Heat transmission through a glass window with a curved venetian blind installed

Abstract

This article reports a study on the effect of installing a curved venetian blind to a glass window on the solar heat transmission into the space. The mathematical model of the combined glass window and venetian blind is developed. Predicted results from the developed mathematical model are compared with the previous experimental ones to verify their accuracy. The variation of the solar heat gain coefficient (SHGC) with the related blind parameters (optical properties of venetian blind, slat spacing, distance between the blind and glass window, slat angle and solar profile angle) are studied. The variation of the SHGC in the shortwave part (ShW SHGC) and in the longwave part (LoW SHGC) with the related blind parameters are also studied. The understanding of their variation will provide the important information for the study of the thermal comfort for a person who stays near the glass window with blind. The SHGC can be further classified as the SHGC for direct solar radiation (SHGCD) and the SHGC for diffuse solar radiation (SHGCd). From the study it is found that installing a curved venetian blind to the glass window causes a significant reduction in solar heat gain compared to the plain glass window. The SHGCD, ShW SHGCD and LoW SHGCD are all dependent on the slat angle and solar profile angle. The slat reflectance of the venetian blind has direct effect on the ShW SHGCD. The slat absorptance of the venetian blind has direct effect on the LoW SHGCD. The glass window and blind with high slat reflectance gives a lower value of SHGCD compared to the glass window and blind with low slat reflectance. The slat curvature also affects the SHGCD of the fenestration system (glass window with blind installed). The slat with more curvature (lower value of slat radius of curvature) causes more reduction in the value of SHGCD compared to the slat with less curvature. The blind with lower slat spacing yields a lower value of SHGCD compared to the blind with higher slat spacing. The effects of slat emittance and distance between the blind and the glass window on the SHGC D of the fenestration system are only appeared on the LoW SHGCD and such effects are quite small.