Scroll compressor
Also known as: spiral compressor
Short definitionA compressor that works with two interleaved spirals. One spiral stays fixed and the other orbits inside it; it has few parts and runs with little noise and vibration.
A scroll compressor has no pistons, crankshaft or valves. The moving spiral does not spin on its own axis; it traces a small orbit inside the fixed spiral. As the pockets between the two spirals shrink towards the centre, the vapour is compressed and discharged from the middle. It has roughly a third of the parts of a reciprocating compressor, which means little wear, quiet running and high efficiency.
Most condensing units in the 2–40 kW range for commercial cold rooms use a hermetic scroll compressor. It is at its most efficient at evaporating temperatures of −10 °C and above; for low temperatures, vapour-injection models are chosen. Phase sequence is checked at commissioning: a three-phase scroll running backwards does not compress and overheats quickly. It tolerates liquid return slightly better than a reciprocating compressor, but the superheat setting still must not be neglected.