xdxadmin
08-31-2004, 09:17 AM
Off-cycle Defrost plays upon the thermostat, the electronic management system, or low pressure control, to allow the compressors to cycle off, or refrigerant feed to be halted in order to operate the evaporator at a temperature / pressure above freezing. The evaporator coil will be completely free of frost before the compressors cycle again. When in defrost, it is often most effective when the flow of refrigerant to the evaporator of the fixture is stopped by de-energizing the liquid solenoid valve.
In recent years, the FDA recommendation, and the resulting acceptable refrigerated product temperatures have been reduced from 45F to 41F. Refrigerated air temperatures need to remain in the Thirties (F) to safely keep refrigerated product below 41F. Refrigerant temperatures and evaporator temperatures now need to be in the Twenties (F) to keep air temperatures in the Thirties (F). At 45F, it was easier to see the evaporator temperature exceed the necessary temperature to completely thaw the evaporator. A certain amount of latent work is accomplished during the off cycle, and the temperature of the refrigerated space is kept cool by the melting frost and circulating air. This was even easier before there were temperature standards, but since the recommended storage conditions are colder, these older systems have been retrofitted to utilize another method of derfost, and in some cases have needed additional capacity increase due to the increase load of reducing storage temperatures and the loss of the latent work accomplished my the melting frost.
Off-Cycle defrost has the benefit of maintaining higher humidity in the conditioned space, or Natural Humidification. XDX is able to allow systems that could not previously defrost by this method to do so, and can allow this defrost methodology to reduce or eliminate scheduled defrost cycles.
In recent years, the FDA recommendation, and the resulting acceptable refrigerated product temperatures have been reduced from 45F to 41F. Refrigerated air temperatures need to remain in the Thirties (F) to safely keep refrigerated product below 41F. Refrigerant temperatures and evaporator temperatures now need to be in the Twenties (F) to keep air temperatures in the Thirties (F). At 45F, it was easier to see the evaporator temperature exceed the necessary temperature to completely thaw the evaporator. A certain amount of latent work is accomplished during the off cycle, and the temperature of the refrigerated space is kept cool by the melting frost and circulating air. This was even easier before there were temperature standards, but since the recommended storage conditions are colder, these older systems have been retrofitted to utilize another method of derfost, and in some cases have needed additional capacity increase due to the increase load of reducing storage temperatures and the loss of the latent work accomplished my the melting frost.
Off-Cycle defrost has the benefit of maintaining higher humidity in the conditioned space, or Natural Humidification. XDX is able to allow systems that could not previously defrost by this method to do so, and can allow this defrost methodology to reduce or eliminate scheduled defrost cycles.