Defrost efficiency for ammonia air cooled evaporator systems.

This paper describes the results of measurements of defrost cycles. Three types of air-cooled evaporators are tested, i.e. bottom, top, and side feed. Two defrosting methods are tested, the more conventional pressure controlled method and the more energy efficient drain controlled method. The energy used throughout the defrost cycles is measured and compared for the different evaporator types and the defrosting methods. The energy used for melting the ice, heating and cooling the coil, heat convection to the room, and the hot gas bypass was measured. For the pressure control defrost method, the defrost efficiency was 21.6% and for the drain controlled defrost method the efficiency increased to 49.4% for the bottom feed evaporator. The drain controlled defrost efficiency for the other types of evaporators was nearly the same.