This article explains the five most common methods: shutting down the condensing unit to allow for natural defrost; hot gas defrost; electric defrost; water defrost; and, other external heat-source defrost. It provides guidance on designing a defrost method, with time to warm coil and wall surfaces being constant for any given system. This article received recognition when it first appeared in the March 1959 issue of ASHRAE Journal.

Units: I-P