Abstract: The low-temperature heating capacity test is a necessary practical test item in the energy efficiency evaluation of heat pump room air conditioners, and it has a crucial impact on determining the energy efficiency rating of the air conditioner. During the testing process, the outdoor unit of the air conditioner may experience transient operation due to frosting and defrosting, posing higher demands on the accuracy of test results. This study investigates three commonly used measures in the laboratory to determine the start and end state points of the defrosting process of the air conditioner: monitoring power value of the tested air conditioner, four-way valve action signals, and outlet static pressure. The study analyzes and compares the cycle period, heating capacity, power consumption, and energy efficiency ratio(EER)measured by different methods, to improve the operational rationality and reliability of the heating capacity test of air conditioners. Experimental findings reveal that compared to using four-way valve actuation signals for judgment, the use of operating power and outlet static pressure as criteria results in a negative deviation of-4.8% and a positive deviation of +3.8% in measured low-temperature heating capacity, respectively. These deviations subsequently impact the calculation of the annual performance factor(APF). Given that four-way valve actuation is intimately tied to the internal control strategies and real-time operating status of the air conditioner, while this method for defrosting process determination is more complex operationally than the other two, it offers greater advantages in enhancing the operational rationality and result reliability of the heating capacity test for air conditioners.

Key words: Room air conditioner, Transient test, Heating capacity, Annual performance factor (APF)