How to specify cold-weather heat pumps

Homeowners should always research HVAC contractors and select certified and trained professional with a proven track record in ductless installations.

As electric utilities across North America continue the act of decarbonization by adding renewable energy sources to their grids, heat pumps have gained popularity as an effective, low-carbon heating solution. These systems use electricity to harness energy from the surrounding air and pump that energy indoors in the form of heat — much like an air conditioner in reverse.

Air source heat pumps have historically been relegated to more moderate climates, such as the southeastern United States. One reason is that models from the 1980s struggled to operate efficiently (or operate at all) in sub-freezing temperatures.

A conventional air-source heat pump uses a single-speed compressor that will turn off depending on whether heating or cooling is needed. But the capacity and efficiency of these single-speed pumps begin to decline as temperatures fall below certain levels. In these situations, if a traditional heat pump is being used in cold climates, the heat pump can’t satisfy the heating needs of a home, which means supplemental sources of heat are required. This often increases energy costs for the consumer and makes those heat pumps unsuitable as climate change solutions. For utilities, single-speed compressor heat pumps are also an issue. A multitude of air source heat pumps operating during cold temperatures can lead to a spike in peak load demand. That is because traditional HP systems (on/off, single stage) have high start-up amps, creating excessive demand during peak hours.

Fortunately, heat pump technology has made great strides. Cold climates are seeing a resurgence of attention on heat pumps, due in part to technological advances that have finally allowed heat pumps to perform in cold temperatures.

In particular, new models of ductless heat pumps now have the ability to perform in cold climates in ways heat pumps never have before, surpassing expectations. These models provide capacity, energy efficiency, and other features such as built-in Wi-Fi and advanced diagnostics that make them an innovative solution for cold climates.

The technology

As we have stated, advanced air-source heat pump technology can now perform better in cold climates. The key feature allowing sub-freezing performance is an advance in variable speed inverter-driven compressor technology, which wasn’t available in mainstream offerings just 10 years ago.

Variable-speed heat pumps can now increase the speed of the compressor in order to elevate the pump’s heating capacity, even as outdoor temperatures fall. For example, they might be able to operate at more than 65% of their maximum capacity when the temperatures reach 10°F. Low-ambient heat pumps, which feature a more advanced variable speed technology, provide more than 75% of their maximum capacity at 10°F.

According to the Electric Power Research Institute (EPRI), an independent, nonprofit energy research and development organization, research shows that newer heat pump technologies can keep homes warm in extremely cold conditions — often without any supplemental heat. One field test conducted during the polar vortex in 2021 involved installing variable heat pumps at several sites in Nebraska during the February cold wave that featured record low temperatures. EPRI found that these heat pumps met an entire home’s heating needs without any supplemental heat, even at 0°F.

Leading products are now capable of so much more than ever before. They can perform well below -10°F and tend to operate at double the efficiency of resistance and gas systems at the same below-zero temperatures. Heat pumps tested in places like Minnesota and up to the Arctic Circle have successfully shown that they can function in some of the most extreme winters known in the Continental United States. New heat pump technologies also include seamless integration with backup electric resistance systems, which adds another layer of defense in these cold climates.

Specifying cold climate models

New cold climate models have the ability to provide year-round comfort with 100% rated heated capacity at 5°F and comfortably warm air down to -31°F. Many of these models provide compatibility between outdoor units and indoor units. They also include high-efficiency Adoption-Pulse Amplitude Modulation (A-PAM) DC inverter control technology, which automatically adjusts the voltage of the DC bus based on the compressor load, increasing the range of operating voltage.

Cold-climate heat pumps can also feature hydrophilic aluminum fins that ensure condensing water flows smoothly. This precoated product is installed to prevent the spraying of water from heat exchangers.

Another key feature for high-performance cold-climate heat pumps is built-in Wi-Fi. The Wi-Fi controls allow occupants to pre-heat or cool rooms from afar, making it easier for them to arrive to a comfortable space. In cold climates, this is especially appealing. In the past, saving energy has meant keeping everything cooled until you step foot into the room—but the wait for a room to heat up can be uncomfortable and distracting. Pre-heating allows for streamlining comfort when the outdoors are merciless.

Wi-Fi heat pumps are smart for all types of occupants. The World Health Organization (WHO) considers rooms colder than 60°F overnight harmful. To provide safe conditions and still save costs, Wi-Fi systems can be programmed to minimum temperatures at night by sensing and reacting to dropping temperatures.

Any situation or lifestyle in which occupants will be out of the house for long periods can benefit from Wi-Fi features, especially in cold climates. People who travel a lot or who maintain a holiday home can control and keep track of temperatures even while they are away. They can double-check the system and feel peace of mind about if the heat has been turned down or up. Those who want to dial in the best cost savings can do so with customized programming. It also allows for a quick pivot whenever the weather turns. In so many cold climates, spring and fall can include a mix of temperatures: one day is warm or hot, the next day temperatures drop, and it snows. Wi-Fi controls can make the quick switch even when occupants are away, and change programs to meet the climate’s erratic behavior.

Homeowners:

Homeowners should always do their due diligence in selecting a qualified HVAC contractor with a proven track record in ductless installations, who is certified and trained by the manufacturer of the product.

Besides selecting for the space they want to heat or cool, homeowners should understand the possibilities and limitations of a ductless heat pump. With a well-chosen HVAC contractor, homeowners can get the most out of a cold-climate ductless heat pump by articulating the needs of a space or multiple spaces. They can select a product with their ideal features in mind, understand correct programming of the unit to optimize its abilities more efficiently, and get diagnostic information so that the product is maintained to last — even in the frostiest of weather.

Contractors:

The contractor should clearly communicate to the homeowner how a ductless heat pump operates in contrast to a conventional gas, oil, or baseboard-type heating system. The heat output of these systems remains constant while a ductless heating output will be reduced as the outside air temperature drops. This is due to the fact that ductless heat pumps use the outside air as a heat source when they operate in heating, and as the outside temperature drops, there is less heat available in the air to heat the home.

In view of these operational factors, a proper heat load calculation must be performed by the installing contractor to make sure that the proper unit is selected and installed and that it will meet the heating demand. Once the heat load calculation is completed, the appropriate mini-split heating and cooling performance table should be consulted to verify that the selected equipment will meet the heating and cooling BTU capacity demands at the appropriate design conditions.

The contractor must install and commission ductless equipment according to the installation guidelines set forth in the specific product installation manual.

Distributors:

Distributors should fully support training initiatives that educate contractors on how to properly size, select, install and troubleshoot ductless equipment.