When the north wind blows into Dillingham, Alaska, in the middle of winter, the temperature can plunge well past 15 degrees below zero on the remote strip of the state’s southern coast. On such days, the oil heaters in many of the homes must run pretty much nonstop to keep people warm.
As you walk through the small fishing town perched on Bristol Bay’s world-class salmon fishery, you can smell the acrid-sweet scent of wood-burning stoves.
But one house stands out from the others. Located on the edge of town—where spruce forest fades into an endless expanse of frozen, snow-covered tundra—it has no chimney, no fuel tank, no combustion of any kind.
The air-source heat pump Tom Marsik installed in his house eight years ago was rare for Alaska. Air-source heat pumps take heat from the outside air, run it through a refrigeration cycle to step up the temperature—just like your refrigerator, but in reverse—and deliver it to a building.
Because they rely on “heat” from the outside air, they were not common in subarctic climates. Yet for five years, Tom’s heat pump kept his family warm even on the chilliest days.
Thanks to what researchers have learned from systems such as his, heat pumps are taking off in Alaska and other cold places as an alternative to traditional oil and natural gas heating systems.
“It’s exciting because they are operating at lower temperatures than they historically have, which means they have the potential to reduce the consumption of fossil fuels in cold climates,” Tom says. “Helping to push the boundaries of clean energy and develop a sustainable future was important to me, especially in my own house, where we were raising our daughter.”
Today, Tom lives in Fairbanks and is chief scientist at the National Renewable Energy Laboratory’s Cold Climate Housing Research Center.
Though he no longer lives in an air-source-heat-pump-heated home, Tom spends a lot of time thinking about it, calculating runtimes and defrost cycles, remembering how he ran downstairs when he heard a new noise from his own unit, and researching how to make heat pumps work better for more Alaskans, who face a severe climate, lack of infrastructure and energy bills five times higher than the average American.
Air-source heat pumps are part of a portfolio of solutions that can advance NREL’s mission to make energy more affordable, equitable and environmentally friendly. However, the role of heat pumps varies across the nation’s vast topography of climates, natural resources and housing types.
In Alaska, ductless heat pumps show the most promise, with an outdoor unit that absorbs heat from the air and an indoor unit on the opposite side of the wall that delivers heat to the room. Because there is no distribution system to spread heat throughout the home, ductless systems are well suited for small, energy-efficient homes often found in Alaska.
While heat pumps have improved during the past decade, they are still affected by low temperatures. The colder it gets, the harder it is to extract heat, making for a less efficient system.
But just how much does their efficiency drop? Tom’s team is studying a heat pump inside a 20-below-zero test chamber in its Fairbanks lab.
Understanding the operating limits of heat pumps will shed light on how they can be expanded nationally.
There is a much larger market for air-source heat pumps in the Lower 48, where cold-climate residents are also looking for affordable, cleaner ways to heat their homes. One benefit of heat pumps is providing both heating and cooling, with the simple switch of a valve.
NREL researcher Jon Winkler leads research into how to get heat pumps into more of the roughly 35 million homes with central, forced-air heating. The switch to heat pumps is easy because units tie into existing ducts.
“They’re using electric resistance heaters, which get the lowest possible heating efficiency,” Jon says. “Installing a heat pump in these homes makes a lot of sense financially.”
Jon is monitoring a dozen heat pumps in Eastern Washington and Montana. Similar to the Alaska study, he is looking at how efficiency drops in colder temperatures, and how to appropriately size a heat pump to provide the right amount of heat and air conditioning.
“For these homes, what is the optimal heat pump size from an energy-efficiency perspective, a cost perspective and from a comfort perspective?” Jon asks.
Furthermore, how can heat pumps be combined with other appliances to provide the most benefit?
“Do you need to provide 100% of the heat with that heat pump?” Jon asks. “Or is it more cost-effective to provide 90% of heating with the heat pump and use an electrical backup resistance heater for those few days of the year it gets really cold?”
That is what Tom did in his Dillingham house and what millions of other homeowners in cold climates could do, too.
Jon’s project will create performance maps that show how heat pumps work in different climates.
While growing market demand drives NREL’s research on heat pumps, it is not just about saving money for consumers, Jon says. A critical piece of moving toward a clean energy economy is to electrify heating—moving buildings to the grid for heating and air conditioning rather than relying on appliances, such as oil boilers or gas furnaces.
This allows green electrons—whether they come from wind, solar, geothermal or something else—to provide thermal comfort as well as power.
“If we want to be purely renewable, we’re going to have to electrify our home heating use,” Jon says, “and heat pumps are currently the best way to do that.”