Energy transfer procession in an air source heat pump unit during defrosting

Mengjie Song, Xiangguo Xu, Ning Mao, Shiming Deng, Yingjie Xu

Research output: Journal article publicationJournal articleAcademic researchpeer-review

61 Citations (Scopus)


To solve their undesired frosting problem, reverse cycle defrosting is always employed. As a transient and nonlinear heat and mass transfer procession, defrosting performance directly affects the occupants’ thermal comfort. During defrosting, the metal energy storage values of indoor and outdoor coils are varied as their temperature fluctuations. It is therefore necessary to investigate the energy transfer procession in an air source heat pump unit and the effect of metal energy storage during defrosting. However, scarce of attentions were paid to this fundamental problem. In this study, two experimental cases with two-working-circuit and three-working-circuit outdoor coils were conducted basing on frost evenly accumulated on their surfaces. After four types of energy supply and five types of energy consumption during defrosting were calculated, a qualitative and quantitative evaluation on the metal energy storage effect was then given. As concluded, after the outdoor coil enlarged 50%, the metal energy storage effect can be changed from positive (0.33%) to negative (−2.18%). The percentages of energy consumed on melting frost and vaporizing retained water were both increased. Defrosting efficiency was improved about 6.08%, from 42.26% to 48.34%. Contributions of this study can effectively guide the design optimization of indoor and outdoor coils and promote the energy saving for air source heat pump units.
Original languageEnglish
Pages (from-to)679-689
Number of pages11
JournalApplied Energy
Publication statusPublished - 1 Jan 2017


  • Air source heat pump
  • Defrosting efficiency
  • Frosting evenness value
  • Metal energy storage
  • Multi-circuit outdoor coil
  • Reverse cycle defrosting

ASJC Scopus subject areas

  • Building and Construction
  • Energy(all)
  • Mechanical Engineering
  • Management, Monitoring, Policy and Law


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