What Type of Compressor is Used in Air Conditioner

Figure 1: An air conditioner compressor.

The compressor is the core component of the air-conditioning refrigeration system, and it plays the role of compressing and driving the refrigerant in the air-conditioning refrigerant circuit.

The compressor in the air conditioner generally adopts a fully enclosed structure, and the motor as the driving force and the compressor that compresses the refrigerant are hermetically sealed in a container, which is equipped with lubricating oil and a lubricating mechanism to make it run smoothly.

1. How an Air Conditioner Compressor Works

The air conditioner compressor extracts the refrigerant from the low-pressure area, compresses it, and then sends it to the high-pressure area for cooling and condensation. The heat is released into the air through the heat sink, and the refrigerant also changes from gaseous to liquid, and its pressure increases.

The air-conditioning compressor keeps working, and it continuously absorbs the heat at one end of the low-pressure area into the refrigerant, and then sends it to the high-pressure area to radiate into the air, which plays a role in regulating the temperature.

2. Different Types of Compressors in Air Conditioner

2.1 Reciprocating AC Compressor

Reciprocating piston compressors, also known as connecting rod piston compressors, refer to a type of positive displacement compressor that rely on one or several reciprocating pistons to change the internal volume of the compression chamber.

As shown in the figure below, both the motor and the compressor are placed in the casing, and the compressor is mainly composed of a cylinder, piston, crankshaft, connecting rod and other components. This kind of compressor generally uses eccentric pressure to deliver lubricating oil, and the working process of compressing gas can be divided into four processes: expansion, suction, compression and exhaust.

Figure 2: Reciprocating Piston compressor structure diagram.

2.2 Scroll AC Compressor

A scroll compressor is a compressor with a compressible volume composed of a fixed scroll and an orbiting scroll (a scroll that is eccentrically orbiting).

As shown below, a scroll compressor is mainly composed of a scroll stator, scroll rotor, anti-rotation mechanism, crankshaft, bracket, casing and so on. During the working process of suction, compression and exhaust, the fixed scroll is fixed on the frame, and the orbiting scroll is driven by the eccentric shaft, so that it rotates in a plane with a small radius around the center of the base circle of the fixed scroll.

The compressible medium enters the crescent-shaped compression chamber formed when the orbiting scroll and the fixed scroll mesh from the outside of the scroll body, and is gradually compressed, and finally discharged through the center hole of the fixed scroll, realizing a relatively continuous air supply mode.

Figure 3: Scroll compressor structure diagram.

The scroll compressor has small torque change, high balance, small vibration and more stable operation. The representative manufacturers are Hitachi and Daikin.

2.3 Screw AC Compressor

In the "∞"-shaped cylinder, two helical rotors that rotate in opposite directions according to a certain transmission ratio and mesh with each other are arranged in parallel. Usually, a rotor with convex teeth outside the pitch circle is called a male rotor (customarily called a driving rotor); a rotor with concave teeth inside a pitch circle is called a female rotor (customarily called a driven rotor).

Figure 4: Sectional view of a screw compressor.

Generally, the male rotor (or through the speed-increasing gear set) is connected with the prime mover, and thus the power is input; the male rotor (or through the synchronous gear set) drives the female rotor to rotate.

The main components of the screw compressor are: a pair of rotors, the body, bearings, synchronous gears (and sometimes speed-increasing gear set), and sealing components. According to different operating modes, screw compressors can be divided into oil-free compressors and oil-injected compressors.

2.4 Rotary AC Compressor

Rotary compressor is also known as rolling piston (rolling rotor) compressor, rotary piston compressor. The rotary piston installed in the cylinder performs rolling motion in the cylindrical cylinder and a slide vane in contact with it does reciprocating motion, achieving gas compression.

As shown in the figure below, the rolling piston compressor is generally a vertical structure, the motor is installed in the upper part of the shell, and the compressor is installed in the lower part. The compressor is mainly composed of a cylinder, a rolling piston, a crankshaft and a fixed frame.

Figure 5: Rolling piston compressor structure diagram.

2.5 Single Rotary Compressor

Single rotary compressors, that is, rolling piston compressors, are favored by many manufacturers due to their relatively low manufacturing costs and relatively high performance.
However, single rotary compressors have two prominent shortcomings. When used in a system with relatively large power, due to the problem of rotor resonance, it will generate large vibration and noise. Second, there are several core components in the single rotary compressor during use, such as sliding vanes and exhaust valves, which are vulnerable parts, affecting the repair rate of the compressor.

Generally speaking, single rotary compressors are generally used in systems with less than 5 hp, such as used in air duct machines and some low-end multi-pipe machines. Relatively good single rotary compressor manufacturers are Mitsubishi Electric and Panasonic.

Figure 6: Common air conditioner rotary compressor.

2.6 Swing Compressor

Swing compressor is an enhanced mode of the single rotary compressor, which increases the service life of the wearing parts of the rotor compressor by changing the form of the sliding vane inside the compressor.

Its advantages is that it is simple and durable, and the disadvantage is that the frequency is reduced in order to reduce noise, resulting in a decrease in the cooling and heating effect. Now it is mostly used in multi-pipe machines with 6 hp or less. The representative manufacturer is Daikin.

Figure 7: Rolling piston compressor vs swing compressor.

2.7 Twin Rotary Compressor

It is the 2.0 version of the single rotary compressor. It adds a compression cylinder and makes the rotor in the new compression cylinder form a 180-degree angle with the original rotor. Therefore, when the compressor is running, the centrifugal force generated by the eccentricity of the two rotors can be offset. Through this offset principle, the twin rotary compressor reduces the vibration and noise problems.

This is also a form of compressor that is mostly used in household central air conditioners. The advantage is that the energy efficiency ratio is high, and the energy saving is better than that of the scroll compressor when the indoor units of the whole house are not switched on at the same time; the performance is reliable and stable,

The disadvantage is that when all the indoor units are turned on, the power consumption is greater than that of the scroll compressor. Therefore, generally speaking, the twin rotary compressor is more advantageous when it is not in the commercial full-on mode. It is more appropriate to choose a twin rotary compressor for a single external unit with 12 hp or less. Representative manufacturers are Toshiba, Panasonic, Mitsubishi Electric.

Figure 8: Cutaway view of twin rotary compressor.

2.8 Rotary Vane AC Compressor

As the name suggests, the rotary vane compressor relies on the eccentric rotor and one or more vanes sliding in the rotor groove to perform rotary motion in the cylindrical cylinder to achieve gas compression.

As shown in the figure below, the rotary vane compressor is mainly composed of three parts: the body, the rotor and the vanes. The rotor with the movable vanes is eccentrically arranged in the cylinder.

When the rotor rotates, due to the centrifugal force, the sliding vanes cling to the inner wall of the cylinder, forming a number of volumetric elements composed of the inner wall of the cylinder, the outer wall of the rotor, and the sliding vanes. As the volumetric elements change repeatedly and continuously from small to large and from large to small, the cycle process of suction, compression and exhaust is completed.

Figure 9: Rotary vane compressor structure diagram.

2.9 Centrifugal AC Compressor

The centrifugal refrigeration compressor works on the gas through the high-speed rotating impeller to increase the flow rate, and then decelerates the gas through the diffuser, converting the kinetic energy of the gas into pressure energy. So the pressure of the gas is correspondingly increased.

Centrifugal refrigeration compressors have the characteristics of large cooling capacity, small size, and stable operation, and are mostly used in large-scale air conditioning systems and petrochemical industries.

Centrifugal refrigeration compressors are divided into two types: single-stage and multi-stage compression. According to the connection mode between the compressor and the motor, it can also be divided into open type and semi-hermetic type.

3. Which Type of Compressor is Best for an Air Conditioner?

If the capacity of the air conditioning unit is small, such as 10KW, the rotary compressor is the best. However, if the air conditioning unit has a medium capacity, from 10KW to 50KW, scroll compressors are more suitable.

In high-power air-conditioning systems, especially for commercial use with large horsepower, scroll compressors are often used, while in low-power, especially outdoor units with 8 horsepower or less, twin rotary compressors are more suitable. is common.

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