Study On Stability And Reducing Transportation Energy Of Variable Flow System

As the requirement of energy-saving and indoor environment gets higher and higher, variable flow technology are widely used in heating and air conditioning systems, namely by changing power or resistance to adjust the flow of the system,subcircuit and terminal equipment so as to match usually mutative dynamic heat(cold) load variation. Flow regulated by resistance change is usually used in subcircuit and terminal equipment. There will be coupling disturbance when using this regulating method, namely when regulating the flow of one subcircuit, flow of others will be changed. If the coupling disturbance is strong, stability of the system is bad; on the contrary, stability is good. Improving stability of the system will be significant for energy saving,heating and air conditioning quality and extending automatic control devices'service life of terminal equipment. With regard to flow regulated by changing power, there will be remarkable energy-saving benefits by changing the speed of pump and fan, and it is deemed to be the best. There is consanguineous relationship between variable speed energy-saving benefits of pump and fan has and pipeline characteristic, so it is important to study the relationship and advance a forecasting method so as to evaluate energy saving benefits of variable control in different engineering and determine whether to adopt it or not. Flow regulated by changing the number of parallel pump or fan, during the regulating, working condition of individual pump or fan will change a lot, there will be two problems, one is efficiency of the pump or fan will decrease; anther is there will be overloading. So, it is necessary to study the variable rules of flow, and advance method to forecast flow of individual pump and the system in order to determine the regulating method, systems design and equipment choosing, and instruct system operation. In addition, we have to use valves to balance system flow in each subcircuite in conventional power centralized system, so there is a lot of energy wasted by valves. In power decentralized system, there are not only pump (fan) installed in main pipes, but also in subcircuites, and by variable speed control to regulate the flow, this method can reduce and even eliminate valves'energy; but the investment is added and control is difficult. So there is significant referenced values in reasonable generalizing power decentralized system by studying valves'energy consumption quotient in power equipment in power centralized system, namely energy-saving extent in power decentralized system.In the field of stability study, main tasks of the paper are:â‘ Aiming at closed cycle water system, using the method that shuts certain subcircuit, and computing flow deviation coefficient of other subcircuits by network solving, then analyzing different factors that influences system stability. Main conclusions are obtained as follows: Decreasing resistances of main pipes, increasing resistances of subcircuits properly, system stability can be improved obviously. Centralized regulation by changing power has no influence to system stability; centralized regulation by changing resistances will worsen system stability. Pump characteristics influences system stability, influence caused by the flat characteristic is superior to the steep one. Stability of DRS, subcircuit that is furthest to the heat source is the worst. Stability of RRS, subcircuit in the middle of the pipe-network is the worst.Overall, stability of RRS is inferior to DRS'.â‘¡based on sensitivity, advancing the method in evaluating stability of closed cycle water system.â‘¢By academic analysis and substantial calculation, comparing the stability of the controlled-loop in several familiar local control modes, conclusions are obtained as follows: stability of constant pressure control is the best, second is constant opening control, and the worst is constant flow control.â‘£participating in developing ZY47 type self-operated pressure control valve and other four kinds of valves, by which can remarkable enhance system stability and pergormance security of heating and air conditioning hydronic system.simultaneously, carrying performance experiments on the above valves systemically, and studying their applicable condition and method in engineering.By analyzing the change rules that variable-speed working condition varies with back pressure, lucubrating variable speed energy saving benefits of pump and fan that influenced by back pressure, following conclusions are obtained: energy-saving benefit of variable-speed control in the system without back pressure is the best, in the system with back pressure, energy-saving benefit of variable-speed control decreases gradually with the increase of back pressure, when back pressure adds up to some extent, the axis power of variable-speed control condition is very close to that of throttle control condition. If take the efficiency of variable-speed installation into account, both practical energy consumption of two conditions are rather close. Thus, the method of variable-speed control will lose the significance of energy-saving. Based on the energy-saving benefit calculation of many different types of pumps, using non-dimensional method to settle the results, this paper advances a forecasting method of energy-saving benefit of variable-speed control.According to number-changed regulation of parallel pump/fan, at first, this paper analyses factors that influence flow increment of parallel operation, points out the problem that is like to happen when the flow increment is small during the number-changed regulating. Then discussing flow change rules of individual pump during the regulating. Based on the rules, the paper advances non-dimensional method in forecasting flow change of individual pump and the system during the regulating, using the method, one can judge whether the individual pump is overloading and the regulation can reach the need of system flow.Based on hydraulic balance principle in fluid system, analyzing valves'energy consumption share in the power equipment's output power in power centralized system. The results show, the larger the system is, the more the energy consumed by valves. In the design working condition, according to heating supply system, the share can exceed 20%, while in large or medium systems it may reach or exceed 30%. So, there is significant energy savings when adopting power decentralized system in large or medium systems. The paper has carried flow characteristic experiments on SP type balance valves, based on experimental data, at first, points out the direction of how to amend it; secondly, for the purpose of engineering applied need, the paper expresses the relation of caliber,flow,pressure drop and opening in mathematic mode.