The application of controls for hot-Gas Defrost Ammonia Evaporators

To defrost ammonia evaporators, sometimes you need to check plumbing arrangement and valves used to accomplish the task. To enable hot gas defrost systems to work successfully, you must consider several factors. There must be a sufficient supply of hot gas. The gas must be not less than 100 pounds per square inch. The defrost cycle must be accurately timed. For condensate removal or storage shall be provided. Automatic liquid or heat reservoir should be used to protect the compressor from refrigerant liquid slugs, if a surge drums or other evaporators are not sufficient for treatment of excess gas and condensates (see Fig. 10-7).

Controls should be used for direct and control of pressure and flow ammonia and hot gas during refrigeration and defrost.