The evaluation of optimal discharge pressure in a water-precooler-based transcritical CO2 heat pump system

A water-precooler-based transcritical CO2 system is presented for promoting the modified CO2 system to the space heating fields in which the water return temperature is too high to the standard transcritical CO2 systems. The theoretical results found that the optimal discharge pressure, similar to the standard system, is also a remarkable parameter for the water-precooler-based system. Furthermore, four prediction approaches for the standard system are cited and the comparison of the optimal discharge pressure between the standard and the water-precooler-based system is carried out. Upon the results, it can be concluded that the optimal discharge pressure of the water-precooler-based system is higher than that of the standard system in all the simulation range. Moreover, on the basis of abundant simulation data, an empirical correlation for the water-precooler-based CO2 system is proposed to evaluate the optimal discharge pressure by the ambient, water return and supply temperature as the independent variables.