Types and Operating Principles of Compressors
03 November 2020What is a Compressor?
COMPRESSOR is one of the four main components of a refrigeration system; the other components connected to the system are the condenser, evaporator, and expansion valve. The compressor circulates the refrigerant fluid within the system in a continuous cycle.
Types and Operating Principles of Compressors
There are two main types of compressors: positive displacement and dynamic. Positive-displacement compressors increase the pressure of the refrigerant vapor by reducing the volume of the compression chamber with the force applied to the compressor mechanism. Types of positive-displacement compressors include reciprocating, rotary, rotary vane, single screw and twin screw, scroll, and trochoidal compressors.
Dynamical compressors use angular momentum to increase the pressure of the refrigerant vapor and thus maintain the continuous flow of the refrigerant cycle. Centrifugal compressors operate on these principles..
The performance of a compressor is the result of a design that takes into account the physical limitations of the refrigerant, compressor, and motor, while striving to achieve the following::
- -Expectation of seamless operation life
- -Maximum cooling effect with minimum power input
- -Lowest cost
- -Ability to operate under a wide range of conditions
- -Acceptable vibration and noise levels.
Factors affecting compressor capacity and lifespan:
- -Low and high pressure levels (ΔP)
- -Amount of suction superheat
- -Amount of discharge superheat
- -Amount of subcooling
- -Compressor speed
- -Refrigerant quality
- -Operating temperature of the compressor environment
- -Properly selected other system components
- -Additional subcooling
Types of Compressors
There are two types: semi-hermetic and hermetic. Semi-hermetic compressors can be repaired unlike hermetic compressors. Piston compressors are widely used in our country along with new generation compressors. Its use has been decreasing worldwide. They are usually preferred for low and medium pressure applications.
Scroll compressors, have almost completely replaced semi-hermetic piston compressors. They are preferred due to their reasonable price, gas diversity, long life, and very high efficiency. They are generally preferred for medium and high-pressure applications. There are also types used for low pressure, but to a lesser extent.
Screw compressors, are found in fixed large systems. As screw compressors become more economical and their benefits are increasingly recognized in different industries, this trend is beginning to change. While only a few manufacturers used to produce screw compressors, these compressors are now being produced by more and more companies worldwide. They are preferred in low, medium, and high pressure applications and in all large-capacity facilities. Their repairability makes servicing easier.
Rotary compressors are generally preferred in high-pressure applications, such as air conditioners, heat pumps, etc. They are very economical compared to other compressors. They are hermetic and cannot be repaired. They need to be replaced with a new one. Even if they are repaired, a new one will be more economical. The majority of production is done in Asian countries..
Centrifugal compressors are typically used in large chiller applications. These machines change the angular momentum between a continuously rotating mechanical element and a fixed flow fluid. Due to their continuous flow, centrifugal compressors have larger volumetric capacity compared to positive displacement devices..
For efficient momentum transfer, the rotational speeds should be higher, but due to the stability of the motion and the absence of contacting parts, very little vibration or wear results. Centrifugal compressors are very suitable for air conditioning.
Distribution of compressor types used in air conditioners:
Scroll: 10,850,324 units
Screw: 75,399 units
Centrifugal: 5,950 units
Piston: 7,732,716 units
Rotary 2 cyl: 3,293,277 units
Rotary 1 cyl: 64,280,894 units.
Distribution of compressor types used in refrigeration:
Screw: 26,393 units
Scroll: 235,277 units
Piston: 16,350,668 units
Rotary 2 cyl: 2,979,385 units
Refrigerator: 97,585,925 units