Most people don’t really understand or does not even have the slightest clue on what air conditioner compressors are and how they work. Others may not even know that their air cons have these.
It is not as if people really look in to the operating systems of their air conditioners when they buy them, all we really give notice to is how much horse power they have or how comfortable it would make us feel once we have installed them in our homes.
In this article, we will discuss about this vital piece of air conditioner anatomy, the types of compressors and its pros and cons of each compressor systems. After finished reading, you will have very good knowledge on how compressors work.
Are you ready?
Let us start now…
What is a compressor?
An aircon compressor is the heart of your cooling system. It is the most commonly misdiagnosed component in the system. It helps to take out the hot vapor refrigerant from the aircon unit’s evaporator system.
In layman’s terms, the compressor condenses the vapor into a reduced volume at a high temperature. There are some compressors that operate with a pulley and belt system and there are also some that use electric motors.
The compressor encompasses reed valves which helps it to regulate the circulation of refrigerants in the pumping process. If they are not tightly held, gas might ooze back into the low side during the compression stroke.
Most of the compressor units consists of a relief valve which helps to control the pressure of the unit. If the system discharge pressure exceeds norms, the valve will open automatically and stay open until the pressure drops. The noise that you hear from your aircons can also be pointed to the compressor mount.
Aircon conditioner compressors can be broadly classified into five types: Reciprocating, Scroll, Screw, Rotary, and Centrifugal. I will discuss each to you later on.
How do they work?
Aircon units help to reduce the temperature of a single room, a complete house, or even a building. By using chemicals, aircon units convert from a gas to liquid and repeat the same process over and again. These chemicals help to transfer heat energy from the air inside a space and expels it to the air outside, thus bringing down the temperature.
The compressor and the condenser are usually located on the outside portion of the air conditioner. The working fluid reaches at the compressor as a chilled, low-pressure gas. The compressor then condenses the fluid which renders the molecules of the fluid to stay together.
As they stay more closer, energy and temperature associated with it would be more. The working fluid then leaves the compressor as a hot and high pressure gas which then flows into the condenser. After it leaves the condenser, its temperature is much cooler now and has changed from a gas to liquid under high pressure.
The liquid then goes into the metering device which is a flow restricting device that provides pressure drop point. After that, the fluid will goes to evaporator. Now the fluid comes out of the evaporator as a chilled, low pressure gas. It then moves back to the compressor unit to start its movement through it all over again.
It is a continuous cycle until the room reaches the temperature you want the room cooled to.
What are the different types of compressors?
As we have mentioned earlier in the article, there are 5 types of air conditioner compressors that are commonly used in the HVAC (Heating, Ventilation, and Air Conditioning) industry. They are
- Reciprocating Compressor
- Rotary Compressor
- Centrifugal Compressor
- Screw Compressor
- Scroll Compressor
All five of them work the same way, but their methods of compressing refrigerant vapor are different from one another. we will talk about specific details on each compressor and how they work to give you a closer look on how they help your air conditioner systems work perfectly.
1. Reciprocating Compressor
Reciprocating compressor is also known as piston compressor. The reciprocating compressor makes use of a piston, which moves within a cylinder, to compress the refrigerant propelled by a crankshaft.
Vapor emanating from the suction line is carried to the intake valve as the piston is pushed down. When it goes up, it compresses the vapor refrigerant. It is then moved through the exhaust valve which later finds path to the condenser. This rotary motion is achieved by the use of a motor and the construction is quite similar to that of a car engine.
Absorption of air and expelling is performed by two valve sets. One-way valves ensure that the air which is absorbed cannot seep through. It also makes sure that the compressed air would not move back as the piston goes down again.
This type of compressor may have multiple cylinders that is called as the multi-cylinder compressor. There are different types like two-cylinder, four-cylinder, eight-cylinder compressors and the like. This type of compressors can deliver power in range of small (a few HP) to medium sized. It is based on the air needed.
Reciprocating compressors are divided into different types like Single-acting reciprocating compressor, Double-acting reciprocating compressor and Diaphragm reciprocating compressor.
2. Rotary Compressor
Rotary compressors are sealed tightly, which brings about an enhanced drive method. compressor and motor are positioned inside a single enclosed space. Hence, there is continuous interaction between motor and refrigerant element.
As the gas is compressed, a pressure variance is created in the rotary compressor which assists in easy movement of the refrigerant easily through the system. Gas compression is achieved by means of rotor movement with respect to pump chamber.
Working of stationary rotary compressor
An electric motor drives the cam. The cam causes the ring to rotate along with the cam. Ring now moves to external rim across the cylinder’s wall. Evaporator produces vapour which then finds its way to condenser across the holes made inside the frame of compressor.
Compression of gas is achieved by the help of an offset-rotating ring. There is a barrier which splits up both ports (intake and exhaust). As the compressor absorbs the vapour, barrier is grasped against ring with the help of spring. Ring now moves around cylinder and performs the gas compression. It is then moved into the condenser.
Working of rotating- blade compressor
There would be 2 roller blades which are aligned 180 degrees apart. Blades move across cylinder’s side. Roller is erected in such a way that it could get in contact with the cylinder in between both ports (discharge and intake).
Now when the roller moves, vapour flows to intake port which finds its way to the cylinder.Vapour is sealed inside. When the subsequent blade moves past the point of contact, vapour would be compressed. Once the pressure reaches a certain value, vapour finds its way through exhaust port and then moves to condenser.
3. Centrifugal Compressor
Centrifugal compressors are also know as radial compressors. It is used in refrigerating system with bigger capacity. In centrifugal compressor, the vapor is rotated in a circular motion which is termed as centrifugal force.
An impeller (disk) which consists of radial blades rotate quickly within this housing which drives the gas to attain higher speed. Now, a diffuser transforms this energy into pressure energy which is then oozed into the condenser. As the speed increase, pumping efficiency. Therefore, centrifugal compressors are conceived to work at more velocity.
Traditional centrifugal compressors works with hydrodynamic bearings that demand a mixture of pumps, filters and monitoring units. Latest units make use of a mixture of refrigerant and oil, or solely the refrigerant alone, to lubricate the rolling bearings.
Removing oil as a lubricant decreases the intricacy and expense associated with the unit while increasing compressor efficiency and dependability.
Working of Centrifugal compressors are comparable to that of axial compressors. They also consists of rotating airfoil based compressors. One of the main difference of centrifugal compressors from axial compressor is that they make use of a higher change in radius from inlet to exit of the rotor or impeller.
Centrifugal compressors are well-known for their straightforward design, lower number of moving parts, and improved energy efficiency when they need to operate in multiple stages.
4. Screw Compressor
A lot of buildings especially engineering plants require compressed air that can be obtained with this type of compressor. Screw compressor is driven by either an electric motor or a diesel engine.
As the name indicates, Screw compressors make use of a couple of helical rotors or screws which interlace together to compress the refrigerant as the rotors revolve in the cylinder. Both male and female rotors are fabricated within the cylinder. The low pressure refrigerant finds its way to one end of the compressor and the subsequent high pressure refrigerant is expelled into other side of the condenser.
Male rotor consists of 4 helical-structured lobes which connect with 6 flutes which correspond to female rotor. It is propelled by coupling it with the step-up gears. Then, its lobes rotate into the female rotor flutes. They are usually used to replace piston compressors which demands huge volumes of high-pressure air.
In HVAC, they are usually used in systems with 20 ton capacities and above. They can generate greater pressure for a lower gas quantity and demands lower power compared to other compressor units.
Huge quantity of lubrication oil lowers the temperature of compressed air, therefore inter coolers are not necessary in screw air compressors. The oil closes the clearance gaps.
5. Scroll Compressor
Get clean and noise free compressed air with a scroll compressor, which is a quiet and reliable type of compressor. The scroll compressor is another popular type of compressor.
It is commonly used in fridges, freezers, and chillers to pump around the Freon. But it can also be used to compress air in you workshop or factory. These are also widely used in automotive aircon systems.
This compressor is a wonderful invention, since it has only one moving part. The compressor exists of two spiral elements. One moves in eccentric circles and the other one is stationary. When this happens, the pockets of refrigerant between the two scrolls are slowly pushed to the center of the two scrolls causing the reduction of the volume of gas. It is then discharged through the center port of the condenser.
A scroll compressor working in reverse mode is called as scroll expander. These are used to create mechanical energy and work on the basis of expansion of fluid, compressed air or gas. Scroll compressors are usually used in most of residential central heat pump and aircon units. They also find their place in some of the automobile aircon units.
The Pros and Cons of Each Compressor
1. Reciprocating Compressor
Pros: They are relatively cheap, has a simple design and easy to operate. It is also low maintenance since it is easy to understand the inner workings.
Oil or lubrication is not required in reciprocating compressors and is suitable for high pressures. Compared to an usual diaphragm compressor, service life is higher for reciprocating compressors. Hence, users could realize decreased maintenance charges while using this.
It also helps to decrease energy expenses drastically compared to other units. One of the key highlight of this compressor is that nearly 100% of the energy going into the unit is used as heat loss is trivial.
Cons: They are very noisy, especially the oil- free compressors. It consumes a high volume of oil for air piping and it has a high outlet temperature of compressed air.
The moving parts are vulnerable to problems so it means expensive maintenance. It is vulnerable to dirt and liquid especially the packing, rings, and valves. Also, it has a separate heavy foundation. The mass of concrete required for the foundation can be considerable.
Due to pulsation on the suction and discharge of the machines, pulsation suppression devices are required to dampen the pressure wave amplitudes, which are damaging to the compressor valves and connecting piping.
2. Rotary Compressor
Pros: Efficiency of rotary compressor is high as they are able absorb the refrigerant and compress it concurrently. They are easy to install. They also consists of lower number of mobile parts and lower rotational speeds. They also demand lower initial and maintenance costs which adds to its charm.
They can also work efficiently in unclean atmosphere with ease. It also gives a quiet operation that delivers high volume of air with a steady flow.
You can use it without wearing ear protection.
Compared to piston-type compressors of the same size, it has lower energy cost and is suitable for continuous operation. Rotary compressors can also use energy recovery.
Rotary compressors are very powerful which enables it to supply huge quantity of compressed air.
Cons: They are usually confined to lower gas volume and generate lower pressure compared to other compressor units. Although, it has a lower energy cost, the actual cost to buy a rotary compressor is higher than piston compressors
It is also not suitable for long stand-stills and it has oil carryover. Rotary compressors are difficult to operate in dirty or outdoor environments which also contribute to a short lifespan.
Minimal air use is needed to prevent water condensate forming which will give you rust problems. Rotary compressors exhibit complex designs which implies that they are more prone to failure. Regular maintenance is of utmost importance for this type of compressor.
3. Centrifugal Compressor
Pros: The main advantage of this type of compressor is that there are no valves, pistons, or cylinders. Centrifugal compressors are used widely in the HVAC industry as they consists of lesser rubbing parts. This enables it to provide more better airflow compared to a other compressors of similar size.
They are very efficient and are able to generate high pressures. Centrifugal compressors are desirable for their simple design, few moving parts, and energy efficiency when operating multiple stages.
Cons: One of the main disadvantage of this compressor is that they are unable to attain high compression ratio with single stage. Some one-stage centrifugal compressors could attain pressure ratios greater than 10:1. This if a result of stress concerns which seriously confine the compressor’s security, robustness and longevity.
The wearing parts that need attention though are the main bearings making it a higher investment. It is quite difficult to maintain because of its advanced operational and monitoring systems.
Centrifugal compressors also demand higher investment for effective operation. Advanced operational and monitoring systems, difficult maintenance etc. are some other disadvantages of centrifugal compressors.
4. Screw Compressor
Pros: Screw compressor delivers higher efficiency while working as opposed to other compressor types. They are well-known for delivering huge quantity of compressed air. One of the unique USPs of screw compressor is that noise level is pretty low. You can work in the factory without using any kind of ear protection devices.
This type of compressor is conceived to make possible constant running of the system. They can also last longer and is suitable for greater pressure and flow requirements.
Cons: Screw compressor is quite expensive compared to other types of compressors. Design is bit intricate compared to other models and it also demands more maintenance. Usage of air should be limited to minimum in order to stop the formation of water condensate. Else, it can pave the way to issues like rust on the aircon unit.
Some of the other disadvantages associated with screw compressor is that footprint is larger and it is bulkier as well. It also demands larger HP motors to run the compressor which in turn require higher energy levels. For proper usage, screw compressor often demands system for rectifying its temperature and elimination of moisture.
5. Scroll Compressors
Pros: They are very quiet. Like, really quiet. It is compact as it is smaller than the other types of compressors.
The design is also not as complicated as the other types and it does not have a lot of parts and less torque variation compared to the reciprocating compressor. It has an oil-free design so it means there is hardly any maintenance needed for this type of compressor.
Cooling capacity is higher for scroll compressors and they are widely used in HVAC and refrigeration purposes. Moreover, power requirement is lower for scroll compressors.
Scroll aircon compressors also offer very good cooling capabilities and hence they are widely used in refrigerators and aircons. They can cool more quantity of air rapidly compared to other types of aircon compressors.
Cons: It is relatively expensive especially for a compressor type that has a low capacity. the compressor-element crashes, you may need to consider replacing the whole element itself. The compressed air can become too warm as opposed to other kinds of aircon compressors.