Analysis of Energy-saving Optimization Control of Cold Water Pump in Building Control System
A large number of investigations have shown that 13, in large and medium-sized buildings in China, the energy consumption of air conditioning and refrigeration systems accounts for 40% to 50% of the total building energy consumption, which is more than 30% higher than the average level of developed countries. Among the total energy consumption of the entire air-conditioning refrigeration system, the energy consumption of the freezing station equipment (chiller units, cooling towers, water pumps, etc.) accounted for more than 50%, of which the energy consumption of frozen water pumps accounted for more than 10%. Therefore, the self-controlled optimal design of the refrigeration pump and the cooling pump and the adoption of energy-saving reform measures can produce very significant economic and social benefits. By analyzing the performance of the chilled water pump of the air-conditioning system, dynamic load tracking is achieved to achieve energy-saving effects. This paper takes the reconstruction of the refrigerating station of a cigarette factory production workshop as an example. Through the analysis of the characteristics of the refrigerating pump and the cooling pump, the energy-saving optimization reform measures are proposed. 1 Overview of Cold Water Pumping System The cooling station is a facility that provides cold source for central air-conditioning units in the whole plant. It includes 2 chillers, 3 chilled water pumps and 3 cooling water pumps. The total installed capacity is about 500 kW, which is the main part of the whole plant. Energy-consuming equipment, all equipment before the transformation are manual start-stop operation mode.According to the characteristics of the pump's own operating parameters, in order to implement a comprehensive monitoring of the controlled equipment, the program will be divided into conventional DDCI/O monitoring of the refrigeration station Point monitoring and communication integrated monitoring: DDC controller is used for pump operation parameters, over-voltage and over-current alarm, remote start-stop, etc., and is monitored and controlled through water flow switches, smart meters, electric control box interfaces, etc.; Equipment such as inverters are monitored and controlled through communication interfaces, and the corresponding control strategies are implemented to achieve the goal of energy conservation and consumption reduction. 2Cooling pumps parallel operation frequency control strategy Table 1 Refrigeration station chilled water pump configuration head/speed/motor power/number/stage refrigeration pump 476 650―01, according to its technical manual, evaporator rated flow is condenser rated flow of 467m3/ h The minimum alarm flow rate is 200m3/h. In actual operation, two 45kW head pumps with a head of 24m are supercharged by a supercharging device, and their heads can reach 38m. The flow rate after Q pressurization is 476X24+38300m: Vh. In this way, it is feasible to achieve the same lift of the three pumps through the process transformation and to make the three chilled pumps run in parallel. Parallel operation water supply can be adjusted through frequency conversion control mode to control the speed of 3 pumps. 2.1 Analysis of operating conditions of parallel operation of chilled pumps According to the analysis of the characteristics of pumps, the characteristic curves of 3 pumps operating in parallel are more flat, because the water supply valve of air conditioning units is dynamic according to temperature conditions. Adjusting the amount of water supply leads to dynamic changes in resistance and local resistance along the pipelines of the system, and thus the characteristics of the pipeline are different. This paper summarizes the control methods into two types: the steep increase of the pipeline characteristics and the gradual increase of the pipeline characteristics ( For example, points 1, 2 and 3 represent the operating status points when the A pump, 2 A pumps, 2 A pumps and 1 B pump are connected in parallel. It can be seen that, due to the steep increase in the characteristic curve of the pipeline, the flow rate of the three pumps in parallel operation increases little. (Ffter increase of the characteristic pipeline and the parallel operation of a pump The operation of the water turbine is not necessary from the perspective of energy conservation. All of them are turned on, and only two of them can be turned on, as shown in Table 2. The number of chillers to be turned on requires circulating water Am3.h - two chilled water pumps are turned on. It can be seen that the flow of three pumps in parallel increases greatly and can be satisfied. Chiller operation requirements, so three pumps can be adjusted at the same time frequency. The steep increase and slow increase operation modes can be selected and set from the configuration software according to the site conditions, so that different pump operation conditions are automatically put into operation according to the characteristic mode. 2.2 Refrigeration pumps running in parallel FM control process describes the schematic diagram of the air conditioning system piping, water pump pressure head, in addition to the consumption of chillers, pipes, pipe fittings, mainly consumed in the air conditioning unit two-way control valve and coil . Maintaining a relatively constant pressure difference between the two-way regulating valve and the coil is an important condition for good regulation quality. In the middle, the pump starts to operate at the point 1 in the figure. At this time, the flow is, the head is the calendar, the pipe characteristic curve is, and the pump running speed is ni. When the air conditioning load is reduced, the valve Ti opening decreases and the flow decreases. , The tube resistance increases. If the frequency conversion is not adjusted at this time, the tube resistance characteristic curve changes from Ri to R2. At this time, the flow becomes 02 head to H2, and the operating point becomes 2H2―Hi is consumed on the valve Ti. Excessive energy. If variable frequency control is used, the pump speed is reduced to 2 and the operating status point is changed to 3, the pump head will be H3, and the shaft power of the pump will be reduced. Pump frequency modulation operating conditions The pump speed can not be arbitrarily reduced, it is to maintain the basic goal of APi + AP2 constant, but also to ensure the minimum flow requirements of the chiller, and in order to make the pump run at higher efficiency, generally It is required to operate above 25Hz. Therefore, in most cases, the water pump cannot operate at the state point 302 through the bypass valve to return to the return pipe. The FM pump's FM operation control process is as shown. Frequency modulation operation control flow of frozen water pump 2.3 Regulating valve between main channel of chilled water supply and return water As shown in the figure, the adjustment valve needs to be installed on the main pipe for return water so that the cold water machine can be ensured when the opening degree of the two-way valve of coil is small. The minimum amount of circulating water. Cigarette factory refrigerating station chiller evaporator rated flow of 392m3 / h minimum flow of 200m3 / h assuming the boot in the most unfavorable circumstances, the design of the supply and return bypass pipe flow 250m3 / h, check the air conditioning design manual design speed The pipe diameter calculated for im/s is DNi50. Therefore, the DNi50 electric control valve is added to the main pipe of the supply and return water. Normally, the electric control valve T2 is in the closed or minimum state. When the freezing pump is operated at 25Hz, the differential pressure of the chilled water supply and return pipe is still greater than the pressure difference APi+AP2 on both sides of the terminal air conditioning coil, the two coils The valve Ti has a small opening and the electric control valve T2 starts to regulate, on the one hand to ensure that the pressure difference APi+AP2 is constant and on the other hand to guarantee the minimum flow requirement of the chiller. 3 Cooling pumps parallel operation control strategy Air conditioning system schematic table 3 Cooling station cooling pump configuration Flow rate / chiller condenser rated flow of 467 m3 / h, cooling water pump frequency operation. 3.1 Cooling water pump parallel operation conditions analysis As the power of 75 kW head 38m cooling pump flow is only 486, than the single chiller rated flow is only large ", if the pipeline special cooling station cooling water pump configuration as shown in Table 3 Show. The curve of the pump can't make the operating status of the pump at the rated status of the cooling pump, so it is difficult to meet the requirement for the flow when the chiller reaches the full load operation. Therefore, when a single chiller is in operation, two cooling pumps with a head of 38m can be started at the same time, or one cooling pump with a head of 32m (a flow rate of 790m/h) can be started. When two chillers are running at the same time, they are rated. The flow requirement is 934mVh. Therefore two pumps with a head of 38m in parallel operation (maximum parallel flow of 972m3/h) or a single cooling pump with a head of 32m (flow rate of 790mVh) cannot meet the flow requirements. However, the parallel operation of three pumps can easily cause the phenomenon of large pumps and small pumps. Therefore, the cooling pumps must be configured with three pumps of the same type. 3.2 Increase the multi-function control valve at the outlet of the cooling pump When the centrifugal pump starts, there is no water speed in the pump outlet pipe, so there is no pipe resistance and height resistance resistance, the pump head is very low, and the flow rate is very large. At this time, the pump motor ( The shaft power) output is very large (according to the pump performance curve) is easily overloaded, causing damage to the motor and the line of the pump. Therefore, the outlet valve must be closed at startup in order for the pump to operate normally. When the outlet pressure rises to the normal value, the outlet valve is fully opened in time to prevent the fluid in the outlet valve from opening for a long time. In order to ensure the normal operation of the water pump, gate valves and check valve parts are installed on the outlet pipe of the pump. These two valve parts play different roles during the operation of the water pump: the valve is normally closed and the pump starts. The gate valve opens slowly and the valve closes slowly when the pump stops. The closed-gate start and closed parking of the pump can effectively prevent the water hammer from being turned on and stop the water hammer at the pump. At the same time, the motor load at the time of starting the water pump is reduced. The shaft power of the water pump at the zero flow rate is the smallest, generally only the power of the design shaft. 30%. Another function of the gate valve is to provide a safe inspection condition for the valve and the pump, such as the check valve installed between the gate valve and the pump, to prevent backflow of the water with pressure pipe. The check valve can prevent the change of flow direction caused by sudden power off and prevent reverse flow. The cooling plant's cooling water pump power is 75kW 110kW, the rated current is 136A, 200A, the current when the water pump starts directly is up to 190A, 280A, so when the pump is turned on, a star-delta start-up method is used to install the cooling water pump outlet automatically. Function control valve, automatic start and stop control. 4 concludes the speech This text has proposed a concrete transformation solution to the characteristic of the existing water pump equipment, has analyzed the characteristic change of the parallel characteristic of the water pump, through the frequency conversion control, increases the side energized control valve and other related measures, can achieve the optimized control, the energy conservation reduces the consumption purpose. Jiangmen Kunxin new Material Technology Co.,Ltd , https://www.kunxinglobal.com