First, project introduction
The central air-conditioning system of Shenzhen Central Business Plaza consists of rt1-rt3 and rt4 systems. The rt1-rt3 system is composed of three centrifugal main engines and four 55kw chilled water pumps. Four chilled water pumps and four cooling water pumps operate in a three-use, one-stand-by mode. It is an industrial frequency operation. The Rt4 system is composed of two 30kw cooling water pumps in one Ligan host. Two chilled water pumps and two cooling water pumps are operated in a single-use and one-stand-by mode, which is run at industrial frequency. Due to changes in seasons, climate, and users, the amount of air-conditioning is constantly changing. The frozen-water pumps and cooling water pumps that are operated at industrial frequencies cannot adjust the amount of chilled water and cooling water in response to the amount of air-conditioning, resulting in great waste of electrical energy. Energy-saving retrofitting of chilled water pumps and cooling water pumps.
Second, the air conditioning system composition and working principle
The central air-conditioning system consists of the following components:
1. Chilling unit: This is the "cryogenic source" of the central air-conditioning system. The circulating water leading to each room is subjected to "internal heat exchange" by the refrigeration unit and cooled to "chilled water".
2. Cooling tower: Used to provide "cooling water" for the chiller unit.
3. "External heat exchange" system: consists of two circulatory systems:
A. Cold East Water Circulation System: Composed of a refrigerating pump and a chilled water pipe. The chilled water that flows out from the refrigeration unit is fed into the chilled water pipeline by the freezing pump, and the heat in each room reduces the temperature in the room. The chilled water that flows into the room from the freezing unit is referred to as "water"; the frozen water tank that returns to the freezing unit after flowing through all the rooms is called "backwater".
B. Cooling water circulation system: It consists of cooling pump, cooling water pipe and cooling tower. The chiller unit exchanges heat so that the water temperature cools and at the same time it will release a lot of heat. This heat is absorbed by the cooling water and raises the temperature of the cooling water. The cooling pump presses the warmed cooling water into the cooling tower, exchanges it with the atmosphere in the cooling tower, and then returns the cooled cooling water to the refrigeration unit. This cycle continues to take away the heat released by the cooling unit.
It can be seen that the working process of the central air-conditioning system is an energy conversion process that continuously performs heat exchange. Here, the chilled water and cooling water circulation system is the main transmitter of energy. Therefore, the control of the chilled water and cooling water circulation system is an important part of the central air conditioning system.
The external heat exchange of central air conditioning in Shenzhen Central Business Plaza is completed by two circulating water systems. The difference between the return water temperature and the inlet/outlet water temperature of the circulating water system reflects the heat that needs to be exchanged. Therefore, controlling the flow rate of the circulating water based on the difference between the temperature of the return water and the temperature of the incoming/outgoing water to control the speed of heat exchange is a more reasonable control method.
Third, the principle of frequency conversion energy-saving
According to the principle of the fan (water pump), we know that the flow rate of the fan (water pump) is proportional to the primary speed, the pressure is proportional to the rotational speed, and the shaft power is proportional to the third power of the rotational speed.
Q2/Q1=n2/n1 (1)
H2/H1=(n2/n1)2 (2)
P2/P1=(n2/n1)3 (3)
Curve 1 is the fan (water pump) resistance characteristics, curve 2 is the flow rate and pressure curve at the power frequency speed. At this time, when the fan pump works at point A, the shaft power P1 is equal to the product of Q1 and H1, which is the area AQ10H1A in the figure. Proportional. To reduce the flow rate from Q1 to Q2, if a damper (baffle) is used, the working point moves from A to C, the flow rate decreases, the pressure rises, and the shaft power decreases less; if frequency conversion is used, the working point is A moves to B. Under the condition that the same flow rate Q2 is satisfied, the pressure also decreases and the shaft power is greatly reduced.
Because the design must consider the maximum amount of use, the margin is generally more than 20%. Assume that the operating frequency of the motor is reduced from the power frequency to 40Hz, that is, the water flow is reduced to 80% of the maximum usage.
P(40)/P(50)=(40/50)3=51.2%
Saving rate = 1-51.2% = 48.8%
Even if the operating frequency of the motor is reduced from the power frequency to 45Hz, that is, the water flow is reduced to 90% of the maximum usage, the power saving rate = 1-P(45)/P(50)=1-73%=27%
Fourth, frequency conversion energy analysis
In the central air-conditioning system of Shenzhen Central Business Plaza, the RT1-RT3 system, four 55KW chilled water pumps and four 55KW cooling water pumps all operate in a three-in-one mode. Set the pump with industrial frequency operation (power frequency pump) to provide the flow Qn, then:
4.1 One pump's variable frequency operation and energy saving
4.1.1 When the required flow is 1.5Qn
At this time, one pump is running at a frequency, providing a flow rate of Qn, and a variable frequency pump only providing a flow of 50% of Qn. The power consumption of the variable frequency pump is 55X0.53=6.875KW.
The total power consumption is: 55+6.875=61.875(KW)----48.125KW compared with no frequency conversion, and the power saving rate is 43.75%.
4.1.2 When the Required Traffic is 2.5Qn
At this time, 2 pumps are operated at industrial frequency to provide a flow rate of 2Qn. The frequency conversion pump only needs to provide 50% of Qn flow. The power consumption of the variable frequency pump is: 55X0.53=6.875KW.
The total power consumption is: 55+55+6.875=116.875(KW)----The power consumption is 48.125KW compared with no frequency conversion, and the energy saving rate is 29.17%.
4.2 Energy Savings of Frequency Conversion Operation of Two Water Pumps
4.2.1 When the Required Traffic is 1.5Qn
At this time, 2 pumps are operated in variable frequency, each pump only needs to provide 75% of Qn flow, and the power consumption of the variable frequency pump is: 55x0.753=23.2 (KW)
The total power consumption is: 23.2x2=46.4 (KW)---lower than the power consumption of one pump. Compared with no frequency conversion (two industrial frequency pumps), the power consumption is 63.6KW, and the energy saving rate is 57.82%.
4.2.2 When the Required Traffic is 2.5Qn
At this time, 1 pump is running at industrial frequency, providing 1Qn flow rate, 2 pumps running in variable frequency, each frequency conversion pump only needs to provide 75% of Qn flow, and the power consumption of the variable frequency pump is: 55x0.753=23.2 (KW)
The total power consumption is: 55+23.2x2=101.4 (KW)----Save 63.6KW compared with no frequency conversion, and the power saving rate is 38.55%.
4.3 Energy Savings of Frequency Conversion Operation of Three Water Pumps
4.3.1 When the Required Traffic is 1.5Qn
At this time, 3 pumps are operated in variable frequency, each pump only needs to provide 50% Qn flow, and the power consumption of the variable frequency pump is: 55x0.53=6.875 (KW)
The total power consumption is: 6.875x3=20.625(KW) ----The power consumption of the pump is lower than that of a single pump. Compared with no frequency conversion (two sets of industrial frequency pumps), the power consumption is 89.375KW, and the energy saving rate is 81.25%.
4.3.2 When the Required Traffic is 2.5Qn
At this time, 3 pumps are running at variable frequency, and each variable frequency pump only needs to provide 83.33% of Qn flow, and the power consumption of variable frequency pump is: 55x0.83333=31.83 (KW)
The total power consumption is: 31.83x3=95.49(KW) ----Save 69.51KW compared to no frequency conversion, save electricity rate 42.13%
4.4 Frequency Conversion Energy Saving List
According to the above calculations, the energy saving rate (%) for different energy-saving conversions at different flow rates can be obtained as follows:
Flow rate of one pump Frequency conversion of two pumps Frequency conversion of three pumps
Energy Saving Rate Operation Mode Energy Saving Rate Operation Mode Energy Saving Rate Operation Mode
0.7Qn 65.70 1 frequency conversion 65.70 1 frequency conversion 65.70 1 frequency conversion 1 frequency
0.8Qn 48.80 1 frequency conversion 48.80 1 frequency conversion 48.80 1 frequency conversion 1 frequency
0.9Qn 27.10 1 frequency conversion 27.10 1 frequency conversion 27.10 1 frequency conversion 1 frequency
1.0Qn 1 frequency 75.00 2 frequency conversion 75.00 2 frequency conversion 2 frequency
1.1Qn 2 frequency 83.36 2 frequency conversion 83.36 2 frequency conversion 2 frequency
1.2Qn 2 power frequency 78.40 2 frequency conversion 78.40 2 frequency conversion 2 power frequency
1.3Qn 2 power frequency 72.54 2 frequency conversion 72.54 2 frequency conversion 2 power frequency
1.4Qn 2 power frequency 65.70 2 frequency conversion 65.70 2 frequency conversion 2 power frequency
1.5Qn 43.75 1 frequency 1 frequency conversion 57.82 2 frequency conversion 81.25 3 frequency conversion 2 frequency
1.6Qn 39.20 1 frequency 1 frequency conversion 48.80 2 frequency conversion 77.24 3 frequency conversion 2 frequency
1.7Qn 32.85 1 frequency 1 frequency conversion 38.59 2 frequency conversion 72.71 3 frequency conversion 2 frequency
1.8Qn 24.40 1 frequency 1 frequency conversion 27.10 2 frequency conversion 67.60 3 frequency conversion 2 frequency
1.9Qn 13.55 1 frequency 1 frequency conversion 14.26 2 frequency conversion 61.89 3 frequency conversion 2 frequency
Flow rate of one pump Frequency conversion of two pumps Frequency conversion of three pumps
Energy Saving Rate Operation Mode Energy Saving Rate Operation Mode Energy Saving Rate Operation Mode
2.0Qn 2 frequency 37.5 1 frequency 2 frequency conversion 55.56 3 frequency conversion 2 frequency
2.1Qn 3 frequency 55.575 1 frequency 2 frequency conversion 65.70 3 frequency conversion 3 frequency
2.2Qn 3 frequency 52.27 1 frequency 2 frequency conversion 60.56 3 frequency conversion 3 frequency
2.3Qn 3 frequency 48.36 1 frequency 2 frequency conversion 54.49 3 frequency conversion 3 frequency
2.4Qn 3 frequency 43.80 1 frequency 2 frequency conversion 48.80 3 frequency conversion 3 frequency
2.5Qn 29.17 2 frequency 1 frequency conversion 38.54 1 frequency 2 frequency conversion 42.13 3 frequency conversion 3 frequency
2.6Qn 26.13 2 frequency 1 frequency conversion 32.53 1 frequency 2 frequency conversion 34.90 3 frequency conversion 3 frequency
2.7Qn 21.90 2 frequency 1 frequency conversion 25.725 1 frequency 2 frequency conversion 27.10 3 frequency conversion 3 frequency
Note: In practice, each pump has no-load loss, and the lower limit operating frequency of each pump is generally not less than 25Hz, which is equivalent to 0.5Qn.
Fifth, the advantages of frequency conversion energy-saving
The use of frequency converters for the energy-saving renovation of fans and pumps has the following advantages:
1. Save a lot of electricity.
2. The inverter can soft start the motor, greatly reducing the impact current, reducing the motor bearing wear and extending the bearing life.
3. Adjusting the flow and pressure of the water pump fan can be done directly by changing the operating frequency of the frequency converter. The baffle and valve can be reduced or eliminated, and the precision and performance of the control can be greatly improved.
4. Such as the use of air-conditioning automatic control system to achieve closed-loop control, motor speed changes with the seasons, climate and user automatic adjustment, to achieve maximum energy-saving control, energy efficiency is higher. At the same time, due to the realization of automatic control and management of equipment, personnel maintenance can be reduced, personnel costs can be saved, and the overall management level can be improved, accidents occurring and equipment damaged can be reduced, thereby bringing potential benefits.
The central air-conditioning system of Shenzhen Central Business Plaza consists of rt1-rt3 and rt4 systems. The rt1-rt3 system is composed of three centrifugal main engines and four 55kw chilled water pumps. Four chilled water pumps and four cooling water pumps operate in a three-use, one-stand-by mode. It is an industrial frequency operation. The Rt4 system is composed of two 30kw cooling water pumps in one Ligan host. Two chilled water pumps and two cooling water pumps are operated in a single-use and one-stand-by mode, which is run at industrial frequency. Due to changes in seasons, climate, and users, the amount of air-conditioning is constantly changing. The frozen-water pumps and cooling water pumps that are operated at industrial frequencies cannot adjust the amount of chilled water and cooling water in response to the amount of air-conditioning, resulting in great waste of electrical energy. Energy-saving retrofitting of chilled water pumps and cooling water pumps.
Second, the air conditioning system composition and working principle
The central air-conditioning system consists of the following components:
1. Chilling unit: This is the "cryogenic source" of the central air-conditioning system. The circulating water leading to each room is subjected to "internal heat exchange" by the refrigeration unit and cooled to "chilled water".
2. Cooling tower: Used to provide "cooling water" for the chiller unit.
3. "External heat exchange" system: consists of two circulatory systems:
A. Cold East Water Circulation System: Composed of a refrigerating pump and a chilled water pipe. The chilled water that flows out from the refrigeration unit is fed into the chilled water pipeline by the freezing pump, and the heat in each room reduces the temperature in the room. The chilled water that flows into the room from the freezing unit is referred to as "water"; the frozen water tank that returns to the freezing unit after flowing through all the rooms is called "backwater".
B. Cooling water circulation system: It consists of cooling pump, cooling water pipe and cooling tower. The chiller unit exchanges heat so that the water temperature cools and at the same time it will release a lot of heat. This heat is absorbed by the cooling water and raises the temperature of the cooling water. The cooling pump presses the warmed cooling water into the cooling tower, exchanges it with the atmosphere in the cooling tower, and then returns the cooled cooling water to the refrigeration unit. This cycle continues to take away the heat released by the cooling unit.
It can be seen that the working process of the central air-conditioning system is an energy conversion process that continuously performs heat exchange. Here, the chilled water and cooling water circulation system is the main transmitter of energy. Therefore, the control of the chilled water and cooling water circulation system is an important part of the central air conditioning system.
The external heat exchange of central air conditioning in Shenzhen Central Business Plaza is completed by two circulating water systems. The difference between the return water temperature and the inlet/outlet water temperature of the circulating water system reflects the heat that needs to be exchanged. Therefore, controlling the flow rate of the circulating water based on the difference between the temperature of the return water and the temperature of the incoming/outgoing water to control the speed of heat exchange is a more reasonable control method.
Third, the principle of frequency conversion energy-saving
According to the principle of the fan (water pump), we know that the flow rate of the fan (water pump) is proportional to the primary speed, the pressure is proportional to the rotational speed, and the shaft power is proportional to the third power of the rotational speed.
Q2/Q1=n2/n1 (1)
H2/H1=(n2/n1)2 (2)
P2/P1=(n2/n1)3 (3)
Curve 1 is the fan (water pump) resistance characteristics, curve 2 is the flow rate and pressure curve at the power frequency speed. At this time, when the fan pump works at point A, the shaft power P1 is equal to the product of Q1 and H1, which is the area AQ10H1A in the figure. Proportional. To reduce the flow rate from Q1 to Q2, if a damper (baffle) is used, the working point moves from A to C, the flow rate decreases, the pressure rises, and the shaft power decreases less; if frequency conversion is used, the working point is A moves to B. Under the condition that the same flow rate Q2 is satisfied, the pressure also decreases and the shaft power is greatly reduced.
Because the design must consider the maximum amount of use, the margin is generally more than 20%. Assume that the operating frequency of the motor is reduced from the power frequency to 40Hz, that is, the water flow is reduced to 80% of the maximum usage.
P(40)/P(50)=(40/50)3=51.2%
Saving rate = 1-51.2% = 48.8%
Even if the operating frequency of the motor is reduced from the power frequency to 45Hz, that is, the water flow is reduced to 90% of the maximum usage, the power saving rate = 1-P(45)/P(50)=1-73%=27%
Fourth, frequency conversion energy analysis
In the central air-conditioning system of Shenzhen Central Business Plaza, the RT1-RT3 system, four 55KW chilled water pumps and four 55KW cooling water pumps all operate in a three-in-one mode. Set the pump with industrial frequency operation (power frequency pump) to provide the flow Qn, then:
4.1 One pump's variable frequency operation and energy saving
4.1.1 When the required flow is 1.5Qn
At this time, one pump is running at a frequency, providing a flow rate of Qn, and a variable frequency pump only providing a flow of 50% of Qn. The power consumption of the variable frequency pump is 55X0.53=6.875KW.
The total power consumption is: 55+6.875=61.875(KW)----48.125KW compared with no frequency conversion, and the power saving rate is 43.75%.
4.1.2 When the Required Traffic is 2.5Qn
At this time, 2 pumps are operated at industrial frequency to provide a flow rate of 2Qn. The frequency conversion pump only needs to provide 50% of Qn flow. The power consumption of the variable frequency pump is: 55X0.53=6.875KW.
The total power consumption is: 55+55+6.875=116.875(KW)----The power consumption is 48.125KW compared with no frequency conversion, and the energy saving rate is 29.17%.
4.2 Energy Savings of Frequency Conversion Operation of Two Water Pumps
4.2.1 When the Required Traffic is 1.5Qn
At this time, 2 pumps are operated in variable frequency, each pump only needs to provide 75% of Qn flow, and the power consumption of the variable frequency pump is: 55x0.753=23.2 (KW)
The total power consumption is: 23.2x2=46.4 (KW)---lower than the power consumption of one pump. Compared with no frequency conversion (two industrial frequency pumps), the power consumption is 63.6KW, and the energy saving rate is 57.82%.
4.2.2 When the Required Traffic is 2.5Qn
At this time, 1 pump is running at industrial frequency, providing 1Qn flow rate, 2 pumps running in variable frequency, each frequency conversion pump only needs to provide 75% of Qn flow, and the power consumption of the variable frequency pump is: 55x0.753=23.2 (KW)
The total power consumption is: 55+23.2x2=101.4 (KW)----Save 63.6KW compared with no frequency conversion, and the power saving rate is 38.55%.
4.3 Energy Savings of Frequency Conversion Operation of Three Water Pumps
4.3.1 When the Required Traffic is 1.5Qn
At this time, 3 pumps are operated in variable frequency, each pump only needs to provide 50% Qn flow, and the power consumption of the variable frequency pump is: 55x0.53=6.875 (KW)
The total power consumption is: 6.875x3=20.625(KW) ----The power consumption of the pump is lower than that of a single pump. Compared with no frequency conversion (two sets of industrial frequency pumps), the power consumption is 89.375KW, and the energy saving rate is 81.25%.
4.3.2 When the Required Traffic is 2.5Qn
At this time, 3 pumps are running at variable frequency, and each variable frequency pump only needs to provide 83.33% of Qn flow, and the power consumption of variable frequency pump is: 55x0.83333=31.83 (KW)
The total power consumption is: 31.83x3=95.49(KW) ----Save 69.51KW compared to no frequency conversion, save electricity rate 42.13%
4.4 Frequency Conversion Energy Saving List
According to the above calculations, the energy saving rate (%) for different energy-saving conversions at different flow rates can be obtained as follows:
Flow rate of one pump Frequency conversion of two pumps Frequency conversion of three pumps
Energy Saving Rate Operation Mode Energy Saving Rate Operation Mode Energy Saving Rate Operation Mode
0.7Qn 65.70 1 frequency conversion 65.70 1 frequency conversion 65.70 1 frequency conversion 1 frequency
0.8Qn 48.80 1 frequency conversion 48.80 1 frequency conversion 48.80 1 frequency conversion 1 frequency
0.9Qn 27.10 1 frequency conversion 27.10 1 frequency conversion 27.10 1 frequency conversion 1 frequency
1.0Qn 1 frequency 75.00 2 frequency conversion 75.00 2 frequency conversion 2 frequency
1.1Qn 2 frequency 83.36 2 frequency conversion 83.36 2 frequency conversion 2 frequency
1.2Qn 2 power frequency 78.40 2 frequency conversion 78.40 2 frequency conversion 2 power frequency
1.3Qn 2 power frequency 72.54 2 frequency conversion 72.54 2 frequency conversion 2 power frequency
1.4Qn 2 power frequency 65.70 2 frequency conversion 65.70 2 frequency conversion 2 power frequency
1.5Qn 43.75 1 frequency 1 frequency conversion 57.82 2 frequency conversion 81.25 3 frequency conversion 2 frequency
1.6Qn 39.20 1 frequency 1 frequency conversion 48.80 2 frequency conversion 77.24 3 frequency conversion 2 frequency
1.7Qn 32.85 1 frequency 1 frequency conversion 38.59 2 frequency conversion 72.71 3 frequency conversion 2 frequency
1.8Qn 24.40 1 frequency 1 frequency conversion 27.10 2 frequency conversion 67.60 3 frequency conversion 2 frequency
1.9Qn 13.55 1 frequency 1 frequency conversion 14.26 2 frequency conversion 61.89 3 frequency conversion 2 frequency
Flow rate of one pump Frequency conversion of two pumps Frequency conversion of three pumps
Energy Saving Rate Operation Mode Energy Saving Rate Operation Mode Energy Saving Rate Operation Mode
2.0Qn 2 frequency 37.5 1 frequency 2 frequency conversion 55.56 3 frequency conversion 2 frequency
2.1Qn 3 frequency 55.575 1 frequency 2 frequency conversion 65.70 3 frequency conversion 3 frequency
2.2Qn 3 frequency 52.27 1 frequency 2 frequency conversion 60.56 3 frequency conversion 3 frequency
2.3Qn 3 frequency 48.36 1 frequency 2 frequency conversion 54.49 3 frequency conversion 3 frequency
2.4Qn 3 frequency 43.80 1 frequency 2 frequency conversion 48.80 3 frequency conversion 3 frequency
2.5Qn 29.17 2 frequency 1 frequency conversion 38.54 1 frequency 2 frequency conversion 42.13 3 frequency conversion 3 frequency
2.6Qn 26.13 2 frequency 1 frequency conversion 32.53 1 frequency 2 frequency conversion 34.90 3 frequency conversion 3 frequency
2.7Qn 21.90 2 frequency 1 frequency conversion 25.725 1 frequency 2 frequency conversion 27.10 3 frequency conversion 3 frequency
Note: In practice, each pump has no-load loss, and the lower limit operating frequency of each pump is generally not less than 25Hz, which is equivalent to 0.5Qn.
Fifth, the advantages of frequency conversion energy-saving
The use of frequency converters for the energy-saving renovation of fans and pumps has the following advantages:
1. Save a lot of electricity.
2. The inverter can soft start the motor, greatly reducing the impact current, reducing the motor bearing wear and extending the bearing life.
3. Adjusting the flow and pressure of the water pump fan can be done directly by changing the operating frequency of the frequency converter. The baffle and valve can be reduced or eliminated, and the precision and performance of the control can be greatly improved.
4. Such as the use of air-conditioning automatic control system to achieve closed-loop control, motor speed changes with the seasons, climate and user automatic adjustment, to achieve maximum energy-saving control, energy efficiency is higher. At the same time, due to the realization of automatic control and management of equipment, personnel maintenance can be reduced, personnel costs can be saved, and the overall management level can be improved, accidents occurring and equipment damaged can be reduced, thereby bringing potential benefits.