A new performance index for constant speed air-source heat pumps based on the nominal output heating capacity and a related modeling study

Wei Wang, Yiming Cui, Yuying Sun, Shiming Deng, Xu Wu, Shimin Liang

Research output: Journal article publicationReview articleAcademic researchpeer-review

15 Citations (Scopus)


Air source heat pump (ASHP) units have been widely used for space heating in recent years. While a space heating ASHP unit is normally rated at its nominal operating condition, however, during its actual space heating operation, it rarely works at the nominal condition. The actual output heating capacity can remarkably deviate from that at the nominal condition, due to the influences of ambient air temperature and frosting-defrosting operation. Therefore, to enable a comprehensive and convenient evaluation of the operating performance of ASHP units with frosting-defrosting operation and to provide designers with appropriate design guidelines to size a space heating ASHP unit, a new performance index has been proposed. The new performance index, ɛNL, or the loss coefficient in the nominal output heating energy, was actually based on the nominal output heating capacity of ASHP units, which was readily available and stayed unchanged irrespective when and where ASHP units were operated. In this paper, the definition of ɛNL was firstly given, following a detailed explanation of the frosting-defrosting operation of an ASHP unit. Secondly, a GRNN model for predicting the ɛNL of a field ASHP unit was established following a correlation analysis using a total of 473 groups of field measured data from the field ASHP unit. Finally, a modeling study using the developed GRNN model was carried out, and the study results suggested that when an ASHP unit was operated at a fixed ambient condition, defrosting initiating time would affect the ɛNL, and there may exist an optimal defrosting initiating time at which ɛNL was at its minimum. The model results also demonstrated that an increase in ambient air relative humidity or a decrease in ambient air temperature would result in an increase in ɛNL, when an ASHP unit was operated with a fixed defrosting initiating time.

Original languageEnglish
Pages (from-to)205-215
Number of pages11
JournalEnergy and Buildings
Publication statusPublished - 1 Feb 2019


  • ASHP units
  • Frosting-defrosting operation
  • GRNN modeling
  • Loss coefficient in the nominal output heating energy
  • Operating performances

ASJC Scopus subject areas

  • Civil and Structural Engineering
  • Building and Construction
  • Mechanical Engineering
  • Electrical and Electronic Engineering

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