The central air-conditioning system can be divided into three categories: the central air-conditioning water system, the fluorine system, and the air system. The central air-conditioning water system uses water as the refrigerant and is larger than the traditional fluorine system. The central air-conditioning water system is generally used in large buildings and is energy-efficient when the simultaneous startup rate is above 90%. American brands account for the main share of the market, mainly targeting the commercial market. The water system type is a small semi-centralized fan coil system, where all the indoor loads are borne by the chilled and hot water units. The fan coils in each room are connected to the chilled and hot water units through pipes, and they use the provided chilled and hot water for cooling and heating. The water system has a flexible layout, good independent adjustment performance, and a very high level of comfort. It can meet the needs of dispersed use in complex room types and the independent operation of each room. In addition, the current new type of water system air conditioner is also one of the best solutions for the application of the floor heating system. Through the effective combination with the floor heating, the method of large-area low-temperature radiant heating with medium and low water temperatures is adopted, which is more comfortable and energy-efficient than the traditional fan coil heating system. A typical central air-conditioning unit is mainly composed of three parts: the chilled water circulation system, the cooling water circulation system, and the main unit:
1. Chilled Water Circulation System
This part is composed of a chilled water pump, indoor fans, and chilled water pipes, etc. The low-temperature chilled water flowing out from the evaporator of the main unit is pressurized by the chilled water pump and sent into the chilled water pipes (outlet water), enters the room for heat exchange, takes away the heat in the room, and finally returns to the evaporator of the main unit (return water). The indoor fans are used to blow air over the chilled water pipes, reduce the air temperature, and accelerate the indoor heat exchange.
2. Cooling Water Circulation Part
This part is composed of a cooling water pump, cooling water pipes, a cooling tower, etc. While the chilled water circulation system conducts indoor heat exchange, it will inevitably take away a large amount of heat energy from the room. This heat energy is transferred to the cooling water by the refrigerant in the main unit, causing the temperature of the cooling water to rise. The cooling water pump presses the heated cooling water into the cooling tower (outlet water), making it exchange heat with the atmosphere, and then sends it back to the condenser of the main unit (return water) after the temperature is reduced.
3. Main Unit
The main unit part is composed of a compressor, an evaporator, a condenser, and the refrigerant, etc., and its working circulation process is as follows:
First, the low-pressure gaseous refrigerant is pressurized by the compressor and enters the condenser, gradually condensing into a high-pressure liquid. During the condensation process, the refrigerant will release a large amount of heat energy. This part of the heat energy is absorbed by the cooling water in the condenser and sent to the outdoor cooling tower, and finally released into the atmosphere. Subsequently, when the high-pressure liquid refrigerant in the condenser flows through the throttling and pressure-reducing device in front of the evaporator, it vaporizes due to the sudden change in pressure and forms a gas-liquid mixture that enters the evaporator. The refrigerant continuously vaporizes in the evaporator, and at the same time, it will absorb the heat in the chilled water to make the chilled water reach a lower temperature. Finally, the vaporized refrigerant in the evaporator becomes a low-pressure gas again and re-enters the compressor, and so on in a cycle.