Abstract:
A control method includes supplying, by a second cooling apparatus, air at a first airflow rate to a plurality of computers each of which provides a first cooling apparatus; acquiring information on power consumption of the plurality of first cooling apparatuses and power consumption of the second cooling apparatus; supplying, by the second cooling apparatus, air at a second airflow rate, having a value obtained by changing the first airflow rate by a predetermined amount to the plurality of computers; acquiring information on the power consumption of the plurality of first cooling apparatuses and the power consumption of the second cooling apparatus; and changing an airflow rate of the second cooling apparatus by the predetermined amount, based on a comparison result between a changed amount of the power consumption of the plurality of first cooling apparatuses and a changed amount of the power consumption of the second cooling apparatus.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2014-036979, filed on Feb. 27, 2014, the entire contents of which are incorporated herein by reference. 
       FIELD 
       [0002]    The embodiments discussed herein are related to a system, a control method of the system, and a storage medium. 
       BACKGROUND 
       [0003]    Conventionally, there has been known an air-conditioning system including an electronic equipment housing rack, a main air conditioner that is installed in a room where the rack is installed and controls the temperature in the room, and a control circuit that is provided in the rack and controls power supply to an exhaust fan (for example, see Japanese Laid-open Patent Publication No. 2004-286365). The control circuit sends operation information on the exhaust fan or information on the power consumption of the electronic equipment housed in the rack to the main air conditioner. Further, the main air conditioner controls output based on the received information. 
         [0004]    In a data center, it is preferable to appropriately cool information processing apparatus by built-in fans in the information processing apparatus and a cooling apparatus. Further, it is preferable to reduce the total power consumption (electric power consumption in the data center) which is the sum of the power consumption of the information processing apparatus and the power consumption of the cooling apparatus. 
       SUMMARY 
       [0005]    According to an aspect of the invention, a control method of a system including a plurality of computers each of which provides a first cooling apparatus, and a second cooling apparatus that cools the plurality of computers by supplying air thereto, the control method includes supplying, by the second cooling apparatus, air at a first airflow rate to the plurality of computers; acquiring first information on power consumption of the plurality of first cooling apparatuses in the plurality of computers and power consumption of the second cooling apparatus under the supply of the air at the first airflow rate; supplying, by the second cooling apparatus, air at a second airflow rate to the plurality of computers after the first information is acquired, the second airflow rate having a value obtained by changing the first airflow rate by a predetermined amount; acquiring second information on the power consumption of the plurality of first cooling apparatuses in the plurality of computers and the power consumption of the second cooling apparatus under the supply of the air at the second airflow rate; and changing the airflow rate of the second cooling apparatus by the predetermined amount, based on a comparison result between a changed amount of the power consumption of the plurality of first cooling apparatuses in the plurality of computers and a changed amount in the power consumption of the second cooling apparatus under the condition that the airflow rate is changed from the first airflow rate to the second airflow rate. 
         [0006]    The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims. 
         [0007]    It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, as claimed. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0008]      FIG. 1  is a perspective view illustrating an example of a container-type data center; 
           [0009]      FIG. 2  is a top view illustrating an example of a modular-type data center; 
           [0010]      FIG. 3  is a top view illustrating an example of a server; 
           [0011]      FIG. 4  is a diagram illustrating an example of a control system of the data center; 
           [0012]      FIG. 5  is a flowchart illustrating an example of processing executed by a fan controller of the server; 
           [0013]      FIG. 6A ,  FIG. 6B , and  FIG. 6C  are explanation graphs of an example of a setting method of a target CPU temperature; 
           [0014]      FIG. 7A ,  FIG. 7B , and  FIG. 7C  are graphs illustrating relations between the airflow rate of an air conditioning fan and the temperatures of components in the server (part  1 ); 
           [0015]      FIG. 8A  and  FIG. 8B  are graphs illustrating relations between the airflow rate of the air conditioning fan and the temperatures of the components in the server (part  2 ); 
           [0016]      FIG. 9  is a graph illustrating a relation between the environment temperature and a duty ratio of a server built-in fan; 
           [0017]      FIG. 10  is a graph illustrating a relation between the airflow rate of the air conditioning fan and air conditioner power consumption; 
           [0018]      FIG. 11  is a flowchart illustrating an example of processing executed by a management manager; and 
           [0019]      FIG. 12  is a flowchart illustrating another example of processing executed by the management manager. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0020]    Hereinafter, embodiments will be explained in detail with reference to the attached drawings. 
         [0021]      FIG. 1  is a perspective view schematically illustrating an example of a container-type data center. A container-type data center  1  is a system that includes a container  2 . In the container  2 , formed are an air-intake port  20  of outside air and an air-exhaust port  22 . The positions of the air-intake port  20  and the air-exhaust port  22  may be flexibly determined. In the example illustrated in  FIG. 1 , the air-intake port  20  and the air-exhaust port  22  are formed on opposing side surfaces in the container  2 . Another air-intake port  21  may be formed in the container  2 . 
         [0022]    Racks  30  and a cooling apparatus  40  are disposed in the container  2 . Each of the racks  30  houses therein servers  50  (an example of information processing apparatus). The racks  30  are typically provided in plurality with respect to one container  2 . The servers  50  are provided in plurality with respect to one rack  30 . 
         [0023]    The cooling apparatus  40  includes a cooler  42  that creates cold air, and a container fan  44  (an example of a cooling fan). The cooler  42  may employ any creation principle for obtaining cold air, and may employ an evaporation method, for example. The cooler  42  and the container fan  44  may be provided in any numbers. The cooling apparatus  40  is disposed closer to the air-intake port  20  than the racks  30  in the container  2 , for example, as illustrated in  FIG. 1 . The container fan  44  introduces outside air through the air-intake port  20  in the container  2  when the cooling apparatus  40  is operated, as illustrated by an arrow P 1  in  FIG. 1 . The outside air introduced in this manner is cooled by the cooler  42 . The outside air cooled by the cooler  42  flows to the racks  30  due to an effect of the container fan  44 , as illustrated by an arrow P 2  in  FIG. 1 . With this, all the servers  50  housed in the rack  30   s  are cooled. The outside air used for the cooling of the servers  50  is discharged via the air-exhaust port  22  to the outside of the container  2  due to the effect of the container fan  44 , as illustrated by an arrow P 3  in  FIG. 1 . This implements the cooling of the servers  50  housed in the racks  30 . The airflow rate as a whole created by the cooling apparatus  40  is determined depending on the rotational speed (drive duty ratio) of the container fan  44 . 
         [0024]    The container-type data center  1  illustrated in  FIG. 1  is merely an example. The positions and the like of the cooling apparatus  40  and the racks  30  may be flexibly determined. 
         [0025]      FIG. 2  is a top view illustrating an example of a modular-type data center.  FIG. 2  schematically illustrates the flow of air in the modular-type data center by arrows. 
         [0026]    A modular-type data center  1 A is a system that includes the racks  30 , and a cooling apparatus  40 B. Each of the racks  30  similarly houses therein servers (not illustrated). 
         [0027]    The cooling apparatus  40 B is an air conditioner provided with a cooler  42 B (see  FIG. 4 ), and an air conditioning fan  44 B (an example of a cooling fan, see  FIG. 4 ). The cooling apparatus  40 B may send, similar to the cooling apparatus  40 , air containing cold air to the racks  30 . For example, the cooler  42 B includes a compressor for creating cold air. In the example illustrated in  FIG. 2 , one cooling apparatus  40 B is set with respect to four racks  30  in the modular-type data center  1 A of eight-rack blocks. Note that, the numbers of the cooling apparatuses  40 B and the racks  30  and the arrangement forms thereof may be flexibly determined. 
         [0028]    The modular-type data center  1 A alternately includes a cold aisle  62  and a hot aisle  64  between columns of the racks  30 . In the example illustrated in  FIG. 2 , the cold aisle  62  is formed between a first rack column  301  and a second rack column  302 . The hot aisle  64  is formed between the second rack column  302  and a third rack column  303 . As schematically illustrated by the arrows in  FIG. 2 , to the cold aisle  62 , sent are the cold air from the cooling apparatus  40 B in the first rack column  301  and the cold air from the cooling apparatus  40 B in the second rack column  302 . The air in the cold aisle  62  is used for cooling of the servers in the first rack column  301  and the second rack column  302 . As schematically illustrated by the arrows in  FIG. 2 , to the hot aisle  64 , sent are the air used for the cooling of the servers in the second rack column  302  and the air used for the cooling of the servers in the third rack column  303 . The air in the hot aisle  64  may be discharged to the outside of the modular-type data center  1 A. 
         [0029]      FIG. 3  is a top view illustrating an example of the server  50 . In  FIG. 3 , the server  50  is illustrated in a state where a cover is open for understanding the inner structure. Although one of the servers  50  is representatively illustrated in  FIG. 3 , the other servers  50  may be the same as the one server  50 . 
         [0030]    The server  50  includes a CPU  52 , a server built-in fan  54 , a power distribution unit (PDU)  56 , an environment temperature sensor  59 . 
         [0031]    The CPU  52  includes therein a CPU temperature sensor  58  (see  FIG. 4 ) that measures the temperature of the CPU  52  (hereinafter, referred to as “CPU temperature”). In the example illustrated in  FIG. 3 , although two CPUs  52  are mounted with respect to one server  50 , the number of the CPUs  52  may be flexibly determined. The server built-in fan  54  is provided to cool electronic components (for example, the CPU  52 , the PDU  56 , and the like) in the server  50 . 
         [0032]    The server built-in fans  54  are typically provided in plurality as illustrated in  FIG. 3 . The server built-in fan  54  may be provided at any position in the server  50 . 
         [0033]    The PDU  56  functions as a power supply for various kinds of loads (the CPU  52 , the server built-in fan  54 , and the like) in the server  50 . The PDU  56  includes therein a power consumption meter  57  (see  FIG. 4 ) that measures the electric power consumption of the server  50  (hereinafter, also referred to as “server power consumption”). The power consumption meter  57  may include a current sensor that detects the supply current and a voltage sensor that detects the supply voltage, from the PDU  56  to the various kinds of loads. In this case, the server power consumption is calculated based on the product of a current value and a voltage value. 
         [0034]    The environment temperature sensor  59  measures the environment temperature. The environment temperature sensor  59  may be disposed at the air-intake side in the server  50 . 
         [0035]      FIG. 4  is a diagram illustrating an example of a control system of a data center. Hereinafter, as an example, the data center is assumed to be the modular-type data center  1 A illustrated in  FIG. 2 . As for the container-type data center  1 , in the following explanation, “the cooling apparatus  40 B” may be regarded as “the cooling apparatus  40 ”, “the cooler  42 B” may be regarded as “the cooler  42 ”, and “the air conditioning fan  44 B” may be regarded as “the container fan  44 ”. 
         [0036]    The control system of the modular-type data center  1 A includes, as illustrated in  FIG. 4 , a management manager  100  (an example a cooling apparatus controller), a fan controller  56  in the server  50 , and an air conditioning controller  46  in the cooling apparatus  40 B. 
         [0037]    The fan controller  56  is provided in each of the multiple servers  50  in the modular-type data center  1 A, as illustrated in  FIG. 4 . Note that, only one fan controller  56  may be provided common to the multiple servers  50  in the modular-type data center  1 A. 
         [0038]    The air conditioning controller  46  is provided in each of the multiple cooling apparatuses  40 B in the modular-type data center  1 A, as illustrated in  FIG. 4 . Note that, only one air conditioning controller  46  may be provided common to the multiple cooling apparatuses  40 B in the modular-type data center  1 A. 
         [0039]    The management manager  100  may be implemented by a computer. The management manager  100  may be disposed inside the modular-type data center  1 A, or may be disposed outside the modular-type data center  1 A. 
         [0040]    The management manager  100  includes, for example, as illustrated in  FIG. 4 , a controller  101 , a main storage unit  102 , an auxiliary storage unit  103 , a drive device  104 , a network I/F unit  106 , and an input unit  107 . The controller  101  is a calculation device that executes a program stored in the main storage unit  102  or the auxiliary storage unit  103 . The controller  101  receives data from the input unit  107  or a storage device, calculates and processes the data, and then outputs the data to the storage device or the like. The main storage unit  102  is a read only memory (ROM), a random access memory (RAM), or the like. The main storage unit  102  is a storage device that stores or temporarily stores therein a program or the related data, such an OS as basic software or application software executed by the controller  101 . The auxiliary storage unit  103  is, for example, a hard disk drive (HDD) or the like. The auxiliary storage unit  103  is a storage device that stores therein data related to the application software or the like. The drive device  104  reads out a program from a recording medium  105 , for example, a flexible disk, and installs the program on the storage device. The recording medium  105  houses therein a predetermined program. The program housed in the recording medium  105  is installed on the management manager  100  via the drive device  104 . The installed predetermined program is executable by the management manager  100 . The network I/F unit  106  is an interface between the management manager  100  and peripheral devices (for example, the servers  50  and the like) that are coupled via a network constructed by data transmission lines such as wired and/or wireless channels and the like and have a communication function. The input unit  107  includes a key board provided with cursor keys, numeric input keys, various kinds of function keys, and the like, a mouse, a slide pad, and the like. In the example illustrated in  FIG. 4 , it is possible to implement the processing explained below and illustrated in  FIG. 11  and the like by causing the management manager  100  to execute a program. Alternatively, it is also possible to implement the processing explained below and illustrated in  FIG. 11  and the like by recording a program on the recording medium  105 , and causing the management manager  100  to read the recording medium  105  on which the program is recorded. The recording medium  105  is, for example, a recording medium, such as a CD-ROM, a flexible disk, and a magneto-optical disk, that optically, electrically and magnetically records information thereon. The recording medium  105  is, for example, a semiconductor memory, such as a ROM or a flash memory, which electrically records information thereon. Various types of the recording medium may be used as the recording medium  105 . A carrier wave is not included as the recording medium  105 . 
         [0041]    The management manager  100  is capable of communicating with all the servers  50  based on, for example, an intelligent platform management interface (IPMI). The management manager  100  acquires information (hereinafter, referred to as “server power consumption information”) indicating the power consumption and the like, from the servers  50 . The management manager  100  may notify all the servers  50  of a target CPU temperature. 
         [0042]    The management manager  100  is capable of communicating with all the cooling apparatuses  40 B based on, for example, a transmission control protocol (TCP). The management manager  100  acquires information (hereinafter, referred to as “air conditioner power consumption information”) indicating the electric power consumption (hereinafter, also referred to as “air conditioner power consumption”) and the like, from the cooling apparatuses  40 B. Each of the cooling apparatuses  40 B is provided with a power consumption meter  48 . The power consumption meter  48  measures the power consumption consumed by the cooling apparatus  40 B. The power consumption meter  48  may include a current sensor that detects the supply current and a voltage sensor that detects the supply voltage, to various kinds of loads (the air conditioning fan  44 B, the cooler  42 B, and the like) in the cooling apparatus  40 B. In this case, the air conditioner power consumption is calculated based on the product of a current value and a voltage value. The management manager  100  notifies each of the cooling apparatuses  40 B of a control target value of the air conditioning fan  44 B. The control target value may be a target value of any physical amount related to the airflow rate, for example, may be a target airflow rate itself or may be a target value related to the rotational speed of fan, the duty ratio of fan, or the like. 
         [0043]      FIG. 5  is a flowchart illustrating an example of processing executed by the fan controller  56  of the server  50 . Herein, although processing of one of the servers  50  is explained, processing of the other servers  50  may be the same. The processing illustrated in  FIG. 5  is started up, for example, when a power supply of the server  50  is turned on, and thereafter, is repeatedly executed for every predetermined cycle. 
         [0044]    At S 500 , the fan controller  56  receives a target CPU temperature from the management manager  100 . The target CPU temperature is set within the temperature range not more than an allowable upper limit value of the CPU temperature. An example of a setting method of the target CPU temperature is described later. 
         [0045]    At S 502 , the fan controller  56  determines control target values of the respective server built-in fans  54  such that the target CPU temperature is implemented in accordance with a deviation between the CPU temperature based on the detection result by the CPU temperature sensor  58  and the target CPU temperature, and controls the server built-in fans  54 . The control target values may be different from one another among the server built-in fans  54 . The control target values are typically the same among the server built-in fans  54 . In this manner, in accordance with the deviation between the CPU temperature and the target CPU temperature, the server built-in fans  54  are feedback-controlled. The mode of the feedback control may be flexibly determined. For example, proportional integral (PI) control may be used, or proportional integral derivative (PID) control, model control, and the like may be used. The control target value of the server built-in fan  54  may be a target value of any physical amount related to the airflow rate. For example, the control target value of the server built-in fan  54  may be a target airflow rate itself or may be a target value related to the rotational speed of fan, the duty ratio of fan, or the like. 
         [0046]    At S 502 , the CPU temperature becomes lower than the target CPU temperature in some cases even if the minimum airflow rate of the server built-in fan  54  is set such as a case where the server  50  is in an idle state. In this case, the fan controller  56  determines a target value of the server built-in fan  54  such that the airflow rate of the server built-in fan  54  becomes a minimum value (for example 0). 
         [0047]    At S 504 , the fan controller  56  creates server power consumption information indicating the current power consumption of the server  50  based on the detection result by the power consumption meter  57 , and transmits the server power consumption information to the management manager  100 . In the example illustrated in  FIG. 5 , the server power consumption information is transmitted to the management manager  100  for every predetermined cycle. However, the server power consumption information may be transmitted to the management manager  100  for multiple cycles, or may be transmitted to the management manager  100  in response to a request from the management manager  100 . 
         [0048]    All the processes at S 502  and S 504  are repeated for every predetermined cycle while the power supply of the server  50  is on state. 
         [0049]    As for the process at S 502  illustrated in  FIG. 5 , when the CPUs  52  in plurality are present in the server  50 , the server built-in fans  54  may be controlled such that the CPU temperatures can become the target CPU temperature. The target CPU temperature may be different among the CPUs  52  (which is described later with reference to  FIG. 6 ), or may be the same for all the CPUs  52 . Alternatively, the server built-in fans  54  may be controlled such that the highest CPU temperature among the CPU temperatures can be decreased to the target CPU temperature. 
         [0050]      FIG. 6A ,  FIG. 6B , and  FIG. 6C  are explanation graphs of an example of a setting method of a target CPU temperature.  FIG. 6A  is a graph illustrating a relation between, in one server  50 , the CPU temperature of the CPU  52  and the power consumption of the CPU  52  (CPU power consumption).  FIG. 6B  is a graph illustrating a relation between the CPU temperature and the power consumption of the server built-in fan  54  (fan power consumption).  FIG. 6C  is a graph illustrating a relation between the CPU temperature and the server power consumption. 
         [0051]    The CPU  52  with a load applied thereto consumes the power. The high CPU temperature results in generation of a leak current in a circuit of the CPU  52 . The relation between the leak current and the CPU temperature is determined in accordance with the circuit of the CPU  52  and the type of the CPU  52 . The leak current is in proportion to the CPU temperature. Therefore, the CPU power consumption linearly increase with increase in the CPU temperature, as illustrated in  FIG. 6A . 
         [0052]    Meanwhile, as for the relation between the rotational speed of the server built-in fan  54  and the power consumption of the server built-in fan  54 , the power consumption of the server built-in fan  54  exponentially increases as the rotational speed of the server built-in fan  54  increases. Decreasing the rotational speed of the server built-in fan  54  results in the less airflow rate for cooling the CPU  52 . Accordingly, the CPU temperature is raised. Therefore, a relation of an exponential function as illustrated in  FIG. 6B  is obtained as the relation between the CPU temperature and the fan power consumption. 
         [0053]    Herein, simply assuming that the server power consumption is a total of the CPU power consumption and the fan power consumption, a relation between the server power consumption and the CPU temperature as in  FIG. 6C  is obtained. In other words, a curve illustrated in  FIG. 6C  corresponds to the sum of a curve illustrated in  FIG. 6A  and a curve illustrated in  FIG. 6B . As illustrated in  FIG. 6C , a minimal value of the server power consumption is obtained at a specific CPU temperature Tt. Therefore, the CPU temperature Tt may be set to the target CPU temperature. With this, it is possible to implement such control that the minimum server power consumption is obtained on the server  50  basis. 
         [0054]    The characteristics illustrated in  FIG. 6  represent a characteristic of one CPU  52 , and a characteristic of one server built-in fan  54 . The server  50  may actually include the multiple CPUs  52  and the multiple server built-in fans  54  as described above. Therefore, in that case, the characteristics are added up to obtain the relation between the server power consumption and the CPU temperature as illustrated in  FIG. 6C . Also in this case, a minimal value similarly appears, so that the CPU temperature at which the minimal value appears may be set as the target CPU temperature. 
         [0055]    The CPU temperature Tt at which the abovementioned minimal value is obtained is known at a design stage by a test and the like. However, by considering that an individual difference of the servers  50  or a change in the characteristics with time, the CPU temperature Tt at which the minimal value appears may be derived for each of the servers  50 , and/or may be updated on a periodic basis. For example, it is preferable to change the target CPU temperature with respect to the CPU temperature Tt obtained at the design stage within the range of ±3° C., compare the amounts of server power consumption among the target CPU temperatures, and use the target CPU temperature at which the server power consumption is minimum. In this case, the target CPU temperature may differ for each of the CPUs  52 . The abovementioned CPU temperature Tt at which the minimal value is obtained differs in accordance with the environment temperature, so that the CPU temperature Tt may be derived in advance in accordance with the environment temperature. In this case, at S 500  in  FIG. 5 , the target CPU temperature in accordance with the environment temperature is received from the management manager  100 . 
         [0056]      FIG. 7A ,  FIG. 7B , and  FIG. 7C  are graphs illustrating relations between the airflow rate of the air conditioning fan  44 B and the temperatures of components in the server  50 .  FIG. 7A  illustrates a case where the server built-in fan  54  is driven at a duty ratio of 40%.  FIG. 7B  illustrates a case where the server built-in fan  54  is driven at a duty ratio of 60%.  FIG. 7C  illustrates a case where the server built-in fan  54  is driven at a duty ratio of 80%. The measured temperatures of the components include the temperatures of the two CPUs  52 , and the temperature of a system board. 
         [0057]    As illustrated in  FIG. 7A ,  FIG. 7B , and  FIG. 7C , it is understood that the CPU temperatures and the temperature of the system board is lowered as the airflow rate of the air conditioning fan  44 B increases. It is understood that the temperature lowering width becomes larger as the duty ratio of the server built-in fan  54  is smaller (as the rotational speed is lower). 
         [0058]      FIG. 8A  and  FIG. 8B  are graphs illustrating relations between the airflow rate of the air conditioning fan  44 B and the temperatures of components in the server  50 .  FIG. 8A  illustrates a case where the environment temperature is 25° C.  FIG. 8B  illustrates a case where the environment temperature is 30° C.  FIG. 8A  and  FIG. 8B  illustrate the abovementioned relation when the server built-in fan  54  is driven at a duty ratio of 60%.  FIG. 7A ,  FIG. 7B , and  FIG. 7C  illustrate data when the environment temperature is 18° C. The environment temperature in the data of  FIG. 7B  is different from that in the data of  FIG. 8A  and  FIG. 8B . 
         [0059]    As illustrated in  FIG. 8A  and  FIG. 8B , it is understood that even when the server built-in fan  54  is driven at a duty ratio of 60% that is not more than 100%, the airflow rate of the air conditioning fan  44 B increases to allow the CPU temperature to be suppressed less than an allowable upper limit value T u  of the CPU temperature. 
         [0060]      FIG. 9  is a graph illustrating a relation between the environment temperature and the duty ratio of the server built-in fan  54 .  FIG. 9  illustrates three cases where the airflow rate of the air conditioning fan  44 B is 2500 m 3 /h, where 6000 m 3 /h, and where 10000 m 3 /h.  FIG. 9  illustrates the abovementioned relation when the CPU temperature becomes not more than the allowable upper limit value T u  (in this case, 89° C.) with 100% of the load factor of the CPU  52 . 
         [0061]    As illustrated in  FIG. 9 , for example, at the environment temperature of 18° C., in the cases where the airflow rate of the air conditioning fan  44 B is 2500 m 3 /h and 6000 m 3 /h, the duty ratio of the server built-in fan  54  becomes approximately 60%. On the other hand, at the environment temperature of 18° C., in the case where the airflow rate of the air conditioning fan  44 B is 10000 m 3 /h, the duty ratio of the server built-in fan  54  becomes approximately 40%. Accordingly, it is understood that the airflow rate of the air conditioning fan  44 B is increased to allow the duty ratio of the server built-in fan  54  to be reduced while the CPU temperature is maintained at not more than the allowable upper limit value T u . 
         [0062]    Similarly, for example, at the environment temperature of 30° C., in the case where the airflow rate of the air conditioning fan  44 B is 2500 m 3 /h, the duty ratio of the server built-in fan  54  becomes approximately 80%. On the other hand, at the environment temperature of 30° C., in the cases where the airflow rate of the air conditioning fan  44 B is 10000 m 3 /h and 6000 m 3 /h, the duty ratio of the server built-in fan  54  becomes approximately 60%. Accordingly, it is understood that the airflow rate of the air conditioning fan  44 B is increased to allow the duty ratio of the server built-in fan  54  to be reduced while the CPU temperature is maintained at not more than the allowable upper limit value T u . 
         [0063]      FIG. 10  is a graph illustrating a relation between the airflow rate of the air conditioning fan  44 B and the power consumption of the cooling apparatus  40 B (air conditioner power consumption).  FIG. 10  illustrates three cases where the environment temperature is 18° C., where the environment temperature is 25° C., and where the environment temperature is 30° C. 
         [0064]    As illustrated in  FIG. 10 , it is understood that the air conditioner power consumption increases as the airflow rate of the air conditioning fan  44 B increases. In the example illustrated in  FIG. 10 , a difference between the maximum power consumption and the minimum power consumption is approximately 2 kW. 
         [0065]    As illustrated in  FIG. 7A ,  FIG. 7B ,  FIG. 7C ,  FIG. 8A ,  FIG. 8B ,  FIG. 9 , and  FIG. 10 , the airflow rate of the air conditioning fan  44 B is increased to allow the duty ratio of the server built-in fan  54  to be reduced while the CPU temperature is maintained at not more than the allowable upper limit value T u . This means that the airflow rate of the air conditioning fan  44 B is increased to allow the duty ratio of the server built-in fan  54  to be reduced while the CPU temperature is maintained at the target CPU temperature. At this time, if the total reduced amount of the server power consumption due to increase in the airflow rate of the air conditioning fans  44 B is more than the increased amount of the air conditioner power consumption due to increase in the airflow rate of the air conditioning fans  44 B, it is possible to reduce the power consumption of the modular-type data center  1 A as a whole. Hereinafter, processing executed by the management manager  100  based on such a finding will be explained. 
         [0066]      FIG. 11  a flowchart illustrating an example of processing executed by the management manager  100 . The processing illustrated in  FIG. 11  is started up, for example, when the modular-type data center  1 A is started to be operated, and is thereafter repeatedly executed for every predetermined cycle during the operation. The following processing is collectively executed with respect to the multiple cooling apparatuses  40 B in the modular-type data center  1 A. In other words, it is assumed that the multiple cooling apparatuses  40 B are controlled so as to achieve the same airflow rate among the air conditioning fans  44 B in the cooling apparatuses  40 B. 
         [0067]    At S 1100 , the management manager  100  sets a predetermined initial value as a control target value (for example, the target airflow rate) of the cooling apparatuses  40 B in the modular-type data center  1 A. Herein, the predetermined initial value is the minimum airflow rate when the power consumption of the air conditioning fan  44 B becomes approximate minimum. For example, as illustrated in  FIG. 10 , when the environment temperature is 30° C., for example, up to an approximate 4000 m 3 /h of the airflow rate of the air conditioning fan  44 B, the power consumption of the air conditioning fan  44 B is an approximate minimum value. Accordingly, in this case, the predetermined initial value is set to 4000 m 3 /h. As is also clear from  FIG. 10 , the predetermined initial value may be varied depending on the environment temperature. Alternatively, simply, the predetermined initial value may be a fixed value such as 2500 m 3 /h. 
         [0068]    At S 1102 , the management manager  100  acquires air conditioner power consumption information from each of the cooling apparatuses  40 B in the modular-type data center  1 A. 
         [0069]    At S 1104 , the management manager  100  acquires server power consumption information from each of the servers  50  in the modular-type data center  1 A. 
         [0070]    At S 1106 , the management manager  100  calculates, based on the information acquired at S 1102  and the information acquired at S 1104 , current power consumption of the modular-type data center  1 A. The power consumption of the modular-type data center  1 A may be calculated as a total of the air conditioner power consumption and the server power consumption. 
         [0071]    At S 1108 , the management manager  100  increases the control target value of the cooling apparatuses  40 B in the modular-type data center  1 A by a predetermined amount ΔV. With the smaller the predetermined amount ΔV, it is possible to obtain an optimum value (a control target value of the cooling apparatuses  40 B at which the power consumption of the modular-type data center  1 A is a minimal value) with higher accuracy, however, a processing load increases. Accordingly, the predetermined amount ΔV may be determined as appropriate based on the relation between the accuracy to be desired and the processing load. The predetermined amount ΔV may be, for example, 500 m 3 /h. The control target value changed in this manner is transmitted to the cooling apparatuses  40 B. In response to this, the air conditioning controllers  46  in the cooling apparatuses  40 B control the corresponding air conditioning fans  44 B so as to implement the changed control target value. This control mode may be flexibly determined, for example, a feedback control and the like similar to that employed in the server built-in fan  54  may be employed. 
         [0072]    Herein, when the process at S 1108  is executed, the airflow rate of the air conditioning fan  44 B in each of the cooling apparatuses  40 B increases. Accordingly, the duty ratio of each of the server built-in fans  54  in the modular-type data center  1 A tends to be reduced. In other words, as illustrated in  FIG. 7A ,  FIG. 7B ,  FIG. 7C , and the like, when the airflow rate of the air conditioning fan  44 B in the cooling apparatus  40 B increases, the CPU temperature tends to be lowered. Accordingly, the airflow rate of each of the server built-in fans  54  tends to decrease by the amount corresponding to the lowered CPU temperature. Such reduction in the airflow rate of each of the server built-in fans  54  is implemented by the processing illustrated in  FIG. 5 . In other words, the server built-in fans  54  are feedback-controlled such that the CPU temperature becomes the target CPU temperature. Accordingly, when the CPU temperature tends to be lowered due to increase in the airflow rate of the air conditioning fans  44 B, the airflow rate of each of the server built-in fans  54  also tends to decrease. Actually, even when the airflow rate of the air conditioning fans  44 B in the cooling apparatuses  40 B increases, the duty ratio of each of the server built-in fans  54  in the modular-type data center  1 A may not be reduced in some cases. This is because, for example, when the environment temperature and/or the load factor are high, and the airflow rate of the air conditioning fans  44 B is increased, the CPU temperature may not be significantly lowered in some cases. 
         [0073]    At S 1110 , the management manager  100  acquires air conditioner power consumption information after the airflow rate of the air conditioning fan  44 B increases at S 1108  described above from each of the cooling apparatuses  40 B in the modular-type data center  1 A. 
         [0074]    At S 1112 , the management manager  100  acquires server power consumption information after the airflow rate of the air conditioning fan  44 B increases at S 1108  described above from each of the servers  50  in the modular-type data center  1 A. 
         [0075]    At S 1114 , the management manager  100  calculates, based on the air conditioner power consumption information (a difference between a current value and a previous value) acquired at S 1110  described above, an increased amount ΔWf 2  of air conditioner power consumption due to increase in the airflow rate of the air conditioning fan  44 B at S 1108  described above. Only the increased amount ΔWf 2  corresponding to one specific cooling apparatus  40 B may be calculated by assuming that the increased amounts ΔWf 2  are identical among the cooling apparatuses  40 B. In this case, the air conditioner power consumption information may be acquired from the one specific cooling apparatus  40 B. 
         [0076]    At S 1116 , the management manager  100  calculates, based on the server power consumption information (a difference between a current value and a previous value) acquired at S 1112  described above, a decreased amount ΔWf 1  of server power consumption due to increase in the airflow rate of the air conditioning fan  44 B at S 1108  described above. The decreased amount ΔWf 1  is preferably calculated for each of the servers  50 . 
         [0077]    At S 1118 , the management manager  100  determines whether a total (=ΔWf 1   total  of the decreased amounts ΔWf 1  of server power consumption in all the servers  50  is more than a total (=ΔWf 2   total  of the increased amounts ΔWf 2  of air conditioner power consumption in all the cooling apparatuses  40 B. If the ΔWf 1   total  is more than the ΔWf 2   total , the processing returns to S 1108 , and the processes from S 1108  are repeated. On the other hand, if the ΔWf 1   total  is not more than the ΔWf 2   total , the processing proceeds to S 1120 . 
         [0078]    In this manner, the airflow rate of the air conditioning fan  44 B is increased by the predetermined amount ΔV before the ΔWf 1   total  becomes not more than the ΔWf 2   total . The ΔWf 1   total  more than the ΔWf 2   total  means that the power consumption in the modular-type data center  1 A is reduced due to increase in the airflow rate of the air conditioning fans  44 B. Therefore, while the airflow rate of the air conditioning fans  44 B is increased by the predetermined amount ΔV, an optimum value (optimum value of the airflow rate of the air conditioning fans  44 B) when the power consumption in the modular-type data center  1 A is at a minimal value is searched. 
         [0079]    At S 1120 , the management manager  100  decreases the control target value of each of the cooling apparatuses  40 B in the modular-type data center  1 A by the predetermined amount ΔV. In other words, the management manager  100  cancels the abovementioned processing at S 1108 . This is because the ΔWf 1   total  not more than the ΔWf 2   total  means that the airflow rate of the air conditioning fans  44 B before being increased was the minimal value of power consumption in the modular-type data center  1 A. This allows the modular-type data center  1 A to be returned in a state where the power consumption therein is at the minimal value. 
         [0080]    At S 1122 , the management manager  100  determines whether the number of the servers operating in the modular-type data center  1 A is changed. The number of the operating servers may be the number of the servers  50  operating at a predetermined load factor or more. This is because when the number of the operating servers is changed, the airflow rate of the air conditioning fan  44 B when the power consumption in the modular-type data center  1 A is at the minimal value may be changed. When the number of the servers operating in the modular-type data center  1 A is changed, the processing returns to S 1100 , again searches for an optimum value, and performs the processes from S 1100 . On the other hand, when the number of the operating servers is not changed, the management manager  100  does not change the airflow rate of the air conditioning fan  44 B, and maintains the current state. 
         [0081]    With the processing illustrated in  FIG. 11 , it is possible to obtain the control target value with which the power consumption in the modular-type data center  1 A is at the minimal value while increasing the control target value of the air conditioning fan  44 B in each of the cooling apparatuses  40 B. This allows the airflow rate of the air conditioning fan  44 B in each of the cooling apparatuses  40 B to be set such that the power consumption in the modular-type data center  1 A is at the minimal value. As a result, it is possible to reduce the power consumption in the modular-type data center  1 A while maintaining the CPU temperature to the suitable temperature (in this example, the target CPU temperature). 
         [0082]    The processing illustrated in  FIG. 11  is executed, as a precondition, under a situation in which the CPU temperature is normally controlled so as to be the target CPU temperature or less with the processing illustrated in  FIG. 5 . Therefore, for example, when the CPU temperature significantly exceeds the target CPU temperature in a state where the duty ratio of each of the server built-in fans  54  is set to 100%, the processing illustrated in  FIG. 11  may be suspended. In other words, when the CPU temperature significantly exceeds the target CPU temperature even if the duty ratio of each of the server built-in fans  54  is set to 100%, the fan controllers  56  in the servers  50  may request the management manager  100  to increase the airflow rate of the air conditioning fans  44 B. In this case, the management manager  100  may suspend the processing illustrated in  FIG. 11 , and immediately increase the control target value for the air conditioning fan  44 B in each of the cooling apparatuses  40 B. Alternatively, the processing illustrated in  FIG. 11  may be suspended, in the state where the duty ratio of each of the server built-in fans  54  is set to 100%, when the CPU temperature has a predetermined margin or less with respect to the allowable upper limit value T u  (see  FIG. 8B ). In other words, even in the state where the duty ratio of each of the server built-in fans  54  is set to 100%, when the CPU temperature has a predetermined margin or less with respect to the allowable upper limit value T u , the fan controller  56  may request the management manager  100  to increase the airflow rate of the air conditioning fan  44 B. In this case, similarly, the management manager  100  may suspend the processing illustrated in  FIG. 11 , and immediately increase the control target value for the air conditioning fan  44 B in each of the cooling apparatuses  40 B. 
         [0083]    In the example illustrated in  FIG. 11 , in the process at S 1118 , as described above, the management manager  100  compares the total of the decreased amounts ΔWf 1  of server power consumption after the airflow rate of the air conditioning fans  44 B is increased with the total of the increased amounts ΔWf 2  of air conditioner power consumption after the airflow rate of the air conditioning fans  44 B is increased. However, in the process at S 1118 , the management manager  100  may compare the power consumption in the modular-type data center  1 A before the airflow rate of the air conditioning fan  44 B is increased with the power consumption in the modular-type data center  1 A after the airflow rate of the air conditioning fans  44 B is increased, in an equivalent manner. In this case, if the power consumption in the modular-type data center  1 A after the airflow rate of the air conditioning fans  44 B is increased is smaller than the power consumption before the airflow rate thereof is increased, the processing returns to the process at S 1108 , and in the other cases, the processing may proceed to S 1120 . 
         [0084]    In the example illustrated in  FIG. 11 , at S 1122 , as described above, the management manager  100  determines whether the number of the operating servers is changed. Further, if the number of the operating servers is changed, the processing returns to S 1100 . However, the processing may return to S 1100  under another condition. For example, when a predetermined period of time (for example, five minutes) is elapsed after the process at S 1120  is performed, the processing may return to S 1100 . Alternatively, after the process at S 1120 , when another change (for example, significant change in the environment temperature or the like) that causes the optimum value when the power consumption in the modular-type data center  1 A is at the minimal value to be varied occurs, the processing may return to S 1100 . 
         [0085]    The processing illustrated in  FIG. 11  is preferable especially when the number of the operating servers  50  is large. This is because the total (=ΔWf 1   total ) of the decreased amounts ΔWf 1  of server power consumption in all the servers  50  when the airflow rate of the cooling apparatuses  40 B is increased tends to become larger as the number of the operating servers  50  becomes larger. Therefore, the processing illustrated in  FIG. 11  may be executed when the number of the operating servers is a predetermined number or more. 
         [0086]      FIG. 12  is a flowchart illustrating another example of processing executed by the management manager  100 . The processing illustrated in  FIG. 12  is started up, for example, when the modular-type data center  1 A is started to be operated, and is thereafter repeatedly executed for every predetermined cycle during the operation. The following processing is collectively executed with respect to the multiple cooling apparatuses  40 B in the modular-type data center  1 A. In other words, it is assumed that the multiple cooling apparatuses  40 B are controlled so as to achieve the same airflow rate among the air conditioning fans  44 B in the cooling apparatuses  40 B. 
         [0087]    The processing illustrated in  FIG. 12  is different from the processing illustrated in  FIG. 11  in the following point. In the example illustrated in  FIG. 11 , the predetermined initial value at S 1100  corresponds to the minimum airflow rate of the air conditioning fan  44 B. Further, the management manager  100  searches the optimum value when the power consumption in the modular-type data center  1 A is at the minimal value while gradually increasing the airflow rate of the air conditioning fans  44 B. In contrast, in the processing illustrated in  FIG. 12 , the predetermined initial value corresponds to the maximum airflow rate of the air conditioning fan  44 B. Further, the management manager  100  searches the optimum value when the power consumption in the modular-type data center  1 A is at the minimal value while gradually decreasing the airflow rate of the air conditioning fans  44 B. 
         [0088]    In the processing illustrated in  FIG. 12 , the processes from S 1202  to S 1206  are respectively the same as those from S 1102  to S 1106  illustrated in  FIG. 11 . In the processing illustrated in  FIG. 12 , the processes at S 1210 , S 1212 , and S 1222  are respectively the same as those at S 1110 , S 1112 , and S 1122  illustrated in  FIG. 11 . Hereinafter, the configuration specific to the processing illustrated in  FIG. 12  will be explained. 
         [0089]    At S 1200 , the management manager  100  sets a predetermined initial value as a control target value (for example, the target airflow rate) of the cooling apparatuses  40 B in the modular-type data center  1 A. Herein, the predetermined initial value is the maximum airflow rate of the air conditioning fan  44 B. For example, the predetermined initial value is set to 10000 m 3 /h. 
         [0090]    At S 1208 , the management manager  100  decreases the control target value of the cooling apparatuses  40 B in the modular-type data center  1 A by a predetermined amount ΔV. The predetermined amount ΔV may be, for example, 500 m 3 /h. The control target value changed in this manner is transmitted to the cooling apparatuses  40 B. In response to this, the air conditioning controllers  46  in the cooling apparatuses  40 B control the corresponding air conditioning fans  44 B so as to implement the changed control target value. 
         [0091]    Herein, when the process at S 1208  is executed, the airflow rate of the air conditioning fan  44 B in each of the cooling apparatuses  40 B decreases. Accordingly, the duty ratio of each of the server built-in fans  54  in the modular-type data center  1 A tends to be increased. In other words, as illustrated in  FIG. 7A ,  FIG. 7B ,  FIG. 7C , and the like, when the airflow rate of the air conditioning fan  44 B in the cooling apparatus  40 B decreases, the CPU temperature tends to be raised, so that the airflow rate of each of the server built-in fans  54  tends to increase by the amount corresponding to the raised CPU temperature. Such increase in the airflow rate of each of the server built-in fans  54  is implemented by the processing illustrated in  FIG. 5 . In other words, the server built-in fans  54  are feedback-controlled such that the CPU temperature becomes the target CPU temperature. Accordingly, when the CPU temperature tends to be raised due to decrease in the airflow rate of the air conditioning fans  44 B, the airflow rate of each of the server built-in fans  54  also tends to increase. Actually, even when the airflow rate of the air conditioning fans  44 B in the cooling apparatuses  40 B decreases, the duty ratio of each of the server built-in fans  54  in the modular-type data center  1 A may not be increased in some cases. This is because, for example, when the environment temperature and/or the load factor are low, and the airflow rate of the air conditioning fans  44 B is decreased, the CPU temperature may not be significantly raised in some cases. 
         [0092]    At S 1214 , the management manager  100  calculates, based on the air conditioner power consumption information (a difference between a current value and a previous value) acquired at S 1210  described above, a decreased amount ΔWf 4  of air conditioner power consumption due to decrease in the airflow rate of the air conditioning fan  44 B at S 1208  described above. Only the decreased amount ΔWf 4  corresponding to one specific cooling apparatus  40 B may be calculated by assuming that the decreased amounts ΔWf 4  are identical among all the cooling apparatuses  40 B. In this case, the air conditioner power consumption information may be acquired from the one specific cooling apparatus  40 B. 
         [0093]    At S 1216 , the management manager  100  calculates, based on the server power consumption information (a difference between a current value and a previous value) acquired at S 1212  described above, an increased amount ΔWf 3  of server power consumption due to decrease in the airflow rate of the air conditioning fan  44 B at S 1208  described above. The increased amount ΔWf 3  is preferably calculated for each of the servers  50 . 
         [0094]    At S 1218 , the management manager  100  determines whether a total (=ΔWf 4   total ) of the decreased amounts ΔWf 4  of server power consumption in all the servers  50  is more than a total (=ΔWf 3   total ) the increased amounts of ΔWf 3  of air conditioner power consumption in all the cooling apparatuses  40 B. If the ΔWf 4   total  is more than the ΔWf 3   total , the processing returns to S 1208 , and the processes from S 1208  are repeated. On the other hand, if the ΔWf 4   total  is not more than ΔWf 3   total , the processing proceeds to S 1220 . 
         [0095]    In this manner, the airflow rate of the air conditioning fan  44 B is decreased by the predetermined amount ΔV before the ΔWf 4   total  becomes not more than the ΔWf 3   total . The ΔWf 4   total  more than the ΔWf 3   total  means that the power consumption in the modular-type data center  1 A is reduced due to decrease in the airflow rate of the air conditioning fans  44 B. Therefore, while the airflow rate of the air conditioning fans  44 B is decreased by the predetermined amount ΔV, an optimum value (optimum value of the airflow rate of the air conditioning fans  44 B) when the power consumption in the modular-type data center  1 A is at a minimal value is searched. 
         [0096]    At S 1220 , the management manager  100  increases the control target value of each of the cooling apparatuses  40 B in the modular-type data center  1 A by the predetermined amount ΔV. In other words, the management manager  100  cancels the abovementioned processing at S 1208 . This is because the ΔWf 4   total  not more than the ΔWf 3   total  means that the airflow rate of the air conditioning fans  44 B before being decreased was the minimal value of power consumption in the modular-type data center  1 A. This allows the modular-type data center  1 A to be returned in a state where the power consumption therein is at the minimal value. 
         [0097]    With the processing illustrated in  FIG. 12 , an effect substantially similar to that with the processing illustrated in  FIG. 11  may be obtained. In other words, with the processing illustrated in  FIG. 12 , it is possible to obtain the control target value with which the power consumption in the modular-type data center  1 A is at the minimal value while decreasing the control target value of the air conditioning fan  44 B in each of the cooling apparatuses  40 B. This allows the airflow rate of the air conditioning fan  44 B in each of the cooling apparatuses  40 B to be set such that the power consumption in the modular-type data center  1 A is at the minimal value. As a result, it is possible to reduce the power consumption in the modular-type data center  1 A while maintaining the CPU temperature to the suitable temperature (in this example, the target CPU temperature). 
         [0098]    The concept of the processing illustrated in  FIG. 12  may be combined with the concept of the processing illustrated in  FIG. 11 . For example, if the affirmative determination is made at S 1222 , the processing does not return to S 1200  but may return to S 1208 . As a result, if the affirmative determination is made at S 1218 , the processing returns to S 1208 , whereas if the negative determination is made at S 1218 , the processing may proceed to S 1108  in  FIG. 11 , and perform the processes from S 1108 . 
         [0099]    Although the embodiments have been described in detail, the present disclosure is not limited thereto but the various modifications and changes could be made hereto without departing from the spirit and scope of the disclosure. It is also possible to combine all of or a plurality of the constituent components in the embodiments described above. 
         [0100]    For example, in the embodiments described above, the server built-in fan  54  is controlled such that the CPU temperature becomes the target CPU temperature. However, the server built-in fan  54  may be controlled such that the temperature at another portion in the server  50  becomes a predetermined target temperature. 
         [0101]    In the embodiments described above, the air conditioning fans  44 B of the cooling apparatuses  40 B are collectively controlled by the common control target value. However, the air conditioning fans  44 B of the cooling apparatuses  40 B may be independently controlled by specific control target values. In this case, in the processing in  FIG. 11 , the management manager  100  may set specific control target values at S 1100 , S 1108 , and the like. 
         [0102]    In the embodiments described above, a control method of the cooler  42 B in each of the cooling apparatuses  40 B may be flexibly determined. For example, the cooler  42 B may be controlled based on the environment temperature and the like. 
         [0103]    In the embodiments described above, a part of or all parts of the function of the management manager  100  may be implemented by another controller (for example, the air conditioning controller  46  or the fan controller  56 ). A part of or all parts of the another controller (for example, the air conditioning controller  46  or the fan controller  56 ) may be implemented by the management manager  100 . 
         [0104]    In the embodiments described above, each of the racks  30  houses therein the servers  50 . However, the racks  30  may house therein other information processing apparatus. 
         [0105]    All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiments of the present invention have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.