Air-source heat pumps

as a new

energy-saving

and environmentally friendly technology

are widely applied in various heating applications

yet their reliable operational efficiency at low ambient temperatures is a concern. In this study

a simple

low-cost

and reliable heat pump system is constructed using safety and environmentally friendly binary refrigerant CO2/R1233zd(E)

and the system performances such as the coefficient of performance (COP)

volumetric heating capacity

suction pressure

and exhaust pressure are obtained through optimization analyses at ambient temperatures from -30 to -10 ℃. By comparing the vapor-injection heat pump system and cascade heat pump system

it was deduced that a recuperative heat pump system using a binary refrigerant can maintain high efficiency at low ambient temperatures. At ambient temperatures ranging from -30 to -10 ℃

the COP of the recuperative heat pump system decreases by 9.8% to 20.6%

whereas the volumetric heating capacity increases by 3.5% to 56.1% compared to the R410A vapor-injection heat pump system. Moreover

the compressor pressure ratio and its variation with ambient temperature are lower than other heat pump systems. Owing to the simple structure of the recuperative system and the adoption of the safe and environmentally friendly binary refrigerant CO2/R1233zd(E)

the solution proposed in this study has unique advantages in heat pump applications in regions with low ambient temperatures.