Why does the Water System of Central Air Conditioning Require Constant Pressure Water Make-up System

1. Why does the Water System of Central Air Conditioning Require Constant Pressure Water Make-up System?

1) Constant pressure is to stabilize the system pressure and prevent cavitation in the pump. Replenishing water is because the system water may be leaking or something.

2) There are several types of constant pressure make-up systems: expansion tank water make-up system and expansion tank (floor-standing) water make-up system, etc.

2. Working Principle of Constant Pressure Water Make-up System

The constant pressure water make-up system uses the system static pressure as the designed initial pressure head in the expansion water tank, and uses the pressure that ensures that the hot water in the system does not vaporize as the terminal pressure head in the expansion water tank. During the initial operation, the water replenishing pump is first started to fill the system and the water chamber in the air pressure tank. After the system is full, the excess water is squeezed into the capsule. Because of the incompressibility of water, as the amount of water continues to increase, the volume of the water chamber continues to expand and when the air chamber is compressed, the pressure inside the tank also continues to increase. When the pressure reaches the design pressure, the water replenishing pump is shut down through the pressure controller. When the water in the system expands due to heat and the system pressure rises above the design pressure, the excess water is discharged to the water replenishment tank through the safety valve for recycling. When the water in the system shrinks in volume due to leakage or temperature drop, and the system pressure decreases, the capsule The water in the system is continuously pressed into the pipe network to supplement the pressure drop loss of the system. When the system pressure reaches the lowest pressure allowed by the design, the pressure controller restarts the water replenishing pump to replenish water into the pipe network and the air pressure tank, and so on.

3. Three Common Central Air Conditioning Constant Pressure Water Make-up System

1) Atmospheric Tank Constant Pressure Water Make-up System

Working Principle of Atmospheric Tank

Advantages: Flexible layout, not subject to height restrictions; centralized control and management of equipment, more convenient maintenance and use; reduced oxidation corrosion of the system; better prevention of vaporization and water hammer in the system; adaptable to the needs of large-area and tall buildings.

Disadvantages: The water replenishing pump starts frequently, and the life of the pump is short; the system pressure fluctuates greatly, and it cannot effectively prevent the problem of system overpressure under abnormal conditions; the power cannot be cut off, which causes a large waste of energy and high operating costs; it is large and takes up a lot of space.

2) Expansion Tank Constant Pressure Water Make-up System

Working Principle of Expansion Tank

The principle of constant pressure of the expansion water tank is to achieve the function of water replenishment (overflow) through the buffering adjustment effect of the water tank volume and the control of the high and low water levels of the water tank to adjust the volume changes of the system medium (water) caused by changes in system water temperature or leakage, and maintain The pressure of the hot and cold media (water) in the system is relatively constant. It is one of the constant pressure devices commonly used in small and medium-sized systems and air conditioning systems.

Advantages: It has simple installation, safety, less maintenance, low operating costs, stable pressure, no need for electricity, etc.; it can effectively eliminate overpressure under abnormal working conditions of the system.

Disadvantages: There are spatial location requirements for the highest point; the system has oxidation corrosion defects; it is not suitable for large areas and the needs of high-rise and super-high-rise buildings.

4. Frequency Conversion Pump Constant Pressure Water Make-up System

The frequency conversion speed regulation constant pressure water make-up system was developed after the constant pressure tank and is a combination of frequency conversion speed regulation technology and expansion water tank technology. The basic principle is to adjust the power frequency through logical calculation according to the changes in water pressure of the system collected by the sensor, and smoothly and steplessly adjust the speed of the water replenishment pump, that is, adjust the water replenishment amount, so as to achieve the purpose of achieving a relatively constant pressure at the constant pressure point of the system.

The key equipment of this constant pressure method is the frequency converter. Its working principle is to first convert the universal 50HZ alternating current into direct current, and then convert the direct current into alternating current at the required frequency through the frequency converter. By changing the power frequency of the water supply pump, the speed of the water supply pump and the amount of water supply can be adjusted, thereby adjusting the system water pressure.