Water Cooled Unit Principle of Operation and Parameter Failure Analysis

I. Working Principle and System Composition of Chiller Units
Chiller units are the refrigeration source and "heart" of central air conditioning. The circulating water to various rooms undergoes "internal exchange" in the chiller unit and is cooled down to "cooling water". It consists of a refrigerator, a cooling water circulation system, a chilled water circulation system, a fan coil system, and a cooling tower.
Working principle: The refrigerator compresses the refrigerant into a liquid state through a compressor and then sends it to the evaporator for heat exchange with chilled water, cooling the chilled water.

The chilled water pump sends the chilled water to the cooling coils at the air outlets of each fan, and the fan blows it to achieve the purpose of cooling. The refrigerant after evaporation releases heat and becomes gaseous in the condenser. The cooling pump sends the cooling water to the cooling tower, where the tower fan sprays and cools it, conducts heat exchange with the atmosphere, and dissipates heat into the atmosphere.
The external heat exchange system consists of two circulating water systems: the chilled water circulation system and the cooling water circulation system.
Chilled water circulation system: It consists of a chilled water pump and chilled water pipelines. The chilled water flowing out of the chiller unit is pressurized by the chilled water pump and sent into the chilled water pipelines. Heat exchange occurs in each room, taking away the heat in the room and lowering the temperature in the room.
Cooling water circulation system: It consists of a cooling pump, cooling water pipelines, and a cooling tower. When the chiller unit conducts heat exchange, while cooling the water temperature, it will inevitably release a large amount of heat. This heat is absorbed by the cooling water, raising the temperature of the cooling water. The cooling pump presses the heated cooling water into the cooling tower, where it conducts heat exchange with the atmosphere in the cooling tower. Then, the cooled cooling water is sent back to the chiller unit. This continuous circulation takes away the heat released by the chiller unit.
The fans of chiller units can be divided into two types:
Indoor fan: Installed in the room that needs cooling. It is used to blow the air cooled by chilled water into the room to accelerate the heat exchange in the room.
Cooling tower fan: Used to lower the water temperature of the cooling tower and accelerate the dissipation of the heat brought back by the "return water" into the atmosphere.
II. Operating Parameters and Common Fault Analysis of Chiller Units
Different types and the same type but different models of units, due to their own working principles and different refrigerants used, have more or less differences in operating parameters and operating characteristics. Understanding and mastering the normal operating signs and refrigeration capacity adjustment methods of the managed chiller units is the basis for mastering and using the unit well. For chiller units in operation, the following situations mainly need to be paid attention to:
The temperature and pressure at the inlet and outlet of chilled water in the evaporator;
The temperature and pressure at the inlet and outlet of cooling water in the condenser;
The pressure and temperature of the refrigerant in the evaporator;
The pressure and temperature of the refrigerant in the condenser;
The current and voltage of the main motor;
The pressure and temperature of the lubricating oil;
Whether the compressor unit operates smoothly and whether there is any abnormal noise;
Whether there is any leakage in each valve of the unit;
Whether the joints with each water pipe are tight.
Also pay attention to some appearance manifestations of the chiller unit. For example, if the suction pipe of the compressor is frosted, it indicates that the refrigeration capacity of the chiller unit is too large, the evaporation temperature is too low, the suction superheat of the compressor is small, and the suction pressure is low.
For piston units and screw units, it will cause "liquid hammer"; for centrifugal chiller units, it will cause surging.
In addition, you can also touch various parts and pipelines of the chiller unit, such as gas pipes, liquid pipes, water pipes, oil pipes, etc., and feel the working temperature and vibration of the compressor; the inlet and outlet temperatures of the two heat exchangers; the oil stains and distribution at the pipeline joints.
Under normal circumstances, the compressor operates smoothly, the temperature difference between suction and discharge air is large, and the temperature rise of the unit body is not high; the condensation temperature is high, and the temperature difference between the inlet and outlet of cooling water is large; there is no refrigerant leakage at each pipeline joint, so there is no oil stain, etc.; any performance opposite to the above situation means that there are fault factors in the corresponding parts.
You can also listen to whether the overall sound of the chiller unit during operation conforms to the normal working sound law. The key is to listen for abnormal sounds from equipment such as solenoid valves and throttle valves in systems such as compressors, lubricating oil pumps, and chiller units.

For example, if a slight "rustle, rustle, rustle" sound or a continuous and uniform light "buzz, buzz" sound is heard from the compressor during operation, it indicates that the compressor is operating normally; if a "thump, thump, thump" sound or a rotating sound of the impeller that is sometimes fast and sometimes slow, or an abnormal vibration sound is heard, it indicates that the compressor has experienced liquid hammer or end vibration.
When there is a problem with the chiller unit, comprehensive analysis should be conducted on the data and materials obtained from relevant indicating instruments and through observation, listening, and touching of the chiller unit's operation to find out the basic cause of the fault and consider what emergency measures should be taken.