California has set ambitious climate goals to achieve carbon neutrality by 2045 including an 85 percent reduction in greenhouse gas emissions. Electrification of space heating is one of the first steps toward a broader goal of decarbonizing buildings in the United States. Heat pump technologies provide greater heating efficiency than gas furnaces while also emitting less greenhouse gas. Beginning in 2025, residential unitary heat pump systems in California must use a refrigerant with lower global warming potential than what is commonly used today. This presents new challenges for manufacturers and installers as heat pump installations scale up to meet the new state requirement.
This report describes the results from a project aimed at developing and demonstrating affordable and efficient heat pumps using refrigerants with low global warming potential (<750). The project team developed a near-term solution to address the existing need for affordable and efficient heat pump options that meet the upcoming refrigerant regulations. The medium-term solution advances air-to-water heat pump technology that offers a solution if refrigerant regulations become more stringent, requiring the use of highly flammable or toxic refrigerants.
Demonstrations of a new heat pump technology developed by Rheem Manufacturing Company were performed in 10 homes in California in climate zones 2 and 12. Results showed an increase in utility costs for many sites, though greenhouse gas emissions were reduced by 44 to 90 percent for the heat pump systems relative to the natural gas heating systems replaced in the project. These results demonstrate significant progress toward decarbonization, while also documenting user experience during the retrofit process, including the contractor and tenant experience.
Lab testing and modeling of the microchannel polymer heat exchanger, which was developed to improve the performance of air-to-water heat pumps, showed improvement over conventional coils. The research team validated heat exchanger performance in the laboratory, and modeling of injection molded versions showed 15 to 20 percent improved effectiveness compared to the commercial coil. Laboratory testing showed a 5 percent improvement in coil effectiveness resulted in 5 percent improved efficiency for the air-to-water heat pump system. The heat exchanger also showed the potential to lower the cost by 8 to 20 percent compared to similar commercial coils.
Author(s)
Curtis Harrington, Vinod Narayanan, Jingjuan Dove Feng, Sarah Outcault, Erfan Rasouli, Antonea Frasier, Emily Fricke, Valentina Arevalo Arredondo, Sagal Alisalad
