Working principle, composition and fault analysis of water chillers

The refrigeration chiller consists of three interrelated systems: a refrigerant circulation system, a water circulation system, and an electrical automatic control system.
1) Refrigerant circulation system:
The liquid refrigerant in the evaporator absorbs heat from the water and begins to evaporate. The liquid refrigerant also completely evaporates into a gaseous state, which is then sucked in and compressed by the compressor. The gaseous refrigerant absorbs heat through the condenser and condenses into a liquid. After being throttled by a thermal expansion valve (or capillary tube), it becomes a low-temperature low-pressure refrigerant and enters the evaporator, completing the refrigerant circulation process.
2) Basic composition of the refrigeration system:
Compressor: The compressor is the core component in the refrigeration system, which is used to convert the input electrical energy into mechanical energy and compress the refrigerant.
Condenser: During the refrigeration process, the condenser serves to output heat energy and condense the refrigerant. After the high-pressure superheated steam discharged from the refrigeration compressor enters the condenser, the heat absorbed from the evaporator and refrigeration compressor as well as in the pipeline is transferred to the surrounding medium (water or air) and taken away; The refrigerant high-pressure superheated vapor recondenses into a liquid.
Liquid receiver: The liquid receiver is installed behind the condenser and is directly connected to the discharge pipe of the condenser. The refrigerant liquid of the condenser should flow smoothly into the reservoir, so that the cooling area of the condenser can be fully utilized. On the other hand, when the heat load of the evaporator changes, the demand for refrigerant liquid also changes. At that time, the liquid reservoir plays a role in regulating and storing refrigerant.
Drying filter: During the refrigeration cycle, it is necessary to prevent the entry of water and dirt (oil, iron, copper). If the water in the system is not completely discharged, when the refrigerant passes through the throttle valve (thermal expansion valve or capillary tube), sometimes the water will solidify into ice due to the drop in pressure and temperature, causing channel blockage, affecting the normal operation of the refrigeration device.
Thermal expansion valve: In refrigeration systems, thermal expansion valve is both a flow regulating valve and a throttle valve. It is installed between the drying filter and the evaporator in refrigeration equipment, and its temperature sensing package is wrapped at the outlet of the evaporator. Its main function is to throttle and depressurize the refrigerant liquid at high pressure and normal temperature when flowing through the thermal expansion valve, and turn it into a low temperature and low pressure refrigerant wet vapor (which enters the evaporator and vaporizes and absorbs heat in the evaporator to achieve the purpose of refrigeration and cooling.
Evaporator: Evaporator is a heat exchange device that relies on the evaporation of refrigerant liquid to absorb the heat of the cooled medium. Its function in a refrigeration system is to absorb heat (or output cold energy). In order to ensure a stable and lasting evaporation process, it is necessary to continuously use a refrigeration compressor to extract the evaporated gas to maintain a certain evaporation pressure.
Refrigerant: NTC uses R22 as the refrigerant. Its function is to carry heat and achieve heat absorption and release when the state changes.
3. Water circulation system:
The water circulation system is a device where water is pumped from the water tank to the user for cooling by a water pump. After the heat is taken away by the chilled water, the temperature rises and it returns to the chilled water tank.
4. Electrical automatic control system:
The electrical automatic control system includes a power supply part and an automatic control part.
The power supply part supplies power to the compressor, fan, water pump, etc. through a contactor.
The automatic control part includes a temperature controller, pressure protection, time delay device, relay, overload protection, etc., which are combined to achieve automatic start and stop, protection, and other functions according to the water temperature.
3) Maintenance of water chillers:
The compressor of a refrigeration unit is a very critical component in the unit. The quality of the compressor directly affects the stability of the unit, so regular maintenance is required. Common maintenance includes:
1. Replace the lubricating oil
After long-term use of the refrigeration unit, the oil quality of the lubricating oil deteriorates, and impurities and moisture in the oil increase. Therefore, it is necessary to regularly observe and check the oil quality. Once problems are found, they should be replaced in a timely manner. The brand of the replaced lubricating oil must comply with the technical data.
2. Replace the drying filter
The drying filter is an important component to ensure the normal circulation of refrigerant. Due to the incompatibility between water and refrigerant, if the system contains water, it will greatly affect the operating efficiency of the unit. Therefore, it is important to keep the system dry inside, and the filter element inside the drying filter must be replaced regularly.
3. Calibration of safety valve
The condenser and evaporator on the water chiller are both pressure vessels. According to regulations, a safety valve should be installed on the high-pressure end of the unit, that is, the condenser body. Once the unit is under abnormal working conditions, the safety valve can automatically relieve pressure to prevent possible harm to human body caused by high pressure. Therefore, regular calibration of safety valves is very important for the safety of the entire unit.
4. Condenser and evaporator cleaning
As the cooling water of a water cooled condenser is an open circulating circuit, the tap water commonly used is recycled through a cooling tower. When the content of calcium and magnesium salts in water is large, it is extremely easy to decompose and deposit on the cooling water pipes, forming scale, affecting heat transfer. Excessive scaling can also reduce the flow cross-section of cooling water, reduce water volume, and increase condensation pressure. Therefore, when the quality of the cooling water used is poor, clean the cooling water pipes at least once a year to remove scale and other contaminants from the pipes. There are generally two methods for cleaning condenser water pipes:
Use a special pigging gun to clean the pipe.
Use a special cleaning agent for circulating flushing, or fill it with cooling water, and wait for 24 hours before changing the solution until it is completely cleaned.