What is the direct expansion solar heat pump system compressor return temperature control device?

The invention relates to a return air temperature control device and a method for a compressor of a direct-expansion solar energy heat pump system, the invention comprises a direct-expansion solar energy heat pump unit: a Solar Energy Collector evaporator, a compressor, a condenser, a first electronic expansion valve, a first controller, a first temperature sensor and a first pressure transmitter; The Return Air Temperature Control Unit: the Second Electronic Expansion Valve, the second controller, the second temperature sensor and the second pressure transmitter; the return air temperature control method includes simple mode: the evaporation temperature of the control system Te ≤ TCEMAX, the return air temperature Tr ≤ Tcrmax; Protection Mode: The first electronic expansion valve controls the evaporation temperature te = TCEMAX, and the second electronic expansion valve controls the return air temperature Tr ≤ Tcrmax. By the method, the evaporating temperature and the returning air temperature of the control system can be controlled within the allowable range of the compressor when the solar radiation is large, so as to avoid the compressor being burnt because of the high evaporating temperature and the returning air temperature, ensure the normal operation of the compressor to extend the life of the system to ensure efficient operation throughout the year.