By treating the venetian blind as an diathermanous layer (layer which the radiative heat can be transferred across the layer, i.e. the radiative heat from the surface of the inner glass can flow across the blind to the inner space), the inward–flowing fraction of the absorbed energy for kth layer in the system, k N , and the overall heat transfer coefficient can be found from the concept of the resistance of the heat flow as shown in reference [21].
With the developed mathematical model, the solar heat gain coefficient and the overall heat transfer coefficient for the glass window installed with a curved venetian blind can now be determined.