Energy performance of switchable window insulated shades for US residential buildings

Abstract

This paper evaluates the potential energy savings when novel switchable insulated shading systems are applied to smart windows for US residential buildings. These switchable shades utilize dynamic and controllable transparent insulating layers to protect smart windows. Control strategies allow the shades vary dynamically their R-value and the smart windows to adjust their solar heat gain coefficient to achieve desired objectives. In this analysis, switchable insulated shades are applied to smart windows to minimize heating and cooling thermal loads for US housing units. First, switchable insulated shades using transparent insulating materials deployed as blinds for smart windows are described. The special case of switchable opaque insulated shades to act as automated blinds for conventional windows is also considered. Then, the modeling approach for switchable transparent and opaque insulated shades as integrated within a whole-building simulation environment is described to predict their performance under various design and operation strategies. Moreover, simplified 2-step controls rule-based control sets are outlined to operate the switchable windows in order to improve the building energy performance under heating and cooling operation modes. The energy analysis carried out for a prototypical housing unit located in four US cities indicates that switchable windows can save up to 59.1% and 64.9% in annual heating and cooling energy, respectively, for dwellings located in Golden, CO. Moreover, it is found that even when switchable opaque insulated shades are used with conventional double-pane windows, over 40% reduction in both heating and cooling energy end-uses can be achieved for residential buildings located in mild US climates.