Control and adjustment equipment for effective application of heat

With the reform of the heat metering and charging system, temperature control valves began to be installed on each radiator. Therefore, during heating operation, as the user continuously adjusts the temperature control valve, the flow rate of the heating network continues to change. In this way, the heating network becomes a variable flow operation, and the initiative of flow adjustment is in the hands of the user, and the heating company will be unable to predict and control the changes in flow. In the case of variable flow operation of this thermostatic valve, the regulating control device must be installed correctly to function. Otherwise, the system will not only fail to meet the adjustment requirements, but sometimes it will be counterproductive.
1. Adjustment device

1.1. Self-operated flow control valve. The characteristic of this valve is that it does not require external power and relies on the characteristics of fluid flow. When the upstream and/or downstream resistance changes within a certain range, it can adjust and open automatically through changes in pressure within the pipeline. degree, so that the flow rate remains basically unchanged.

1.2. Balance valve. From the basic principle of regulation, the balance valve is actually a manual control valve with an opening indication. Install a pressure measuring hole at the upstream and downstream ends of the balance valve to measure the pressure drop of the fluid passing through the valve. When in use, the flow rate through the valve can be calculated by measuring the pressure drop of the valve and reading the opening. Its function is equivalent to the combination of a regulating valve and an equivalent orifice flowmeter, so that the flow distribution of each branch meets the requirements. When the total circulation pump operates at variable speed, the flow distribution ratio of each branch remains unchanged.

1.3. Self-operated differential pressure control valve. The characteristics of the self-operated differential pressure control valve are similar to those of the self-operated flow control valve. It does not require external power and only relies on the characteristics of the fluid flow. The resistance in the upstream and/or downstream is within a certain range. When changes occur, it can adjust the opening by itself through changes in pressure within the pipeline, so that changes in pressure drop when the fluid passes through the valve core can compensate for changes in pipeline resistance, so that the user’s inlet pressure difference remains basically unchanged. Only the above three regulating devices are discussed here, and these regulating devices are not installed on the heating risers, but at the thermal entrance of the building.

2. Adjustment and control of the constant flow operation system without a temperature control valve. The constant flow operation mentioned here means that the flow rate of the heating network remains unchanged during the entire heating season. 2.1. Direct connection network Generally speaking, the direct connection network is divided into two parts: the main network and the branch network with the thermal station as the boundary. The main network is from the heat source to the thermal station, and the branch network is from the thermal station to the heat users.

2.1.1. Main network adjustment The control strategy of the main network is to adjust the opening of the water supply valve of the thermal station so that the return water temperature of all thermal stations becomes consistent. The main network should be equipped with microcomputer control, which can ensure the quality of heating and reduce operating costs at the same time. However, when investment is limited or the heating network is small and the scale of the heating network is relatively stable, microcomputer control may not be used, but the relatively simple adjustment method described in the branch network below may be used. 2.1.2. Adjustment of branch network. Since the investment in microcomputer control of heating network is high, only the main network is generally controlled. There are many ways to adjust the branch network.

2.1.2.1. Manual adjustment Manually adjust the relevant valves of each branch so that the flow rate of each user basically reaches the design flow rate. However, there is generally no flow measurement device on the branch road, so the flow rate cannot be directly observed to determine whether the adjustment meets the requirements. There are two methods: observe the return water temperature of each branch and continuously adjust the valves of the branches to make the return water temperature of each branch close to the same; or use a portable ultrasonic flow meter to observe the flow rate of each branch to adjust. The actual flow rate of each branch can be adjusted to the design required value. Adjustment using the return water temperature requires a relatively long adjustment period because the building has a large thermal inertia; adjustment using a portable ultrasonic flow meter is simple and easy, but requires the purchase of corresponding equipment.

2.1.2.2 Self-operated flow control valve Install a self-operated flow control valve on each branch or hot inlet, and adjust the setting knob of the control valve so that its flow indication meets the design flow requirements. In this way, the flow rate of each branch can basically meet the design requirements during operation.

2.1.2.3 Balance valve Install a balance valve on each branch or hot inlet. According to the adjustment method of the balance valve and the design flow of the branch, adjust the opening of the balance valve so that the flow meets the design requirements. In this way, the flow rate of each branch can meet the design requirements during operation.

2.1.2.4 Self-operated differential pressure control valve Install a self-operated differential pressure control valve on each branch or hot inlet, and adjust the setting knob of the differential pressure control valve so that the indicated pressure differential value meets the requirements of the designed pressure head. Generally speaking, the design flow rate given by the designer should be relatively close to the actual required flow rate, so the above two adjustment methods are more accurate; the required pressure head is not only related to the design flow rate, but also to the pipeline resistance coefficient, but The actual resistance coefficient of the branch may be quite different from the design value. In this way, even if the actual pressure difference is adjusted to the design available pressure head, the actual flow rate may not reach the design flow rate due to the difference in resistance coefficient, resulting in uneven cooling and heating. .

2.1.2.5 Comparison of adjustment methods For a heating network that uses a fixed flow rate throughout the heating season, all of the above adjustment methods can be used. Manual adjustment and balance valve adjustment belong to the same type of adjustment method. In fact, they are both initial adjustments, that is, after the adjustment is completed, the distribution ratio of the flow in each branch is maintained to meet the requirements, but when the heating network adds new users or original users work After the situation changes, the traffic distribution ratio changes, so it needs to be readjusted. At the same time, due to the coupling relationship between each user during the adjustment process, for example, the traffic of user A is adjusted to the design required value, but after user B is adjusted, the traffic of user A changes again due to the coupling effect. If the coupling is serious, User A also needs to be readjusted. Therefore, using this adjustment method, decoupling must be done when the coupling of each user is serious. The self-operated flow control valve and the self-operated pressure difference control valve are different from the above two adjustment methods. Their function is not to ensure the flow distribution ratio, but to ensure that the flow (pressure difference) on the branch responsible for the valve remains unchanged. Therefore, when a new user is added to the heating network and the flow of the original branch is affected, it can automatically adjust to adapt to this change, thereby keeping the flow of the branch unchanged. The self-operated flow (pressure difference) of the original branch ) The control valve does not need to be readjusted. Of course, all adjustment methods will add a certain amount of resistance to the system, and the system must have sufficient adjustment margin.

2.2. Inter-connected network and mixed-connected network. From a control perspective, the difference between mixed-connected network and inter-connected network is that the thermal station has different methods of controlling the water supply temperature of the secondary network. For inter-connected networks, adjust the valve of the primary network of the thermal station to control the return water temperature of the secondary network, and adjust the flow rate of the circulating water pump of the secondary network to control the water supply temperature of the secondary network; for mixed-connected networks, the same is true for adjusting the thermal power The valve of the primary network is used to control the return water temperature of the secondary network, but the water supply temperature of the secondary network is controlled by adjusting the flow rate of the mixing water pump. In an intermediately connected or mixed-connected primary network, each thermal station is equivalent to a thermal user, so the primary network is equivalent to a directly connected network, and the above adjustment method for the directly connected network is also applicable; for the secondary network, the thermal power station is equivalent to a directly connected network. The station is equivalent to the heat source, and the secondary network is equivalent to a directly connected network, so the above adjustment method for the directly connected network is also fully applicable. Therefore, the adjustment method of direct-connected networks can be extended to intermediate-connected networks and mixed-connected networks.

3. Adjustment and control of the staged variable flow operation system without a temperature control valve. Staged variable flow divides the entire heating season into several stages. The flow rate remains unchanged in each stage, but the transition from one stage to another is stage, the flow rate changes. For example, the entire heating season is divided into three stages: initial heating period – severe cold period – final heating period, and the heating network flow rate has three flow values: small flow – large flow – small flow. Throughout the heating season, the flow rate is no longer completely fixed. Therefore, for this operating mode, the adjustment methods described in the previous section may not all be suitable. It can be seen from the above section that as long as the adjustment of direct-connected networks is clearly discussed, the adjustments of indirect-connected networks and mixed-connected networks can be inferred by analogy. Therefore, here we only take the directly connected network as an example for analysis.

3.1. Self-operated control valve In this operating mode, the self-operated flow control valve is no longer applicable. Because the set flow rate of the self-operated flow control valve is generally the design flow rate of the system, it is suitable for an operating mode in which the flow rate of the heating network remains unchanged throughout the heating season. For example, when the operating conditions are not at the design operating flow rate, the automatic adjustment function of the self-operated flow control valve will come into play to make the flow rate of the road as close as possible to the design operating flow rate. During the low flow operation in the initial and final stages of heating, the flow of the entire heating network becomes smaller, for example, when it is 75% of the design flow, the flow of each user should also be reduced to 75%. For users close to the heat source, if their self-operated flow control valve senses that the actual flow rate (75%) is less than the set flow rate (100%), the self-operated flow control valve will automatically open to make the flow rate as close as possible to the set flow rate. Therefore, the actual flow rate of the near-end user is greater than required and is overheated, while the actual flow rate of the remote user must be less than required and is overcooled. Of course, when the flow rate is 100% during the severe cold period, the self-operated flow control valve ensures that the flow rate of each user meets the requirements, thereby ensuring uniform heating for all users. The regulating characteristics of the self-operated differential pressure control valve are the same as those of the self-operated flow control valve, so the same conditions occur in this operating mode. In other words, the self-operated differential pressure control valve is not suitable in this operating mode.

3.2. Balance valve Balance valve is very suitable for this operating mode. Because once the balance valve is adjusted, it does not have the function of self-adjustment according to changes in working conditions like a self-operated flow and differential pressure quality control valve. Therefore, when the total flow rate changes, the balancing valve can maintain equal proportional changes in the flow rate of each user. For example, when the total traffic is 75% of the designed traffic, the traffic allocated to each user is also 75%. Therefore, in this operating mode, the balancing valve can ensure that the flow distribution in each stage meets the usage requirements.

4. Adjustment and control of the system after installing the temperature control valve. After the implementation of heat metering and charging, the indoor system can be divided into two categories: one is a double-pipe system with a shared riser indoors, and the other is a system with spanning pipes. Vertical single pipe systems or horizontal single pipe systems with shared risers and indoor span pipes. After the temperature control valve is adjusted, the two types of systems have different effects on the total flow. Figure 1 shows the control principle of the system. In the figure, the control valves for the hot inlets of users A, B, and N can be self-operated flow control valves, or self-operated differential pressure control valves or balance valves. The temperature control valve represents all or part of the temperature control valves inside the corresponding heat users. The radiator is not marked out. Indoor systems can be either of the two categories mentioned above.

4.1. A system with a shared riser and double pipes indoors. As the indoor load changes, the temperature control valve will automatically change accordingly. In this way, the flow rate through the radiator also changes, which means that the flow rate of the heating network changes at any time.

4.1.1 The hot inlet control valve is a self-operated flow control valve. The function of the self-operated flow control valve is to keep the flow rate of the pipeline unchanged when the working conditions change. After the temperature control valve is installed, the flow rate in the pipeline is constantly changing, which obviously contradicts the function of the self-operated flow control valve. If a self-operated flow control valve is installed on the pipeline where the temperature control valve is installed, it will be harmful to the regulating effect of the temperature control valve rather than beneficial. As shown in Figure 1, when the indoor load decreases, the temperature control valve automatically closes, and the corresponding pipeline flow should decrease; but if the pipeline has a self-operated flow control valve, the self-operated flow control valve will automatically open after sensing the decrease in flow. Large, thereby increasing the pipeline flow to achieve its purpose of keeping the pipeline flow unchanged. At this time, the relative increase in pipeline flow (actually keeping the original flow rate unchanged) will cause the thermostatic valve to be further closed, thus forming a cycle, and finally causing the thermostatic valve to be closed to the minimum, while the indoor temperature may still be higher than required. ,vice versa. Therefore, a system with a shared standpipe and double-pipe indoors where the temperature control valve is installed cannot be installed with a self-operated flow control valve.
4.1.2 The hot inlet control valve is a balancing valve. The balancing valve actually plays a role in initial adjustment. When the balance valve is initially adjusted, it is adjusted according to the flow rate of each pipeline under the design working conditions. After the initial adjustment of all balancing valves is completed and the pipeline resistance coefficient no longer changes, the flow distribution ratio of each pipeline remains unchanged. When the pipeline resistance coefficient changes, the flow distribution ratio also changes. After the temperature control valve operates, essentially the resistance coefficient of the temperature control valve changes, and the corresponding pipeline flow rate also changes. Therefore, the functions of the temperature control valve and the balancing valve do not conflict. After the temperature control valve is installed, the actual opening of the temperature control valve changes with the load. If the user load on pipeline B in Figure 1 increases, the corresponding temperature control valve on the pipeline will be opened larger, resulting in an increase in the flow of the pipeline. However, if the loads of all other users except pipeline B do not change, it stands to reason that their corresponding high temperature structural ceramic control valves and their required flow rates should not change. However, changes in the flow rate of pipeline B will inevitably affect the increase in the total flow rate, which will in turn lead to changes in the flow rates of other pipelines such as A and N. It has been assumed previously that the user loads other than B have not changed, so the temperature control valves on the A and N pipelines should not operate. However, due to the influence of changes in the flow rate of the B pipeline, the temperature control valves on the A and N pipelines must also operate and make necessary adjustments. In other words, after the balance valve is installed, there is still mutual influence between the pipelines, which prompts the balance valve to continuously adjust. On the other hand, if all users except N pipeline require an increase in flow, the total flow rate may be too large, resulting in insufficient pressure head at N users. Even if the temperature control valves on N pipeline are opened to the maximum, It is also possible that the requirements cannot be met. In short, installing a balancing valve for initial adjustment can better maintain the normal function of the temperature control valve than blind manual initial adjustment. However, the balancing valve cannot eliminate the mutual coupling effect between the branches, and sometimes it cannot meet the adjustment requirements of the temperature control valve.

4.1.3 The hot inlet control valve is a self-operated differential pressure control valve. The combination of the self-operated differential pressure control valve and the temperature control valve can ensure the normal functioning of the temperature control valve. When the load of user A corresponding to Figure 1 decreases, the temperature control valve is closed, and the corresponding pipeline flow rate decreases, thus causing the total flow rate to decrease and the system water pressure diagram to change. As shown in Figure 2, the solid line represents the water pressure distribution before the temperature control valve is adjusted, △P is the resource pressure head required by the user; the dotted line represents the water pressure distribution after the temperature control valve is adjusted. As the total flow rate decreases, the pressure loss on the main pipe also decreases, and the pressure head provided by the external network to user A increases to △P′. If user A does not install a self-operated differential pressure control valve, the temperature control valve will be further closed due to the increase in the pressure head provided by the external network. This will repeatedly form a positive feedback, making the temperature control valve unable to perform its function normally. However, if a self-operated pressure difference control valve is installed, the self-operated pressure difference control valve can automatically adjust according to changes in pressure difference.