Principle, composition and failure cases of air conditioning centrifugal chiller

Chiller, also known as freezer, refrigeration unit, ice water unit or cooling equipment, is a device that uses a refrigeration cycle system to provide cooling water or coolant to meet the cooling needs of industry, commerce and some living areas. It absorbs and transfers heat to reduce the temperature of water or other media and is an important part of modern refrigeration technology.

1. Classification of chillers
According to the cooling method: air-cooled chiller; water-cooled chiller;

According to the application temperature range: warm water chiller; low temperature industrial chiller;
According to compressor type: screw chiller; scroll chiller; centrifugal chiller;

2. Principle and structural composition of chiller

Evaporation process: The low-temperature and low-pressure liquid refrigerant absorbs heat from the chilled water (or process water) in the evaporator and evaporates into a low-temperature and low-pressure gaseous refrigerant, thereby cooling the chilled water.

Compression process: The gaseous refrigerant is sucked into the centrifugal compressor. Under the action of the high-speed rotating impeller, the refrigerant gas obtains kinetic energy and converts the kinetic energy into pressure energy through the diffuser, turning it into a high-temperature and high-pressure gas. Centrifugal compressors have the characteristics of compact structure, high efficiency, and are suitable for large cooling capacity occasions.

Condensation process: High-temperature and high-pressure gaseous refrigerant enters the condenser, exchanges heat with cooling water (or air), releases heat and condenses into high-temperature and high-pressure liquid refrigerant.

Throttling process: The high-pressure liquid refrigerant passes through a throttling device (such as an electronic expansion valve or an orifice plate), and the pressure drops suddenly. Part of the liquid flashes into gas, forming a low-temperature and low-pressure gas-liquid mixture, which re-enters the evaporator to complete a complete refrigeration cycle.

The entire system continuously takes away heat from the chilled water by continuously cycling the above four processes, and discharges the heat to the outdoor environment through the cooling water (or cooling tower), thereby achieving a stable cooling effect. Centrifugal chillers are commonly used in large commercial buildings, data centers, hospitals, industrial plants and other places due to their high energy efficiency ratio (COP), large cooling capacity and smooth operation.

3. Structural composition and function description
The centrifugal unit is composed as follows: including centrifugal compressor, evaporator, condenser, throttle orifice plate, oil supply device, control cabinet, etc. The compressor is mainly composed of a suction chamber, an impeller, a diffuser, a bend and a return flow device, and a volute.
Centrifugal compressor: The core of a centrifugal compressor is a high-speed rotating impeller driven by an electric motor or steam turbine.

Evaporator: There are heat exchange tubes inside the evaporator, and the refrigerant evaporates from liquid to gas in these tubes. Low-temperature and low-pressure liquid refrigerant flows through the tube, while the medium to be cooled (such as water) flows outside the tube or directly contacts the refrigerant in the tube through the coil.

Condenser: The condenser also works through the heat exchange process, but contrary to the evaporator, its purpose is to allow the high-pressure and high-temperature gaseous refrigerant to release heat to the external environment

Reason analysis:

Possible factors include: low actual load rate, aging equipment, reduced cooling system efficiency (such as poor cooling tower heat dissipation, water quality scaling), high return water temperature, etc., which together lead to a reduction in the thermodynamic efficiency of the system.

Optimization measures:

Chemically clean the evaporator and condenser of the cold machine to remove dirt on the heat exchange surface;

Implement in-depth maintenance of cooling towers and quality management of circulating water (including corrosion inhibition, scale inhibition, and sterilization treatment);

Calibrate the operating parameters and replenish the appropriate amount of refrigerant to restore the optimal charge.

Shanghai KUB Refrigeration Equipment Co., Ltd.

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