Numerical Analysis of the Use of R-407C in Direct Expansion Solar Assisted Heat Pump

Abstract

The paper illustrates preliminary results of a numerical study carried out to investigate energy features of a direct expansion solar assisted heat pump that uses R-407C as working fluid and that provides space heating. The analysis is carried out through a steady state mathematical model of the heat pump whose evaporator consists of unglazed flat plate solar collectors. Several simulations are carried out in order to analyze the effect of ambient temperature, solar radiation and solar field surface on heat pump COP and heating capacity, on compressor rotational frequency and on the use of the solar field surface and collector efficiency. The results allow to state that the heat pump COP is strongly influenced by ambient temperature and solar radiation, whereas it is nearly independent on solar field surface. The efficiency of the solar collector is generally found to be high due to the low evaporation temperature that leads to low collector to ambient heat losses. Finally, the use of a modular solar field and of a variable speed compressor is essential for the heat pump to properly match the building heating demand.