A method for coordinated control of energy-saving high and low temperature series chiller units

Abstract

The application discloses an energy-saving high-low temperature series ice water unit cooperative control method, sets an upper computer and takes the controllers of high and low temperatures as lower computers, and based on temperature intervals and temperature change trends, the upper computer uniformly coordinates and controls the running frequency and start-stop of compressors of high and low temperature units. Compared with the prior art, the problems of uncoordinated control, large temperature fluctuation and low energy efficiency are solved, and the following unexpected technical effects are realized: the inefficient and start-stop loss interval is effectively avoided, the high-efficiency running time proportion of the compressor group is stably improved to more than 95%, and the bottleneck of more than 5 percentage points of industry cognition is broken through; under the same hardware conditions, the ultra-high water temperature control precision of ±0.3 DEG C is realized, the system COP is improved to 5.5-5.7 by eliminating control internal loss and realizing optimal load distribution, and the energy-saving rate is improved by 15-20%.

Description

Technical Field

[0001] This invention relates to the field of industrial refrigeration control technology, and in particular to a collaborative control method for energy-saving high and low temperature series chiller units. Background Technology

[0002] In large-scale industrial refrigeration systems, high and low temperature series chiller units are often used. That is, the outlet of the high temperature stage unit is connected in series with the inlet of the low temperature stage unit. The outlet of the low temperature stage unit is the final water supply to the process end of the system. The high and low temperature stage units are each equipped with a controller.

[0003] Existing high- and low-temperature stage unit controllers are based on symmetrical or near-symmetrical regulation logic with local feedback (i.e., the high- and low-temperature stage compressors bear approximately proportional load changes during load increase / decrease), making independent decisions "each fighting its own battle," leading to overall system instability and energy efficiency degradation. Specifically:

[0004] When the total system load increases, the high-temperature stage unit tends to increase its frequency to improve its cooling capacity. Simultaneously, it lowers the water temperature entering the low-temperature stage. This causes the low-temperature stage unit to misjudge the reduced system load due to the lower inlet water temperature and instead reduce its frequency. This "high-temperature stage frequency increase, low-temperature stage frequency decrease" control antagonism not only causes the total system output cooling capacity to fail to match actual demand, leading to severe water temperature fluctuations, but also forces both compressors to frequently cross inefficient zones and even repeatedly start and stop. Those skilled in the art have long considered this an inherent control problem and have attempted to stabilize it by setting more conservative thresholds (such as expanding the temperature dead zone). However, this approach sacrifices system response speed and energy efficiency and does not address the core of the problem.

[0005] From an energy consumption perspective, the compressors in high and low temperature chiller units frequently cross inefficient operating ranges (below 50% load), resulting in a low-efficiency operating time of 8-12% for the system. The COP of the compressor in the low-efficiency range can decrease by more than 10% compared to its COP under full-load conditions. During each start-up and shutdown, the motor starting current can reach 3-5 times the rated current, causing significant additional energy loss due to repeated start-ups and shutdowns. Industry test data shows that the highest percentage of efficient operation (referring to operation in the 25-60Hz range) for this type of series chiller system is only 90%, with an overall COP typically between 4.6 and 4.8, and energy consumption per unit cooling capacity approximately 18% higher than under ideal coordinated operating conditions. Summary of the Invention

[0006] The present invention aims to solve the above-mentioned technical problems existing in the prior art by providing an energy-saving high and low temperature series chiller unit coordinated control method.

[0007] The technical solution of the present invention is as follows: There is a host computer and two controllers at high and low temperature levels as slave computers; the host computer performs the following operations: First, start the high-temperature compressor and collect the key parameters of the unit operation. If the unit operates stably and all compressors in at least one level are put into operation, then make a judgment on whether the load increases, decreases, or remains unchanged; if it increases, according to whether the already operating compressors are fully loaded, control the compressors to execute the collaborative compressor addition or collaborative frequency increase instructions; if it decreases, according to whether the frequency of the already operating compressors has dropped to the lowest efficient frequency threshold, control the compressors to execute the collaborative frequency decrease or collaborative compressor reduction instructions; the judgment on whether the load increases, decreases, or remains unchanged, the collaborative compressor addition, collaborative compressor reduction, collaborative frequency increase, and collaborative frequency decrease instructions are all made based on the temperature range and the temperature change trend.

[0008] Preferably, the judgment on whether the load increases, decreases, or remains unchanged is as shown in Table 1:

[0009] Table 1

[0010]

[0011] Where: to is the temperature range, ts is the target set value, tf is the average value of the collected outlet water temperature within the preset energy adjustment period; tm is the temperature change range within the preset energy adjustment period, which is the difference between the highest outlet water temperature th and the lowest outlet water temperature tl, nh is the ordinal number of the highest outlet water temperature th collected, nl is the ordinal number of the lowest outlet water temperature tl collected; nl > nh indicates that the temperature rises, and nl < nh indicates that the temperature drops.

[0012] Preferably, the execution of the collaborative compressor addition or collaborative compressor reduction instructions is as shown in Table 2:

[0013] Table 2

[0014]

[0015] When adding compressors, adjust the frequency of the already operating compressors to the efficient frequency for compressor addition, and then set the frequency of the newly started compressors to the lowest efficient frequency threshold;

[0016] The compressor reduction is preferably borne by the high-temperature compressor, and each time when reducing compressors, preferably select the compressor with a long operating time to turn off first; after turning off one high-temperature compressor, adjust the frequency of the remaining operating compressors to the first efficient value for compressor reduction, and after turning off the last high-temperature compressor and the low-temperature compressor, adjust the frequency of the remaining operating compressors to the second efficient value for compressor reduction;

[0017] The "maintain" means to maintain the current operating mode of the compressors.

[0018] Preferably, the execution of the collaborative frequency increase or collaborative frequency decrease instructions is as shown in Table 3:

[0019] Table 3

[0020]

[0021] The frequency increase priority is undertaken by the compressor with the lower frequency. If all operating compressors have the same frequency, the frequency is increased synchronously. The frequency decrease priority is undertaken by the compressor with the higher frequency. If all operating compressors have the same frequency, the frequency is decreased synchronously. The number of steps for fast frequency increase and fast frequency decrease is greater than the number of steps for slow frequency increase and slow frequency decrease.

[0022] The specific steps of the host computer control are as follows:

[0023] Step 1. Start the high-temperature compressor and run it to the rated frequency;

[0024] Step 2. Collect key operating parameters of the unit;

[0025] Step 3. Determine if any abnormality has occurred during operation. If yes, eliminate the abnormality and return to Step 2; otherwise, proceed to Step 4.

[0026] Step 4. Determine if at least one stage of the compressor in the unit is in operation. If yes, proceed to step 5; otherwise, return to step 2.

[0027] Step 5. Determine whether the load is increasing, decreasing, or remaining unchanged. If it is increasing, proceed to step 6; if it is decreasing, proceed to step 7; if it remains unchanged, return to step 2.

[0028] Step 6. Determine if the running compressor is fully loaded. If yes, execute the coordinated compressor boosting command and return to step 2. If no, execute the coordinated frequency boosting command and return to step 2.

[0029] Step 7. Determine whether the running compressor has reached the minimum high-efficiency frequency threshold. If not, execute the coordinated frequency reduction command and return to step 2. If yes, execute the coordinated compressor reduction command and return to step 2.

[0030] The preferred energy regulation cycle is 8 seconds.

[0031] Preferably, the high-efficiency frequency for increasing the frequency is 45Hz, the minimum high-efficiency frequency threshold is 25Hz, the first high-efficiency value for decreasing the frequency is 32Hz, and the second high-efficiency value for decreasing the frequency is 39Hz.

[0032] This invention employs a host computer and separate controllers for high and low temperatures as slave computers. The host computer coordinates and controls the operating frequency and start / stop of each compressor in the high and low temperature stages based on temperature ranges and trends. Compared to existing technologies, this invention solves the problems of uncoordinated control, large temperature fluctuations, and low energy efficiency, achieving the following unexpected technical effects: effectively avoiding inefficient and start-stop loss zones, stabilizing the proportion of high-efficiency operation time for the compressor group to over 95%, exceeding the industry's perceived bottleneck by more than 5 percentage points; under the same hardware conditions, achieving ultra-high water temperature control accuracy of ±0.3℃, while eliminating control internal losses and achieving optimal load distribution, increasing the system COP to 5.5~5.7, with energy savings of up to 15~20%. Attached Figure Description

[0033] Figure 1 This is a control flow diagram of the host computer in an embodiment of the present invention. Detailed Implementation

[0034] The energy-saving high-low temperature series chiller unit used in this embodiment of the invention has the same structure as the prior art, except that the outlet of the high-temperature chiller unit and the inlet of the low-temperature chiller unit are connected in series. The outlet of the low-temperature chiller unit is the final water supply to the process heat load. The high-temperature chiller unit includes compressors C1 and C2, and the low-temperature chiller unit includes compressors C3 and C4. It also includes a high-temperature chiller unit controller I and a low-temperature chiller unit controller II. Unlike the prior art, it also includes a host computer (DCS / PLC) for system coordination and control. The host computer communicates with controllers I and II to monitor key operating parameters of the units collected by controllers I and II and to issue priority execution commands to controllers I and II.

[0035] The control objective of this invention is to stably control the final outlet water temperature of the system at 0.5℃ (this setting is based on the high precision requirement of ±0.3℃ for ice water temperature in beer brewing process); the theoretical optimal value of the high-temperature stage outlet water (i.e., intermediate temperature) under the design conditions (system return water 28℃) is 11℃, and it can be dynamically optimized according to the changes in system return water temperature during actual operation.

[0036] The control flow diagram of the host computer is as follows: Figure 1 As shown, proceed as follows:

[0037] Step 1. Start the high-temperature compressor and run it at the rated frequency (e.g., 60Hz);

[0038] Step 2. Collect key operating parameters of the unit (outlet water temperature, compressor operating frequency, unit fault signals, and other key system parameters);

[0039] Step 3. Determine whether there is an abnormality in the operation. If yes, eliminate the abnormality and return to Step 2. If no, proceed to Step 4; the elimination of the abnormality is when a certain compressor fails and stops operating, its load is distributed to other normally operating compressors of the same level; or when it is detected that the water temperature fluctuates violently, the current operation is suspended until it is stable, etc.;

[0040] Step 4. Determine whether all compressors of at least one stage of the unit are in operation. For example, determine whether all of the high-temperature compressors C1, C2 or the low-temperature compressors C3, C4 are in operation. If yes, proceed to Step 5. If no, at this time, the upper computer is not used for collaborative control, so the upper computer does not intervene, and return to Step 2. The high-temperature compressors C1, C2 or the low-temperature compressors C3, C4 are still controlled by the Controller I and the Controller II respectively;

[0041] Step 5. Determine whether the load is increasing, decreasing or remaining unchanged. If it is increasing, execute Step 6. If it is decreasing, execute Step 7. If it remains unchanged, return to Step 2;

[0042] Determining whether the load is decreasing, decreasing or remaining unchanged is based on the matrix shown in Table 1:

[0043] Table 1

[0044]

[0045] Where: to is the temperature range, ts is the target set value (0.5°C), tf is the average value of the collected outlet water temperature (0.2°C) within the preset energy regulation period (8 seconds); tm is the temperature change trend within the preset energy regulation period, which is the difference between the highest outlet water temperature th and the lowest outlet water temperature tl; nh is the ordinal number of the highest outlet water temperature th collected, and nl is the ordinal number of the lowest outlet water temperature tl collected. For example, the first collection is 1, the second is 2..., or the time stamp of the collected data can be used as the ordinal number. The temperature change trend with nl>nh is a temperature drop, and the temperature change trend with nl<nh is a temperature rise; the maintenance is to maintain the current operation mode of the compressor.

[0046] The energy regulation period can be adjusted between 4 and 60 seconds. In the embodiment of the present invention, it is preferably set to 8 seconds. The system performance under different periods of 4 seconds, 8 seconds and 20 seconds was experimentally compared: when the period is 4 seconds, the control instructions are too frequent, and the frequency modulation operation reaches 5 times per minute on average, resulting in system oscillation and an increase in energy consumption of about 5%; when the period is 20 seconds, the sampling and decision-making lag is serious, and the water temperature control deviation reaches ±0.4°C; when the 8-second period is adopted, the system performs 1-2 frequency modulations per minute, which can not only respond to load changes in a timely manner, but also stabilize the water temperature fluctuation within ±0.1°C, achieving the optimal balance between response speed and control accuracy.

[0047] The threshold values ​​for judging the temperature change trend mentioned above are 0.15℃ and 0.30℃, respectively. Testing revealed that the high and low temperature series chiller system exhibits approximately a lag of about 5 seconds from the occurrence of water temperature fluctuations to the detection by the sensor and the execution of control commands. Experiments show that frequency modulation for small fluctuations less than 0.15℃ leads to over-adjustment, causing a reverse water temperature fluctuation of ±0.2℃; while a slow frequency modulation strategy is used for fluctuations exceeding 0.30℃, the delayed response results in excessive water temperature (fluctuation > 0.8℃). Therefore, this embodiment of the invention divides the change trend into 5 levels (unchanged, slow heating, slow cooling, rapid heating, and rapid cooling) and different temperature ranges, forming a matrix for judging whether the load increases, decreases, or remains unchanged.

[0048] Step 6. Determine if the running compressor is fully loaded. If yes, execute the coordinated compressor boosting command and return to step 2. If no, execute the coordinated frequency boosting command and return to step 2.

[0049] Step 7. Determine whether the running compressor has reached the minimum high-efficiency frequency threshold. If no, execute the coordinated frequency reduction command and return to step 2. If yes, execute the coordinated compressor reduction command and return to step 2.

[0050] The coordinated increase or decrease of generating capacity commands are based on a control command matrix derived from the effluent temperature range and its temperature change trend collected under stable operating conditions of the generating units. The specific control command matrix is ​​shown in Table 2.

[0051] Table 2

[0052]

[0053] The coordinated frequency increase or coordinated frequency decrease commands are also based on the control command matrix generated from the effluent temperature range and its temperature change trend collected under stable unit operation conditions. The specific control commands are shown in Table 3.

[0054] Table 3

[0055]

[0056] The frequency adjustment range for each slow increase / decrease is selected within the range of 0.5~2Hz to adapt to scenarios with slow temperature changes and avoid system oscillation; the frequency adjustment range for each fast increase / decrease is selected within the range of 1~5Hz, but the number of decrease steps for fast increase and fast decrease must be greater than the number of steps for slow increase and slow decrease.

[0057] The core principle behind constructing the matrices shown in Tables 1, 2, and 3 is to prioritize the most energy-efficient regulation method while ensuring stable water temperature.

[0058] In this embodiment of the invention, when adding compressors, the frequency of the already running compressors is first adjusted to the high-efficiency frequency to avoid energy redundancy caused by long-term full-load operation. Then, the frequency of the newly started compressors is set to the minimum high-efficiency frequency threshold to avoid the low-frequency, low-efficiency operating range. This ensures that the system responds quickly while actively locking the operating point in the high-efficiency range. Frequency increase is preferentially undertaken by compressors with lower frequencies. If all running compressors have the same frequency, they are increased synchronously to ensure that the compressor group always operates in the high-efficiency range during the addition process.

[0059] In this embodiment of the invention, the high-efficiency frequency for boosting compressors is set to 45Hz, and the minimum high-efficiency frequency threshold is set to 25Hz. If both C1 and C2 are detected to be fully loaded (frequency reaching 60Hz), and a boosting command is required according to Table 2, the host computer delays for 60 seconds (the delay time can be modified between 20 and 600 seconds) before issuing a command to start the first cryogenic stage compressor, C3. Once C3 is detected to have started successfully, the frequencies of the already running C1 and C2 are first synchronously reduced from 60Hz to 45Hz, and then the frequency of the newly started C3 is set to 25Hz. Afterward, the boosting command issued by the host computer will be preferentially handled by the cryogenic stage compressor C3 until the frequency of C3 equals the frequencies of C1 and C2 (e.g., both 45Hz). Then, all running compressors C1, C2, and C3 enter synchronous boosting mode. If the system still needs additional compressors, the host computer will start the second compressor C4 in the low-temperature stage. First, keep the frequency of the already running compressors C1, C2, and C3 unchanged at 45Hz, and then set the frequency of C4 to 25Hz. Subsequent frequency increases should be carried out by C4 first, until its frequency rises to 45Hz. Then, all running compressors C1, C2, C3, and C4 will enter the synchronous frequency increase mode.

[0060] In this embodiment of the invention, frequency reduction is prioritized by compressors with higher frequencies. If all operating compressors have the same frequency, frequency reduction is synchronized. Reduced compressor capacity is prioritized by high-temperature compressors, and each time a compressor is reduced, the compressor with the longest operating time is prioritized for shutdown to balance unit losses. After shutting down one high-temperature compressor, the frequency of the remaining operating compressors is adjusted to the first high-efficiency reduction value to ensure that the system load after reduction is borne by fewer compressors within the high-efficiency range, avoiding energy efficiency losses due to low-load operation of a single unit. After shutting down the last high-temperature compressor, the frequency of the remaining operating compressors is adjusted to the second high-efficiency reduction value to avoid the energy efficiency trap of the last high-temperature compressor operating at low load. If there is still a need to reduce compressor capacity, the low-temperature compressor with the longest operating time is shut down, and the frequency of the remaining operating compressors is adjusted to the second high-efficiency reduction value.

[0061] In this embodiment of the invention, the first high-efficiency reduction value is set to 32Hz, and the second high-efficiency reduction value is set to 39Hz. If it is detected that all operating compressors C1, C2, C3, and C4 have not dropped to 25Hz (the minimum high-efficiency frequency threshold), and a frequency reduction command needs to be executed according to Table 2, the compressor with the highest frequency will take the lead. If compressor C1 has the highest frequency, the frequency reduction command will be executed first until it drops to 25Hz; then, among the remaining compressors C2, C3, and C4, the compressor with the highest frequency will take the lead in frequency reduction until it drops to 25Hz. If there are operating compressors with the same frequency and the compressor with the highest frequency needs to take the lead in frequency reduction, the compressors with the same frequency will reduce their frequency synchronously until they drop to 25Hz. If it is detected that all operating compressors C1, C2, C3, and C4 have the same frequency and have not dropped to 25Hz, then all four compressors will reduce their frequency synchronously until they drop to 25Hz.

[0062] If all operating compressor frequencies have dropped to 25Hz, and it is determined that there is still a need to reduce compressor frequency, the host computer delays for 60 seconds before initiating the compressor reduction logic. Based on the principle of prioritizing the shutdown of high-temperature stage compressors, the host computer selects the high-temperature stage compressor with the longest operating time (e.g., C1) to execute the shutdown command. Upon detecting that C1 is shut down, the host computer immediately increases the frequency of the remaining operating compressors C2, C3, and C4 from 25Hz to 32Hz. If there is still a need to reduce compressor frequency, the above reduction logic is repeated: if high-temperature stage compressor C2 is still running, then C2 is shut down, and the frequencies of the remaining operating compressors C3 and C4 are increased to 39Hz; if all high-temperature stage compressors have been shut down, but there is still a need to reduce compressor frequency (i.e., to shut down low-temperature stage compressors), the low-temperature stage compressor C3 with the longest operating time is shut down first based on its cumulative operating time, and after shutting down, the frequency of the remaining low-temperature stage compressor C4 is adjusted to 39Hz.

[0063] In this embodiment of the invention, the high-efficiency frequency for increasing capacity is set to 45Hz, the minimum high-efficiency frequency threshold is 25Hz, the first high-efficiency value for decreasing capacity is 32Hz, and the second high-efficiency value for decreasing capacity is 39Hz, all determined based on the compressor energy efficiency curve. The minimum high-efficiency frequency threshold of 25Hz was determined through the following experiment: A test system was constructed using a high-temperature chiller unit (rated cooling capacity of 1370kW at a chilled water outlet temperature of 11℃) with a Bitzer CSW10573-290Y compressor and a low-temperature chiller unit (rated cooling capacity of 940kW at a chilled water outlet temperature of 0.5℃) with the same compressor. The test was conducted under the conditions of an ambient temperature of 35℃, a cooling water inlet temperature of 32℃, and a system target outlet water temperature of 0.5℃. Experimental results show that when the compressor operating frequency is below 25Hz (e.g., 20Hz), the coefficient of performance (COP) of the high-temperature chiller unit drops to around 6.0, and the COP of the low-temperature chiller unit drops to around 4.2, a decrease of about 10% compared to operating at 25Hz. However, when the frequency is maintained at 25Hz or higher, the COP of the high-temperature chiller unit remains between 6.4 and 6.6, and the COP of the low-temperature chiller unit remains between 4.5 and 4.7. Therefore, 25Hz has been established as the minimum high-efficiency frequency threshold that balances system energy efficiency and operational stability.

[0064] For example, the first high-efficiency value of the compressor reduction is 32Hz. This frequency is the compensation frequency after the compressor reduction is determined through system energy efficiency optimization experiments. It can ensure that the remaining compressor still operates in the high-efficiency range after taking over the extra load, thereby avoiding the decrease in system COP caused by excessively high or low single-unit load. Implementation effect

[0065] Stability: In the embodiments of the present invention, the temperature fluctuation of the outlet water is strictly controlled within ±0.3℃, which fully meets the high precision requirements of the beer brewing process for ice water temperature, and the number of alarm shutdowns is reduced by more than 90%.

[0066] Energy efficiency: By eliminating the control losses of individual high and low temperature stages, the compressor operates in the high-efficiency range of 25-60Hz for more than 95% of the time. Under the same test cycle and operating conditions, the overall COP of this invention is stable between 5.5 and 5.7. Compared with the benchmark test using the traditional independent control strategy (overall system COP of 4.6 to 4.8), the energy efficiency is improved by about 18%, and the energy consumption per unit cooling capacity is reduced by about 15%.

[0067] To quantify the effectiveness of this invention, a 12-hour comparative test was conducted under the same hardware and operating conditions. The key performance indicators are shown in Table 4.

[0068] Table 4

[0069]

[0070] Note:

[0071] 1) Overall system COP = (High-temperature stage cooling capacity + Low-temperature stage cooling capacity) / (High-temperature stage power consumption + Low-temperature stage power consumption);

[0072] 2) The above test data were all measured according to the specific requirements of the application scenario in accordance with GB / T 18430.1-2024 "Vapor compression cycle chiller (heat pump) units Part 1: Chiller (heat pump) units for industrial or commercial and similar purposes".

[0073] The above data fully demonstrates the comprehensive advantages of this invention in terms of energy efficiency, stability, and reliability.

Claims

1. An energy-saving high-low temperature series ice water chiller unit cooperative control method, characterized in that The upper computer is provided and two controllers of high and low temperature levels are lower computers; the upper computer performs the following operations: firstly, starting the high temperature level compressor and collecting key parameters of the unit operation, if the unit operation is stable and all compressors of at least one level are put into operation, making a judgment of load increase, decrease or no change; If increasing, according to whether the running compressor is full load, the compressor executes the cooperative increase machine or cooperative increase frequency instruction; if decreasing, according to whether the frequency of the running compressor is reduced to the lowest efficient frequency threshold, the compressor executes the cooperative decrease frequency or cooperative decrease machine instruction; the judgment of load increase, decrease or no change, the cooperative increase machine, cooperative decrease machine, cooperative increase frequency and cooperative decrease frequency instruction are made based on temperature interval and temperature change trend; The judgment of load increase, decrease or no change is shown in Table 1: Table 1 ； Wherein, to is temperature interval, ts is target setting value, tf is the average value of collected outlet water temperature in the preset energy regulation period, tm is the temperature change amplitude in the preset energy regulation period, which is the difference between the highest outlet water temperature th and the lowest outlet water temperature tl, nh is the serial number of the highest outlet water temperature th, nl is the serial number of the lowest outlet water temperature tl, nl>nh indicates temperature rise, nl<nh indicates temperature drop; The upper computer control steps are specifically as follows: Step 1. starting the high temperature machine compressor and making it run to rated frequency; Step 2. collecting key parameters of the unit operation; Step 3. judging whether the operation is abnormal, yes, eliminating the abnormality and returning to step 2, no, performing step 4; Step 4. judging whether all compressors of at least one level are put into operation, yes, performing step 5, no, returning to step 2; Step 5. judging whether the load belongs to increase, decrease or no change, if increasing, performing step 6, if decreasing, performing step 7, if no change, returning to step 2; Step 6. judging whether the running compressor is full load, yes, controlling to execute the cooperative increase machine instruction and returning to step 2, no, controlling to execute the cooperative increase frequency instruction and returning to step 2; Step 7. judging whether the running compressor reaches the lowest efficient frequency threshold, no, controlling to execute the cooperative decrease frequency instruction and returning to step 2; yes, controlling to execute the cooperative decrease machine instruction and returning to step 2.

2. The energy-saving high-low temperature series ice water chiller cooperative control method according to claim 1, characterized in that The execution of the cooperative increase machine or cooperative decrease machine instruction is shown in Table 2: Table 2 ； The increase machine is to adjust the frequency of the running compressor to the increase machine efficient frequency, and set the frequency of the newly started compressor to the lowest efficient frequency threshold; The decrease machine is preferentially borne by the high temperature level compressor, and each time the decrease machine is preferentially selected to close the compressor with long running time; after closing one high temperature level compressor, adjusting the frequency of the remaining running compressors to the first decrease machine efficient value, after closing the last high temperature level compressor and closing the low temperature level compressor, adjusting the frequency of the remaining running compressors to the second decrease machine efficient value; The keeping is to maintain the current operation mode of the compressor.

3. The energy-saving high-low temperature series ice water chiller cooperative control method according to claim 2, characterized in that The execution of the cooperative increase frequency or cooperative decrease frequency instruction is shown in Table 3: Table 3 ； The frequency increase is preferentially borne by the compressor with low frequency, and if the frequency of all running compressors is consistent, the frequency is increased synchronously; the frequency decrease is preferentially borne by the compressor with high frequency, and if the frequency of all running compressors is consistent, the frequency is decreased synchronously; the step number of fast frequency increase and fast frequency decrease is greater than that of slow frequency increase and slow frequency decrease.

4. The energy-saving high-low temperature series ice water chiller cooperative control method according to claim 3, characterized in that: The energy regulation period is 8 seconds.

5. The energy-saving high-low temperature series ice water chiller cooperative control method according to claim 4, characterized in that: The high efficient frequency of the frequency increase is 45 Hz, the minimum high efficient frequency threshold is 25 Hz, the first high efficient value of the frequency decrease is 32 Hz, and the second high efficient value of the frequency decrease is 39 Hz.

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