First, the necessity of pump energy-saving reform
Central air-conditioning is a big power consumer in the building. The air-conditioning power consumption accounts for about 60% of the annual electricity bill. Therefore, the energy-saving renovation of central air-conditioning is particularly important.
Due to the design, the central air-conditioning system must be designed with the hottest weather and maximum load, and leave a design margin of 10-20%. However, in reality most of the time, the air-conditioning system will not operate under full load. The surplus, so the potential for energy saving is relatively large. Among them, the freezing machine can be loaded or deloaded according to the load changes. The chilled water pump and the cooling water pump can not be adjusted accordingly with the load change, and there is a great waste.
The flow rate and pressure difference of the pump system are achieved by the valve and bypass regulation. Therefore, the phenomenon of large cut-off loss, large flow rate, high pressure, and low temperature difference inevitably exists, which not only wastes a lot of electric energy, but also causes the central air-conditioning The end does not achieve reasonable results. In order to solve these problems, the water pump needs to adjust the water flow and close the bypass as the load changes.
Because the water pump adopts the Y-start method, the starting current of the motor is 3 to 4 times of its rated current. The starting current of a 90KW motor will reach 500A. Under the impact of such large current, the contactor and the motor The service life is greatly reduced. At the same time, the mechanical shock during start-up and the phenomenon of water droop when the pump is stopped are liable to cause damage to mechanical parts, bearings, valves, pipes, etc., thereby increasing maintenance workload, spare parts and spare parts costs.
In summary, in order to save energy and costs, the pump system needs to be reconstructed, and mature inverters are used to achieve market research and understanding so as to save energy and extend the use of motors, contactors, and mechanical parts, bearings, valves, and pipes. life.
This is because the frequency converter can adjust the rotation speed of the water pump motor according to the change of the load of the freezing water pump and the cooling water pump, and adjust the freezing water pump and the cooling water pump accordingly to meet the normal work of the central air conditioning system so as to achieve the purpose of energy saving. As the speed of the water pump motor drops, the electrical energy absorbed by the motor from the grid will be greatly reduced.
Its reduced power consumption P=P0[1-(N1/N0)3] (1) Reduced flow rate Q=Q0[1-(N1/N0)] (2)
N1 is the speed after the change, N0 is the original speed of the motor, P0 is the power consumption of the motor in the original motor speed, and Q0 is the pump flow rate in the original motor speed.
It can be seen from the above equation that the reduction of the flow rate is proportional to the one-way reduction of the rotation speed, but the reduction of the power consumption is proportional to the third power of the reduction of the rotation speed.
For example, assuming that the original flow rate is 100 units and the energy consumption is also 100 units, if the rotation speed is reduced by 10 units, (2) The formula Q=Q0[1-(N1/N0)]=100*[1-(90) /100)]=10 It can be found that the flow rate has changed by 10 units, but the power consumption is given by (1) Formula P=P0[1-(N1/N0)3]=100*[1-(90/100)3] It can be concluded that the power will be reduced by 27.1 units, which is a reduction of 27.1% from the original.
Since the inverter is a soft-start method, after the inverter is used to control the motor, there is no inrush current during start-up and operation of the motor, and the inrush current is the most important and most direct factor affecting the life of the contactor and the motor. After the inverter controls the motor, it can also avoid the phenomenon of water droop, so it can greatly prolong the service life of the motor, contactor and mechanical parts, bearings, valves and pipes.
Second, the pump energy-saving reform program
The central air-conditioning system is usually divided into two systems of freezing (medium) water and cooling water (as shown in the figure below, the left part is the freezing (medium) water system, and the right part is the cooling water system). According to the latest information at home and abroad, and through many successful investigations of the closed-loop control reform of the central air-conditioning pump system, the energy-saving retrofit schemes for the pump system are now mostly implemented using frequency converters.
1. Closed-loop control of freezing (medium) water pump system
〔1〕Closed-loop control of chilled water pump system in cooling mode
This solution ensures the minimum operating frequency of a cryopump converter when it is guaranteed that the chilled water flow rate is supplied at the end of the equipment. It is set to the lower limit frequency and locked, and the frequency regulation of the frequency conversion frozen water pump is installed in the chilled water system. The temperature sensor on the return supervisor detects the return temperature of the chilled water, and then controls the frequency of the frequency converter to increase or decrease via the temperature set by the temperature controller. The control method is that the frequency is increased when the temperature of the frozen return water is greater than the set temperature.
〔2〕Closed-loop control of chilled water pump system under heating mode
This mode is a control scheme for the chilled water pump system when the central heat pump is operating (ie, heating). As in the cooling mode control scheme, under the condition that the supply of chilled water at the end of the equipment is guaranteed, the minimum operating frequency of a refrigerating pump frequency converter is determined, and it is set as the lower limit frequency and locked, and the frequency adjustment of the frequency conversion frozen water pump is passed. A temperature sensor installed on the return water main of the chilled water system detects the return temperature of the chilled water, and then controls the frequency of the frequency converter to increase or decrease via the temperature set by the temperature controller. The difference is: when the temperature of frozen return water is lower than the set temperature, the frequency is infinitely adjusted. When the temperature of the return water of frozen water detected by the temperature sensor is higher, the output frequency of the inverter is lower.
The series of intelligent frequency converters produced by Wuxi Ilek Electric Co., Ltd. have the above functions. They are detected by a temperature sensor mounted on the return pipe of the chilled water system (eg, mounted on the A of the return pipe of the chilled water system). Water return temperature, and can directly adjust the parameters of the inverter so that the system temperature is controlled within the required range.
In addition, for the shortcomings of insufficient temperature exchange during the first operation of the previous retrofit program, the series of intelligent inverters produced by Wuxi Illek Electric Co., Ltd. have increased the function of first-time full-speed operation, and the chilled-water system can be fully set by setting the frequency converter parameters. Exchange for a period of time, then according to the temperature of the frozen return water, steplessly adjust the frequency, and the inverter output frequency is obtained by detecting the return water temperature signal and the temperature set value by PID operation.
2. Closed-loop control of cooling water system
At present, the scheme for reforming the cooling water system is the most common, and the power saving effect is also significant. The solution also ensures that the cooling tower has a certain amount of cooling water flowing out, and the cooling water flow is adjusted by controlling the output frequency of the frequency converter. When the temperature of the central air-conditioning cooling water outlet is low, the cooling water flow is reduced; the central air-conditioning cooling water When the outlet water temperature is high, the flow of cooling water is increased so as to achieve the purpose of saving energy and increasing efficiency under the premise of ensuring the normal operation of the central air conditioning unit.
Most of the existing control methods first determine the minimum operating frequency of a cooling pump frequency converter and set it as the lower limit frequency and lock it. The frequency of the frequency conversion cooling water pump is adjusted by taking the temperature difference between the inlet and outlet of the cooling pipe and the outlet temperature signal. When the inlet and outlet water temperature difference is greater than the set value, the frequency is infinitely increased. When the inlet and outlet water temperature difference is less than the set value, the frequency is infinitely adjusted. At the same time, when the cooling water outlet water temperature is higher than the set value, the frequency priority is increased without limit, when the cooling When the water outlet water temperature is lower than the set value, the frequency is adjusted according to the temperature difference change. The greater the temperature difference between inlet and outlet water, the higher the output frequency of the inverter; the smaller the inlet and outlet water temperature difference, the lower the output frequency of the inverter.
Wuxi Yilaike Electric Co., Ltd. through market research and understanding, and multi-practical application and demonstration, the current series of intelligent inverter used for closed-loop control of cooling water system adopts the same control mode as the closed-loop control of refrigeration pump system under cooling mode.
Compared with other manufacturers' control methods, the advantages are:
1. Simply install a temperature sensor at the water outlet of the central air-conditioning cooling pipe (as shown in Figure B, which is installed in the cooling water system's central air-conditioning cooling water outlet mains B), which is simple and reliable.
2. When the cooling water outlet temperature is higher than the temperature upper limit setting value, the frequency is directly increased to the upper limit frequency.
3. When the cooling water outlet temperature is lower than the temperature lower limit setting value, the frequency is directly reduced to the lower limit frequency. It is difficult to achieve this by adjusting the temperature difference between the inlet and outlet of the cooling pipe.
4. When the temperature of the cooling water outlet water falls between the lower temperature setting value and the upper temperature setting value, PID calculation is performed on the cooling water outlet water temperature and temperature upper and lower limit setting values ​​to achieve the stepless speed regulation of the frequency and the closed loop. Control is quick and accurate.
5, energy-saving effect is more obvious. When the cooling water outlet temperature is lower than the temperature upper limit setting value, the cooling pipe inlet and outlet water temperature difference adjustment method does not add the factor of low outlet water temperature to the energy-saving consideration range, and only the temperature difference controls the frequency steplessly. , And use the upper and lower temperature to adjust the way to fully consider this factor, so the energy-saving effect is more obvious, through a number of user market surveys, the average power saving rate to increase more than 5%, saving rate of 20% to 40% .
6, with the first start full speed operation function. By setting the values ​​in the frequency converter parameters, the water system can be fully exchanged for a period of time, avoiding the system water flow being too small due to insufficient heat exchange at the start of operation.
The long-term use of dozens of units in Suxichang and Shanghai, Hangzhou, Henan, Jiangxi, Zhenjiang, Shandong, Nanjing, etc., the energy-saving rate of series of intelligent inverters produced by Wuxi Yingfu Electric Co., Ltd. are all around 40%, and the energy-saving effect is remarkable. , The product performance is reliable, but also can greatly extend the service life of the motor, contactor and mechanical parts, bearings, valves, pipes, which can bring better economic benefits for the central air-conditioning units.