Differences between a Single Rotary and a Twin Rotary Compressor

As mentioned earlier, ‘twin’ in the twin rotary compressor refers to two compression chambers.
That is the reason it is also known as the dual rotary compressor. Since the rotary compressor compresses through the eccentric motion of the roller; two compression chambers mean two eccentrics, 2 cylinders, 2 rollers and 2 vanes.
Let’s discuss the difference between the single rotary and the twin rotary compressor in detail in the next question.

Down below is an illustration of a single rotary and a twin rotary compressor to make the differences easier to understand for our readers.

As you can see in the picture, three parts— roller, vane and cylinder— are doubled in the twin rotary compressor as compared to the single rotary. However, there is another sub-component whose quantity remains the same, but the structure is changed in a twin rotary compressor. You guessed it right – it’s a crankshaft.

In the structure below the difference between the crankshaft of a twin rotary and a single rotary is clear. As can be observed from the illustration above, there is only one eccentric portion in the single rotary, causing the weight to be inclined toward one side. On the contrary, the twin rotary compressor’s crankshaft has two eccentric portions making it aligned toward the center.

A twin rotary compressor has at least three more components than a single rotary and the crankshaft’s framework is different. But what makes a twin rotary compressor so widely used? There are many advantages to a twin rotary compressor, but today we will discuss its merits in terms of reduced vibration. 

As was discussed in the previous blog, the working principle of a rotary compressor is changing the volume and compressing. To change the volume of the compression chamber, the roller must rotate eccentrically; there is an eccentric component in the crankshaft to rotate the roller eccentrically. There is one problem caused by this eccentric component. Eccentricity literally means that the center is biased to one side, so vibration occurs when the center is not aligned. 

All rotating bodies generate vibrations when they rotate. In particular, single rotary compressors vibrate a lot because there is an eccentric component in the rotating compression chamber. Product developers who use compressors invest a lot of resources in improving this vibration. 

Does that mean the twin rotary compressor doesn’t have an eccentric? No, as you can see it has two eccentrics. Since there are two eccentrics, it is possible for the center to be aligned with the two eccentrics as above.

※ As a reference, the compressor is a part of the outdoor unit.
As mentioned earlier, a compressor compresses the low-temperature, low-pressure refrigerant gas from the evaporator and sends the high-temperature, high-pressure refrigerant gas to the condenser. The pipes in which the refrigerant flows in and out are called suction pipes and discharge pipes, respectively.

Since the vibration value in this area is very important data, compressor manufacturers measure the vibration in the suction pipe and discharge pipe. Below are the vibration measurement values of a single and twin rotary compressor.

It can be seen that the vibration value of the twin rotary compressor is remarkably low. If the vibration is low, from the standpoint of the air conditioner maker, it is possible to reduce the development load by significantly reducing the materials and development manpower needed to lower the vibration.
With the use of a twin rotary compressor, which has significantly lower vibration compared to the single rotary compressor, manufacturers will be able to reduce resources, manpower and materials invested to improve vibration and noise in a given heating or cooling system, giving their final product a more competitive edge.

This time, we looked at the structural differences between the twin rotary compressor and the single rotary compressor and learned about the excellent merits of the twin rotary compressor in terms of reduced vibration resulting from those differences.

Next time, we will be back with another interesting rotary compressor by LG Compressor and Motor.