Study And Development Of A Novel Temperature-Humidity-Time Defrosting Control Method Based On A Frosting Map

Complying with the needs of energy saving, environmental protection and development, the technology of air source heat pump(ASHP) is widely used in China. However, frost formed on the heat exchangers decreases the heating capacity in winter, for which appropriate defrost control must be included. Currently defrosting control methods can not make the accurate decision. Such as the most widely used temperature-time(TT) defrosting control method still can not make the accurate decision, although it is simple and cheap. Therefore, to improve the defrosting accuracy and the energy efficiency of the ASHP under frosting and defrosting conditions, a novel Temperature-Humidity-Time(THT) defrosting control method, based on a frosting map for the ASHP unit, is proposed in this paper.Lab and field tests were conducted firstly. Through a parametric analysis, and a numerical frosting model, a frosting map was obtained. Based on field tests the indicative defrosting intervals for ASHPs operated at different zones. Based on the frosting map, a novel THT defrosting control method was proposed. To verify the feasibility and applicability of the novel THT defrosting control method and the advantages compared to TT defrosting control method, eight cases were chosen. Cases 1 to 4 were chosen to reveal the THT performance under different frosting conditions. Cases 5a, 5b and Cases 6a, 6b were two groups of cases to compare the advantages of the THT method against the conventional TT method.Test results show that no matter what kind of frosting conditions, defrosting was always initiated in an accurate decision under different frosting conditions by the novel THT defrosting control method. In Cases 5a and 5b, it was found that the TT method initiated the defrosting operation 31 times within 24 hours. However, none of the defrosting operations was conducted for the THT method. In Cases 6a and 6b, for the TT method and THT method, the defrosting accuracy was 37% and 100%, respectively. Compared with TT method, THT method made the average COP increased by about 5%. These results indicated that the novel THT method is suitable for the defrosting control of the ASHP, and has a more competitive performance than the conventional TT method.