Theoretical study of three zeotropic mixtures for high temperature heat pump

Based on the double-heat-source high temperature heat pump, the impacts of R245fa fraction in three different mixtures including R245fa/R134a, R245fa/R152a and R245fa/RC270 on the thermodynamic performance of the system were theoretically analyzed. It is found that the performances of heat pump using zeotropic mixtures are all better than those using the pure refrigerants. Keeping the outlet of hot water at 80℃, the maximum values of COP for different refrigerant mixtures of R245fa/R134a, R245fa/R152a and R245fa/RC270 can be achieved with R245fa mass fraction of 0.64, 0.7 and 0.88, respectively. Accordingly, the values are 4.74, 4.68 and 5.15. Among three different mixtures, R245fa/RC270 (0.88/0.12) shows the best performance. As compared with the system using pure refrigerant R152a, the COP of system using R245fa/RC270 (0.88/0.12) is, respectively, improved by about 20%, and the work consumption per unit mass of hot water produced is reduced by 16.6%. Also, the discharge temperature and pressure of compressor are greatly lowered by using zeotropic mixtures. Besides, the temperature matching characteristics between the hot and cold fluids in the evaporator and condenser are also analyzed by T-Q diagram, it is indicated that the temperature variations of the hot and cold fluid in the heat exchanges matches better after using the zeotropic mixtures, and the temperature matching characteristics is the best by using R245fa/RC270 (0.88/0.12).