Further analysis of the influence of interstage configurations on two-stage vapor compression heat pump systems

Two-stage vapor compression technology can effectively improve system performance, mainly due to the thermal effects of different interstage configurations. The thermal effects should be further analyzed to obtain quantitative results for different refrigerants. Based on mathematical analysis and numerical methods, the influences of the two thermal effects, i.e., subcooling and desuperheating, on the heating coefficient of performance (COPh) are analyzed. The results show that the subcooling promotes the COPh regardless of what refrigerant is employed; and the larger the molar specific heat capacity (evaluated by C-p,m(0)) of the refrigerant is, the greater the subcooling promotes the COPh. When C-p,m(0) is less than 60 J mol(-1) K-1, the desuperheating improves the COPh, whereas when is larger than 70 J mol(-1) K-1, it reduces the COPh. The maximum improvement in the COPh caused by interstage subcooling can reach up to 23%, while that caused by desuperheating is less than 6%.