Calculating Center-Glass Performance Indices of Glazing Systems with Shading Devices

Abstract

Building energy consumption and loads are strongly influ-enced by solar gain and heat transfer through the centre-glass area of windows. Methods have been devised to calculate the corresponding energy performance indices (e.g., SHGC and U-factor). Simulation offers the opportunity to examine design options such as low-emissivity or solar-control coatings, glass tints, substitute fill gases and diathermanous glazing layers. Current models use a radiosity-based approach to quantify longwave radiant exchange. A new method is presented for the thermal analysis of multilayer systems. This method, by using a resistor network to quantify both convective and radiant exchange, offers exceptional generality. “Jump” resistors allow for airflow between layers, or diathermanous layers, or any combination of the two. The air and mean radiant temper-atures can differ on both the indoor and outdoor sides. In addi-tion a more general method has been devised for calculating indices of merit without restricting the generality of the simu-lation model – for any set of environmental temperature and insolation conditions. These methods are especially useful for the analysis of glazing systems used in combination with shad-ing layers such as venetian blinds, curtains, roller blinds and insect screens. These methods also offer new possibilities, speed and convenience when used in conjunction with whole building performance simulations.