Patent Publication Number: US-2022228766-A1

Title: Device management apparatus, heat source system, management apparatus, and device management system

Description:
TECHNICAL FIELD 
     The present disclosure relates to a device management apparatus, a heat source system, a management apparatus, and a device management system. 
     BACKGROUND ART 
     There has been available a heat source system including a plurality of refrigerating machines through which a heat medium circulates, such as a refrigeration system described in PTL 1 (Japanese Unexamined Patent Application Publication No. 10-89742). Some of such heat source systems are configured to perform control to change the number of refrigerating machines in operation to change the refrigerating capacity of the refrigerating machines in accordance with the amount of heat to be supplied. To suppress hunting of a control variable in such a refrigeration system, for example, a method in the refrigeration system described in PTL 1 for adjusting a control gain on the basis of the number of refrigerating machines in operation, the operating state of the refrigerating machines, the outside air temperature, and so on is disclosed. 
     SUMMARY OF INVENTION 
     &lt;Technical Problem&gt; 
     However, the adjustment of the control gain based on the number of refrigerating machines in operation, the operating state of the refrigerating machines, the outside air temperature, and so on, as described in PTL 1, involves complex control, and it is difficult to manufacture and adjust the heat source system. 
     A device management system for managing a specific device that changes the state of a heat medium circulating through a heat source system has to address reducing extra change operations for the capacity of the specific device without increasing the complexity of the heat source system. 
     &lt;Solution to Problem&gt; 
     A device management apparatus according to a first aspect is a device management apparatus for managing a specific device that changes a state of a heat medium circulating through a heat source system. The device management apparatus receives a state value of the heat medium that is measured by a sensor included in the heat source system, and prohibits a change operation of a capacity of the specific device on the basis of a parameter related to a change in the state value. 
     The device management apparatus according to the first aspect can reduce extra change operations of the capacity of the specific device with a simple configuration. 
     A device management apparatus according to a second aspect is the device management apparatus according to the first aspect, in which the parameter includes a variable related to at least one of the number of extreme values of the state value and a fluctuation range of the state value in a predetermined period. 
     The device management apparatus according to the second aspect can reduce unnecessary change operations in a situation where the state value is unstable. 
     A device management apparatus according to a third aspect is the device management apparatus according to the second aspect, in which the parameter is a variable related to the number of extreme values of the state value and a variance of the state value in the predetermined period. 
     The device management apparatus according to the third aspect can improve the accuracy of suppressing unnecessary operations in accordance with the behavior of fluctuations in the state value. 
     A device management apparatus according to a fourth aspect is the device management apparatus according to any of the first aspect to the third aspect, in which the device management apparatus determines a threshold value of the parameter indicating a limit for prohibiting the change operation of the capacity of the specific device, from a relationship between a value of the parameter and the number of times the capacity of the specific devices is changed. 
     The device management apparatus according to the fourth aspect can easily prohibit the change operation of the capacity of the specific device at an appropriate timing by using the threshold value. 
     A heat source system according to a fifth aspect is the system according to any of the first aspect to the fourth aspect, in which the device management apparatus notifies whether the device management apparatus is in a state in which the change operation is prohibited or in a state in which the change operation is not prohibited. 
     The heat source system according to the fifth aspect can inform outside of the management state. 
     A heat source system according to a sixth aspect includes a specific device that changes a state of a heat medium circulating through the heat source system, a sensor that measures the state of the heat medium, and a device management apparatus that receives a state value of the heat medium that is measured by the sensor and prohibits a change operation of a capacity of the specific device on the basis of a parameter related to a change in the state value, in which the sensor is a temperature sensor that measures a temperature of the heat medium, a flow rate sensor that measures a flow rate of the heat medium, or a pressure sensor that measures a pressure of the heat medium. 
     The heat source system according to the sixth aspect can reduce extra change operations of the capacity of the specific device with a simple configuration in which the value of the temperature, flow rate, or pressure of the heat medium is used as the state value of the heat medium. 
     A heat source system according to a seventh aspect is the system according to the sixth aspect, in which the specific device is a heat source device that changes the temperature of the heat medium, the sensor is an outlet temperature sensor that measures a temperature of the heat medium exiting from the heat source device, and when a difference between an outlet temperature measured by the outlet temperature sensor and a target temperature is larger than a predetermined value, the prohibition of the change operation of a capacity of the heat source device to change the temperature of the heat medium is canceled. 
     The heat source system according to the seventh aspect can appropriately perform the change operation of the capacity when the difference between the outlet temperature and the target temperature is large and the capacity is to be changed. 
     A heat source system according to an eighth aspect is the system according to the sixth aspect or the seventh aspect, in which the specific device is a chiller, a cooling tower, or a pump. 
     The heat source system according to the eighth aspect can reduce extra change operations of the capacity of the chiller, the cooling tower, or the pump with a simple configuration. 
     A device management apparatus according to a ninth aspect is a device management apparatus for managing a heat source device that changes a temperature of a heat medium circulating through a heat source system. The device management apparatus determines a standby time in accordance with a parameter relating to a circulation flow rate of the heat medium, the standby time being a time for prohibiting a change operation for a predetermined period from a previous change operation, the change operation being an operation for changing a capacity of the heat source device to change the temperature of the heat medium, and prohibits the change operation of the capacity of the heat source device during the standby time. 
     The device management apparatus according to the ninth aspect can perform management in which suppression of an increase in the energy consumption of the heat source system and comfort are balanced. 
     A device management apparatus according to a tenth aspect is the device management apparatus according to the ninth aspect, in which a plurality of the heat source devices are provided, and the change operation is to change the number of heat source devices that are in operation. 
     The device management apparatus according to the tenth aspect can perform management, in which suppression of an increase in energy consumption and comfort are balanced, on the heat source system including a plurality of heat source devices. 
     A device management apparatus according to an eleventh aspect is the device management apparatus according to the ninth aspect or the tenth aspect, in which the parameter is a variable related to at least one of a capacity of a circulation pump that circulates the heat medium, a degree of flow rate adjustment of a use-side device that uses the heat medium, and a pressure difference between the heat medium flowing into the use-side device and the heat medium flowing out of the use-side device. 
     The device management apparatus according to the eleventh aspect can easily determine the standby time by using at least one of the capacity of the circulation pump, the degree of flow rate adjustment, and the pressure difference of the heat medium. 
     A device management apparatus according to a twelfth aspect is the device management apparatus according to any of the ninth aspect or the tenth aspect, in which the parameter is a variable related to a flow rate of a circulation pump that circulates the heat medium, or a variable related to the flow rate of the circulation pump and a retained amount of water in the heat source system. 
     The device management apparatus according to the twelfth aspect determines the standby time by using the flow rate of the circulation pump, which makes the standby time more likely to be appropriate for the circulation of the heat medium. 
     A device management apparatus according to a thirteenth aspect is the device management apparatus according to the twelfth aspect, in which the retained amount of water is a value described in a design specification or a value calculated from a pipe length and a pipe cross-sectional area described in a drawing. 
     A device management apparatus according to a fourteenth aspect is the device management apparatus according to any of the ninth aspect to the thirteenth aspect, further including an outlet temperature sensor that measures a temperature of the heat medium exiting from the heat source device, in which when a difference between an outlet temperature measured by the outlet temperature sensor and a target temperature is larger than a predetermined value, the prohibition of the change operation of the capacity of the heat source device to change the temperature of the heat medium is canceled. 
     The management apparatus according to the fourteenth aspect can improve the accuracy of management of the heat source device in which suppression of an increase in energy consumption and comfort are balanced at the time of activation of the heat source system. 
     A management apparatus according to a fifteenth aspect is the management apparatus according to any of the ninth aspect to the fourteenth aspect, in which the management apparatus notifies whether the management apparatus is in a state in which the change operation is prohibited or in a state in which the change operation is not prohibited. 
     The management apparatus according to the fifteenth aspect can inform outside of the management state. 
     A heat source system according to a sixteenth aspect includes a chiller, a cooling tower, or a water heater that changes a temperature of a heat medium circulating through the heat source system, and a management apparatus that determines a standby time in accordance with a parameter relating to a circulation flow rate of the heat medium, and prohibits a change operation for changing a capacity of the chiller, the cooling tower, or the water heater until a time interval from a previous change operation exceeds the standby time. 
     The heat source system according to the sixteenth aspect can perform management, in which suppression of an increase in the energy consumption of the heat source system and comfort are balanced, on the chiller, the cooling tower, or the water heater. 
     A device management system according to a seventeenth aspect is a system for managing the number of operating devices among heat source devices. The device management system includes a number-of-device determination unit and a standby time determination unit. The number-of-device determination unit determines an increase or a decrease in the number of operating devices when a condition for changing the number of operating devices regarding a thermal load is continuously satisfied for a predetermined standby time. The standby time determination unit determines a length of the standby time on the basis of predicted thermal load information. 
     This contributes to controlling the number of operating devices among the heat source devices to an appropriate number. 
     A device management system according to an eighteenth aspect is the system according to the seventeenth aspect, further including a thermal load calculation unit and an accumulation unit. The thermal load calculation unit calculates thermal load information. The accumulation unit accumulates the thermal load information calculated by the thermal load calculation unit. The predicted thermal load information is calculated on the basis of the thermal load information accumulated in the accumulation unit. 
     Accordingly, the number of operating devices among the heat source devices is controlled to an appropriate number on the basis of the actual thermal load. 
     A device management system according to a nineteenth aspect is the system according to the seventeenth aspect or the eighteenth aspect, in which the standby time determination unit, on the basis of the predicted thermal load information, reduces the length of the standby time in a case where the number of operating devices among the heat source devices is predicted to be insufficient. Alternatively, the standby time determination unit increases the length of the standby time in a case where the number of operating devices among the heat source devices is predicted to be excessive. 
     This suppresses an insufficiency in the number of operating devices among the heat source devices or an excess in the number of operating devices among the heat source devices and contributes to controlling the number of operating devices among the heat source devices to an appropriate number. 
     A device management system according to a twentieth aspect is the system according to any of the seventeenth aspect to the nineteenth aspect, in which the accumulation unit accumulates information on the number of operating devices among the heat source devices for processing the thermal load, in association with the thermal load information. 
     A device management system according to a twenty-first aspect is the system according to any of the seventeenth aspect to the twentieth aspect, in which the thermal load calculation unit calculates the thermal load information on the basis of an inlet temperature that is a temperature of a heat medium entering the heat source devices and an outlet temperature that is a temperature of the heat medium exiting from the heat source devices. The accumulation unit further accumulates the thermal load information calculated by the thermal load calculation unit, weather information, and/or operating device information of the heat source devices in association with each other. 
     A device management system according to a twenty-second aspect is the system according to any of the seventeenth aspect to the twenty-first aspect, in which the standby time determination unit determines, as the length of the standby time, a value obtained by, in a case where the number of occurrences of a predicted thermal-load local maximum value included in the predicted thermal load information is one, dividing a time required from an operating start time of the heat source devices to a time at which the predicted thermal-load local maximum value occurs by the required number of times the number of devices is increased to make the number of operating devices among the heat source devices at a time of occurrence of the predicted thermal-load local maximum value. The predicted thermal-load local maximum value is a local maximum value of predicted values of the thermal load included in the predicted thermal load information. 
     Accordingly, in a case where the number of occurrences of the predicted thermal-load local maximum value is one, the number of operating devices among the heat source devices is controlled to an appropriate number. 
     A device management system according to a twenty-third aspect is the system according to any of the seventeenth aspect to the twenty-second aspect, in which in a case where the number of occurrences of a predicted thermal-load local maximum value included in the predicted thermal load information is plural, the standby time determination unit sets the length of the standby time from a time at which the predicted thermal-load local minimum value included in the predicted thermal load information occurs until the predicted thermal-load local maximum value next occurs, to a value obtained by dividing a time required from the time at which the predicted thermal-load local minimum value included in the predicted thermal load information occurs until the predicted thermal-load local maximum value next occurs by the number of times the number of operating devices is increased or decreased in the time slot. The predicted thermal-load local maximum value is a local maximum value of predicted values of the thermal load included in the predicted thermal load information. The predicted thermal-load local minimum value is a local minimum value of predicted values of the thermal load included in the predicted thermal load information. 
     Accordingly, in a case where the number of occurrences of the predicted thermal-load local maximum value is plural, the number of operating devices among the heat source devices is controlled to an appropriate number. 
     A device management system according to a twenty-fourth aspect is the system according to any of the seventeenth aspect to the twenty-second aspect, in which the standby time determination unit calculates a time at which the number of operating devices among the heat source devices is increased or decreased, on the basis of the thermal load information and the information on the number of operating devices among the heat source devices. Further, the standby time determination unit sets, as the length of the standby time, a time period from when the number of operating devices is changed to when the number of operating devices is next changed. 
     This contributes to controlling the number of operating devices among the heat source devices to an appropriate number. 
     A device management system according to a twenty-fifth aspect is the system according to any of the seventeenth aspect to the twenty-fourth aspect, further including a deviation information output unit. The deviation information output unit outputs deviation information in a case where a deviation of an actual thermal load in the heat source devices from the thermal load information is larger than a predetermined threshold value. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a block diagram illustrating an overview of an example configuration of a heat source system according to an embodiment. 
         FIG. 2  is a block diagram illustrating an overview of an example detailed configuration of the heat source system according to the embodiment. 
         FIG. 3  is a flowchart for describing a determination flow for prohibiting a change operation of the capacity of a specific device. 
         FIG. 4A  is a graph for describing pull-down rate control. 
         FIG. 4B  is a graph for describing a problem of pull-down rate control. 
         FIG. 4C  is a graph for describing pull-up rate control. 
         FIG. 5A  is a graph illustrating an example gradual temperature change with large amplitudes and long periods. 
         FIG. 5B  is a graph illustrating an example fine temperature change with small amplitudes and short periods. 
         FIG. 6  is a graph for describing types of temperature changes. 
         FIG. 7  is a graph for describing the number of extreme values of temperature changes. 
         FIG. 8  is a graph for describing variances of temperature changes. 
         FIG. 9  is a graph for describing values of parameters related to temperature changes. 
         FIG. 10  is a block diagram illustrating an overview of an example configuration of a heat source system according to an embodiment. 
         FIG. 11  is a block diagram illustrating an overview of an example detailed configuration of the heat source system according to the embodiment. 
         FIG. 12  is a graph for describing an example parameter relating to the circulation flow rate of a heat medium. 
         FIG. 13  is a graph for describing another example parameter relating to the circulation flow rate of the heat medium. 
         FIG. 14  is a block diagram illustrating an overview of an example configuration of a heat source system according to Modification 2A. 
         FIG. 15  is a block diagram illustrating an overview of an example configuration of a heat source system according to Modification 2B. 
         FIG. 16  is a block diagram illustrating an overview of an example configuration of a heat source system according to Modification 2C. 
         FIG. 17  is a block diagram illustrating an overview of an example configuration of a heat source system according to Modification 2D. 
         FIG. 18  is a schematic configuration diagram of a device management system. 
         FIG. 19  is a schematic configuration diagram of a chiller unit. 
         FIG. 20  is a block diagram illustrating the configuration and functional units of a controller. 
         FIG. 21  is a graph illustrating a thermal load. 
         FIG. 22  is a graph illustrating predicted values of the thermal load. 
         FIG. 23  is a flowchart illustrating a process flow for determining a standby time. 
         FIG. 24  is a graph illustrating predicted values of the thermal load, 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     First Embodiment 
     (1) Overall Configuration 
     As illustrated in  FIG. 1 , a heat source system  1  includes heat source devices  10 , a use-side device  20 , a flow path  30 , a pump  40 , and a device management apparatus  50 . The heat source devices  10  are devices each configured to change the temperature of a heat medium circulating through the heat source system  1 . In other words, in this embodiment, the heat source devices  10  are each a specific device configured to change the state of a heat medium circulating through the heat source system  1 . Examples of the heat source devices  10  include chillers, cooling towers, and water heaters. The use-side device  20  is a device that uses the heat medium. Examples of the use-side device  20  include an air handling unit, a fan coil unit, and an air conditioner including a water heat exchanger. The heat source system  1  according to this embodiment includes three heat source devices  11 ,  12 , and  13 . Reference numeral “ 10 ” is used to indicate all of the heat source devices, and reference numerals “ 11 ,  12 , and  13 ” are used to indicate individual heat source devices. In embodiments, the three heat source devices  11 ,  12 , and  13  will be described as an example. However, the heat source system  1  may include two heat source devices or four or more heat source devices. 
     The flow path  30  is mainly a pipe connecting the heat source devices  10  and the use-side device  20 . The heat medium of the heat source system  1  circulates between the heat source devices  10  and the use-side device  20  through the flow path  30 . The flow path  30  includes a return header  31  and a feed header  32 . Water fed out of the pump  40  is distributed to the heat source devices  11  to  13  by the return header  31 . Cold water exiting from the heat source devices  11  to  13  is mixed by the feed header  32  and fed to the use-side device  20 . The pump  40  applies pressure to the heat medium in the flow path  30  to circulate the heat medium. The pump  40  is configured to be capable of changing the amount of circulation of the heat medium circulating through the flow path  30 . Examples of the method for changing the amount of circulation include a method for changing the number of revolutions of the pump  40 , which is of a variable capacity type and is inverter controlled, according to the frequency of the inverter to change the amount of discharge. Other examples of the method for changing the amount of circulation include a method for connecting a plurality of constant-speed pumps, which rotate at constant speeds, in parallel and changing the number of constant-speed pumps to be operated. 
     The device management apparatus  50  manages the heat source devices  10 . The device management apparatus  50  has a function of determining whether to prohibit a change operation, on the basis of a parameter related to a change in state value. The device management apparatus  50  prohibits a change operation for changing the capacity of the heat source devices  10 , on the basis of a parameter related to a change in state value. In this embodiment, the change operation prohibited by the device management apparatus  50  is an operation of changing the number of heat source devices  10  that are in operation. 
     The device management apparatus  50  includes a number control controller  51  for performing number control of the heat source devices  10 . The number control controller  51  includes a determination unit  52 , a change operation prohibition unit  53 , and a notification unit  54 . The determination unit  52  determines whether to prohibit a change operation on the basis of a parameter related to a change in state value. The change operation prohibition unit  53  prohibits the change operation of the capacity of the heat source devices  10  on the basis of the determination result of the determination unit  52 . In the device management apparatus  50 , the notification unit  54  notifies whether the device management apparatus  50  is in a state in which the change operation is prohibited or in a state in which the change operation is not prohibited. Examples of the notification method performed by the notification unit  54  include a method of notifying a state in which the change operation is prohibited by using a buzzer, a method of notification by displaying, on a display device, whether to prohibit the change operation, and a method of transmitting information indicating whether to provide notification via a public line. 
     The device management apparatus  50  is implemented by, for example, a computer. The device management apparatus  50  includes a control calculation device and a storage device. The control calculation device can be implemented using a processor such as a CPU or a GPU. The control calculation device reads a program stored in the storage device and performs predetermined image processing and calculation processing in accordance with the program. Further, the control calculation device can write a calculation result to the storage device or read information stored in the storage device in accordance with the program.  FIG. 1  illustrates various functional blocks of the device management apparatus  50  implemented by the control calculation device. The storage device can be used as a database. The device management apparatus  50  may be installed in a property such as a building in which the heat source devices  10  are installed, or may be installed in a remote place away from the property. Examples of the installation in a remote place include installation of the device management apparatus  50  in a cloud server (computer) configured to he capable of communicating with the heat source devices  10 . 
     (2) Detailed Configuration 
     A description will be given here of a case where the device management apparatus  50  uses the temperature of the heat medium as a state value of the heat medium and prohibits a change operation of the capacity of the specific devices on the basis of a temperature change of the heat medium as a parameter related to a change in state value. In the description of a determination flow, a description will be given of a case where the three heat source devices  11 ,  12 , and  13  are chillers. As illustrated in  FIG. 2 , in a case where the heat source devices  10  are chillers  111 ,  121 , and  131 , the heat medium is water, and cold water is fed from the chillers  111 ,  121 , and  131  to the use-side device  20  through the flow path  30 . The heat source system  1  includes an outlet temperature sensor  63  arranged downstream of the feed header  32 . The outlet temperature sensor  63  detects the temperature of the cold water fed out of the feed header  32 , The determination unit  52  receives the temperature of the cold water detected by the outlet temperature sensor  63  as a state value. 
     (2-1) Example Configuration of Heat Source System  1   
     A description will be given of a case where, as illustrated in  FIG. 2 , the use-side device  20  of the heat source system  1  includes four fan coil units  201 ,  202 ,  203 , and  204 . The fan coil units  201  to  204  cool spaces to be air conditioned (not illustrated) using cold water fed from the chillers  111 ,  121 , and  131 . Each of the fan coil units  201  to  204  includes a flow rate adjustment valve  21 , an air heat exchanger  22 , and a fan  23 . The air heat exchanger  22  performs heat exchange between the cold water fed from the chillers  111 ,  121 , and  131  and the air in the space to be air conditioned. The flow rate adjustment valve  21  adjusts the flow rate of the cold water to be caused to flow to the air heat exchanger  22 . The fan  23  generates a flow of air that passes through the air heat exchanger  22 . 
     The heat source system  1  includes an inlet temperature sensor  61 , differential pressure sensors  62 , and the outlet temperature sensor  63 . The inlet temperature sensor  61  measures the return water temperature. The return water temperature is the temperature of water returning to the chillers  111 ,  121 , and  131 . The differential pressure sensors  62  measure a differential pressure between the pressure of cold water to be fed to the fan coil units  201  to  204  and the pressure of water returning from the fan coil units  201  to  204 . 
     The pump  40  is inverter controlled and is configured to be capable of changing a discharge amount. The device management apparatus  50  controls the discharge amount of the pump  40  so that the differential pressure detected by the differential pressure sensors  62  is constant. 
     (2-2) Example Operation of Heat Source System  1   
     Each of the chillers  111 ,  121 , and  131  includes therein a water heat exchanger (not illustrated) and a chiller controller (not illustrated). The respective chiller controllers of the chillers  111 ,  121 , and  131  individually perform control for the chillers  111 ,  121 , and  131  so that the outlet water temperature of each of the chillers  111 .  121 , and  131  becomes a set water temperature. The set water temperature is the temperature of the heat medium (water) sent out of a device that is in operation among the chillers  111 ,  121 , and  131 . 
     The operation of the heat source system  1  will be described taking as an example a case where the heat source system  1  is operated in a stable state with a set water temperature of 7° C. and a return water temperature of 13° C. It is assumed that, in this stable state, the chiller  111  is in operation (in an on state) and the chillers  121  and  131  are at a stop (in an off state). It is also assumed that the chiller  111  is operated at a capacity of 50% of the maximum capacity in the stable state. 
     If the load of the fan coil units  201  to  204  rapidly increases, a larger amount of heat needs to be processed by the fan coil units  201  to  204 . Accordingly, the fan coil units  201  to  204  open the flow rate adjustment valves  21  to allow a large amount of cold water to flow to the air heat exchangers  22 . When the flow rate adjustment valves  21  are opened, the differential pressure detected by the differential pressure sensors  62  decreases. When the differential pressure sensors  62  detect such a decrease in differential pressure, the device management apparatus  50 , which has received the detection result of the differential pressure sensors  62 , performs control to increase the discharge amount of the pump  40  and return the differential pressure to the original state. 
     With the rapid increase in the load of the fan coil units  201  to  204 , the chiller  111  needs to process a larger amount of heat and thus increases the capacity from 50% to 100%, for example. If the capacity of the chiller ill is still insufficient even after the capacity of the chiller  111  reaches 100% (maximum capacity), for example, the return water temperature increases to 19° C., and the temperature of the cold water supplied from the chiller  111  increases to 12° C. 
     The device management apparatus  50  determines the number of heat source devices  10  to be operated from the capacity of the chiller  111  and the return water temperature. As described above, if the temperature of the cold water becomes higher than the set water temperature, the device management apparatus  50  causes the chiller  121  to also operate. The increase in the number of heat source devices  10  in operation is referred to as an increase in the number of operating devices. Conversely, the decrease in the number of heat source devices  10  in operation is referred to as a decrease in the number of operating devices. In the device management apparatus  50 , on the basis of the determination result of the determination unit  52 , the change operation prohibition unit  53  prohibits a change operation of the number of chillers in operation after the chiller  121  is additionally operated. 
     For example, with the additional operation of the chiller  121  described above, the water temperature of the cold water fed out of the feed header  32  changes from 12° C. to 10° C., and the return water temperature also changes from 19° C. to 16° C. with the passage of time. 
     With the further passage of time, for example, the water temperature of the cold water changes from 10° C. to 8° C., and the return water temperature also changes from 16° C. to 13° C. However, since the water temperature of the cold water fed out of the feed header  32 , which is 8° C., is higher than a set temperature of 7° C., the heat source system  1  may also operate the chiller  131  additionally. In such a case, even if the chillers  111 ,  121 , and  131  are operated at a capacity of 50%, the capacity of the heat source devices  10  becomes excessive, and the water temperature of the cold water fed out of the feed header  32  is likely to decrease to 6° C. (a temperature lower than the set temperature). As described above, if the capacity of the heat source devices  10  becomes excessive, the heat source system  1  is likely to attempt to decrease the number of operating devices. 
     To prevent the capacity of the heat source devices  10  from becoming excessive due to the increase in the number of operating devices described above, the device management apparatus  50  takes the rate of change in outlet temperature in a certain time period and prohibits an increase in the number of operating devices in a transitional state in which the change is large. 
     (3) Determination Flow 
     A determination flow performed by the determination unit  52  of the device management apparatus  50  will be described with reference to  FIG. 3 . The determination unit  52  performs pull-down rate control by using the temperature of the cold water. The determination unit  52  determines the pull-down rate of the outlet temperature of a chiller detected by the outlet temperature sensor  63 . In the pull-down rate control, a determination is made based on a temperature change between two points, namely, the start point in time and the end point in time of a certain time period (hereinafter also referred to as a window). An example calculation formula of the pull-down rate is equation (1) as follows. 
     
       
         
           
             
               
                 
                   
                     Pull-down rate 
                   
                   = 
                   
                     
                       ( 
                       
                         
                           temperature at start point in time of window 
                         
                         - 
                         
                           temperature at end point in time of window 
                         
                       
                       ) 
                     
                     + 
                     
                       ( 
                       
                         length of window 
                       
                       ) 
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
     The pull-down rate is expressed in [° C./minute], the temperature at the start point in time of the window and the temperature at the end point in time of the window are expressed in [° C.], and the length of the window is expressed in [minute]. 
     For example, if the temperature at the start point in time of the window is 12° C., the temperature at the end point in time of the window is 10° C., and the length of the window is 0.5 minutes (30 seconds), the pull-down rate is 4° C./minute. It is assumed that a preset first threshold value is 4° C./minute and that the first threshold value is stored in a memory (not illustrated) of the device management apparatus  50 . The determination unit  52  reads the first threshold value from the memory and determines that the pull-down rate of the outlet temperature of the chiller is greater than or equal to the first threshold value (Yes in step ST 1 ). 
     If the pull-down rate is greater than or equal to the first threshold value, the device management apparatus  50  prohibits additional operation of another chiller (step ST 2 ). 
     If the pull-down rate is less than the first threshold value (No in step ST 1 ), there is a possibility that the transitional state has been eliminated, or there is possibility that the transitional state has not been eliminated.  FIG. 1A  illustrates a typical temperature change of the cold water after the number of operating devices is increased. The temperature change of the cold water illustrated in  FIG. 4A  is a monotonic decrease. However, as illustrated in  FIG. 4B , the temperature of the cold water may oscillate after the number of operating devices is increased. If the temperature is oscillating, the determination unit  52  is more likely to be unable to perform appropriate determination. Consequently, if the temperature is oscillating, the change operation prohibition unit  53  is more likely to be unable to appropriately prohibit the change operation. For example, if the temperature at the start point in time of the window is 12° C. and the temperature at the end point in time of the window is 12° C., the pull-down rate is 0° C./minute even if the temperature temporarily decreases to 10° C. between the start point in time and the end point in time (even in a state in which the number of operating devices is to be increased). 
     To overcome the shortcoming of the pull-down rate control as described above, it is conceivable to reduce the length of the window (the time period from the start point in time to the end point in time). However, if the length of the window is reduced, the increase in the number of operating devices may be prohibited even for a gentle temperature change with oscillation, resulting in a failed increase in the number of operating devices at a timing when the number of operating devices is to he increased. Insufficient capacity of the chillers  111 ,  121 , and  131  may provide discomfort to persons in the spaces to be air conditioned by the fan coil units  201  to  204 . 
     A temperature oscillation as illustrated in  FIG. 4B  is determined to be a transitional state, which makes it more likely that better pull-down rate control can be performed. 
     Accordingly, even if the pull-down rate is greater than or equal to the first threshold value, the determination unit  52  makes a determination in steps ST 3  and ST 4  not to prohibit increasing the number of operating devices. 
     If the temperature difference between the outlet temperature of the chiller and the set temperature is greater than or equal to a predetermined value (Yes in step S 13 ), the determination unit  52  determines that the increase in the number of operating devices is not to be prohibited (step ST 5 ). The outlet temperature of the chiller is a temperature detected by the outlet temperature sensor  63  in the configuration in  FIG. 2 . 
     If the temperature difference between the outlet temperature of the chiller and the set temperature is less than the predetermined value (No in step ST 3 ), the determination unit  52  determines a parameter indicating a change in temperature (state value)) (step ST 4 ). If the determination unit  52  determines that the value of the parameter indicating a change in temperature is greater than or equal to a second threshold value (Yes in step ST 4 ), the change operation prohibition unit  53  prohibits increasing the number of operating devices (step ST 2 ). Conversely, if the determination unit  52  determines that the value of the. parameter indicating a change in temperature is less than the second threshold value (Yes in step ST 4 ), the change operation prohibition unit  53  does not prohibit increasing the number of operating devices (step ST 5 ). 
     To supply hot water, the determination unit  52  performs pull-up rate control, In the pull-up rate control, a determination is made based on a temperature change between two points, namely, the start point in time and the end point in time of a certain time period (window). An example calculation formula of the pull-up rate is equation (2) as follows. 
     
       
         
           
             
               
                 
                   
                     Pull-up rate 
                   
                   = 
                   
                     
                       ( 
                       
                         
                           temperature at end point in time of window 
                         
                         - 
                         
                           temperature at start point in time of window 
                         
                       
                       ) 
                     
                     + 
                     
                       ( 
                       
                         length of window 
                       
                       ) 
                     
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
     The pull-up rate is expressed in [° C./minute], the temperature at the start point in time of the window and the temperature at the end point in time of the window are expressed in [° C.], and the length of the window is expressed in [minute]. 
     For example, if the temperature at the start point in time of the window is 20° C., the temperature at the end point in time of the window is 22° C., and the length of the window is 0.5 minutes (30 seconds), the pull-up rate is 4° C./minute. It is assumed that a preset first threshold value is 4° C./minute and that the first threshold value is stored in a memory (not illustrated) of the device management apparatus  50 . In this case, the determination unit  52  reads the first threshold value from the memory and determines that the pull-up rate of the outlet temperature of the chiller is greater than or equal to the first threshold value. If the pull-down rate is greater than or equal to the first threshold value, the device management apparatus  50  prohibits additional operation of another chiller. 
     If the pull-up rate is less than the first threshold value, there is a possibility that the transitional state has been eliminated, or there is possibility that the transitional state has not been eliminated.  FIG. 4C  illustrates a typical temperature change of hot water after the number of operating devices is increased. The temperature change of the hot water illustrated in  FIG. 4C  is a monotonic increase. However, the temperature of the hot water may oscillate after the number of operating devices is increased. If the temperature is oscillating, the determination unit  52  is more likely to be unable to perform appropriate determination. Consequently, if the temperature is oscillating, the change operation prohibition unit  53  is more likely to be unable to appropriately prohibit the change operation. 
     A temperature oscillation is determined to be a transitional state, which makes it more likely that better pull-up rate control can be performed. Accordingly, even if the pull-up rate is greater than or equal to the first threshold value, the determination unit  52  makes a determination not to prohibit increasing the number of operating devices. 
     If the temperature difference between the outlet temperature of the chiller and the set temperature is greater than or equal to a predetermined value, the determination unit  52  determines that the increase in the number of operating devices is not to be prohibited. 
     If the temperature difference between the outlet temperature of the chiller and the set temperature is less than the predetermined value, the determination unit  52  determines a parameter indicating a change in temperature (state value). If the determination unit  52  determines that the value of the parameter indicating a change in temperature is greater than or equal to a second threshold value, the change operation prohibition unit  53  prohibits increasing the number of operating devices. Conversely, if the determination unit  52  determines that the value of the parameter indicating a change in temperature is less than the second threshold value, the change operation prohibition unit  53  does not prohibit increasing the number of operating devices. 
     (4) Parameter Related to Change in State Value 
     (4-1) Parameter Related to Change in Temperature 
     There are various patterns of change in temperature. Examples of the change in temperature include a gradual temperature change with large amplitudes and long periods (see  FIG. 5A ), and a fine temperature change with small amplitudes and short periods (see  FIG. 5B ). In  FIG. 5A  and  FIG. 5B , the vertical axis represents temperature, and the horizontal axis represents time.  FIG. 5A  and  FIG. 5B  illustrate how the temperature changes up and down with respect to the center of the amplitude when oscillating. 
     A description will be given of a case where the determination unit  52  performs determination using the number of extreme values and the fluctuation range as parameters related to a change in temperature. The number of extreme values serving as a parameter related to a change in temperature is the number of extreme values occurring between the start point in time and the end point in time of the window. In the temperature change as illustrated in  FIG. 5A , the number of extreme values is 2. In the temperature change as illustrated in  FIG. 5B , the number of extreme values is 12. The fluctuation range serving as a parameter related to a change in temperature is the maximum fluctuation range occurring between the start point in time and the end point in time of the window. In the temperature change as illustrated in  FIG. 5A , the fluctuation range is 8. In the temperature change as illustrated in  FIG. 5B , the fluctuation range is 1. 
       FIG. 6  illustrates three different temperature changes. In  FIG. 6 , the first temperature change TC 1  finely oscillates with a medium fluctuation range, the second temperature change TC 2  gently oscillates with a medium fluctuation range, and the last temperature change TC 3  finely oscillates with a large fluctuation range. Multiplying the number of extreme values and the fluctuation range enables quantification of an increasing degree of oscillation in the order of the last temperature change TC 3 , the first temperature change TC 1 , and the second temperature change TC 2  illustrated in  FIG. 6 . 
       FIG. 7  illustrates the number of extreme values NE 1  for the first temperature change TC 1 , the number of extreme values NE 2  for the second temperature change TC 2 , and the number of extreme values NE 3  for the last temperature change TC 3 . Referring to  FIG. 7 , it can be seen that the number of extreme values NF 1  of the first temperature change TC 1  and the number of extreme values NE 3  for the last temperature change TC 3  are relatively large, whereas the number of extreme values NE 2  for the second temperature change TC 2  is relatively small. 
     Examples of the variable corresponding to the fluctuation range include variance.  FIG. 8  illustrates a variance Va 1  for the first temperature change TC 1 , a variance Va 2  for the second temperature change TC 2 , and a variance Va 3  for the last temperature change TC 3 . Referring to  FIG. 8 , it can be seen that the variance Va 1  of the first temperature change TC and the variance Va 2  for the second temperature change TC 2  are medium, whereas the variance Va 3  for the last temperature change TC 3  is relatively large. 
     Here, the number of extreme values×variance represents a parameter value TP related to a change in temperature.  FIG. 9  illustrates a parameter value TP 1  related to the first temperature change TC 1 , a parameter value TP 2  related to the second temperature change TC 2 , and a parameter value TP 3  related to the last temperature change TC 3 . 
     (4-2) Method for Determining Second Threshold Value for Prohibition of Increasing Number of Operating Devices 
     The second threshold value for determining prohibition of increasing the number of operating devices is determined from, for example, data in a trial operation period. In the production-model trial operation period, the change in temperature detected by the outlet temperature sensor  63 , a parameter value TP related to a change in temperature, and a change in the number of devices in operation are observed. For example, if hunting is observed for the parameter value TP 3  and no hunting is observed for the parameter values TP 1  and TP 2 , the second threshold value is set to a value indicated by a straight line Ln 1  in  FIG. 9 . These satisfies the relationship of the parameter values TP 1  and TP 2 &lt;the value indicated by the straight line Ln 1 &lt;the parameter value TP 3 . For example, if hunting is observed for the parameter values TP 2  and TP 3  and no hunting is observed for the parameter value TP 1 , the second threshold value is set to a value indicated by a straight line Ln 2  in  FIG. 9 . These satisfies the relationship of the parameter value TP 1 &lt;the value indicated by the straight line Ln 2 &lt;the parameter values TP 2  and TP 3 . 
     (5) Features 
     (5-1) 
     The device management apparatus  50  described above receives the temperature of cold water, which is the state value of the heat medium measured by the outlet temperature sensor  63  included in the heat source system  1 . The device management apparatus  50  prohibits a change in the number of devices in operation, which is the change operation of the capacity of the chillers  111 ,  121 , and  131  serving as specific devices, on the basis of a parameter related to a change in temperature. As described above, with a simple configuration including the determination unit  52  that determines whether to prohibit a change operation of the capacity on the basis of a parameter related to a temperature change, the device management apparatus  50  can reduce extra change operations of the capacity of the chillers  111 ,  121 , and  131 . 
     (5-2) 
     The device management apparatus  50  described above uses, as parameters related to a change in state value, variables related to the number of extreme values of the state value and the fluctuation range of the state value within a window, which is a predetermined period. The number of extreme values or the fluctuation range of the state value may be used as a parameter related to a change in state value. Using, as a parameter related to a change in state value, a variable related to at least one of the number of extreme values of the state value and the fluctuation range of the state value, the device management apparatus  50  can reduce unnecessary change operations in a situation where the state value is unstable. 
     (5-3) 
     The device management apparatus  50  described above uses, as parameters related to a change in state value, variables related to the number of extreme values of the state value and the variance of the state value within a window, which is a predetermined period. As a result, as described with reference to  FIG. 9 , the device management apparatus  50  described above can accurately suppress unnecessary operations in accordance with the behavior of fluctuations in the state value. 
     (5-4) 
     As described with reference to  FIG. 9 , the device management apparatus  50  described above determines the second threshold value, which is a threshold value of a parameter indicating a limit for prohibiting a change operation of the capacity of the specific devices, from a relationship between the value of the parameter and the number of times the capacity of the specific devices is changed. As a result, it is possible to easily prohibit the change operation of the capacity of the specific devices at an appropriate timing by using the second threshold value indicated by the straight line Ln 1  or Ln 2  in  FIG. 9 . 
     (5-5) 
     In the device management apparatus  50 , the notification unit  54  can notify whether the device management apparatus  50  is in a state in which the change operation is prohibited or in a state in which the change operation is not prohibited, and inform outside of the management state. With this notification, it is possible to inform outside of the period of transition during which the change of the capacity is prohibited, which makes it easier for the user or the like to allow adjustment of the capacity of the heat source system  1 . 
     (5-6) 
     A sensor included in the heat source system  1  to measure the state of the heat medium can be implemented as a temperature sensor that measures the temperature of the heat medium, such as the outlet temperature sensor  63 , a flow rate sensor that measures the flow rate of the heat medium, or a pressure sensor that measures the pressure of the heat medium. With a simple configuration in which the value of the temperature, flow rate, or pressure of the heat medium measured by such a sensor is used as the state value of the heat medium, the heat source system  1  can reduce extra change operations of the capacity of the specific devices. 
     (5-7) 
     In a case where the outlet temperature sensor  63  is used in the heat source system  1  to measure the state of the heat medium, the heat source system  1  can perform an appropriate change operation of the capacity when the difference between the outlet temperature and the target temperature is large and the capacity is to be changed. 
     (6) Modifications 
     (6-1) Modification 1A 
     In the embodiment described above, the description has been given of a case where the heat medium is water. However, the heat medium is not limited to water. The heat medium may be, for example, brine, refrigerant, or oil. 
     (6-2) Modification 
     In the embodiment described above, the description has been given of the chillers  111 ,  121 , and  131  as specific devices. However, the specific devices are not limited to chillers. 
     The specific devices may be, for example, the heat source devices  10  other than chillers, The heat source devices  11 ,  12 , and  13  can be three cooling towers instead of the three chillers  111 ,  121 , and  131 . In this case, for example, a chiller in which cooling water of the cooling towers circulates is the use-side device  20 . Alternatively, the specific devices may be devices other than the heat source devices  10 . Examples of a specific device other than the heat source devices  10  include the pump  40  of the heat source system  1 . For example, in a case where the pump  40  includes a plurality of constant-speed pumps, the change operation of the capacity to he prohibited by the change operation prohibition unit  53  of the device management apparatus  50  is to increase or decrease the number of operating devices among the plurality of constant-speed pumps. 
     In a case where the specific devices are the chillers  111 ,  121 , and  131 , cooling towers, or pumps, it is possible to reduce extra change operations of the capacity of the chillers  111 ,  121 , and  131 , the cooling towers, or the pumps with a simple configuration. 
     (6-3) Modification 1C 
     In the embodiment described above, the description has been given of a case where the state value of the heat medium is the temperature. However, the state value may be a value other than the temperature. For example, the flow rate of cold water flowing through the flow path  30  of the heat source system  1  may be used as the state value, and the flow path  30  may be provided with a flow rate sensor. Alternatively, the pressure of cold water flowing through the flow path  30  of the heat source system  1  may be used as the state value, and the flow path  30  may be provided with a pressure sensor. In a case where the flow rate or the pressure is used as the state value, the specific devices are, for example, the heat source devices  10  or the pump  40 . In a case where the flow rate or the pressure is used as the state value, a flow rate sensor or a pressure sensor is used instead of the inlet temperature sensor  61  and the outlet temperature sensor  63 . 
     (6-4) Modification 1D 
     In the embodiment described above, the description has been given of a case where a parameter related to a change in state value is a variable related to at least one of the number of extreme values of the state value and the fluctuation range of the state value. However, the parameter related to a change in state value is not limited to the variable related to at least one of the number of extreme values of the state value and the fluctuation range of the state value. The device management apparatus  50  can use, for example, a period, a frequency, or a wavelength, instead of the number of extreme values, as a parameter related to a change in state value. The device management apparatus  50  can use, for example, a standard deviation, a difference between a maximum value and a minimum value, or an amplitude, instead of the variance, as a parameter related to a change in state value. 
     Second Embodiment 
     (1) Overall Configuration 
     As illustrated in  FIG. 10 , a heat source system  301  according to a second embodiment includes heat source devices  310 , a use-side device  320 , a flow path  330 , a pump  340 , and a device management apparatus  350 . The heat medium of the heat source system  301  circulates between the heat source devices  310  and the use-side device  320  through the flow path  330 . The flow path  330  includes a return header  331  and a feed header  332 . Water fed out of the pump  340  is distributed to heat source devices  311  to  313  by the return header  331 . Cold water exiting from the heat source devices  311  to  313  is mixed by the feed header  332  and fed to the use-side device  320 . The heat source system  301  according to the second embodiment includes the three heat source devices  311 ,  312 , and  313 . 
     The device management apparatus  350  manages the heat source devices  310 . The device management apparatus  350  has a function of determining a standby time. The device management apparatus  350  prohibits a change operation for changing the capacity of the heat source devices  310  for a predetermined period from the previous change operation. The length of the predetermined period during which the change operation of the capacity of the heat source devices  310  is prohibited is the standby time. The device management apparatus  350  determines the standby time in accordance with a parameter relating to the circulation flow rate of the heat medium. The device management apparatus  350  prohibits the change operation of the capacity of the heat source devices  310  during the standby time. In other words, the device management apparatus  350  allows the change operation of the capacity of the heat source devices  310  after the lapse of the standby time. In this embodiment, the change operation to be prohibited by the device management apparatus  350  is an operation of changing the number of heat source devices  310  that are in operation. 
     The device management apparatus  350  includes a number control controller  351  for performing number control of the heat source devices  310 . The number control controller  351  includes a standby time determination unit  352  and a change operation prohibition unit  353 . The standby time determination unit  352  calculates a standby time by using the parameter relating to the circulation flow rate of the heat medium. The change operation prohibition unit  353  prohibits the change operation of the capacity of the heat source devices  310  only during the standby time to suppress the change of the capacity of the heat source devices  310  in the transitional state. 
     The device management apparatus  350  is implemented by, for example, a computer.  FIG. 10  illustrates various functional blocks of the device management apparatus  350  implemented by a control calculation device. 
     (2) Detailed Configuration 
     (2-1) Example Configuration of Heat Source System  301   
     In the heat source system  301  illustrated in  FIG. 11 , the heat medium is water, the heat source devices  311 ,  312 , and  313  are chillers  411 ,  421 , and  431 , and the use-side device  320  includes four fan coil units  501 ,  502 ,  503 , and  504 . The components included in the heat source system  301  are components having functions similar to those of the components of the heat source system presented in the first embodiment. Each of the fan coil units  501  to  504  includes a flow rate adjustment valve  321 , an air heat exchanger  322 , and a fan  323 . The heat source system  301  includes an inlet temperature sensor  361  and differential pressure sensors  362 . The pump  340  is inverter controlled and is configured to be capable of changing the discharge amount. The device management apparatus  350  controls the discharge amount of the pump  340  so that a differential pressure detected by the differential pressure sensors  362  is constant. 
     (2-2) Example Operation of Heat Source System  301   
     Each of the chillers  411 ,  421 , and  431  includes therein a water heat exchanger (not illustrated) and a chiller controller (not illustrated). The respective chiller controllers of the chillers  411 ,  421 , and  431  individually perform control for the chillers  411 ,  421 , and  431  so that the outlet water temperature of each of the chillers  411 ,  421 , and  431  becomes a set water temperature. 
     The device management apparatus  350  determines the number of heat source devices  310  to be operated from the capacity of the chiller  411  and the return water temperature. If the temperature of the cold water becomes higher than the set water temperature, the device management apparatus  350  causes the chiller  421  to also operate. In the device management apparatus  350 , the standby time determination unit  352  determines the standby time after the operation of the chiller  421  is started. To determine the standby time, the device management apparatus  350  acquires the parameter relating to the circulation flow rate of the heat medium and changes the standby time in accordance with the flow rate of the water flowing through the flow path  330 . The parameter relating to the circulation flow rate will be described below. 
     For example, the heat source system  301  having a reference flow rate of 100 liters/minute and a reference standby time of 60 seconds will be described as an example, With the heat source system  301  having such a configuration, when the flow rate after the operation of the chiller  421  is started is larger than the reference flow rate and is 200 liters/minute, the device management apparatus  350  can be configured to determine the standby time to be 30 seconds (=60×100/200). Conversely, when the flow rate after the number of operating devices is increased is less than the reference flow rate and the flow rate after the chiller  421  is additionally operated is 50 liters/minute, the device management apparatus  350  can be configured to determine the standby nine to be 120 seconds (=60×100/50). Here, for ease of description, the description has been given of a case where the flow rate is used as a parameter related to the circulation flow rate of the heat medium. However, the flow rate is not necessarily computed to determine the standby time by using the flow rate as a parameter. For example, a table indicating a relationship between the flow rate and the standby time may be prepared in advance, and the flow rate may be matched against the table to determine the standby time. 
     In the device management apparatus  350 , the change operation prohibition unit  353  prohibits the change operation of the number of chillers in operation during the standby time after the chiller  421  is additionally operated. After the lapse of the standby time, the device management apparatus  350  causes the chiller  431  to operate if the capacity is still insufficient, or causes the chiller  411  or the chiller  421  to stop operating, conversely, if the capacity is excessive, 
     If the standby time is excessively long after the number of operating devices is increased, the additional operation of the chiller  431  or stopping the operation of the chiller  411  or  421  after the operation of the chiller  421  is started is delayed. If the additional operation of the chiller  431  is delayed, the capacity of the fan coil units  501  to  504  often becomes insufficient. If the capacity of the fan coil units  501  to  504  becomes insufficient, the temperatures of the spaces to be air conditioned do not drop easily, which provides discomfort to people in the spaces to be air conditioned. 
     If the standby time is excessively short after the number of operating devices is increased, the additional operation of the chiller  431  or stopping the operation of the chiller  411  or  421  after the operation of the chiller  421  is started is accomplished too early. If the additional operation of the chiller  431  is accomplished too early, the capacity of the heat source devices  310  often becomes excessive. The excessive capacity of the heat source devices  310  leads to extra energy consumption. 
     Consideration will be given to the decrease in the number of operating devices when the chillers  411 ,  421 , and  431  are operated and the operation of the chiller  431  is stopped. If the standby time is excessively short after the decrease in the number of operating devices described above, stopping the operation of the chiller  411  or  421  or the additional operation of the chiller  431  after the operation of the chiller  431  is stopped is accomplished too early. If stopping the operation of the chiller  411  or  421  is accomplished too early, the capacity of the heat source devices  310  often becomes too low. The too low capacity of the heat source devices  310  causes repeating the start and stop of the heat source devices  310  (in this case, one of the chillers  411  and  421 ). 
     If the standby time is excessively long after the number of operating devices is decreased, stopping the operation or the additional operation of the chiller  411  or  421  of the chiller  431  after the chiller  431  is stopped is delayed. If stopping of the operation of the chiller  411  or  421  is delayed, the capacity of the heat source devices  310  often becomes excessive. The excessive capacity of the heat source devices  310  leads to extra energy consumption. 
     An appropriate standby time, which prevents the increase or decrease in the number of operating devices from being accomplished too early or too late, is considered to be a time taken to stabilize the water temperature state in the pipe. Therefore, it is preferable that the standby time dynamically changes in accordance with, for example, the velocity of the flow in the pump  340  and the response of the chillers  411 ,  421 , and  431 . For example, it is assumed that the water temperature of the cold water fed out of the feed header  332  changes from 13° C. to a set water temperature of 7° C. with the additional operation of the chiller  421  described above. Then, the cold water having the set water temperature returns to the pump  340  again, and the influence of the change of the temperature of the cold water at the feed header  332  to 7° C. is reflected in the return water temperature. To prevent the standby time from being excessively short, the standby time is preferably set to be longer than a circulation time that is taken until the water exiting from the pump  340  returns to the pump  340  again. The standby time has a tendency that the large circulation flow rate reduces the circulation time and thus reduces the standby time, whereas the small amount of circulation increases the circulation time and thus also increases the standby time. 
     During the standby time, for example, since the return water temperature is as high as 20° C., the chillers  411  and  421  are operated at a capacity of 80% of the maximum capacity, and the water temperature of the cold water fed out of the feed header  332  is lowered to 10° C. At this time, the temperature of the cold water entering the fan coil units  501  to  504  is still kept at 13° C., and the temperature of the water immediately after leaving the fan coil units  501  to  504  is still as high as 20° C. 
     After the lapse of the standby time, for example, the return water temperature decreases to 13° C., and the chillers  411  and  421  are operated at a capacity of 60% of the maximum capacity. At this time, the water temperature of the cold water at the feed header  332  and the temperature of the cold water entering the fan coil units  501  to  504  also have a set temperature of 7° C., and the water immediately after leaving the fan coil units  501  to  504  has a temperature of 13° C. 
     (2-3) Parameter Relating to Circulation Flow Rate 
     Examples of the parameter relating to the circulation flow rate may include the capacity of the pump  340 . For example, if the pump  340  is inverter controlled, the frequency of the pump  340  after the increase in the number of operating devices relative to the maximum frequency can be used as a parameter. For example, if the reference frequency is 50%, the flow rate is increased when the frequency of the pump  340  is 80%, so that the standby time is controlled to be reduced, and the flow rate is decreased when the frequency is 20%, so that the standby time is controlled to be increased. However, the parameter indicating the capacity of the pump  340  is not limited to the frequency and may be any other parameter such as the number of revolutions or the amount of discharge determined from a pump characteristic curve. For example, the device management apparatus  350  may store a relationship between the capacity of the pump  340  and the standby time in the form of a table. Such a table can he created by, for example, production-model measurement performed in advance. 
     For example, in a case where the pump  340  is configured such that a plurality of constant-speed pumps each having a constant number of revolutions are connected in parallel, the number of constant-speed pumps in operation can be changed to adjust the flow rate. With such a configuration, the device management apparatus  350  can use the number of constant-speed pumps that are in operation as a parameter relating to the circulation flow rate. Other examples of the parameter relating to the circulation flow rate may include the capacity of the pump  340  and the resistance of the pipe. For example, the valve opening degrees of the flow rate adjustment valves  321  of the fan coil units  501  to  504  and the frequency of the pump  340  may be used as parameters relating to the circulation flow rate. A curve Cv 1  illustrated in  FIG. 12  is a curve indicating the relationship between the pressure and the flow rate in a case where the pipe resistance is large due to, for example, small valve opening degrees of the flow rate adjustment valves  321  of the fan coil units  501  to  504 . A curve Cv 2  illustrated in  FIG. 12  is a curve indicating the relationship between the pressure and the flow rate in a case where the pipe resistance is medium due to, for example, medium valve opening degrees of the flow rate adjustment valves  321  of the fan coil units  501  to  504 . A curve Cv 3  illustrated in  FIG. 12  is a curve indicating the relationship between the pressure and the flow rate in a case where the pipe resistance is small due to, for example, fully open valve opening degrees of the flow rate adjustment valves  321  of the fan coil units  501  to  504 . A curve Cv 4  illustrated in  FIG. 12  is a curve indicating the relationship between the pressure and the flow rate when the operation frequency of the pump  340  is 80% of the maximum frequency. A curve Cv 5  illustrated in  FIG. 12  is a curve indicating the relationship between the pressure and the flow rate when the operation frequency of the pump  340  is 50% of the maximum frequency. A curve Cv 6  illustrated in  FIG. 12  is a curve indicating the relationship between the pressure and the flow rate when the operation frequency of the pump  340  is 20% of the maximum frequency. For example, when the frequency of the pump  340  is 50% and the pipe resistance is medium, the flow rate of the cold water flowing through the flow path  30  is a flow rate corresponding to the point of intersection of the curve Cv 2  and the curve Cv 5 . The device management apparatus  350  may store the relationship among the capacity of the pump  340 , the resistance of the pipe, and the standby time in the form of a table, for example. Such a table can be created by, for example, production-model measurement performed in advance. 
     In a case where the pump  340  includes constant-speed pumps, the resistance of the pipe may be used as a parameter relating to the circulation flow rate. For example, the device management apparatus  350  may store the relationship between the resistance of the pipe and the standby time in the form of a table. Such a table can be created by, for example, production-model measurement performed in advance. 
     The capacity of the pump  340  and the differential pressure may also be used as parameters relating to the circulation flow rate. The differential pressure can be detected by the differential pressure sensors  362 . A curve Ln 1  illustrated in  FIG. 13  is a curve indicating the relationship between the differential pressure and the flow rate in a case where the pipe resistance is large. A curve Ln 2  is a curve indicating the relationship between the differential pressure and the flow rate in a case where the pipe resistance is medium. A straight line Ln 3  is a curve indicating the relationship between the differential pressure and the flow rate in a case where the pipe resistance is small. A curve Cv 7  illustrated in  FIG. 13  is a curve indicating the relationship between the differential pressure and the flow rate when the operation frequency of the pump  340  is 80% of the maximum frequency. A curve Cv 8  is a curve indicating the relationship between the differential pressure and the flow rate when the operation frequency of the pump  340  is 50% of the maximum frequency. A curve Cv 9  is a curve indicating the relationship between the differential pressure and the flow rate when the operation frequency of the pump  340  is 20% of the maximum frequency. For example, when the frequency of the pump  340  is 50% and the pipe resistance is medium, the flow rate of the cold water flowing through the flow path  30  is a flow rate corresponding to the point of intersection of the straight line Ln 2  and the curve Cv 8 . For example, the device management apparatus  350  may store the relationship among the capacity of the pump  340 , the differential pressure, and the standby time in the form of a table. Such a table can be created by, for example, production-model measurement performed in advance. The differential pressure is, for example, a differential pressure detected by the differential pressure sensors  362 . 
     In a case where the pump  340  includes constant-speed pumps, the differential pressure may also be used as a parameter relating to the circulation flow rate. For example, the device management apparatus  350  may store the relationship between the differential pressure and the standby time in the form of a table. Such a table can be created by, for example, production-model measurement performed in advance. 
     The standby time determination unit  352  can determine the standby time by using the relationship between the flow rate of the pump  340  and the retained amount of water. The retained amount of water circulating through the heat source system  301  can be determined, for example, when the heat source system  301  is designed. The determined retained amount of water is stored in a memory (not illustrated) of the device management apparatus  350 . In such a case, the retained amount of water is a value described in the design specification. Alternatively, the retained amount of water can he calculated using the pipe length and the pipe cross-sectional area described in the drawing of the heat source system  301 . 
     The flow rate can be determined from a pump characteristic curve and a pipe resistance curve. To easily determine the flow rate, the relationship among the frequency of the pump  340  or the number of pumps in operation, the flow rate adjustment valves  321  of the fan coil units  501  to  504 , and the flow rate is measured during trial operation and stored in the memory of the device management apparatus  350  as a table. For example, if the retained amount of water is 100 liters and the flow rate is 100 liters/minute, the standby time can be calculated to be 1 minute from the computation of 100 liters÷100 liters/minute. This is a time (circulation time) taken for water to circulate once through the heat source system  301 . In consideration of the response characteristics of the heat source devices  310 , the standby time may be set to be slightly longer than the circulation time. The standby time determination unit  352  may be configured to set the standby time by, for example, multiplying the circulation time by a correction coefficient. 
     (3) Modifications 
     (3-1) Modification 2A 
     The heat source system  301  according to the second embodiment described above prohibits the change operation at all times during the standby time. However, the device management apparatus  350  may be configured such that the prohibition of the change operation can be canceled even during the standby time if a predetermined condition is satisfied. The heat source system  301  illustrated in  FIG. 14  includes an outlet temperature sensor  63  that detects the temperature of the cold water fed out of the feed header  332 . The device management apparatus  350  illustrated in  FIG. 14  includes the standby time determination unit  352 , the change operation prohibition unit  353 , and a change prohibition cancellation unit  354 . When the difference between the outlet temperature measured by the outlet temperature sensor  63  and the target temperature is larger than a predetermined value, the change prohibition cancellation unit  354  cancels the prohibition of the change operation of the capacity of the heat source devices  310  to change the temperature of the heat medium. For example, in a case where the outlet temperature is 15° C. although the set temperature, which is the target temperature, is 7° C., the capacity of the heat source devices  310  is obviously insufficient. At this time, if only the chiller  411  is in operation, it is preferable to make a change to bring the chiller  421  into operation and also bring the chiller  431  into operation as quickly as possible. Setting the predetermined value to, for example, 14° C. allows the change prohibition cancellation unit  354  to quickly shift from a state in which only the chiller  411  is in operation to a state in which all of the three chillers  411 ,  421 , and  431  are in operation, in response to the outlet temperature sensor  63  detecting an outlet temperature of 15° C., even during the standby time. 
     (3-2) Modification 2B 
     As illustrated in  FIG. 15 , the device management apparatus  350  of the heat source system  301  according to Modification 2B includes a notification unit  355 . In the device management apparatus  350 , the notification unit  355  notifies whether the device management apparatus  350  is in a state in which the change operation is prohibited or in a state in which the change operation is not prohibited. Examples of the notification method performed by the notification unit  355  include a method of notifying a state in which the change operation is prohibited by using a buzzer, a method of notification by displaying, on a display device, whether to prohibit the change operation, and method of transmitting information indicating whether to provide notification via a public line. 
     (3-3) Modification 2C 
     The heat source system  301  according to the embodiment described above has been described taking as an example a case where the heat source devices  311 ,  312 , and  313  are the chillers  411 ,  421 , and  431 . However, the heat source devices  311 ,  312 , and  313  are not limited to chillers. Examples of the heat source devices  311 ,  312 , and  313  include cooling towers  412 ,  422 , and  432 , as illustrated in  FIG. 16 . The heat source system  301  illustrated in  FIG. 16  includes the cooling towers  412 ,  422 , and  432  serving as the heat source devices  310 , the flow path  330 , the pump  340 , and the use-side device  320 . Cooling water is circulated by the pump  340  between the cooling towers  412 ,  422 , and  432  and the use-side device  320  through the flow path  330 . The use-side device  320  includes a chiller  211 , an air handling unit  212  and a pump  213 . The operation of the use-side device  320  has been described in the embodiment, and the description thereof will thus he omitted here. The cooling water circulating through the flow path  330  is used in the chiller  211  to cool the cold water circulated by the pump  213  through the use-side device  320 . 
     In the heat source system  301  in  FIG. 16 , the cooling water is circulated through the flow path  330  as a heat medium by the pump  340 . In the steady state of the heat source system  301 , for example, the temperature of the cooling water at the inlet of the chiller  211  is 20° C., and the temperature of the cooling water at the outlet of the chiller  211  is 26° C. The pump  340  changes the frequency so that the temperature difference of the cooling water between the inlet and outlet of the chiller  211  becomes a target temperature difference. If the temperature difference of the cooling water between the inlet and the outlet is larger than the target temperature difference, the heat source system  301  increases the frequency of the pump  340 . Conversely, if the temperature difference of the cooling water between the inlet and the outlet is smaller than the target temperature difference, the heat source system  301  decreases the frequency of the pump  340 . 
     The heat source system  301  changes the number of cooling towers  412 ,  422 , and  432  in accordance with the temperature of the cooling water at the outlet of the feed header  332 . For example, if the set temperature of the cooling water at the outlet of the feed header  332  is 20° C. and the temperature detected by the outlet temperature sensor  63  is lower than 20° C. (set temperature) by a threshold value or more (set temperature−threshold value≥detected temperature), the number of operating devices among the cooling towers  412 ,  422 , and  432  is decreased. Conversely, if the temperature detected by the outlet temperature sensor  63  is higher than 20° C. (set temperature) by the threshold value or more (set temperature+threshold value≤detected temperature), the number of operating devices among the cooling towers  412 ,  422 , and  432  is increased. 
     As in the embodiment, when increasing or decreasing the number of operating devices among the cooling towers  412 ,  422 , and  432 , the device management apparatus  350  determines the standby time and prohibits the change operation. The components denoted by the same reference numerals as those in the embodiment, such as the device management apparatus  350  and the pump  340  according to Modification 2C, can have same configuration as that in the embodiment. 
     In a case where the standby time is excessively long after the number of operating devices is increased, the increase in the number of operating devices related to the cooling towers  412 ,  422 , and  432  is delayed, and a problem such as abnormal stop of the chiller  211  occurs. If such a problem of the chiller  211  occurs, the temperature of the space to be air conditioned does not drop easily, which provides discomfort to people in the space to he air conditioned. In a case where the standby time is excessively short after the number of operating devices is increased, the increase in the number of operating devices related to the cooling towers  412 .  422 , and  432  is accomplished too early, leading to extra energy consumption. 
     In a case where the standby time is excessively short after the number of operating devices is decreased, the decrease in the number of operating devices related to the cooling towers  412 ,  422 , and  432  is accomplished too early, leading to hunting in which any of the cooling towers  412 ,  422 , and  432  repeats operation and stop. In a case where the standby time is excessively long after the number of operating devices is decreased, the decrease in the number of operating devices related to the cooling towers  412 ,  422 , and  432  is delayed, leading to extra energy consumption. 
     (3-4) Modification 2D 
     In Modification 2C, the description has been given of a case where the heat source devices  311 ,  312 , and  313  are the cooling towers  412 ,  422 , and  432 . However, as illustrated in  FIG. 17 , the heat source devices  311 ,  312 , and  313  may be water heaters  413 ,  423 , and  433 . 
     The heat source system  301  illustrated in  FIG. 17  includes, as the flow path  330 , a flow path  330   a  that circulates through chillers  411 ,  421 , and  431 , and a flow path  330   b  that circulates through the water heaters  413 ,  423 , and  433 . The heat source system  301  illustrated in  FIG. 17  further includes, as the pump  340 , a pump  340   a  that circulates cold water in the flow path  330   a,  and a pump  340   b  that circulates hot water in the flow path  330   b.  Examples of the water heaters  413 ,  423 , and  433  include boilers. 
     The use-side device  320  includes two air handling units  221  and  222 . For example, the air handling units  221  and  222  cool spaces to be air conditioned (not illustrated) by using cold water, and heat the spaces to be air conditioned (not illustrated) by using hot water. A heat source unit  1  in  FIG. 17  includes electromagnetic valves  223 ,  224 ,  225 , and  226 . When the electromagnetic valve  223  is closed, the supply of the cold water from the chillers  411 ,  421 , and  431  to the air handling unit  221  is stopped. When the electromagnetic valve  224  is closed, the supply of the cold water from the chillers  411 ,  421 , and  431  to the air handling unit  222  is stopped. When the electromagnetic valve  225  is closed, the supply of the hot water from the water heaters  413 ,  423 , and  433  to the air handling unit  221  is stopped. When the electromagnetic valve  226  is closed, the supply of the hot water from the water heaters  413 .  423 , and  433  to the air handling unit  222  is stopped. 
     As in the embodiment, when increasing or decreasing the number of operating devices among the chillers  411 ,  421 , and  431 , the management device  50  determines the standby time and prohibits the change operation to increase or decrease the number of operating devices among the chillers  411 ,  421 , and  431  during the standby time. Further, when increasing or decreasing the number of operating devices among the water heaters  413 ,  423 , and  433 , the management device  50  determines the standby time and prohibits the change operation to increase or decrease the number of operating devices among the water heaters  413 ,  423 , and  433  during the standby time. 
     (3-5) Modification 2E 
     In the embodiment and modifications described above, the description has been given of a case where the heat medium is water. However, the heat medium is not limited to water. The heat medium may be, for example, brine, refrigerant, or oil. 
     (4) Features 
     (4-1) In the heat source system  301  described above, the standby time determination unit  352  determines the standby time in accordance with a parameter relating to the circulation flow rate of the heat medium, and the change operation prohibition unit  353  prohibits the change operation of the capacity of the heat source devices  310  during the standby time. As a result, the heat source system  301  can perform the change operation at an appropriate timing without performing the change operation too early or too late. Accordingly, the device management apparatus  350  can perform management in which suppression of an increase in the energy consumption of the heat source system  301  and comfort are balanced. 
     (4-2) In the case of the heat source devices  310  including the plurality of heat source devices  311  to  313 , the heat source system  301  can increase or decrease the number of operating devices at an appropriate timing without increasing or decreasing the number of operating devices too early or too late. Accordingly the device management apparatus  350  can perform management, in which suppression of an increase in energy consumption and comfort are balanced, on the heat source system  301  including the plurality of heat source devices  311  to  313 . 
     (4-3) While a description has been given with reference to  FIG. 12 ,  FIG. 13 , and the like, the parameter relating to the circulation flow rate of the heat medium, which is used for the device management apparatus  350  described above to determine the standby time, is, for example, at least one of the capacity of the pump  340 , the valve opening degrees of the flow rate adjustment valves  321 , and the differential pressure detected by the differential pressure sensors  362 . The capacity of the pump  340  is a variable related to the capacity of a circulation pump that circulates the heat medium. The valve opening degrees of the flow rate adjustment valves  321  are each a variable related to the degree of flow rate adjustment of a use-side device that uses the heat medium. The differential pressure detected by the differential pressure sensors  362  is a variable related to the pressure difference between the heat medium flowing into the use-side device and the heat medium flowing out of the use-side device. As described above, the device management apparatus  350  can easily determine the standby time by using at least one of the capacity of the circulation pump, the degree of flow rate adjustment, and the pressure difference of the heat medium. 
     (4-4) At least one of the frequency and number of the pump  340  is a variable related to the flow rate of a circulation pump that circulates the heat medium. In the embodiment described above, a method for determining the standby time by using such at least one of the frequency and number of the pump  340  has been described. Further, the determination of the standby time from the flow rate of the pump  340  and the retained amount of water in the heat source system  301  has been described above. The device management apparatus  350  determines the standby time by using the flow rate of the pump  340 , which is a circulation pump. Thus, the standby time is more likely to be appropriate for the circulation of water, which is the heat medium. 
     (4-5) The device management apparatus  350  described in Modification  2 A includes the change prohibition cancellation unit  354  (see  FIG. 14 ). When the difference between the outlet temperature measured by the outlet temperature sensor  63  and the target temperature is larger than a predetermined value, the change prohibition cancellation unit  354  cancels the prohibition of the change operation of the capacity of the heat source devices  310  to change the temperature of the heat medium. The state in which the difference between the target temperature and the outlet temperature is large often occurs at the time of activation of the heat source system  301 . Thus, the device management apparatus  350  as illustrated in  FIG. 14  can improve the accuracy of management of the heat source devices  310  in which suppression of an increase in the energy consumption of the heat source system  301  and comfort are balanced at the time of system activation. 
     (4-6) In the device management apparatus  350 , the notification unit  355  can notify whether the device management apparatus  350  is in a state in which the change operation is prohibited or in a state in which the change operation is not prohibited, and inform outside of the management state. With this notification, it is possible to inform outside of the period of transition during which the change of the capacity is prohibited, which makes it easier for the user or the like to allow adjustment of the capacity of the heat source system  301 . 
     (4-7) The heat source system  301  includes the chillers  411 ,  421 , and  431 , the cooling towers  412 ,  422 , and  432  or the water heaters  413 ,  423 , and  433  that change the temperature of a heat medium circulating through the heat source system  301 , and the device management apparatus  350  that determines the standby time in accordance with a parameter relating to the circulation flow rate of the heat medium and prohibits a change operation for changing the capacity of the chillers  411 ,  421 , and  431 , the cooling towers  412 ,  422 , and  432 , or the water heaters  413 ,  423 , and  433  (for example, an operation of increasing or decreasing the number of operating devices) until a time interval from the previous change operation exceeds the standby time. As a result, the heat source system  301  can perform management, in which suppression of an increase in the energy consumption of the heat source system  301  and comfort arc balanced, on the chillers  411 ,  421 , and  431 , the cooling towers  412 ,  422 , and  432 , or the water heaters  413 ,  423 , and  433 . 
     Third Embodiment 
     (1) Schematic Configuration of Device Management System 
       FIG. 18  is a schematic configuration diagram of a device management system  510  according to an embodiment of the present invention. The device management system  510  is capable of supplying air adjusted to an optimum temperature to a space to be air conditioned while optimally maintaining the number of operating devices among heat source devices of the system  510 . The device management system  510  is mainly installed in a relatively large structure such as a building, a factory, a hospital, or a hotel. 
     As illustrated in  FIG. 18 , the device management system  510  mainly includes a chiller unit group  520 , a use unit group  530 , connection pipes L 1  to L 4  (corresponding to a first pipe), a communicating pipe L 5  (corresponding to a second pipe), pumps  544   a  to  544   f  (corresponding to a pump), and a controller  580  (corresponding to a control calculation unit  583 ). The device management system  510  further includes a flow meter  545 , a power meter  546 , and a plurality of temperature detection sensors T 1 , T 2 , T 3   a  to T 3   f,  and T 4   a  to T 4   f    
     The chiller unit group  520  includes a plurality of chiller units  5520   a  to  520   f  (corresponding to heat source devices) each having formed therein a refrigerant circuit  521  illustrated in  FIG. 19 . As illustrated in  FIG. 18 . furthermore, the chiller unit group  520  is also connected to a cooling tower  570 , and these components form a heat dissipation circuit  560 . As illustrated in  FIG. 18 , furthermore, the pumps  544   a  to  544   f,  the chiller unit group  520 , the use unit group  530 , and so on form a heat medium circuit  540 . 
     In  FIG. 18 , the illustration of components such as connection pipes of the device management system  510  is omitted, as appropriate, for convenience. In addition, the number of components of the device management system  510  illustrated in  FIG. 18  is not limited and may be changed as appropriate. 
     (2) Detailed Configuration of Device Management System 
     (2-1) Chiller Unit Group and Refrigerant Circuit 
     The chiller unit group  520  according to this embodiment includes the plurality of chiller units  520   a  to  520   f  The chiller units  520   a  to  520   f  are each a water-cooled heat source unit and are connected in parallel to each other, Each of the chiller units  520   a  to  520   f  includes the refrigerant circuit  521  illustrated in  FIG. 19 . 
     The refrigerant circuit  521  is configured by sequentially connecting a compressor  522 , a radiator  523 , an expansion valve  524 , an evaporator  525 , and so on. The refrigerant circuit  521  is filled with refrigerant. 
     The operating capacity of the compressor  522  is adjustable. The compressor  522  has a motor to which power is supplied via an inverter. Changing the output frequency of the inverter changes the number of revolutions, or the rotational speed, of the motor, and changes the operating capacity of the compressor  522 . 
     The radiator  523  includes a first heat transfer tube connected to the refrigerant circuit  521 , and a second heat transfer tube connected to the heat dissipation circuit  560 . The radiator  523  performs heat exchange between the refrigerant flowing in the first heat transfer tube on the refrigerant circuit  521  side and the heat medium flowing through the second heat transfer tube on the heat dissipation circuit  560  side. 
     The expansion valve  524  is used to decompress the refrigerant in the refrigerant circuit  521  and allow the decompressed refrigerant to flow out, and is configured as an electric expansion valve. 
     The evaporator  525  includes a third heat transfer tube connected to the refrigerant circuit  521 , and a fourth heat transfer tube connected to the heat medium circuit  540 . The evaporator  525  performs heat exchange between the refrigerant flowing in the third heat transfer tube on the refrigerant circuit  521  side and the heat medium flowing through the fourth heat transfer tube on the heat medium circuit  540  side. 
     Each of the chiller units  520   a  to  520   f  including the refrigerant circuits  521  having such a configuration cools or heats water serving as a heat medium. In this embodiment, a capacity control lower limit a 2  of each of the chiller units  520   a  to  520   f  is set to 20%, and a capacity control upper limit a 1  of each of the chiller units  520   a  to  520   f  is set to 100%. The capacity control lower limit a 2  and the capacity control upper limit al of each of the chiller units  520   a  to  520   f  can be appropriately set according to the chiller unit to be used. 
     Alternatively, the capacity control lower limit a 2  and the capacity control upper limit a 1  of each of the chiller units  520   a  to  520   f  may each be set to a different value. In this embodiment, the capacity control lower limit a 2  and the capacity control upper limit al of each of the chiller units  520   a  to  520   f  are the lower limit and the upper limit of the output (capacity) when each of the chiller units  520   a  to  520   f  is controlled in accordance with a load. 
     In this embodiment, the capacity control lower limit a 2  and the capacity control upper limit a 1  are represented by % (the maximum output is set to 100% and the output in the stop state is set to 0%). However, the capacity control lower limit a 2  and the capacity control upper limit a 1  may be represented by kW or the like. 
     (2-2) Heat Dissipation Circuit 
     The heat dissipation circuit  560  is filled with water as a heat medium. The heat dissipation circuit  560  is mainly configured by sequentially connecting the radiator  523  in each of the chiller units  520   a  to  520   f,  a water pump  561 . and the cooling tower  570 . The water pump  561  is configured such that the discharge flow rate is adjustable, and circulates water in the heat dissipation circuit  560 . In the cooling tower  570 , the water circulating through the heat dissipation circuit  560  is cooled. 
     In  FIG. 18 , the water pump  561  is assigned an arrow indicating the direction of flow of the water in the heat dissipation circuit  560 . 
     (2-3) Heat Medium Circuit, Flow Meter, and Temperature Detection Sensor 
     The heat medium circuit  540  forms a closed circuit, which is filled with water as a heat medium. The heat medium circuit  540  is mainly configured such that the pumps  544   a  to  544   f,  the respective evaporators  525  in the chiller units  520   a  to  520   f,  a bypass valve  543 , the bypass valve  543 , and use-side heat exchangers  533   a,    533   b , and  533   c  and use-side valves  532   a,    532   b , and  532   c  in use units  530   a,    530   b,  and  530   c  constituting the use unit group  530  are sequentially connected by the connection pipes L 1  to L 4 . Further, the heat medium circuit  540  is also configured such that the inlet side and the outlet side of the chiller units  520   a  to  520   f  are connected by the communicating pipe L 5 . 
     Specifically, ends of the connection pipes L 1  are coupled to ends of the evaporators  525  on the outlet side of the chiller units  520   a  to  520   f,  and other ends of the connection pipes L 1  are coupled to a feed header  542 . An end of the connection pipe L 2  is coupled to the outlet of the feed header  542 , The other end of the connection pipe L 2  is branched in the middle, and the distal ends of branched portions are coupled to the use-side heat exchangers  533   a  to  533   c  on the inlet side of the use units  530   a  to  530   c.  Ends of the connection pipes L 3  arc coupled to the outlet side of the use-side valves  532   a  to  532   c  on the outlet side of the use units  530   a  to  530   c.  Other ends of the connection pipes L 3  merge in the middle, and the distal end of the merging portion is coupled to a return header  541 . The connection pipes L 4  are disposed in accordance with the number of chiller units  520   a  to  520   f  Ends of the connection pipes L 4  are coupled to the return header  541 , and other ends of the connection pipes L 4  are coupled to other ends of the evaporators  525  on the inlet side of the chiller units  520   a  to  520   f    
     That is, the connection pipes L 1  to L 4  connect the chiller units  520   a  to  520   f  and the use units  530   a  to  530   c  in a cyclic manner. Water serving as a heat medium flows in the connection pipes L 1  to L 4 . 
     The communicating pipe L 5  connects the inlet side and the outlet side of all of the chiller units  520   a  to  520   f  (specifically, the inlet side and the outlet side of the evaporators  525 ) through the feed header  542  and the return header  541 . Specifically, the connection pipes L 1  connected to the inlet side of the chiller units  520   a  to  520   f  are connected to the feed header  542 , and the connection pipes L 4  connected to the outlet side of the chiller units  520   a  to  520   f  are connected to the return header  541 . The communicating pipe L 5  connects the feed header  542  and the return header  541  such that the inlet side and the outlet side of the chiller units  520   a  to  520   f  can be connected without the intervention of the use units  530   a  to  530   c.  In the communicating pipe L 5 , water that is a heat medium flowing out of the chiller units  520   a  to  520   f  and that does not flow in the use units  530   a  to  530   c  flows toward the return header  541 . That is, the communicating pipe L 5  can be said to be a pipe for returning water that is not used in the use units  530   a  to  530   c  to the chiller units  520   a  to  520   f  again. 
     The pumps  544   a  to  544   f  are disposed on the connection pipes L 4  in such a manner as to correspond to the chiller units  520   a  to  520   f,  respectively. The pumps  544   a  to  544   f  are pumps of a variable capacity type in which the capacity is adjustable and the discharge capacity is adjustable, and are inverter driven by the controller  580 . As indicated by arrows attached to the pumps  544   a  to  544   f  in  FIG. 18 , the pumps  544   a  to  544   f  send water as the heat medium flowing out of the use units  30   a  to  30   f  (more specifically, the use-side valves  532   a  to  532   c ) to the chiller units  520   a  to  520   f,  thereby circulating the water in the heat medium circuit  540 , In other words, the pumps  544   a  to  544   f  cause the heat medium (i.e., water) flowing in the connection pipes L 1  to L 4  to circulate between the chiller units  520   a  to  520   f  and the use units  530   a  to  530   c.    
     The bypass valve  543  adjusts the flow rate of the water flowing in the chiller unit  520   a.  The flow rate of the water flowing through the chiller unit  520   a  is determined by the opening degree of the bypass valve  543 . 
     The use-side valves  532   a  to  532   c  and the use-side heat exchangers  533   a  to  533   c  in the use units  530   a,    530   b,  and  530   c  will be described in “(2-4) Use Unit Group”. 
     Further, the flow meter  545  and the plurality of sensors T 1 , T 2 , T 3   a  to T 3   f,  and T 4   a  to T 4   f  are attached to the heat medium circuit  540 . The flow meter  545  is attached to the merging portion of the connection pipes L 3  through which the water flowing out of the use units  530   a  to  530   c  flows, in front of the return header  541 . The flow meter  545  measures the total flow rate of the water flowing through the use units  530   a  to  530   c.    
     The temperature detection sensor T 1  is attached to a portion of the connection pipe L 2  before the pipe L 2  is branched, near the second feed header  543 . The temperature detection sensor T 1  detects the temperature of the water as the heat medium flowing in the connection pipe L 2 . The temperature detection sensor T 2  is attached to the merging portion of the connection pipes L 3 , near the return header  541 . The temperature detection sensor T 2  detects the temperature of the water as the heat medium flowing in the connection pipes L 3 . The temperature detection sensors T 3   a  to T 3   f  are disposed near the inlets of the chiller units  520   a  to  520   f  on the connection pipes L 4  in such a manner as to correspond to the chiller units  520   a  to  520   f,  respectively. The temperature detection sensors T 3  detect the temperatures of the water as the heat medium flowing in the connection pipes L 4 , that is, inlet temperatures b 1  of the chiller units  520   a  to  520   f  The temperature detection sensors T 4   a  to T 4   f  are disposed near the outlets of the chiller units  520   a  to  520   f  on the connection pipes L 1  in such a manner as to correspond to the chiller units  520   a  to  520   f,  respectively. The temperature detection sensors T 4  detect the temperatures of the water as the heat medium flowing in the connection pipes L 1 , that is, outlet temperatures b 2  of the chiller units  520   a  to  520   f.    
     The information detected by the flow meter  545  and the temperature detection sensors T 1  to T 2 , T 3   a  to T 3   f,  and T 4   a  to T 4   f  is acquired by the controller  580  and is used for various types of control. 
     (2-4) Use Unit Group 
     As illustrated in  FIG. 18 , the use unit group  530  includes the plurality of use units  530   a  to  530   c  connected in parallel to each other. 
     The use units  530   a  to  530   c  have casings  531   a  to  531   c  each having a substantially rectangular parallelepiped shape, respectively. Each of the casings  531   a  to  531   c  has formed therein an air passage through which air flows. An air inflow end of the air passage is connected to an end of a suction duct, and an air outflow end of the air passage is connected to an end of an air supply duct. The other end of the suction duct and the other end of the air supply duct are connected to the space to be air conditioned. 
     The casings  531   a  to  531   c  have disposed therein the use-side valves  532   a  to  532   c  and the use-side heat exchangers  533   a  to  533   c,  which form the heat medium circuit  540 , and fans  536   a,    536   b,  and  536   c.    
     The use-side valves  532   a  to  532   c  adjust the amounts of water flowing through the use-side heat exchangers  533   a  to  533   c,  respectively. That is, the flow rates of the water flowing through the use units  530   a  to  530   c  are determined by the opening degrees of the use-side valves  532   a  to  532   c,  respectively. 
     Each of the use-side heat exchangers  533   a  to  533   c  performs heat exchange between the air in the space to be air conditioned and the water in the heat medium circuit  540  to cool the air. Specifically, the use-side heat exchangers  533   a  to  533   c  are fin-and-tube heat exchangers each having a plurality of heat transfer fins and heat transfer tubes passing through the heat transfer fins. Water circulating through the heat medium circuit  540  flows through the heat transfer tubes of the use-side heat exchangers  533   a  to  533   c,  and the heat of the water is supplied to the air through the heat transfer tubes and the heat transfer fins to cool the air. 
     The fans  36   a  to  36   c  are each a fan whose number of revolutions can be changed stepwise by inverter control such that the volume of blowing the cooled air can he adjusted. 
     (2-5) System Controller 
     The controller  580  is used for the overall control of the device management system  510 . The controller  580  will be described in detail below. 
     (3) Basic Operation of Device Management System 
     Next, the operation of the device management system  510  will be described. The device management system  510  is capable of performing a cooling operation for cooling air. The device management system  510  may be configured to be capable of also performing a heating operation, a dehumidifying operation, and a humidifying operation. 
     (3-1) Cooling Operation 
     In a cooling operation illustrated in  FIG. 21 , the compressor  522 , the pumps  544   a  to  544   f , and the fans  36   a  to  36   c  are operated. 
     In the cooling operation, a refrigeration cycle is performed in the refrigerant circuit  521 . Specifically, the refrigerant compressed by the compressor  522  radiates heat to the water flowing through the heat dissipation circuit  560  and condenses in the radiator  523 . The refrigerant cooled by the radiator  523  is decompressed by the expansion valve  524 . Thereafter, the refrigerant absorbs heat from the water flowing through the heat medium circuit  540  and evaporates in the evaporator  525 . The refrigerant evaporated in the evaporator  525  is sucked into and compressed by the compressor  522 . The water flowing through the heat dissipation circuit  560 , which is heated by the radiator  523 , radiates heat to the outdoor air in the cooling tower  570 . In the heat medium circuit  540 , the water cooled by the evaporator  525  of the refrigerant circuit  521  cools the air flowing through the respective air passages of the casings  531   a  to  531   c  of the use-side heat exchangers  533   a  to  533   c.  The water that has passed through the use-side heat exchangers  533   a  to  533   c  returns to the evaporator  525  of the refrigerant circuit  521  and is cooled again. In the heat medium circuit  540 , the cold energy obtained by the water from the refrigerant in the evaporator  525  is conveyed to the use-side heat exchangers  533   a  to  533   c  and is supplied to the air. 
     In the use units  530   a  to  530   c,  as described above, the indoor air taken in from the spaces to be air conditioned through the suction ducts flows through the air passages of the casings  531   a  to  531   c.  The air is cooled and dehumidified in the use-side heat exchangers  533   a  to  533   c  by using the water in the heat medium circuit  540 . The air cooled by the use-side heat exchangers  533   a  to  533   c  is supplied to the respective spaces to be air conditioned through the air supply ducts as supply air. 
     (4) Detailed Description of System Controller 
       FIG. 20  is a block diagram schematically illustrating the configuration of the controller  580  according to this embodiment and various devices connected to the controller  580 . As illustrated in  FIG. 20 . the controller  580  is implemented by a computer. The controller  580  includes a control calculation device and a storage device. The control calculation device can be implemented using a processor such as a CPU or a GPU. The storage device is constituted by a RAM, a ROM, a computer-readable storage medium, and the like. The storage device can be used as a database. The control calculation device reads a program stored in the storage device and performs predetermined information processing and calculation processing in accordance with the program. Further, the control calculation device can write a calculation result to the storage device or read information stored in the storage device in accordance with the program. As illustrated in  FIG. 20 , the controller  580  includes an acquisition unit  581 , a storage unit  582 , a control calculation unit  583 , and an output unit  584 . 
     (4-1) Acquisition Unit 
     The acquisition unit  581  is an interface that acquires various types of information for calculating thermal load information c 1 , predicted thermal load information c 3 , and the like from the various devices and the like connected to the controller  580 . 
     Specifically, the acquisition unit  581  acquires, as information for calculating the thermal load information c 1 , the inlet temperatures b 1  and the outlet temperatures b 2  of the chiller units  520   a  to  520   f,  which are the detection results of the temperature detection sensors T 3   a  to T 3   f  and T 4   a  to T 4   f.    
     The acquisition unit  581  further acquires, as information for calculating the predicted thermal load information c 3 , information b 3  on the number of operating devices among the chiller units  520   a  to  520   f,  actual operating device information b 4  of the chiller units  520   a  to  520   f,  weather information b 5 , and the like. The information b 3  on the number of operating devices among the chiller units  520   a  to  520   f  includes information on whether each of the chiller units  520   a  to  520   f  is operating. For example, the information b 3  on the number of operating devices among the chiller units  520   a  to  520   f  indicates that the chiller units  520   a  to  20   c  are operating and the chiller units  20   d  to  20   f  are not operating and indicates that three out of the six chiller units  520   a  to  520   f  are operating simultaneously. The actual operating device information b 4  of the chiller units  520   a  to  520   f  includes information on the respective operating conditions of the chiller units  520   a  to  520   f.  For example, the operating device information b 4  of the chiller units  520   a  to  520   f  indicates that the chiller unit  520   a  is operating at a capacity of 80% and the chiller unit  520   f  is operating at a capacity of 0% (not operating). The weather information b 5  is information received from a sensor disposed in the device management system  510  or from an external system and is information indicating the outside air temperature, weather, humidity, and the like in the vicinity of the device management system  510 . The information b 3  on the number of operating devices among the chiller units  520   a  to  520   f,  the actual operating device information b 4  of the chiller units  520   a  to  520   f,  and the weather information b 5  are stored in the storage unit  582  in association with the thermal load information c 1 . 
     The acquisition unit  581  may acquire other information, if necessary. The acquisition unit  581  acquires the information described above at any time interval (for example, every minute) or in response to a request from the external system. The various types of information acquired by the acquisition unit  581  are stored and accumulated in appropriate areas of the storage unit  582 . 
     (4-2) Storage Unit  582   
     The storage unit (accumulation unit)  582  stores and accumulates information used for a program, the information acquired by the acquisition unit  581 . information processed and generated by the control calculation unit  583  through computation or the like, and so on. For convenience, information stored in advance in the storage unit  582  as the information used for the program is assigned the suffix a, the information acquired and accumulated by the acquisition unit  581  is assigned the suffix b, and the information processed and generated by the control calculation unit  583  is assigned the suffix c. The route of acquisition of the various types of information is not limited to this. 
     The storage unit  582  stores, as the information used for the program, the capacity control lower limit a 2 , the capacity control upper limit a 1 , and an operating priority a 3  of each of the chiller units  520   a  to  520   f.  The operating priority a 3  is the order of operation of the chiller units  520   a,  to  520   f.    
     The storage unit  582  further stores, as the information used for the program, a first standby time a 4  that is set in advance by the administrator or the like of the device management system  510 . The first standby tune a 4  is information indicating the standby tune for the device management system  510  to change the number of operating devices among the chiller units  520   a  to  520   f.  A number-of-device determination unit of the control calculation unit  583  described below increases the number of operating devices among the chiller units  520   a  to  520   f  if a preset number change condition is continuously satisfied for the first standby time a 4 . The number change condition can be set in advance such that, for example, the output of the operating chiller units  520   a  to  520   f  is 85% or more. If a second standby time c 6  is calculated by a standby time determination unit  583   d  of the control calculation unit  583  described below, a number-of-operating-device determination unit  583   f  increases the number of operating devices among the chiller units  520   a  to  520   f  on the basis of the second standby time c 6 . 
     The storage unit  582  is capable of storing the inlet temperatures b 1 , the outlet temperatures b 2 , the information b 3  on the number of operating devices among the chiller units  520   a  to  520   f,  the operating device information b 4  of the chiller units  520   a  to  520   f,  and the weather information b 5 , which are acquired by the acquisition unit  581 , in association with each other on the basis of the times at which the acquisition unit  581  acquired the respective pieces of information. 
     The storage unit  582  accumulates, as the information processed and generated by the control calculation unit  583  through computation or the like, the thermal load information c 1 , a thermal-load local maximum value c 2 , the predicted thermal load information c 3 , a predicted thermal-load local maximum value c 4 . predicted number-of-operating-device information c 5 , information on the second standby time c 6 , and deviation information c 7 . 
     The thermal load information el is information indicating a thermal load calculated by a thermal load calculation unit  583   e,  which is a functional unit of the control calculation unit  583  described below. In this embodiment, the thermal load information c 1  is calculated by using the information on the inlet temperatures b 1  and the outlet temperatures b 2  of the chiller units  520   a  to  520   f  stored in the storage unit  582 . However, the thermal load information c 1  may be calculated by using other information related to the device management system  510 . The thermal load information c 1  is calculated by the thermal load calculation unit  583   e  at intervals of a predetermined time (for example, every minute) and is accumulated in the storage unit  582  in association with each preset period (for example, each period of 9:00 to 20:00, which is an operating time period of the device management system  510 ).  FIG. 21  is a graph representing the thermal load information c 1  accumulated in the storage unit  582 . 
     In the thermal load information ci accumulated in the storage unit  582 , a local maximum value of the thermal load in a preset period (9:00 to 20:00 on a certain day) and the time at which the local maximum value occurs are accumulated in the storage unit  582  as the thermal-load local maximum value c 2  in the period in association with the thermal load information c 1 . For example, in  FIG. 4 , the thermal-load local maximum value c 2  is the value of the thermal load at 13:00. 
     The predicted thermal load information c 3  is information calculated by a thermal load prediction unit  583   a,  which is a functional unit of the control calculation unit  583 , and is information indicating a predicted value of the thermal load in a predetermined period in the future (for example, 9:00 to 20:00 on the next day). The predicted thermal load information c 3  in this embodiment is calculated on the basis of information stored in the storage unit  582 , such as the thermal load information c 1 , the thermal-load local maximum value c 2 , the actual operating device information b 4  of the chiller units  520   a  to  520   f,  and the weather information b 5 . The thermal load prediction unit  583   a  calculates a predicted value of the thermal load at predetermined time intervals (for example, every minute), and the calculated predicted value of the thermal load is accumulated in the storage unit  582  in association with each preset period (for example, each period of 9:00 to 20:00, which is an operating time period of the device management system  510 ). For example,  FIG. 22  is a graph representing the predicted thermal load information c 3  calculated on the basis of the thermal load information c 1  in  FIG. 21 , the thermal-load local maximum value c 2 , the operating device information b 4  of the chiller units  520   a  to  520   f,  and the weather information b 5 . 
     In  FIG. 22 , the vertical axis represents the predicted number-of-operating-device information c 5  indicating the number of operating devices among the chiller units  520   a  to  520   f,  which is required to process the thermal load. The predicted number-of-operating-device information c 5  is calculated by a number-of-operating-device prediction unit  583   b.    
     In the predicted thermal load information c 3 , a local maximum value among predicted values of the thermal load in a preset period is accumulated in the storage unit  582  as the predicted thermal-load local maximum value c 4  in the period. For example, in  FIG. 22 , the predicted thermal-load local maximum value c 4  is the predicted value of the thermal load at 13:00. 
     The deviation information c 7  is information calculated by a deviation determination unit  583   g,  which is a functional unit of the control calculation unit  583 , and is information indicating the degree of deviation of the actual thermal load information c 1  (the actual value of the thermal load) from the predicted thermal load information c 3  (the predicted value of the thermal load). For example, if the predicted thermal load information c 3  and the actual thermal load information c 1  completely match, the deviation information c 7  is 0%. In contrast, if the predicted thermal load information c 3  and the actual thermal load information c 1  are different, the deviation information c 7  has a value of 1% or more based on the degree of the difference. In this embodiment, the deviation information c 7  is represented by %. However, the deviation information c 7  may be represented by any other unit or the like. 
     (4-3) Control Calculation Unit 
     The control calculation unit  583  includes the thermal load prediction unit  583   a,  the number-of-operating-device prediction unit  583   b,  a standby time judgment unit  583   c,  the standby time determination unit  583   d,  the thermal load calculation unit  583   e,  the number-of-operating-device determination unit  583   f,  and the deviation determination unit  583   g  serving as functional units whose functions are implemented by a control calculation device and a storage device. 
     The thermal load prediction unit  583   a  calculates the predicted thermal load information c 3 . The predicted thermal load information c 3  calculated by the thermal load prediction unit  583   a  is accumulated in the storage unit  582 . 
     The number-of-operating-device prediction unit  583   b  calculates the predicted number-of-operating-device information c 5  on the basis of the predicted thermal load information c 3  calculated by the thermal load prediction unit  583   a  and the capacity of the chiller units  520   a  to  520   f . The predicted number-of-operating-device information c 5  is information indicating the number of operating devices among the chiller units  520   a  to  520   f , which is required to process the predicted value of thermal load included in the predicted thermal load information c 3 . The predicted number-of-operating-device information c 5  is accumulated in the storage unit  582  in association with the predicted thermal load information c 3 , 
     The standby time judgment unit  583   c  determines whether the predicted thermal-load local maximum value c 4  included in the predicted thermal load information c 3  can be processed by increasing the number of operating devices among the chiller units  520   a  to  520   f  based on the first standby time a 4 . Specifically, the standby time judgment unit  583   c  determines whether the number of operating devices can be increased to the number of operating devices among the chiller units  520   a  to  520   f , which is required to process the predicted thermal-load local maximum value c 4 , for a period from the operating start time of the chiller units  520   a  to  520   f  to the time at which the predicted thermal-load local maximum value c 4  occurs. If the standby time judgment unit  583   c  determines that the process described above is possible, the number-of-operating-device determination unit  583   f  described below determines whether to increase the number of operating devices on the basis of the first standby time a 4 . On the other hand, if the standby time judgment unit  583   c  determines that the process described above is not possible, the number-of-operating-device determination unit  583   f  described below determines whether to increase the number of operating devices on the basis of the second standby time c 6  accumulated in the storage unit  582 . 
     The standby time determination unit  583   d  calculates information indicating the second standby time c 6 . The second standby time c 6  is information indicating the length of the standby time calculated on the basis of the predicted thermal load information c 3 . The information on the second standby time c 6  in this embodiment is calculated by, if the predicted thermal load information c 3  includes one predicted thermal-load local maximum value c 4 . dividing the elapsed time from the start of a predetermined period in the future to the time of occurrence of the predicted thermal-load local maximum value c 4  by the number of times the number of operating devices among the chiller units  520   a  to  520   f  for processing the predicted thermal-load local maximum value c 4  is increased. For example, the second standby time c 6  calculated on the basis of the predicted thermal load information c 3  in  FIG. 22  is obtained by dividing the elapsed time from the start to the predicted thermal-load local maximum value c 4 , which is 48 hours (from 9:00 to 13:00), by the number of times the number of operating devices is increased, which is 5 (from one device to six devices). Therefore, the second standby time c 6  is 48 minutes. The second standby time c 6  calculated. by the standby time determination unit  583   d  is stored in the storage unit  582 . 
     The thermal load calculation unit  583   e  calculates, as the thermal load information c 1 , the actual value of the thermal load to be processed by the chiller units  520   a  to  520   f  on the basis of the inlet temperatures b 1  and the outlet temperatures b 2 . The thermal load calculation unit  583   e  calculates the thermal load information c 1  every minute, for example. The thermal load information c 1  calculated by the thermal load calculation unit  583   e  is accumulated in the storage unit  582 . 
     If a preset number change condition is continuously satisfied for the first standby time a 4  or the second standby time c 6 , the number-of-operating-device determination unit  583   f  determines that the number of operating devices among the chiller units  520   a  to  520   f  is to be increased. If the number-of-operating-device determination unit  583   f  determines that the number of operating devices among the chiller units  520   a  to  520   f  is to be increased, information indicating the increase in the number of operating devices among the chiller units  520   a  to  520   f  is transmitted to the chiller units  520   a  to  520   f , and any of the chiller units  20   b  to  20   f starts operating. 
     The deviation determination unit  583   g  determines the degree of deviation of the actual thermal load information c 1  acquired by the acquisition unit  581  and stored in the storage unit  582  from the predicted thermal load information c 3  calculated by the thermal load prediction unit  583   a  and stored in the storage unit  582 , and generates the deviation information c 7  as information indicating the degree of deviation. The deviation information c 7  is stored in the storage unit  582 . The deviation determination unit  583   g  determines the degree of deviation at intervals of a predetermined time (for example, every minute) and generates the deviation information c 7 . 
     (4-4) Output Unit 
     The output unit  584  is a display, a touch panel, a speaker, or the like capable of outputting information accumulated in the storage unit. The output unit  584  can function as a deviation information c 7  output unit that outputs the deviation information c 7  stored in the storage unit  582 . 
     (5) Standby Time Determination Process 
       FIG. 23  illustrates a process flow for determining the standby time in the device management system  510  according to this embodiment. As illustrated in  FIG. 23 , the thermal load prediction unit  583   a  of the control calculation unit  583  calculates the predicted thermal load information c 3  on the basis of the information accumulated in the storage unit  582  and stored in the storage unit  582 , such as the thermal load information c 1 , predicted local maximum information, predicted local minimum information, the operating device information b 4  of the chiller units  520   a  to  520   f , and the weather information b 5  (step ST 1 ). 
     Here, the thermal load prediction unit  583   a  calculates the predicted thermal load information c 3  at predetermined time intervals (for example, every minute) in a preset predetermined period in the future (for example, 9:00 to 20:00 on the next day). The (plurality of pieces of) thermal load information c 1  calculated by the thermal load prediction unit  583   a  is accumulated in the storage unit  582  (step ST 2 ). At this time, in the thermal load information c 1 , a predicted thermal-load local maximum value in the predetermined period and the time at which the local maximum value occurs are stored in the storage unit  582  in association with the thermal load information c 1  (step ST 3 ). Further, the number-of-operating-device prediction unit  583   b  calculates the predicted number-of-operating-device information c 5  on the basis of the predicted thermal load information c 3  and the capacity of the driller units  520   a  to  520   f , and stores the predicted number-of-operating-device information c 5  in the storage unit  582  in association with the predicted thermal load information c 3  (step ST 4 ). Here, the predicted thermal load information, the predicted local maximum information, and the predicted number-of-operating-device information c 5  may be stored in association with each other as in, for example, the graph illustrated in  FIG. 22 . 
     Then, the standby time judgment unit  583   c  of the control calculation unit  583  determines whether the predicted thermal-load local maximum value can be processed by processing based on the first standby time a 4  (step ST 5 ). Specifically, for example, if the predicted thermal load information c 3  calculated in step ST 1  is that illustrated in  FIG. 22 , the thermal-load local maximum value c 2  is the value of the thermal load at 13:00. Further, the six chiller units  520   a  to  520   f  are required to process the thermal load. 
     Here, for example, if the first standby time a 4  set in advance by the administrator or the like of the device management system  510  is 30 minutes, the six chiller units  520   a  to  520   f  can be caused to operate at 13:00. Thus, the standby time judgment unit  583   c  determines that the process is possible (YES). If this determination is made, the device management system  510  performs control to increase the number of operating devices by using the first standby time a 4  Specifically, if a preset number change condition is continuously satisfied for the first standby time a 4 , the device management system  510  determines that control is to be performed to increase the number of operating devices among the chiller units  520   a  to  520   f  in accordance with a program (step ST 6 ). 
     On the other hand, for example, if the first standby time a 4  set in advance is 1 hour, it requires 5 hours to operate the six chiller units  520   a  to  520   f  and it is not possible to cause the six chiller units  520   a  to  520   f  to operate at 13:00. Thus, the standby time judgment unit  583   c  determines that the process is not possible (NO). If this determination is made, the standby time judgment unit  583   c  determines that control is to be performed to increase the number of operating devices by using the second standby time c 6  calculated by the standby time determination unit  583   d  (step ST 7 ). 
     In step ST 7 , the standby time determination unit  583   d  performs calculation by dividing the elapsed time from the start time of a predetermined period in the future (for example, 9:00) to the time of occurrence of the predicted thermal-load local maximum value c 4  (for example, 13:00) by the number of times the number of operating devices among the chiller units  520   a  to  520   f  for processing the predicted thermal-load local maximum value c 4  is increased. For example, if the elapsed time is 4 hours illustrated in  FIG. 22  and the number of times the number of operating devices is increased is 5, the second standby time c 6  is 48 minutes. 
     As described above, through this processing, the device management system  510  determines whether to perform processing for increasing the number of operating devices among the chiller units  520   a  to  520   f  on the basis of a first time period, or perform processing for increasing the number of operating devices among the chiller units  520   a  to  520   f  on the basis of a second time period. If a preset number change condition is continuously satisfied for the first standby time a 4  or the second standby time c 6 , the number-of-operating-device determination unit  583   f  determines that the number of operating devices among the chiller units  520   a  to  520   f  is to be increased (step ST 8 ). 
     (6) Features 
     (6-1) The device management system  510  according to this embodiment is a system for managing the number of operating devices among the chiller units  520   a  to  520   f  serving as heat source devices. The device management system  510  includes the number-of-operating-device determination unit  583   f  and the standby time determination unit  583   d . When a condition for changing the number of operating devices regarding a thermal load is continuously satisfied for a predetermined standby time, the number-of-operating-device determination unit  583   f  determines that the number of operating devices is to be increased. The standby time determination unit determines the length of the standby time on the basis of the predicted thermal load information c 3 . 
     There is available an existing system that adopts a plurality of heat source devices, in which the number of operating devices among heat source devices is changed in accordance with a thermal load. In such a system, the thermal load may be predicted on the basis of previous information on the thermal load, and the number of operating devices among the heat source devices may be determined. In prediction based on the previous information on the thermal load, however, the actual thermal load during the operation of the heat source devices may greatly deviate from the previous information on the thermal load depending on the operating condition of the heat source devices or the weather condition. If the system is operated in such a state, a large load is imposed on the heat source devices, leading to extra power consumption. 
     With the configuration described above, the device management system  510  according to this embodiment determines the standby time for changing the number of operating devices among the heat source devices. This makes it possible to predict the thermal load on the basis of the previous information on the thermal load and manage the number of operating devices among the heat source devices on the basis of the actual thermal load during the operation of the heat source devices. The device management system  510  according to this embodiment appropriately manages the number of operating devices among the heat source devices, thereby reducing the load on the heat source devices and contributing to reduction in extra power consumption. 
     (6-2) The device management system  510  according to this embodiment further includes the thermal load calculation unit  583   e  and the storage unit  582  serving as an accumulation unit. The thermal load calculation unit  583   e  calculates the thermal load information c 1 . The storage unit  582  accumulates the thermal load information c 1  calculated by the thermal load calculation unit  583   e . The predicted thermal load information c 3  is calculated on the basis of the thermal load information c 1  accumulated in the storage unit  582 . 
     This contributes to more accurate prediction of the thermal load and contributes to controlling the number of operating devices among the heat source devices to an appropriate number. 
     (6-3) In the device management system  510  according to this embodiment, if the number of operating devices among the chiller units  520   a  to  520   f  is predicted to be insufficient, the standby time determination unit  583   d  reduces the length of the standby time on the basis of the predicted thermal load information c 3 . If the number of operating devices among the chiller units  520   a  to  520   f  is predicted to be excessive, the standby time determination unit  583   d  increases the length of the standby time. 
     This contributes to more accurate prediction of the thermal load and contributes to controlling the number of operating devices among the heat source devices to an appropriate number. 
     (6-4) The storage unit  582  of the device management system  510  according to this embodiment accumulates the information b 3  on the number of operating devices among the chiller units  520   a  to  520   f  for processing the thermal load, in association with the thermal load information c 1 . 
     (6-5) The thermal load calculation unit  583   e  of the device management system  510  according to this embodiment calculates the thermal load information c 1  on the basis of the inlet temperatures, which are the temperatures of the heat medium entering the chiller units  520   a  to  520   f , and the outlet temperatures, which are the temperatures of the heat medium exiting from the chiller units  520   a  to  520   f . The storage unit  582  further accumulates the thermal load information cl calculated by the thermal load calculation unit  583   e , the weather information b 5 , and/or the operating device information of the chiller units  520   a  to  520   f  in association with each other. 
     This contributes to more accurate prediction of the thermal load and contributes to controlling the number of operating devices among the heat source devices to an appropriate number. 
     (6-6) If the number of occurrences of the predicted thermal-load local maximum value c 4  included in the predicted thermal load information c 3  is one, the standby time determination unit  583   d  of the device management system  510  according to this embodiment determines, as the length of the standby time, a value obtained by dividing the time required from the operating start time of the chiller units  520   a  to  520   f  to the time of occurrence of the predicted thermal-load local maximum value c 4  by the required number of times the number of devices is increased to make the number of operating devices among the chiller units  520   a  to  520   f  at the time of occurrence of the predicted thermal-load local maximum value c 4 . The predicted thermal-load local maximum value c 4  is a local maximum value of predicted values of the thermal load included in the predicted thermal load information c 3 . 
     This contributes to more accurate prediction of the thermal load and contributes to controlling the number of operating devices among the heat source devices to an appropriate number. 
     (6-7) The standby time determination unit  583   d  of the device management system  510  according to this embodiment calculates the time at which the number of operating devices among the chiller units  520   a  to  520   f  is increased, on the basis of the thermal load information c 1  and the information b 3  on the number of operating devices among the chiller units  520   a  to  520   f . Further, the standby time determination unit  583   d  sets, as the length of the standby time, the time period from when the number of operating devices is changed to when the number of operating devices is next changed. 
     This contributes to more accurate prediction of the thermal load and contributes to controlling the number of operating devices among the heat source devices to an appropriate number. 
     (6-8) The device management system  510  according to this embodiment further includes the deviation information output unit  584 . if the deviation of the actual thermal load in the chiller units  520   a  to  520   f  from the thermal load information c 1  is larger than a predetermined threshold value, the deviation information output unit  584  outputs the thermal load deviation information c 7 . 
     (7) Modifications 
     (7-1) Modification 1 
     In the embodiment described above, a process for determining an increase in the number of operating devices among the chiller units  520   a  to  520   f  has been described. However, the device management system  510  according to this embodiment can also be used in a process for determining a decrease in the number of operating devices among the chiller units  520   a  to  520   f.    
     In the device management system  510  according to this embodiment, the storage unit  582  may store a third standby time for decreasing the number of operating devices that is set in advance by the administrator or the like of the device management system  510 . The third standby time is information indicating a standby time for the device management system  510  to decrease the number of operating devices among the chiller units  520   a  to  520   f . If a preset number change condition is continuously satisfied for the third standby time, the number-of-device determination unit of the control calculation unit  583  decreases the number of operating devices among the chiller units  520   a  to  520   f . The number change condition can be set in advance such that, for example, the output of the operating chiller units  520   a  to  520   f  is less than or equal to 50%. If a fourth standby time is calculated by the standby time determination unit  583   d  of the control calculation unit  583 , the number-of-operating-device determination unit  583   f  decreases the number of operating devices among the chiller units  520   a  to  520   f  on the basis of the fourth standby time. 
     The fourth standby time is information indicating the length of the standby time calculated on the basis of the predicted thermal load information c 3  and is calculated by, if the predicted thermal load information c 3  includes one predicted thermal-load local maximum value c 4 , dividing the elapsed time from the time of occurrence of the predicted thermal-load local maximum value c 4  to the end time of a predetermined period in the future by a required number of times the number of operating devices is decreased. For example, in the case illustrated in  FIG. 22 , the elapsed time from the time of occurrence of the predicted thermal-load local maximum value c 4  to the end time of a predetermined period in the future is 7 hours (from 13:00 to 20:00), and the required number of times the number of operating devices is decreased is 5 (from six devices to one device). Therefore, the fourth standby time is 84 minutes. 
     Accordingly, the device management system  510  according to this embodiment can predict the thermal load on the basis of previous information on the thermal load, and manage the number of operating devices among heat source devices on the basis of the actual thermal load during the operation of the heat source devices. The device management system  510  according to this embodiment appropriately manages the number of operating devices among the heat source devices, thereby reducing the load on the heat source devices and contributing to reduction in extra power consumption. 
     (7-2) Modification 2 
     In the embodiment described above, the description has been given of a case where the number of occurrences of a peak load included in the thermal load information c 1  is one. However, the device management system  510  according to this embodiment can be used even if a peak load occurs a plurality of times. 
     For example.  FIG. 24  illustrates the predicted thermal load information c 3  in a different period (9:00 to 20:00 on a different day) from that in  FIG. 22 . In  FIG. 24 , predicted thermal-load local maximum values c 4  are the predicted value of the thermal load at 13:00, and the predicted value of the thermal load at 15:00. Further, a local minimum value of the thermal load between the two predicted thermal-load local maximum values c 4  in  FIG. 24  is accumulated in the storage unit  582  as a predicted thermal-load local minimum value c 8  in a preset period. The predicted thermal-load local maximum values c 4  and the predicted thermal-load local minimum value c 8  in the preset period are accumulated in the storage unit  582  in association with each other, The number of predicted thermal-load local maximum values c 4  in the preset period may be one or more, and the number of predicted thermal-load local minimum values c 8  may be one or more or zero (no predicted thermal-load local minimum value c 8 ). 
     If a plurality of predicted thermal-load local maximum values c 4  are present, the standby time determination unit  583   d  calculates, as a fifth standby time, a standby time from the time of occurrence of the predicted thermal-load local minimum value c 8  to the time of occurrence of the next predicted thermal-load local maximum value c 4 . The fifth standby nine is calculated by dividing the elapsed time from the time of occurrence of the predicted thermal-load local minimum value c 8  to the time of occurrence of the next predicted thermal-load local maximum value c 4  by the number of times the number of operating devices is increased during the elapsed time. For example, in the predicted thermal load information c 3  illustrated in  FIG. 24 , the elapsed time is 1 hour (from 14:00 to 15:00), and the number of times the number of operating devices is increased is 1 (from five devices to six devices). Therefore, the fifth standby time is 30 minutes. 
     If the number of occurrences of the predicted thermal-load local maximum value c 4  included in the predicted thermal load information c 3  is plural, the standby time determination unit  583   d  of the device management system  510  according to this embodiment sets the length of the standby time from the time at which the predicted thermal-load local minimum value c 8  included in the predicted thermal load information c 3  occurs until the predicted thermal-load local maximum value c 4  next occurs, to a value obtained by dividing the time required from the time at which the predicted thermal-load local minimum value c 8  included in the predicted thermal load information c 3  occurs until the predicted thermal-load local maximum value c 4  next occurs by the number of times the number of operating devices is increased or decreased in the time slot. The predicted thermal-load local maximum value c 4  is a local maximum value of predicted values of the thermal load included in the predicted thermal load information c 3 . The predicted thermal-load local minimum value c 8  is a local minimum value of predicted values of the thermal load included in the predicted thermal load information c 3 . 
     While embodiments of the present disclosure have been described, it will be understood that forms and details can be changed in various ways without departing from the spirit and scope of the present disclosure as recited in the claims. 
     REFERENCE SIGNS LIST 
     
         
           1  heat source system 
           10 ,  11 ,  12 ,  13  heat source device (example of specific device) 
           40  pump (example of specific device) 
           50  device management apparatus 
           111 ,  121 ,  131  chiller (example of specific device) 
           62  differential pressure sensor 
           63  outlet temperature sensor 
           301  heat source system 
           310 ,  311 ,  312 ,  313  heat source device 
           320  use-side device 
           340  pump 
           350  management apparatus 
           363  outlet temperature sensor 
           411 ,  421 ,  431  chiller 
           412 ,  422 ,  432  cooling tower 
           413 ,  423 ,  433  water heater 
           510  device management system 
           520   a  to  520   f  heat source device 
           582  accumulation unit 
           583   d  standby time determination unit 
           583   e  thermal load calculation unit 
           583   f  number-of-operating-device determination unit 
           584  deviation information output unit 
         b 1  inlet temperature 
         b 2  outlet temperature 
         b 3  information on the number of operating devices 
         b 5  weather information 
         c 1  thermal load information 
         c 3  predicted thermal load information 
         c 4  predicted thermal-load local maximum value 
         c 7  deviation information 
         c 8  predicted thermal-load local minimum value 
       
    
     CITATION LIST 
     Patent Literature 
     PTL 1: Japanese Unexamined Patent Application Publication No. 10-89742