Central air conditioner air-water coordination control method based on most unfavorable tail end requirements

Abstract

The invention discloses a central air-conditioning air-water coordination control method based on the most unfavorable terminal demand, which comprises the following steps: when a central air-conditioning system is started for the first time every day, starting a pre-pressurization control process, entering a pre-pressurization stage, and carrying out pre-pressurization operation on a chilled water side; when any parameter of chilled water supply temperature or host starting time reaches a pre-pressurization set value, the pre-pressurization stage is ended, the chilled water pump is kept in a full-frequency operation state, the operation frequency of the chilled water pump is adjusted through gradient frequency, and the worst end pressure difference protection value on the current day is judged and taken; then daily energy-saving operation control is carried out based on the worst end differential pressure protection value of the current day, and a daily operation energy-saving group control mode is entered; according to the method, for indirect variable judgment of the most unfavorable terminal operation condition in the air conditioner terminals, the overall energy-saving efficiency of the air conditioner system is improved on the premise that the energy consumption and stability of the system starting stage are optimized and the terminal use state is guaranteed.

Description

Technical Field

[0001] The present invention belongs to the technical field of HVAC system control, relates to a central air-conditioning air-water coordination control method, and particularly relates to a central air-conditioning air-water coordination control method based on the demand of the most unfavorable end. Background Art

[0002] In the control of large central air-conditioning systems, especially in application scenarios such as large commercial complexes or office buildings, there is at least one system-level startup and shutdown situation every day. Most central air-conditioning control systems use fixed protection values obtained from technicians' experience to protect the differential pressure control of the chilled water supply and return pressure, that is, the minimum protection for the differential pressure of the chilled water supply and return during the frequency conversion operation of the chilled water pump is fixed. This results in the system being unable to dynamically adjust according to the actual demand of the end. When the protection differential pressure is too high, there is energy waste, and when the protection differential pressure is too low, the demand of the most unfavorable end cannot be met. It can be seen that the differential pressure protection value of the existing technology cannot adapt to the daily load change in the planned area of the end.

[0003] The Chinese patent application "Central Air-Conditioning Chilled Water System Control Method, Device, Equipment and Medium" with the application number 202411574161.1 discloses a central air-conditioning chilled water system control method, which requires obtaining the set differential pressure value of the central air-conditioning chilled water system. However, when adjusting the set differential pressure value, this method needs to determine the optimal working area of the chilled water pump and the preset fuzzy PID algorithm according to the preset differential pressure change characteristic analysis diagram, determine the target set differential pressure value as the adjusted set differential pressure value, and also needs to generate a differential pressure change characteristic analysis diagram based on the pump characteristic curve, the pipe network resistance characteristic curve, and the variable given differential pressure characteristic curve. This method has high requirements for the software and hardware of the central air-conditioning system, and the operation is relatively complex and has high requirements for the operators, so the application difficulty is relatively high.

[0004] Therefore, it is necessary to study a more convenient and easier-to-apply central air-conditioning air-water coordination control method to obtain the minimum supply and return water pressure differential protection value every day. Summary of the Invention

[0005] The purpose of the present invention is to optimize the central air-conditioning air-water coordination control method for large central air-conditioning systems to solve the problems of high difficulty and complex operation in obtaining the minimum supply and return water pressure differential protection value every day.

[0006] The technical solution adopted by the present invention is a central air-conditioning feng shui coordinated control method based on the most unfavorable end demand. When the central air-conditioning system is started for the first time every day, the pre-pressurization control process is started and the pre-pressurization stage is entered, and the pre-pressurization operation is carried out on the chilled water side. The key lies in that when any one of the parameters of the chilled water supply temperature or the host startup time reaches the set value of the pre-pressurization, the pre-pressurization stage ends, the chilled water pump maintains a full-frequency operation state, and the operation frequency of the chilled water pump is adjusted by gradient frequency to judge and obtain the protection value of the most unfavorable end pressure difference on the same day, and then the daily energy-saving operation control is carried out based on the protection value of the most unfavorable end pressure difference on the same day, and the daily operation energy-saving group control mode is entered.

[0007] Specifically, the above pre-pressurization control process includes:

[0008] S1-1. Adjust the valves of the enabled air-conditioning terminal coils or air handling units to the maximum opening through the terminal valve control module;

[0009] S1-2. Adjust the chilled water pump to the full-frequency operation state;

[0010] S1-3. Start the central air-conditioning host;

[0011] S1-4. Pre-pressurization completion judgment: When any one of the parameters of the chilled water supply temperature or the host startup time reaches the set value of the pre-pressurization, the pre-pressurization stage ends, the chilled water pump maintains a full-frequency operation state, and the valves of the enabled air-conditioning terminal coils or air handling units remain at the maximum opening.

[0012] It should be noted that in step S1-1, the number of valves of the enabled air-conditioning terminal coils or air handling units is determined according to the actual area to be opened for system setting.

[0013] Furthermore, the process of adjusting the operation frequency of the chilled water pump by gradient frequency is that the chilled water pump starts from the full-frequency operation state and sequentially performs gradient frequency reduction and gradient frequency increase operations at a fixed frequency modulation gradient and a dynamic frequency modulation interval.

[0014] Specifically, the above gradient frequency reduction reduces the frequency at a fixed frequency modulation gradient and a dynamic frequency modulation interval until the first return water temperature mutation occurs in the chilled water return temperature; when the system operation after this frequency reduction operation ends, the gradient frequency increase operation starts.

[0015] Specifically, the above gradient frequency increase increases the frequency at a fixed frequency modulation gradient and a dynamic frequency modulation interval until the second return water temperature mutation occurs in the chilled water return temperature; when the system operation after this frequency increase operation ends, the judgment and obtaining stage of the protection value of the most unfavorable end pressure difference ends; the chilled water supply and return water pressure difference corresponding to the highest value of the chilled water return temperature during the second return water temperature mutation process is taken as the protection value of the most unfavorable end pressure difference on the same day, and the daily operation energy-saving group control mode is entered.

[0016] Preferably, the above fixed frequency modulation gradient is 3 Hz; the above dynamic frequency modulation interval is calculated according to Equation 1 for the time of one cycle of the chilled water circulation, and then the time of one cycle of the chilled water circulation is extended by 5 s. The specific formula is:

[0017]

[0018] In Equation 1, T represents the frequency modulation interval, in s; V represents the total designed circulation water volume of the chilled water, in m 3 ; Q represents the full-frequency flow rate of the chilled water pump, in m 3 / s; f represents the actual operating frequency of the chilled water pump, in Hz; f p represents the full-frequency of the chilled water pump, in Hz.

[0019] Optimally, the method for judging the sudden change of the return water temperature is that steps can be shown on the chilled water return temperature curve or when the change difference of the chilled water return temperature before and after the frequency adjustment reaches 3 times or more.

[0020] It should be noted that when entering the daily operation energy-saving group control mode, it is necessary to release the maximum opening control of the terminal valve, and the terminal valve adjusts the opening by itself.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] The protection pressure difference value in the prior art is set according to empirical values, and there are often cases where the set value is too high. Because it is necessary to ensure that there is water at the most unfavorable end, but according to the opening situation of the terminal air-conditioning equipment, the most unfavorable end will change. Therefore, for commercial buildings, office buildings, schools, hospitals and other types of buildings where the terminal situation does not change very frequently, the opening of the terminal is associated with whether the floor or area is opened. This requires adjusting the chilled water supply and return pressure difference protection value every day, and dynamically adjusting the target according to the terminal adjustment to solve the problem of energy waste caused by the fixed and too high setting of the supply and return pressure difference.

[0023] In the present invention, during the process from pre-pressurization to steady-state convergence, by controlling, judging and recording the water pump, terminal valve, chilled water supply and return temperature sensors, and chilled water supply and return pressure sensors, the minimum value of the chilled water supply and return pressure difference is automatically obtained and set without increasing the system disturbance. More importantly, the present invention adjusts the minimum value of the chilled water supply and return pressure difference every day, which can improve the control matching between the chilled water station and the terminal.

[0024] In summary, the present invention judges the operating conditions of the most unfavorable end in the air-conditioning terminal for indirect variables, and improves the overall energy-saving efficiency of the air-conditioning system on the premise of optimizing the energy consumption and stability in the system startup stage and ensuring the terminal use state. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is the logic framework diagram of the central air-conditioning feng shui coordination control - pre-pressurization stage in the first embodiment of the present invention.

[0026] Figure 2 It is the logic framework diagram of the central air-conditioning feng shui coordination control - the stage of judging and obtaining the protection value of the pressure difference at the most unfavorable end in the first embodiment of the present invention.

[0027] Figure 3 It is the curve graph of the change in the return water temperature of the chilled water in the second embodiment of the present invention.

[0028] In the attached drawings, 1 is the lowest point of the return water temperature during the first return water temperature mutation process, and 2 is the highest point of the return water temperature during the second return water temperature mutation process. Specific implementation manners

[0029] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0030] Embodiment 1

[0031] This embodiment is described by taking a large central air conditioner applied in scenarios such as commercial complexes or office buildings as an example. The corresponding control logic framework diagram can be seen in Figure 1 and 2 , and the specific method is as follows:

[0032] S1. The system starts and enters the pre-pressurization stage:

[0033] When the central air-conditioning system is powered on for the first time every day, start the pre-pressurization control process, enter the pre-pressurization stage, and perform pre-pressurization operations on the chilled water side, including:

[0034] S1-1. Adjust the valves of the enabled air-conditioning terminal coils or air handling units to the maximum opening through the terminal valve control module; determine the number of valves of the enabled air-conditioning terminal coils or air handling units according to the actually to-be-opened area to ensure sufficient flow at each end in the initial stage;

[0035] S1-2. Adjust the chilled water pump to the full-frequency operation state to ensure the rapid establishment of the system circulation flow;

[0036] S1-3. Start the central air-conditioning host, provide cooling capacity to the chilled water system, and continuously monitor the chilled water supply temperature through the temperature sensor, and continue to maintain the full-frequency operation of the pump and the fully open state of the valve;

[0037] S1-4. Judgment of pre-pressurization completion:

[0038] When any one of the chilled water supply temperature or the host startup time reaches the set value of pre-pressurization, the pre-pressurization stage ends, the chilled water pump maintains a full-frequency operation state, and the valves of the enabled air-conditioning terminal coils or air handling units remain at the maximum opening.

[0039] S2. Judgment and value selection of the most unfavorable terminal pressure difference protection value:

[0040] The system enters the sampling program for judging the most unfavorable terminal pressure difference protection value, that is, starting from the full-frequency operation state, the chilled water pump performs gradient frequency reduction and gradient frequency increase operations in sequence with a fixed frequency modulation gradient and a dynamic frequency modulation interval:

[0041] First, enter the gradient frequency reduction stage, reduce the frequency with a fixed frequency modulation gradient and a dynamic frequency modulation interval, and reduce the frequency by 3Hz each time. The specific process is as follows:

[0042] Calculate the frequency modulation interval according to Equation 1, denoted as T1. If the first return water temperature mutation does not occur within the T1 time period, calculate the frequency modulation interval again according to Equation 1 and the actual operating frequency of the chilled water pump at this time, denoted as T2; if the first return water temperature mutation does not occur, calculate for the third time according to Equation 1 to obtain T3; and so on. If the i-th frequency reduction is performed and the first return water temperature mutation occurs during the operation after the i-th frequency reduction, wait until the end of this operation and start the gradient frequency increase operation;

[0043] Then, enter the gradient frequency increase stage, increase the frequency with a fixed frequency modulation gradient and a dynamic frequency modulation interval, and increase the frequency by 3Hz each time. The specific process is as follows:

[0044] Calculate the frequency modulation interval according to Equation 1 and the actual operating frequency of the chilled water pump at this time, denoted as T i+1 , if the second return water temperature mutation does not occur, calculate the frequency modulation interval again according to Equation 1 and the actual operating frequency of the chilled water pump at this time, denoted as T i+2 ; if the second return water temperature mutation still does not occur, calculate again according to Equation 1 to obtain T i+3 ; and so on. If the j-th frequency increase is performed and the second return water temperature mutation occurs during the operation after the j-th frequency reduction, wait until the end of this operation, that is, end the judgment and value selection stage of the most unfavorable end pressure difference protection value, and enter the daily operation energy-saving group control mode; take the chilled water supply and return water pressure difference corresponding to the highest value of the chilled water return water temperature during the second return water temperature mutation as the most unfavorable end pressure difference protection value for the day.

[0045] The above-mentioned first return water temperature mutation or second return water temperature mutation can be determined based on the fact that there are obvious steps on the chilled water return temperature curve, that is, the curve is smooth before the mutation moment and smooth after the mutation moment. It can also be analyzed from the numerical value of the chilled water return temperature. When the change difference of the sampled chilled water temperature changes more than three times, it is considered a mutation. During the operation process, it is more intuitive to observe the change of the chilled water return temperature curve.

[0046] In this embodiment, the frequency modulation interval is to extend the time for one cycle of the chilled water circulation by 5 s. The specific formula 1 is:

[0047]

[0048] In formula 1, T represents the frequency modulation interval, with the unit of s; V represents the total designed circulation water volume of the chilled water, with the unit of m 3 ; Q represents the full-frequency flow rate of the chilled water pump, with the unit of m 3 / s; f represents the actual operating frequency of the chilled water pump, with the unit of Hz; f p represents the full-frequency of the chilled water pump, with the unit of Hz.

[0049] Since f represents the actual operating frequency of the chilled water pump and is a dynamic parameter during the gradient frequency modulation process, the frequency modulation interval T is also a dynamic parameter.

[0050] S3. The whole system enters the normal operation energy-saving group control mode: Release the maximum opening control of the terminal valve. After this moment, the terminal valve can adjust its opening by itself, and the entire chilled water station control system enters the normal energy-saving group control state, and conducts daily energy-saving operation control based on the most unfavorable end differential pressure protection value of the day.

[0051] Embodiment 2

[0052] This embodiment takes a large central air conditioner in a 44-story office building as an example for illustration. The specific method is as follows:

[0053] S1. The system starts and enters the pre-pressurization stage:

[0054] When the central air-conditioning system is started for the first time every day, start the pre-pressurization control process and enter the pre-pressurization stage to perform pre-pressurization operation on the chilled water side, including:

[0055] S1-1. Through the terminal valve control module, adjust the valves of the enabled air-conditioning terminal air handling units to the maximum opening; in this embodiment, the enabled areas are floors 1-13, 16-23, and 28-43, and the number of valves of the enabled large air handling units of the air-conditioning terminals is determined to be 37 through system settings;

[0056] S1-2. Adjust the chilled water pump to the full-frequency operation state. When at full frequency, the full-frequency of the chilled water pump is f p= 50Hz, the total designed circulating water volume V of the chilled water is 30m 3 , the full-frequency flow rate Q of the chilled water pump is 540m 3 / h, that is, 0.15m 3 / s;

[0057] S1-3. Start the central air-conditioning host, provide cooling capacity to the chilled water system, and continuously monitor the chilled water supply temperature through the temperature sensor, and continue to maintain the full-frequency operation of the pump and the fully open state of the valve;

[0058] S1-4. Judgment of pre-pressurization completion:

[0059] When any one of the parameters of the chilled water supply temperature or the host startup time reaches the set value of pre-pressurization; in this embodiment, when the chilled water supply temperature reaches 7.5°C or the host startup time reaches 30 minutes, the pre-pressurization stage can end. When the chilled water supply temperature reaches 7.5°C, the pre-pressurization stage ends, the chilled water pump maintains the full-frequency operation state, and the valves of the enabled air-conditioning terminal air handling units remain at the maximum opening.

[0060] S2. Judgment and value selection of the most unfavorable terminal pressure difference protection value:

[0061] The system enters the sampling program for judging the most unfavorable terminal pressure difference protection value, that is, starting from the full-frequency operation state of the chilled water pump, it performs gradient frequency reduction and gradient frequency increase operations in sequence. For the schematic diagram of the change curve of the chilled water return temperature, see Figure 3 :

[0062] First, enter the gradient frequency reduction stage. Starting from the full-frequency operation, that is, f p = 50Hz, gradually reduce the frequency. 3Hz is a frequency reduction step. According to formula 1, the frequency modulation interval is calculated to be 205 seconds. If there is no first sudden change in the return water temperature during the operation after this frequency reduction operation, then adjust the frequency to 47Hz and calculate the frequency modulation interval again according to formula 1, and get a new frequency modulation interval of 217.766 seconds. Then, use 217.766 seconds as the frequency reduction interval and a frequency reduction gradient of 3Hz to continue reducing the frequency, and so on for gradient frequency reduction; Figure 3 The point 1 in is the lowest return water temperature point of the first sudden change in the return water temperature. At this time, the actual operating frequency is 29Hz. It is necessary to wait until the end of this gradient frequency reduction operation before entering the gradient frequency increase. This process can show obvious steps on the chilled water return temperature curve, that is, the curve is smooth before the mutation moment and the curve is smooth after the mutation moment;

[0063] Then, enter the gradient frequency-up phase. Starting from 29 Hz, with a 3-Hz frequency-up step, the frequency modulation interval is calculated to be 349.8276 seconds according to Formula 1. During the operation after this frequency-up operation, there is no second sudden change in the return water temperature. Then, calculate the frequency modulation interval again according to Formula 1, and the new frequency modulation interval is 317.5 seconds. Continue to increase the frequency by 3 Hz and so on for gradient frequency-up; Figure 3 Point 2 in Figure 3 is the highest point of the return water temperature of the second sudden change in the return water temperature. At this time, the actual operating frequency is 41 Hz. It is necessary to wait for the end of this gradient frequency-up operation to end the judgment and value-taking stage of the most unfavorable end differential pressure protection value; during this process, the chilled water return water temperature of 12.95 °C corresponding to point 2 is the highest return water temperature during the second sudden change in the return water temperature. The chilled water supply and return water pressure difference corresponding to point 2 is 218 kPa. Then, take 218 kPa as the most unfavorable end differential pressure protection value for the day. After the end of this gradient frequency-up operation, end the judgment and value-taking stage of the most unfavorable end differential pressure protection value and enter the daily operation energy-saving group control mode.

[0064] S3. The whole system enters the normal operation energy-saving group control mode: Release the maximum opening control of the terminal valve. After this moment, the terminal valve can adjust the opening by itself, and the entire chilled water station control system enters the normal energy-saving group control state, and performs daily energy-saving operation control based on the most unfavorable end differential pressure protection value for the day.

Claims

1. A central air conditioning wind and water coordination control method based on the most unfavorable terminal demand, when the central air conditioning system is turned on for the first time every day, the pre-pressurization control process is started, the pre-pressurization stage is entered, and the chilled water side is pre-pressurized, characterized in that: When any one of the parameters of the chilled water supply temperature or the host startup time reaches the pre-pressurization set value, the pre-pressurization stage ends, the chilled water pump maintains full-frequency operation, and the operating frequency of the chilled water pump is adjusted by gradient frequency to judge and determine the most unfavorable end pressure difference protection value of the day, and then daily energy-saving operation control is performed based on the most unfavorable end pressure difference protection value of the day, entering the daily operation energy-saving group control mode.

2. A central air conditioning feng shui coordinated control method based on the most unfavorable terminal demand according to claim 1, characterized in that: The pre-pressurization control process includes: S1-1, adjust the valve of the enabled air conditioning terminal coil or air cabinet to the maximum opening through the terminal valve control module; S1-2, adjust the chilled water pump to full frequency operation; S1-3, start the central air conditioning host; S1-4, pre-pressurization completion judgment: When any one of the parameters of the chilled water supply temperature or the host startup time reaches the pre-pressurization set value, the pre-pressurization stage ends, the chilled water pump maintains full-frequency operation and the valve of the enabled air-conditioning terminal coil or air cabinet maintains the maximum opening.

3. A central air conditioning feng shui coordinated control method based on the most unfavorable terminal demand according to claim 2, characterized in that: In step S1-1, the system is set up to determine the number of valves of the air conditioning terminal coil or air cabinet to be enabled according to the area actually to be opened.

4. The method for coordinated control of central air conditioning feng shui based on the most unfavorable terminal demand according to claim 1, characterized in that: The process of adjusting the operating frequency of the chilled water pump by gradient frequency is that the chilled water pump starts from a full-frequency operating state, and performs gradient frequency reduction and gradient frequency increase operations in sequence with a fixed frequency modulation gradient and a dynamic frequency modulation interval.

5. A central air conditioning feng shui coordinated control method based on the most unfavorable terminal demand according to claim 4, characterized in that: The gradient frequency reduction is to reduce the frequency with a fixed frequency modulation gradient and a dynamic frequency modulation interval until the return temperature of the chilled water shows the first sudden change in return temperature; when the system operation after this frequency reduction operation is completed, the gradient frequency increase operation is started.

6. A central air conditioning feng shui coordinated control method based on the most unfavorable terminal demand according to claim 4, characterized in that: The gradient frequency increase is to increase the frequency with a fixed frequency modulation gradient and a dynamic frequency modulation interval until the chilled water return temperature has a second return water temperature mutation; when the system operation after this frequency increase operation is completed, the judgment and value-taking stage of the most unfavorable end pressure difference protection value is ended; the chilled water supply and return water pressure difference value corresponding to the highest value of the chilled water return water temperature during the second return water temperature mutation is taken as the most unfavorable end pressure difference protection value of the day, and the daily operation energy-saving group control mode is entered.

7. A central air conditioning feng shui coordinated control method based on the most unfavorable terminal demand according to any one of claims 5 or 6, characterized in that: The fixed frequency modulation gradient is 3 Hz; the dynamic frequency modulation interval is calculated based on Formula 1 to obtain the time for one chilled water cycle, and then the time for one chilled water cycle is extended by 5 seconds. The specific formula is: In formula 1, T represents the frequency modulation interval, in seconds; V represents the total water volume of the chilled water design cycle, in m 3 ; Q represents the full frequency flow of the refrigeration pump, the unit is m 3 / s; f represents the actual operating frequency of the chilled water pump, in Hz; f p Indicates the full frequency of the chilled water pump in Hz.

8. The method for coordinated control of central air conditioning feng shui based on the most unfavorable terminal demand according to claim 4, characterized in that: The method for judging the sudden change of return water temperature is that the steps can be shown on the chilled water return water temperature curve or the difference of the change of chilled water return water temperature before and after the frequency adjustment reaches 3 times or more.

9. The method for coordinated control of central air conditioning feng shui based on the most unfavorable terminal demand according to claim 1, characterized in that: When entering the daily operation energy-saving group control mode, it is necessary to release the maximum opening control of the terminal valve, and the terminal valve adjusts the opening automatically.

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