Twin PNNL houses prove efficiency of insulated windows

By Annette Cary, Tri-City HeraldAugust 20, 2012 

Pacific Northwest National Laboratory has collected its first energy efficiency research data from a pair of new houses sitting on its Richland campus.

One house is typical of a Tri-City home. Its energy use is compared to its twin, where the latest in energy efficiency features are evaluated.

First up was an evaluation of highly insulated windows this past winter, which found that during 70 days, the house with the extra-insulating windows used 11 percent less energy than the project's baseline home. It has the aluminum-frame windows typically found around the Tri-Cities.

The comparison also looked at comfort in the houses.

In the 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.

But the sunny days also affected the energy savings, said PNNL research engineer Sarah Widder.

The highly insulating windows did a good job of insulating the inside of the house from the outside cold, but they also blocked light that could have provided solar heat for the house on sunny days.

Now researchers are analyzing data collected from the two houses this summer to see how the windows compared in keeping the buildings cool.

Preliminary results indicate the energy savings will be greater than during the winter, Widder said.

The Department of Energy Office of Energy Efficiency and Renewable Energy wants to see if the energy used in a typical home could be cut 50 percent by making a range of improvements that include highly efficient windows, additional insulation, eliminating air leaks, solar or heat pump water heaters and highly efficient heating and cooling systems.

Residential buildings account for 22 percent of the nation's annual energy use, giving opportunities for substantial energy savings for the nation.

That 50 percent goal will be difficult to reach without highly efficient windows, Widder said.

"When you don't address windows, you really have holes in the building envelope," she said.

When homes were retrofitted to increase energy efficiency in the recent past, work usually started with attic insulation and weather stripping, and then energy efficient heating and cooling systems and appliances might be considered.

But the perception was that adding highly efficient windows would be too expensive and would not save enough energy, Widder said.

However, technical advances in the windows, plus utility incentives and the Department of Energy Windows Volume Purchase Program, which promotes volume purchases for builders, are making them more attractive, she said.

The retrofit of the windows and sliding glass doors in a home similar to the houses used for PNNL's research would cost an estimated $4,300 to $7,600, much of that for labor. The additional cost in a new home would be much less at about $830, according to PNNL.

Researchers will determine the return on investment for highly insulated windows, including how long it takes to recoup costs, after data is compiled from the summer cooling season.

Next up for the twin houses will be a study of the cost savings of installing "smart" appliances that can respond to a utility pricing signal.

The energy efficient house has a refrigerator, dishwasher, oven, clothes washer and dryer, hot water heater and thermostat capable of responding to information to curb activity when electricity is expensive and resume full operations when it is plentiful and cheap. An electrical vehicle charging station also is being added.

The study will see how well the system would work in practice, including possible issues of having multiple appliances turning off and on in response to the same pricing signals.

The two houses, each 1,500-square-foot manufactured homes, were in place for fall 2011. However, engineers needed to make sure they were identical, including comparing the amount of air leakage from each and sealing up the leakier one until both matched.

Although no one lives in the houses, they are programmed as if identical families live in each. Lights are programmed to turn on and off on a set schedule. Water in the sink runs on a schedule and a known quantity of water is evaporated. The ventilation system is programmed to simulate opening and closing the outside doors.

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

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