Chad D. Bowers

Development of High Efficiency Carbon Dioxide Commercial Heat Pump Water Heater

Although heat pump water heaters are widely accepted in both Japan and Europe, where energy costs are high and government incentives for their use exist, acceptance of such products in the United States has been limited. This trend is slowly changing with the introduction of heat pump water heaters into the residential market, but acceptance remains low in the commercial sector. The objective of the presented work is the development of a high-efficiency R744 heat pump water heater of approximately 35-kW (10-ton) heating capacity for commercial applications with effective utilization of the cooling capability for air conditioning and/or refrigeration. This unit will be targeted at commercial use where some cooling load is typically needed year round, such as restaurants, hotels, nursing homes, and hospitals. The improvement process concentrated on the heat exchangers of the system. Further optimization potential was identified by investigating the gas cooler as well as the expansion device of the heat pump water heater by using a two-phase ejector. In addition, a comparison to a commercially available baseline R134a unit of the same capacity and footprint was made where significant package size reduction potential of the R744 heat pump water heater was discovered as well as performance improvement, especially at high water temperature lifts.

Design and evaluation of interior permanent magnet compressor motors for commercial transcritical CO 2 (R-744) heat pump water heaters

This paper describes the design and experimental evaluation of two high efficiency interior permanent magnet (IPM) motors for use in a commercial transcritical CO2 (R-744) heat pump water heater (HPWH). Two IPM topologies, 36 slot 6 pole and 9 slot 6 pole, were selected, optimized, and prototyped using a common, flat bar interior permanent magnet rotor. The experimental analysis includes standard measurements of electrical machine quantities, and light load dynamometer tests. Initial measurements of the CO2 compressor and HPWH system performance with a stock line fed induction machine have been completed.

Design and Evaluation of Interior Permanent-Magnet Compressor Motors for Commercial Transcritical

This paper describes the design and experimental evaluation of two high-efficiency interior permanent-magnet (IPM) motors for use in a commercial transcritical CO2 (R-744) heat pump water heater (HPWH). Two IPM topologies, a 36-slot 6-pole topology and a 9-slot 6-pole topology, were selected, optimized, and prototyped using a common flat-bar IPM rotor. The experimental analysis includes standard measurements of electrical machine parameters, and dynamometer tests. The initial measurements of the CO2 compressor performance with a stock line-fed induction machine and the 36-slot 6-pole IPM configuration have been completed. This paper finds a small isentropic compressor efficiency improvement from using the 36-slot 6-pole IPM motor compared to the stock line-fed induction machine at rated operating conditions (essentially constant speed). This paper also expands the open literature on the impact of high-efficiency motor drives on CO2 compressor operation and CO2 HPWH systems.