Heating system operating conditions
The circulation flow of the heating system directly affects the heating quality and heating effect. The choice of heating flow is too large, resulting in an increase in investment and operating costs; the choice of circulating flow is too small, not only can not guarantee the quality of heating, but also will lead to greater waste. The general design calculation cycle flow is calculated as follows:
G=Q/C(tg-th)×3.6×a1×a2[2]
In the formula:
G: Calculate the circulating flow, m3/h
Q: design heat load, kw
C: specific heat of water, kJ / (kg · ° C)
Tg, th: designed for return water temperature, °C
A1: heat loss correction factor, 1.05-1.1
A2: correction coefficient of water supply rate, 1.05-1.02
The water temperature of the net design should be 115-130 °C according to the specifications, and the return water temperature should be 70-80 °C. The water supply temperature in our school can reach 90-100 °C, the return water temperature is 80 °C, the temperature difference. It also does not meet the 45-50 °C standard. Under the premise of constant flow, the temperature difference between the supply and return water directly affects the temperature of the household, and the thermal load and the temperature difference directly determine the flow. Therefore, the design flow calculated by the above formula is very different.
The constant flow and quality heating method is also the common way of our school in China. It should be excessive to the variable flow heating method in the Nordic area, that is, the indoor room temperature requirement is 20-25 °C, and the indoors only need to maintain 6 The duty heating temperature of -8 °C, first of all, must have sufficient capacity of heat source and perfect operation and control means. However, our school has insufficient heat sources and is less likely to be improved in the near future. Therefore, only by using regulation and control can we improve the status quo.
1. Unbalanced
The heating system in operation is in the state of “large flow, low water temperature, small temperature difference, high power consumptionâ€. The reason is that the water supply flow caused by the imbalance of water imbalance between the heating pipe network loops is not in place. However, this kind of operation does not relieve the serious hydraulic imbalance, but increases the pump power consumption. Many outdoor heating pipes are unbalanced, the flow is not in place, the user flow near the heat source is too large, the room temperature is too high, the window is cooled, a lot of heat is lost, the user flow away from the heat source is insufficient, the room temperature is too low, “near heat is far cold†The phenomenon is more serious. In order to increase the room temperature of the end user, one is to increase the circulating flow rate, and the other is to increase the water supply temperature or heat supply. In short, it is not to increase the power consumption, or to increase the heat consumption to eliminate the thermal imbalance, to cover the existence of hydraulic imbalance. In this way, the "cold" users are satisfied, and a few non-hot users have also improved, but the "hot" users are even hotter.
The main cause of hydraulic imbalance in the heating pipe network is that the resistance in the system is improperly distributed and cannot be operated according to the design requirements. As a result, the flow distribution in the system is uneven, and the imbalance of near-heat and cold is occurring. This situation is not solved by simply changing the pipe diameter, flow rate and using ordinary valve adjustments. The manual regulating valve is a statically adjusted hydraulic balancing component. When the balance adjustment of the heating pipe network is realized, only the sequence is repeated multiple times to approach the balance, and the heating range is larger, and the number of repeated adjustments is more. Repeated debugging is required when the load increases and decreases, and it must be re-commissioned every year. Since this static balancing element does not automatically eliminate the residual head in the heating system, it is generally only used under the premise of small scale, load and working conditions.
2, high energy consumption
Circulating water pump is one of the important equipments in the central heating system. It relies on the resistance along the way and sends heat to thousands of households. At the same time, it is a big consumer of electricity. In the hot water heating system, the working point of the circulating water pump, that is, the intersection of the GH characteristic curve of the circulating water pump and the network characteristic curve. Only at this point of flow, the pump produces the same pressure head as the network requires, and the pump's operating point can operate at optimum efficiency. However, the calculated network characteristic curve and the actual network characteristic curve, due to the hydraulic imbalance of the system, the actual flow of the system will be greater than the calculated flow, and the result is that the "designed" operating point is shifted to the right of the GH characteristic curve ( See below). The degree of work point offset is related to the magnitude of the system hydraulic imbalance. Since many heat networks are currently operating in a large flow mode, the working point of the pump is often operated under uneconomical working conditions. Since the flow rate is in a cubic relationship with the power of the pump shaft, the operation mode of the large flow means that the power consumption is increased. Large, such as the heating system with a construction area of ​​about 30,000 square meters, the electric power of the circulating water pump is between 15-30kW. If the circulating water volume of the system is increased by 1.4 times, the electric power of the pump is increased by 2.7 times, reaching 41-82kW heating heating network. .
Third, the solution: self-operated flow control valve - to achieve dynamic balance of the heating system pipe network
If the severe hydraulic imbalance of the primary network and the secondary network system cannot be fundamentally solved, then as the heating area increases, not only will the energy be wasted but the heating quality will continue to decrease. After many investigations, our school selected the self-operated flow control valve produced by Gu'an Aineng Heating Equipment Co., Ltd., taking the administrative campus as a pilot. After nearly one heating season, the primary network system was replaced by various heat exchange stations. The flow rate is reasonably distributed, so that the temperature difference between the far and near ends of the secondary network is reduced to 0-2 °C, so that the heat exchange effect of the last station is close to the heat exchange effect of the first station, the heating effect is obviously improved, and the indoor temperature of the end heat user is reached. 18 ± 2 ° C.
1, the principle
The self-operated flow controller is a multi-hole plate combination linkage device, which is a relatively reliable dynamic hydraulic balance component in China. It consists of a flow setting visual control valve, namely a manual orifice plate (equivalent to a static hydraulic balancing element) and two valve flaps and a spring-and-diaphragm dynamic adjustment device, ie an automatic adjustable orifice plate (equivalent to A dynamic hydraulic balance component).
The manual adjustable orifice plate is the circulating flow value of the user according to the design heat load. Use the special equipment to rotate the flow visual adjustment line, and adjust the required flow value to the flow tick indication value. Once the flow rate is set, its value is forever balanced, and is not affected by the differential pressure and heat load of the heating system. The automatic orifice plate in the self-operated flow controller will automatically adjust the resistance by means of the differential pressure of the system until the residual head of the system is completely eliminated, thus ensuring that the flow setpoint remains the same. Therefore, no matter how the heat load of the heating pipe network changes, as long as a self-operated flow controller is installed horizontally on the return pipe of the user's hot inlet, the heating pipe network system can automatically achieve balance under the action of the dynamic adjustment function.
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