Computer-aided Study of the Heat Pump Loop Exergic Efficiency with Approximating the Thermodynamic Properties of R407C Refrigerant
The development of a heat pump mathematical model and computer program with fully automated calculations is necessary for determining the optimal parameters of heat pump units (HPU). Proper selection of HPU operating parameters reduces the capital and operating costs for the installation. Calculations cannot be fully automated unless a procedure for automatically determining the working fluid parameters at any point of the heat pump (HP) working process is elaborated. A procedure for obtaining polynomial expressions approximating the thermodynamic properties of R407C refrigerant is described, and the methods for automatically determining, by means of software, the working fluid properties through a search from tables and by using polynomial expressions are compared with each other. A fully automated computer program for calculating the parameters of an HP operating on R407C refrigerant has been developed. The effect the temperature difference of fluids at the outlet from the evaporator, condenser, intermediate heat exchanger, and sub-cooler has on the HP exergy efficiency is investigated using the developed computer program. Three configurations of heat pump main equipment, namely, with vapor compression, with an intermediate heat exchanger, and with a sub-cooler and heat recovery are considered. The study results have shown that it is inexpedient to use heat exchangers of the same standard size as the HP condenser and evaporator, because an attempt to use such solution results in either failure to attain the maximum possible efficiency or in discarding the possibility of saving on the evaporator’s material.