Characteristics of an air source heat pump with novel photoelectric sensors during periodic frost-defrost cycles

► Characteristics of the ASHP under periodic frost-defrost cycles are tested. ► Great deficiency is found for the characteristics of ASHP during the test. ► A novel type of photoelectric sensor TEPS is proposed and also tested in this paper. ► Test results confirm the expected potential for TEPS to control defrosting process. ► The agreeable structure configuration for the proposed TEPS is achieved.