Heat pump using solar and outdoor air heat sources

摘要

A heat pump system uses a non-reversing refrigeration circuit having a water-cooled condenser and a counterflow chiller fed by a thermostatic expansion valve to permit operation at close to zero superheat. To protect the compressor in the refrigeration circuit from possible flood-back at this low superheat, a combination suction-liquid heat exchanger-suction accumulator is employed. A hold-back valve serves to maintain constant compressor suction pressure regardless of evaporator pressure fluctuations caused by changing chiller fluid temperatures. The system is designed to operate in four distinct modes: (1) water source heat pump heating; (2) direct solar heating; (3) air source heat pump heating; and (4) heat pump cooling. To switch the refrigeration circuit to heat pump mode from the cooling mode or vice versa, four three-way valves and three fluid pumps are selectively operated. The fluid circuit of the system consists of two separate coils in an air-handling unit. One coil is connected to the solar collector circuit and may be used for either heating or cooling. A second coil is connected to the condenser circuit and works during the heat pump cycle.