Thermal Performance of Managed Window Systems

The primary factors that determine the net thermal performance of a window system are its overall heat transfer rate (U-value), its air leakage characteristics and its sun control capability. With managed window systems these basic properties may be drastically altered on an hourly basis as movable insulating and shading devices are deployed over the prime windows. A large building energy analysis computer program, DOE-2, has been modified to model the thermal performance of a variety of window management devices. The deployment of these devices is simulated based upon fixed hourly schedules or the value of critical climatic factors such as solar intensity. Automatic operation may be modeled or manual operation with varying degrees of human fallibility may be simulated. The model couples reductions in infiltration rate to the deployment of an insulating or shading device. Results of heating load calculations are presented for the cases of single- and double-glazed windows in a typical house with glass-to-floor area ratios of 15 to 40%, and for window management devices with varying thermal resistance, air leakage rates and different modes of operation .