Human responses to outdoor thermal environments
thesisposted on 25.11.2009, 09:25 by Ju Youn Kwon
This thesis presents a series of studies into the responses of people to outdoor thermal conditions experienced over all seasons in the United Kingdom. The aim was to investigate practical methods for predicting human responses to outside weather conditions, which would be useful in predicting effects on human comfort and health. The studies involved both laboratory experiments and field trials. One particular aspect of outside conditions, not usually investigated in laboratory studies, is the contribution of solar radiation. Single subject and thermal manikin studies were used to determine the contribution of solar radiation to human response. In addition to this, a total of 168 subjects responses were recorded during trials at the Loughborough University weather station compound. (latitude 52.47N and longitude 01.11W). The trials were distributed between July 2007 and October 2008. This provided a comprehensive data-base for the evaluation of thermal indices. The thesis is divided into four parts. Part one provides an introduction to the subject and a comprehensive literature review. It also describes equipment, calibration procedures and methods used. Part two quantified the contribution of solar radiation to the heat load on a person. A human subject and a heated thermal manikin were exposed to outdoor thermal conditions, while in light clothing and (for the person) conducting a step test. They were then exposed to identical conditions in a thermal chamber, but without the contribution of the sun. The conditions outside were 23˚C air temperature, 42˚C mean radiant temperature and 54% relative humidity with an average air velocity of 0.75 ms-1. The difference in sweat rate (person) and heat required (manikin) between outdoor and indoor conditions were used to estimate the contribution of the sun. Using three different analyses estimates were 14 Wm-2, 35 Wm-2 and 50 Wm-2 depending upon the assumptions made. Part three describes current thermal indices that can be used to assess the effects of weather conditions on people. It also presents the results of weather station measurements over the time period considered. In chapters 8 and 9 field trials are described which capture both the thermal conditions and human physiological and subjective responses to those conditions. Chapter 10 uses the data collected to provide an evaluation of current thermal indices for predicting human responses. The range of air temperature and relative humidity (at 2 pm) over a year was -2˚C to 29˚C and 34% to 95% respectively. Wind speed varied and was greater in winter and spring than in summer and autumn. Solar radiation was influenced by the altitude of the sun which depended upon season. Mean solar radiation increased from December to June and decreased from June to December. The subjective and physiological responses for 130 people (65 males and 65 females) over a range of outdoor weather conditions are presented. Physiological responses for females generally showed a stronger relationship with environmental variables and subjective responses than those for males. The subjective and physiological responses of four groups (one in each season of the year - involving a total of 38 people), are presented. It was found that there were significant individual differences in response. Part four provides a suggestion for an improved thermal index. The PMV (Predicted Mean Vote) out of four thermal indices (WBGT, PMV, WCI/tch and Twc) had the strongest relationship with environmental variables and physiological responses but had a weak relationship with subjective responses. A PMVoutdoors index was developed to improve the prediction of subjective responses for the outdoor conditions investigated. Conclusions and recommendations for future research are provided.