It’s time to switch to triple-glazed windows. That’s the message of a series of studies conducted by the Department of Energy’s Pacific Northwest National Laboratory in conjunction with a coalition of public and private partners.

“Lower costs, greater availability and the drive to reduce carbon emissions are pushing us towards a tipping point where triple-glazed windows are starting to make a lot of economic sense,” said Kate Cort, research economist at PNNL. and program manager for the current field. validation studies for triple glazing.

It’s no secret that windows in a home can waste a lot of energy. They can leak, and even the latest double-glazed window designs contribute significantly to a home’s energy consumption and cost. For a new home, windows typically make up about 8% of the exterior area, but are responsible for half of the heat loss or gain. This passive energy loss makes windows a major contributor to home heating and cooling costs.

Meanwhile, evidence of the energy and cost savings of triple-glazed windows has been slowly accumulating for years, since the first prototypes were introduced around 1989. Previous studies have shown that triple-glazed windows are more energy efficient than industry standard double glazed windows. variety of panes, but market adoption has been slow due to cost and availability.

Those downsides are about to change, Cort said. A new generation of thin triple-glazed windows is less expensive and can be more easily fitted into existing double-glazed frames. As the name suggests, triple pane windows have three panes of glass that create a two-story sandwich, which is filled with an inert gas, such as krypton, which provides additional insulating power. These next-generation windows take advantage of the economies of scale provided by the same advanced glass manufacturing technology that produces thin, yet durable television and computer screens.

Over the past three years, Cort and his colleagues have systematically evaluated the energy savings and economic factors that will determine how quickly they will be accepted by builders. This work was supported by the DOE Building Technologies Office and the Bonneville Power Administration.

Now utility regulators are starting to take notice. Recently, the State of Michigan used data from a PNNL field study of triple-glazed windows to include them in the state’s Technical Resource Manual list of eligible approved energy-saving measures. incentives and utility discounts.

New energy standards create urgency

Another recent study by Cort, his PNNL colleague Edward Louie, and Robert Hart of Lawrence Berkeley National Laboratory showed that for new home construction, triple-glazed windows can help builders meet 2021 energy codes more cheaply. more stringent for new homes. Their study, published in the March 2022 issue of ASHRAE Review have shown that when a home builder upgrades the windows of a new home from double to triple glazing, the energy performance of the windows can improve by 40% or more. This extra performance increases the total insulating value of the entire exterior of the house, often referred to as the building envelope.

“Our study has shown that increasing the energy efficiency of windows gives builders greater flexibility in design and the ability to compromise with other components of the envelope, such as wall insulation. exteriors, while respecting the code,” Cort said. The overall effect is to provide builders with more options and better assurance of building code compliance, while improving homeowner comfort.

What is the lifespan of triple glazed windows?

Builders play a key role in adopting new home building technologies, Cort said. In 2020, she and her colleagues surveyed 29 homebuilders who participated in the DOE Zero Energy Ready Home program. They asked builders to explain their decision-making process for window selection during the 2018 to 2019 building season. Forty-one percent of these builders used triple-glazed windows in all of their new homes and 28 percent in the most or some of their homes. For those not using triple-glazed windows, the most important factor was cost.

“The price differential between double-glazed and triple-glazed windows has been a problem for builders,” Cort noted. But she added that the added cost increase for triple-glazed window materials is now around $700 to $2,400 for a 2,400-square-foot wood-frame home. That’s about the same cost as adding an extra inch of rigid wall insulation to the same house.

Some builders have also said that the indirect cost of bespoke installation for triple-glazed windows, which can be 25% to 50% heavier than similarly sized double-glazed windows, also factored into their choice.

“Most builders are unfamiliar with the new thinner and lighter triple glazing technology,” Cort said. But the survey showed most would be willing to try them if the cost and availability made it convenient for them.

Some of the builders the Cort team interviewed noted that consumers appreciate the comfort and quiet of triple-glazed windows. A recent study confirmed that installing triple-thin panes reduced sound infiltration by an average of 8-10 decibels compared to homes with double-glazed metal-framed windows, which is roughly equivalent to reducing sound infiltration by half perceived noise level.

“When someone walks into the house and you close the door, it’s like getting into a Mercedes or a BMW,” said a Seattle builder. “It’s so solid and quiet. We are building homes next to Boeing Field airport in Seattle. The planes fly right above our heads so close you can see them clearly from the houses, and it’s so quiet inside you can’t hear them.

Demonstration projects lead the way

When there are new approaches to building homes, Cort said, builders need to be sure that the materials will be available when needed, that they will stand up to use, and that they will make the improvements. promised.

To help meet these expectations, PNNL has partnered with DOE, Lawrence Berkley National Laboratory and the Northwest Energy Efficiency Alliance to launch the Partnership for Advanced Window Solutions. With support from the DOE, this public-private partnership works with builders, utilities and manufacturers to drive demand and increase production for thin-pane triple-glazed window designs and other high-performance window solutions.

The PNNL team recently compared the energy efficiency performance of these windows in their Lab Homes, a pair of identical prefabricated houses used to study energy efficiency. During the 2019 winter heating season and the 2020 summer cooling season, the researchers recorded energy consumption and temperatures in all homes. Over the two 10-week evaluation periods, the windows saved an average of 12% on heating and 28% on cooling for 1,500 square foot structures. Additionally, the house with the triple-glazed windows reduced outside noise and maintained much more comfortable and even temperatures throughout the house during the summer and winter test periods.

The research team is currently field testing the windows in 10 locations nationwide, from manufactured homes in Pasco, Washington, to a net zero apartment complex in Rotterdam, NY. In these field demonstration projects, the additional cost over standard ENERGY STAR® windows was $6 per square foot or less, Cort said. Over the past year, several versions of thin-glass triple-glazed units have been developed, certified by the National Fenestration Rating Council, and have become available to builders.

“At this point, it’s about raising awareness for manufacturers, builders, utility programs and consumers,” Cort said. “It’s time to look at windows, not just through them.”