A study into the feasibility of introducing a CO2 network system for district heating and cooling in Tokyo

Reducing CO₂emissions by the effective use of renewable energy is one of the most important issues globally. Therefore, research has focused on both the development of individual high-performance equipment and also district heating and cooling systems. In Japan, installations of the conventional district heating and cooling system, which utilizes steam and chilled water, are rare. In recent years, a promising alternative, the CO₂network system, has been proposed by researchers at Swiss Federal Institute of Technology in Lausanne. The system uses the latent heat of vaporization of the CO₂refrigerant to transport and exchange unused heat to specific areas via decentralized heat pumps on the demand-side. The proposed system is expected to significantly reduce energy consumption compared with the conventional system. In this study, we analyzed the energy-saving effects of introducing a CO₂network system in Tokyo, with consideration of the environmental conditions and the typical energy demand profiles. The effects of modifying the central unit and the demand-side decentralized heat pump systems were examined in the context of Tokyo. When using the CO₂network, the annual energy consumption resulting from equipment operation can be reduced by approximately 80% compared with the conventional system. This effect is almost of the same magnitude as the effect observed in previous research conducted in Switzerland. Furthermore, we examined the optimum connection pattern of the decentralized heat pumps and the optimum temperature of the CO₂supplied to the network.