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Heating metering charges, the radiator is equipped with temperature control valve. Due to the regulation of the thermostatic valve, the heating system is changed from a constant flow (ie, mass adjustment) operation to a variable flow operation. However, the change of the system circulation flow is caused by the throttling effect of the temperature control valve (or the electric regulating valve) at this moment.
Observed from the working curve of the circulating pump, the operating point will shift to the left, resulting in increased pump head, flow decreases, while the motor output power, a considerable proportion of consumption in the throttling of the control valve, resulting in electric energy Unnecessary waste. At present, a considerable amount of hot and cold water supply system, the use of pressure regulator for variable flow regulation. Specifically, the pressure regulator is installed on the bypass pipe of the heat source or the cold source. When the user needs to change the load of heat (cold) and the regulating valve on the radiator (or the fan coil), it will cause the bypass pipe On the pressure difference changes, this time the pressure regulator to play a role in maintaining the bypass pressure constant, in order to regulate the user system changes in circulation flow. It should be said that this adjustment method for improving the user control valve (such as temperature control valve, electric control valve) is good for working conditions, but from the power point of view, there is no improvement.
From the goal of improving the system energy efficiency, in the design of the heating system for the measurement of charges, the variable flow design of the system circulating pump should be synchronized. Minimize the energy loss caused by unnecessary throttling. In doing so, you can at least bring the following benefits:
First, improve system energy efficiency. Circulating water pump to achieve variable flow control, during the entire operation, saving at least 30-50%. This technical measure, the actual energy saving potential is far more than the current discussion about the choice of circulating pump head should not be too obvious effect.
Second, to improve the control valve (temperature control valve, electric control valve) of the working conditions. If the circulating pump to implement constant flow operation, when the load demand changes greatly, the opening of the control valve will be within a wide range of changes, not only affect its service life, but also prone to failure. When the circulating pump to achieve variable flow control, the size of its flow, with load changes in timely control. In this way, the control valve is always in fine-tuning state, not only improved regulation, but also greatly improve their working conditions, the superiority is obvious.
Second, but also with the adjustment function of self-balancing valve. For self-balancing valve, the domestic has gradually been widely used. For self-balancing valve, the constant flow system (such as the circulating pump speed operation, installation of three-way valve, etc.), its superiority has been recognized by the majority of professionals.
But in the variable flow system, but also the use of self-balancing valve? Has become a hot topic of concern to the industry. It should be recognized that the use of self-balancing valves is defective in variable flow systems where the circulating pump is running at a fixed speed. People are familiar with: The function of self-balancing valve is to automatically limit the system flow to set the flow rate. When the system needs a small flow conditions, the control valve (temperature control valve, electric control valve, etc.) will be closed, this time self-balancing valve to maintain the original set flow, the valve tends to open big. This appears regulating valve and self-balancing valve action uncoordinated phenomenon. If we then use a circulating pump variable flow control, the total system flow will decrease with the load in real time become smaller, resulting in self-balancing valve before and after the differential pressure is less than the working pressure of its spring, then self-balancing valve is no longer open , Uncoordinated phenomenon can disappear.
So some people may ask, in the variable flow system, why install self-balancing valve? In my opinion, it is also very important that the primary function is to automatically perform the initial regulation function within the system. In order to achieve a complete realization of the circulating pump variable flow control, the structure of the system must be properly adjusted, that is to say that two-stage pumping system should be vigorously promoted. At present, we rarely use this system in the domestic heating system, almost all of them are a single-stage pump system of circulating water pump. The so-called single-stage pump system, is the circulating pump that is hot (cold) source circulation pump pipe network circulation pump. The two-stage pump system, the hot (cold) source circulation pump and pipe network circulation pump separately. In the choice of circulating pumps, the circulating flow of the system design flow. Only the choice of head is different, hot (cold) source of circulation pump head only consider the resistance of hot (cold) source; pipe network circulating pump only consider the resistance of the pipe network and users.
Why should we emphasize circulating pump variable flow control to match the two-stage pump system? The purpose is to fully tap the potential of saving. We know that, for boilers or chillers, the circulating water flow is generally controlled not less than 70% of the design value. This greatly limits the regulation of the system circulating flow rate. In order for the system to circulate at less than 70% of the design flow and without affecting the normal operation of the boiler or refrigerator, the use of a two-stage pump system is a natural occurrence. However, the problem now is that the real application of this technology in practical projects has encountered many difficulties. Mainly designers are not familiar with two-stage pump system, refused to adopt this design. Therefore, how to achieve consensus in the industry, it has become imperative.
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