Figs. 5e7 showed variations of COP, heating capacities, power
consumption and outlet water temperature of tank in using
three different refrigerants, where ambient temperature was
30 C and solar radiation was 355 W m2. It can be concluded
that the four factors of three refrigerants presented an analogous
relation with the growth of time. Heating capacities
decreased gradually with the increased of outlet water temperature.
Correspondingly, power consumption increased in
opposite, which resulted in COP dropping constantly. In
addition, regardless COP or heating time, the system performance
of R22 was the best. R134a only had a little difference
with R22. It is worth noting that the heating time of the whole
heating process is the longest for R744. Simultaneously, COP
was the lowest. Based on the study, this is related to heating
capacities of R744. From Figs. 5e7, it also could be concluded
that the average heating capacities of R22 and R134a were