How to Choose Types of Compressor Used in Chiller?

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Chiller compressor types. In this video, we&#;re going to be looking at the most common types of refrigerant compressors used in chillers. We&#;re going to have a review of the four most common types, that being the centrifugal, the screw, the scroll and the reciprocating.

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We&#;re going to have a look at the real world examples of how these look in the plant rooms, so that you can spot these when you&#;re walking around and we&#;ll also have a brief look at how each one works.

Centrifugal Compressor

Centrifugal Chiller

The first one we&#;re going to look at is the centrifugal type compressor. The centrifugal type compressor looks a lot like this and is quite easy to spot as the compressor is above the chiller with a large volute shaped pipe curling around into the condenser.

Centrifugal Compressor

The refrigerant flows in through the suction line, hits into the the centre of the impeller where it will be directed by the blades. The blades rotate and that imparts an angular velocity onto the particles of the refrigerant. This angular velocity makes the refrigerant particles fly out at high velocity, in all directions, and collects in the volute (the outer curl) where it increases in pressure from the kinetic energy, it then passes down into the condenser. This type of compressor/chiller is a very common set up for a central plant in large buildings.

Turbocor Compressor

Turbocor compressor

A variation of the centrifugal type is the Turbocor compressor. Turbocor compressors are much smaller units mounted also to the top of the chillers. These work very similar to the centrifugal type, but they have two stage compressors inside. The refrigerant flows in through the front, passes through the two different compressors and then the refrigerant exits and travels down into the condenser. These usually have magnetic bearings and electronic motors inside, which make these units very efficient. Turbocor are becoming much more common and they are set to continue this trend.

Screw compressors

Screw compressor chiller

Screw compressors are used for both water cooled and air cooled chillers. With water cooled type the compressor is on top of the chiller and with air cooled type the compressors is under the chiller. Indoor water cooled chillers will often be insulated whereas air cooled may not be. This type takes the refrigerant off of the evaporator and passes through into the compressor. Inside the compressor are two interconnecting screws.

The refrigerant will enter into a void between the two screws, but as the screws rotates they push the socket of refrigerant further into the compressor and squeeze it into a small space. The refrigerant will exit at high pressure high temperature and flows to the expansion valve.

Air cooled chiller screw compressor

Above is a photo of an air cooled chiller with two screw compressors. It&#;s common to find 1-2 small screw compressors on air cooled chillers. These will work in parallel and some designs allow for staging by turning off one of the compressors.

Scroll compressors

Scroll compressor chiller

The scroll compressor is used mostly on air cooled chillers but you can also find them on water cooled. Usually one compressor isn&#;t enough to meet the cooling load so several will be joined together in a bank. In the example above the blue cylinders under the chiller are the compressors which are joined to form a bank.

With these type of compressors, the refrigerant usually enters via the bottom and is fed into the compressor discs. One disc will be stationary whilst the other is rotated to compress the refrigerant into a tighter space. The refrigerant is forced around the spiral as the disc moves which causes it to compress, it will then leave via the top and head to the expansion valve.

Reciprocating compressors

Reciprocating compressor chiller

The last one we&#;re going to look at is the reciprocating type compressor. These type are becoming less common because newer, more efficient, technology has been replacing it so these are slowly being phased out in commercial refrigeration at least. It&#;s still quite popular in industrial refrigeration. These are very strong and reliable compressors which seem to just work forever with the right maintenance. There are a lot of moving parts though so they can be expensive to operate.

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In reciprocating types the refrigerant will often pass over the electrical motor to proving cooling to the electrical coils and then head into the compression chamber. The compression chamber is simply a number of piston and chambers which the refrigerant will flow into. The piston is on a crank which moves it up and down. As it moves it will compress the refrigerant into the chamber and at a timed interval the refrigerant will exit at a high pressure.

If you are currently in the industrial chiller market, you have probably noticed that different chiller units have different compressor types. You may be wondering what the details of these different compressors are. Having a basic understanding of the core mechanisms of your unit not only provides you with a better appreciation for the unit, but also helps in your general maintenance and troubleshooting efforts.

Compressors are vitally important to the overall chiller system. They take in low-pressure refrigerant vapor from the evaporator and compress it. The resulting hot, high-pressure gas is discharged to the condenser.  Once cooled in the condenser, the refrigerant continues through the expansion device and enters the evaporator. There, it chills the process fluid.  Without a working compressor, the refrigerant cycle simply cannot function.

Chase Chillers feature four different types of positive displacement compressors: reciprocating, rotary vane, scroll, and screw. The compressor type largely aligns with the size and capacity of the chiller itself. Continue reading below for more information on the basics of the different compressor types.  

Reciprocating Compressors

Reciprocating compressors use a piston and cylinder to compress incoming refrigerant. As the piston moves downward, refrigerant is drawn into the cylinder. The piston then moves upwards compressing the refrigerant and discharging it downstream to the condenser. Intake and exhaust valves ensure that the refrigerant does not flow backwards.  These types of compressors are very economical and efficient in smaller applications.  As with rotary vane and scroll compressors discussed below, reciprocating compressors consist of a hermetically sealed design. Chillers set up for small to medium heat loads, such as QBS and some QBE models match well with this type of compressor.

Rotary Vane

Rotary vane compressors typically are quieter than other options. They consist of vanes or blades that are attached to a core rotor. The rotor is positioned off-center within its cylinder, creating multiple areas of varying sizes. The refrigerant enters the cylinder at the largest of these areas. As the rotor turns, the fluid is forced into smaller areas and compresses. Once compressed, the fluid exits the cylinder and continues through the rest of the system. Typically, industrial chillers with this compressor type only contain one compressor per unit. This compressor type is available in certain QBE models and the smallest CWT model.

Scroll

The most common compressor type in industrial chillers is the scroll. It is a powerhouse of a design and is able to handle significantly larger loads than the other compressor types. Found in our larger units, CWB, CWE & CWT, scroll compressors work by compressing the refrigerant between two spiral plates, one stationary and one orbiting. As the spirals move in an offsetting pattern, the trapped air is forced into smaller spaces as it moves towards the center. The compressed fluid exits through the center outlet and into the rest of the system. Multiple scroll compressors can be used in a single cooling unit, a feature great for building in redundancy and providing highly efficiency partial loads. With fewer moving parts, they are often more reliable and efficient than reciprocating options.

Screw

Rotary screw compressors have two interlocking helical rotors mounted inside a casing. As the rotors turn, the gas is forced from the suction end of the casing to the discharge end. The available space between the rotors and the casing becomes increasingly smaller as the gas moves along the length of the screw, increasing the pressure. Screw compressors are useful for varying the cooling output and are found in the largest chiller units. This design is able to limit how much refrigerant is delivered and lends itself well to meeting the variable needs of some cooling processes. Chillers in the CWV series have this compressor type.

The chart below outlines which compressor type is present in which Chase Chillers model:

ReciprocatingRotary VaneScrollScrewQBS &#; QBE &#; &#; &#; CWT &#; &#; CWE &#; CWB &#; CWV&#;

Regardless of which unit you choose, you can trust that it will be backed by the Chase Cooling Systems quality assurance. Each compressor type has its perks and benefits certain systems over others. To make sure you have the best unit for your system, work with one of our cooling experts. They are available for consultation regardless of where you stand in the buying process. We want you to find the best fit for your needs. Our years of experience and knowledge make us a strong resource for this process.

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