15min 31min 85min 91min 15min VS 31min 85min VS 91min

S5 -0.1±0.6 -0.7±0.8 -0.8±0.7 0.0±1.0 *** ***

S11 1.1±0.6 -0.3±0.6 -0.8±0.6 1.0±0.7 *** ***

S15 0.5±0.8 0.2±0.8 -0.5±0.7 0.4±0.9 0.352 **

Note: * P<0.05, ** P<0.01, *** P<0.001.

Direction and amplitude effects of temperature steps on self-reported symptoms and thermal perceptions were analysed using ANOVA (Table 2). The instant change of eyestrain after temperature up-step in S5 is significantly differs from that in S11 and S15. Similarly, instant change of perspiration after temperature down-step in S5 is also remarkably diverse from that in S11 and S15. Besides, temperature step magnitude has significant effect on ATSV and ATC for both temperature up-step and down-step changes. With the increase of step magnitude, instant changes of thermal sensation become larger while that of thermal comfort rises to its maximum absolute value at S11. Asymmetry exists in human response to temperature step change of same magnitude but reverse directions (Table 2). In S15, the immediate changes of perspiration, dizziness and thermal comfort after down-step are significantly more intensive than that after up-step. Moreover, instant change in thermal comfort after down-step is profoundly larger than that after up-step in S11. Those facts that the subcutaneous depths of cold and warm receptor are 0.15mm~0.17mm and 0.3~0.6mm respectively, and the number of cold receptors is about ten times that of warm receptors may account for such phenomenon [8].

Table 2. Direction and amplitude effects of temperature steps on health symptoms and thermal perceptions.

Direction effect Up-steps Amplitud e effect Down-steps

S5 S11 S15 S5 vs S11 S11 vs S15 S5 vs S15 S5 vs S11 S11 vs S15 S5 vs S15

Perspiration 0.257 * *** 0.871 0.081 0.062 ** 0.149 ***

Dizziness 0.655 0.317 * N/A N/A N/A 0.943 0.150 0.369

Accelerated respiration 0.157 1.000 0.564 0.589 0.579 1.000 0.609 1.000 0.609

Eyestrain 0.166 0.083 0.414 * 0.954 * 0.528 0.329 0.711

Accelerated heart rate 0.564 0.317 0.157 1.000 N/A 0.579 0.696 0.311 0.455

Thermal sensation 0.241 0.106 0.171 *** * *** ** 0.077 ***

Thermal comfort 0.351 * * ** *** 0.126 *** ** 0.616

Note: * P<0.05, ** P<0.01, *** P<0.001.

4. Conclusions

Perspiration, eyestrain, dizziness, accelerated respiration and heart rate are found to be sensitive self-reported symptoms in response to temperature step-changes. Thermal sensation and thermal comfort just before temperature step are significantly distinguished from that immediately after step change except for thermal comfort under up step situation of S15 (22oC-37oC). Temperature step magnitude has significant impact on human response to temperature steps. Besides, there exists asymmetry in human response to temperature steps with same magnitude but diverse

varying direction as instant change of perspiration, dizziness and thermal comfort after temperature up-step are significantly smaller than that after down-step in S15.

Acknowledgements

This work is financially supported by Key Program of National Natural Science Foundation of China (51238005). References

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