Air, electric and hot-gas defrost compared
The three cycles
- Air defrost — off-cycle: the fans simply run while the compressor rests. Only works above about +2 °C room temperature, uses zero extra energy.
- Electric defrost — heaters inside the coil, timed or demand-controlled. Works at any temperature; the default for freezer rooms; costs 1–3 % of total energy.
- Hot-gas defrost — discharge gas is routed through the coil. Fast and gentle on the coil, needs a valve station and a receiver; the standard on larger remote systems.
Setting the interval
Start from four defrost pulses per day on a freezer, watch the coil sensor and the drain line for one full loading cycle, then adjust. Demand-controlled defrost (defrost only when the coil is actually iced) cuts the count to two or three and saves both energy and product temperature stability.
Drain-line details that matter
- Trap the drain line after the evaporator — without a trap, warm humid air short-circuits back into the room.
- Heat the drain line (trace cable) for the first metre outside the room in freezer applications.
- Give the line a continuous fall of at least 1 cm per metre; a flat line is an ice plug waiting to happen.