In December, John and Rachel Rea’s home was hit by a bomb cyclone, temperatures dropping below freezing and closer to Colorado as the couple’s basement no longer has a gas stove.
Three months ago they replaced the oven with a heat pump, and now the new contraption is going to be seriously tested. Even on a cold day, heat pumps capture residual heat in the air, but when the temperature drops to minus 20 degrees, is there any heat left to capture?
The Rheas “pre-heated” their Boulder townhouse, turned on the thermostat before the storm, and benefited from neighboring houses on both sides and new insulation in the basement.
However, they are not sure how well a Mitsubishi heat pump will perform. The device was designed for normal operation up to 13 degrees below zero. On the night of December 22, temperatures in Boulder dropped below 18 degrees.
During cold snaps, the heat pump runs almost around the clock, Rea says, but the house is still comfortable. “If you stay in the house, you won’t notice anything.”
Electric-powered heat pumps are finding their way into Colorado thanks to improved technology that makes units more efficient in cold weather, as well as financial incentives from utilities and local, state, and federal governments.
“Heat pumps are ready to go,” said Neil Colway, director of industrial programs for the Southwest Energy Efficiency Program. “A lot is already in place.”
The number of heat pump rebates provided by Xcel Energy, the state’s largest electricity supplier, has more than tripled between 2021 and 2022 to 1,220. The number of rebates for the Tri-State Generation and Transmission Association, the second largest electricity supplier, has increased by 40 percent to 942.
There are two types of heat pump systems: those that extract heat from the air, and geothermal systems that rely on digging into the ground to provide constant heat.
An air source system including a compressor, air duct, or a separate wall and ceiling unit connected to the compressor can cost anywhere from $15,000 to $30,000. Geothermal heat pumps, which are based on wells drilled 300 feet below the house, are more efficient but twice as expensive.
Although not as visible as solar panels or electric vehicles, heat pumps are a key element in the transition to cleaner, more energy efficient homes—heating and cooling account for less than half of a home’s total energy use, according to the US Environmental Protection Agency. The Bureau.
“The fact that we burn natural gas in our homes is very inefficient,” says Lacey Tan, head of the carbon-free building program at energy consultancy RMI. “We need to think about how to make our homes more energy efficient.”
Heat pumps are the answer. “A heat pump, like a cauliflower, comes of age,” Tan said. like cauliflower? “Yes, who has ever eaten cauliflower? Now it’s wrapped in rice and a pizza crust. It’s because of a major technological innovation.”
Heat pumps, invented by Czech inventor Peter von Rittinger in 1857, were originally used to dry salt from salt marshes. They have been widely used in European homes since the 1950s.
This technology, which simultaneously heats and cools homes, is gaining momentum in the United States, with 50,000 to 60,000 units installed annually by 2008, mostly in the South, where hot summers and mild winters are common.
In cold climates, the efficiency of heat pumps dropped sharply as temperatures rose—until recently.
“Cold climate readiness for heat pumps has always been a challenge,” said Dave Lees, director of technology and market solutions for the Northeast Energy Partnership (NEEP), a non-profit organization promoting efficient and clean energy strategy.
The problem lies in the air itself, since the heat pump does not burn anything to produce heat, but takes heat from the air. The trick is to grab it on the coldest days.
An “air source heat pump” works like this: a low-boiling refrigerant, about minus 55 degrees, flows through pipes open to outside air, and even a small amount of heat evaporates the refrigerant.
The heat-carrying vaporized refrigerant passes through the compressor – well, compresses it, raises the temperature to about 105 degrees and enters the house.
The refrigerant, which is again a liquid, is expelled to the outside to capture more heat. In summer, this process can be reversed by transferring heat from the inside to the outside, cooling the house.
Most homes already have some sort of heat pump. “Your air conditioner is a heat pump and your refrigerator is a heat pump,” says Josh Lake, co-founder of Elephant Energy, a Boulder-based company that renovates homes using heat pumps and other electrical technologies. “They both use electricity to move heat.”
Because a heat pump simply moves heat rather than generating it, it can produce two to four times more heat than it consumes, according to the US Department of Energy.
The problem with colder regions is that the lower the temperature, the less heat in the air, so the heat pump has to work harder and harder and become less efficient.
Numerous technical changes were made in Colorado and Maine to make heat pumps viable. These include more advanced heat exchangers, more advanced fans, variable speed compressors and sophisticated electronic control systems.
“In a cold winter, there is still heat to move around, but it’s not very warm, so the compressor has to do more work,” said David Petray, whose company NTS Energy develops heat pump systems for homes and businesses.
At 50 degrees, a heat pump can deliver four units of heat per kilowatt-hour of electricity used, but at zero degrees, efficiency drops to two units of heat per kilowatt-hour of electricity, Petroi says.
Variable speed compressors can be more efficient over a certain range of temperatures and can actually improve performance at low temperatures.
One of the main differences between installing a heat pump and a stove is that a heat pump system requires a little more design when upgrading an existing home or building a new home. Some homeowners also need backup heating, such as electric space heaters, small propane burners, or pellet stoves.
When installing a stove, heating and air conditioning contractors rely on Manual J calculations, a formula that includes variables such as house size, insulation, and occupancy.
“There is a lot of thought involved when designing a heat pump system, especially in an all-electric home, which may also require a larger electrical panel to be installed,” said Petroj.
Instead of just installing one large unit in a basement, for example, the evaporating refrigerant can be piped from the compressor to separate wall and ceiling units called mini-splits, allowing homeowners to control the temperature floor by floor, room by room.
While the heat pump market is in its infancy in Colorado, it has been growing in the Northeast for a decade, growing at an average rate of almost 30 percent per year since 2017 and with more than 250,000 units installed by 2021.
NEEP works to develop programs that encourage public policy—its territory stretches from New Jersey to Maine—through education and participation in the promotion of heat pumps, the development of competent heating and air conditioning or HVAC networks, contractors, and the creation of a climate heat pump cold list. .
Some of the coldest areas in the region were early adopters. “When we saw the initial surge in heat pumps, we saw a lot of fuel delivered to places like Maine and Vermont,” Lees said. “This greatly improves the economics of heating with a heat pump.”
About 61 percent of Maine’s 600,000 homes are heated by oil, and another 11 percent by propane. 9% of houses are heated with wood, the rest use electricity and gas.
According to the Maine Efficiency Trust, which manages energy efficiency programs in Maine including heat pump rebates, the average annual cost of heating a home in Maine with a heat pump is $2,300, almost half the cost of oil or propane.
“When we launched our rebate program in 2012, there were two groups in Maine, one group didn’t know what a heat pump was, and the other group knew it didn’t work in cold weather,” said Andy Meyer, Senior Efficiency Officer. Maine Say. Residential project manager.
Since then, the program has provided rebates ranging from $1,200 to $2,400 for about 100,000 heat pumps, and demand has not abated. “We provide discounts on heat pumps every six minutes,” Meyer said. “This is a fundamental revolution.”
Some families in Maine buy one or two smaller wall or window heat pumps that cost several thousand dollars and look like air conditioners.
“They will heat one room, maybe the next room, where the third room is cold,” Meyer said. “It’s very similar to heating with wood.”
Like Maine, much of rural Colorado relies on expensive propane to heat homes, said Peter Rusin, Tri-State membership manager.
Electricity wholesaler Tri-State and its 18 Colorado rural electricity cooperatives are promoting heat pumps, with the association offering rebates of up to $2,400.
Some mountain towns sell propane for $4 a gallon, Rusin said, nearly double the state average. “Switching to a heat pump has really reduced the energy load,” he said. “No other technology, no other opportunity to reduce rural energy poverty like this one.”
Meyer says a skilled fitter team is needed to meet demand, and when Efficiency Maine started its program, it had to find 20 contractors across the state. To date, 800 people have passed the trust test.
“Contractors are really important,” Rusin said, “because they are the ones who sell the system and actually educate the public.”
When electrical engineer Sebastian Canaday contacted HVAC contractors to install a heat pump at his home in Boulder County, some of them tried to talk him out of it, and whoever canceled the spec returned to bid on a gas stove.
A neighbor recommended Save Home Heat, which installed a dual-fuel system with a heat pump and back-up gas oven for about $30,000. The compressor, heat pump and oven are integrated and can be controlled from a Canaday mobile phone. “They talk to each other,” he said.
The Canaday system connects to the existing piping of the old gas furnace, and a compressor directs the vaporized refrigerant to coils on top of the new furnace. While Rea mini-split heat pumps are designed to operate at 75% capacity below freezing13, ducted heat pumps (such as those from Canaday) are designed to operate below freezing3.
Thus, the Canaday system is set to transfer to the furnace at 6 degrees. According to him, in December the firebox heated about 30 percent.