Electric defrost heats the ice from outside with heating elements, and its energy comes from the electricity meter. In hot gas defrost the 60–80 °C vapour discharged by the compressor is routed to the evaporator by valves; the ice is warmed from inside the tubes and melts in 5–10 minutes. The heat is heat the system already produces; extra electricity is used only for the compressor. Because the fins warm evenly the ice melts completely and less heat is released into the room.
The pipework needs a separate hot gas line from the discharge line to the evaporator, three-way or solenoid valves, a bypass around the expansion valve and an arrangement for returning the refrigerant that condenses during defrost. In small single-evaporator systems "reverse cycle" (swapping the roles of condenser and evaporator) is applied; in multi-evaporator systems one evaporator defrosts while the others keep cooling and supply the hot gas.
It is standard in blast freezing tunnels, large frozen stores, central systems and CO₂/ammonia plants; in small cold rooms electric defrost is preferred because of the cost and complexity of the pipework. When selecting an evaporator, models intended for hot gas defrost are built with a special tube circuit; this is indicated in our catalog.