Central air conditioner cooling side optimization control method based on lowest energy consumption

Abstract

The invention discloses a central air conditioner cooling side optimization control method based on the lowest energy consumption. The method specifically comprises the steps that S1, an optimization mechanism is periodically triggered; s2, a cooling water pump and a cooling tower fan run at full frequency, and the number of cooling towers is limited; s3, gradient frequency reduction and combined power optimization are carried out to obtain a cooling water host side inlet and outlet water temperature difference delta T; s4, taking delta T as an adjusting target value of the cooling water pump in the current period; s5, the cooling tower control limitation in the optimizing period is released, an automatic control mode is executed, and the cooling system is made to operate in the optimal state; the power consumption of the cooling water pump and the cooling tower is effectively reduced on the premise of ensuring the heat dissipation requirement of the host by regulating and controlling the power sum of the cooling liquid pump and the host, the host and the cooling water pump are associated through the power sum of the host and the cooling water pump, and the cooling water pump and the cooling tower are associated through the cooling water flow. And the main machine, the cooling pump and the cooling tower are connected more tightly.

Description

Technical Field

[0001] The present invention belongs to the technical field of central air-conditioning control, and relates to a central air-conditioning cooling side optimization control method based on minimum energy consumption. Background Art

[0002] In large industrial plants, urban complexes, commercial complexes, and high-rise office buildings, central air conditioning systems typically consume 15% to 20% of their total energy consumption through cooling. Currently, the industry generally adopts a fixed temperature differential control strategy, such as maintaining a constant 5°C inlet and outlet temperature difference between the cooling water and the cooling water pumps. This strategy also relies on manual experience to configure the number of cooling towers in operation, leading to the following system issues:

[0003] The main engine condenser operating condition is mismatched, that is, the main engine condenser cannot work in the optimal working condition;

[0004] The decoupling of the number of cooling towers opened and the dynamic water flow leads to double waste, namely, excessive energy consumption of the cooling system or low energy efficiency of the host, and mismatch between the number of cooling towers opened and the cooling water flow.

[0005] The existing central air-conditioning cooling station control strategy separates the energy consumption relationship between the main unit, water pump, and cooling tower. It lacks a global optimization mechanism and a mechanism for automatically matching the dynamic control variables of the cooling system to the main unit, resulting in limited energy saving effects or a year-on-year decline in system energy efficiency. Summary of the Invention

[0006] The purpose of the present invention is to solve the impact of changes in the operating conditions of the air-conditioning condenser on the energy efficiency of the system after the main unit of the cooling water system is put into operation, to solve the cooling tower control and cooling water flow matching method, to achieve efficient heat dissipation while avoiding the situation where some cooling towers are out of water. The present invention develops a global optimization control method, which establishes a dynamic coupling model of the main unit power consumption, water pump power consumption and cooling tower power consumption, and achieves the minimum overall energy consumption of the main unit and cooling side while ensuring the heat dissipation requirements.

[0007] The technical solution adopted by the present invention is an optimization control method for the cooling side of a central air-conditioning system based on the lowest energy consumption. The key lies in the following: S1, periodically triggering the optimization mechanism; S2, running the cooling water pump and cooling tower fan at full frequency and limiting the number of cooling towers; S3, gradient frequency reduction, and combined power optimization to obtain the inlet and outlet water temperature difference ΔT on the cooling water main unit side; S4, using ΔT as the adjustment target value of the cooling water pump in this cycle; S5, releasing the cooling tower control restrictions during the optimization period, executing the automatic control mode, and making the cooling system operate in the optimal state.

[0008] Specifically, the cycle in the above step S1 is 5 days, and the optimization triggering time is 12 noon of the same day, when the cooling load is the maximum value of the day and the fluctuation rate is less than 5%.

[0009] Specifically, in the above step S2, the number of cooling towers in operation is limited by the current cooling water flow rate, and the upper limit of the number of cooling towers in operation is calculated according to formula 1, and the integer is taken:

[0010] Number of cooling towers in operation = current cooling water flow / (rated flow of a single cooling tower × 60%)

[0011] (Formula 1).

[0012] Furthermore, the gradient frequency reduction in the above step S3 is to reduce the cooling water pump frequency by a gradient of 3 Hz every 10 minutes; the lowest point of the sum of the host power and the cooling water pump power is detected in real time, and the cooling water inlet and outlet temperature difference corresponding to the lowest point is recorded as ΔT.

[0013] Preferably, the above-mentioned lowest point determination rule is: after the cooling water pump frequency is reduced, if the sum of the host power and the cooling water pump power is detected to be increasing for two consecutive times, it is determined that the lowest point has been passed, and the cooling water inlet and outlet water temperature difference corresponding to the last frequency reduction before the increase occurs is recorded as ΔT.

[0014] Furthermore, in the above step S4, ΔT is used as a fixed set value, and the cooling water pump frequency is adjusted by PID; the PID control period is ≤30 seconds, and the output frequency is limited to 25Hz~50Hz.

[0015] Furthermore, the above step S5 includes:

[0016] S51. Dynamic calculation of the upper and lower limits of the number of cooling towers:

[0017] According to formula 2, the upper limit of the number of cooling towers in operation is calculated dynamically and rounded to an integer:

[0018] The upper limit of the number of cooling towers in operation = current cooling water flow / (rated flow of a single cooling tower × 60%) (Formula 2);

[0019] According to formula 3, the lower limit of the number of cooling towers in operation can be calculated dynamically.

[0020] Lower limit of number of cooling towers in operation = round up (current cooling water flow rate / (rated flow rate of a single cooling tower × 100%)) (Formula 3);

[0021] S52. Unify the cooling tower fan frequency: reduce the running cooling tower fan frequency to a preset frequency lower limit, which is 25 Hz to 30 Hz;

[0022] S53, based on the cooling water outlet temperature T 目标 Execute the number of units adjustment and carry out the process of adding or reducing machines.

[0023] It should be noted that T 目标=Outdoor wet-bulb temperature + deviation value. The deviation value is generally 2℃~5℃ and should be adjusted according to the local climate.

[0024] Furthermore, the current outlet water temperature is higher than T 目标 , then the adding process is executed; the adding process is to gradually add machines and open the cooling tower, and the newly opened cooling tower fan is synchronously frequency-adjusted to make the cooling water outlet temperature close to T 目标 However, when the number of cooling towers in operation reaches the upper limit of the number of cooling towers corresponding to the current cooling water flow rate, and the cooling water outlet temperature is still higher than T 目标 When the fan speed regulation phase begins, the fan frequency of all the cooling tower fans that have been turned on is adjusted by PID so that the cooling water outlet temperature approaches T 目标 ; Continue to determine whether the cooling tower fan frequency has reached the lower frequency limit. If not, determine whether the number of cooling tower operating units has reached the upper limit. If the number of cooling tower operating units has not reached the upper limit, and the upper limit of the number of cooling tower operating units has changed, then the number of cooling tower operating units will be directly added or subtracted to the new upper limit of the number of cooling tower units, and then continue to adjust the cooling tower fan frequency; if the number of cooling tower operating units has reached the upper limit, then adjust the cooling tower fan frequency through PID to make the cooling water outlet temperature approach T 目标 ; If yes, continue to add or subtract the machine according to the outdoor wet-bulb temperature.

[0025] Furthermore, the current outlet water temperature is lower than T 目标 , the reduction process is executed; the reduction process is to first reduce the fan frequency of all the opened cooling towers to the lower frequency limit, gradually reduce the number of cooling towers, and shut down the cooling towers until the number of cooling towers in operation reaches the lower limit of the number of cooling towers in operation corresponding to the current cooling water flow rate; if the fan operating frequency is between the upper and lower limits during the reduction process, and the upper limit of the number of cooling towers changes, the fans are directly added or subtracted to the new upper limit of the number of cooling towers; when the number of cooling towers in operation has reached the upper limit, the cooling tower fan frequency is adjusted through PID to make the cooling water outlet temperature approach T 目标 .

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] Compared with the existing technology, the present invention effectively reduces the power consumption of the cooling water pump and the cooling tower while ensuring the heat dissipation requirements of the host by regulating the sum of the coolant pump and the host power. The host and the cooling water pump are associated through the sum of the host and cooling water pump power, and the cooling water pump and the cooling tower are associated through the cooling water flow rate, making the relationship between the host, cooling pump and cooling tower closer. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is the first part of the control logic block diagram of the present invention.

[0029] Figure 2 This is the second part of the control logic block diagram of the present invention. DETAILED DESCRIPTION

[0030] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0031] Example

[0032] In this embodiment, the cooling side optimization control of the central air conditioner is performed, and the specific steps are as follows:

[0033] S1. Periodically trigger the optimization mechanism:

[0034] The cooling water optimization program is performed on the central air-conditioning system every 5 days. The optimization program is performed at 12 noon on the same day. At this time, the cooling load is the maximum load point of the day and is stable, that is, the cooling load fluctuation rate is less than 5%.

[0035] S2. Cooling water pumps and cooling tower fans run at full frequency, and the number of cooling towers is limited:

[0036] For example, if the cooling water pump frequency is set to 50Hz, the number of cooling towers is calculated based on the current flow rate, that is, the upper limit of the number of cooling towers in operation is calculated according to formula 1, and the integer is taken:

[0037] Number of cooling towers in operation = current cooling water flow / (rated flow of a single cooling tower × 60%) (Formula 1);

[0038] Set the cooling tower fan operating frequency to 50Hz.

[0039] S3, gradient frequency reduction, combined with power optimization to obtain the inlet and outlet water temperature difference ΔT on the cooling water main unit side:

[0040] Gradient frequency reduction is to reduce the cooling water pump frequency by 3Hz every 10 minutes, detect the lowest point of the sum of the host power and the cooling water pump power in real time, and record the cooling water inlet and outlet temperature difference corresponding to the lowest point as ΔT;

[0041] The rule for determining the lowest point is that after the cooling water pump frequency is reduced, if the sum of the host power and the cooling water pump power is detected to be increasing for two consecutive times, it is determined that the lowest point has been passed, and the cooling water inlet and outlet temperature difference corresponding to the last frequency reduction before the increase occurs is recorded as ΔT.

[0042] S4. Take ΔT as the target value for the cooling water pump in this cycle:

[0043] When the sum of the host power and the cooling water pump power reaches its lowest point, record the cooling water inlet and outlet temperature difference at this time, recorded as ΔT. This value will be used as the basis for cooling water pump frequency control for 5 natural days to perform fixed temperature difference cooling water pump PID adjustment. The PID control period is ≤30 seconds, and the output frequency is limited to 25Hz~50Hz.

[0044] The PID control period in this embodiment is 30 seconds, and the output frequency limit is 30 Hz.

[0045] S5. Release the cooling tower control restrictions during the optimization period and execute the automatic control mode to make the cooling system operate in the optimal state:

[0046] S51. Determine the upper and lower limits of the number of cooling towers by cooling water flow:

[0047] According to formula 2, the upper limit of the number of cooling towers in operation is calculated dynamically and rounded to an integer:

[0048] The upper limit of the number of cooling towers in operation = current cooling water flow / (rated flow of a single cooling tower × 60%) (Formula 2);

[0049] The lower limit of the number of cooling towers in operation is calculated dynamically according to Formula 3, and rounded up to (current cooling water flow / (rated flow of a single cooling tower × 100%)) (Formula 3).

[0050] S52, Unified cooling tower fan frequency:

[0051] The frequency of the cooling tower fan in operation is reduced to a preset frequency lower limit. The preset frequency lower limit is generally 25 Hz to 30 Hz. This embodiment takes 30 Hz as an example.

[0052] S53: Based on the cooling water outlet temperature T target, the number of units is adjusted to add or reduce units:

[0053] Under the premise of keeping the cooling tower fan frequency at the lower limit, the cooling water outlet temperature is adjusted by increasing or decreasing the number of cooling towers in operation to determine whether the current outlet water temperature reaches the target value, where the target value is expressed as T 目标 Indicates that T 目标 = outdoor wet-bulb temperature + deviation value. The deviation value is generally 2°C to 5°C and is adjusted according to the local climate. This embodiment takes 3°C as an example.

[0054] The addition and subtraction of the machine is carried out according to the outdoor wet-bulb temperature, which can be divided into the following three situations:

[0055] Case 1: If the current outlet water temperature reaches T 目标 , the current number of running towers and fan frequency are maintained. In this state, if the outdoor wet-bulb temperature changes, that is, situation 2 or situation 3 occurs, the process of adding or reducing units will be started.

[0056] Case 2: If the current outlet water temperature is higher than T 目标 , then execute the machine adding process:

[0057] Determine whether the number of cooling towers in operation has reached the upper limit. If not, adjust the cooling tower fan frequency until there is room for additional cooling towers.

[0058] That is, gradually add more machines and open the cooling towers, and the fans of the newly opened cooling towers are synchronously frequency-adjusted to make the cooling water outlet temperature close to T 目标 However, when the number of cooling towers in operation reaches the upper limit of the number of cooling towers corresponding to the current cooling water flow rate, and the cooling water outlet temperature is still higher than T 目标 When the fan speed regulation phase begins, the fan frequency of all the cooling tower fans that have been turned on is adjusted by PID so that the cooling water outlet temperature approaches T 目标 .

[0059] Continue to determine whether the cooling tower fan frequency has reached the lower frequency limit:

[0060] If not, determine whether the number of cooling towers in operation has reached the upper limit. If the number of cooling towers in operation has not reached the upper limit, and the upper limit of the number of cooling towers in operation has changed, the number of cooling towers in operation will be directly increased or decreased to the new upper limit, and then the cooling tower fan frequency will continue to be adjusted; if the number of cooling towers in operation has reached the upper limit, the cooling tower fan frequency will be adjusted through PID to make the cooling water outlet temperature approach T 目标 ;

[0061] If yes, continue to add or subtract the machine according to the outdoor wet-bulb temperature.

[0062] Case 3: If the current outlet water temperature is lower than T 目标 , then execute the machine reduction process:

[0063] That is, the process of reducing the number of cooling towers is to first reduce the fan frequency of all the opened cooling towers to the lower frequency limit, gradually reduce the number of cooling towers and shut down the cooling towers until the number of cooling towers in operation reaches the lower limit of the number of cooling towers in operation corresponding to the current cooling water flow rate; if the fan operating frequency is between the upper and lower limits during the process of reducing the number of cooling towers, and the upper limit of the number of cooling towers changes, the fan will be directly added or subtracted to the new upper limit of the number of cooling towers; when the number of cooling towers in operation has reached the upper limit, the cooling tower fan frequency will be adjusted through PID to make the cooling water outlet temperature approach T 目标 .

[0064] The control method of the present invention first attempts to control by adding and subtracting machines. Only when the number of machines reaches the upper limit and still cannot meet the temperature requirements, it switches to relying primarily on fan PID control. The control strategy of the present invention is a layered adjustment, which prioritizes the use of discrete, large-volume adjustment methods, and then uses continuous, fine-tuning methods. By linking the main unit, cooling pump, and cooling tower, the cooling system is optimized to operate. The optimal cooling water temperature difference is found under stable cooling load conditions, reducing the adverse fluctuations in system energy efficiency caused by changes in condenser efficiency due to the operation of the air conditioning main unit.

Claims

1. A central air conditioning cooling side optimization control method based on minimum energy consumption, characterized in that: Specifically include: S1. Periodically trigger the optimization mechanism; S2. Run the cooling water pump and cooling tower fan at full frequency and limit the number of cooling towers; S3. Gradual frequency reduction and combined power optimization to obtain the inlet and outlet water temperature difference ΔT on the cooling water main side; S4. Use ΔT as the adjustment target value of the cooling water pump in this cycle; S5. Release the cooling tower control restrictions during the optimization period and execute the automatic control mode to make the cooling system operate in the optimal state.

2. The central air conditioning cooling side optimization control method based on minimum energy consumption according to claim 1 is characterized in that: The cycle in step S1 is 5 days, and the optimization triggering time is 12 noon of the same day, when the cooling load is the maximum value of the day and the fluctuation rate is less than 5%.

3. The central air conditioning cooling side optimization control method based on minimum energy consumption according to claim 1 is characterized in that: In step S2, the number of cooling towers in operation is limited by the current cooling water flow rate, and the upper limit of the number of cooling towers in operation is calculated according to formula 1, and the integer is taken: Number of cooling towers in operation = current cooling water flow / (rated flow of a single cooling tower × 60%) (Formula 1).

4. The method for optimizing the cooling side of a central air conditioner based on minimum energy consumption according to claim 1, characterized in that: The gradient frequency reduction described in step S3 is to reduce the cooling water pump frequency by a gradient of 3 Hz every 10 minutes; the lowest point of the sum of the host power and the cooling water pump power is detected in real time, and the cooling water inlet and outlet temperature difference corresponding to the lowest point is recorded as ΔT.

5. The method for optimizing the cooling side of a central air conditioner based on minimum energy consumption according to claim 4, characterized in that: The rule for determining the lowest point is: after the cooling water pump frequency is reduced, if the sum of the host power and the cooling water pump power is detected to be increasing for two consecutive times, it is determined that the lowest point has been passed, and the cooling water inlet and outlet temperature difference corresponding to the last frequency reduction before the increase occurs is recorded as ΔT.

6. The method for optimizing the cooling side of a central air conditioner based on minimum energy consumption according to claim 1, characterized in that: In step S4, ΔT is used as a fixed set value, and the cooling water pump frequency is adjusted by PID; the PID control period is ≤30 seconds, and the output frequency is limited to 25Hz to 50Hz.

7. The method for optimizing the cooling side of a central air conditioner based on minimum energy consumption according to claim 1, characterized in that: The S5 step includes: S51. Dynamic calculation of the upper and lower limits of the number of cooling towers: According to formula 2, the upper limit of the number of cooling towers in operation is calculated dynamically and rounded to an integer: The upper limit of the number of cooling towers in operation = current cooling water flow / (rated flow of a single cooling tower × 60%) (Formula 2); According to formula 3, the lower limit of the number of cooling towers in operation can be calculated dynamically. Lower limit of number of cooling towers in operation = round up (current cooling water flow rate / (rated flow rate of a single cooling tower × 100%)) (Formula 3); S52. Unify the cooling tower fan frequency: reduce the running cooling tower fan frequency to a preset frequency lower limit, wherein the preset frequency lower limit is 25 Hz to 30 Hz; S53, based on the cooling water outlet temperature T 目标 Execute the number of units adjustment and carry out the process of adding or reducing machines.

8. The central air conditioning cooling side optimization control method based on minimum energy consumption according to claim 7 is characterized in that: T 目标 =Outdoor wet-bulb temperature + deviation value. The deviation value is generally 2℃~5℃ and should be adjusted according to the local climate.

9. The method for optimizing the cooling side of a central air conditioner based on minimum energy consumption according to claim 7, characterized in that: The current outlet water temperature is higher than T 目标 , then the adding process is executed; the adding process is to gradually add machines and open the cooling tower, and the newly opened cooling tower fan is synchronously frequency-adjusted to make the cooling water outlet temperature close to T 目标 However, when the number of cooling towers in operation reaches the upper limit of the number of cooling towers corresponding to the current cooling water flow rate, and the cooling water outlet temperature is still higher than T 目标 When the fan speed regulation phase begins, the fan frequency of all the cooling tower fans that have been turned on is adjusted by PID so that the cooling water outlet temperature approaches T 目标 ; Continue to determine whether the cooling tower fan frequency has reached the lower frequency limit. If not, determine whether the number of cooling tower operating units has reached the upper limit. If the number of cooling tower operating units has not reached the upper limit, and the upper limit of the number of cooling tower operating units has changed, then the number of cooling tower operating units will be directly increased or decreased to the new upper limit of the number of cooling tower units, and then continue to adjust the cooling tower fan frequency; If the number of cooling towers in operation has reached the upper limit, the fan frequency of the cooling tower is adjusted through PID to make the cooling water outlet temperature approach T 目标 ; If yes, continue to add or subtract the machine according to the outdoor wet-bulb temperature.

10. The central air conditioning cooling side optimization control method based on minimum energy consumption according to claim 7, characterized in that: The current outlet water temperature is lower than T 目标 , the reduction process is executed; the reduction process is to first reduce the fan frequency of all the cooling towers that are turned on to the lower frequency limit, gradually reduce the number of cooling towers and shut down the cooling towers until the number of cooling towers in operation reaches the lower limit of the number of cooling towers in operation corresponding to the current cooling water flow rate; If the fan operating frequency is between the upper and lower limits during the process of reducing the number of cooling towers, and the upper limit of the number of cooling towers changes, the fan will be directly added or reduced to the new upper limit of the number of cooling towers; When the number of cooling towers in operation has reached the upper limit, the fan frequency of the cooling tower is adjusted through PID to make the cooling water outlet temperature approach T 目标 .

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