Berkeley Lab Study Evaluates Impact of Triple-Pane Windows in California Homes

When it comes to energy efficiency in California buildings, windows are a weak link. About half of the state’s homes still have inadequate, single-pane windows. A significant portion of these homes are in communities throughout the state that may have more vulnerable populations. 

Windows pose a key opportunity both to reduce carbon emissions from California’s buildings and to boost energy equity in homes. Researchers at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) are deploying a newly developed thin-glass triple-pane window system into two multifamily sites and 30 single-family housing units to quantify its field performance and the building energy savings. The work is funded by the California Energy Commission.

“Given that more than 6.5 million families statewide have inefficient windows in their homes, success in this project has broad implications. So many homes need affordable, proven window retrofits,” said Robert Hart, a researcher at Berkeley Lab and principal investigator of this study.

Berkeley Lab's thin-glass triple-pane insulating glass unit (IGU) concept is constructed  like traditional triple-pane IGUs, but uses thin-glass as the center pane, a single spacer, and argon or krypton gas fill, enabling the IGUs to directly replace industry standard double-pane IGUs. The thin-glass triple-pane technology offers the performance benefits of traditional triple-pane with little increase in weight or cost, enabling incremental costs competitive with alternative energy reduction solutions for the building envelope. 

Thin-glass triple-pane IGUs were designed to easily replace existing double-glazed IGUs without having to modify the window frame, making them a more cost-effective market-ready technology. The project on the multifamily site consists of a 12-month pre-retrofit monitoring period with equipment attached to HVAC, windows, and a free smart thermostat. The participants receive new windows and have the same equipment in place for another 12 months post-retrofit.  

So far, the Berkeley Lab team has worked with two multifamily sites in Santa Rosa and Fairfield locations through Eden Housing, a nonprofit with properties throughout California. The research team held several community engagement meetings with residents to provide background information and encourage local community participation. After discussing benefits and risks, as well as answering any questions the participants had, the researchers confirmed 27 participating multifamily units.

“If you have subpar windows in a home, you’re losing heat or cooling energy,” said Hart. “That translates to higher utility bills. It’s also a problem in meeting the state’s emissions targets, because we’re pouring too much energy into inefficient, leaky building envelopes.” 

This demonstration will help researchers quantify energy savings of the thin-glass triple-pane windows, which provides both the potential for residents to save on their energy bills and to increase comfort in their homes. Better windows could also build resilience by improving thermal comfort and health even when the power fails.