Study on the performance of Closed-Loop heat recovery heat pump drying systems under different operating conditions

This study applied exergy analysis to a heat pump dryer (humidity-difference-controlled compressor, temperature-difference-controlled heater). Experiments determined operating parameters’ effects on energy consumption, Specific Moisture Extraction Rate (SMER), Moisture Extraction Rate (MER), total exergy destruction, and exergy efficiency for optimization. Increasing drying temperature raised energy consumption and MER but lowered SMER and exergy efficiency while increasing total exergy destruction. Higher humidity decreased MER but increased exergy efficiency, with total exergy destruction initially rising then falling. Increased fan frequency raised energy consumption, SMER, and MER, while exergy efficiency and total destruction first increased then decreased. Greater loading increased SMER and MER; exergy efficiency first decreased then increased, while total destruction first decreased then increased. The condenser caused the highest exergy destruction, followed by the compressor; the evaporator and expansion valve incurred minimal losses. Stable operation occurred at 40°C, 20% relative humidity, 45 Hz fan frequency, and 77.5 kg loading, consuming 51.5 kWh. This yielded an SMER of 1.01 kg/kWh, MER of 14.73 kg/h, total exergy destruction of 3.866 kW, and exergy efficiency of 0.303.