The Differences between a Scroll Compressor and a Rotary Compressor

Scroll and rotary compressors are built differently and that is why they operate differently. The key difference between both compressors is their mechanical structure and design.

A rotary compressor’s compression chamber is located at the bottom of the compressor, whereas in a scroll compressor, it is located at the top.

A scroll compressor can further be divided into smaller subcomponents such as a fixed scroll, an orbiting scroll, a motor, bypass valves, a thermal protector, an internal pressure relief valve, a discharge check valve, an overload protector, etc.

Components such as a thermal protector, internal pressure relief valve, discharge check valve, and overload protector protect the compressor from potential damage.

On the other hand, a rotary compressor consists of a cylinder, an accumulator, a main bearing and a sub-bearing, a crank shaft, a roller, and a vane.

It can easily be observed that a rotary and a scroll compressor do not share any components except for a motor. The biggest difference between a scroll and a rotary compressor is the mechanical structure.

A difference in structure signifies a difference in the working mechanism as well. Both compressor types have different components making their operation mechanism different from each other.

In a scroll compressor, compression of the refrigerant takes place inside the scroll wrap with the help of scrolls. In contrast to this, a rotary compressor compresses refrigerant inside its compression chamber with the help of the rotary motion of the roller and vertical movement of the vane. A scroll compressor compresses continuously, but refrigerant is only compressed on completion of one rotation in a rotary compressor.

A scroll compressor compresses using the circular motion of the scroll, but a rotary compressor compresses by changing the volume of refrigerant via an eccentric motion of the roller.
As mentioned earlier, a scroll compressor has a torque fluctuation of 50% because, unlike a rotary compressor, it performs continuous compression. For that reason, it is superior in terms of low vibration and noise.

To get a better idea of the differences in compression mechanisms, let’s take a look at how both compressors compress the refrigerant.
In the case of a scroll compressor, the fixed scroll and orbiting scroll are interlocked and the orbiting scroll moves in a circular motion to compress the refrigerant flowing inside the wrap. In this manner, the temperature and pressure of the refrigerant is increased.

Whereas, a rotary compressor, the roller moves eccentrically inside the cylinder to change the volume of refrigerant.

Although, unlike the scroll compressor— where the refrigerant is directly sucked into the compression chamber (scroll wrap)— in a rotary compressor, refrigerant is not directly sucked into the compression chamber, and has to pass through the accumulator first. The accumulator acts as a filter and filters out impurities from the refrigerant.

A compressor is one of the most important parts of an air conditioner, and it is very important to select a compressor that matches your system’s requirements.

Since compressors generally have a great impact on an air conditioner’s capacity, noise and vibration, a compressor should be selected considering its performance in these three areas.

As we discussed above, a rotary compressor and a scroll compressor have different compression mechanisms, and the load varies depending on it. Because scrolls have typically 50% less load than rotary compressors, noise and vibration issues are alleviated. Lesser vibration means it can be designed into a compressor of higher capacity.

From the cost point of view, rotary compressors have leverage because the number of parts is fewer and the working mechanism is simpler compared to scroll compressors. For this very reason, rotary compressors are more competitively priced compared to scroll compressors. Air conditioner manufacturers should select a compressor suitable for their requirements.

From our observations so far, it can be concluded that both compressors have their pros and cons and are suitable for different uses.
In conclusion, the selection of an appropriate compressor depends on the user's specific needs and environment. It is always a good idea to consult a compressor specialist who can guide you in the right direction.