Experiment: Low-E Storm Windows
A storm window is a secondary window or panel that attaches to the inside or outside of the primary (or existing) window. Modern storm windows stay installed year round to insulate and air seal existing windows improving energy efficiency without the need for full window replacement. Low-E storm windows have a nearly invisible low-emissivity coating on the glass that reduces heat loss in the winter and can also help reduce heat gain in the summer.
Results from modeling studies and monitoring data from homes with low-E storm windows installed have shown exciting promise for the energy savings and cost effectiveness of low-E storm windows. DOE has asked for more data to corroborate these results. In response, PNNL is fully evaluating the energy savings potential, occupant comfort impacts, and condensation risks of installing low-E storm windows over typical double-pane aluminum windows.
At PNNL's two Lab Homes, tests have been conducted on the performance of low-E storm windows during several weeks of a cooling and heating season. Low-E storm windows have been installed on the exterior of the existing windows in the Experimental Home, while no storm windows were installed over the double-pane clear-glass, aluminum-frame windows in the Baseline Home. Identical monitoring equipment was installed in each home to test each home’s heating, ventilation, and air conditioning (HVAC) system; interior and surface glass temperatures; and relative humidity levels during heating and cooling seasons. In a real occupied home, people give off heat and humidity that could impact window performance. The Lab Homes use heat sources and humidifiers to simulate this human impact. The beauty of the Lab Homes is that because this occupant behavior is simulated, both homes can be set to identical simulated occupancy schedules so that the performance of the low-E storm windows will be isolated from all other variables.
After the data was collected for a full heating and cooling season, PNNL research staff used EnergyPlus software to extrapolate data to model expected low-E storm window performance for all major U.S. climate zones.
PNNL and DOE have provided the performance data to utility companies and other regional and national stakeholders who have an interest in low-E storm windows as an energy-efficiency measure. Also, the results have been used to inform a concurrent effort to develop a rating system for low-E storm windows.
|Thermal and Optical Properties of Low-E Storm Windows and Panels||July 2015||TD Culp, SH Widder, and KA Cort. 2015. Thermal and Optical Properties of Low-E Storm Windows and Panels PNNL-24444, Pacific Northwest National Laboratory, Richland, WA.
Abstract |Full Publication
Installing low-emissivity (low-E) storm windows and panels over existing windows has been identified as a cost-effective new approach for improving the energy efficiency of existing buildings where window replacement is impractical or too expensive. As such, it is desirable to characterize the key energy performance properties of low-E storm windows and panels when installed over different types of existing primary windows. this paper presents the representative U-factors, solar heat gain coefficients (SGHCs) and visible transmittance properties of the combined assemblies of various storm windows and panel types installed over different primary windows.
|Interior and Exterior Low-E Storm Window Installation||September 2014||TD Culp, SH Widder, and KA Cort. 2015. Interior and Exterior Low-E Storm Window Installation Video PNNL-24444, Pacific Northwest National Laboratory, Richland, WA.
Abstract | Video
Until recently, energy-efficient window retrofit options have largely been limited to repair or replacement; leaving the homeowner to decide between affordability and deeper energy savings. A new and improved low-e storm window boasts a combination of curb appeal and energy efficiency, all for a fraction of the cost of window replacement. A recent whole-home experiment performed by PNNL suggests that attaching low-e storm windows can result in as much energy savings replacing the windows.
|Evaluation of Low-E Storm Windows in the PNNL Lab Homes||May 2014||Knox, JR, and SH Widder. 2014. Evaluation of Low-E Storm Windows in the PNNL Lab Homes. PNNL-23355, Pacific Northwest National Laboratory, Richland, WA.
Abstract |Full Publication
This study examines the performance of exterior and interior low-e storm panels with a controlled whole home experimental design using PNNL's Lab Homes. Summing the estimated annual average heating and cooling savings, the installation of low-e storm panels resulted in approximately 10% annual energy savings. The results of the experiment will be used to determine and validate performance of low-e storm windows over double pane clear glass windows in a whole home setting.
|DOE's Building America Low-E Storm Window Adoption Program||September 2013||Cort KA. 2013. "DOE's Building America Low-E Storm Window Adoption Program." Presented by Cort, Katherine (Invited Speaker) at 10th Annual CEE Industry Partners Meeting: Residential Windows Working Group Workshop, Atlanta, Georgia, GA on September 17, 2013. PNNL-SA-98315.
Abstract | Full Publication
This presentation was used to guide discussion on the topic of low-e storm windows -- benefits and market adoption strategies -- during the Consortium for Energy Efficiency's (CEE's) annual Industry Partners meeting, Window Working Group Workshop.