What are Scroll Air Compressors? Definition, Works, Applications

In this article, we will learn all about the scroll air compressors, including definition, how does scroll compressors work, advantages, disadvantages, applications, etc.

Let’s explore!

What are Scroll Air Compressors?

Scroll Air Compressor Basics

Let’s learn the basics of scroll air compressors! When we need to increase the pressure of fluid but at the same time need to increase it by reducing the volume of a fluid, the only component which comes to our mind is the compressor.

  • The compressor works on the principle that when air comes into a tank, it compresses it and builds up pressure, and this pressurized air is then used for various applications.
  • In this blog, we are going to learn about the most efficient and the ones which run quicker and smoother than any reciprocation compressor known as “Scroll Compressor”.

What is Scroll Compressor?

Scrolls compressors are actually positive-direction displacement devices that work on a principle of internal compression. The Intake air is drawn in a tank, trapped in it, then its volume gets reduced, and this high pressurized air is then discharged through an outlet port.

  • This unique concept of scroll-type compressor has been around the corner for more than over a century, but in most recent researches, the scroll compressor became the most common name in the world of compressors. The main reason behind the success of the scroll compressor is its design as well as its intricate and advanced functions.
  • Two main components of scroll compressors are a stationary scroll and one moving scroll. These two scrolls are identical in shape and appearance. Each of the scrolls is accurately manufactured using modern machining technologies, or we can cast in the shape of a spring which is actually involute in shape.
  • The secondary spiralled involute scroll is rotated 180 with respect to the first scroll, and these scrolls mesh with each other. They connected with each other by means of a flat plate and its cover assembly.

Construction of Scroll Air Compressors

  • A scroll Compressor consists of two interleaving meshed spiralled scrolls which are then used to pump the compressed fluid or a pressurized fluid (can be liquid or gas). The design or we can say the geometry of the scroll is involute, and hence it gives accuracy in operation.
  • Both of the scrolls are in contact with each other, although another scroll or secondary scroll is connected eccentrically, and hence these give freedom to rotate each of the scrolls freely in its own path. The eccentricity also allows fluid to get locked tightly between the pockets, and hence its volume gets decreased.
  • This eccentric motion may allow the scroll to move in an orbital path, but the scroll must prevent itself from rotating without a directional guide. To ensure scroll’s safe and function rotation, typically eccentric idler shafts or joints (bellow joints).
  • Sometimes while operating with the scroll compressors, the axial gaps cause leaks. Engineers found the solution to prevent these leaks; these leaks can be prevented by using spiral-shaped seals.
  • Spiral-shaped tip seals were then added to the grooves on both scrolls. These tips are actually amazing in function; they not only stop the leaking in the casing but also reduce the friction between the scroll parts. Also, they can be removed after they wear out. These reduce the cost of replacing the whole construction.
  • The other type of compressors used compressed pressurized gas which can be discharged through the casing, which actually pushes both the scrolls together and hence it tightens the scrolls and stops it from leaking.
  • It also eliminates the cost required for tip seals and increases the life span of the whole assembly. These types of compressors are known as wear-in compressors.

How Do Scroll Compressor work?

  • As we have studied earlier, the moving scroll is fixed on the eccentric path, and actually, it is offset from the centre of the stationary scroll. The motor which we used to drive the whole assembly moves the assembly in a pre-determined orbital circumference.
  • This orbital motion creates a suction that drives the gas from the inlet ports of the compressor. The fluid then gets trapped into moon-shaped pockets between the two spiralled assemblies.
  • The continuous motion of both of the compressors then moves the fluid quietly towards the centre, the volume of fluid is reduced.
  • Due to a reduction in the volume of fluid, the whole fluid gets compressed, and it increases the pressure of the fluid. This pressurized highly compressed fluid then discharges through the outlet port.
  • The design of the discharge port mainly determines the intake capacity of the fluid. Due to its unique design, it allows more compression of the fluid with low consumption of power.
  • The maximum amount of compression capacity mainly depends upon the size, shape, geometry, and thickness of the whole assembly walls.
  • The scroll compressor’s whole tough design intakes more fluid than that of other reciprocating compressors. Its intricate and operational design makes it more functional than a screw compressor. It also generates high pressure around more than 100psi in a single unit.

Efficiency of Scroll Compressors

  • The simplified design of scroll compressors makes them much more efficient. That’s the reason why all the leading industries often go for the scroll compressors for designated special systems to meet all the basic requirements needing from a general compressor. Scroll compressors meet the highest volumetric efficiency level, which is 100% because there are no pistons to compress the gas.
  • Because of the highest volumetric efficiency, it reduced energy costs in many of the applications of compressors. The presence of pistons typically resulted in re-expansion losses, which can be subtracted by using scroll compressors.
  • This high volumetric efficiency is also the by-production of omission of valves because suction valves also do not exist in scroll compressor assembly.
  • During the whole process of fluid compression and discharge, centrifugal force keeps up the continued compression and leads to constant leak-free contact between them. This leads to a reduction in heat transfer loss due to the separation of suction fluid and discharge fluid.

Types of Scroll Compressors

There are two most widely used scroll compressors used in industries,

  • Inverter scroll compressor
  • Digital scroll compressor

Inverter Scroll compressor

An inverter Scroll compressor is considered as the advanced version of the scroll compressor which offers variable speed technology for factory applications in refrigeration and air conditioning.

  • It allows the scroll compressors to make themselves a better place in HVAC. Variable speed technology also comes in role to overcome the problem of variable energy regulations.
  • These inverter scroll compressors are considered the best devices to gain and help to increase the energy standards with high load and high efficiency.
  • It also helps to provide various other key benefits.
  • These inverter scroll compressors also provide some top-notch technologies such as cooling, humidity reduction and management, low torque current, and energy efficiency benefits.
  • It also offers high value to consumers, and it is economical for end users.

Digital Scroll Compressor

A digital scroll compressor is a specially designed compressor that possesses some properties like Scroll compressors which are compressing the fluid to match the required conditions, but it also has a specific mechanical design that helps to match the compressor’s output to the whole process’s cooling needs.

  • These digital compressors can be used in numerous operations such as air conditioning systems, transportation services, and mainly for refrigeration needs.
  • Digital scroll compressor’s simple yet constant modulation concluded in highly precise temperature control.
  • The loads which are actually input for the digital scroll compressors constantly change, and thus digital compressors are designed in such a way that they are highly flexible to match those varying loads.
  • When the temperature is more stable, it is keen to maintain the perfect food storage conditions, which then resulted in better food quality.
  • These digital scroll compressors offer longer life than any other compressors since it reduces the compressor cycling. As energy efficiency is required for refrigeration, the digital scroll compressor overcomes this problem by running at a low time to save energy operations.

Advantages of Scroll compressors

For high-end users, the Scroll compressor can offer numerous benefits.

  • The fewer moving parts for the fluid compression allows the scroll compressors to reach the highest volumetric efficiency, for some cases, it may reach more than 95%, which is much higher than that of any other compressor.
  • Scroll Compressors are very simple in design, and that’s why it makes them easily available everywhere. Due to simplicity in design means, there are very few moving parts, and hence we can conclude them as friction-free.
  • High volumetric efficiency causes low energy consumption; hence, it causes low cost per fuel consumption.
  • Lesser moving parts, lesser vibration, and minimum friction also mean these compressors are durable and hence increases the life span of the device helps the user. Fewer moving parts also add one more advantage; it causes less torque variation during operation. This benefit translated to smooth and quiet during the whole operation.
  • Simpler design, meaning they usually operate at a very low sound and eliminate the vibration level. In research, it is concluded that the scroll compressors are approximately three to four times quieter than that of the other reciprocating compressor models.
  • Elimination of the suction valve resulted in such an amazing feature of smooth operation and next to no vibration.
  • This no sound, no vibration feature of the scroll compressor provides customers with greater flexibility in terms of system design and placement of the whole assembly. It also translates the requirement of the most wanted users’ requirement of the smooth and quiet operation. That’s why researchers have named the scroll compressors as “one of the most significant modern-day new development in the HVAC industry in decades.”
  • Adding more to the point of the fewer moving parts, few moving parts means the whole operation of the scroll compressor is considerably quieter during its whole functional operation than that of the other reciprocating compressors. Let’s understand this with an example; the scroll compressor is usually 5-10 times quieter than that of the other reciprocating compressors.
  • Scroll compressors can be operated as oil-free, oil-free scroll compressors, hence they can run without oil, and thus oil leaks can be avoided.
  • Due to lower voice and low vibration during the operation, it eliminates the need for spring suspension and reduces the cost of the spring suspension assembly. The reduced gas pulsation is one more benefit we get from the elimination of spring assembly.
  • It consumes lower space as it is not bulkier in shape and size also; its weight and footprints are relatively lower.

Disadvantages of the Scroll Compressors

  • As the whole assembly of the scroll compressor is connected to each other, makes it sort of complicated. This is perhaps the biggest disadvantage of scroll compressors, that if it gets damaged during operation or stops working we might need to replace the whole assembly. In simpler words we need to buy whole new assembly, it makes them un-repairable.
  • In the case of many of the reciprocating compressors, they are able to rotate its moving parts in both the direction but in the case of scroll compressors,  we have restrictions to move in both the directions and hence its restricts its applications in some ways.
  • In scroll compressors there are also size restrictions, to a certain limit. Let’s understand this with a simpler example. For a smaller size of scroll compressors, the small leak paths, the small driveways for fluids leads to a smaller discharge port.
  • This smaller discharge port can be problematic up to a certain level since this won’t fulfil the demand for a higher supply of pressurized fluid. By looking at the above points, one may think about for opting large-size compressors but there are also limitations to that.
  • Large sizes of scroll compressors require extensively high centrifugal force to drive the whole assembly. This high centrifugal force can turn out to be damaging for the scrolls and hence it should be avoided.
  • Scroll compressors are a bit pricy as compared to other compressors, as some customized them for premium and intricate options. But this high cost can compensate through low power consumption as well as by lowering the maintenance cost of the overall assembly.

Applications of the Scroll Compressors

Domestic conditioning

The unique characteristics of the scroll compressors meet the basic requirements of the household users of low noise during operation, the small dimension of the whole assembly, and reduction in weight as compared to other reciprocating compressors. It meets the requirement of comfort conditioning.

Also, the single-phase power consumption requirement for starting the compressors can also be fulfilled with scroll compressors, and that’s why they are more preferable to other reciprocating compressors in domestic uses.

Industrial conditioning

The refrigeration capacity of scroll compressors is more than enough to meet the requirements of conditioning required in the industrial sector.

Also, the scroll compressor conditioning is also used in many of the other sectors such as commercial shops, travel agencies, commercial banks, fast food chains, schools, colleges, and many other important sectors.

Water chillers specially used in food industries cannot even do a single operation without using scroll compressors. Its oil-free features provide special benefits to food industries since contamination through oil can be easily avoided.

The transportation industry also accepted the advantages of scroll compressors and since then extensively used them in automobile air conditioning.

Air-conditioning in big computer labs and IT sectors

The large computer-using industries need continuous refrigeration to keep the systems at low temperatures to smoothly carry out the whole operation. The single unit of this sector requires approximately 8000 h/year energy. That’s why it is expected to provide the constant supply at the exchange of constant service. By providing such conditions, we can say that the scroll compressors have a significant favorable effect on energy consumption. This energy consumption is reduced by using a scroll compressor due to its high efficiency.

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Centrifugal compressors: Principles, Operation and design

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The Scroll compressor has been proved itself with its simple design and amazing features as an important part of the HVAC applications. Due to these features, the acceptance of the scroll compressors has been quick, and it created a demand for a huge number of units over the past 3 decades.

Continuous research for the better and better development of the scroll compressor had been a lot of help to prove its reliability. Their distinctly appealing qualities such as their highest volumetric efficiency, noise-free operation, reliability make them a better option than other reciprocating compressors in the market.

Only 2-3 single units of the scroll compressors are enough to run the fully functional single industries like milk processing industries, food industries, grocery refrigeration, marine containers, and domestic air conditioning.


Hello Everyone! We, Rituparna Guha & Firan Mondal, are delighted to present our Mechanical Engineering articles. We will capture all types of articles and try to explain in the simplest way with a lot of diagrams! Happy Reading....

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