The metering charge mainly uses three ways to save energy: firstly, the flow regulating valve is installed to achieve the flow balance, which overcomes the uneven heat and cold phenomenon. Secondly, through the role of the temperature control valve, the solar energy, home appliances, lighting, etc. are utilized. The free heat of the equipment; the third is to improve the energy-saving awareness of the residents who use the heat, and reduce the unnecessary heat dissipation of the windows. And two of these three energy-saving ways are realized by flow regulating valves. It can be seen that the flow regulating valve occupies an important position in the heating system for metering and charging. Therefore, how to correctly design the flow regulating valve is very important.
1, electric control valve
The electric control valve is a device for flow regulation in a computer monitoring system. It is generally used in unattended thermal stations. The electric control valve consists of a valve body, a drive mechanism and a transmitter. The thermostatic valve is a self-operated flow regulating device through a temperature sensing package, and does not require an external power supply. The electric regulating valve generally requires a single-phase 220V power supply, and is usually used as an actuator of a computer monitoring system (adjusting flow). Electric regulating valves or temperature control valves are the most important devices for regulating the flow rate in the heating system, and others are auxiliary equipment.
2, balance valve
The balancing valve is divided into a manual balancing valve and a self-balancing balancing valve. Regardless of the manual balancing valve or the self-balancing balancing valve, their role is to increase the resistance of the proximal end of the heating system, and limit the actual operating flow not to exceed the design flow; in other words, its role is to overcome the excess resources of the near end of the heating system. The indenter allows the electric or temperature control valve to operate under a licensed head. Therefore, manual balancing valves and self-balancing balancing valves are auxiliary flow regulating devices for temperature control valves or electric regulating valves, but they are very important. If the selection is improper or the design is unreasonable, the electric regulating valve or temperature control The valves are not working very well.
2.1, manual balancing valve
2.1.1, working principle of manual balancing valve
The manual balancing valve is manually adjusted at one time, and can not automatically change the drag coefficient according to the system operating conditions, so it is called static balancing valve. The object of the manual balancing valve is the resistance, which can function as a manually adjustable orifice plate to balance the resistance of the pipe network system and achieve the balance of resistance of each loop. It can solve the steady-state offset problem of the system: when the operating condition is different from the design working condition, the circulating water volume is more or less than the design working condition. Because the balance valve balances the system resistance, the new water quantity can be balanced according to the design calculation ratio. Distribution, so that the flow of each branch will increase or decrease at the same time, still meet the corresponding traffic requirements under the current load
2.1.2. Problems in the selection and design of manual balancing valve
(1) The valve characteristic curve determines the regulation performance of the valve, such as the flow curve of the shut-off valve. If it is considered that the flow change between 95% and 100% is meaningless, then the opening degree is from 0 to 5%. The whole process changes, such a valve can not be used as a balance adjustment of hydraulic conditions. Since the theoretical characteristic curve of the valve is measured under the top pressure difference, the actual working condition is as long as the valve weight is not 1, the pressure difference between the valve before and after the small opening degree valve is large, and the large opening is the small pressure difference between the valve and the valve, resulting in the valve dG The value of /dC becomes larger at a small opening degree, and becomes smaller at a large opening degree, so that the actual working curve of the valve is shifted toward the quick opening direction, and the smaller the valve weight is, the larger the offset is, and the valve for the linear characteristic is due to the actual performance. The offset will result in a smaller opening space for the effective adjustment of the valve, so the theoretical curve of the valve below the chord is as good as the percentage. For the equal percentage characteristic curve valve, the actual working curve may be close to the linear characteristic when the valve weight is 0.3~0.5.
(2) Generally, the valve flow rate is too high at a small opening degree, and a vortex zone with vigorous turbulence is formed after the valve. The vortex zone and the new pressure are very low, and the pressure is lower than the saturation pressure corresponding to the water temperature. The flashing of water vapor causes the phenomenon of steam and water hammer: severe noise, vibration of valves and pipes, damage of valves, pipes and pipe supports. The prevention and control of such accidents firstly considers that the valve plug and the valve seat form a narrow throttle channel at a small opening degree to restrict the formation of a vigorous turbulent vortex; secondly, the valve is used as much as possible. Degree to avoid the valve running at a small opening. In addition, the alkali balance valve should be installed on the return water pipe with a lower water temperature when the pressure condition is not involved.
2.2, self-operated balancing valve
The self-operated balancing valve automatically balances the flow of the system without an external power supply. The self-operated balancing valve achieves flow limitation by maintaining a constant pressure difference between the orifice plate (fixed orifice) and, therefore, the flow valve can also be weighed.
The constant flow valve acts on the flow and locks the amount of water flowing through the valve, rather than the balance of resistance. He can solve the dynamic imbalance problem of the system: in order to maintain the high efficiency operation of a single refrigerator, boiler, cooling tower, heat exchanger, it is necessary to control the flow of these devices fixed at the rated value; from the end of the system, in order to avoid The interaction of dynamic adjustment also requires limiting flow at the end device or branch.
It should be noted in the design that the disadvantage of the self-operated flow control valve is that the valve has the minimum working difference requirement. The general product requires a minimum working pressure difference of 20KPa. If it is installed on the most unfavorable circuit, it is necessary to increase the circulating water pump by 2 meters. Work lift, so should be taken near-end installation, remote uneasy method. Do not install this self-operated flow control valve when the user is away from the heat source by more than 80% of the heating radius.
3, temperature control valve
3.1. Construction and working principle of radiator temperature control valve
Temperature control in the user's room is achieved by the radiator thermostatic control valve. The radiator thermostatic control valve is composed of a thermostat controller, a flow regulating valve and a pair of connecting members, wherein the core component of the thermostat controller is a sensor unit, that is, a warm pack. The temperature pack can sense the change of the ambient temperature and produce a volume change, which drives the valve spool to generate displacement, and then adjusts the amount of water in the radiator to change the heat dissipation of the radiator. The temperature setting of the thermostatic valve can be artificially adjusted, and the thermostatic valve will automatically control and adjust the water volume of the radiator according to the setting requirements, so as to achieve the purpose of controlling the indoor temperature. The temperature control valve is usually installed in front of the radiator, and the room temperature required by the residents is realized by automatically adjusting the flow rate. The temperature control valve has two-way temperature control valve and three-way temperature control valve. The three-way temperature control valve is mainly used for a single pipe system with a spanning pipe. The splitting coefficient can be varied from 0 to 100%, and the flow adjustment room is large, but the price is relatively expensive and the structure is complicated. Two-way temperature control valves are used for double pipe systems, and some are used for single pipe systems. The two-way temperature control valve for the double pipe system has a large resistance; the resistance for the single pipe system is small. The temperature sensing package of the temperature control valve is generally assembled with the valve body, and the temperature sensing package itself is the on-site indoor temperature sensor. If required, a remote temperature sensor can be used; the remote temperature sensor is placed in a room where temperature control is required, and the valve body is placed in a location on the heating system.
3.2. Selection and design of temperature control valve
The thermostatic valve is the most important regulating device for the flow regulation of the heating system. The other regulating valves are auxiliary devices, so the thermostatic valve is a must. A heating system cannot be called a thermal metering system if it is not equipped with a temperature control valve. In the design of the temperature control valve, the correct selection is very important. The purpose of the temperature control valve is to determine the KV value (flow coefficient) according to the design flow rate (under known heat load), and then determine the diameter (model) of the temperature control valve from the KV value. Therefore, the design catalog or the manufacturer's sample must give the relationship between the KV value and the diameter, otherwise it is not convenient for the designer to use.
In the selection design of the temperature control valve, it is not a simple matter to simply select the temperature control valve with the same diameter as the pipe. Rather, it is necessary to create an ideal differential pressure operating condition for the selected thermostatic valve during the selection process. A typical temperature control valve has a working pressure difference between 2 and 3 mH2O and a maximum of 6 to 10 mH2O. To this end, it is necessary to give a range of preset values ​​of the temperature control valve to prevent noise and affect the normal operation of the temperature control valve. When there are more than two kinds of caliber choices under the same KV value, the temperature control valve with small diameter should be preferred, and the purpose is to improve the adjustment performance of the temperature control valve.
4, differential pressure regulating valve
4.1, the principle of differential pressure regulating valve
The principle of the differential pressure regulating valve is essentially the same as the self-operating balancing valve. In the self-operated balancing valve, the orifice plate exists as a component in the valve body; and the differential pressure regulating valve does not have the orifice plate component, but the system behind the differential pressure regulating valve is regarded as an orifice plate. Therefore, the differential pressure value of the regulating valve actually refers to the difference in system inlet and outlet pressure thereafter. It can be seen from the structure of the differential pressure regulating valve that the purpose of the regulating valve is to control the difference between the inlet and outlet pressures of the system. The basic function is to automatically adjust the operating flow of the hot user according to the thermal load demand of the hot user. When a building requires some room temperature to decrease due to the heat user, the opening of the temperature control valve of the corresponding room becomes smaller, resulting in a larger differential pressure of the differential pressure regulating valve, exceeding the set value, and the differential pressure regulating valve is automatically Close the small spool to increase the throttling effect and reduce the system pressure difference until it returns to the set value. The final result is to reduce the flow and adapt to the heat demand of the heat user, so as to reduce the frequent operation of the temperature control valve. When the heat user requests to increase the room temperature, the differential pressure regulating valve functions in the opposite direction.
4.2. Problems that should be paid attention to during design
Some people think that the differential pressure regulating valve should be installed on each indoor system or riser. After simulation calculation: if the balance valve (including manual, self-operated) or differential pressure regulating valve (including the design is reasonable) is installed in the heat inlet of the building, the indoor temperature control valve is within any adjustment range, and the front and rear pressure The difference will not exceed 6 ~ 10mH2O, that is, the temperature control valve can work under reasonable conditions. Therefore, it is not necessary to install the differential pressure regulating valve too much, and it is also uneconomical.
5. When the circulating water pump is running at a variable flow rate, the selection of the flow regulating valve
Here mainly refers to the choice of manual balancing valve, self-balancing balancing valve and differential pressure regulating valve. When the circulating water pump is running at variable flow rate, the manual balancing valve is out of proportion, which is most beneficial to the operation of the temperature control valve; however, the disadvantage is that there are too many manual operations, and it is difficult to achieve ideal adjustment. The circulating water pump is operated at variable flow rate, and the optimal set pressure difference for each heat user inlet should be the temperature of the outdoor air. For this, the self-operated balancing valve and the differential pressure regulating valve are not ideal, but there is no loss of regulation. This type of regulating valve can therefore be used, which is advantageous for improving the conditioning performance of the heating system.