The Biden administration and 25 state governors who make up the U.S. Climate Alliance last week (Sept. 21) announced a goal to increase the number of heat pumps in American homes by 2030 from 4.7 million to 20 million. The nearly five-fold increase would be driven by a 30% federal tax credit, up to $2,000, for buying and installing a new heat pump under the terms of the administration’s climate law, the Inflation Reduction Act.
Some states and utilities offer subsidies on top of the federal tax credits.
Electric-powered heat pumps, which provide both heating and air conditioning, would replace oil and gas-fired heating systems common in most American homes. The fossil-fueled heating systems make up about 30% of global greenhouse gas emissions.
CBS News quoted Washington Democratic Gov. Jay Inslee calling heat pumps “almost a miraculous solution” to three common energy tasks, “heating in the winter, cooling in the summer, and a reduction of carbon pollution.” Unlike oil and gas, heat pumps don’t create heat, they move it. In the summer, they remove heat from a dwelling, and shift it outside. In winter, they remove heat from outside and move it in. Brown University ecology professor Stephen Porder said, “A furnace makes heat by burning something, (but) moving heat is more efficient than making it.”
Yet heat pumps, which have been around for decades, have garnered a reputation of not being very efficient in cold winters, and many heat pumps have a cold-weather phase, where they supplement the outdoor heat with electric resistance heating coils. Heat pumps are also not entirely innocent of contributing to global warming, as the source of at least some of the electricity they use to move heat around is likely to come from fossil fuels, notably gas and coal.
But the rap against heat pumps as hindered by cold may be overstated, according to a recent commentary in the scholarly journal Joule. The article by three associates of the Regulatory Access Project (RAP) and an Ulster University professor note, “A question frequently raised is how well these devices perform when temperatures drop below freezing, as some commentators and the media have repeatedly suggested that heat pumps cannot deliver useful efficiencies at lower temperatures.”
The researchers tested that allegation against real-world data for air-source heat pumps. They find “that well below 0°C, heat pump efficiency is still significantly higher than fossil fuel and electric resistive heating systems at an appliance level. The standard heat pumps investigated in this commentary demonstrate suitable coefficients of performance for providing efficient heating during cold winters where temperatures rarely fall below −10°C, i.e., most of Europe.”
For temperatures considerablhy below freezing, “where the lowest temperatures approach −30°C, performance data have shown that heat pumps can provide heat at efficiencies up to double that of resistive heating; however, more analysis is required. Even though heat pump efficiency declines during the extreme cold and back-up heating may be required, air-source heat pumps can still provide significant energy system efficiency benefits on an instantaneous and annual basis compared with alternatives.”
The study found that “backup heating was typically only engaged when the outside temperature dropped past −10C (14F) or lower. Above −10C (14F), heat pumps were able to provide the required heat at relatively high efficiency.”
According to the report, some of Europe’s coldest countries have very high heat pump penetrations. “As of 2021, Norway had just over 60 heat pumps installed per 100 households, followed by Sweden and Finland (around 45 each) and Estonia (35), respectively. These countries also experienced the highest per capita sales in Europe during 2022.”
The study notes, “Some heat pumps are specifically designed for extreme cold. Though installing cold-climate heat pumps may de-risk performance in the coldest weather, there are potential trade-offs. For one, performance may suffer during milder temperatures. This is because the cold-climate systems are designed more specifically for frigid temperatures and higher heating demands. Physical components such as the expansion valve and compressor may struggle to operate at lower outputs.”
The Joule study concludes: “Our view is that the widespread rollout of air-source heat pumps around the world as part of decarbonization efforts can be successful with existing technology in most areas that have space heating demand. Ground-source heat pumps and hybrid air-source systems may have significant value in the coldest climates.”
According to the This Old House website, air source “heat pumps cost between $3,500 to $7,500 on average.” That includes the unit and professional installation. An even more efficient option – ground source heat pumps (aka “geothermal heat pumps”), which can be buried at various depths and have access to more constant temperatures — can cost considerably more. The cost largely depends on the depth of the field where the heat exchanger pipes are buried.
–Kennedy Maize
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