A comparative thermal properties evaluation for residential window retrofit solutions for U.S. markets

The most widely known method of reducing energy loss through windows is to replace inefficient single- pane window units with their newer, more energy efficient counterparts. However, there are also other methods that involve retrofit solutions, including the use of curtains, drapes, blinds, screens, and shutters. While these products are often selected for aesthetic or privacy concerns, they can also provide an effective means of limiting heat transfer. This paper describes the performance criteria such as reduction in heat conductance, solar heat gain, daylighting, thermal comfort, condensation potential, air leakage, cost, ease of operation, privacy, and aesthetics for each retrofit solution. The focus of the study is to evaluate the reduction in thermal conductivity and solar heat gain coefficient with variation of parameters specific to each retrofit measure. Window retrofit attributes are evaluated based on data and information available in the open literature and those provided by product manufacturers as well as using software such as WINDOW and THERM. This study outlines some guidelines for selection of retrofit options and for better understanding of different solutions with respect to heat loss prevention and other attributes.