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Dynamic Balance Valve and Its Application in HVAC Engineering
With the rapid development of our country's national economy, the construction scale of cities is getting larger and larger, people's requirements for the indoor environment are also getting higher and higher. In particular, the construction of commercial buildings in prime locations, how to improve the effective commercial area ratio: to ensure the use and operation of air-conditioning system does not increase energy consumption? HVAC professionals and construction developers common concern. 1 HVAC design of hydraulic system status Whether it is air conditioning or heating projects, due to conditions and can not be fully adopted the same system. In the actual design of the out-of-doors system, in order to ensure the most adverse end of the system capital ring head pressure, all other air-conditioning heating equipment end of the capital head pressure is often greater than the design requirements, especially in large-scale construction Complex projects, the long-distance pipeline, the end of the resistance difference between the equipment and the end of the air-conditioning system at the end of a large difference in the location close to the cold source of capital head margin is too large, often appear to flow distribution deviate from the design state , Leading to its system hydraulic imbalance. Discrepancy in the flow rate will cause the air-conditioning near the cold and heat source to be too cold or the heating is not hot. Not only can not guarantee the use of the function, but also caused a waste of energy. 2 ways to solve the imbalance of water 2.1 plus throttle plate In the heat inlet or air conditioning near the cold source loop part of the increase in the throttle plate. The premise for solving the hydraulic imbalance using this method is that the water system resistance calculation is accurate and the flow at the end of the heat or air conditioning can not be changed. So when the end of the flow changes will still cause hydraulic imbalance and energy waste. 2.2 Install manual control valve For large air-conditioning system, the use of manual control valve adjustment process is complex, manually adjust the front valve, the back flow will be affected. Rear-end adjustment of traffic, front-end traffic will change. So the adjustment time-consuming and laborious; for complex systems, regulating valve engineers require experience. And once the system pressure or load changes still need to re-adjust the hydraulic system. 2.3 Install dynamic flow balance valve Thermal inlet or air conditioning equipment at the end of the design flow is determined, according to the flow and the valve at the pressure range of changes selected dynamic balance valve, set the valve can be used. As long as the pressure difference at the valve changes within the design pressure range of the valve, no manual adjustment is required. 3 characteristics of dynamic balancing valve 3.1 Dynamic balancing valve works: By changing the valve spool flow area to adapt to changes before and after the valve, so as to achieve the purpose of controlling the flow. Dynamic balance valve is a local resistance can change the throttle element, for the flow of incompressible fluid to simplify the flow equation is: Q = KA (△ P) Where: Q - flow through the balance valve; K - valve open Degree of flow coefficient; A - the spool of the flow area △ P - the valve inlet and outlet pressure differential As the valve opening unchanged under the premise of the change in K value can be ignored, so the valve flow should be constant Control A (△ P)? No change. The balance valve by the variable flow area of ​​the valve gall bladder and high-precision (± 5%) of the spring and support structure. The effect of the spring pressure difference automatically controls the size of the over-flow area on the bile to keep the flow through the valve constant. 3.2 The working process of the valve: When the pressure difference before and after the balance valve is less than the minimum starting pressure is the spring is not compressed, the maximum circulation area. When the valve before and after the pressure difference in the working range of the valve gall bladder compression spring, into the working state, the water flows through the hole on both sides of the valve gall bladder and the geometry of the passage through the valve gall bladder in motion, both sides of the geometry flow channel changes - The circulation area of ​​the valve body is constantly changing, and the flow of water is basically kept constant within the range of this pressure difference. When the differential pressure across the front and back of the valve is beyond the scope of work, the valve gall bladder completely compressed spring, the flow of water only from the round hole on both sides of the valve gall bladder, gall bladder valve into a fixed regulator, flow and pressure is proportional to pressure The difference increases and increases. The dynamic balancing valve has the characteristics of limiting the maximum flow rate and automatic constant flow of the air-conditioning terminal equipment within a certain pressure range, simplifying the system debugging and shortening the commissioning in projects of large engineering, complex and air-conditioning heating load is not constant time. In particular, the balance valve is used in the outflow water system to balance the hydraulic conditions easily and meet the requirements of the design environment temperature. In the operation of the air conditioning system, the end devices can not interfere with the start and stop of other ends. 4 dynamic balance valve in the practical application of 4.1 district heating thermal inlet dynamic balancing valve used to ensure that the system required flow. Indoor heating system, thermostatic valve to ensure that each radiator through the required flow, dynamic balance valve to ensure that all riser flow constant, to solve the level of disorders. 4.2 Air-conditioning system Large-scale air-conditioning system, air conditioning equipment (air handling machine and fan coil) set the balance valve at the end, through the tee (or two) electric valve to ensure the required flow of equipment, balance valve to achieve hydraulic conditions. In the cold heat source, cooling towers, pumps, etc. when the design pipeline is limited. Balance valve to avoid load partial load, to ensure the normal operation of equipment. 5 air conditioning system design dynamic balance valve disgusting due to the issue of attention 5.1 dynamic balance valve only from the role of hydraulic balance can not be used for load regulation due to the misunderstanding of the dynamic balance valve, balance valve can easily be considered balance air conditioning or heating load, Balance valve to replace the electric three-way valve or two-way valve. However, with the dynamic changes of the structural load or the indoor load (personnel, equipment, lighting, etc.), the amount of water required by the air-conditioning equipment also changes dynamically so as to meet the requirements of indoor temperature and saves Role. In a large air-conditioning system, air-conditioning equipment set up after the balance valve; start and stop of each device will not interfere with the impact of other equipment, water flow, balancing valve has played a role in hydraulic balance; and electric three-way or two-way valve throttling can Adjust the amount of environmental load required. At present, the dynamic balancing valve with electric self-control function has been available. It is easier to implement energy-saving by dynamically balancing the air-conditioning system according to the load demand. Therefore, with dynamic balancing valve with electric automatic control function, the hydraulic balance and load adjustment can be combined, and the flow can be directly controlled by the computer. It also simplifies the installation and facilitates the installation in a small space. 5.2 Dynamic balance valve should not be multi-polar settings in the air-conditioning settings, manual control valve is multi-pole design. However, according to this method, the design concept of multi-pole dynamic balance valve is wrong. The reason is that if one or more devices in the lower level turn off the motorized valve and the upper balancing valve keeps the flow unchanged, the traffic of the lower non-closed device will increase, which not only increases the noise of the water flow but also affects the using function, And it also adds unnecessary economic investment. 5.3 air conditioning design should be based on the supply and return water temperature winter and summer reasonable set of water balance valve Dynamic balance valve in the four-control air conditioning system with two balance valve is to meet the winter and summer different water requirements, when the winter and summer air-conditioning heating, cold water When the temperature difference is different, the water flow varies greatly. Therefore, the balance valve should be set according to the requirements of different flow rates in winter and summer in the two-pipe water system. Method One: Set the variable flow type dynamic balance valve to switch the valve during winter and summer seasons. Method Two, set two balance valve, valve 1 according to the winter flow to select the valve, valve 2 according to the summer, winter, the difference between the maximum amount of water to choose the valve, winter valve 1, two valves in summer, with two valves to achieve four air-conditioning control Features. Method three, using a dynamic balance valve with automatic control device through the computer to set the flow. Otherwise, due to the different air-conditioning water flows in winter and summer, simply setting a fixed-flow dynamic balancing valve on the air-conditioner end would not be able to meet the water balance for both seasons. 6 Dynamic Balance Valve Engineering Design Example 6.1 Project Profile Located in the prosperous Wangfujing Commercial Street in Beijing Xin Dong'an market, by the Beijing Dongan Group and Hong Kong Sun Hung Kai Properties Limited joint venture to build a project, covers an area of ​​about 21400m2. The project construction is huge in scale. The building plan is divided into four sections: A, B, C and D, of which A, B and B are the market segments of Xin Dong An; and D is the moving part of Zengcheng District. Three underground floors, six on the ground, podium above the office for the eleven layers. (Figure 1 schematic diagram of the Xin Dong An market flat area) Xin Dong'an market, the total load of the refrigeration room is 10450RT (about 36750KW). Air conditioning water from the underground three-story freezer led to the ground floor. In order to reduce non-commercial area. The water system is for the next two-pronged system. From the second floor to 20 air-conditioned plumbing wells. Fan coil water system according to the characteristics of the construction load is divided into inner zone, outer zone two loops. The inner area is for chilled water only and the outer area is for winter hot water supply. According to the climate and indoor conformity situation, through the building automatic control system in the basement by electric control of the shaft to switch the dual zone warm and cold water outside the hot and cold water switch. 6.2 Air-conditioning design of the balance valve program For the freezing unit and the freezing pump, in order to avoid the load eccentric load due to various factors, in the freezer and constant flow of the secondary pump outlet installed balance valve. Due to the large building layout of the new Dongan market and the high commercial floor area required by the "Golden Land" by the owners and architects, the area of ​​equipment rooms and pipe wells is small and its location is also unfavorable. As a result, there is a significant increase in the area of ​​108m in longitudinal direction and 270m Of the pipeline system, the pipeline resistance balance and system debugging difficulties is quite large. In order to address the difficulty of "long and difficult pipelines" in water systems, two sets of balance plans were developed during the design process. Option 1: Multipole set up normal balance of water pipe installation between the wells ①In the main line and 20 HVAC pipe installation balance valve ②In the shaft outlet installation of balancing valve ③In each air-conditioning tank installation balance valve ④ In each Install balance valve on outlet of tenant Solution 2: Use dynamic balancing valve ①Install balance valve on fan coil of end device ② Install balance valve on air conditioner box of end device After economic comparison, the balance valve scheme finally adopted is ①Air conditioner box End balance valve and self-control valve installed ② retail and office space within the office two or three fan coil with a balance valve and self-control valve, the outer office fan coil for each balance valve and self-control valve. 6.3 balance valve application summary ①long-range pipeline large-scale system multi-stage installation of ordinary balance valve prices higher than the end of the device a dynamic balance valve. ② install dynamic balance valve on the end device, the scope of the impact of small maintenance, and the tenant air-conditioning start and stop the impact. ③ dynamic balance valve comes with a filter to avoid dirt in the water system piping on the self-control valve damage. ④ Because the error of the dynamic balance valve within a certain pressure range is only ± 5%, the opening or closing of some of the devices has almost no influence on the flow of other devices, which ensures the stability of the water flow of the terminal device. New Dongan market project is the government concerned about the project, tight schedule; with the changes in the market also caused many changes in engineering design. As a result, the project was not opened yet and the commissioning was not completed yet. Although the commissioning work has not yet been fully carried out, owners have benefited from the use of dynamic balancing valves and 180,000 square meters of air-conditioning system. The whole new Dongan market building functions more complicated, including write ,, computer network center, shopping malls, retail stores, restaurants, cinemas and the like, the architectural complex and varied. Its architectural function can not be relatively concentrated. The owners demanded that the design be dynamically adapted to the changes in the market - in the light of the ever-changing nature of the air-conditioning load. The maximum load time of air-conditioners in all districts and types of air-conditioners is also different. However, the correct design and the dynamic balance valve, which is not disturbed by the start-stop of other air-conditioners, are adopted formally, and the flow of each open end is maintained dynamically to ensure the safe and normal operation of this huge out-of-water air-conditioning water system. To date, no "tenant complaint" caused by hydraulic imbalance has been found. From the current situation, it is successful to use the dynamic balance valve in the new Dongan market project.
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