Derivation of optimum equipment configuration and operating point of CO2 network system for cooling/heating ratio of demand

Abstract

In recent years, “CO2 network system” has been proposed by researchers in EPFL, Switzerland. The system uses the latent heat of CO2 refrigerant to transport and exchange unused heat to specific areas by employing distributed heat pumps on demandside. The purpose of this study is to derivate of optimum equipment configuration of the decentralized heat pump and the CO2 temperature supplying to the network from the central plant for the cooling/heating ratio of demand. In this report, first, we analyzed the effect of the cooling/heating ratio of demand and the temperature of CO2 refrigerant on the performance of CO2 network system. As a result, we found that when the cooling/heating ratio of demand is 1.13 or more, the connection pattern in which CO2 supplied from the network and indoor air exchange heat directly was optimal for the air conditioner for cooling. In other cases, the connection pattern in which CO2 supplied from the network was directly used as the refrigerant for the decentralized heat pump was suitable. Second, we calculated the annual energy consumption using the derived optimal CO2 temperature supplying to the network from the central plant for typical energy demand in urban areas in Japan where a district heating and cooling system using steam and chilled water as a heat transport medium was introduced. It was clarified that when the CO2 temperature supplying to the network from the central plant was constant at 12 °C for a year, the electricity consumption was almost the same as that when the CO2 temperature was set optimally.