Numerical study on the characteristics of frost formation on air source heat pump using extended effectiveness-NTU method.

Numerical study on air source heat pump under frost condition is carried out to investigate the characteristics and effect of frost formation on heat pump system. In order for the study, a numerical model for air-source heat pump under frost condition is developed. Extended form of effectiveness-NTU (ε-NTU) method is proposed to calculate the combined heat and mass transfer under frost condition. The method is compared with existing normal ε-NTU method in this paper. The simulation model includes compressor, evaporator, condenser, expansion valve, and accumulator. As a result of numerical study, tendencies and effect of frost formation on heat pump system are suggested according to several system conditions including air temperature, air humidity and compressor speed. Air temperature is found to be a key parameter for frost formation tendencies, because it affects both the amount of frost accumulation and frost density. Humidity ratio and compressor speed are also found to be critical parameters for frost formation.