This study investigates an air-source heat pump (ASHP) with an economizer in terms of its heating conditions and designs four groups of experiments to evaluate its heating performance. The results show that under each experimental condition

the main electronic expansion valve has the best opening

which is the maximum opening corresponding to a certain superheat range. Under the best opening conditions

the maximum heat of the heat pump unit is 85.99%

76.58%

57.46%

and 38.25% of the rated working condition. The corresponding energy efficiencies are 2.21

2.08

1.95

and 1.55

respectively. The opening of the replenishment electronic expansion valve can effectively improve the heating capacity; however

with an increase in the opening of the replenishment valve

the energy efficiency of the system decreases. If energy efficiency is used as the optimization objective of the heat pump unit

it may lead to insufficient heating capacity. Liquid return is also the main factor affecting the heating capacity and energy efficiency of the heat pump unit. When the replenishment port does not return the liquid

the heating capacity of the heat pump unit increases by 18.35%

12.14%

and 25.95%; when the replenishment port returns the liquid

the heating capacity is reduced by 15.22%.