Abstract :
As people spend most of their time indoors, steady state models may be appropriate for thermal comfort assessments there, while, for the relatively short times spent outdoors (mostly less than 1 h), those models tend to overestimate discomfort. This discrepancy is larger for cool outdoor conditions than for warm ones. For example, for a person leaving a room in thermal comfort (Tsk=33.5 °C, Tcore=37 °C) into cold winter outdoor conditions (Ta=Tmrt=0 °C, VP=5 hPa, v=1 m/s) obtaining steady state will take many hours, while leaving into hot conditions (Ta=30 °C, Tmrt=60 °C, VP=15 hPa, v=0.5 m/s) it will be reached within less than 30 min. Consequently, especially for outdoor thermal comfort assessments in cold conditions, non-steady state models should be applied. This, among other new aspects, will be considered in a new internationally standardised Universal Thermal Climate Index (UTCI), which is currently being developed by a working group of the International Society of Biometeorology. Besides such physical/physiological approaches, psychological factors also have to be considered, i.e. diverging thermal expectations indoors and outdoors. Consequently, different approaches are necessary for assessing indoor or outdoor thermal comfort.
