Heat Pumps for Cold Climates
In 2022, California’s building code became the first in the nation to establish heat pumps as baseline technology for new homes, marking a huge step forward in transitioning the state’s building stock away from fossil fuels and towards reliance on clean energy. In addition to statewide code updates, California’s air quality agencies have approved or proposed amendments to existing regulations that will soon require zero-NOx appliances for some space and water heating applications across a variety of building types, although legal challenges are expected. The combination of these measures along with improved technology has led to an increase in heat pump adoption across the state.
Though widespread adoption has occurred in many regions, concerns remain about the viability of heat pumps in colder climates. Recent studies indicate that heat pump systems can work well in cold climates when properly sized and selected. Technological advances also continue, through efforts such as the US Department of Energy Cold Climate Heat Pump Technology Challenge described below.
Heat Pumps Overview
Air-source heat pumps (ASHPs) provide cooling and heating to a building and are powered solely by electricity. In the heating mode, instead of converting fuel to heat via combustion, a heat pump utilizes the refrigeration cycle to transfer heat from the air outside to the air inside the building. This makes ASHPs about two to three times more efficient than gas furnaces or electric resistance space heaters. Of course, the efficiency of any system depends on a variety of factors. Equipment sizing and installation, climate, a home’s insulation and weatherproofing, and ongoing maintenance will affect the day-to-day performance.
Considering Outside Air Temperature
In heating mode, heat pumps have a harder time extracting heat from cold outside air, which can lead to performance issues due to a loss in efficiency and rated heating capacity. To address this issue, the US Department of Energy (DOE) conducted the Residential Cold Climate Heat Pump Challenge to incentivize manufacturers to improve system performance at lower temperatures (below 32° F).
For outside air temperatures above 32° F, performance degradation is not very significant and standard ASHPs suffice. Between 32° F and 5° F, ASHPs designed to the cold climate portion of Energy Star’s heat pump specification maintain good efficiency and capacity. DOE’s Challenge sought to further improve heat pump performance at 5° F and even -15° F. The DOE published findings from its challenge in the 2024 ACEEE Summer Study Energy Efficiency in Buildings. In the field, the tested CCHPs proved reliable and were able to provide equal or better comfort to homes compared to the previous furnace systems. Initial evaluations of the performance and efficiency of the units indicate promising results with all units capable of providing heat with little assistance from auxiliary elements even during the coldest weather.
The DOE announced in October 2024 that all eight manufacturers in the Residential Cold Climate Heat Pump Challenge completed rigorous laboratory and product field testing to demonstrate energy efficiency and improved performance in cold weather.
Performance Requirements
All CCHP prototypes tested in the challenge were centrally ducted units with electric resistance auxiliary heat backup sources and demand response capabilities. Two ranges of heat pumps were tested: one with CCHPs optimized for operation at 5° F and another with CCHPs optimized for operation at -15° F. All systems were required to meet or exceed the following performance requirements:
