The optical properties due to the diffuse radiation are determined from the integration of the local optical properties over the sky and ground elements.
The effect of slat curvature and slat thickness on the optical properties is included in the developed mathematical model.
The comparison between the optical properties of the curved slat blind with thickness and the optical properties of the flat slat blind with negligible thickness calculated from the 6 surface closed enclosure method is made.
The effect of slat curvature and slat thickness is clearly seen on the direct-to-direct transmittance and the direct-to-diffuse transmittance when the slat is aligned with the solar radiation direction (sum of the profile angle and slat angle is equal to 0).
The effect of slat curvature and slat thickness is also clearly seen on the direct-to-diffuse transmittance and reflectance when the slat is in the position that fully blocked from the sun.
The effect of slat curvature and slat thickness is more pronounced when the values of the slat reflectance, slat curvature radius and slat thickness are increased.
The optical properties of the curved slat blind with thickness calculated from the developed model are compared with the optical properties of the curved slat blind with thickness calculated by using the Monte Carlo ray tracing method.
The agreement is quite good for a low reflectance blind.
The difference in the results predicted by two methods is found in the values of the direct-to-diffuse transmittance and reflectance when the lower part of the slat is exposed to the sun especially in the case of a high slat reflectance blind.
The comparison between the results obtained from the developed model and other previous models (EnergyPlus, Pfrommer, Parmelee model) are performed.
The difference in the predicted values of the optical properties from different models are clearly seen in this case (i.e. high slat curvature and high slat thickness).
One of the reasons may come from that none of the considered models has the capability to account for the slat curvature and slat thickness at the same time.