LBNL Report Number
Over the past 15 years, low-emissivity and other technological improvements have significantly improved the energy efficiency of windows sold in the United States. However, as interest increases in the concept of zero-energy homes—buildings that do not consume any nonrenewable or net energy from the utility grid—even today's highest-performance window products will not be sufficient. This simulation study compares today's typical residential windows, today's most efficient residential windows, and several options for advanced window technologies, including products with improved fixed or static properties and products with dynamic solar heat gain properties. Nine representative window products are examined in eight representative U.S. climates. Annual energy and peak demand impacts are investigated. We conclude that a new generation of window products is necessary for zero-energy homes if windows are not to be an energy drain on these homes. Windows with dynamic solar heat gain properties are found to offer significant potential in reducing energy use and peak demands in northern and central climates, while windows with very low (static) solar heat gain properties offer the most potential in southern climates.