Life cycle energy, emissions and cost evaluation of CO2 air source heat pump system to replace traditional heating methods for residential heating in China: System configurations

Abstract

Heat pump is an efficient method to substitute traditional boilers for cleaner space heating. A new configuration of CO2 heat pump system integrated with vapor injection and dedicated mechanical subcooling (VIDMS) is proposed, and compared with five configurations of CO2 heat pump system and three traditional heating methods. The life cycle model of energy consumption, pollutant emissions, and economic performance is developed. Assessment is conducted by taking seven typical cities located in different climate regions of China as scenarios. Coefficient of performance (COP) of VIDMS system is superior to other transcritical CO2 systems, and the COP is enhanced more notably in the case of severe cold or cold regions. The COP reaches up to 2.13 at the low ambient temperature of −20 °C, 36.51% higher than the baseline (BASE) CO2 system. The primary energy consumption (PEC) of the other five CO2 systems and coal-fired boiler (CFB) can decrease by 4.15–18.26% and 19.27%, respectively, when VIDMS is adopted. Moreover, the PEC reduction is more prominent when used in severe cold region. Life cycle climate performance (LCCP) decreases significantly by employing VIDMS compared with other transcritical CO2 systems and traditional heating methods. CO2 emissions can be reduced by 13.81–23.20% and 16.56–34.31% in contrast to BASE and CFB, respectively. Furthermore, the gaseous (NOx and SO2) and particulate matter (PM2.5 and PM10) emissions also decrease. Life cycle cost (LCC) by using VIDMS is much lower than the other transcritical CO2 systems. The payback period is reduced from 5.58 to 3.55 years if the price of electricity and CO2 compressor are both reduced by 20%. The new proposed VIDMS is a more promising CO2 heat pump solution to replace traditional heating methods.