LOC-GFO-19-301-1 Advanced Air-to-Water Heat Pumps Space Conditioning Systems (ET)

This project will develop high efficiency air-to-water heat pump technologies, and further develop low-cost, polymer water-to-air heat exchangers that have improved performance (effectiveness/pressure drop) at lower cost.  System will have a primary loop consisting of flammable low GWP refrigerants and secondary loop using water. Utilize primary secondary loops to isolate flammable refrigerants. Additional thermal storage capabilities to manage load shift as well as domestic hot water.

Electrification of space heating is one of the first steps toward a broader goal of decarbonizing U.S. buildings. 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 utilize a refrigerant with lower global warming potential (GWP) 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 low-GWP heat pumps. 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 (ATW) 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 ten homes in California. Results showed an increase in utility costs for many sites, though greenhouse gas emissions were reduced by 44-90% 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 contractor handling of the new refrigerant and tenant experience with the new heat pump technology. Lab testing and modeling of the microchannel polymer heat exchanger, which was developed to improve the performance of ATW heat pumps, showed improvement over conventional coils. The research team validated heat exchanger performance in the laboratory, and modeling of injection molded versions showed 15-20% improved effectiveness compared to the commercial coil. Laboratory testing showed a 5% improvement in coil effectiveness resulted in 5% improved efficiency for the ATW heat pump system.