Lowest work temperature of air source heat pump systems

There is a suitable lowest work temperature for air source heat pumps in winter. According to the thermodynamic analysis on the compressor of the heat pump system, obtains the suitable lowest work temperature for  the compressor. By use of the variation law of COP with the evaporating temperature and the Bin parameters in Beijing region, develops a mathematic model of the lowest work temperature considering economical efficiency as objective function, and discusses the solution for this model.