Performance improvement of a residential heat pump water heater by modifying stratification of water temperature

Ce Shi, Pega Hrnjak

Research output: Chapter in Book/Report/Conference proceedingConference contribution


This paper presents experimental operation of a heat pump water heater (HPWH) at various draw rates to investigate the effect of tank stratification on system performance. Measurements are made both on refrigerant and water sides. Exergy analysis and mixing coefficient were introduced to characterize tank stratification. Performance is evaluated based on COPsys and recovery efficiency as measures. Results show that with increase of draw rate, stratification worsens causing higher condensing temperature, which results to lower system performance. Three-Dimensional Computational Fluid Dynamics (CFD) method was introduced to describe and explore the thermal tank numerically. The results from experiments for effect of draw rate on stratification agrees with CFD results. Performance of HPWHs is strongly influenced by the thermal stratification in the water tank. Destratification and mixing is more pronounced as draw rate increases. Improvement options are discussed that can improve performance with asymptotic approach to a perfectly stratified tank.

Original languageEnglish (US)
Title of host publicationICR 2019 - 25th IIR International Congress of Refrigeration
EditorsVasile Minea
PublisherInternational Institute of Refrigeration
Number of pages8
ISBN (Electronic)9782362150357
StatePublished - 2019
Event25th IIR International Congress of Refrigeration, ICR 2019 - Montreal, Canada
Duration: Aug 24 2019Aug 30 2019

Publication series

NameRefrigeration Science and Technology
ISSN (Print)0151-1637


Conference25th IIR International Congress of Refrigeration, ICR 2019


  • CFD
  • COP
  • Entropy
  • Exergy
  • Heat Pump Water Heater
  • Mix
  • Stratification

ASJC Scopus subject areas

  • Control and Systems Engineering
  • Electrical and Electronic Engineering
  • Mechanical Engineering
  • Condensed Matter Physics


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