Anti-freezing control method and anti-freezing control device for air conditioning system

Abstract

The application discloses a kind of freeze protection control method and freeze protection control device of air conditioning system.The freeze protection control method includes: obtaining the ambient temperature of the indoor environment where each indoor fan coil is located;According to the relationship between ambient temperature and preset freeze protection temperature, determine whether each indoor fan coil triggers freeze alarm signal;Detect freeze alarm signal, and control the opening and closing state of the water valve of each indoor fan coil and the opening and closing state of the circulating water pump of air conditioning system according to freeze alarm signal;Wherein, when any one indoor fan coil triggers freeze alarm signal, control circulating water pump to open;When all indoor fan coils do not trigger freeze alarm signal, control circulating water pump to close.The freeze protection control method of the application can at least solve the problem that the fan coil is frozen and damaged due to low indoor ambient temperature in the prior art.

Description

Technical Field

[0001] This application relates to the field of air conditioning system technology, and more specifically, to an antifreeze control method and antifreeze control device for an air conditioning system. Background Technology

[0002] In related technologies, fan coil units use water as a refrigerant to circulate heat within the heat exchanger pipes, offering stable operation and good indoor comfort. However, in winter, if water remains inside the heat exchange pipes and the indoor ambient temperature is below the freezing point of water, the water will freeze. The increased volume of the frozen water creates continuous expansion stress within the heat exchange pipes. As the freezing area expands, the expansion stress increases, potentially causing the fan coil unit's heat exchange pipes to rupture, leading to leaks and shortening the fan coil unit's service life. Summary of the Invention

[0003] The main objective of this application is to provide an antifreeze control method and device for an air conditioning system, so as to solve the problem of fan coil unit freezing damage caused by low indoor ambient temperature in the prior art.

[0004] According to one aspect of this application, a method for anti-freezing control of an air conditioning system is provided, the air conditioning system including an outdoor unit and multiple indoor fan coil units, the method for anti-freezing control of the air conditioning system including: Obtain the ambient temperature of the indoor environment where each of the indoor fan coil units is located; Determine whether each indoor fan coil unit triggers an antifreeze alarm signal based on the relationship between the ambient temperature and the preset antifreeze temperature. The antifreeze alarm signal is detected, and the opening and closing status of the water valves of each indoor fan coil unit and the opening and closing status of the circulating water pump of the air conditioning system are controlled according to the antifreeze alarm signal. Specifically, when any one of the indoor fan coil units triggers the antifreeze alarm signal, the circulating water pump is controlled to start; when none of the indoor fan coil units trigger the antifreeze alarm signal, the circulating water pump is controlled to shut down.

[0005] Furthermore, obtaining the ambient temperature of the indoor environment where each of the indoor fan coil units is located includes: when the indoor fan coil unit is powered on and in a power-on or standby state, obtaining the ambient temperature of the indoor environment where the indoor fan coil unit is located through a temperature sensor.

[0006] Further, the preset antifreeze temperature includes a first preset antifreeze temperature and a second preset antifreeze temperature, wherein the first preset antifreeze temperature is lower than the second preset antifreeze temperature; the step of determining whether each indoor fan coil unit triggers an antifreeze alarm signal based on the relationship between the ambient temperature and the preset antifreeze temperature includes: When the ambient temperature is lower than the first preset antifreeze temperature, the indoor fan coil unit is controlled to trigger the antifreeze alarm signal. When the ambient temperature is greater than the second preset antifreeze temperature, the indoor fan coil unit is controlled not to trigger the antifreeze alarm signal; When the ambient temperature is between the first preset antifreeze temperature and the second preset antifreeze temperature, the indoor fan coil unit maintains its current trigger state; wherein, if the antifreeze alarm signal has already been triggered, the triggering of the antifreeze alarm signal continues; if the antifreeze alarm signal has not been triggered, the antifreeze alarm signal is not triggered.

[0007] Furthermore, the step of determining whether each indoor fan coil unit triggers an antifreeze alarm signal based on the relationship between the ambient temperature and the preset antifreeze temperature also includes: when the ambient temperature is greater than the first preset antifreeze temperature, and the rate of temperature drop of the ambient temperature within a preset time is greater than a preset rate, controlling the indoor fan coil unit to trigger the antifreeze alarm signal in advance; and / or, The step of obtaining the ambient temperature of the indoor environment where each of the indoor fan coil units is located includes: obtaining the ambient temperature through a temperature sensor; the step of controlling the indoor fan coil unit to trigger the anti-freeze alarm signal when the ambient temperature is lower than the first preset anti-freeze temperature includes: when the ambient temperature is lower than the first preset anti-freeze temperature and multiple indoor fan coil units are in the same indoor environment, comparing the ambient temperatures obtained by each of the temperature sensors, and controlling the indoor fan coil unit to trigger the anti-freeze alarm signal according to the comparison result; wherein, when the difference between the ambient temperatures obtained by multiple temperature sensors is less than or equal to a predetermined value, the indoor fan coil unit is controlled to trigger the anti-freeze alarm signal; when the difference between the ambient temperatures obtained by multiple temperature sensors is greater than the predetermined value, the indoor fan coil unit is controlled to trigger a sensor abnormality signal.

[0008] Furthermore, the antifreeze alarm signal includes a first-level alarm signal, a second-level alarm signal, and a third-level alarm signal, with the alarm levels of the first-level alarm signal, the second-level alarm signal, and the third-level alarm signal increasing progressively; the preset antifreeze temperature also includes a third preset antifreeze temperature, which is lower than the first preset antifreeze temperature; Specifically, when the ambient temperature is between the first preset antifreeze temperature and the second preset antifreeze temperature, and the indoor fan coil unit has already triggered the antifreeze alarm signal, the indoor fan coil unit is controlled to trigger the first-level alarm signal. When the ambient temperature is greater than the third preset antifreeze temperature and less than the first preset antifreeze temperature, the indoor fan coil unit is controlled to trigger the secondary alarm signal. When the ambient temperature is lower than the third preset antifreeze temperature, the indoor fan coil unit is controlled to trigger the third-level alarm signal.

[0009] Furthermore, when the indoor fan coil unit triggers the first-level alarm signal, a first anti-freeze protection operation is executed; when the indoor fan coil unit triggers the second-level alarm signal, a second anti-freeze protection operation is executed; when the indoor fan coil unit triggers the third-level alarm signal, a third anti-freeze protection operation is executed; wherein the anti-freeze intensity of the first, second, and third anti-freeze protection operations increases progressively; and / or, When the ambient temperature rises from below the third preset antifreeze temperature to between the first and third preset antifreeze temperatures, the alarm level of the indoor fan coil unit is switched from the third-level alarm signal to the second-level alarm signal, and the circulating water pump remains on. When the ambient temperature rises from below the first preset antifreeze temperature to between the first and second preset antifreeze temperatures, the alarm level of the indoor fan coil unit is switched from the second-level alarm signal to the first-level alarm signal, and the circulating water pump remains on. When the ambient temperature is above the second preset antifreeze temperature, the antifreeze alarm signal for the indoor fan coil unit is deactivated. When all indoor fan coil units have deactivated their antifreeze alarm signals, the circulating water pump is shut down.

[0010] Furthermore, controlling the opening and closing status of the water valves of each indoor fan coil unit according to the antifreeze alarm signal includes: When the indoor fan coil unit triggers the antifreeze alarm signal, the water valve of the indoor fan coil unit is controlled to open. When the indoor fan coil unit does not trigger the antifreeze alarm signal, the opening and closing status of the water valve is controlled according to the current operating status of the indoor fan coil unit.

[0011] Furthermore, controlling the opening and closing state of the water valve according to the current operating state of the indoor fan coil unit includes: controlling the water valve to open when the indoor fan coil unit is currently in operation; and controlling the water valve to close when the indoor fan coil unit is currently in a stopped or standby state.

[0012] Furthermore, before executing the control to shut down the circulating water pump, the antifreeze control method of the air conditioning system further includes: When none of the indoor fan coil units trigger the antifreeze alarm signal, the circulating water pump is kept on for a first preset time before being shut down.

[0013] On the other hand, this application also provides an anti-freeze control device for an air conditioning system, which is used to execute the above-described anti-freeze control method for an air conditioning system. The anti-freeze control device for the air conditioning system includes: The acquisition module is used to acquire the ambient temperature of the indoor environment where each of the indoor fan coil units is located; The detection module is used to detect the antifreeze alarm signal; The control module, including the acquisition module and the detection module, is electrically connected to the control module. The control module determines whether each indoor fan coil unit triggers an antifreeze alarm signal based on the relationship between the ambient temperature and the preset antifreeze temperature, and controls the opening and closing states of the water valves of each indoor fan coil unit and the opening and closing states of the circulating water pump of the air conditioning system based on the antifreeze alarm signal. Specifically, when any indoor fan coil unit triggers the antifreeze alarm signal, the circulating water pump is controlled to start; when none of the indoor fan coil units trigger the antifreeze alarm signal, the circulating water pump is controlled to shut down.

[0014] The antifreeze control method of this application acquires the ambient temperature and determines the triggering state of the antifreeze alarm signal accordingly. This directly transforms the low-temperature risk on the indoor side into a recognizable control command, effectively avoiding control lag or misjudgment caused by the inability to accurately perceive the indoor low-temperature operating conditions. When the indoor ambient temperature drops to the threshold that may cause the coil to freeze, the indoor fan coil unit itself generates an alarm signal. After this signal is detected, the system can control the water valve to remain open and maintain the continuous operation of the circulating water pump, keeping the water flow in the system in a dynamic circulation state. This prevents the water in the coil from cooling and freezing due to stagnation, effectively avoiding freezing damage to the indoor fan coil unit caused by low indoor ambient temperature, and improving the reliability of the air conditioning system operating in low-temperature environments. Attached Figure Description

[0015] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, are illustrative and descriptive, serving to explain this application and do not constitute an undue limitation thereof. In the drawings: Figure 1 This is a flowchart of the antifreeze control method for an air conditioning system disclosed in an embodiment of this application; Figure 2 This is a flowchart of the control of the opening and closing status of the circulating water pump of the air conditioning system disclosed in an embodiment of this application; Figure 3 This is a connection diagram of the control device disclosed in the embodiments of this application.

[0016] The above figures include the following reference numerals: 10. Acquisition module; 20. Detection module; 30. Control module. Detailed Implementation

[0017] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0018] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0019] Unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps described in these embodiments do not limit the scope of this application. It should also be understood that, for ease of description, the dimensions of the various parts shown in the drawings are not drawn to actual scale. Techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of the specification. In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples besides the exemplary embodiments may have different values. It should be noted that similar reference numerals and letters in the following drawings denote similar items; therefore, once an item is defined in one drawing, it need not be further discussed in subsequent drawings.

[0020] As described in the background section, in related technologies, fan coil units use water as a refrigerant to circulate heat within the heat exchanger pipes, offering stable operation and good indoor comfort. However, in winter, if water remains inside the heat exchange pipes and the indoor ambient temperature is below the freezing point of water, the water inside will freeze. The increased volume of the frozen water creates continuous expansion stress within the heat exchange pipes. As the freezing area expands, the expansion stress increases, easily causing the fan coil unit's heat exchange pipes to rupture, leading to leaks and shortening the fan coil unit's service life. Therefore, this application provides a new anti-freeze control method, which can at least solve the problem of fan coil unit freezing damage caused by low indoor ambient temperatures in existing technologies. The anti-freeze control method of this application will be described in detail below with reference to the accompanying drawings.

[0021] like Figures 1 to 2 As shown in the figure, this application provides an anti-freeze control method for an air conditioning system. The air conditioning system includes an outdoor unit and multiple indoor fan coil units. The anti-freeze control method for the air conditioning system includes: (1) Obtain the ambient temperature of the indoor environment where each indoor fan coil unit is located.

[0022] Specifically, obtaining ambient temperature is fundamental to antifreeze control. In an air conditioning system, each indoor fan coil unit is equipped with a temperature sensor to collect the temperature of its surrounding space in real time. This temperature sensor can be integrated into the indoor fan or independent of it; this embodiment does not limit this. Due to differences in building insulation performance, orientation, and ventilation conditions between different rooms, the freezing risk faced by each indoor fan coil unit exhibits significant spatiotemporal unevenness. Therefore, this step emphasizes the independent acquisition of the ambient temperature of each indoor fan coil unit, rather than relying on a single / centralized measuring point. This allows for accurate detection of localized cold spots, avoiding missed reports due to insufficient representativeness of single-point temperature measurements. It is understood that the method of obtaining ambient temperature is not limited to directly reading sensor values; it can also include temperature values ​​obtained after filtering, calibrating, or compensating the raw signal, as long as the temperature value corresponds to and characterizes the ambient temperature of the space where the indoor fan coil unit is located.

[0023] (2) Determine whether each indoor fan coil unit triggers the antifreeze alarm signal based on the relationship between the ambient temperature and the preset antifreeze temperature.

[0024] Specifically, the antifreeze alarm signal is an intermediate state variable connecting temperature sensing and action execution. In this embodiment, the antifreeze alarm signal serves as a logical state representing the existence of freezing risk, and its specific triggering condition is determined by the comparison between the ambient temperature and the preset antifreeze temperature. The specific value, form (such as a fixed value, dynamic curve, or multi-level threshold) and judgment logic (such as instantaneous comparison, delayed confirmation, or trend prediction) of the preset antifreeze temperature can be configured according to actual system requirements, and this embodiment does not limit this. When the ambient temperature meets the preset low-temperature risk condition, the corresponding indoor fan coil unit generates or maintains an antifreeze alarm signal. By converting the complex temperature judgment logic into a unified alarm signal, subsequent control logic does not need to focus on specific temperature details, improving the scalability and compatibility of the system architecture.

[0025] (3) Detect the antifreeze alarm signal and control the opening and closing status of the water valves of each indoor fan coil unit and the opening and closing status of the circulating water pump of the air conditioning system according to the antifreeze alarm signal; wherein, when any indoor fan coil unit triggers the antifreeze alarm signal, the circulating water pump is controlled to start; when none of the indoor fan coil units trigger the antifreeze alarm signal, the circulating water pump is controlled to shut down. It should be noted that in this embodiment, the antifreeze alarm signal is detected through the control unit of the outdoor unit.

[0026] Specifically, the outdoor unit, acting as the central coordinator of the entire air conditioning system, is responsible for collecting anti-freeze alarm signals from all indoor fan coil units and coordinating the execution of anti-freeze actions. The opening and closing of water valves and the starting and stopping of the circulating water pump directly affect the flow state of the entire water circuit. If each indoor fan coil unit independently controls its water pump, communication delays or logical conflicts can easily lead to water flow disturbances or even equipment damage. Therefore, in this embodiment, when any indoor fan coil unit triggers an anti-freeze alarm signal, the circulating water pump is controlled to start, and when none of the indoor fan coil units trigger an anti-freeze alarm signal, the circulating water pump is controlled to shut down. With this setup, as long as there is any potential freezing risk point in the air conditioning system, the water circuit must be kept unobstructed to deliver heat, which is the minimum necessary technical condition to prevent the coils from freezing and cracking. At the same time, the control of the water valves is also closely related to the anti-freeze alarm signals. When an indoor fan coil unit triggers an alarm, its corresponding water valve is forcibly opened to open the hot water path; in the absence of an alarm, the water valve can be adjusted according to the normal operating logic. Through the centralized management of the outdoor unit, the timeliness and reliability of anti-freeze protection are ensured.

[0027] Based on the above, it can be seen that the antifreeze control method of this application obtains the ambient temperature and determines the triggering state of the antifreeze alarm signal accordingly. This directly transforms the low-temperature risk on the indoor side into a identifiable control command, effectively avoiding control lag or misjudgment caused by the inability to accurately perceive the indoor low-temperature condition. When the indoor ambient temperature drops to a threshold that may cause the circulating water in the coil to freeze, the indoor fan coil unit itself generates an alarm signal. After this signal is detected, the system can control the water valve to remain open and maintain the continuous operation of the circulating water pump, keeping the water flow in the system dynamically circulating. This prevents the water in the coil from cooling and freezing due to stagnation, effectively avoiding damage to the indoor fan coil unit due to low indoor ambient temperature and improving the reliability of the air conditioning system operating in low-temperature environments.

[0028] In some embodiments, obtaining the ambient temperature of the indoor environment where each indoor fan coil unit is located includes: when the indoor fan coil unit is powered on and in a power-on or standby state, obtaining the ambient temperature of the indoor environment where the indoor fan coil unit is located through a temperature sensor. It is understood that the temperature sensor in this embodiment can be integrated into the indoor fan or can be independent of the indoor fan.

[0029] Specifically, ambient temperature acquisition is not unconditional and continuous, but is limited to a specific effective working window. The system only activates the temperature sensor's reading operation when the indoor fan coil unit has completed power-on initialization and is in either the on or standby state. By binding data acquisition to the actual operating status of the equipment, not only is the accuracy of anti-freeze judgment improved, but the computational load on the main control chip during non-essential periods is also reduced, thereby improving the overall resource utilization efficiency of the system.

[0030] In some embodiments, the preset antifreeze temperature includes a first preset antifreeze temperature and a second preset antifreeze temperature, wherein the first preset antifreeze temperature is lower than the second preset antifreeze temperature; determining whether each indoor fan coil unit triggers an antifreeze alarm signal based on the relationship between the ambient temperature and the preset antifreeze temperature includes: when the ambient temperature is lower than the first preset antifreeze temperature, controlling the indoor fan coil unit to trigger an antifreeze alarm signal; when the ambient temperature is higher than the second preset antifreeze temperature, controlling the indoor fan coil unit not to trigger an antifreeze alarm signal; when the ambient temperature is between the first preset antifreeze temperature and the second preset antifreeze temperature, the indoor fan coil unit maintains its current triggering state; wherein, if an antifreeze alarm signal has already been triggered, the triggering of the antifreeze alarm signal continues; if an antifreeze alarm signal has not been triggered, the antifreeze alarm signal is not triggered.

[0031] Specifically, the antifreeze determination logic in this embodiment adopts a dual-threshold hysteresis control mechanism instead of a single fixed threshold. A first preset antifreeze temperature serves as the trigger lower limit, and a second preset antifreeze temperature serves as the reset upper limit; the temperature range between the two constitutes a state holding band. When the ambient temperature drops below the first preset antifreeze temperature, the system confirms the existence of a freezing risk and triggers an alarm; when the ambient temperature rises above the second preset antifreeze temperature, the system confirms the risk is eliminated and cancels the alarm; and when the ambient temperature is between the two, the system locks the previous state without change. This embodiment solves the critical temperature oscillation problem by adopting a dual-threshold hysteresis control mechanism. In practical applications, temperature sensors themselves have measurement noise, and the indoor environment is affected by door and window opening and closing, personnel movement, or airflow disturbances, often causing temperature readings to fluctuate slightly near the freezing point. If a single-point threshold is used, even small temperature fluctuations will cause the antifreeze alarm signal to frequently switch between trigger and reset states, thereby driving the circulating water pump and water valves to repeatedly start and stop. This condition not only produces continuous mechanical noise but also significantly increases the wear and tear on relay contacts, valve actuators, and water pump motors, shortening the overall service life of the machine. By setting a reasonable hysteresis range, the system can effectively filter out environmental disturbances and sensor noise, ensuring that the actuator only operates when there is a substantial trend change in temperature, thereby guaranteeing the long-term stable operation of the system.

[0032] For example, in a specific application scenario, the first preset antifreeze temperature can be set to 2℃, and the second preset antifreeze temperature can be set to 4℃. When the room temperature slowly drops from 5℃ to 3℃, since 3℃ is still within the hysteresis range of 2℃ to 4℃ and no alarm has been triggered before, the system remains silent; only when the temperature continues to drop to 2℃ will the antifreeze alarm be officially triggered and the water pump start. Conversely, when the water pump runs and the water temperature rises again, and the room temperature rises from 1℃ to 3℃, since 3℃ has not yet exceeded the reset threshold of 4℃, the system continues to maintain the alarm state and the water pump continues to run until the temperature further rises to 4℃ before the alarm is deactivated. It is understood that the above 2℃ and 4℃ are only illustrative values ​​for ease of understanding. In actual engineering, the specific values ​​of the first and second preset antifreeze temperatures can be flexibly configured according to factors such as local climate characteristics, building insulation performance, water system heat capacity, and sensor accuracy, as long as the basic constraint that the first preset antifreeze temperature is less than the second preset antifreeze temperature is met. This embodiment combines an effective acquisition window with dual-threshold hysteresis logic, ensuring both the authenticity and relevance of the input data and the stability and reliability of the output control signal.

[0033] To improve the response speed and reliability of the air conditioning system under extreme conditions, in some embodiments, determining whether each indoor fan coil unit should trigger the antifreeze alarm signal based on the relationship between the ambient temperature and the preset antifreeze temperature also includes: when the ambient temperature is greater than the first preset antifreeze temperature and the rate of temperature drop within a preset time is greater than the preset rate, controlling the indoor fan coil unit to trigger the antifreeze alarm signal in advance.

[0034] Specifically, during the operation of the air conditioning system, not only is the absolute value of the ambient temperature monitored, but the rate of change of the ambient temperature over time is also calculated in real time. When the ambient temperature is detected to be below the first preset antifreeze temperature, but shows a rapid downward trend exceeding the preset rate within a preset time window, the system determines that there is a risk of rapid cooling and freezing, and triggers an antifreeze alarm signal in advance. This setting can compensate for the inherent thermal inertia of water systems. In heat pump water systems, there is a significant time lag from pump startup and hot water circulation to the recovery of coil surface temperature. If only absolute temperature thresholds are relied upon for triggering, in scenarios of sudden drop in ambient temperature (such as sudden opening of doors and windows, a cold wave, or damage to the insulation layer), if the pump is not started until the temperature drops below freezing, the cold water remaining inside the coil is very likely to freeze and expand before the heating cycle, causing damage to the pipeline. This embodiment introduces the rate of temperature change as a criterion, which can reserve a sufficient thermal response buffer period before the risk actually occurs, achieving proactive defense rather than passive remediation.

[0035] In some embodiments, obtaining the ambient temperature of the indoor environment where each indoor fan coil unit is located includes: obtaining the ambient temperature through a temperature sensor; when the ambient temperature is lower than a first preset antifreeze temperature, controlling the indoor fan coil unit to trigger an antifreeze alarm signal includes: when the ambient temperature is lower than the first preset antifreeze temperature and multiple indoor fan coil units are in the same indoor environment, comparing the ambient temperatures obtained by each temperature sensor, and controlling the indoor fan coil unit to trigger an antifreeze alarm signal based on the comparison result; wherein, when the difference between the ambient temperatures obtained by multiple temperature sensors is less than or equal to a predetermined value, controlling the indoor fan coil unit to trigger an antifreeze alarm signal; when the difference between the ambient temperatures obtained by multiple temperature sensors is greater than a predetermined value, controlling the indoor fan coil unit to trigger a sensor abnormality signal.

[0036] Specifically, this embodiment provides a data reliability verification function for large indoor spaces or scenarios with multiple indoor fan coil units connected in parallel. In actual installation, multiple indoor fan coil units may be deployed in the same indoor environment (such as an open office area, lobby, or connected living room). These devices should theoretically sense similar ambient temperatures. When the system detects that the temperature detected by a certain temperature sensor is lower than the first preset anti-freeze temperature, it does not directly accept this single data source, but instead retrieves the temperature readings of other temperature sensors in the same space for cross-comparison. For example, the system calculates the range ΔTmax of the temperature readings of all associated sensors in the space and compares this value with the preset allowable deviation value A. If ΔTmax ≤ A, it indicates that the readings of each sensor are consistent and the low temperature state is true and reliable, and the system triggers the anti-freeze alarm signal normally; conversely, if ΔTmax > A, it indicates that at least one sensor reading deviates significantly from the group average, which is highly likely to be due to a fault in the sensor itself (such as probe detachment, poor wiring contact, ADC drift, or local heat source interference), rather than a true low temperature in the environment. At this point, the system will output a sensor abnormality signal instead of an antifreeze alarm signal, and can simultaneously report a fault code for maintenance personnel to troubleshoot. This effectively distinguishes between actual freezing risk and device failure, avoiding ineffective pump start / stop, energy waste, and user inconvenience caused by false alarms from single-point sensors, significantly improving the system's robustness and intelligence in complex installation environments.

[0037] Specifically, the predetermined value A can be set to 1℃. If three temperature sensors in the same living room read 1.5℃, 1.8℃, and 1.6℃ respectively, with a range of 0.3℃≤1℃, the system determines it to be a true low temperature and triggers antifreeze. If the temperature readings of the three sensors are 1.5℃, 5.2℃, and 4.8℃ respectively, and the calculated range is 3.7℃>1℃, the system determines 1.5℃ to be abnormal temperature data, immediately reports a sensor fault signal, and does not start the circulating water pump to perform antifreeze action. It is understood that the above-mentioned temperature change rate prediction mechanism and multi-sensor cross-verification mechanism are logically independent, and the two can be flexibly combined in an "AND / OR" manner: the system can only enable rate prediction to achieve proactive protection, or only enable sensor verification to improve data reliability, or enable both simultaneously to build a dual-enhanced sensing system. The specific configuration can be selected according to project needs and cost constraints, and this application does not limit it in this regard.

[0038] In some embodiments, the anti-freeze alarm signal includes a first-level alarm signal, a second-level alarm signal, and a third-level alarm signal, with the alarm levels of the first-level alarm signal, the second-level alarm signal, and the third-level alarm signal increasing progressively. The preset anti-freeze temperature also includes a third preset anti-freeze temperature, which is lower than the first preset anti-freeze temperature. Specifically, when the ambient temperature is between the first preset anti-freeze temperature and the second preset anti-freeze temperature, and the indoor fan coil unit has already triggered an anti-freeze alarm signal, the indoor fan coil unit is controlled to trigger a first-level alarm signal. When the ambient temperature is greater than the third preset anti-freeze temperature but less than the first preset anti-freeze temperature, the indoor fan coil unit is controlled to trigger a second-level alarm signal. When the ambient temperature is less than the third preset anti-freeze temperature, the indoor fan coil unit is controlled to trigger a third-level alarm signal.

[0039] Specifically, this embodiment introduces a lower third preset antifreeze temperature based on the first and second preset antifreeze temperatures, thereby discretizing the continuous low-temperature risk into three distinct level ranges. This tiered design enables precise matching of antifreeze resources. In actual operation, not all low-temperature conditions require full-power intervention. When the ambient temperature is only slightly below the safety threshold (i.e., between the first and second preset antifreeze temperatures), the system identifies it as a potential risk zone and triggers a level one alarm signal. At this point, freezing has not yet occurred, and only low-intensity preventative measures are needed to maintain thermal balance. When the temperature further drops to between the third and first preset antifreeze temperatures, the system identifies it as a clear freezing risk zone and triggers a level two alarm signal, indicating that the ambient heat loss has exceeded the normal maintenance capacity, and the protection level needs to be increased. When the temperature falls below the third preset antifreeze temperature, the system identifies it as a severe freezing risk zone and triggers a level three alarm signal, meaning that the water in the coil may have begun or is about to undergo a phase change, and the highest intensity emergency intervention measures must be taken. By using this stepped state quantification, the system avoids excessive energy consumption at slightly low temperatures, while also ensuring sufficient protection margin at extremely low temperatures, achieving an optimal balance between safety and economy.

[0040] In some embodiments, when the indoor fan coil unit triggers a level one alarm signal, a first antifreeze protection operation is executed; when the indoor fan coil unit triggers a level two alarm signal, a second antifreeze protection operation is executed; and when the indoor fan coil unit triggers a level three alarm signal, a third antifreeze protection operation is executed. The antifreeze intensity of the first, second, and third antifreeze protection operations increases progressively. For example, the first antifreeze protection operation involves controlling the outdoor unit to output a warning prompt and opening the corresponding water valve; the second antifreeze protection operation involves the outdoor unit starting a first heating mode to heat the circulating water; and the third antifreeze protection operation involves the outdoor unit switching to a second heating mode to fully heat the circulating water. The first heating mode can be a heating + heat recovery mode, where a portion of the system's heat is recovered in a heat recovery unit to heat domestic hot water, and the remaining heat is supplied to the indoor fan coil unit for circulating water heating. The second heating mode can be a pure heating mode, where all heat in the system is used for fan coil unit heating. Specifically, the progressive increase in antifreeze intensity is reflected in whether heat is injected into the circulating water and the amount of heat injected. During the first antifreeze protection operation, the system controls the outdoor unit to issue a warning signal and controls the water valve to open. At this time, the residual heat of the pipeline can be used for low-power circulation, which not only prevents the stagnant water from freezing, but also minimizes pump consumption. During the second antifreeze protection operation, the system controls the water valve to open and controls the outdoor unit to start the first heating mode to heat the fluid to compensate for the heat loss of the coil. During the third antifreeze protection operation, the system controls the water valve to open and controls the outdoor unit to start the second heating mode to heat the fluid, increasing the heat injection and heating efficiency to combat extreme low temperatures.

[0041] In other embodiments, the first antifreeze protection operation is to control the outdoor unit to output a warning prompt, open the corresponding water valve, and adjust the water flow rate to the first preset flow rate; the second antifreeze protection operation is to open the corresponding water valve to increase the flow rate to the second preset flow rate (the second preset flow rate > the first preset flow rate), and at the same time, the outdoor unit starts the first heating mode to heat the circulating water; the third antifreeze protection operation is to further open the corresponding water valve to increase the flow rate to the third preset flow rate (the third preset flow rate > the second preset flow rate), and the outdoor unit switches to the second heating mode to heat the circulating water at full capacity.

[0042] In other embodiments, the first antifreeze protection operation is to control the outdoor unit to output a warning prompt, open the corresponding water valve, and adjust the water flow rate to a first preset flow rate; the second antifreeze protection operation is to open the corresponding water valve to increase the fluid flow rate to a second preset flow rate (second preset flow rate > first preset flow rate), and simultaneously control the outdoor unit to start the third heating mode and heat the circulating water according to the first heating time so that the temperature of the circulating water reaches the first target temperature; the third antifreeze protection operation is to further open the corresponding water valve to increase the fluid flow rate to a third preset flow rate (third preset flow rate > second preset flow rate), and simultaneously control the outdoor unit to switch to the fourth heating mode and heat the circulating water at full power according to the second heating time so that the temperature of the circulating water reaches the second target temperature; wherein, the heating mode of the third heating mode and the fourth heating mode are the same, the first heating time is less than the second heating time, and the first target temperature is less than the second target temperature. It should be noted that the third and fourth heating modes can be heating + heat recovery modes, where part of the heat generated by the system is recovered in the heat recovery unit to heat domestic hot water, and the remaining heat is supplied to the indoor fan coil unit circulating water for heating. Alternatively, it can be a pure heating mode, where all the heat in the system is used for fan coil unit heating.

[0043] In some embodiments, when the ambient temperature rises from below the third preset antifreeze temperature to between the first and third preset antifreeze temperatures, the alarm level of the indoor fan coil unit is switched from a level three alarm signal to a level two alarm signal, and the circulating water pump is kept running. When the ambient temperature rises from below the first preset antifreeze temperature to between the first and second preset antifreeze temperatures, the alarm level of the indoor fan coil unit is switched from a level two alarm signal to a level one alarm signal, and the circulating water pump is kept running. When the ambient temperature is above the second preset antifreeze temperature, the antifreeze alarm signal of the indoor fan coil unit is canceled, and when all indoor fan coil units have canceled their antifreeze alarm signals, the circulating water pump is shut down.

[0044] Specifically, this reset logic is not simply a reverse triggering process, but includes a crucial safety maintenance mechanism. In the temperature-reset path, when the ambient temperature rises from below the third preset anti-freeze temperature to between the first and third preset anti-freeze temperatures, even if the alarm level is downgraded, the circulating water pump will not immediately stop but will continue running until the ambient temperature steadily rises above the second preset anti-freeze temperature before shutting down. This design ensures that when the ambient temperature has just left the danger zone, ice crystals inside the coils, especially in dead zones such as elbows and valves, may not have completely melted, or the water temperature distribution may still be significantly uneven. If the pump is stopped immediately at this point, the remaining ice nuclei or localized cold spots will quickly refreeze in a static state, leading to a risk of secondary freezing and cracking. This embodiment sets a confirmation period based on temperature hysteresis before the water pump is turned off, forcibly maintaining water circulation and ensuring that heat can fully penetrate to the end of the pipeline. This allows the entire water system to reach a thermodynamically uniform and stable state before exiting the antifreeze mode, effectively avoiding false safety judgments caused by sensor response lag and uneven heat distribution in the water circuit, and improving the reliability of the system under repeated freeze-thaw conditions.

[0045] In some embodiments, controlling the opening and closing state of the water valve of each indoor fan coil unit according to the antifreeze alarm signal includes: when the indoor fan coil unit triggers the antifreeze alarm signal, controlling the water valve of the indoor fan coil unit to open; when the indoor fan coil unit does not trigger the antifreeze alarm signal, controlling the opening and closing state of the water valve according to the current operating state of the indoor fan coil unit.

[0046] Specifically, after receiving the anti-freeze alarm signal, the outdoor unit uses its control logic to implement differentiated control over the corresponding water valves of each indoor fan coil unit. When an indoor fan coil unit triggers the anti-freeze alarm signal, the corresponding water valve is forcibly opened, allowing the circulating water medium to flow into the fan coil unit. The heat carried by the flowing medium raises the temperature, preventing the water inside the coil from cooling down and freezing, thus avoiding cracking and damage. For indoor fan coil units that have not triggered the anti-freeze alarm signal, the water valve opening and closing is determined by their current operating state. There is no need to forcibly change the original working state of the water valve, and it will not interfere with fan coil units in normal operating conditions. This ensures that fan coil units at risk of low temperature can be connected to the circulating water system for anti-freeze protection, while not disrupting the original working logic of other fan coil units without freezing risk, and avoiding unnecessary opening of water valves in areas without freezing risk, thus preventing heat loss caused by cold.

[0047] For example, during the power-on and power-off process of the indoor fan coil units, when the ambient temperature is detected to be below 2°C, the indoor fan coil units at this temperature are controlled to trigger an anti-freeze alarm signal, and their water valves are opened, while the circulating water pump is started. When the ambient temperature is detected to be above 4°C, the indoor fan coil units at this temperature are controlled to deactivate the anti-freeze alarm signal, and the water valves are controlled to open or close according to the current operating status of the indoor fan coil units. Simultaneously, when none of the indoor fan coil units at this ambient temperature have triggered an anti-freeze alarm signal, the circulating water pump is shut down. This configuration monitors the indoor ambient temperature to prevent the indoor fan coil units from freezing.

[0048] In some embodiments, controlling the opening and closing state of the water valve according to the current operating state of the indoor fan coil unit includes: controlling the water valve to open when the indoor fan coil unit is currently in operation; and controlling the water valve to close when the indoor fan coil unit is currently in a stopped or standby state.

[0049] Specifically, when the ambient temperature exceeds the safety threshold and the antifreeze alarm signal is not triggered, the water valve's control authority automatically switches to the system's normal operation control logic. At this time, if the indoor fan coil unit is running (including cooling, heating, or ventilation modes), the water valve remains open to meet normal heat exchange requirements; if the indoor fan coil unit is stopped or in standby mode, the water valve automatically closes. This setting serves two purposes: firstly, closing the water valve during standby or shutdown prevents the continuous flow of low-temperature chilled water into the indoor coil, reducing unnecessary cold air infiltration and heat loss, and improving the overall energy efficiency ratio of the system; secondly, it shortens the time the chilled water remains stagnant inside the coil, physically reducing the probability of freezing and avoiding the problem of excessively low temperatures in localized areas caused by prolonged stagnant water.

[0050] In some embodiments, before controlling the circulating water pump to shut down, the antifreeze control method for the air conditioning system further includes: when all indoor fan coil units have not triggered an antifreeze alarm signal, controlling the circulating water pump to remain on for a first preset time, and then controlling the circulating water pump to shut down. It is understood that the specific value of the first preset time in this embodiment needs to comprehensively consider factors such as the water system volume, pipe length, insulation performance, and pump flow rate, and this application does not impose specific limitations on it.

[0051] Specifically, in actual operation, when the antifreeze alarm signal of the last indoor fan coil unit is canceled, it only means that the ambient temperature at the temperature sensor measuring points of each indoor fan coil unit has risen above the safe threshold, and does not mean that the entire water circulation system has reached a stable state of uniform heat. If the circulating water pump is immediately shut off upon receiving the cancellation signal, the water flow in the pipeline will decelerate rapidly due to inertia until it comes to a complete stop. In areas where water flow stagnates, such as the ends of the coils, pipe bends, and behind valves, incompletely melted ice crystals or low-temperature cold water may still remain. After the continuous supply of flowing hot water is interrupted, the water in the aforementioned local low-temperature areas is very likely to refreeze under static conditions. Therefore, this embodiment sets a first preset time as a mandatory safety confirmation period. During this period, the circulating water pump continues to operate, relying on the sensible heat of the circulating water and the residual heat stored in the pipeline to fully deliver it to all end points of the system, ensuring that the temperature of all potential freezing points is above the freezing point, thereby avoiding secondary freezing.

[0052] On the other hand, this application also provides an anti-freeze control device for an air conditioning system. This anti-freeze control device is used to execute the aforementioned anti-freeze control method for an air conditioning system. Therefore, this anti-freeze control device can achieve all the technical effects corresponding to the aforementioned anti-freeze control method. Since the technical effects of the anti-freeze control method have already been described in detail above, they will not be repeated here.

[0053] like Figure 3 As shown, in some embodiments, the anti-freeze control device of the air conditioning system includes: an acquisition module 10, a detection module 20, and a control module 30. The acquisition module 10 is used to acquire the ambient temperature of the indoor environment where each indoor fan coil unit is located; the detection module 20 is used to detect the anti-freeze alarm signal; both the acquisition module 10 and the detection module 20 are electrically connected to the control module 30. The control module 30 is used to determine whether each indoor fan coil unit has triggered the anti-freeze alarm signal based on the relationship between the ambient temperature and the preset anti-freeze temperature, and to control the opening and closing status of the water valve of each indoor fan coil unit and the opening and closing status of the circulating water pump of the air conditioning system based on the anti-freeze alarm signal; wherein, when any indoor fan coil unit triggers the anti-freeze alarm signal, the circulating water pump is controlled to start; when none of the indoor fan coil units trigger the anti-freeze alarm signal, the circulating water pump is controlled to shut down.

[0054] Specifically, the acquisition module 10 collects the ambient temperature of each indoor fan coil unit in real time as the basic data source for antifreeze determination and transmits the ambient temperature to the control module. The control module 30 compares the collected temperature with the preset antifreeze threshold to determine whether each coil unit is at risk of low-temperature freezing damage and controls whether the indoor fan coil units generate corresponding antifreeze alarm signals. The detection module 20 detects the antifreeze alarm signals uploaded by each indoor fan coil unit and transmits the signals to the control module. The control module outputs control commands based on the received alarm signals to control the water valves and circulating water pumps. The entire device adopts a multi-point distributed temperature measurement and centralized control operation mode of the outdoor unit: when any indoor fan coil unit triggers an antifreeze alarm, the system forcibly opens the water valve corresponding to that indoor fan coil unit and starts the circulating water pump, relying on the continuous circulation of water to deliver heat and prevent local freezing of the pipes; when all indoor fan coil units are in the safe temperature range and there is no antifreeze alarm signal, the system shuts down the circulating water pump, and each water valve switches to autonomous control according to the operating status of the corresponding indoor fan coil unit. It is understandable that this embodiment independently divides the tasks of temperature acquisition, risk assessment, signal transmission and equipment execution, and connects them in an orderly manner, making the anti-freeze response more targeted and timely. It overcomes the limitations of insufficient monitoring points, delayed response or generalized intervention in traditional methods. It can fully cover the anti-freeze protection needs of every indoor fan coil unit, effectively reduce the probability of coil freezing damage in winter, and avoid the power loss caused by the continuous no-load operation of the circulating water pump under no-freeze conditions.

[0055] For ease of description, spatial relative terms such as "above," "on top of," "on the upper surface of," "above," etc., are used herein to describe the spatial positional relationship of a device or feature as shown in the figures to other devices or features. It should be understood that spatial relative terms are intended to encompass different orientations in use or operation beyond the orientation of the device as described in the figures. For example, if the device in the figures were inverted, a device described as "above" or "on top of" other devices or structures would subsequently be positioned as "below" or "under" other devices or structures. Thus, the exemplary term "above" can include both "above" and "below." The device may also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatial relative descriptions used herein will be interpreted accordingly.

[0056] Furthermore, it should be noted that the use of terms such as "first" and "second" to define components is merely for the purpose of distinguishing the corresponding components. Unless otherwise stated, the above terms have no special meaning and therefore cannot be construed as limiting the scope of protection of this application.

[0057] The above are merely preferred embodiments of this application and are not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for antifreeze control of an air conditioning system, characterized in that, The air conditioning system includes an outdoor unit and multiple indoor fan coil units, and the anti-freeze control method of the air conditioning system includes: Obtain the ambient temperature of the indoor environment where each of the indoor fan coil units is located; Determine whether each indoor fan coil unit triggers an antifreeze alarm signal based on the relationship between the ambient temperature and the preset antifreeze temperature. The antifreeze alarm signal is detected, and the opening and closing status of the water valves of each indoor fan coil unit and the opening and closing status of the circulating water pump of the air conditioning system are controlled according to the antifreeze alarm signal. Specifically, when any one of the indoor fan coil units triggers the antifreeze alarm signal, the circulating water pump is controlled to start; when none of the indoor fan coil units trigger the antifreeze alarm signal, the circulating water pump is controlled to shut down.

2. The antifreeze control method for an air conditioning system according to claim 1, characterized in that, The step of obtaining the ambient temperature of the indoor environment where each of the indoor fan coil units is located includes: when the indoor fan coil unit is powered on and in the on or standby state, obtaining the ambient temperature of the indoor environment where the indoor fan coil unit is located through a temperature sensor.

3. The antifreeze control method for an air conditioning system according to claim 1, characterized in that, The preset antifreeze temperature includes a first preset antifreeze temperature and a second preset antifreeze temperature, wherein the first preset antifreeze temperature is lower than the second preset antifreeze temperature; determining whether each indoor fan coil unit triggers an antifreeze alarm signal based on the relationship between the ambient temperature and the preset antifreeze temperature includes: When the ambient temperature is lower than the first preset antifreeze temperature, the indoor fan coil unit is controlled to trigger the antifreeze alarm signal. When the ambient temperature is greater than the second preset antifreeze temperature, the indoor fan coil unit is controlled not to trigger the antifreeze alarm signal; When the ambient temperature is between the first preset antifreeze temperature and the second preset antifreeze temperature, the indoor fan coil unit maintains its current trigger state; wherein, if the antifreeze alarm signal has already been triggered, the triggering of the antifreeze alarm signal continues; if the antifreeze alarm signal has not been triggered, the antifreeze alarm signal is not triggered.

4. The antifreeze control method for an air conditioning system according to claim 3, characterized in that, The step of determining whether each indoor fan coil unit triggers an antifreeze alarm signal based on the relationship between the ambient temperature and the preset antifreeze temperature further includes: when the ambient temperature is greater than the first preset antifreeze temperature, and the rate of temperature drop within a preset time is greater than a preset rate, controlling the indoor fan coil unit to trigger the antifreeze alarm signal in advance; and / or, The step of obtaining the ambient temperature of the indoor environment where each of the indoor fan coil units is located includes: obtaining the ambient temperature through a temperature sensor; the step of controlling the indoor fan coil unit to trigger the anti-freeze alarm signal when the ambient temperature is lower than the first preset anti-freeze temperature includes: when the ambient temperature is lower than the first preset anti-freeze temperature and multiple indoor fan coil units are in the same indoor environment, comparing the ambient temperatures obtained by each of the temperature sensors, and controlling the indoor fan coil unit to trigger the anti-freeze alarm signal according to the comparison result; wherein, when the difference between the ambient temperatures obtained by multiple temperature sensors is less than or equal to a predetermined value, the indoor fan coil unit is controlled to trigger the anti-freeze alarm signal; when the difference between the ambient temperatures obtained by multiple temperature sensors is greater than the predetermined value, the indoor fan coil unit is controlled to trigger a sensor abnormality signal.

5. The antifreeze control method for an air conditioning system according to claim 3, characterized in that, The anti-freeze alarm signal includes a first-level alarm signal, a second-level alarm signal, and a third-level alarm signal, with the alarm levels of the first-level alarm signal, the second-level alarm signal, and the third-level alarm signal increasing progressively; the preset anti-freeze temperature also includes a third preset anti-freeze temperature, which is lower than the first preset anti-freeze temperature; Specifically, when the ambient temperature is between the first preset antifreeze temperature and the second preset antifreeze temperature, and the indoor fan coil unit has already triggered the antifreeze alarm signal, the indoor fan coil unit is controlled to trigger the first-level alarm signal. When the ambient temperature is greater than the third preset antifreeze temperature and less than the first preset antifreeze temperature, the indoor fan coil unit is controlled to trigger the secondary alarm signal. When the ambient temperature is lower than the third preset antifreeze temperature, the indoor fan coil unit is controlled to trigger the third-level alarm signal.

6. The antifreeze control method for an air conditioning system according to claim 5, characterized in that, When the indoor fan coil unit triggers the first-level alarm signal, a first anti-freeze protection operation is executed; when the indoor fan coil unit triggers the second-level alarm signal, a second anti-freeze protection operation is executed; when the indoor fan coil unit triggers the third-level alarm signal, a third anti-freeze protection operation is executed; wherein the anti-freeze intensity of the first, second, and third anti-freeze protection operations increases progressively; and / or, When the ambient temperature rises from below the third preset antifreeze temperature to between the first and third preset antifreeze temperatures, the alarm level of the indoor fan coil unit is switched from the third-level alarm signal to the second-level alarm signal, and the circulating water pump remains on. When the ambient temperature rises from below the first preset antifreeze temperature to between the first and second preset antifreeze temperatures, the alarm level of the indoor fan coil unit is switched from the second-level alarm signal to the first-level alarm signal, and the circulating water pump remains on. When the ambient temperature is above the second preset antifreeze temperature, the antifreeze alarm signal for the indoor fan coil unit is deactivated. When all indoor fan coil units have deactivated their antifreeze alarm signals, the circulating water pump is shut down.

7. The antifreeze control method for an air conditioning system according to claim 1, characterized in that, The step of controlling the opening and closing status of the water valves of each indoor fan coil unit according to the antifreeze alarm signal includes: When the indoor fan coil unit triggers the antifreeze alarm signal, the water valve of the indoor fan coil unit is controlled to open. When the indoor fan coil unit does not trigger the antifreeze alarm signal, the opening and closing status of the water valve is controlled according to the current operating status of the indoor fan coil unit.

8. The antifreeze control method for an air conditioning system according to claim 7, characterized in that, The control of the water valve's opening and closing state based on the current operating state of the indoor fan coil unit includes: controlling the water valve to open when the indoor fan coil unit is currently in operation; and controlling the water valve to close when the indoor fan coil unit is currently in a stopped or standby state.

9. The antifreeze control method for an air conditioning system according to claim 1, characterized in that, Before executing the control to shut down the circulating water pump, the antifreeze control method of the air conditioning system further includes: When none of the indoor fan coil units trigger the antifreeze alarm signal, the circulating water pump is kept on for a first preset time before being shut down.

10. An antifreeze control device for an air conditioning system, characterized in that, The antifreeze control device of the air conditioning system is used to execute the antifreeze control method of the air conditioning system according to any one of claims 1 to 9, and the antifreeze control device of the air conditioning system comprises: Acquisition module (10), the acquisition module (10) is used to acquire the ambient temperature of the indoor environment where each of the indoor fan coil units is located; The detection module (20) is used to detect the antifreeze alarm signal; The control module (30), the acquisition module (10) and the detection module (20) are all electrically connected to the control module (30). The control module (30) is used to determine whether each indoor fan coil unit triggers an antifreeze alarm signal based on the relationship between the ambient temperature and the preset antifreeze temperature, and to control the opening and closing state of the water valve of each indoor fan coil unit and the opening and closing state of the circulating water pump of the air conditioning system based on the antifreeze alarm signal. When any indoor fan coil unit triggers the antifreeze alarm signal, the circulating water pump is controlled to start. When none of the indoor fan coil units trigger the antifreeze alarm signal, the circulating water pump is controlled to shut down.

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