Optimization Selection Of Hydraulic Balance Device In Heating System

In recent years,the central heating system has been widely used because of its advantages of improving heating quality,reducing environmental pollution,and facilitating scientific management in the actual project.But the scale is relatively larger,the pipelines are relatively more complicated,wherefore the hydraulic imbalance problem is easily caused during operation,then affect the heating effect of system.The balance device can be used to adjust the hydraulic balance of the heating system because it can adjust the resistance of the installation branch to eliminate flow disturbances by changing its own opening.However,if the balance device is not appropriately selected to install in the system,which will not only fail to achieve hydraulic balance,but also bring about certain negative impact on the system.Therefore,the purpose of this paper is to optimize the selection of balance devices,so that it can better control the flow of the branch,at the same time stability and economy of the heating system is better.Firstly,in order to evaluate the effect of balance valve selection on system stability in the heating system,a new indicator of ―adjustment sensitivity‖ was proposed.And take a common direct return hot water heating system as an example.Quantitatively compare the effects of different types of balance valves on the system stability and derive the influence patterns.The results showed that: from heat sources near and far,(1)When changing the opening of balance valves at both ends of the pipe network is less disturbing to the flow of other branches,while changing the resistance of the intermediate branches has a greater interference for other branches,and the adjustment of the end loop resistance has a smallest impact on other branches.(2)The farther the branch from the heat source is the worse of system stability for the branch,especially the branch at the end of the pipe network is most vulnerable to interference.Therefore,when adjusting the hydraulic balance of the system,it is better to change the opening of the end balance valve preferentially.Then,the factors affecting the selection of the balance valve were analyzed.The results show that:(1)Increasing available pressure difference of the balance valve can be helpful to improve the stability of overall system,and to reduce the flow disturbance caused by the adjustment of the balance valve;(2)Increasing the caliber of the balance valve can also improve system stability,particularly,there are obvious effects on improving the stability of the front-end branches of the pipe network;(3)the same model but different flow characteristics of the balance valve has different effects on the system stability,the influences from small to big are equal percentage,parabola,linear,and quick opening.Although increasing the available pressure difference of the balance valve or the valve caliber is more beneficial for improving the system stability,there is a restrictive relationship between those two.Therefore,it is necessary to reasonably determine the available pressure difference and valve caliber when selecting the balance valve.Secondly,economic analysis to evaluate the effect of balance valve selection in the heating system,mainly include the two aspects of the initial investment cost and operating costs.The results show that:(1)There is a negative correlation between the β value and the initial investment cost of balance valves.For the SP type balance valve,the initial investment cost of β value of 0.05 is 1.16 times the initial investment cost of β value of 0.5;(2)There is a positive relationship between the energy consumption and β value of the balance valves in the system.When the β value is 0.05,the energy consumption proportion of the balance valves are only 13.83%.When β is increased to 0.5,the energy consumption proportion of the balance valves has reached nearly 30%.Considering the stability and economic of the system,β=0.33 is the optimum valueFinally,considering the stability and economy of the heating system,the following conditions must be satisfied during the selection of the balancing valve:(1)The value of β should be chosen reasonably when determining the differential pressure of the most unfavorable loop balancing valve;(2)All the valve calibers that meet the requirements are selected with larger caliber balancing valves,and the opening of the balancing valve should be in the range of 50% ~ 100%.(3)The balancing valve models should try their best to choose a small flow capacity under the condition of satisfying flow regulation requirements.It is an equal percentage of flow characteristics.