Scroll compressors are orbital motion, positive-displacement type compressors that compress gas with two interfitting scrolls.
How a scroll compressor works
A scroll compressor actually consists of two scrolls or spirals. One scroll is moving, whereas the second one is fixed (attached to the compressor body). The first scroll orbits (rotates) in a path defined by its mating fixed scroll. The orbiting scroll is connected to the compressor's crankshaft. As a result of the scroll's movement, gas pockets are formed between the two scrolls. At the outer part of the scrolls, the pockets suck in gas and then move towards the center of the scroll, where the compressed gas is discharged. As the gas moves into the continuously smaller internal pockets, both its temperature and pressure are increased. Thus a desirable discharge pressure is achieved by the motion of the compressor scrolls.
Figure 1 - Schematic to show how scroll compressors work
Structure of scroll type compessors
Scroll compressors are fully hermetic (enclosed in the compressor's shell, which is usually a cylindrical welded steel shell). Majority of scroll compressors used in refrigeration and HVAC services are of vertical orientation, with the scroll sets typically installed on the upper part of the motor shaft.
Figure 2 - Typical scroll compressor
Advantages of scroll compressors
- The absence of pistons for gas compression enables scroll compressors to reach 100% volumetric efficiency, leading to reduced energy costs.
- Re-expansion losses, a typical feature of each piston stroke encountered in reciprocating models, are eliminated. In addition, valve (ports) losses are eliminated, since suction and discharge valves (ports) do not exist.
- Furthermore, due to the absence of several moving parts, scroll compressors are considerably quieter in operation compared to other types of compressors, like for example reciprocating type ones.
- Their weight and footprint are considerably smaller compared to other bulkier types of compressors in use nowadays.
- Gas pulsation is also minimised, if not eliminated and consequently, they can operate with less vibration.
Disadvantages of scroll compressors
- Being fully hermetic, perhaps the biggest disadvantage of scroll compressors is that they are generally not easily repairable. They cannot be disassembled for maintenance.
- Many reciprocating compressors are tolerant on rotating in both directions. This is usually not the case for scroll compressors.
- Incremental capacity control on systems with several scroll compressors has proven several times to be problematic as well.
Applications of scroll compressors
Since their introduction, scroll compressors have been successfully used in applications involving food and fruit refrigeration, truck transportation, marine containers as well as residential and small to medium scale commercial air-conditioning applications.