Most of the early air-cooled heat pump units used piston refrigeration compressors. In the configuration of the refrigeration compressor, the refrigeration capacity of the compressor manufacturer's sample often does not match the actual, and the manufacturer of the air-cooled heat pump unit does not verify the actual capacity of the configured compressor, resulting in the actual operation of the air-cooled heat pump unit. Performance is declining. The wind-side heat exchangers in the configuration have a great influence on the frost pattern, the resistance, the air intake, the uniformity of the wind speed distribution and the heat transfer performance. For example, open fins are prone to frosting, have large resistance, and the fin spacing is too small. Although the heat exchange area is increased, it is easy to frost. As for the water side heat exchanger, there are shell type, casing type, vertical type (ice water) and plate heat exchanger. Among them, the plate heat exchanger has high efficiency, but the plate wall is thin and easy to be broken; the resistance of the vertical ice water device is large, and the oil returning of the refrigerant is difficult. At present, there are many types of casings, and shell-and-tube type is mostly used in large-scale units. There are two types of thermal expansion valves: one-way and two-way. Currently, two-way thermal expansion valves are used. The quick-freezing cold storage should pay attention to the pressure difference between the two devices (condenser and evaporator).
Dr. Huang Hu analyzed the main problems existing in the application of air-cooled heat pump units. First, the cooling capacity of the unit is insufficient; the second is heating attenuation; the third is the increase in energy consumption caused by defrost, the decrease in efficiency, and the fluctuation of water temperature; the fourth is the problem of inverter control. Dr. Huang pointed out that the COP values ​​marked by some units are too high. In fact, due to the discount on the compressor nameplate and the unreasonable configuration, it cannot be applied by the COP value listed on the sample. Dr. Huang also pointed out that operating under normal heating conditions, using electric auxiliary heating, will cause the return water temperature to be too high, and the condensing temperature will rise, which will adversely affect the operation of the refrigeration compressor, increase the burden on the compressor, or even jobs. In the past, the defrosting discrimination of air-cooled heat pump units has the following four methods: one is to use "time" to judge, that is, the time defrosting; the other is to use "time-temperature", that is, according to the temperature of the fins on the wind-side heat exchanger To judge. But only the temperature is low, and the inlet air humidity is not high, it is also a certain indication that it is frosting. The third is based on the "pressure difference" on both sides of the wind side heat exchanger, but if there is dust on the wind side heat exchanger, it will also cause the pressure difference to increase, not necessarily frosting; the fourth is based on the "temperature difference" That is, the difference between the evaporation temperature of the unit and the condensation temperature, because if the frost is formed, the temperature of the evaporator will decrease, and the temperature difference between the two devices will be judged as frost formation.
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