The Investigation And Analysis Of Outdoor Thermal Comfort In Changsha During The Summer

Most of the previous thermal comfort studies focused on the indoor space where people stayed for a long time. However, people choose to spend more time on outdoor exercise, entertainment and communication with the improvement of the quality of life. Outdoor space is becoming an important platform for the residents to have activities. A comfortable outdoor thermal environment will attract more people to take outdoor activities instead of staying indoors which is beneficial to physical and mental health, and energy consumption of air conditioning and lighting will be reduced as a result of the decrease in indoor residence time.To create a pleasant outdoor environment, we need to understand the influencing factors and action principle of the thermal comfort first, then improvement measures could be proposed in relation to the inadequacies. Outdoor environment is natural and non-steady in which environmental parameters and human adaptation are different from indoors, so evaluation indexes, models and standards for indoor thermal comfort may not be applicable to outdoor. In addition, different regions, climate, culture and customs also have an impact on the thermal comfort, that lead to the foreign research results and conclusions can’t be applied to the domestic conditions directly. Therefore, indigenous studies on outdoor thermal comfort are necessary and meaningful.The paper presents a thermal comfort investigation carried out in squares, parks, residential areas and commercial streets of Changsha during the summer season in 2010. 515 samples of data were collected through the environmental measurement and questionnaire survey. Relevant parameters and sensation votes of the subjects were calculated and counted by using the statistic software SPSS, evaluation models about the thermal sensation, humidity sensation and expectation were established through the linear and logistic regression analysis. We also analyzed the adaptive behavior of the subjects, derived the relationship between the comfort temperature and mean outdoor temperature, and explored other influencing factors besides temperature and humidity. Finally, the paper put forward the corrective measures for outdoor environment from the perspective of urban planning and design in combination with the requirements to human thermal comfort.The mean outdoor temperature (31.5℃) and relative humidity (65%) were high during the test, unacceptability (23%) counted by the direct evaluation of the subjects exceeded the ASHRAE standard stipulation (≤20%). The neutral temperature (29.2℃) and humidity (65%) were higher than the indoor results and standard recommendations, and the acceptable range of temperature (25.5~32.8℃) was wider too, reveals that people staying outdoors have stronger adaptability to high temperature and humidity than indoors. The expected temperature (28.6℃) was 0.6℃lower than the neutral temperature, which suggests that people like the environment temperature slightly cooler than neutral. The comfort temperature of subjects rose 1℃at every 4℃increase of the outdoor air temperature, people expected higher wind velocity and weaker solar radiation as the temperature increases. Different sexuality, residence time and previous thermal state also have an effect on human thermal comfort. These conclusions could be used as a reference to the determination of design parameters and standards development for the outdoor thermal comfort.