The Basics of a Rotary Compressor

A Rotary compressor, as the name suggests, uses a rotary-type positive-displacement mechanism. The rotary compressors use rotary movements to compress the refrigerant.

Let’s take a look inside the Rotary Compressor. Unlike the Scroll Compressor, you can see that there is a cylindrical accumulator, in addition to the body of the compressor. Rotary Compressor is composed of a body and an accumulator. The body can be divided into two parts: an electrical section where the motor is located, and a mechanical section where the compressor is situated.

The compressor compresses the low-temperature, low-pressure refrigerant gas that has passed through the evaporator (which discharges cold air) into a high-temperature, high-pressure gas.

The refrigerant that has passed through the evaporator should be a low-temperature gaseous state refrigerant, but in some situations, the refrigerant in a liquid state may not evaporate and might reach the compressor in liquid state.

It should be noted that liquids are almost incompressible. In other words, liquid refrigerant is not compressed in the compressor; if the compressor tries to compress a liquid refrigerant, it causes damage to the system.

In order to prevent the compressor from this damage, an accumulator with an appropriate capacity is selected when designing a compressor.

The refrigerant from the evaporator is not directly sucked into the compression chamber of the compressor; instead, it passes through the accumulator first. The accumulator helps the liquid refrigerant evaporate before being sucked into the compression chamber.

Also, the compression chamber of the compressor is assembled with extremely fine detail. The accumulator also has a filter that prevents foreign objects from entering the compression chamber. You can think of it as a strainer but for a compressor.

In a nutshell, the accumulator converts liquid refrigerant which has passed through the evaporator into low-temperature and low-pressure gas.

As we learned above, the compression chamber compresses low-temperature, low-pressure refrigerant gas that passed through accumulator into high-temperature, high-pressure refrigerant gas

A rotary compressor compresses the refrigerant by changing its volume.

To understand the operation of a rotary compressor, let’s take a look at the pictures below.
In the first picture, the two circles are concentric, whereas in the second picture, the two circles are eccentric.

In the first figure, even if the inner circle rotates, the volume of space A does not change.
In the second picture, since the inner circle and the outer circle are eccentric, when the inner circle rotates, the volume decreases from space A to space A’ and the pressure rises.

A very common example of this principle can easily be found in our daily lives; when we press a sealed snack packet from the store, the pressure inside the packet rises, and the packet bursts open when the pressure exceeds a certain level.

The compression chamber consists of the following sub-components: cylinder, main bearing and sub-bearing that seal the cylinder from above and below, crank shaft that transfers electrical energy from the motor to the compression chamber, roller that rotates along the eccentric orbit of the shaft and changes the volume of the compression chamber, and the vane that separates the low-pressure chamber from the high-pressure chamber.

The motor consists of a stator and a rotor. It receives electrical energy from an outside source, and converts it into kinetic energy required by the compression chamber of the compressor to compress the refrigerant.

This time we learned about the basics of the rotary compressor, widely used in residential air conditioners. The compressor used as an example in this article was a single rotary compressor with one compression chamber (meaning one cylinder).

Next time, we will be back with a twin rotary compressor which has 2 compression chambers.