Multipurpose Hydronic CO2 Heat Pump for Commercial Buildings

Space cooling, space heating, and domestic hot water (DHW) are major energy end-uses in California. Space heating and domestic hot water needs account for approximately 70 percent of natural gas use across all commercial sector buildings and over 90 percent of natural gas use in multifamily buildings, making these end-uses two of the state’s largest building decarbonization targets. Innovative technologies that are both energy-efficient and cost-effective are necessary to achieve these decarbonization targets and still satisfy demands for all three end-uses.  This study evaluated the design and feasibility of a retrofit multipurpose hydronic CO2 heat pump at one office building and one low-income multifamily building. The technology electrifies and decarbonizes heating, cooling, and DHW systems in a packaged, high- efficiency heat pump system that uses CO2, a refrigerant with low global warming potential (GWP).  The project team assessed the technology at each site through site observations, design and sizing of the new system, cost evaluation methodology, building energy modeling approaches, cost proposals, and modeling results.  Both sites showed potential energy and cost savings compared to gas-fired baselines by reducing natural gas use and improving efficiency, although fuel switching increased peak electricity demand. Site 1 achieved estimated GHG emission reductions of 22 metric tons of CO2e, improved their baseline COP from 1.7 to a peak COP of 3.4, and demonstrated a Total System Benefit (TSB) of about $1,428. Site 2 had larger baseline heating loads and observed estimated GHG emissions reductions of 79 metric tons of CO2e, improved their baseline COP from 1.2 to a peak COP of 2.8, and demonstrated a TSB of about $2,259. These findings highlight the technology’s potential to electrify and decarbonize heating, cooling, and DHW systems in commercial and multifamily buildings. Further research, including pilot demonstrations, is recommended to validate real-world performance, quantify energy impacts, and address market barriers.