The radiative conductance coefficients for exterior surfaces and gaps between layers of the fenestration system that dose not include the diathermanous layer can be firstly determined from the value of the difference between the radiosity of the adjacent layers divided by the difference of their surface temperatures. But when the fenestration system includes the diathermanous layer, Collins and Wright (2006) have suggested a new method to determine the radiative conductance coefficient by revisiting the radiosity balance (Eqs. (45)–(49)) with only one surface emitting at a time. It is assumed that all surfaces of the fenestration system (including the indoor and outdoor conditions) except (for example) surface k had a temperature of 0 K, then only surface k would have emitted component of radiosity based on its known temperature.
The radiosity of all other surfaces would only include reflected components.
Then the radiative conductance coefficient between the adjacent surfaces (for example) j and k are determined by calculating the difference in the net radiosity originating from surface j that reaches surface k and the net radiosity originating from surface k that reaches surface j, divided by the temperature difference between surfaces j and k.
For the inner glass layer which is located next to the venetian blind, there are two radiative conductance coefficient existing; the radiative conductance coefficient between the inner glass surface and the adjacent blind surface and the radiative conductance coefficient between the same inner glass surface and the indoor condition.
Therefore, the relationship for the radiative conductance coefficient can be expressed as