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Dynamic characteristics of an air-to-water heat pump under frosting/defrosting conditions.

Author(s) : HUANG D., YUAN X. L.

Summary

The dynamic characteristics of an air-to-water heat pump with the nominal heating capacity of 55 kW under the frosting/defrosting conditions were investigated experimentally. The thermostatic expansion valve (TEV) had the intermittent hunting during the first two-thirds of the frosting period. The main cause was the airflow maldistribution at the upstream of coils, which resulted in a little liquid refrigerant flowing out of the partial circuits with the less airflow rate. Hence, the overall outlet superheat of the coils was very small and less than the minimum steady superheat for the TEV, the intermittent hunting occurred. Moreover, the TEV had the unceasing hunting during the last one-third of the frosting period, due to the combination of the airflow maldistribution and the airflow drop caused by the frost blocking. Accordingly, the more liquid refrigerant flowed out of the coils and the overall outlet superheat of the coils was much less. Finally, a 'critical point' appeared during the defrosting period, after which the system parameters increased quickly, which is attributed to the change of the heat transfer mode outside the coil tubes.

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Pages: ICR07-B2-799

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Details

  • Original title: Dynamic characteristics of an air-to-water heat pump under frosting/defrosting conditions.
  • Record ID : 2008-0861
  • Languages: English
  • Source: ICR 2007. Refrigeration Creates the Future. Proceedings of the 22nd IIR International Congress of Refrigeration.
  • Publication date: 2007/08/21

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