engleski

Thermal Performance of a Direct Expansion Solar Assisted Heat Pump

Solar assisted heat pump systems are nowadays rarely presented on the growing solar market compared to the conventional solar hot water systems. Due to the high evaporation temperatures that are achieved when using solar irradiation as a dominant heat source for evaporation (instead of surrounding air, sea water, ground heat, etc.), solar heat pumps can yield remarkably higher (2 to 3 times) values of COP. In order to prevent a great deterioration of the COP due to inconsistent weather conditions and irradiation, every such system should be carefully optimized in terms of solar collector area, capacity of compressor, evaporating and condensing temperatures. Analytical and experimental studies were carried out on a solar assisted heat pump consisting of two flat-plate solar collectors acting as an evaporator for the refrigerant R-134a, a variable-frequency reciprocating type compressor, a compact plate heat exchanger (condenser) and an electronic expansion valve. The average values of COP ranged from 4 to 9 and solar collector efficiencies from 60 % to 85 % were recorded during the period characterized by relatively high mean solar irradiation. The results of the system thermal performance simulation were obtained for metrological and heat load conditions during the whole year. The results of simulation were compared to the measured values for the system COP and the power used by the compressor. The developed simulation model enables both, the optimization of the system components and of operating parameters.

solar assisted heat pump; direct expansion; COP

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