Alpen WinSert® Secondary Window Inserts Demonstrate Up to 18% Whole-Building Energy Savings in GSA Green Proving Ground Testing

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LOUISVILLE, Colo., Feb. 22, 2022 /PRNewswire-PRWeb/ — ALPEN HIGH PERFORMANCE PRODUCTS INC., a longtime U.S. leader in high efficiency window technology across commercial and residential markets, announced today that the U.S. General Services Administration (GSA) has finalized and published the results of its nearly year-long testing and evaluation of WinSert® secondary window inserts manufactured by Alpen. The recently patented secondary windows, made with high performance fiberglass frames and an innovative use of ‘thin’ glass technology, were tested and evaluated as part of GSA’s Green Proving Ground (GPG) program. This program uses GSA’s real-estate portfolio to evaluate high-potential, sustainable building technologies that reduce energy usage in federal buildings. The feedback received from building occupants revealed improved thermal performance of the secondary windows improved thermal comfort for the occupants under cold winter conditions.

It has been estimated that windows account for 39% of the annual U.S. energy used to heat commercial buildings and about 28% of the energy used to cool commercial buildings¹. This energy usage can be reduced by replacing the windows entirely, but the process can be extremely expensive and disruptive for building owners and occupants. WinSert secondary window inserts provide an ultra-lightweight, custom retrofit solution to turn existing leaky, low-performing windows into air-tight, high-performing windows to improve the building envelope without the cost, time, and disruption required for window replacement. As demonstrated in a previous study, WinSert’s super-insulating, high-performance patented design performs up to 45% better than competing secondary window options², and many other retrofit solutions simply do not meet the comprehensive needs of the market.

The U.S. Department of Energy’s National Renewable Energy Laboratory evaluated Alpen’s WinSert secondary window inserts at a two-story office building at the Denver Federal Center. For this study, Alpen’s high performance secondary windows (half WinSert Lite–single-pane with an ultra-lightweight piece of ThinGlass laminated to a custom performance film–and half WinSert Plus–double-pane with a ThinGlass, gas-filled, insulated glass unit) were installed in the building, all with super-insulating, low-profile fiberglass frames. Researchers measured glass and frame surfaces of single-pane windows both with and without the added secondary windows to compare and calibrate measurements with models created using the Department of Energy’s WINDOW and THERM software.

The results showed that the double-pane secondary window, WinSert Plus, is cost effective for most climate zones and at GSA medium and high utility rates. Modeling for WinSert Plus compared to a single-pane clear window demonstrated up to 18% whole-building energy savings for medium-sized office buildings with an average of 15% across all modeled climates. The actual energy savings could be higher than what is reflected in the study given that the modeled savings do not include the impact of reduced air infiltration or thermostat adjustment, both of which will generate additional energy savings. The Attachments Energy Ratings Council recently certified the WinSert line in its commercial secondary window database with the lowest U-factor values in the category and a 97% reduction in air leakage compared to the baseline single- and double-pane windows.

On a 21-degree winter day, the window with WinSert Plus measured a center-of-glass interior temperature of 68.2 degrees Fahrenheit–a 20-degree increase from the single-pane baseline window, and interior window condensation resistance improved, as well. Alpen’s secondary window insert achieved these high performance rating improvements and yet required less than 10 minutes to install without any drilled holes or permanent devices. “These thin glass secondary windows improved window performance. Installation was fast and achieved with minimal disruption,” said Tyler Cooper, Mechanical Engineer at GSA Denver Federal Center.

“We are appreciative of the opportunities to partner with the U.S. General Services Administration and National Renewable Energy Laboratory through the Green Proving Ground program – previously to test our high performance quad-pane windows and now to test our newly patented and innovative high performance secondary window insert,” said Brad Begin, CEO of Alpen High Performance Products. “Our mission is to improve building sustainability by making high-efficiency windows a smart business decision. WinSert will help buildings reduce carbon emissions by improving the building envelope where window replacement is too expensive or disruptive to tenants.”

Begin added, “With so much of the built environment contributing to carbon emissions, we hope more building owners, energy contractors, and decision makers use these test results to accelerate product choices to higher performance window retrofit solutions.”

More information about this study and its findings are available on Click here to view the summary report.

GSA’s Green Proving Ground program will be hosting a webinar on March 3, 2022, where researchers and facility managers will discuss findings from the project evaluation, share operational guidance and answer questions. Click here to register.

About GSA’s Green Proving Ground (GPG) Program

GSA’s Green Proving Ground program works with third-party evaluators to test innovative early-commercial building technologies in federally owned buildings. The program enables GSA to make investment decisions in next-generation building technologies based on actual performance. To date, following favorable evaluation results, 23 GPG-evaluated technologies have been deployed in more than 500 facilities in GSA’s real-estate portfolio. For more information about the GPG program, please visit


Alpen High Performance Products manufactures super-insulating, thermally efficient commercial and residential windows and architectural glass with four decades of industry leadership in high performance windows and glass unit manufacturing. The exceptional thermal performance of Alpen’s window and glazing solutions grants the freedom to design with maximum glass across all building types and climate zones. Alpen products provide a powerful combination of blocking summer heat, retaining winter warmth, eliminating harmful ultraviolet rays, reducing noise and maximizing natural daylight while providing exceptional energy savings. As a complementary alternative to Alpen’s ultra high-performance commercial window lines, Alpen has coupled thin glass window expertise with continued development of WinSert™, a high-performance secondary window insert, to further advance the commercial secondary window market. Visit Alpen’s website to learn more.

¹ Window-Related Energy Consumption in the US Residential and Commercial Building Stock. Joshua Apte and Dariush Arasteh (LBNL). As reported in the 2005 Buildings Energy Databook Table 1.3.3 (US DOE Office of Energy Efficiency and Renewable Energy 2005)

² Secondary Glazing System (SGS) Thermal Performance and Annual Energy Use Analysis: 2020 Update. Robert Hurt, Valerie Green, Charlie Curcija (LBNL), September 2020

Media Contact

Danielle Birdsall, Alpen High Performance Products, +1 (303) 834-3509, [email protected]

Craig Maierhofer, Alpen High Performance Products, [email protected]

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SOURCE Alpen High Performance Products

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