Subway station air conditioning system based on return air temperature and control method

Abstract

The invention discloses a subway station air conditioning system based on return air temperature and a control method, the subway station air conditioning system comprises an air system, a chilled water system and a cooling water system, the return air temperature is used as a target value, and the air volume of an air feeder and the water outlet temperature of a water chilling unit are adjusted and controlled through PID; when the load of the metro station is increased, the real-time temperature of the metro station is increased, the air volume of an air feeder is increased according to the load of the station, and the water outlet temperature of the water chilling unit is adjusted till the target return air temperature is met; when the load of the metro station is reduced, the real-time temperature of the metro station is reduced, the air volume of the air feeder is reduced according to the load of the station, and the water outlet temperature of the water chilling unit is adjusted till the target return air temperature is met. According to the description of the scheme, the method has the beneficial effects that the temperature of the station can be quickly and accurately adjusted by adopting a wind-water joint adjusting mode, the comfort level of an air conditioner of the station is improved, and the problem that the overall energy consumption level of the metro station is relatively high due to experience adjustment is avoided.

Description

Technical Field

[0001] The present invention relates to the technical field of energy saving in subway stations, and in particular to a subway station air conditioning system and a control method based on return air temperature. Background Art

[0002] With the continuous improvement of urbanization, subways have become an important means of transportation to solve the problems of road congestion and environmental pollution. The continuous increase in the mileage of subway lines has promoted the development of urban rail transit, but at the same time, subways have also generated huge energy consumption. In the investigation of subway energy consumption, it was found that the ventilation and air-conditioning system of subway stations actually operates at partial load for a long time, and the time it can reach full load is very short, which causes serious energy waste. In addition, during the cooling season with heavy load, the cooling demand of each terminal area is always in a state of change. At this time, it is very important to adjust the air-conditioning system to follow the change in demand. If the air-conditioning system is not adjusted in time or the control method is unreasonable, it will lead to low operating efficiency, which will not only reduce the service life of the equipment, but also cause energy waste. Therefore, effectively reducing the overall energy consumption of subway stations has become a hot spot and focus of subway energy-saving strategy research.

[0003] The load of subway stations is closely related to factors such as passenger flow and weather, and changes dynamically with the changes of these factors. Taking a certain city subway as an example, the current temperature control of the station air conditioning is only achieved by adjusting the outlet water temperature of the chiller based on the experience of the on-site staff, which makes the reaction time to reach the target temperature longer, and the temperature may be too high or too low. In addition, this adjustment method does not consider the problem of energy consumption optimization. Therefore, a subway station air conditioning system and control method based on return air temperature are designed, which can not only ensure the appropriate temperature of the subway station under variable load conditions, but also effectively reduce the energy consumption of the subway station air conditioning system. Summary of the invention

[0004] The present invention aims at the deficiencies in the prior art and provides a subway station air conditioning system and control method based on return air temperature which has a simple structure, reasonable design, and adopts a Feng Shui joint adjustment method to quickly and accurately adjust the station temperature, improve the station air conditioning comfort, and avoid the problem of high overall energy consumption level of subway stations caused by experience-based adjustment.

[0005] In order to achieve the above-mentioned object, the present invention provides a subway station air conditioning system based on return air temperature, including an air system, a chilled water system and a cooling water system; The air system includes a subway station, a return air fan, a surface cooler and a supply air fan which are sequentially connected to form a closed loop, forming an air circulation system that establishes a connection between the station's real-time load and the air side of the surface cooler. The return air fan draws air from each room of the system and enters the surface cooler through the return air duct. After the hot air is cooled by chilled water in the surface cooler, it is sent to each room of the system by the supply air fan. The chilled water system is a circulating water system for a chiller, including a surface cooler, a chilled water pump and a chiller connected in sequence to form a closed loop, forming a chilled water circulation system in which the water side of the surface cooler is connected to the evaporator side of the chiller. The chilled water is cooled after heat exchange with the refrigerant in the evaporator, and then the chilled water is transported to the surface cooler by the chilled water pump for cooling the air, and then transported back to the evaporator for the next cycle after heat exchange; The cooling water system is a cooling tower circulating water system, including a chiller, a cooling tower and a cooling water pump connected in sequence, forming a cooling water circulation system in which the condenser side of the chiller is connected to the cooling tower, and the condenser side of the chiller is heat exchanged with the outdoor cooling tower to become low-temperature water, and the low-temperature cooling water is transported back to the condenser by the cooling water pump for the next cycle; The return air fan, the supply air fan and the chiller are connected to the main controller; the main controller is embedded with a PID control algorithm and is adjusted by a stepper motor; A return air pipeline is connected between the return air fan, the subway station and the surface cooler, and the return air pipeline is provided with a return air temperature sensor; An air supply pipeline is connected between the air supply fan, the subway station and the surface cooler, and the air supply pipeline is provided with a flow sensor; A chilled water outlet pipe is provided between the chiller and the surface cooler, and the chilled water outlet pipe is provided with a chiller outlet water temperature sensor; The return air temperature sensor, flow sensor, and chiller outlet water temperature sensor signals are connected to the main controller.

[0006] Furthermore, the blower is provided with a frequency converter, the frequency converter signal is connected to the main controller, the flow sensor feeds back data to the main controller, and the main controller issues instructions to adjust the frequency converter.

[0007] Furthermore, the return air temperature sensor is arranged on the main pipe of the return air pipeline, and the return air temperature is monitored in real time as the real-time temperature of the station, and is fed back to the main controller.

[0008] Furthermore, the chiller is provided with an outlet water temperature regulator, the outlet water temperature regulator signal is connected to the main controller, the outlet water temperature sensor of the chiller feeds back data to the main controller, and the main controller issues instructions to adjust the outlet water temperature regulator of the chiller.

[0009] A method for controlling a subway station air conditioning system based on return air temperature comprises the following steps: Step 1: Set the initial state: Set the return air target temperature to T , the real-time temperature of the station is T a , temperature deviation Δ T Real-time temperature of the station T a and return air target temperature T The difference between the chiller outlet water temperature and T s ; Set the return air target temperature to the target value of T; Step 2: Start the equipment: Turn on the chilled water pump and cooling water pump to control the chilled water and cooling water flows respectively, and turn the speed of the supply and return fans to the maximum to quickly cool down the station; Step 3: Calculate the real-time load of the station; Step 4: Determine whether the station Feng Shui joint adjustment is activated and the degree of activation based on the station's real-time load, specifically: Taking the return air temperature as the target value, the PID regulation is used to control the air volume of the blower and the outlet water temperature of the chiller; When the real-time load of the station increases, the real-time temperature of the station T a Increase, Δ T If the value is positive, the air volume of the fan will be increased according to the real-time load of the station, and the outlet water temperature of the chiller will be adjusted. T s Until the return air target temperature is met; When the real-time load of the station decreases, the real-time temperature of the station T a Reduce, Δ T If the value is negative, the air volume of the fan is reduced according to the load of the station, and the outlet water temperature of the chiller is adjusted. T s Until the return air target temperature is met.

[0010] Furthermore, the step 3 comprises the following steps: Step 3.1: Fit the relationship between the real-time load of the station and the cooling capacity output by the air-conditioning system to the station: According to the law of conservation of energy, the change in heat stored in the station is the difference between the energy flowing in and the energy flowing out, which can be obtained as ; In the formula, Q i The real-time load of the station changes at any time with factors such as weather temperature, humidity, and passenger flow, kW; Q0 is the cooling capacity output by the air-conditioning system to the station, kW; C n is the heat capacity of the station air, kJ / (kg·℃); m is the air mass, kg; t is time, s; Refrigeration capacity of top-mounted surface cooler Q 0 can be represented as: ; In the formula, K is the heat transfer coefficient, W / (m 2 ℃); A is the effective heat exchange area of ​​the surface cooler, m 2 ; T ch is the return water temperature of the chiller, °C, T s is the outlet water temperature of the chiller, °C; Step 3.2: Fit the relationship between the cooling capacity output by the air conditioning system to the station and the cooling water return temperature: After the chilled water absorbs the heat from the air in the surface cooler, it enters the chiller to release the heat. That is, the cooling capacity of the chiller is equivalent to that of the surface cooler, which can be expressed by the following formula: ; ; In the formula, Q ch is the cooling capacity of the chiller, kW; P ch is the chiller power, kW; COP is the energy efficiency ratio; T cwi is the cooling water return temperature, °C; a 0, a 1, a 2, a 3. a 4. a 5 is the fitting coefficient; Step 3.3: Fit the relationship between cooling water return temperature and cooling water pump flow, wet bulb temperature and cooling tower fan frequency: The inlet water temperature of the cooling tower is the cooling water return temperature, which is expressed by the following formula: ; In the formula, T w is the wet bulb temperature, °C; q cw is the cooling water pump flow, m 3 / s; f fan is the cooling tower fan frequency, Hz;b 0, b 1, b 2, b 3 is the fitting coefficient; Step 3.4: Calculate the real-time load of the station using the above formula.

[0011] Furthermore, the PID regulation control in step 4 adopts an incremental PID control algorithm, and the control output increment of the incremental PID control algorithm is: ; Among them, e(t) is the deviation between the target value and the current value, K p , K i , K d are the proportional, integral and differential coefficients respectively, and ΔU(t) represents the control output increment at the current moment.

[0012] The beneficial effects of this solution can be known from the description of the above solution. Compared with the prior art, it has the following beneficial effects: (1) The Feng Shui joint adjustment method can quickly and accurately adjust the station temperature and improve the station air conditioning comfort; (2) Real-time adjustment is carried out according to the dynamic changes of load, avoiding the problem of high overall energy consumption level of subway stations caused by experience-based adjustment. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a schematic diagram of the structure of the subway station air conditioning system based on return air temperature of the present invention; Figure 2 It is a flow chart of the control method of the subway station air conditioning system based on the return air temperature of the present invention; Figure 3 The return air temperature diagram when the outlet water temperature of the chiller of the present invention is closed-loop regulated according to the return air temperature; Figure 4 This is a comparison diagram of energy consumption before and after the outlet water temperature of the chiller according to the closed-loop control of the return air temperature; Figure 5 It is a return air temperature diagram when the blower of the present invention is regulated according to the return air temperature closed loop; Figure 6 This is a comparison diagram of energy consumption of the blower of the present invention before and after closed-loop control of return air temperature; Figure 7 This is a diagram showing the combination of the blower control signal and the chiller outlet water temperature at different load rates of the present invention.

[0014] In the figure: 1. Subway station; 2. Return air fan; 3. Surface cooler; 4. Supply air fan; 5. Chiller; 5-1. Evaporator side; 5-2. Condenser side; 6. Chilled water pump; 7. Cooling tower; 8. Cooling water pump; 9. Main controller; 10. Return air temperature sensor; 11. Chiller outlet water temperature sensor; 12. Flow sensor. DETAILED DESCRIPTION

[0015] In order to clearly illustrate the technical features of this solution, this solution is described below through a specific implementation method.

[0016] like Figure 1 As shown, this embodiment is a subway station air conditioning system based on return air temperature, including three subsystems: an air system, a chilled water system and a cooling water system; The air system includes a subway station 1, a return air fan 2, a surface cooler 3 and a supply air fan 4 which are sequentially connected to form a closed loop, forming an air circulation system that establishes a connection between the station's real-time load and the air side of the surface cooler 3. The return air fan 2 draws air from each room of the system and enters the surface cooler 3 through the return air pipeline. After the hot air is cooled by chilled water in the surface cooler 3, it is sent to each room of the system by the supply air fan 4. The chilled water system is a circulating water system for a chiller, including a surface cooler 3, a chilled water pump 6 and a chiller connected in sequence to form a closed loop, forming a chilled water circulation system in which the water side of the surface cooler 3 is connected to the evaporator side 5-1 of the chiller. The chilled water is cooled after heat exchange with the refrigerant in the evaporator, and then the chilled water is transported to the surface cooler 3 by the chilled water pump 6 for cooling the air, and then transported back to the evaporator for the next cycle after heat exchange; The cooling water system is a cooling tower circulating water system, including a chiller, a cooling tower 7 and a cooling water pump 8 connected in sequence, forming a cooling water circulation system in which the condenser side 5-2 of the chiller is connected to the cooling tower 7. The condenser side 5-2 of the chiller is converted into low-temperature water after heat exchange with the outdoor cooling tower 7, and the low-temperature cooling water is transported back to the condenser by the cooling water pump 8 for the next circulation.

[0017] The return air fan 2, the supply air fan 4 and the chiller are connected to the main controller 9; the main controller 9 is embedded with a PID control algorithm and is adjusted by a stepper motor; A return air pipeline is connected between the return air fan 2, the subway station 1 and the surface cooler 3, and a return air temperature sensor 10 is provided on the return air pipeline; An air supply pipeline is connected between the air supply fan 4, the subway station 1 and the surface cooler 3, and a flow sensor 12 is provided on the air supply pipeline; A chilled water outlet pipe is provided between the chiller and the surface cooler 3, and a chiller outlet water temperature sensor 11 is provided on the chiller outlet pipe; The signals of the return air temperature sensor 10 , the flow sensor 12 , and the chiller outlet water temperature sensor 11 are connected to the main controller 9 .

[0018] The blower 4 is provided with a frequency converter, the frequency converter signal is connected to the main controller 9, the flow sensor 12 feeds back data to the main controller 9, and the main controller 9 issues instructions to adjust the frequency converter.

[0019] The return air temperature sensor 10 is arranged on the main pipe of the return air pipeline, and monitors the return air temperature in real time as the real-time temperature of the station, and feeds back to the main controller 9.

[0020] The chiller is provided with an outlet water temperature regulator, the outlet water temperature regulator signal is connected to the main controller 9, the chiller outlet water temperature sensor 11 feeds data back to the main controller 9, and the main controller 9 issues a command to adjust the chiller outlet water temperature regulator.

[0021] like Figure 2 As shown, a method for controlling a subway station air conditioning system based on return air temperature comprises the following steps: Step 1: Set the initial state: Set the return air target temperature to T ,℃; the real-time temperature of the station is T a ,℃; Temperature deviation Δ T Real-time temperature of the station T a and return air target temperature T The difference, ℃; the chiller outlet water temperature is T s ,℃; Set the return air target temperature to the target value of T; Step 2: Start the equipment: Turn on the chilled water pump and cooling water pump to control the chilled water and cooling water flows respectively, and turn the speed of the supply and return fans to the maximum to quickly cool down the station; Step 3: Calculate the real-time load of the station, specifically: Step 3.1: Fit the relationship between the real-time load of the station and the cooling capacity output by the air-conditioning system to the station: According to the law of conservation of energy, the change in heat stored in the station is the difference between the energy flowing in and the energy flowing out, which can be obtained as ; In the formula, Q i The real-time load of the station changes at any time with factors such as weather temperature, humidity, and passenger flow, kW; Q 0 is the cooling capacity output by the air-conditioning system to the station, kW; C n is the heat capacity of the station air, kJ / (kg·℃); mis the air mass, kg; t is time, s; Refrigeration capacity of top-mounted surface cooler Q 0 can be represented as: ; In the formula, K is the heat transfer coefficient, W / (m 2 ℃); A is the effective heat exchange area of ​​the surface cooler, m 2 ; T ch is the return water temperature of the chiller, °C, T s is the outlet water temperature of the chiller, °C; Step 3.2: Fit the relationship between the cooling capacity output by the air conditioning system to the station and the cooling water return temperature: After the chilled water absorbs the heat from the air in the surface cooler, it enters the chiller to release the heat. That is, the cooling capacity of the chiller is equivalent to that of the surface cooler, which can be expressed by the following formula: ; ; In the formula, Q ch is the cooling capacity of the chiller, kW; P ch is the chiller power, kW; COP is the energy efficiency ratio; T cwi is the cooling water return temperature, °C; a 0, a 1, a 2, a 3. a 4. a 5 is the fitting coefficient; Step 3.3: Fit the relationship between cooling water return temperature and cooling water pump flow, wet bulb temperature and cooling tower fan frequency: The inlet water temperature of the cooling tower is the cooling water return temperature, which is expressed by the following formula: ; In the formula, T w is the wet bulb temperature, °C; q cw is the cooling water pump flow, m 3 / s; f fan is the cooling tower fan frequency, Hz; b 0, b 1, b 2, b 3 is the fitting coefficient; Step 3.4: The real-time load of the station can be calculated by the above formula; Step 4: Determine whether the station Feng Shui joint adjustment is activated and the degree of activation based on the station's real-time load, specifically: Taking the return air target temperature as the target value, PID regulation is used to control the air volume of the blower and the outlet water temperature of the chiller; the PID regulation control adopts the incremental PID control algorithm, and the control output increment of the incremental PID control algorithm is: ; Among them, e(t) is the deviation between the target value and the current value, K p , K i , K d are the proportional, integral and differential coefficients respectively, and ΔU(t) represents the control output increment at the current moment.

[0022] This PID control algorithm is embedded in the main controller and regulated by the stepper motor.

[0023] When the real-time load of the station increases, the real-time temperature of the station T a Increase, Δ T If the value is positive, the air volume of the fan will be increased according to the real-time load of the station, and the outlet water temperature of the chiller will be adjusted. T s Until the return air target temperature is met; When the real-time load of the station decreases, the real-time temperature of the station T a Reduce, Δ T If the value is negative, the air volume of the fan is reduced according to the load of the station, and the outlet water temperature of the chiller is adjusted. T s Until the return air target temperature is met.

[0024] Data collected from a subway station was selected for 300 hours for algorithm analysis. The main controller set the return air target temperature to 26°C and read the real-time temperature of the station through the return air temperature sensor. Figure 3 and Figure 4 As shown in the figure, according to feedback from field surveys, subway stations currently often fix the chiller outlet water temperature for a period of time. This practice causes large fluctuations in return air temperature, and the chiller is in a low temperature state for a long time, increasing energy consumption. When the chiller outlet water temperature is adjusted in real time according to the return air temperature, the stability of the return air temperature is improved, and since the chiller provides cooling on demand, it is conducive to energy-saving control.

[0025] like Figure 5 and Figure 6As shown in the figure, the effects of fixed frequency operation and variable frequency operation of the air supply fan are compared. When fixed frequency operation is adopted, in order to ensure the return air temperature control requirements, when the cooling load is low, it will cause waste of air volume; when variable frequency control is adopted, the air volume is controlled according to actual needs. Under the premise of meeting the environmental control requirements, the energy consumption can be reduced by 4000kW·h in 300 hours.

[0026] Therefore, when the station load is stable, the station real-time temperature is maintained at 26°C. When the station load increases, the station real-time temperature increases (higher than 26°C), and the temperature deviation ΔT is positive. According to the load size, the fan control signal (the coefficient of the maximum air volume of the fan) is sent to increase the air volume of the fan to the corresponding gear, and the chiller outlet water temperature is adjusted as a compensation control until the return air target temperature is met; When the station load decreases, the station real-time temperature decreases (below 26°C), the temperature deviation is negative, the air volume of the blower is reduced to the corresponding gear according to the load size, and the chiller outlet water temperature is adjusted until the return air target temperature is met. Figure 7 As shown in the figure, when the load rate (ratio of actual load to design load) exceeds 60%, the fan gear is adjusted to the maximum, and the outlet water temperature of the chiller is reduced to meet the return air temperature requirement; when the load rate is less than 20%, the fan gear is adjusted to the minimum; when the load rate is between 20% and 60%, the fan gear increases accordingly with the increase of load. Since the fan is close to the user end, timely adjusting the fan air volume according to load changes has the characteristic of fast response. Adjusting the outlet water temperature of the chiller for compensation control helps to achieve precise temperature control of the site.

[0027] Technical features not described in the present invention can be achieved through or by adopting existing technologies and will not be described in detail herein. Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by ordinary technicians in this technical field within the essential scope of the present invention should also fall within the scope of protection of the present invention.

Claims

1. A subway station air conditioning system based on return air temperature, characterized in that: Including wind system, chilled water system and cooling water system; The air system includes a subway station, a return air fan, a surface cooler and a supply air fan which are sequentially connected to form a closed loop, forming an air circulation system that connects the station's real-time load with the air side of the surface cooler; The chilled water system is a chiller circulating water system, comprising a surface cooler, a chilled water pump and a chiller connected in sequence to form a closed loop, constituting a chilled water circulation system in which the water side of the surface cooler is connected to the evaporator side of the chiller; The cooling water system is a cooling tower circulating water system, comprising a chiller, a cooling tower and a cooling water pump connected in sequence, forming a cooling water circulating system in which the condenser side of the chiller is connected to the cooling tower; The return air fan, the supply air fan and the chiller are connected to the main controller; the main controller is embedded with a PID control algorithm and is adjusted by a stepper motor; A return air pipeline is connected between the return air fan, the subway station and the surface cooler, and the return air pipeline is provided with a return air temperature sensor; An air supply pipeline is connected between the air supply fan, the subway station and the surface cooler, and the air supply pipeline is provided with a flow sensor; A chilled water outlet pipe is provided between the chiller and the surface cooler, and the chilled water outlet pipe is provided with a chiller outlet water temperature sensor; The return air temperature sensor, flow sensor, and chiller outlet water temperature sensor signals are connected to the main controller.

2. The subway station air conditioning system based on return air temperature according to claim 1, characterized in that: The blower is provided with a frequency converter, and the frequency converter signal is connected to the main controller.

3. The subway station air conditioning system based on return air temperature according to claim 1, characterized in that: The return air temperature sensor is arranged on the main pipe of the return air pipeline.

4. The subway station air conditioning system based on return air temperature according to claim 1, characterized in that: The chiller is provided with an outlet water temperature regulator, and the outlet water temperature regulator signal is connected to the main controller.

5. A method for controlling a subway station air conditioning system based on return air temperature, characterized in that: The method for controlling a subway station air conditioning system based on return air temperature as claimed in any one of claims 1 to 4 comprises the following steps: Step 1: Set the initial state: Set the return air target temperature to T， The real-time temperature of the station is T a , temperature deviation Δ T Real-time temperature of the station T a and return air target temperature T The difference between the chiller outlet water temperature and T s ; Set the target value of the return air target temperature; Step 2: Start the equipment: Turn on the chilled water pump and cooling water pump to control the chilled water and cooling water flows respectively, and turn the speed of the supply and return fans to the maximum to quickly cool down the station; Step 3: Calculate the real-time load of the station; Step 4: Determine whether the station Feng Shui joint adjustment is activated and the degree of activation based on the station's real-time load, specifically: Taking the return air temperature as the target value, the PID regulation is used to control the air volume of the blower and the outlet water temperature of the chiller; When the real-time load of the station increases, the real-time temperature of the station T a Increase, Δ T If the value is positive, the air volume of the fan will be increased according to the real-time load of the station, and the outlet water temperature of the chiller will be adjusted. T s Until the return air target temperature is met; When the real-time load of the station decreases, the real-time temperature of the station T a Reduce, Δ T If the value is negative, the air volume of the fan is reduced according to the load of the station, and the outlet water temperature of the chiller is adjusted. T s Until the return air target temperature is met.

6. The subway station air conditioning system control method based on return air temperature according to claim 5, characterized in that: The step 3 comprises the following steps: Step 3.1: Fit the relationship between the real-time load of the station and the cooling capacity output by the air-conditioning system to the station: According to the law of conservation of energy, the change in heat stored in the station is the difference between the energy flowing in and the energy flowing out, which can be obtained as ； In the formula, Q i The real-time load of the station changes at any time with factors such as weather temperature, humidity, and passenger flow, kW; Q 0 is the cooling capacity output by the air-conditioning system to the station, kW; C n is the heat capacity of the station air, kJ / (kg·℃); m is the air mass, kg; t is time, s; Refrigeration capacity of top-mounted surface cooler Q 0 can be represented as: ； In the formula, K is the heat transfer coefficient, W / (m 2 ℃); A is the effective heat exchange area of ​​the surface cooler, m 2 ; T ch is the return water temperature of the chiller, °C, T s is the outlet water temperature of the chiller, °C; Step 3.2: Fit the relationship between the cooling capacity output by the air conditioning system to the station and the cooling water return temperature: After the chilled water absorbs the heat from the air in the surface cooler, it enters the chiller to release the heat. That is, the cooling capacity of the chiller is equivalent to that of the surface cooler, which can be expressed by the following formula: ； ； In the formula, Q ch is the cooling capacity of the chiller, kW; P ch is the chiller power, kW; COP is the energy efficiency ratio; T cwi is the cooling water return temperature, °C; a 0, a 1, a 2, a 3. a 4. a 5 is the fitting coefficient; Step 3.3: Fit the relationship between cooling water return temperature and cooling water pump flow, wet bulb temperature and cooling tower fan frequency: The inlet water temperature of the cooling tower is the cooling water return temperature, which is expressed by the following formula: ； In the formula, T w is the wet bulb temperature, °C; q cw is the cooling water pump flow, m 3 / s; f fan is the cooling tower fan frequency, Hz; b 0, b 1, b 2, b 3 is the fitting coefficient; Step 3.4: Calculate the real-time load of the station using the above formula.

7. The subway station air conditioning system control method based on return air temperature according to claim 5, characterized in that: The PID regulation control in step 4 adopts an incremental PID control algorithm, and the control output increment of the incremental PID control algorithm is: ； Among them, e(t) is the deviation between the target value and the current value, K p , K i , K d are the proportional, integral and differential coefficients respectively, and ΔU(t) represents the control output increment at the current moment.

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