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Hot water heating system is a complex system of hot users, heat network and heat source and circulating water pump. In order to enable the circulating water pump put into operation in the high-efficiency area, and make the circulating water volume meet the need, without causing serious water and heat imbalance, we must analyze the circulation pump (single or multiple) operating in the system status . The result is a system that matches the system's circulating water pump to the maximum possible "full load, high efficiency" operation.
Using the drawing method and the difference method to determine the pump performance parameters and operating points to select the matching pump, the accuracy is poor, and more troublesome; Therefore, using the principle of least squares method for heating circulating pump performance experimental data curve fitting, Discuss the working condition of circulating pump again.
1 circulating pump curve fitting
In this paper, the least squares method to polynomial curve fitting to find the performance curve of circulating pump equations. The basic idea is to set up the error equation through error analysis, to derive the corresponding normal equations under the condition of the smallest error, to obtain the regression coefficient (least squares estimation) by solving the normal equations (linear algebraic equations) Set up a curve fitting polynomial.
2 Applied Research
Introduced in front of the numerical solution of the pump performance fitting curve equation, knowing that the equation can easily know the operation of the pump. If we give the equation of pipeline characteristic and solve them in series, calculate the working point and get the flow and lift of the working point, then we can compare with the total flow and total resistance of the actual pipeline to analyze the system hydraulic conditions , Come to match the pump to determine the solution to the hydraulic imbalance. The examples given in this section are fully analyzed.
2.1 System Overview
Known a heating system, construction area of ​​90,000 m2. The estimated heat load is 5.2MW, the total system water supply temperature is 95 ℃, the return water temperature is 70 ℃, the network heat dissipation and leakage coefficient K is 1.05, and the flow additional coefficient φ is 1.2. The heating radius L is 500m, the friction resistance R is 70 Pa / m, the percentage of local resistance loss relative to the distance takes a as 0.3, the internal resistance of heat source Hr is 10X104Pa, the user system resistance Hy is 1x104Pa, the margin coefficient K is 1.15.
2.2 System Condition Analysis
Therefore, for a serious hydraulic imbalance in heating systems, especially end users is not hot, can not simply use the method to increase the pump to solve. Since the operating point of a single pump is already in the flat area of ​​the pump performance curve, the total flow increase is limited after the pump is increased. If there are two pumps running in parallel, the synthetic curve is more flat, and then add a pump running in parallel, the total flow increase will be smaller or not increase. Therefore, to solve the problem of hydraulic imbalance in heating system, we should first consider adjusting the pipe network through the hot user inlet valve so that the system flow can be rationally distributed. Of course, if the total flow does not meet the requirements, a single pump that matches the system or a combination of more than one pump that makes the pump work in the high-efficiency area should be selected or calculated.
3 Conclusion
(1) For a certain expansion system, with the increase of heat users year by year, original pump has been small, through the pump performance analysis, the use of multiple pumps parallel operation is possible. However, what we often encounter is that the flow and lift of a single pump far exceed the actual needs of a single pump. Due to the imbalance of the network, there are always some users are not hot, in order to make up for the defects brought by the imbalance, the use of multiple pumps in parallel operation. At this point the system of circulating water has increased, but the added value is very small, the pump efficiency is naturally low.
(2) Due to the serious hydraulic imbalance in the network, the pump can not meet the needs of end users after it is connected in parallel. Even replacing high-power and large-flow pumps is of no avail. In fact, if the hydraulic imbalance in the network is serious, as long as the performance of the pipeline is unchanged, the traffic will maintain the same degree of mismatch after the traffic increases. (3) The analysis of hydraulic conditions is the key to understand the operation of the entire system, and the establishment of circulating pump performance curve equation for the hydraulic conditions of great convenience. Circulating pump performance curve equation for the computer to choose a circulating water pump laid the theoretical foundation, but also to achieve the basis of quantitative management
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