Heat pumps for properties in cold climates will soon be able to perform better than before and still remain energy efficient.

On Oct. 23, 2024, the U.S. Department of Energy (DOE) announced the results of its Residential Cold Climate Heat Pump (CCHP) Challenge, which involved eight manufacturers: Bosch, Carrier, Daikin, Johnson Controls, Lennox, Midea, Rheem and Trane Technologies.

All eight manufacturers successfully completed prototype testing at Oak Ridge National Laboratory and other facilities in 2022 and 2023, with some units operating at temperatures as low as -15°F while still meeting efficiency requirements. The companies then moved products into field testing in 23 residential sites across 10 U.S. states and two Canadian provinces.

Manufacturers say that cold climate heat pumps developed as part of the challenge will enter commercial production as soon as this fall, according to the DOE’s announcement.

Heat pumps move heat from one place to another using a vapor compression cycle. In heating mode, the heat pump moves heat from the outdoors to the indoors. In cooling mode, the heat pump reverses the operation to move heat from indoors to outdoors.

Ram Narayanamurthy, deputy director of the DOE’s Building Technologies Office, detailed why heat pumps so far have had problems operating at peak performance in cold climates.

“Because heat pumps move heat from one place to another, and do not generate heat like a furnace does, they can operate at efficiencies three to four times compared to high-efficiency furnaces,” Narayanamurthy said. “However, conventional air-source heat pumps lose heating capacity at low outdoor air temperatures because less heat is available at the lower temperatures.”

To maintain comfort in this scenario, heat pumps often rely on backup heat, which may be electric resistance or fossil-fuel sources. Excessive use of backup heat is energy intensive, which has resulted in a slower uptake of heat pumps in colder climates in the past.

To solve this problem, the DOE launched the Cold Climate Heat Pump Challenges for certain residential and commercial products, with a primary goal of improving heat pump capacity and efficiency at low outdoor air temperatures and minimizing or eliminating the use of backup heat. The cold climate heat pumps developed through these challenges will also use refrigerants with low “global warming potential,” a metric used by the U.S. Environmental Protection Agency.

On the residential side, DOE led a coordinated effort to drive leading U.S. HVAC manufacturers to overcome this obstacle by developing advanced cold climate heat pumps that include new technologies such as inverter-driven variable-speed compressors, advanced vapor injection and improved controls, Narayanamurthy said.

“Better heating capacity retention at lower outdoor air temperatures will reduce the use of backup heat in cold climates, which could potentially lower the electrical power requirements, energy use and utility bills for occupants,” he said.

Another challenge for heat pumps in cold climates is components freezing over, compounded by continuous dripping from melting snow, said Adam Finney, director of global ducted residential systems at Carrier, Palm Beach Gardens, Fla.

“To solve, we incorporated a new feature, advanced defrost, that monitors the outdoor coil to detect the presence of frost before engaging,” Finney said. “It then adjusts the compressor speed to ensure the unit defrosts on time, and once the unit has sensed completion of the frost melt and drain, the defrost mode concludes.”

With continuous testing and enhanced controls, Carrier’s units operated at temperatures as low as -23°F in the manufacturer’s labs.

One of the key takeaways for Carrier during installation was that fan coils, a component of heat pumps in all-electric installations, need a 240V furnace versus the typical 115V furnace. Electric heaters require higher amp loads as determined by the building heating needs, and up to a 100A breaker is needed just for the fan coil’s electric heater.

“Installing fan coils in colder climates is not typical, but as electrification strategies continue to rise in popularity, we’re determining the best ways to fan coil run line sets and changing installations to a bottom return,” Finney said.

Building on the success of the residential challenge, DOE’s Better Buildings program is now working with nine heat pump manufacturers to advance rooftop units for commercial buildings through a new technology challenge as part of the Commercial Building Heat Pump Accelerator. The manufacturers will partner with DOE and national laboratories to create prototypes and test product performance and durability.

Both the Residential and Commercial CCHP Challenges also focus on smart controls and staging of backup heat to minimize peak power consumption, Narayanamurthy said. They require capabilities to meet “advanced demand-response events”—when utility companies need to balance demand with supply, such that the cold climate heat pumps can reduce their power draw by 15%–60% during such events with minimal effect on occupants.

“These advanced demand-response capabilities can help utilities manage peak demand more effectively and avoid expensive electricity generation and transmission investments as more cold climate heat pumps are installed,” he wrote. There are continuing challenges, however: installing heat pumps in certain retrofit scenarios in colder climates may require expensive electrical upgrades due to requirements for backup heat.

“While the Residential and Commercial CCHP Challenge attempt to reduce electrical panel upgrades and installation costs, we recognize that there is a need for additional research and coordination around codes and standards, interoperability, controls and HVAC contractor engagement,” Narayanamurthy said. “DOE will continue to work on these topics to support deployment.”

For the Residential CCHP Challenge, manufacturing partners completed the process from prototype development to market availability of units in just three years.

“The Commercial Building Heat Pump Technology Challenge launched this year is also attempting an ambitious timeline to bring units into the market as quickly as possible,” Narayanamurthy said. “DOE will continue to work with industry partners to introduce the next generation of heat pumps.”