Different aspects of assessing indoor and outdoor thermal comfort

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.