If the environment radiant temperature differs from the air temperature, how does WIS determine the U-value?
If the environment radiant temperature differs from the air temperature, then WIS takes the weighted mean value for determining the U-value. That is correct (see also ISO 15099): it corrects for higher heat loss in case of clear sky for instance. But it does not give insight in the way ‘normally’ the U-value may(!) be defined: on the basis of air temperature difference.
