Energy-saving optimization control method for central air-conditioning system under low load condition

Abstract

The present invention discloses an energy-saving optimization control method for low-load working conditions of a central air-conditioning system, which monitors the on / off state of a chiller, and when it is detected that the load rate of the chiller in the operating state is less than a certain proportion of the preset load rate and the operating time exceeds a certain time, the chiller, cooling water pump and cooling tower are shut down in sequence; in the shutdown state, when it is detected that the rising rate of the return water temperature of the chilled water is less than a certain proportion of the maximum rising rate of this shutdown, the cooling water pump, cooling tower and chiller are started in sequence to enter the next intermittent operation. The present invention calculates the cooling capacity during the shutdown process based on the ratio of the return water temperature rising rate, and when the cooling capacity is less than the preset threshold, it is used as a startup indicator; when the load rate of the chiller is less than the preset threshold, the lower the load rate, the lower the energy efficiency, thereby effectively improving the stability of the operation of the central air-conditioning system and further improving the overall energy saving.

Description

Technical Field

[0001] The invention relates to energy-saving control technology for central air conditioners, in particular to an energy-saving optimization control method for low-load working conditions of a central air conditioner system that operates intermittently according to the rising rate of return water temperature of chilled water and the load rate of a chiller. Background Art

[0002] The energy efficiency of central air conditioning systems at low load rates is low, usually below 70%. At present, intermittent operation strategies based on chilled water return or supply water temperature are usually adopted to improve the energy efficiency of central air conditioning systems at low load rates, that is, by setting the upper limit temperature to start the system and the lower limit temperature to shut down the system. Figure 1 shown.

[0003] In this traditional intermittent operation control mode: (1) In the shutdown state: the chiller, cooling water pump, and cooling tower fan start when the chilled water return temperature reaches the set upper threshold (such as 18°C); (2) In the startup state: the chiller, cooling water pump, and cooling tower fan shut down when the chilled water return temperature reaches the set lower threshold (such as 11°C). This strategy of controlling the on / off of the chiller by setting the temperature threshold can indeed achieve the operation of the chiller at a high load rate under low cooling demand, thereby improving the operating energy efficiency of the refrigeration system. However, under this strategy, when it is dry weather, there is a problem of insufficient utilization of the chilled water temperature and premature shutdown of the chiller, which not only affects the overall energy saving, but also causes unstable operation and cannot achieve automatic adjustment and control.

[0004] For example, a Chinese patent document with a publication date of April 6, 2011 and a publication number of CN102003768A discloses a central air conditioning energy-saving control method and controller, wherein the method includes: the controller sets the stop mode of the auxiliary machine of the refrigerator, the auxiliary machine at least includes a cooling water pump, a cooling tower and a freezing water pump; the operating state of the refrigerator is detected in real time; when it is detected that the refrigerator stops running, the auxiliary machine is stopped according to the stop mode preset by the controller, and when the stop mode preset by the controller is the temperature automatic mode, the temperature on the freezing water supply pipe and the cooling water outlet pipe of the refrigerator is detected in real time through a temperature sensor or a transmitter; when the temperature on the freezing water supply pipe of the refrigerator is greater than the set freezing water pump stop temperature value, the freezing water pump is turned off, and when the temperature on the cooling water outlet pipe of the refrigerator is less than the set cooling water pump stop temperature value, the cooling water pump and the cooling tower are turned off. Using this temperature upper and lower limit control strategy, the staff needs to set it, especially in different climate periods, the upper and lower limits of the temperature are different. Therefore, in response to the requirements of different periods and different upper and lower temperature limits, the operation and maintenance personnel are required to have a high degree of reliance on their experience. Ultimately, the energy saving and on-site operation effects of the central air-conditioning system are directly related to the operation and maintenance personnel.

[0005] Therefore, a more automated control strategy is needed to achieve higher energy savings and more stable operation. Summary of the invention

[0006] In order to solve the above technical problems, the present invention provides an energy-saving optimization control method for low-load working conditions of a central air-conditioning system. The start and stop operation of the chiller, cooling water pump and cooling tower are controlled by detecting the rising rate of the return water temperature of the chilled water and the intermittent operation control strategy of the load rate of the chiller. Specifically, the ratio of the real-time rising rate of the return water temperature of the chiller to the maximum rising rate of the return water temperature of this round can be regarded as the ratio of the cooling capacity during the shutdown process to the cooling capacity before the shutdown; the cooling capacity during the shutdown process can be calculated according to the ratio of the rising rates, and when the cooling capacity is less than the preset threshold, it can be regarded as an indicator for starting the equipment; when the load rate of the chiller is less than the preset threshold, the lower the load rate, the lower the energy efficiency. Thereby improving the stability of the operation of the central air-conditioning system and further improving the overall energy saving.

[0007] The technical solution of the present invention is as follows:

[0008] The energy-saving optimization control method of the central air-conditioning system under low load conditions has the following steps:

[0009] Step 1: Get the chiller power on / off status:

[0010] For chillers in the on state, determine whether to shut down the intermittently running chillers, and whether to shut down the intermittently running cooling water pumps and cooling towers;

[0011] For chillers that are in shutdown state, determine whether to start up the intermittently running cooling water pumps and cooling towers, and whether to start up the intermittently running chillers;

[0012] Step 2: When the chiller is in the on state, enter the intermittent operation shutdown detection control process:

[0013] Step 2.1, first, determine the startup time of the intermittently running chiller: when the current operation time is less than or equal to the preset operation time, continue to detect the intermittently running chiller;

[0014] When it is detected that the current running time is greater than the preset running time, the next step is to judge the current load rate (mainly the electric power and current percentage of the chiller) of the intermittently running chiller:

[0015] Step 2.2, when the current load rate is greater than or equal to a certain proportion of the preset operating load rate, the current load rate of the intermittently operating chiller is continuously detected; until it is detected that the current load rate is less than a certain proportion of the preset operating load rate, a shutdown command is issued to the intermittently operating chiller;

[0016] Step 2.3, after issuing a shutdown command for the intermittently running chiller, detect and obtain the electric power and load rate of the chiller to determine whether the chiller is shut down;

[0017] Step 2.4: If it is confirmed that the chiller is not shut down, re-issue the shutdown command of the intermittently running chiller, and perform step 2.3 again until it is confirmed that the chiller is shut down;

[0018] Step 2.5: If it is confirmed that the chiller has been shut down, a shutdown command is issued to the intermittently running cooling water pump and cooling tower;

[0019] Step 2.6, after issuing the shutdown command of the intermittently running cooling water pump and cooling tower, detect and obtain the power and frequency of the cooling water pump and cooling tower to determine whether the cooling water pump and cooling tower are shut down;

[0020] Step 2.7: If it is confirmed that the cooling water pump and the cooling tower are not shut down, reissue the shutdown command of the intermittently running cooling water pump and cooling tower, and perform step 2.6 again until it is confirmed that the cooling water pump and the cooling tower are shut down;

[0021] Step 2.8: If it is confirmed that the cooling water pump and cooling tower have been shut down, the shutdown process of this intermittent operation is completed;

[0022] Furthermore, in the control process of step 2, the load rate and the running time of the chiller must satisfy the judgment principle at the same time before proceeding to the subsequent steps.

[0023] Step 3: When the chiller is in shutdown state, enter the intermittent operation startup detection control process:

[0024] Step 3.1, first, determine the current chilled water return temperature parameter of the intermittently operated chiller, wherein the current chilled water return temperature parameter refers to the return water temperature rising rate in the current time period;

[0025] When the return water temperature rising rate in the current time period is greater than or equal to a certain proportion of the maximum return water temperature rising rate in the corresponding time period since the current startup operation, the chilled water return water temperature parameters of the intermittently operated chiller are continuously detected; until it is detected that the return water temperature rising rate in the current time period is less than a certain proportion of the maximum return water temperature rising rate in the corresponding time period since the current startup operation, a startup instruction is issued to the intermittently operated cooling water pump and cooling tower;

[0026] Step 3.2, after issuing the start-up command of the intermittently running cooling water pump and cooling tower, detecting and obtaining the electric power of the cooling water pump and cooling tower to determine whether the cooling water pump and cooling tower are started;

[0027] Step 3.3: If it is confirmed that the cooling water pump and the cooling tower are not turned on, re-issue the cooling water pump and the cooling tower start-up instructions, and perform step 3.2 again until the cooling water pump and the cooling tower are confirmed to be turned on;

[0028] Step 3.4: If it is confirmed that the cooling water pump and cooling tower have been turned on, a start-up command is issued to the intermittently running chiller;

[0029] Step 3.5, after issuing the start-up command of the intermittently running chiller, detect and obtain the electric power and load rate of the chiller (i.e., the electric power and current percentage of the chiller) to determine whether the chiller is started;

[0030] Step 3.6: If it is confirmed that the chiller is not turned on, re-issue the start-up command of the intermittently running chiller, and perform step 3.5 again until it is confirmed that the chiller is turned on;

[0031] Step 3.7: If it is confirmed that the chiller has been turned on, the startup process of this intermittent operation is completed.

[0032] For the intermittent shutdown detection control process in step 2, the further design is as follows:

[0033] Furthermore, when the shutdown process of this intermittent operation in step 2 is completed, the central air-conditioning system enters a waiting mode, stops issuing all instructions on starting and stopping the equipment, and the chilled water return temperature begins to rise.

[0034] Furthermore, after the shutdown process of this intermittent operation in step 2 is completed, the chiller, cooling water pump, and cooling tower are all in a stopped state, and the refrigeration water pump is kept running, and the frequency of the refrigeration water pump is the power supply frequency before the shutdown state.

[0035] Furthermore, in step 2, when the chiller, cooling water pump, and cooling tower are all in a stopped state, the chilled water return temperature will continue to rise due to heat exchange in the air-conditioning terminal equipment (such as FCU or AHU). After a period of time, since the three-way valve at the end of the equipment is fully open, the rising rate of the chilled water return temperature begins to decrease continuously.

[0036] The minimum reference value of the certain proportion of the preset operating load rate described in step 2.2 is 50%.

[0037] For the intermittent startup detection control process in step 3, the further design is as follows:

[0038] Furthermore, in step 3, the function of the chilled water return temperature rising process is expressed as:

[0039] ;

[0040] in: t is the chilled water return temperature; t r is the indoor air temperature; t 0 It is the chilled water return temperature when the machine is shut down; x is the downtime duration; C 0 is the coefficient to be determined.

[0041] According to the above function, the coefficients to be determined are obtained by running data fitting C 0 , the maximum allowable downtime of this chiller can be calculated x limit , then according to x limit Plan shutdown and startup times.

[0042] Furthermore, the return water temperature rising rate in the current time period in step 3.1 can be set to 10 minutes, and the return water temperature values ​​within 10 minutes are recorded to obtain the return water temperature rising rate within 10 minutes.

[0043] Furthermore, the minimum reference value of the certain proportion of the maximum return water temperature rising rate in the corresponding time period described in step 3.1 is 70%.

[0044] Furthermore, in step 3.1, the return water temperature rising rate can be used to determine whether the chiller has completed shutdown, and the decrease in cooling capacity of the air-conditioning terminal equipment can be obtained to ensure safe operation of the system.

[0045] For the detection in steps 2.3, 2.6, 3.2, and 3.5 of the method of the present invention, the detection period is a preset period, such as 1 minute, 2 minutes, etc.

[0046] The technical effects of the present invention are as follows:

[0047] 1. Compared with the original control strategy of the upper limit threshold of the startup temperature, the energy efficiency of the host startup state is improved while ensuring the cooling effect at the terminal; the chilled water return temperature is allowed to rise to a higher startup temperature threshold in the shutdown state, which increases the single startup operation time of the chiller under a high load rate operation state (i.e. >70%) while ensuring the cooling capacity at the terminal, reduces the number of startups and shutdowns, and reduces the energy consumption in the startup preparation state, thereby achieving improved energy efficiency and achieving the purpose of effective energy saving.

[0048] 2. Compared with the original shutdown temperature lower limit setting, it prevents the chiller from failing to reach the shutdown temperature lower limit; in this case, because the load rate is higher than expected, the chilled water return temperature cannot reach the shutdown threshold, and thus cannot be shut down, and runs in a low-load and low-efficiency range for a long time. The present invention introduces the monitoring of the chiller load rate. When the cumulative operation time of the chiller load rate less than the set load rate threshold reaches the set shutdown threshold, the chiller is shut down to reduce energy waste.

[0049] 3. The present invention can ensure the cooling capacity of the cooling terminal when the unit is shut down by monitoring the rising rate of the chilled water temperature, and can ensure that the operation time of the low load rate and low energy efficiency range is reduced when the unit is started by monitoring the load rate of the chiller.

[0050] 4. In the overall control process of the present invention, the return water temperature threshold for starting and stopping the equipment can be manually set to operate automatically, which reduces the requirements on the quality of on-site personnel and improves energy saving.

[0051] 5. After adopting the control of the present invention, through multiple detections of the on / off status of the chiller, the freezing water pump and the cooling water pump, the situation that the chiller is running while the freezing water pump or the cooling water pump is turned off can be effectively prevented.

[0052] 6. After adopting the control of the present invention, the cooling capacity of the air-conditioning terminal is guaranteed, preventing the situation where intermittent operation cannot guarantee the cooling capacity of the terminal, so as to ensure the stable operation of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 It is a schematic diagram of the traditional intermittent operation mode of the central air-conditioning system in the background technology.

[0054] Figure 2 Schematic diagram of the intermittent operation mode of the present invention.

[0055] Figure 3 Schematic diagram of various temperature curves of central air-conditioning chilled water in Example 1. DETAILED DESCRIPTION

[0056] The present invention designs a new intermittent operation control strategy for chillers, specifically Figure 3 As shown in the figure, according to the control method of intermittent operation of the chilled water return temperature rising rate and the chiller load rate, the specific control process is as follows:

[0057] First, get the chiller on / off status:

[0058] For chillers in the on state, determine whether to shut down the intermittently running chillers, and whether to shut down the intermittently running cooling water pumps and cooling towers;

[0059] For chillers that are in shutdown state, determine whether to start up the intermittently running cooling water pumps and cooling towers, and whether to start up the intermittently running chillers;

[0060] Then, subsequent tests are carried out to determine the load rate and operating time of the chiller.

[0061] The current load rate of the chiller is determined based on the preset load rate threshold:

[0062] (1) When the load rate of the chiller is less than the set value (such as 70%), and the current startup time is greater than the set value (such as 60 minutes), the chiller shutdown command is output to stop the operation of the chiller.

[0063] (2) After outputting the shutdown command of the chiller, detect the electric power and current percentage of the chiller to confirm that the chiller has completed the shutdown; if the shutdown is not completed, issue the shutdown command again, and the detection cycle is 1 minute.

[0064] (5) After confirming that the chiller has completed shutdown for 5 minutes, output a shutdown command to the associated cooling water pump and cooling tower.

[0065] (6) Check the power and inverter frequency of the associated cooling water pump and cooling tower to confirm that the cooling water pump and cooling tower have completed shutdown; if the shutdown is not completed, issue a shutdown command again, with a detection cycle of 1 minute.

[0066] (7) After completing the above operations, the output shutdown is completed and the machine enters the waiting mode. The stop command is issued and the chilled water return temperature begins to rise.

[0067] Under the condition that the chiller, cooling water pump and cooling tower are all stopped, keep the chilled water pump running, and the chilled water pump frequency is the frequency before shutdown. At this time, the chilled water temperature will continue to rise due to the end heat exchange. After a period of time, the end three-way valve is fully opened, and the rising speed begins to decrease at the same time. When the return water temperature rise rate of the chiller's chilled water every 10 minutes is less than 70% of the highest value of the return water temperature rise rate every 10 minutes since the start of shutdown, it can be considered that the cooling capacity at this time is less than 70% of the stable operation. Start the cooling water pump and cooling tower, detect the power of the cooling water pump and cooling tower to confirm that the cooling water pump and cooling tower have completed the startup. If the startup is not completed, issue the startup command again, and the detection cycle is 1 minute. One minute after confirming that the cooling water pump and cooling tower are started, start the set chiller, detect the current percentage and power of the chiller, and confirm that the chiller startup is completed. If the startup is not completed, issue the startup command again, and the detection cycle is 1 minute. After completing the above operations, the output startup is completed, and the machine enters the waiting mode. The stop command is issued, and the chilled water return temperature begins to drop.

[0068] In this embodiment, the intermittent operation mode of the central air conditioning system is referred to as Figure 2 As shown, the specific operation mode is:

[0069] (1) When the main engine, chilled water pump, cooling water pump and cooling tower are all in operation, if the load rate of the chiller is less than the preset load rate (such as 70%) and the operation time has exceeded 60 minutes, the main engine, cooling water pump and cooling tower are shut down in sequence according to the above shutdown process; at the same time, the chilled water pump is still running;

[0070] (2) After a certain period of shutdown, when the rising rate of the chilled water return temperature is monitored to be less than 70% of the maximum rising rate during this shutdown, the cooling water pump, cooling tower and main unit are started in turn according to the above startup process to enter the next intermittent operation state.

[0071] At the same time, in the above control process, the single operation time and shutdown time of the chiller can be manually set. When the operation time of the chiller reaches the set value, the chiller, cooling water pump, and cooling tower are shut down in sequence. When the shutdown time of the chiller reaches the set value, the cooling tower, cooling water pump, and chiller are started in sequence. This control strategy can also be used when the temperature sensor is offline, so it can effectively monitor the safety and stability of the system operation.

Claims

1. An energy-saving optimization control method for a central air-conditioning system under low-load conditions, characterized in that: Here are the steps: Step 1: Get the chiller power on / off status: For chillers in the on state, determine whether to shut down the intermittently running chillers, and whether to shut down the intermittently running cooling water pumps and cooling towers; For chillers that are in shutdown state, determine whether to start up the intermittently running cooling water pumps and cooling towers, and whether to start up the intermittently running chillers; Step 2: When the chiller is in the on state, enter the intermittent operation shutdown detection control process: Step 2.1, first, determine the startup time of the intermittently running chiller: when the current operation time is less than or equal to the preset operation time, continue to detect the intermittently running chiller; When it is detected that the current running time is greater than the preset running time, the next step is to judge the current load rate of the intermittently running chiller: Step 2.2, when the current load rate is greater than or equal to a certain proportion of the preset operating load rate, the current load rate of the intermittently operating chiller is continuously detected; until it is detected that the current load rate is less than a certain proportion of the preset operating load rate, a shutdown command is issued to the intermittently operating chiller; Step 2.3, after issuing a shutdown command for the intermittently running chiller, detect and obtain the electric power and load rate of the chiller to determine whether the chiller is shut down; Step 2.4: If it is confirmed that the chiller is not shut down, re-issue the shutdown command of the intermittently running chiller, and perform step 2.3 again until it is confirmed that the chiller is shut down; Step 2.5: If it is confirmed that the chiller has been shut down, a shutdown command is issued to the intermittently running cooling water pump and cooling tower; Step 2.6, after issuing the shutdown command of the intermittently running cooling water pump and cooling tower, detect and obtain the power and frequency of the cooling water pump and cooling tower to determine whether the cooling water pump and cooling tower are shut down; Step 2.7: If it is confirmed that the cooling water pump and the cooling tower are not shut down, reissue the shutdown command of the intermittently running cooling water pump and cooling tower, and perform step 2.6 again until it is confirmed that the cooling water pump and the cooling tower are shut down; Step 2.8: If it is confirmed that the cooling water pump and cooling tower have been shut down, the shutdown process of this intermittent operation is completed; Step 3: When the chiller is in shutdown state, enter the intermittent operation startup detection control process: Step 3.1, first, determine the current chilled water return temperature parameter of the intermittently operated chiller, wherein the current chilled water return temperature parameter refers to the return water temperature rising rate in the current time period; When the return water temperature rising rate in the current time period is greater than or equal to a certain proportion of the maximum return water temperature rising rate in the corresponding time period since the current startup operation, the chilled water return water temperature parameters of the intermittently operated chiller are continuously detected; until it is detected that the return water temperature rising rate in the current time period is less than a certain proportion of the maximum return water temperature rising rate in the corresponding time period since the current startup operation, a startup instruction is issued to the intermittently operated cooling water pump and cooling tower; Step 3.2, after issuing the start-up command of the intermittently running cooling water pump and cooling tower, detecting and obtaining the electric power of the cooling water pump and cooling tower to determine whether the cooling water pump and cooling tower are started; Step 3.3: If it is confirmed that the cooling water pump and the cooling tower are not turned on, re-issue the cooling water pump and the cooling tower start-up instructions, and perform step 3.2 again until the cooling water pump and the cooling tower are confirmed to be turned on; Step 3.4: If it is confirmed that the cooling water pump and cooling tower have been turned on, a start-up command is issued to the intermittently running chiller; Step 3.5, after issuing the start-up command of the intermittently running chiller, detect and obtain the electric power and load rate of the chiller to determine whether the chiller is started; Step 3.6: If it is confirmed that the chiller is not turned on, re-issue the start-up command of the intermittently running chiller, and perform step 3.5 again until it is confirmed that the chiller is turned on; Step 3.7: If it is confirmed that the chiller has been turned on, the startup process of this intermittent operation is completed.

2. The energy-saving optimization control method for a central air-conditioning system under low-load conditions according to claim 1 is characterized in that: When the shutdown process of this intermittent operation in step 2 is completed, the central air-conditioning system enters the waiting mode, stops issuing all instructions about the start and stop of the equipment, and the chilled water return temperature begins to rise.

3. The energy-saving optimization control method for a central air-conditioning system under low-load conditions according to claim 1 is characterized in that: When the shutdown process of this intermittent operation in step 2 is completed, the chiller, cooling water pump and cooling tower are all in a state of stopping operation, and the chilled water pump is kept running, and the frequency of the chilled water pump is the power supply frequency before the shutdown state.

4. The energy-saving optimization control method for a central air-conditioning system under low-load conditions according to claim 1 is characterized in that: In step 2, when the chiller, cooling water pump and cooling tower are all in a stopped state, the chilled water return temperature continues to rise. After the air conditioning system continues to operate for a certain period of time, the rising rate of the chilled water return temperature begins to decline continuously.

5. The energy-saving optimization control method for a central air-conditioning system under low-load conditions according to claim 1 is characterized in that: The current load rate of the chiller in step 2.1 includes the chiller electrical power and current percentage.

6. The energy-saving optimization control method for a central air-conditioning system under low-load conditions according to claim 1 is characterized in that: The minimum reference value of the certain proportion of the preset operating load rate described in step 2.2 is 50%.

7. The energy-saving optimization control method for a central air-conditioning system under low-load conditions according to claim 1 is characterized in that: The minimum reference value of a certain proportion of the maximum return water temperature rise rate in the corresponding time period described in step 3.1 is 70%.

8. The energy-saving optimization control method for a central air-conditioning system under low-load conditions according to claim 1, characterized in that: The load factor of the chiller in step 3.5 includes the electrical power and current percentage of the chiller.

9. The energy-saving optimization control method for a central air-conditioning system under low-load conditions according to claim 1, characterized in that: For the detections in steps 2.3, 2.6, 3.2, and 3.5, the detection cycles are all preset cycles, and the preset cycles have the same duration.

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