The use of flange gate valve in the operation regulation of heating system

The use of flange gate valve in the operation regulation of heating system

Hydraulic misalignment is one of the factors affecting the quality of heat supply. Heating system operation, due to hydraulic disorders caused by the distance from the heat source or floor above and below the different users appear overcooling or overheating and other anomalies, the use of balancing valves to regulate, to achieve the design of the hydraulic condition, to ensure the stability of the heating system.

0 Introduction

Hydraulic misalignment is one of the factors affecting the quality of heat supply. With the national emphasis on energy saving and environmental protection, municipal centralized heat supply in urban heating has been the direction and trend. In recent years, the rapid development of the real estate industry, the heating range of residential neighborhoods is also increasing, reaching hundreds of thousands of m2 has not been uncommon. But likewise, it causes hydraulic disorders and other abnormal phenomena will be more prominent. Especially the implementation of centralized heating sub-metering reform policy, the quality of heating directly affects the people's standard of living and the implementation of charge metering, so the heating system operation and regulation must be enough attention.

1 heating system operation condition analysis

Hydraulic conditions refers to the system pipe network pressure, flow and differential pressure. Hydraulic balance is manifested in the reasonable distribution of the user flow. Heat supply pipe network, water is the heat carrier medium, the reasonable distribution of flow is the basis of the balance of thermal conditions. Calculation of hydraulic working conditions is the system design of the user flow in the theoretical condition determined by the pipe and the maximum flow rate limitations, resulting in the system pipeline characteristic resistance number of ratio and design requirements of the pipeline characteristic resistance number of ratio is not consistent, which is inherent in the system itself. Heating system is a complex hydraulic system, the hydraulic conditions between the loops affect each other and constrain each other. In operation, any one of the user's flow changes will cause the other user's flow with the changes that occur in the system, the user's flow will be redistributed, so that the user's actual flow and calculation of the flow is not consistent, resulting in hydraulic disorders, resulting in the phenomenon of hot and cold uneven. The hydraulic condition of the heating system is formed by the intersection of the output pressure working curve of the pump and the characteristic curve of the external network. The water pressure diagram of the heating system is a theoretical representation of the external network pressure conditions for safe and reliable operation of the system and determination of the optimal operating point. Heating system into operation, due to the circulating water pump characteristic curve is relatively gentle, the total pressure drop of the change is very small, and the characteristic curve of the external network must be, so the operation of the hydraulic condition of the adjustment process is essentially based on the system pressure diagram, in accordance with the calculation of the user's flow rate of the distribution of heat media adjustment process. That is, set up hydraulic balancing equipment, to overcome the excess capital pressure head at the near end of the heating system, increase the resistance at the near end, to realize the operation of the system water pressure diagram and hydraulic working condition design of the formation of the water pressure diagram tends to be close to the process. In this way, achieved with the design requirements of the pipeline characteristics of the resistance number of ratio of the same value, the system running flow and design of the total flow of the same, the end user flow to achieve the calculation of the flow rate, the distribution of uniform and reasonable, the realization of the hydraulic balance of the heating system to achieve the safe and reliable operation, hydraulic stability and heating quality purposes.

2 heating system hydraulic disorder analysis

Heating system hydraulic disorder is a common problem. The main reasons exist in: one. The design of the heating network hydraulic calculation is not accurate, only note the most unfavorable point (usually at the end of the system) necessary to use the head, and other points of the head is always greater than the calculated value, the closer to the location of the heat source of the head of the position of the head of the head of the head of the head of the head of the head of the head of the head of the head. And the loop itself does not have the independent hydraulic adjustment function, there is bound to be a flow distribution deviation from the design state, resulting in the user hot and cold uneven hydraulic disorders (usually near the end of the overheating, the far end is not hot). Secondly, in the case of reasonable system design, the pump selection is too large, the operation of the flow deviates from the design state (large flow small temperature difference), also leading to the system's hydraulic disorders. Third, the increase in the number of new users and the expansion of the heating network, but not in time to transform the calibration, but only to replace the pump (increase the flow and head of the pump) to make the system more complex operation and management, resulting in new hydraulic disorders. Usually set up a large flow, high head pumps, using a large flow of small temperature difference in this way and can not solve the hydraulic imbalance phenomenon. According to relevant information, large flow small temperature difference in the operation of the system will increase the investment of more than 20%, consume 15% -20% of the thermal energy, more than 30% of the power consumption.

3 balance valve on the heating system hydraulic disorder regulation

3.1 In the introduction of the mouth of the pipe section to install throttle orifice or install gate valves, shut-off valves, etc., balanced piping system resistance and regulate the flow rate, eliminating the user system residual pressure head. However, the disadvantage is that the aperture of the throttling orifice plate is calculated according to the design conditions, when the heat load changes, it is necessary to recalculate and replace the throttling orifice plate. Moreover, the aperture of the throttling orifice plate is too small and easily clogged.

Similarly, gate valves, globe valves have poor regulating performance, essentially only appropriate as a shut-off valve.

Especially after the implementation of household measurement measures, if any user system valve opening changes, due to throttle orifice plate and other fixed flow rate of its regulation, will be redistributed to the flow rate of new water disorders generated after the phenomenon, the need to recalculate the adjustment, action lag, operational complexity, poor flexibility.

3.2 In the introduction of the mouth of the pipe section on the installation of balance valves, self-operated flow control valves and self-operated differential pressure control valves, etc., its high degree of automation, flexibility and agility. Domestic use in recent years, the effect is good. Balance valves, self-operated flow control valves and self-operated differential pressure control valves belong to the category of control valves. The core equipment of these regulating devices is the valve body, the regulating principle is to change the spool stroke to change the throttling area and the valve resistance, so as to regulate the flow through the valve, change the flow resistance through the valve, in the absence of external power supply, automatically realize the flow balance of the system so as to achieve the purpose of regulating and controlling the flow. Balance valve is set in the regulation of the opening, the operation of its opening does not change with the flow rate; self-operated flow control valve is set in the regulation of the flow rate through itself, the operation of its opening with the flow rate changes and automatically change, so that the flow rate through itself to maintain a basic constant; self-operated differential pressure control valve in the regulation of the pressure difference between the two pressure points set in the operation of the opening with the pressure difference and automatically change, can make the two pressure points to change automatically. During operation, its opening degree changes automatically with the change of pressure difference, which can make the pressure difference between the two pressure measuring points remain basically unchanged. Comparison with the throttle orifice plate and other regulating devices, balancing valve with linear flow characteristics, that is, in the case of constant pressure difference between the valve before and after the flow and opening was linear; accurate opening indication; opening locking device, non-management personnel can not change the opening; valve body has two pressure measurement holes and intelligent instrumentation with a hose connection, you can easily display the valve before and after the pressure difference and flow.

3.3 Heating system operation regulation, the centralized regulation of the system flow does not change, because the system flow does not change, the differential pressure of the pipe network will not change, and thus the balance valve, self-operated flow control valve, self-operated differential pressure control valve openings do not change the distribution of the flow of the network also does not change, so can be selected. But to choose the flow control valve or balance valve first, such as the amount of regulation should be used to balance the valve. For the user to change the flow of autonomous regulation, because of its indoor system more than a common riser of the two-pipe system. Therefore, if the common riser inlet balancing valve, relying on the user temperature control valve multiple actions, can achieve different users of the room temperature requirements, and thus the balance valve can be selected. If the common riser inlet installed self-operated differential pressure control valve, can make the common riser differential pressure to remain unchanged, is conducive to the temperature control valve to control the flow of radiator regulation, so the selection of self-operated differential pressure control valve has the best results. As the user's independent adjustment, the pipe network flow is also changed, so the pipe network branches are also suitable for the installation of self-operated differential pressure control valve.

4 balance valve application examples

A unit of heating system renovation process installed balance valve, after several heating season operation results show that the installation of the balance valve can be a good solution to the system's hydraulic imbalance phenomenon, improve the quality of heating, and achieved good energy efficiency and economic benefits. Operation comparison is shown in Table 1.

Table 1 a residential district heating installed balance valve flow deviation comparison table

Balance valve in the operation of the heating system regulating the use of

The data show that the district heating system installed balancing valve, each branch system flow distribution can reach the design of the calculated flow, the original for many years has not been hot user indoor temperature adjustment to more than 18 ℃; system exists in the over-flow and under-flow areas of the flow can be adjusted to the design of the calculated value of the end of the user flow can be guaranteed, the local phenomenon of overheating and overcooling can be resolved, the heating effect of stabilization. Some users due to private modification of the pipeline, resulting in part of the unit resistance is too large, through the balancing valve flow balance distribution, but also to achieve the calculated flow.

5 Balance valve on the heating system operation regulation experience

① hot and cold uneven phenomenon is eliminated, the quality of heat supply is guaranteed, the user complaint rate is reduced. ② heat source equipment capacity is given full play. (After the implementation of a district balancing valve renovation, the original boiler room to provide 190,000 m2 of heating area, the heating area increased to 230,000 m2, the heating effect is still stable and good. ③The purpose of energy saving in operation regulation is achieved. The heating system can accurately regulate the heating according to the temperature difference between supply and return water and the outdoor temperature, which achieves the purpose of energy saving and consumption reduction. (A residential district after the implementation of the balancing valve transformation, the building heating system return water temperature deviation of no more than 3 ℃) ④ to ensure that the circulating water pumps run in high-efficiency zone. Both save the operating costs and extend the service life of the circulating water pump.

6 Conclusion

① The application of balancing valve in the heating system realizes the hydraulic balance of the heating system and achieves the purpose of safe and reliable operation, hydraulic stability and heating quality. ② Because of the prevalence of large diameter of indoor heating system entry pipe in single building, the application of balancing valve for heating pipe network system regulation is a necessary means of hydraulic balance of the pipe network system. Similarly, from the application of residential district practice, the city heating system of the first level of site is also one of the methods to achieve hydraulic balance. ③ Reasonable arrangement of loops and selection of pipe diameters according to the principle of hydraulic balance is a complete concept to realize the static balance of the system. However, the method of configuring balancing valve should not be used instead of setting up juice and hydraulic balance calculation of the loop. ④ The hydraulic balance of the heating system will save energy by 15-20%, and the application of hydraulic balance technology is an effective way to improve the status quo of the heating system and promote energy-saving renovation, which has significant economic and social benefits.