Abstract: Under low-temperature operating conditions, frost layer is easy to appear on the evaporator coil surface of the refrigerated dehumidifier, thus its dehumidification performance is deteriorated. In order to improve the dehumidification performance of the refrigerated dehumidifier under low-temperature conditions, a variable-frequency dehumidifier performance test system was builded. The effect of the electronic expansion valve opening on the operating parameters, dehumidification performance, and frost phenomenon of the dehumidification system was experimentally investigated under low-temperature operating conditions with different combinations of compressor frequency and fan speed. The following conclusions were drawn: the increase in the electronic expansion valve opening can increase the evaporating temperature, so that the lowest temperature point of the evaporator is postponed to the second half of the process, and the frost layer appears first in areas with sparse condensate distribution, alleviating the frost phenomenon and improving the dehumidification performance. When the evaporating temperature reaches near -4℃, the frost covering rate is close to 100%, and the evaporator coil surface is seriously frosted, at the same time the suction pressure is abnormally lowered to 0.2 MPa. The experimental results shows, the evaporating temperature of -4℃ and the suction pressure of 0.2 MPa can be used as a general criterion for the start of defrosting. The research results can provide optimization direction and reference basis for the dehumidification performance enhancement of refrigerated dehumidifier under low-temperature operating conditions.

Key words: Inverter dehumidifier, Low-temperature condition, Electronic expansion valve opening, Frosting, Dehumidification performance