Can multi-function heat pumps with low-global warming potential refrigerant effectively decarbonize heating for low-income homes?

Electrification of homes is a critical part of reducing greenhouse gas (GHG) emissions. However, space constraints, installation complexity, and the potential impact on energy costs slows the pace of retrofit electrification efforts. Also, the addition of electrical circuits for heat pumps and the increased household electrical demand often necessitates electrical panel upgrades, which increases costs and slows installation. Multi-Function Heat Pumps (MFHPs) use a single compressor to provide heating, cooling, and domestic hot water (DHW) –which represent the most intensive thermal loads of a home –and can ease the process of retrofit electrification. MFHPs are potentially more economical than typical split HVAC heat pumps (HPs) and heat pump water heaters(HPWHs), as they consolidate systems, require fewer circuits, streamline installation, and enable efficiency opportunities, such as recovering waste heat from cooling to heat DHW. The current study evaluates one MFHP product, a split HP with indirect water heater and ducted air handler, using a low-global warming potential (GWP) refrigerant (R454B). This MFHP has a unique defrost operation that pulls heat from the DHW tank instead of the indoor air, which avoids cold drafts on occupants. This allows for better thermal comfort without requiring an electrical resistance backup heater and costly panel upgrades. The MFHP was installed in two low-income apartments, evaluated for ease of installation, and monitored through the heating season to assess reliability, energy efficiency, and performance.