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Professional industrial air conditioner manufacturers - Jin become your answer "How to adjust the air conditioning system hydraulic balance"
In air conditioning water systems, hydraulic imbalance is a relatively common problem. Due to the hydraulic imbalance, the system flow distribution is unreasonable, the heat is unreasonable, which causes waste of energy, or to solve this problem, improve the pump lift, but still produce heat (cold) unevenness and greater power waste. This paper describes the reasons for selecting the hydraulic balance valve in the air conditioning water system, and introduces the characteristics of the hydraulic balance valve, as well as the steps and methods of applying the hydraulic balance valve to adjust the hydraulic balance of the water system, the requirements, process and evaluation of the system joint adjustment.
As an important part of the air conditioning system, the air conditioning water system not only determines whether the whole air conditioning system can achieve high efficiency and energy saving, but also determines whether the air conditioning system can operate normally and stably. The air-conditioning water system has developed more comprehensive theory after nearly a hundred years of development, but there are few studies on its adjustability and balance. In actual engineering, there is often a phenomenon in which the water system is not well regulated and the hydraulic imbalance is caused.
Air Conditioning System
At present, a lot of work on the research and development of air-conditioning energy-saving is mainly aimed at the research and development of high-efficiency refrigeration equipment and the matching of building forms and air-conditioning forms. However, the emphasis on the adjustment and optimization control and design of water systems is not enough, resulting in good design solutions. There is a phenomenon of poor regulation and hydraulic imbalance of the water system. With the emergence of various new technologies and new equipment, people have increased the control accuracy requirements of air-conditioning systems and higher requirements for energy-saving, making the air-conditioning water system the focus of recent air-conditioning technology research. In order to achieve the rationality of system energy utilization, the system needs to have good adjustability and balance, which is also a big problem faced by current water systems.
First, the common method of hydraulic balance
To ensure the good operation of the air conditioning chilled water system, the hydraulic balance of the system should first be met. At present, as the scale of the system expands and the complexity of the system increases, the hydraulic balance becomes more and more important. Numerous groups and scholars have conducted extensive research on hydraulic balance issues.
1.1 Hydraulic balance of the constant flow system
The constant flow water system is a common hydraulic system in central air conditioning. The system does not contain any dynamic valves. The valve opening is generally not changed after the commissioning is completed. During the operation, the flow of each branch circuit of the system remains basically unchanged. change. The constant flow system is mainly used for systems where the end equipment does not need to be adjusted by flow, such as an end device with a three-way regulating valve, a fan coil with a three-speed switch, and an air conditioning system with a variable air handling unit. The fixed flow system only has static hydraulic imbalance, and there is no dynamic hydraulic imbalance. Therefore, it is only necessary to install static hydraulic balance equipment at the corresponding position. Commonly used hydraulic balancing devices for constant flow systems are orifice plates, manual regulator valves and static balancing valves, and dynamic flow balancing valves.
When the water volume of the end equipment does not change, an orifice plate, a manual regulating valve and a static balancing valve, and a dynamic flow balancing valve can be installed on the return pipe of each loop.
1.2 Hydraulic balance of variable flow system
In order to save energy, variable flow water systems are increasingly used in air conditioning projects. During the operation of the variable flow system, the flow of each branch circuit changes as the load changes. Since the air conditioning system operates under partial load conditions for most of the year, the system water flow is mostly lower than the design flow. Therefore, the variable flow system is efficient and energy efficient. However, there is a big disadvantage in the variable flow water system that the parallel loops are highly viable, and the hydraulic forces will cause interactions with dynamic hydraulic imbalances.
To achieve dynamic hydraulic balance, it is necessary to meet the flow rate of each end device in the water system to reach the actual instantaneous load demand, and the change of the flow rate is only affected by the change of the equipment load, and is not affected by the system pressure fluctuation. The dynamic hydraulic balance of the variable flow system is to ensure the instantaneous consistency of the supply and demand of the system (this function is realized by various types of regulating valves), which avoids the mutual interference of the flow changes of the end devices, thereby ensuring the efficient and stable flow of the system. Accurate delivery to each end device.
Second, the choice of control valve
A common method of adjusting the cold heat output of an air conditioning system is to throttle the chilled water of the air conditioning system. Throttle is accomplished by a variety of regulating valves, which are a component of the piping system and an important part of the automatic regulating system. Therefore, the choice of regulating valve in the air conditioning water system is very important.
The adjustment characteristics of the regulating valve also change when the pressure difference across the regulating valve changes. In order to ensure the reliability of the regulating valve in the pressure change, it is necessary to adjust the valve authority of the valve. The valve weight of the regulating valve is defined as the ratio of the pressure difference between the valve and the total pressure difference of the valve when the regulating valve is fully open.
1. When the control valve is fully open, the differential pressure ΔPmin is equal to the total pressure difference minus the pressure drop of the end device, the pipeline and its accessories. When the control valve is closed, since the flow rate is zero, there is no pressure drop on the other components, and the pressure difference ΔPmax is all applied to the control valve. Where ΔPmin is the pressure difference at which the design flow is obtained when the valve is opened. When the valve is nearly closed, the pressure difference across the valve will increase to cause a deviation in valve characteristics. The degree of deviation depends on the valve authority. At the same time, it should be noted that when the system pressure changes, ΔPmin and ΔPmax will change simultaneously at the same ratio, and the valve weight SV remains constant. Valve authority is only related to the initial selection of the control valve.
The purpose of the control valve is to create a supplemental pressure drop in the hydraulic circuit to limit the amount of water to the desired value. The choice of control valve is to enable the valve operating under design conditions to provide the required flow rate at the applied differential pressure.
When the control valve selection is too large, the control valve has to work frequently near the closed position, resulting in unstable control. During the system startup phase, when the valve is over-sized, the flow will exceed the design flow, while other devices will owe the flow.
In the selection process of the control valve, the key is to estimate the pressure difference across the valve. In practice, the pressure drop produced by the valve should be equal to the total pressure difference minus the pressure drop of the circuit it controls. These pressure drops are estimated by the design flow. In the actual valve selection, it is generally required that the selected regulating valve is usually smaller than the pipe diameter, mainly because the small diameter can improve the adjustment precision and save investment.
Third, the system hydraulic balance adjustment
The task of the central air conditioning system is to provide users with a comfortable indoor environment at a lower cost (operating cost). Among them, due to the large capacity of the water system to transport cold and heat, it is the main means of long-distance transportation of cold heat commonly used in large-scale air conditioning projects. According to current statistics, in the actual operation of the central air-conditioning system, there is a general hydraulic imbalance problem. Therefore, it is necessary to analyze the hydraulic balance of the air conditioning water system.
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