Performance optimization of CO2 heat pump water heater

Kashif Nawaz, Bo Shen, Ahmed Elatar, Van Baxter, Omar Abdelaziz

Research output: Contribution to journalArticlepeer-review

75 Scopus citations

Abstract

A preliminary analysis was conducted to analyze the performance of a heat pump water heater (HPWH) that uses CO2 as the refrigerant. A model to predict the performance was developed and calibrated based on the experimental data for an existing HPWH using a CO2 refrigerant. The calibrated model was then used to run a parametric analysis in which factors such as water supply temperature, water circulation rate, tank stratification, and condenser configuration were considered. The performance of a commercial CO2 system was compared with that of a similar system using R-134a as the refrigerant. It was found that CO2 HPWH performance was comparable to that of an R-134a HPWH, more so for a separated gas cooler configuration. For comparable performance, the compressor size and the tube-in-tube heat exchanger (condenser/gas cooler) size were compared for CO2- and R-134a-based systems. The impact of the water circulation rate on the water temperature stratification in the tank, an essential requirement for higher performance for CO2 HPWH systems was also investigated.

Original languageEnglish
Pages (from-to)213-228
Number of pages16
JournalInternational Journal of Refrigeration
Volume85
DOIs
StatePublished - Jan 2018

Funding

The authors acknowledge the support provided by the DOE Building Technologies Office and Technology Manager Antonio Bouza. This work was sponsored by the US Department of Energy, Building Technology Office (DOE/BTO) of under Contract No. DE-AC05-00OR22725 with UT-Battelle, LLC.

Keywords

  • Alternative refrigerants
  • Carbon dioxide
  • Heat pump
  • Water heater

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