When is crankcase heat particularly needed in a heat pump system?

Crankcase heat is particularly needed when the compressor is off. This is crucial because, when the system is not operating, the refrigerant can condense back into a liquid in the compressor, which can lead to difficulties when the compressor starts up again. The crankcase heater prevents refrigerant from accumulating in the compressor by maintaining a suitable temperature, which helps to keep the refrigerant in a gaseous state. This ensures a smoother start-up and protects the compressor from potential damage due to liquid slugging.

It's important to note that during operation, the compressor generates heat which helps to maintain the refrigerant's state, so crankcase heat isn't needed at that time. Likewise, during high heating loads or in cooling mode, the compressor is actively running, so the need for crankcase heat diminishes. The function of maintaining the compressor's integrity during periods of inactivity aligns perfectly with the role of crankcase heating.