Environmental and economical analyses of transcritical CO₂ heat pump combined with direct dedicated mechanical subcooling (DMS) for space heating in China

An environmental and economical assessment model is developed, in order to evaluate the performances of transcritical CO₂ heat pump system with dedicated mechanical subcooling (CO₂ HP_DMS). Introducing DMS to traditional CO₂ HP system is an efficient method to reduce the primary energy consumption, which can be further decreased by using small temperature difference fan-coil unit (STD-FCU) as heating terminal. Using CO₂ heat pump system for space heating is an environmentally-friendly heating method. The corresponding pollution emissions are only inferior to those of the wall hanging gas heater. The initial capital cost and operating cost of CO₂ HP_DMS system are both lower than those of CO₂ HP_BASE system, and the CO₂ compressor cost accounts for about 80% of the overall initial capital cost. In contrast to other traditional heating methods, the payback periods of CO₂ HP_DMS system are not more than 9 years in most cases. If the CO₂ compressor and electricity price are reduced by 20% and 28.79% respectively, the life cycle cost of CO₂ HP_DMS will be competitive to that of coal-fired boiler. In China, it is a promising way to adopt CO₂ HP_DMS for space heating in the near future with the assistant of electricity price subsidy and compressor price reduction.