PNNL research finds highly insulating windows come at high cost

Energy efficient triple-pane windows may keep your home more comfortable, but you'll have to be patient to recoup their cost in energy savings.

That's the conclusion of the first full study completed at Pacific Northwest National Laboratory's new twin houses on its Richland campus.

The identical manufactured houses are used to gather data on energy efficiency, with one outfitted like an average Tri-City house and its twin used to test energy efficient products and strategies. In this research, the double-pane, clear-glass, aluminum-framed windows commonly seen in Tri-City houses were compared to highly insulating triple-pane windows in the second house.

The new windows can cut the energy required in a Tri-City home by 12.2 percent, the study found.

That's substantial, said PNNL researcher Graham Parker, a founder of the lab homes project. "But the windows are expensive," he said.

It would take 23 to 55 years to save enough on a utility bill to cover the higher cost of the windows, based on national electricity costs. It could take even longer in the Tri-Cities, given its lower-cost electricity.

The high end of the time range includes the labor to retrofit older houses with energy efficient windows, but the cost could be paid off sooner in new homes since labor is needed whether traditional or triple-pane windows are installed.

However, research engineer Sarah Widder does not believe the decades-long payback time is the final word on highly insulating windows.

The triple-pane windows, which have an inert gas in the spaces between the frames to reduce heat transmission, are still a niche product, Widder said. As the market for them grows, the price should come down.

"I hope we can see the payback window closer to 10 years, which would be more palatable to utilities and homeowners," she said.

There are other benefits provided by the triple-pane windows.

They keep out noise and a house more comfortable, helping prevent hot and cold spots near windows.

In the PNNL house with the old-style windows, the temperature reached an uncomfortably high 84 degrees in the kitchen during some sunny winter days while the home's heating system sat idle. In the house with the better windows, the temperature stayed at a more comfortable 75 degrees.

In summer the problem was greater, with the cooling system in the traditionally outfitted house struggling to keep up on hot, sunny days.

It's possible that new houses built with triple-pane windows could require smaller heating and cooling systems, which would make the windows more economically attractive, Widder said.

The windows showed a greater energy efficiency benefit during the summer than the winter, making it possible that they could prove more attractive to homeowners in the southern United States. While the overall energy savings year round came to 12.2 percent, that increased to 18.4 percent during summer in the Tri-Cities.

Triple-pane windows also are newly available that are better for cold-weather locations than the windows used in the PNNL study, Widder said. They block the transmission of cold air but allow solar heat.

Research at the twin energy efficiency houses has moved on to test another, and possibly more cost effective, window system to reduce energy use -- storm windows with a coating that improves efficiency.

"These are not your parents' storm windows," Widder said.

They can be installed by homeowners, can be left on all year and in some cases improve the appearance of a house, she said. The cost is at most a quarter of installing the highly insulating triple-pane windows because homeowners can put them up themselves, she said.

-- Annette Cary: 582-1533; acary@tricityherald.com; Twitter: @HanfordNews