Anti-freeze system for air conditioner and control device for air conditioner

Abstract

To secure a sufficient flow rate necessary for freeze prevention even when cold-water coil inlet pressure deviates from a value at the introduction of equipment due to disturbance, deterioration or the like.SOLUTION: When a detected cold water temperature Tm is lower than a prescribed freeze prevention threshold temperature, a controller 12 determines an opening command value A* corresponding to the detected cold water temperature Tm from a temperature-opening map in which cold water temperatures and degrees of opening of a control valve 30 are associated with each other. The controller 12 also determines a target flow rate Q* corresponding to the detected cold water temperature Tm from a temperature-flow rate map in which cold water temperatures and cold water flow rates are associated with each other. The controller 12 also determines a difference flow rate ΔQ, which is an actual measurement flow rate Qm of water backflow piping 28 after setting the opening of the control valve 30 to the opening command value A* minus the target flow rate Q*. When the difference flow rate ΔQ is a positive value, the controller 12 resets the opening command value A* to an increasing direction. When the difference flow rate ΔQ is equal to or smaller than zero, the controller maintains the opening command value A*.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] Disclosed herein is an anti-freeze system for an air conditioner and a control device for an air conditioner. [Background technology]

[0002] For example, a central air conditioning system is equipped with an air conditioner. The air conditioner takes in outside air, heats or cools it, and dehumidifies or humidifies it as needed to generate conditioned air, which is then supplied to the space to be conditioned, such as a tenant or office space.

[0003] To cool outside air, the air conditioner is equipped with a cold water coil to which cold water is supplied. To heat outside air, the air conditioner is equipped with a hot water coil to which hot water is supplied. These coils are installed between the outside air inlet of the air conditioner and the air supply fan. For example, the various devices are arranged in the following order: outside air inlet → cold water coil → hot water coil → air supply fan. Outside air introduced into the air conditioner (introduced outside air) is cooled or heated by passing through each coil.

[0004] For example, in winter, when the incoming outside air needs to be heated and there is no need for cooling, the supply of cold water to the chilled water coil is stopped. This causes cold water to accumulate in the chilled water coil. When a cold wave passes through in cold regions, the incoming outside air passes through the chilled water coil, causing the chilled water to freeze and expand, which may lead to damage to the chilled water coil.

[0005] Therefore, even in the winter when air conditioning is not required, chilled water is allowed to flow (move) at a specified flow rate to prevent freezing. For example, when the discharge pressure of the pump that delivers chilled water is constant, the pressure at the inlet to the chilled water coil is constant, and since there is a proportional relationship between the opening of the control valve and the flow rate, it is possible to control the flow rate by adjusting the opening.

[0006] As an anti-freezing means for such an air conditioner, for example, in Patent Document 1, when the temperature of the cold water circulating in the cold water coil falls below a predetermined specific temperature, a part of the hot water flowing in the hot water circulation path is supplied to the cold water circulation path including the cold water coil. In Patent Document 2, in anti-freezing operation, the temperature of the anti-freezing water at the outlet of the water passage of the cooling heat exchanger is adjusted to a set anti-freezing temperature by adjusting the amount of anti-freezing water passing through the water passage of the cooling heat exchanger. Furthermore, in Patent Document 3, when the outside air temperature falls below a preset temperature, the flow control valve is fully opened to prevent freezing. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2019-78501 A [Patent Document 2] JP 2012-154543 A [Patent Document 3] Japanese Patent Application Publication No. 5-215382 Summary of the Invention [Problem to be solved by the invention]

[0008] However, even if the set value of the discharge pressure for the pump is constant, the actual chilled water coil inlet pressure may drop below the value at the time of installation due to pump deterioration, rust in the chilled water piping, etc. Also, when the chilled water piping is branched and supplied to another air conditioner, the actual chilled water coil inlet pressure may deviate from the value at the time of installation due to the sudden opening and closing of the control valve in the other air conditioner.

[0009] Therefore, this specification discloses an anti-freeze system for an air conditioner and a control device for an air conditioner that can ensure sufficient flow rate to prevent freezing even if the chilled water coil inlet pressure deviates from the value at the time the equipment was installed due to external disturbances, deterioration, etc. [Means for solving the problem]

[0010] This specification discloses a freeze prevention system for an air conditioner. The system includes a chilled water coil, a control valve, a water temperature sensor, a flow rate sensor, and a control device. The chilled water coil is supplied with chilled water from a water supply pipe by a pump, and heat exchange occurs between the chilled water coil and air passing through the chilled water coil. The control valve is provided in a return water pipe to which return chilled water from the chilled water coil is sent, and adjusts the flow rate of the return chilled water. The water temperature sensor and the flow rate sensor are provided in the return water pipe. The control device generates an opening command for the control valve based on a detected chilled water temperature detected by the water temperature sensor. When the detected chilled water temperature is less than a predetermined freeze prevention threshold temperature, the control device determines an opening command value corresponding to the detected chilled water temperature from a temperature-opening map in which the chilled water temperature and the opening of the control valve are associated. The control device determines a target flow rate corresponding to the detected chilled water temperature from a temperature-flow rate map in which the chilled water temperature and the chilled water flow rate are associated. The control device also determines a differential flow rate by subtracting an actual measured flow rate in the return water pipe after the opening of the control valve is set to the opening command value from the target flow rate. Furthermore, the control device resets the opening command value in the increasing direction when the differential flow rate has a positive value, while maintaining the opening command value when the differential flow rate has a value equal to or less than zero.

[0011] According to the above configuration, when the differential flow rate is a positive value, i.e., when the measured flow rate has not reached the target flow rate, the opening command value is increased. On the other hand, when the differential flow rate is equal to or less than zero, i.e., when the measured flow rate is equal to or greater than the target flow rate, the opening command value is maintained from the viewpoint that a sufficient flow rate for preventing freezing is ensured.

[0012] This specification also discloses a control device for an air conditioner. The air conditioner includes a control device, a cold water coil, a control valve, a water temperature sensor, and a flow rate sensor. Cold water is supplied to the cold water coil from a water supply pipe by a pump, and heat exchange occurs between the cold water coil and air passing through the cold water coil. The control valve is provided in a return water pipe to which return cold water from the cold water coil is sent, and adjusts the flow rate of the return cold water. The water temperature sensor and the flow rate sensor are provided in the return water pipe. The control device generates an opening command for the control valve based on a detected cold water temperature detected by the water temperature sensor. The control device includes a temperature-based opening calculation unit, a temperature-based flow rate calculation unit, and an opening adjustment unit. When the detected cold water temperature is lower than a predetermined anti-freeze threshold temperature, the temperature-based opening calculation unit determines an opening command value corresponding to the detected cold water temperature from a temperature-opening map in which the cold water temperature and the opening of the control valve are associated. The temperature-based flow rate calculation unit determines a target flow rate corresponding to the detected cold water temperature from a temperature-flow rate map in which the cold water temperature and the cold water flow rate are associated. The opening adjustment unit calculates a differential flow rate by subtracting the actual measured flow rate in the return water piping after the opening of the control valve is set to the opening command value from the target flow rate, and if the differential flow rate is a positive value, it resets the opening command value to an increasing value, while maintaining the opening command value if the differential flow rate is equal to or less than zero. Effect of the Invention

[0013] According to the anti-freeze system for an air conditioner and the control device for an air conditioner disclosed in this specification, it is possible to ensure a flow rate sufficient for preventing freezing even if the chilled water coil inlet pressure deviates from the value at the time the equipment was installed due to external disturbances, deterioration, etc. [Brief description of the drawings]

[0014] [Figure 1] 1 is a diagram illustrating a configuration of an air conditioning system including an anti-freeze system for an air conditioner according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a diagram illustrating an example of functional blocks of a controller. [Diagram 3] FIG. 13 is a diagram illustrating a temperature-opening degree map (TA map). [Figure 4] FIG. 1 is a diagram illustrating a temperature-flow rate map (TQ map). [Diagram 5] FIG. 4 is a diagram illustrating an example of an opening adjustment map. [Figure 6] FIG. 4 is a diagram illustrating a flow of setting the opening degree of a control valve according to the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] 1 illustrates an anti-freeze system for an air conditioner according to this embodiment. This system includes an air conditioner 10 and a controller 12 (control device). Signal lines are indicated by dashed lines. Also, devices that are less related to the anti-freeze of the chilled water coil 14, such as a filter or a micro-differential pressure switch that detects a clogged filter, and a humidification mechanism, are appropriately omitted from the illustration.

[0016] The air conditioner 10 takes in outside air to generate conditioned air, which it supplies to a space to be air-conditioned, such as a tenant or office space. A damper 16 and a damper motor 18 are provided on the outside air side of the air conditioner 10. The air conditioner 10 comprises, in order from the outside air side, a chilled water coil 14, a hot water coil 20, and an air supply fan 22.

[0017] The damper 16 is a so-called air volume control damper (VD) that adjusts the amount of outside air (OA) introduced by adjusting the opening of the outside air duct 24. The damper 16 is formed, for example, from a plate member. The damper motor 18 drives the damper 16 to adjust the opening of the outside air duct 24. The damper motor 18 is formed, for example, from a pulse motor.

[0018] The upstream end of the chilled water coil 14 is connected to a chilled water supply pipe 26. The downstream end of the chilled water coil 14 is connected to a return water pipe 28. A pump 60 supplies chilled water from the water supply pipe 26 to the chilled water coil 14. The chilled water coil 14 exchanges heat with air (outside air) that is introduced from an outside air duct 24 and passes through it. In the embodiment shown in FIG. 1, the air that exchanges heat with the chilled water coil 14 includes not only the outside air but also a portion of the return air returned from the space to be air-conditioned.

[0019] A chiller 62 is connected to the upstream end of the water supply pipe 26 and the downstream end of the water return pipe 28. The chilled water that has passed through the chilled water coil 14 is returned to the chiller 62 through the water return pipe 28. A pump 60 is provided on the water return pipe 28. When the pump 60 is driven, the chilled water circulates through the flow path of the pump 60 → chiller 62 → water supply pipe 26 → chilled water coil 14 → water return pipe 28 → pump 60.

[0020] Although not shown in FIG. 1, a plurality of water supply pipes 26 and return water pipes 28 branch off from the chiller 62, making it possible to supply chilled water from the chiller 62 to a plurality of air conditioners.

[0021] In addition, the return water piping 28 is provided with a control valve 30 for adjusting the flow rate of the return chilled water flowing through the return water piping 28, a water temperature sensor 32 for measuring the temperature of the return chilled water, and a flow rate sensor 34 for measuring the flow rate of the return chilled water. As will be described later, the controller 12 adjusts the opening of the control valve 30 based on the measurements of the water temperature sensor 32 and the flow rate sensor 34 to prevent the chilled water in the chilled water coil 14 from freezing.

[0022] The hot water coil 20, like the cold water coil 14, exchanges heat with air (outside air) introduced from the outside air duct 24 and passing through it, and with a portion of the return air. The hot water coil 20 is connected to a water supply pipe 36. A boiler 72 is provided at the upstream end of the water supply pipe 36. The hot water that has passed through the hot water coil 20 is returned to the boiler 72 from a return water pipe 38.

[0023] The return water pipe 38 is provided with a control valve 40 that adjusts the flow rate of the return hot water flowing through the return water pipe 38. Furthermore, the return water pipe 38 is provided with a pump 70. When the pump 70 is driven, the hot water circulates through the flow path of the pump 70 → boiler 72 → water supply pipe 36 → hot water coil 20 → return water pipe 38 → pump 70.

[0024] Although not shown in FIG. 1, a plurality of water supply pipes 36 and return water pipes 38 branch off from the boiler 72, making it possible to supply hot water from the boiler 72 to a plurality of air conditioners.

[0025] Basically, only one of the cold water coil 14 and the hot water coil 20 is used. For example, when cooling outside air, cold water is supplied to the cold water coil 14 while the supply of hot water to the hot water coil 20 is stopped (control valve 40 is closed). When heating (warming) outside air, hot water is supplied to the hot water coil 20 while the supply of cold water to the cold water coil 14 is stopped (control valve 30 is closed).

[0026] In addition, in so-called dry operation in which the introduced outdoor air is dehumidified, reheat control may be executed in which the outdoor air is cooled (supercooled) to a temperature below the target temperature and then heated. In such a case, cold water and hot water are supplied to the cold water coil 14 and the hot water coil 20, respectively. The conditioned air that has been cooled, heated, dehumidified, or humidified as necessary is sent from the air supply fan 22 through the air supply duct 42 to each of the spaces to be air-conditioned.

[0027] The controller 12, which is a control device for the air conditioner 10, is composed of, for example, a PLC (Programmable Logic Computer). The controller 12 may be compliant with the communication protocol BACnet (Building Automation and Control Network) to be compatible with, for example, BA (Building Automation). In accordance with this BACnet, the controller 12 is capable of communicating with a central monitoring device (not shown).

[0028] 1 shows an example of a hardware configuration diagram of the controller 12. The controller 12 is capable of controlling various devices connected to an internal bus.

[0029] The controller 12 includes a CPU 44, a RAM 46, a ROM 47, a user interface 48 (UI), and an external interface 50. The user interface 48 is used when inputting user information and is also used when displaying information.

[0030] The external interface 50 is used for connection with external devices and data communication. Specifically, the water temperature sensor 32 sends a detected chilled water temperature Tm, which is the detected temperature of the return chilled water flowing through the return water pipe 28. The flow rate sensor 34 sends an actual flow rate Qm of the return chilled water flowing through the return water pipe 28. The supply air temperature sensor 52 of the air supply duct 42 sends a measured value of the supply air temperature.

[0031] The ROM 47 includes a non-volatile memory such as a hard disk drive (HDD) or a solid state drive (SSD). The ROM 47 stores a program for configuring the controller 12 into functional blocks (see FIG. 2) described later. The ROM 47 further stores a temperature-opening map (TA map), a temperature-flow rate map (TQ map), an opening adjustment map, and the like, which will be described later.

[0032] The controller 12 executes the opening setting flow illustrated in Fig. 6 and sets the opening of the control valve 30. The set opening is sent to the control valve 30 via the external interface 50. Also, an opening command is sent from the controller 12 to the control valve 40 provided in the hot water return pipe 38 via the external interface 50. Furthermore, an opening command for the outside air duct 24 is sent from the controller 12 to the damper motor 18 via the external interface 50.

[0033] A functional block diagram of the controller 12 is illustrated in Fig. 2. This functional block diagram is configured by the CPU 44 executing a program capable of executing the opening setting flow illustrated in Fig. 6. This program is stored in the ROM 47 or in a non-transitory computer-readable storage medium such as a DVD.

[0034] The controller 12 includes a temperature-based opening calculation unit 54, a temperature-based flow rate calculation unit 56, and an opening adjustment unit 58.

[0035] The temperature-based opening calculation unit 54 stores a temperature-opening map (TA map) as shown in Fig. 3. The temperature-opening map has the chilled water temperature on the horizontal axis and the opening command value of the control valve 30 on the vertical axis, and defines a characteristic line L1 that associates the chilled water temperature with the opening of the control valve 30.

[0036] The temperature-opening map is created to prevent the cold water in the cold water coil 14 from freezing. For example, based on past data, the opening of the control valve 30 that can prevent freezing is plotted for each return cold water temperature.

[0037] For example, a plurality of data sets are obtained from past records regarding the temperature of the return chilled water, the opening of the control valve 30, and whether or not the return water pipe 28 is frozen at a constant discharge pressure of a pump having a rated output equivalent to that of the pump 60. The chilled water temperature detected by the water temperature sensor 32 is obtained as the temperature of the return chilled water.

[0038] These multiple data sets based on past performance are plotted on a temperature-opening map, and a characteristic line L1 is determined so as to pass through plots where the return water pipe 28 was not frozen. For example, the characteristic line L1 is determined as a boundary line between a plot group where the return water pipe 28 was frozen (frozen plot group) and a plot group where the return water pipe 28 was not frozen (freezing avoided plot group). Alternatively, the characteristic line L1 is determined in an area closer to the freezing avoided plot group than the boundary line.

[0039] In Fig. 3, a straight line is shown as the characteristic line L1, but the shape of the characteristic line L1 is determined according to the distribution of the above two plot groups. However, qualitatively, the higher the detected cold water temperature Tm, the more the opening command value A* of the control valve 30 required for freezing prevention is narrowed. In other words, the characteristic line L1 has a shape that slopes downward to the right as a whole.

[0040] The temperature-based opening calculation unit 54 plots the cold water temperature Tm detected by the water temperature sensor 32 on a temperature-opening map, and determines the control valve opening command value A* corresponding to the detected cold water temperature Tm.

[0041] The temperature-based flow rate calculation unit 56 stores a temperature-flow rate map (TQ map) as shown in Fig. 4. The temperature-flow rate map has the return chilled water temperature on the horizontal axis and the target flow rate of the return chilled water passing through the control valve 30 on the vertical axis, and defines a characteristic line L2 that associates the chilled water temperature with the chilled water flow rate.

[0042] The temperature-flow rate map is created to prevent freezing of the chilled water in the chilled water coil 14. For example, based on past data, the chilled water flow rate that can prevent freezing is plotted for each return chilled water temperature.

[0043] For example, multiple data sets are obtained from past performance data regarding the temperature of the return chilled water, the flow rate of the return chilled water, and whether or not the return water piping 28 is frozen at a constant discharge pressure of a pump with the same rated output as pump 60.

[0044] These multiple data sets based on past performance are plotted on a temperature-flow rate map. A characteristic line L2 is determined so as to pass through plots where the return water pipe 28 was not frozen. For example, the characteristic line L2 is determined as a boundary line between a plot group where the return water pipe 28 was frozen (frozen plot group) and a plot group where the return water pipe 28 was not frozen (freezing avoided plot group). Alternatively, the characteristic line L2 is determined in an area closer to the freezing avoided plot group than the boundary line.

[0045] In Fig. 4, a straight line is shown as the characteristic line L2, but the shape of the characteristic line L2 is determined according to the distribution of the two plot groups mentioned above. However, qualitatively, the higher the detected chilled water temperature Tm, the smaller the target chilled water flow rate Q* required to prevent freezing can be. In other words, the characteristic line L2 has a shape that slopes downward to the right as a whole.

[0046] The temperature-based flow rate calculation unit 56 plots the detected cold water temperature Tm obtained from the water temperature sensor 32 on a temperature-flow rate map, and determines the target flow rate Q* of the return cold water corresponding to the temperature Tm.

[0047] In addition, considering that theoretically the main factor in suppressing freezing of the return cold water flowing through the return water piping 28 is the flow velocity of the return cold water, a temperature-flow velocity map (TV map) may be used instead of a temperature-flow rate map (TQ map).

[0048] For example, the flow velocity V is calculated based on the inner diameter of each pipe for the data group based on past performance used in creating the temperature-flow rate map of Fig. 4. Furthermore, on a plane with the horizontal axis of Fig. 4 representing the flow velocity, data based on past performance, for example, a set of data representing the temperature of the return chilled water, the flow velocity of the return chilled water, and whether or not the return water pipe 28 is frozen at a constant discharge pressure of a pump with a rated output equivalent to that of pump 60, is plotted.

[0049] Furthermore, a characteristic line L2' is determined so as to pass through the plots among the above-mentioned plot groups where the return water pipe 28 was not frozen. For example, the characteristic line L2' is determined as a boundary line between the plot group where the return water pipe 28 was frozen (frozen plot group) and the plot group where the return water pipe 28 was not frozen (freezing avoided plot group). Alternatively, the characteristic line L2' is determined in an area closer to the freezing avoided plot group than the above-mentioned boundary line.

[0050] In this case, the temperature-based flow rate calculation unit 56 plots the return chilled water temperature Tm acquired from the water temperature sensor 32 on a temperature-flow rate map, and calculates a target flow rate V* of the return chilled water corresponding to the temperature Tm. Furthermore, the temperature-based flow rate calculation unit 56 calculates a target flow rate Q* based on the target flow rate V* and the inner diameter φ of the return water pipe 28.

[0051] The opening adjustment unit 58 calculates an opening adjustment value ΔA for the control valve 30 based on the difference between the actual measured flow rate Qm after the opening command value A* calculated by the temperature-based opening calculation unit 54 is set as the set opening of the control valve 30 and the target flow rate Q* calculated by the temperature-based flow calculation unit 56.

[0052] The opening adjustment unit 58 stores an opening adjustment map as shown in Fig. 5. The opening adjustment map has a differential flow rate ΔQ obtained by subtracting the actual measured flow rate Qm from the target flow rate Q* on the horizontal axis, an opening adjustment value ΔA to the control valve 30 on the vertical axis, and a characteristic line L3 that associates the differential flow rate ΔQ with the opening adjustment value ΔA.

[0053] The opening adjustment map is created to ensure a sufficient flow rate of chilled water to freeze the chilled water in the chilled water coil 14, and is obtained from, for example, past data. If the measured flow rate Qm does not reach the target flow rate Q*, that is, if ΔQ>0, even though the opening setting of the control valve 30 is set to the opening command value A*, the water supply pressure in the chilled water circulation path including the pump 60 and the control valve 30 may have decreased. For example, the water supply pressure may decrease due to deterioration of the pump 60, deterioration of the piping, or sudden opening and closing of the control valve of another air conditioner branching off from the chiller 62.

[0054] Even in such a case, characteristic line L3 is determined to ensure a flow rate necessary and sufficient to prevent freezing of the chilled water coil 14. Qualitatively, characteristic line L3 is shaped such that the opening adjustment value ΔA increases as the differential flow rate ΔQ increases. For example, characteristic line L3 is expressed as a linear function with a positive slope starting from the origin (ΔQ=0, ΔA=0).

[0055] When ΔQ is equal to or less than zero (ΔQ≦0), that is, when the measured flow rate Qm is equal to or greater than the target flow rate Q*, the set opening A* is maintained at the value that was set once, because a flow rate sufficient to prevent freezing of the chilled water coil 14 is ensured. That is, the characteristic line L3 has a value of ΔA=0 in the region where ΔQ≦0.

[0056] <Freezing prevention flow> 6 illustrates an example of an opening setting flow by the controller 12, which is a control device. The controller 12 acquires the temperature Tm of the return chilled water flowing through the return water pipe 28 from the water temperature sensor 32 (S10). Next, the controller 12 determines whether or not the detected chilled water temperature Tm is below a predetermined threshold temperature (below an anti-freeze threshold temperature) (S12). The threshold temperature is, for example, a temperature at which the chilled water does not freeze in the chilled water coil 14 even if the control valve 30 is fully closed, and is, for example, +5°C.

[0057] If the detected chilled water temperature Tm is equal to or higher than the threshold temperature, the process waits for a predetermined period of time (S30), then proceeds to the end of this flow (Return) and returns to the start point (Start) of the flow again. If the detected chilled water temperature Tm is lower than the threshold temperature (lower than the freeze prevention threshold temperature), the controller 12 acquires the flow rate Qm0 of the return chilled water flowing through the return water pipe 28 (S14).

[0058] Next, the controller 12 sets the opening of the control valve 30 to prevent freezing. Furthermore, the temperature-based opening calculation unit 54 refers to the characteristic line L1 of the TA map (FIG. 3) to determine an opening command value A* corresponding to the detected cold water temperature Tm obtained in step S10 (S20). The determined opening command value A* becomes the set opening of the control valve 30 (S22), and the control valve 30 opens the valve until it reaches the opening command value A*. After the set opening of the control valve 30 is set to the opening command value A*, for example, one minute after the setting, the opening adjustment unit 58 obtains the actual measured flow rate Qm1 of the return cold water from the flow sensor 34 (S24).

[0059] Here, in parallel with the process of obtaining the opening command value A* in step S20, the target flow rate Q* is obtained (S18). The temperature-based flow rate calculation unit 56 obtains the target flow rate Q* corresponding to the detected chilled water temperature Tm obtained in step S10 by referring to the characteristic line L2 of the TQ map.

[0060] The opening adjustment unit 58 calculates a differential flow rate ΔQ by subtracting the measured return chilled water flow rate Qm1 calculated in step S24 from the target flow rate Q*. Furthermore, the opening adjustment unit 58 calculates an opening adjustment value ΔA corresponding to the differential flow rate ΔQ by referring to the characteristic line L3 of the opening adjustment map in Fig. 5 (S26). Note that, as described above, when the differential flow rate ΔQ≦0, ΔA=0.

[0061] Furthermore, the controller 12 resets the opening of the control valve 30 in the direction increasing it by ΔA (S28). For example, the controller 12 resets the set opening of the control valve 30 to a value (A*+ΔA) obtained by adding the opening adjustment value ΔA to the already set opening command value A*. Note that if ΔA=0, the set opening is maintained at the opening command value A*. After a further waiting period (S30), the flow in FIG. 6 is returned to the starting point (Start).

[0062] In the above-described embodiment, the opening degree of the control valve 30 is adjusted to prevent freezing of the cold water in the cold water coil 14, but the anti-freeze system for an air conditioner and the control device for an air conditioner according to the present embodiment are not limited to this form. For example, when the supply of hot water to the hot water coil 20 is stopped, the hot water remaining in the hot water coil 20 may freeze due to outside air passing through the hot water coil 20. Therefore, a water temperature sensor and a flow rate sensor may also be provided in the hot water return pipe 38, and the opening degree setting flow of Fig. 6 may be executed by the controller 12 for the control valve 40 of the return pipe 38. [Explanation of symbols]

[0063] 10 air conditioner, 12 controller (control device), 14 cold water coil, 16 damper, 18 damper motor, 20 hot water coil, 22 air supply fan, 24 outdoor air duct, 26 cold water supply pipe, 28 cold water return pipe, 30 control valve, 32 water temperature sensor, 34 flow sensor, 42 air supply duct, 52 air supply temperature sensor, 54 temperature-based opening calculation unit, 56 temperature-based flow rate calculation unit, 58 opening adjustment unit, 60, 70 pump, 62 chiller, 72 boiler.

Claims

1. A chilled water coil, into which chilled water is supplied from a water supply pipe by a pump and heat exchange is performed with air passing through the chilled water coil; a control valve provided in a return water pipe to which the return cold water from the cold water coil is sent, the control valve adjusting the flow rate of the return cold water; A water temperature sensor and a flow rate sensor provided in the return water pipe; a control device that generates an opening command for the control valve based on a detected cold water temperature detected by the water temperature sensor; An anti-freezing system for an air conditioner comprising: The pump has a discharge pressure set to a constant value, When the detected cold water temperature is less than a predetermined anti-freeze threshold temperature, the control device A position command value corresponding to the detected chilled water temperature is obtained from a temperature-position map in which the chilled water temperature is associated with the position of the control valve, the map being based on data obtained from the operation record of the pump when the discharge pressure is the set value and when the return water pipe is not frozen; A target flow rate corresponding to the detected chilled water temperature is calculated from a temperature-flow rate map in which chilled water temperature and chilled water flow rate are correlated based on data obtained from the operation record of the pump when the discharge pressure is the set value and when the return water pipe is not frozen; A differential flow rate is calculated by subtracting an actual measured flow rate of the return water pipe after the opening of the control valve is set to the opening command value from the target flow rate; resetting the opening command value in an increasing direction when the differential flow rate is a positive value, while maintaining the opening command value when the differential flow rate is a value equal to or less than zero; Anti-freeze system for air conditioners.

2. A chilled water coil, into which chilled water is supplied from a water supply pipe by a pump and heat exchange is performed with air passing through the chilled water coil; a control valve provided in a return water pipe to which the return cold water from the cold water coil is sent, the control valve adjusting the flow rate of the return cold water; A water temperature sensor and a flow rate sensor provided in the return water pipe; A control device for an air conditioner, the control device generating an opening command for the control valve based on a detected cold water temperature detected by the water temperature sensor, The pump has a discharge pressure set to a constant value, a temperature-based opening calculation unit that, when the detected cold water temperature is lower than a predetermined anti-freeze threshold temperature, determines an opening command value corresponding to the detected cold water temperature from a temperature-opening map that associates the cold water temperature with the opening of the control valve based on data obtained from the operation record of the pump when the discharge pressure is at the set value and when the return water pipe is not frozen; a temperature-based flow rate calculation unit that calculates a target flow rate corresponding to the detected chilled water temperature from a temperature-flow rate map that correlates chilled water temperature and chilled water flow rate based on data obtained from the operation record of the pump when the discharge pressure is the set value and when the return water pipe is not frozen; an opening adjustment unit that calculates a differential flow rate by subtracting an actual measured flow rate of the return water piping after the opening of the control valve is set to the opening command value from the target flow rate, and resets the opening command value in an increasing direction when the differential flow rate has a positive value, while maintaining the opening command value when the differential flow rate has a value of zero or less; A control device for an air conditioner, comprising:

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