SELECTION OF COMPRESSOR IN CHILLER DEVICES
Compressors used in chiller devices are quite diverse. Since the compressor functions as the heart of the devices with gas cooling system, the type and quality of the compressor used is important. Below, we have tried to indicate the brief information and usage areas of frequently used compressors.
Hermetic compressors: Gas compression process is done with a piston that goes back and forth in a cylinder. These are called hermetic since the engine and piston assembly are in a single body. It is generally used in chillers and coolers of small capacities.
Scroll compressors: They are compressors that have been developed especially in recent years and have a very wide usage area. It consists of two spiral elements, one of which is fixed and the other rotating and operating with narrow tolerance ranges. They have important features such as being more resistant to extreme liquid rates, high efficiency, low sound and vibration levels. However, material strength, bedding and lubrication processes should be done well since the sealing between the spirals should be as good as possible and the friction between the elements is quite high.
Figure 1: Operating mode of scroll type compressors
It is mostly used in domestic applications and small capacity air-cooled chiller devices.
Semi-hermetic compressors: In simple terms, they are the types of compressors in which the engine and piston assembly are separate from each other. They are frequently used in cooling groups up to 500 kW capacity. Since the engine and piston sections are separate from each other, they can be easily intervened during repair and maintenance.
Figure 2: Semi-hermetic type compressor
Screw type compressor: They are produced in two different types as single screw and double screw. In principle, it works according to the principle of compressing the refrigerant between the helical shaft and the gate rotor or between two helical shafts. Although screw compressors served as air compressors at first, they started to be used in cooling devices in later years and found a very wide application area. It is generally used in chiller units with a capacity between 450 and 1500 kW. In addition to the positive values such as long operating life, repair and maintenance possibilities, internal gradual operation of screw compressors also provides benefits in terms of electricity consumption.
Figure 3: Compression of gas in a screw compressor
Centrifugal compressor: Unlike piston, scroll or screw type compressors, centrifugal compressors that perform cooling with a vapor compression cycle perform compression by utilizing centrifugal forces instead of positive compression process. Since it is possible to easily move fluids with high specific volume, it is generally applied in large-capacity deep freezing processes. With this type of compressor groups, it is possible to achieve capacities that cannot be achieved with other compressors.
Abovementioned compressors are mostly used even though there are other different types of compressors. While the capacity you need is the main determining factor when making a selection, factors such as availability of spare parts and environmental conditions in the region where the system will operate can also be a determining factor.
