Heat pumps are increasingly recognized as a key solution for decarbonizing our buildings and infrastructure. These systems operate using electricity instead of fossil fuels, which are commonly used in traditional furnaces and boilers. This shift allows them to integrate seamlessly with renewable energy sources. Additionally, heat pumps offer the dual functionality of both heating and cooling. This versatility eliminates the need for separate heating and air conditioning systems, simplifying building climate control and potentially reducing energy consumption.
Unlike traditional heating systems that generate new heat, heat pumps efficiently transfer existing heat from one place to another. The three primary types are air source (ASHPs), which exchange heat with the outside air; ground source or geothermal (GSHPs), utilizing the earth’s constant underground temperature; and water source (WSHPs), drawing on heat from nearby water bodies. Ground and water source heat pumps often outperform air source pumps in efficiency due to the more stable temperatures of the ground and water, allowing for effective heat transfer even in cold conditions. Previously, ASHPs were considered less efficient in very cold climates, but recent advancements have begun to change this perception, demonstrating their potential effectiveness even in extreme cold.
A new European report called Coming In From the Cold: Heat Pump Efficiency at Low Temperatures explains just how well ASHPs perform even in cold conditions. Researchers published their findings from seven different field studies in various climates last September. What they found was that “The results from the field testing suggest that heat pumps are an efficient heating solution across mild cold climates.” It uses a heating system coefficient of performance (COP) as a measure of how efficient it is to heat a building. A COP of 1, for example, means that for every unit of energy that the system uses, it is able to create the same amount of heat energy.
The report did find that the efficiency of heat pumps decreased when temperatures dropped but that they were still more efficient than other heat sources. “Below 0°C, the COP maintains a level well above 2 in all cases,” the report said. Typical COP values for heat pumps are around 3 to 6, so this does represent a decrease, but even with this level of efficiency, “air-source heat pump would operate at more than twice the efficiency of combustion or resistive electric heating technology.”
When air temperatures fall below 0°C, the efficiency of heat pump systems in adequately heating a building starts to diminish. At these lower temperatures, the Coefficient of Performance (COP) of most heat pumps decreases to below 2. This decline in efficiency, coupled with the increased heating demand needed to maintain warmth in a building during colder conditions, indicates that additional heating sources may be necessary. The report notes that “some form of back-up heating may be required” in these scenarios.
The report offers some suggestions for improving the efficiency of ASHPs, including reducing the temperature at which heat is delivered into the building. A lot of older or less efficient heating systems use quite hot water, around 140-158°F, to heat up the space. If we can lower this temperature, the heat pump doesn’t have to work as hard to increase the temperature of the water to that high level, which makes it run more efficiently. In systems that use water to carry heat around the building (hydronic systems), you don’t even need to replace all the radiators to make a difference. By swapping out just a few for ones that work well at lower temperatures, you can significantly improve how efficiently the heat pump operates. This means you can get the same amount of warmth in your building while using less energy.
For building owners looking to upgrade their heating systems in regions prone to extreme cold, the researchers said it is advisable to consider retaining the existing furnace or boiler as a backup. This precaution ensures that there is a reliable alternative for heat during severe cold spells, especially when heat pumps may struggle to meet the heightened heating demands. This strategy can provide a more seamless and reliable approach to maintaining a comfortable indoor temperature during periods of extreme cold.
An effective alternative to ASHPs in very cold climates are GSHPs. These systems operate by using coils installed underground to absorb heat, a method that bypasses the fluctuating air temperatures that can affect ASHP efficiency. One barrier to GSHPs is the substantial upfront expenses associated with drilling and installing them. This is being overcome by collaborative efforts and initiatives led by governments and utility companies. For example, in New York City, authorities are repurposing the space previously occupied by gas pipelines—part of the now-prohibited traditional heating systems—to lay the groundwork for GSHPs, aligning with the city’s shift towards these more sustainable heating solutions.
Even though heat pump technology is quite efficient, it’s not being used as much as it could be in the commercial sector across the U.S. Specifically, in the Northeast, about 25% of commercial buildings are still using fuel oil to heat their spaces. When we look at the entire U.S., around 31% of commercial buildings are fully electric, but heat pumps are the main source of heating in only about a quarter of these electric buildings. This means heat pumps are found in just about 8% of all commercial buildings, highlighting how slowly this technology is being adopted.
To increase the use of heat pumps, it’s important to change the outdated belief that ASHPs don’t work well in cold weather. The truth is, with today’s technology, ASHPs can be effectively used in most climates and settings for reducing carbon emissions. In the very coldest areas, using ground-source heat pumps or a combination of air-source systems could provide significant advantages. Embracing heat pump technology, alongside advancements and improvements in efficiency even in the coldest climates, represents a significant step forward in our collective efforts to decarbonize buildings and infrastructure.