Comprehensive Introduction to Chilled Water Systems of Large - scale Central Air - conditioners

Today, let's study the chilled water system in large - scale central air - conditioning systems together.

In an air - conditioning system, it includes the cooling water system, the chilled (refrigerant) water system, and the condensate drainage system.

The function of our water system is to provide cooling and heating for our air - conditioning units.

Air - conditioning chilled water: It is the working medium that transports the cooling capacity prepared by the evaporator to the end - use devices of the air - conditioner through the chilled water pump, also known as refrigerant water.

We can regard the chilled water system of an air - conditioner as the blood circulation of a human body. The pump is equivalent to our heart, which provides power for our system. The water supply system can be seen as our arteries, providing cooling capacity for our air - conditioning units. The end - use devices of each air - conditioner can be regarded as various organs of our body, and the return water of the chilled water can be seen as the veins of our body.

Composition of the air - conditioning chilled water system
In the chilled water system of an air - conditioner, its main components are the water pipe system, the pump, and various accessories, such as pressure gauges, thermometers, valves, filters, air - release valves, expansion tanks, and its water - make - up system, etc.

What does the design of the air - conditioning chilled water system plan include? First, when designing the air - conditioning chilled water system, we need to determine its form selection and zoning, consider adjustment and control measures, as well as the configuration and selection of its auxiliary equipment and accessories. It also includes the layout and direction of the pipe network, as well as the anti - corrosion, insulation, and protection of the pipes.

What factors should we consider when determining the water system plan? First, we need to consider the basic building information, the location of the air - conditioning machine room, the layout of the equipment floor. We also need to consider the selection and zoning of the air - conditioning system, the layout of the pipelines, the reservation of pipe holes, the domestic and fire - fighting water systems, the air - conditioning duct system, electrical systems, and interior decoration, etc., to determine the air - conditioning water system plan.

Types of air - conditioning water systems
When setting up the chilled water system, it can generally be divided into direct - return and reverse - return types according to the layout form of its pipelines.
In the direct - return type, a main total return water pipe is added. Therefore, in the direct - return type, the loops of each user are equal, and the resistance is easy to balance. It is recommended to use this type. In the reverse - return type, the paths that each user takes are different. So, we can generally choose this reverse - return type in small - scale systems. The direct - return type system adds a total return water pipe, so its cost will be increased accordingly.
In the air - conditioning chilled water system, according to whether the pipelines are shared in winter and summer, it can be divided into two - pipe, three - pipe, and four - pipe systems.
According to the form of the pump used, it can be divided into primary - pump and secondary - pump systems.

Configuration and selection of chilled water pumps
Each chiller should be equipped with one chilled water pump. It is advisable to set up one standby pump, which is pre - connected to the pipeline system and can be switched for use at any time.
If there are two chillers, three pumps are usually configured, with one of them being a standby pump that can be switched for use.

If the evaporator has sufficient pressure - bearing capacity, it should be set in the pressure - out section of the pump, which is beneficial to safe operation and maintenance. If the evaporator has a relatively small pressure - bearing capacity, it should be set in the suction section.
Centrifugal clean - water pumps with a rotational speed of 30 - 150 revolutions per second are usually selected. The flow rate should be 1.

1 - 1.2 times the rated flow rate of the chiller (1.1 for a single unit, 1.2 for two units in parallel).
The head of the pump should be 1.

1 - 1.2 times the total water pressure drop of the most unfavorable loop in the supply and return water pipe network.

Configuration and selection of hot water pumps
For a water system that shares cooling and heating, if the cooling and heating water flow rates are the same or do not differ much, the pumps can be shared, but the pumps should be able to withstand a temperature of 60℃.
If the cooling and heating water flow rates differ greatly, the cooling and heating water pumps should be selected separately, or a two - speed pump should be selected.

In summary, the task of the chilled water system is to provide cooling capacity for air - conditioning equipment, which plays a crucial role in the air - conditioning effect. We should comprehensively analyze the building characteristics, initial investment, operating costs, etc., and design and select a reasonable plan.