Thermal comfort in vehicles: the effects of solar radiation

This thesis presents laboratory and field studies into the effects of solar radiation on the thermal comfort of vehicle occupants. Whilst, thermal comfort has been widely studied in built environments, there have been relatively few studies into thermal comfort in vehicles. Those studies that have been conducted have noted that the effect of solar radiation is considerable in these confined microclimates. The aim of this thesis was to provide baseline data for the effects of solar radiation on thermal sensation and determine how this information can be integrated to provide a method for the assessment of vehicle thermal comfort. This was achieved using a specially constructed whole body solar chamber in a series of four laboratory studies looking at different aspects of solar radiation on human thermal comfort and an extensive field trial conducted in Seville, Spain. The laboratory studies were as follows:- 1, The effect of the intensity of direct simulated solar radiation on human thermal responses. Eight male subjects were exposed to 4 different intensity solar radiation conditions. Physiological and psychological measurements were taken. It was established that a mean response to 200 Wm"2 of direct simulated solar radiation will give a thermal sensation shift of one positive scale point. 2, The effect of the spectral content of simulated solar radiation on human thermal responses. Eight male subjects were exposed to 4 different spectral radiation conditions, with the same total radiation intensity, 400 wm·2 • There was found to be no significant difference in the thermal sensation responses due to spectra. 3, The effects of glazing type on human thermal comfort responses. Eight male subjects were exposed to 4 different automotive glazings, with a fixed external solar radiation level of 1000 wm·2 • The spectral qualities of glazing can significantly effect human thermal comfort. The lower the transmission of visible radiation through the glazing, the lower the thermal sensation felt by subject in a neutral environment. 4, The effect of direct short wavelength and long wavelength radiation on human thermal comfort. Nine male subjects were exposed to short wavelength, long wavelength and combined short and long wavelength radiation. For the conditions investigated it was established that the addition of reradiation from internal components has an effect on thermal sensation when combined with direct solar radiation. However, it is not considered that it will be a major factor in a real world situation, as dashboards generally do not maintain high surface temperatures in vehicles without high air temperatures. Using the data collected in the laboratory studies a predictive model, PMV sotu, was developed which integrated directed solar radiation into an existing thermal comfort model (PMV) in the form of a factor, Rsolar· Rsolar is a correction factor for the addition of short wavelength radiation which converts actual measured solar radiation to a thermal sensation scale adjustment The PMV solar model was validated with other models in field trials conducted in Seville, Spain. Four male subjects, undertook a series of 32, one hour long experiments over 8 days, whilst travelling on a Spanish highway. Environmental, physiological and psychological measurements were taken throughout the experiments to provide data for validation of THE PMV solar model. The assessment of human thermal comfort in vehicles is complex. Variation in environmental parameters in terms of both spatial and temporal changes, make accurate prediction of thermal comfort difficult. However, the PMV solar model provides an improved level of prediction of the state of thermal comfort of the vehicle occupants, in environments which have a high solar radiation level over existing thermal indices.