Working principle of air conditioning system Switching on and off operation process of chiller

1. Working principle of air conditioning system

In the steam compression refrigeration system, the compressor, condenser, throttling device and evaporator are four essential components.

Evaporator: a device for transporting cold air, in which the refrigerant absorbs the heat of the cooled object to achieve evaporative cooling; Compressor: the heart of the refrigeration system, which plays the role of absorbing, compressing and transporting refrigerant vapor; Condenser: a device that releases heat, which transfers the heat absorbed in the evaporator together with the heat converted by the power consumption of the compressor to the cooling medium; Throttling device: The refrigerant has a throttling and pressure-reducing effect, while controlling and adjusting the amount of refrigerant liquid entering the evaporator, and dividing the system into two major parts: the high-pressure side and the low-pressure side.

In the actual refrigeration system, in addition to the above four major parts, there are also some auxiliary equipment, such as:

Solenoid valve;

One-way valve;

Distributor;

Filter drier;

Temperature sensor;

Pressure controller;

.........

And other components are set up to improve the safety, reliability and economy of the refrigeration and air-conditioning system.

2. Classification of air conditioner host types

Water-cooled chiller air-conditioning unit: uses water as the cold and heat source, and its condensing side is a water heat exchanger, which needs to work through a cooling water circulation pump and be used in conjunction with a cooling tower.

Air-cooled chilled water air conditioning unit: uses ambient air as the cold and heat source, and the condensing side of the main unit is operated by a fin-tube heat exchanger plus a fan motor.

Multi-split air conditioning unit: The multi-split system is simple, and only requires the use of refrigerant copper pipes to connect the indoor and outdoor units; the refrigerant and air exchange heat directly, so the heat exchange efficiency is high. Each room can be controlled separately.

Air-cooled scroll heat pump unit: It has its own fan to release heat to the air, and a scroll compressor to provide hot and cold water. It can generally be combined with multiple modes for expansion. The heat pump unit can achieve cooling and heating through the reversing of the four-way valve of the refrigeration system. The air-cooled scroll chiller has no four-way valve and can only provide cooling.

Water-cooled centrifugal chiller: Water-cooled: no air-cooled heat dissipation, heat is indirectly discharged to the atmosphere through circulating cooling water through cooling tower; Centrifugal: centrifugal compressor is used, and the capacity is usually above 500RT; Chilled water: cold water is produced and discharged to the circulating chilled water, and the refrigerant is only circulated in the main engine. Water-cooled screw chiller: Water-cooled: no air-cooled heat dissipation, heat is indirectly discharged to the atmosphere through circulating cooling water through cooling tower; Screw: screw compressor is used, and the capacity is usually below 500RT; Chilled water: cold water is produced and discharged to the circulating chilled water, and the refrigerant is only circulated in the main engine. Water-cooled vortex chiller: Water-cooled: no air-cooled heat dissipation, heat is indirectly discharged to the atmosphere through circulating cooling water through cooling tower; vortex: vortex refrigeration compressor is used; Chilled water: cold water is produced and discharged to the circulating chilled water, and the refrigerant is only circulated in the main engine.

3. Operation process of turning on and off the chiller Pre-startup inspection 1. Check whether the voltage is within the rated value ±10%; 2. Check whether the unit has any faults and whether the signal indicators are normal; 3. Check and ensure that the chilled water and cooling water inlet and outlet valves of the chiller are open; 4. Check whether the relevant inlet and outlet valves of the chilled water pump, cooling water pump, cooling tower, etc. are open; 4. Check whether the pressure of the water system and the water replenishment facilities are normal; Startup 1. Start more than 1/3 of the number of air-conditioning terminals corresponding to the units; 2. Turn on the cooling tower fan; 3. Start the chilled water pump and cooling water pump corresponding to the unit. After starting, confirm whether the chilled water and cooling water inlet and return water pressures and pressure differences are within the qualified range; 4. Reference value of water inlet pressure chilled water: 0.24~0.32MPa; 5. Reference value of cooling water: 0.15~0.24MPa; 6. Reference value of inlet and return water pressure difference: about 0.05MPa; 7. Turn on the unit. After the compressor is started, the main control parameters such as the unit's operating current, evaporator pressure, condenser pressure, etc. need to be continuously observed during the loading process. Wait until all main control parameters are stable and normal, and the unit has no abnormal vibration, noise or abnormal odor before leaving the machine room.

Shutdown 1. When a shutdown command occurs, the chiller will automatically unload and shut down; 2. After the compressor stops, stop the chilled water pump, cooling water pump, and cooling fan after 5 minutes. 3. After all are shut down, the compressor should continue to preheat; 4. In case of abnormality, the unit can be shut down using the emergency stop button; 5. Gradually shut down the air conditioner terminal. Seasonal shutdown In winter or when the temperature is extremely cold, the host and the chilled/cooling water pump should be protected from freezing; the inlet and outlet of the host condenser and evaporator should be closed, the drain valve and the vent valve should be opened, and the remaining water should be blown clean with compressed air, and the cooling water and chilled water pipelines should be drained.

Note: In actual operation, there are often the following misoperations: 1. When starting up, the inlet and outlet water valves on the evaporator of the non-starting unit are not closed first, causing part of the cold water to flow out of the evaporator of the non-starting unit, affecting the refrigeration effect of the unit under working condition. 2. Before starting up, the inlet valve of the condenser on the unit that does not need to be turned on is not closed, causing water leakage. Part of the cooling return water flows out of the condenser of the non-starting unit, reducing the cooling water flow in the condenser of the running unit, causing the condensation pressure to rise. The operating current of the host increases. The cooling capacity of the unit decreases, and in severe cases, the unit will stop running. It not only wastes electricity, but also reduces the refrigeration effect and easily damages the equipment. 3. Due to the previous misoperation, the condensation pressure and cooling water outlet temperature of the host increase. It causes misjudgment to the operator. The condenser inlet valve and cooling water pump outlet valve are opened because it is mistakenly believed that there is not enough cooling water, and some even increase the cooling tower fan, causing the water pump and cooling tower fan to consume more power. 4. Blindly add a cooling water pump. Although adding cooling water pumps can indeed reduce the cooling water temperature and condensing pressure, the electricity used to run a water pump is wasted after all.

3. Common alarm troubleshooting and cases