The methods for defrosting control of air-cooled hot and cold water units generally include time control method, time temperature control method, and difference control method between evaporation temperature and atmospheric temperature. The time control method is an early defrosting control method. In order to prevent the frost on the surface of the fin tube from affecting the unit work, the heating work time is often set according to the worst case, which will cause unnecessary defrosting action and cause energy loss. It affects the stable operation of the unit; the time temperature control method introduces the temperature quantity, which is better than the simple time control, but still can not achieve the defrosting according to the need, still cause unnecessary defrosting action or serious knot on the surface of the fin tube The frost does not defrost; due to the airflow resistance of the wind side heat exchanger and the thermal resistance of the frost layer, the difference between the atmospheric temperature and the evaporating temperature of the unit determines whether the defrosting is to some extent. Reflects the unit's response to frosting.
Another problem in the defrosting process is how to control the defrosting time, the defrosting time is short, and there is residual moisture on the surface of the fin. In the next heating cycle, the water quickly forms ice on the surface of the fin, which deteriorates the heating performance of the unit. Therefore, the mass flow rate in the system is rapidly increased. If the defrosting time is too long, the condensing pressure in the system is increased, and even the high pressure protection is caused. For this reason, the fan can be started in advance before the defrosting work is finished, which can be used on the fins. Residual water is quickly carried away by the air, which reduces the fluctuation of the suction and exhaust pressure at the beginning of a heating cycle. When the fan is started, it can be determined according to the exhaust pressure.
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