Design and evaluation of interior permanent-magnet compressor motors for commercial transcritical CO2 (R-744) heat pump water heaters

Ian P. Brown, Matthew W. Critchley, Jiamin Yin, Stephen B. Memory, Gennadi Y. Sizov, Stefan Elbel, Chad D. Bowers, Michael Petersen, Predrag Stojan Hrnjak

Research output: Contribution to journalArticlepeer-review


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.

Original languageEnglish (US)
Article number6823666
Pages (from-to)576-586
Number of pages11
JournalIEEE Transactions on Industry Applications
Issue number1
StatePublished - Jan 1 2015
Externally publishedYes


  • Heat pump water heaters
  • Hermetic motors
  • Interior permanent-magnet machines
  • Interior permanentmagnet motors
  • Permanent-magnet machines
  • Permanent-magnet motors
  • R-744

ASJC Scopus subject areas

  • Control and Systems Engineering
  • Industrial and Manufacturing Engineering
  • Electrical and Electronic Engineering


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