Exergetic Review on Thermal Performance of Window Systems

According to an advancement of exergy research in relations to thermal comfort and built environment for the last fifteen years, the availability of “warm” or “cool” radiant exergy emitted by the interior surfaces of building envelope systems is crucially important in providing building occupants with adaptive opportunity for thermal comfort both in summer and in winter. This paper demonstrates some numerical examples showing how the thermal performance of window systems affects the availability of “warm” and “cool” radiant exergies. In winter, thermal insulation of window systems together with appropriate internal solar control brings about ten to twenty times larger “warm” radiant exergy, while in summer external shading of window systems reduces “warm” radiant-exergy emission towards the indoor environment by more than 80% comparing to internal shading device, and allows the built environmental space to be filled with “cool” radiant exergy emitted by other interior surfaces of building envelopes.