The core problem of compressor oper
How to adjust the hydraulic balance of air conditioning system
In air conditioning water systems, hydraulic imbalance is the most common problem. Due to the hydraulic imbalance, the system flow distribution is unreasonable and the heat is unreasonable, which causes a waste of energy, or to solve this problem, increase the pump head, but still produce uneven heat (cold) and greater electrical waste. This article explains the reasons for the selection of hydraulic balance valves in air conditioning water systems, and introduces the characteristics of hydraulic balance valves, as well as the steps and methods of applying hydraulic balance valves to hydraulic balance adjustment of the water system, and the requirements, process and evaluation of system joint adjustment.
As an important part of the air conditioning system, the rationality of its design not only determines whether the entire air conditioning system can achieve high efficiency and energy saving, but also determines whether the air conditioning system can operate normally and stably. After nearly a hundred years of development, the overall theoretical development of the air-conditioning water system is relatively complete, but there is less research on its adjustability and balance. In actual projects, the water system is not well adjusted and the water power is out of balance.
At present, a lot of work on energy saving of air-conditioning is mainly aimed at the research and development of high-efficiency refrigeration equipment and the matching of building forms and air-conditioning forms. However, insufficient attention has been paid to the adjustment and optimization control and design of the water system, resulting in good design schemes. Poor adjustability of the water system and hydraulic imbalance appear. With the emergence of various new technologies and new equipment, people have increased requirements for the control accuracy of the air conditioning system 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 the biggest problem faced by the current water system.
1. Common methods of hydraulic balance
To ensure the good operation of the air-conditioning chilled water system, the hydraulic balance of the system should first be satisfied. At present, as the scale of the system expands and the complexity of the system increases, hydraulic balance becomes more and more important. Many groups and scholars have done a lot of research on hydraulic balance.
1.1 Hydraulic balance of 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. After the system is debugged, the valve opening generally does not change anymore. The flow of each branch loop of the system basically remains unchanged during operation. change. Constant flow systems are mainly used for systems where terminal equipment does not need to be adjusted by flow, such as terminal equipment with three-way regulating valves, fan coils regulated by three-speed switches, and air conditioning systems with variable air volume air handling units. The constant flow system only has static hydraulic imbalance, and there is no dynamic hydraulic imbalance, so it is only necessary to install static hydraulic balance equipment in the corresponding position. Commonly used hydraulic balancing equipment for constant flow systems are throttle orifices, manual control valves, static balancing valves, and dynamic flow balancing valves.
When the water volume of the terminal equipment does not change, a throttle orifice, a manual regulating valve, a static balance valve, and a dynamic flow balance 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 loop changes with the load. Since the air-conditioning system operates under part-load conditions for most of the year, and the system water flow is lower than the design flow most of the time, the variable flow system is highly efficient and energy-saving. But the variable flow water system has a big shortcoming in that the parallel loops have a strong cohesion, and the hydraulics will cause mutual influence and dynamic hydraulic imbalance.
To achieve dynamic hydraulic balance, it is necessary to satisfy that the flow rate of each terminal device in the water system reaches the actual instantaneous load requirement flow rate. At the same time, the flow rate change is only affected by the change of the equipment load, and not interfered by system pressure fluctuations. The purpose of the dynamic hydraulic balance of the variable flow system is to ensure the instantaneous consistency of the system supply and demand water (this function is realized by various regulating valves), avoid the mutual interference of the flow changes of each terminal equipment, so as to ensure the efficient and stable flow of the system Accurately convey to each terminal device.
Two, the choice of control valve
The common method of adjusting the cold and heat output of the air conditioning system is to throttle the chilled water of the air conditioning system. Throttling is accomplished through various regulating valves. The regulating valve is an element in the piping system and at the same time an important link in the automatic regulating system. Therefore, the selection of the regulating valve in the air conditioning water system is very important.
When the pressure difference across the regulating valve changes, the regulating characteristics of the regulating valve will also change. In order to ensure the reliability of the regulating valve during pressure changes, the valve authority of the regulating valve must be considered. The valve authority of the regulating valve is defined as the ratio of the pressure difference on the valve to the total pressure difference of the system when the regulating valve is fully opened, as shown in Figure 1.
When the control valve is fully opened, the pressure difference ΔPmin is equal to the total service pressure difference minus the pressure drop of the terminal device, pipeline and its accessories. When the control valve is closed, since the flow is zero, there is no pressure drop on other components, and the available pressure difference ΔPmax all acts on the control valve. The ΔPmin refers to the pressure difference to obtain the design flow when the valve is opened. When the valve is close to closing, the pressure difference between the two ends of the valve will increase and cause the deviation of the 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 at the same time at the same ratio, and the valve authority SV remains constant. Valve authority is only related to the initial selection of the control valve.
Figure 2 Schematic diagram of series-parallel system
3) Measure the actual flow Q real of the hydraulic balance valve V1~V18, and calculate the flow ratio q=Q real/Q design;
4) Analyze the flow ratio of the hydraulic balance valve in each parallel valve group. For example, analyze the flow ratio of the hydraulic balance valve V1~V3 of the first-level parallel valve group 1. If q1
6) Measure the actual flow of the hydraulic balance valves G1~G6 in the two-stage parallel valve group I, and calculate the flow ratio Q1-Q6;
7) Adjust the main valve G of the system so that the actual flow of G is equal to the design flow.
In the air-conditioning water system, the hydraulic balance equipment should be selected reasonably according to the project investment and the accuracy requirements of the system, the hydraulic balance valve should be installed reasonably, and the system joint adjustment should be carried out by the correct method, which can greatly improve the hydraulic characteristics of the system and make the system close to Or reach the hydraulic balance, which not only provides a guarantee for the normal operation of the system, but also saves energy and enables the system to operate economically and efficiently.
Fourth, concluding remarks
As an important part of the air conditioning system, the rationality of its design not only determines whether the entire air conditioning system can achieve high efficiency and energy saving, but also determines whether the air conditioning system can operate normally and stably. A good system is based on good design, so it is very important to build a reasonable and good air conditioning water system. Based on the huge potential of air-conditioning water system in building energy saving, in order to complete the task of fluid distribution more cost-effectively and to solve the common phenomenon of poor balance and controllability of air-conditioning water system.
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