Field test study of a novel defrosting control method for air-source heat pumps by applying tube encircled photoelectric sensors

• TEPS is a tube encircled photoelectric sensor used to monitor the degree of frosting.
• A novel TEPS defrosting control method was proposed and a field test was conducted.
• Accuracy and stability of the TEPS method under different conditions are confirmed.
• Advantages of the TEPS method compared to the conventional T-T method are presented.
• The TEPS method is a promising alternative defrosting control method for ASHP.

To improve the defrosting accuracy of air source heat pumps (ASHPs), this paper proposes a novel defrosting control method by applying tube encircled photoelectric sensors (TEPSs). A field test was conducted for two heating seasons in Beijing, China, to verify the feasibility and practicality of the novel TEPS method. The test results revealed that irrespective of the environmental conditions, the TEPS method can initiate defrosting in similar situations: most of the heat exchanger surface had been covered by frost; the compressor suction temperature decreased by ~9 °C; the compressor discharge temperature increased by ~16 °C; and the heating capacity decreased by ~30%. Furthermore, the TEPS method was verified to make more accurate and more reasonable defrosting decisions than the traditional T-T method under both frosting and non-frosting conditions. The results indicate that the TEPS method is a competitive defrosting control method that can be used for ASHPs.