Abstract:
A cooling apparatus includes: a pump transports a refrigerant; and a controller controls a discharge amount of the pump depending on a calorific value of a heat generating body. And a cooling method includes: measuring a calorific value of a heat generating body; and controlling a discharge amount of a pump, which transports a refrigerant used for cooling the heat generating body, depending on the calorific value.

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. 2015-111113, filed on Jun. 1, 2015, the entire contents of which are incorporated herein by reference. 
       FIELD 
       [0002]    The embodiments discussed herein are related to a cooling apparatus, a cooling method, and a data processing system. 
       BACKGROUND 
       [0003]    A high-performance calculator called a super-computer generates a large amount of heat at it operates. When the temperature of the calculator exceeds a permissible upper-limit temperature, a failure, such as, for example, a malfunction, a trouble, or a reduction in processing capability occurs. Therefore, means for cooling the calculator is required. 
         [0004]    In general, a water-cooling type cooling apparatus is adopted to cool a high-performance calculator. In the water-cooling type cooling apparatus, the cooling apparatus and the calculator are connected to each other via a pipe such that heat generated from the calculator is transported to the cooling apparatus by cooling water (refrigerant) to be radiated from the cooling apparatus to the atmosphere. 
         [0005]    Since a lot of power is used to cool the high-performance calculator, a reduction in power consumed by the cooling apparatus is requested from the view point of energy saving. In order to reduce the power consumption of the cooling apparatus, it may be considered that the cooling capability of the cooling apparatus is changed depending on the operating state of the calculator, for example. 
         [0006]    However, although the amount of heat generated in the calculator is suddenly changed depending on the operating state of the calculator, it is difficult to suddenly change the cooling capability of the cooling apparatus. 
         [0007]    Thus, there has been proposed a technology in which a bypass pipe and a flow regulating valve are provided between a pipe of a cooling water outlet side and a pipe of a cooling water inlet side of the cooling apparatus so that an opening degree of the flow regulating valve is regulated depending on the temperature of the cooling water supplied to the calculator. Herein, water or other refrigerants used for cooling the calculator are referred to as the “cooling water,” for convenience. 
         [0008]    However, the power of the cooling apparatus is not sufficiently saved simply by regulating the opening degree of the flow regulating valve depending on the temperature of the cooling water supplied to the calculator. 
         [0009]    The followings are reference documents.
   [Document 1] Japanese Laid-Open Patent Publication No. 60-138382, and   [Document 2] International Publication Pamphlet No. WO 2004/079805.   
 
       SUMMARY 
       [0012]    According to an aspect of the invention, a cooling apparatus includes: a pump transports a refrigerant; and a controller controls a discharge amount of the pump depending on a calorific value of a heat generating body. 
         [0013]    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. 
         [0014]    It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restirctive of the invention, as claimed. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0015]      FIG. 1  is a block diagram illustrating an exemplary cooling apparatus and an exemplary data processing system including the cooling apparatus; 
           [0016]      FIG. 2  is a schematic view illustrating a configuration of a cooling apparatus and a data processing system including the cooling apparatus according to a first exemplary embodiment; 
           [0017]      FIG. 3  is a flowchart illustrating an operation of the cooling apparatus according to the first exemplary embodiment; 
           [0018]      FIG. 4  is a view illustrating an exemplary table used to determine operating conditions; 
           [0019]      FIG. 5  is a view illustrating an effect of the first exemplary embodiment; 
           [0020]      FIG. 6  is a view illustrating exemplary time-dependent changes in a calorific value of a calculator, opening degree of a flow regulating valve, and an output of a pump; 
           [0021]      FIG. 7  is a schematic view illustrating a configuration of a cooling apparatus and a data processing system including the cooling apparatus according to a second exemplary embodiment; 
           [0022]      FIG. 8  is a view illustrating exemplary changes in calorific value of a calculator, an opening degree of a flow regulating valve, an opening degree of a bypass valve, and an output a pump; 
           [0023]      FIG. 9  is a schematic view illustrating a configuration of a cooling apparatus and a data processing system including the cooling apparatus according to a third exemplary embodiment; 
           [0024]      FIG. 10  is a flowchart illustrating an operation of the cooling apparatus according to the third exemplary embodiment; 
           [0025]      FIG. 11  is a view illustrating an energy saving effect when the operating rate of a calculator is 100%; 
           [0026]      FIG. 12  is a view illustrating an energy saving effect when the operating rate of a calculator is 75%; and 
           [0027]      FIG. 13  is a view illustrating an energy saving effect when the operating rate of a calculator is 50%. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0028]    Hereinafter, preliminary matters will be described in order to enable exemplary embodiments to be easily understood, prior to describing the exemplary embodiments. 
         [0029]      FIG. 1  is a block diagram illustrating an exemplary cooling apparatus and an exemplary data processing system including the cooling apparatus. 
         [0030]    The cooling apparatus  10  illustrated in  FIG. 1  includes a chiller unit  11  and a CDU (Coolant Distribution Unit)  15 . The chiller unit  11  includes a refrigerator  12  and a pump  13 . Further, the CDU  15  includes a heat exchanger  16 , a pump  17 , and a three-way valve (flow regulating valve)  18 . The heat exchanger  16  includes a first path through which primary cooling water flows and a second path through which secondary cooling water flows, and performs heat exchange between the cooling water flowing through the first path and the cooling water flowing through the second path. 
         [0031]    A cooling water outlet of the refrigerator  12  and a suction port of the pump  13  are connected by a pipe  21   a , and a delivery port of the pump  13  and a first connecting port of the three-way valve  18  are connected by a pipe  21   b . Further, a second connecting port of the three-way valve  18  and a primary cooling water inlet of the heat exchanger  16  are connected by a pipe  21   c , and a primary cooling water outlet of the heat exchanger  16  and a cooling water inlet of the refrigerator  12  are connected by a pipe  21   d . Furthermore, a third connecting port of the three-way valve  18  and the pipe  21   d  are connected by a bypass pipe  21   e.    
         [0032]    A secondary cooling water outlet of the heat exchanger  16  and a suction port of the pump  17  are connected by a pipe  22   a , and a delivery port of the pump  17  and a cooling water inlet of a calculator  25  are connected by a pipe  22   b . Further, a cooling water outlet of the calculator  25  and a secondary cooling water inlet of the heat exchanger  16  are connected by a pipe  22   c.    
         [0033]    Further, a temperature sensor  19  configured to detect the temperature of cooling water flowing in the pipe  22   b  and a controller  20  configured to control the three-way valve  18  depending on the output of the temperature sensor  19  are provided within the CDU  15 . The controller  20  controls the three-way valve  18  such that the temperature of the cooling water detected by the temperature sensor  19  becomes, for example, 18° C.±1° C. 
         [0034]    In this kind of cooling apparatus  10 , the operation state of the chiller unit  11  is set to sufficiently cool the calculator  25  even if the operating rate of the calculator  25  is 100%. 
         [0035]    Herein, the cooling water, which comes out from the refrigerator  12  and returns to the refrigerator  12  through the heat exchanger  16  or the bypass pipe  21   e , is referred to as the primary cooling water, and the cooling water, which comes out from the heat exchanger  16  and returns to the heat exchanger through the calculator  25 , is referred to as the secondary cooling water. 
         [0036]    In general, the chiller unit  11  is installed outdoors, and the CDU  15  is installed in the vicinity of the calculator  25  (indoors). Therefore, since the length of the pipe between the chiller unit  11  and the CDU  15  is often  20  m or more, causing pressure loss, a relatively large pump is used as the pump  13 . 
         [0037]    However, under the situation where such a large pump is used and the length of the pipe is long, it is difficult to suddenly change or finely regulate the flow rate of the cooling water fed from the chiller unit  11 . Thus, in the cooling apparatus  10  illustrated in  FIG. 1 , the number of revolutions of the pump  13  is set to be constant and the flow rate of the cooling water flowing into the heat exchanger  16  is changed by the three-way valve (flow regulating valve)  18  so as to cope with a sudden change in the calorific value of the calculator  25 . 
         [0038]    A heat insulating treatment (e.g., winding an insulation material) is applied to the pipe between the chiller unit  11  and the CDU  15 . However, the temperature of the cooling water discharged from the pump  13  rises by about 1° C. to 3° C. until the cooling water reaches the three-way valve  18 , due to the effect of environmental temperature. Moreover, the temperature of the cooling water rises by about 1° C. to 3° C. while the cooling water returns to the chiller unit  11  through the bypass pipe  21   e.    
         [0039]    Thus, the chiller unit  11  unnecessarily consumes power so as to cool the cooling water while the cooling water returns to the chiller unit  11  through the bypass pipe  21   e.    
         [0040]    When the calculator  25  generates a large calorific value, little (or no) cooling water flows in the bypass pipe  21   e  so that the waste of power by the cooling water passing through the bypass pipe  21   e  is negligibly small. However, when the calorific value of the calculator  25  becomes small, the flow rate of the cooling water flowing in the bypass pipe  21   e  is increased so that the waste of power by the cooling water passing through the bypass pipe  21   e  becomes large. 
       First Exemplary Embodiment 
       [0041]      FIG. 2  is a schematic view illustrating a configuration of a cooling apparatus and a data processing system including the cooling apparatus according to a first exemplary embodiment. Components common to  FIGS. 1 and 2  will be denoted by the same reference numerals. 
         [0042]    The cooling apparatus  30  according to the present exemplary embodiment includes a chiller unit  11 , a CDU  15 , and a main controller  35 . The chiller unit  11  includes a refrigerator  12  and a pump  13 . Further, the CDU  15  includes a heat exchanger  16 , a pump  17 , a three-way valve (a flow regulating valve)  18 , and a sub-controller  36 . Meanwhile, the refrigerator  12  is an exemplary cooling unit. 
         [0043]    A cooling water outlet of the refrigerator  12  and a suction port of the pump  13  are connected by a pipe  21   a , and a delivery port of the pump  13  and a first connecting port of the three-way valve  18  are connected by a pipe  21   b . Further, a second connecting port of the three-way valve  18  and a primary cooling water inlet of the heat exchanger  16  are connected by a pipe  21   c , and a primary cooling water outlet of the heat exchanger  16  and a cooling water inlet of the refrigerator  12  are connected by a pipe  21   d . Furthermore, a third connecting port of the three-way valve  18  and the pipe  21   d  are connected by a bypass pipe  21   e.    
         [0044]    The pipe  21   a  is an exemplary first pipe, the pipe  21   b  is an exemplary second pipe, the pipe  21   c  is an exemplary third pipe, the pipe  21   d  is an exemplary fourth pipe, and the bypass pipe  21   e  is an exemplary fifth pipe. 
         [0045]    A secondary cooling water outlet of the heat exchanger  16  and a suction port of the pump  17  are connected by a pipe  22   a , and a delivery port of the pump  17  and a cooling water inlet of a calculator  25  are connected by a pipe  22   b . Further, a cooling water outlet of the calculator  25  and a secondary cooling water inlet of the heat exchanger  16  are connected by a pipe  22   c . The pipes  22   a  and  22   b  are an exemplary sixth pipe, and the pipe  22   c  is an exemplary seventh pipe. 
         [0046]    A temperature sensor  31   a  configured to detect the temperature of the cooling water flowing in the pipe  22   b  and a flow sensor  32  configured to detect the flow rate of the cooling water flowing in the pipe  22   b  are provided in the pipe  22   b . Further, a temperature sensor  31   b  configured to detect the temperature of the cooling water flowing in the pipe  22   c  is provided in the pipe  22   c . The temperature sensor  31   a  is an exemplary first sensor, the flow sensor  32  is an exemplary second sensor, and the temperature sensor  31   b  is an exemplary third sensor. 
         [0047]    The outputs of the temperature sensors  31   a  and  31   b  and the flow sensor  32  are transmitted to the main controller  35 . The main controller  35  controls the number of revolutions of the pump  13 , based on the outputs of the temperature sensors  31   a  and  31   b  and the flow sensor  32 . 
         [0048]    Further, the sub-controller  36  disposed in the CDU  15  regulates the opening degree of the three-way valve (a flow regulating valve) 18  such that the temperature detected by the temperature sensor  31   a  becomes a set value (e.g., 18° C.±1° C.), and controls the flow rate of the primary cooling water passing through the bypass pipe  21   e . Further, the pump  17  rotates at a constant number of revolutions. 
         [0049]    Meanwhile, in the present exemplary embodiment, a high-performance calculator configured to include a network (wiring) that connects a plurality of nodes with each other is assumed as the calculator  25 . 
         [0050]    Hereinafter, an operation of the above-described cooling apparatus  30  will be described with reference to a flowchart of  FIG. 3 . 
         [0051]    First, at step S 11 , the main controller  35  detects the temperature T 1  of the cooling water fed to the calculator  25 , the flow rate Q of the cooling water, and the temperature T 2  of the cooling water discharged from the calculator  25 , based on the outputs of the temperature sensors  31   a  and  31   b  and the flow sensor  32 . 
         [0052]    Subsequently, proceeding to step S 12 , the main controller  35  calculates an instantaneous calorific value E′ of the calculator  25  by the following equation (1). 
         [0000]        E′=Cp·ρ·Q·ΔT    (1)
 
         [0053]    In this equation, E′ is an instantaneous value (kW) of the a calorific value of the calculator  25 , Cp is a specific heat (in kJ/kg·K) of the cooling water, ρ is a density (in kg/L) of the cooling water, Q is a flow rate (in L/sec) of the cooling water, and ΔT is a difference K between a measured value T 1  of the temperature sensor  31   a  and a measured value T 2  of the temperature sensor  31   b.    
         [0054]    Subsequently, proceeding to step S 13 , the main controller  35  calculates a ratio of the instantaneous calorific value E′ of the calculator  25  to a maximum calorific value E 0  the calculator  25  (E=(E/E 0 )×100(%)), and sets the operating condition of the pump  13  of the chiller unit  11 , based on the value of E. 
         [0055]    Meanwhile, the maximum calorific value E 0  may be calculated based on the specification of the calculator  25 . Further, the operating condition is set using, for example, the table of  FIG. 4 . 
         [0056]    In the case of using the table of  FIG. 4 , when the value of E is 57.5% or less (E≦57.5%), the main controller  35  determines that the calculator  25  is in a low-load state (a state where the calorific value is low), and sets the operating condition of the pump  13  to 70% of the maximum number of revolutions. Further, when the value of E ranges from 57.5% to 75% (57.5%&lt;E≦75%), the main controller  35  determines that the calculator  25  is in a medium-load state (a state where the calorific value is medium), and then sets the operating condition of the pump  13  to 85% of the maximum number of revolutions. Furthermore, when the value of E exceeds 75% (75%&lt;E), the main controller  35  determines that the calculator  25  is in a high-load state (a state where the calorific value is high), and sets the operating condition of the pump  13  to the maximum number of revolutions (100%). 
         [0057]    Subsequently, proceeding to step S 14 , the main controller  35  operates the pump  13  under a set operating condition. As illustrated in  FIG. 4 , when the operating condition of the pump  13  is 70%, the power consumption of the pump  13  is reduced by  30 %. When the operating condition of the pump  13  is 85%, the power consumption of the pump  13  is reduced by 15%. 
         [0058]    After the pump  13  starts operating under the operating condition that is determined at step S 14 , the main controller  35  returns to step S 11  and repeats the above-described steps. 
         [0059]      FIG. 5  is a view illustrating an effect of the present exemplary embodiment. Here, when the calorific value of the calculator  25  is maximum (when the operating rate is 100%), the flow rate of the cooling water discharged from the pump  17  is set to 100%. Further, each of the hatched portions of  FIG. 5  illustrates the maximum flow rate of the cooling water flowing in the bypass pipe  21   e . The flow rate of the cooling water flowing in the bypass pipe  21   e  is changed depending on the opening degree of the three-way valve  18 , and the opening degree of the three-way valve  18  is controlled by the sub-controller  36 , based on the output of the temperature sensor  31   a , as described above. 
         [0060]    In this exemplary embodiment, as described above, the operating condition of the pump  13  of the chiller unit  11  is changed stepwise depending on the calorific value (instantaneous value) generated in the calculator  25 , and the opening degree of the three-way valve (flow regulating valve) 18  is regulated depending on the temperature of the secondary cooling water. Thus, the power consumed in the chiller unit  11  is reduced compared to that consumed in the cooling apparatus  10  of  FIG. 1  while coping with a sudden change in the calorific value of the calculator  25 . 
         [0061]      FIG. 6  is a view illustrating exemplary time-dependent changes in the calorific value of the calculator  25 , the opening degree of the flow regulating valve (flow regulating valve  18 ), and the output of the pump  13  (the flow rate of the cooling water that is discharged from the pump  13  (the same shall apply hereafter)). 
         [0062]      FIG. 6  illustrates time-dependent changes in the opening degree of the flow regulating valve (three-way valve  18 ) and the output of the pump  13  when the calorific value of the calculator  25  is reduced from 100% to 50%. Further, Example  1  illustrates time-dependent changes when the cooling apparatus  30  according to the present exemplary embodiment is used, and a comparative example illustrates time-dependent changes when the cooling apparatus  10  of  FIG. 1  is used. 
         [0063]    Further, in Example  1 , it takes about  180  seconds until the output of the pump  13  is stabilized. Meanwhile, a time required to stabilize the output of the pump  13  depends on the length of the pipe as well as the kind of the pump. That is, the longer the length of the pipe is, the longer the time required to stabilize the output of the pump  13  is. 
         [0064]    As illustrated in  FIG. 6 , in the comparative example, even if the calorific value of the calculator  25  is changed, the output of the pump  13  is constant, and the flow rate of the cooling water fed to the heat exchanger  16  is regulated by changing the opening degree of the flow regulating valve (the three-way valve  18 ). 
         [0065]    Meanwhile, in the case of Example  1 , even if the calorific value of the calculator  25  is changed, the output of the pump  13  is not immediately changed. In the example illustrated in  FIG. 6 , after the calorific value of the calculator  25  is changed, the output of the pump  13  is gradually reduced and stabilized after about  180  seconds. Further, the opening degree of the flow regulating valve (the three-way valve  18 ) is finely changed until the output of the pump  13  is stabilized after the calorific value of the calculator  25  is changed. 
         [0066]    As described above, in the comparative example, since the output of the pump  13  is constant, the opening degree of the flow regulating valve (the three-way valve  18 ) becomes the opening degree depending on the calorific value of the calculator  25 . In contrast, according to the present exemplary embodiment, the output of the pump  13  is changed depending on the change in the calorific value of the calculator  25 . Further, the opening degree of the flow regulating valve (the three-way valve  18 ) is finely changed, until the output of the pump  13  is stabilized so that the flow rate of the cooling water fed to the heat exchanger  16  is appropriately regulated. 
         [0067]    Meanwhile, in the present exemplary embodiment, the main controller  35  is installed separately from the calculator  25 , as illustrated in  FIG. 2 . However, a dedicated calculator may be disposed in a housing (rack) of the calculator  25  to serve as the main controller  35 , or the function of the main controller  35  may be realized using a part of the calculator  25  (a part of processing capability). 
         [0068]    Further, according to the present exemplary embodiment, the operating condition of the pump  13  is changed depending on the calorific value of the calculator  25 . However, in order to more precisely control the temperature of the cooling water, the operating condition of the refrigerator  12  may be changed together with that of the pump  13 . 
         [0069]    Moreover, although the cooling of the high-performance calculator has been described in the present exemplary embodiment, the disclosed technology may be applied to the cooling of a server, a storage unit, or other data processing units. 
         [0070]    Further, although a heat generating body (the calculator  25 ) is cooled via the heat exchanger  16  in the present exemplary embodiment, the cooling water may be fed directly from the chiller unit  11  to the heat generating body. 
       Second Exemplary Embodiment 
       [0071]      FIG. 7  is a schematic view illustrating a configuration of a cooling apparatus and a data processing system including the cooling apparatus according to a second exemplary embodiment. Components common to  FIGS. 2 and 7  will denoted by the same reference numerals. 
         [0072]    As illustrated in  FIG. 7 , the cooling apparatus  40  according to the present exemplary embodiment includes a buffer tank  14  and a three-way valve (a bypass valve)  33  that are provided in a housing of a chiller unit  11 . Further, a two-way valve (a flow regulating valve)  34  is provided in a CDU  15 . 
         [0073]    A first connecting port of the three-way valve 33  is connected to a discharge port of the pump  13  through a pipe  23   a , and a second connecting port is connected the two-way valve 33  and a pipe  23   c  to a primary cooling water inlet of a heat exchanger  16  through a pipe  23   b . Further, a third connecting port of the three-way valve  33  is connected to the buffer tank  14  through a bypass pipe  23   d . The bypass pipe  23   d  is also disposed in the housing of the chiller unit  11 . 
         [0074]    In order to suppress the temperature of the cooling water passing through the bypass pipe  23   d  from rising, the length of the bypass pipe  23   d  may be set as short as possible. Further, a heat insulating treatment (e.g., winding an insulation material having a high heat insulating effect) may be applied to the bypass pipe  23   d.    
         [0075]    The cooling water, which is returned from the heat exchanger  16  through the pipe  23   e  and the cooling water, which passes through the bypass pipe  23   d  from the three-way valve 33 , are introduced into the buffer tank  14 . Further, the buffer tank  14  is connected to a water inlet port of the refrigerator  12  through a pipe  23   f.    
         [0076]    The pipe  21   a  is an exemplary first pipe, the pipes  23   a  and  23   b  are exemplary second pipes, the pipe  23   c  is an exemplary third pipe, the pipes  23   e  and  23   f  are exemplary fourth pipes, and the bypass pipe  23   d  is an exemplary fifth pipe. 
         [0077]    Similarly to the first exemplary embodiment, the main controller  35  controls the number of revolutions of the pump  13  depending on the outputs of the temperature sensors  31   a  and  31   b  and the flow sensor  32 . Further, the sub-controller  36  controls the two-way valve (a flow regulating valve)  34  such that the temperature detected by the temperature sensor  31   a  becomes a set value (e.g., 18° C.±1° C.). 
         [0078]    Meanwhile, the present exemplary embodiment uses, as the two-way valve (flow regulating valve)  34 , a valve having a time constant T 3  of a change in opening degree that is shorter than a time constant T 2  of a change in opening degree of the three-way valve (bypass valve)  33  (T 3 &lt;T 2 ). Further, the present exemplary embodiment uses, as the three-way valve  33 , a valve having the time constant T 2  of the change in opening degree that is shorter than a time constant T 1  at the time of changing the output of the pump  13  (T 2 &lt;T 1 ). The time constant T 3  at the time of changing the opening degree of the two-way valve  34  is, for example, a few seconds, the time constant T 2  at the time of changing the opening degree of the three-way valve  33  is, for example, tens of seconds, and the time constant T 1  at the time of changing the output of the pump  13  is, for example, a few minutes. 
         [0079]    When the two-way valve  34  is suddenly closed, there is a case in which a water hammer phenomenon occurs. In order to avoid the water hammer phenomenon, a two-way valve in which a countermeasure against the water hammer phenomenon is taken may be used as the two-way valve  34 . 
         [0080]    Hereinafter, the operation and effects of the present exemplary embodiment will be described. 
         [0081]    As described above, similarly to the first exemplary embodiment, in the present exemplary embodiment, the operating condition of the pump  13  in the chiller unit  11  is changed stepwise depending on the calorific value of the calculator  25  (see, e.g.,  FIG. 4 ). In this case, the output of the pump  13  is not instantaneously changed in response to a signal from the main controller  35 , but becomes a target output after a certain time (e.g., several minutes) elapses. Meanwhile, the three-way valve  33  reaches a target opening degree within a relatively short time in response to a signal from the main controller  35 . 
         [0082]    In the case where several minutes are required until the output of the pump  13  is stabilized, in the first exemplary embodiment, an excessive amount of cooling water is transmitted from the pump  13  to the CDU  15  even if the opening degree of the three-way valve  18  is being reduced. Further, the excessive amount of cooling water flows from the three-way valve  18  to the bypass pipe  21   e  and then returns to the chiller unit  11 . Thus, in the first exemplary embodiment, for a few minutes until the output of the pump  13  is stabilized, power is unnecessarily consumed in the chiller unit  11  so as to cool the excessive amount of cooling water. 
         [0083]    In order to solve the problem, the present exemplary embodiment uses, as the flow regulating valve, the two-way valve  34  that has a small time constant of the change in opening degree. Further, the three-way valve (a bypass valve)  33  and the bypass pipe  23   d  are provided in the chiller unit  11 , and a valve having a time constant of the change of opening degree than that of the two-way valve  34  is used as the three-way valve  33 . 
         [0084]    Therefore, even if an excessive amount of cooling water is discharged from the pump  13  for several minutes until the output of the pump  13  is stabilized, the excessive amount of cooling water passes through the bypass pipe  23  in the chiller unit  11  and then enters the buffer tank  14 . In this case, since the cooling water merely moves in the chiller unit  11 , the temperature hardly rises by the effect of environmental temperature. 
         [0085]    Accordingly, the present exemplary embodiment exhibits an effect of further reducing the power consumption of the chiller unit  11  compared with the first exemplary embodiment. 
         [0086]    Meanwhile, the present exemplary embodiment provides the buffer tank  14  within the chiller unit  11 . Although the buffer tank  14  is not essential, the present exemplary embodiment provides the buffer tank  14  for the following reasons. 
         [0087]    That is, there is a case in which the operating condition of the refrigerator  12  may be significantly changed depending on the change of the discharge amount of the pump  13  of the primary cooling water path side so that the temperature of the cooling water fed into the CDU  15  may not be stabilized. However, when the buffer tank  14  is provided at the cooling water inlet side of the refrigerator  12 , the change in temperature of the cooling water introduced into the refrigerator  12  is mitigated so that the change in temperature of the cooling water output from the refrigerator  12  becomes small. 
         [0088]      FIG. 8  is a view illustrating exemplary chronological changes in the calorific value of the calculator  25 , the opening degree of the flow regulating valve (the two-way valve  34  or the three-way valve  18 ), the opening degree of the bypass valve (the three-way valve  33 ), and the output of the pump  13 . 
         [0089]    In  FIG. 8 , Example  2  illustrates a change with the lapse of time when the cooling apparatus  40  according to the present exemplary embodiment is used, while a comparative example illustrates a change with the lapse of time when the cooling apparatus  10  illustrated in  FIG. 1  is used. Further, in Example  2 , it takes about  600  seconds until the output of the pump  13  is stabilized. 
         [0090]    As illustrated in  FIG. 8 , in the comparative example, even if the calorific value of the calculator  25  is changed, the output of the pump  13  is constant, and the flow rate of the cooling water fed into the heat exchanger  16  is regulated by changing the opening degree of the flow regulating valve (the three-way valve  18 ). 
         [0091]    Meanwhile, in the case of Example  2 , even if the calorific value of the calculator  25  is changed, the output of the pump  13  is not immediately changed. In the example illustrated in  FIG. 8 , after the calorific value of the calculator  25  is changed, the output of the pump  13  is gradually reduced and is stabilized after about  600  seconds. Further, the opening degrees of the bypass valve (the three-way valve  33 ) and the flow regulating valve (the two-way valve  34 ) are finely changed until the output of the pump  13  is stabilized after the calorific value of the calculator  25  is changed. 
         [0092]    As described above, in the present exemplary embodiment, the output of the pump  13  is changed together with the change in the calorific value of the calculator  25 . Further, the flow regulating valve (the two-way valve  34 ) and the bypass valve (the three-way valve  33 ) are interlocked with each other depending on the change in the output of the pump  13  so that the flow rate of the cooling water fed to the heat exchanger  16  is properly regulated. 
         [0093]    Although the two-way valve  34  is used as the flow regulating valve in the present exemplary embodiment, the three-way valve may be used as the flow regulating valve and the bypass pipe may be provided between the third connecting port of the three-way valve and the pipe on the primary cooling water outlet of the heat exchanger  16 , as in the first exemplary embodiment. 
       Third Exemplary Embodiment 
       [0094]      FIG. 9  is a schematic view illustrating a configuration of a cooling apparatus and a data processing system including the cooling apparatus according to a third exemplary embodiment. 
         [0095]    The present exemplary embodiment is different from the first exemplary embodiment in that the main controller  35  controls the cooling capability of the chiller unit  11  according to an operation plan, and the other configuration of the present exemplary embodiment is basically similar to that of the first exemplary embodiment. Therefore, components common to  FIGS. 2 and 9  will be denoted by the same reference numerals, and the detailed descriptions thereof will be omitted. 
         [0096]    The high-performance calculator hardly executes one job using all computational resources of the calculator. In general, the high-performance calculator divides the processing capability of the calculator into a plurality of sections and allocates the respective sections to a plurality of users to use the sections for a predetermined period. In this case, a daily operation plan of the high-performance calculator is drafted, and the calculator is operated according to the operation plan. 
         [0097]    When the operation plan is determined, the number of nodes (hereinafter, referred to as “the number of operating nodes”) required to execute the job input into the calculator may be estimated. Although there is a case in which the number of operating nodes is the same as the number of all the nodes included in the calculator, there is also a case in which the number of operating nodes is smaller than the number of all the nodes included in the calculator. 
         [0098]    Thus, in the present exemplary embodiment, the operation plan  37  of one day or a half day is input to the main controller  35 . The operation plan  37  includes data on the number of operating nodes per day or half a day. 
         [0099]    Hereinafter, the operation of the cooling apparatus  50  according to the exemplary embodiment will be described with reference to the schematic view of  FIG. 9  and the flowchart of  FIG. 10 . 
         [0100]    First, at step S 21 , the operation plan  37  is input to the main controller  35  by an operator. Subsequently, proceeding to step S 22 , the main controller  35  determines the operating rate of the calculator  25  in a predetermined period (one day or half a day), based on the operation plan  37 . 
         [0101]    For example, when the number of the operating nodes in a certain period is the same as the number of all the nodes included in the calculator  25 , the main controller  35  sets the operating rate of the calculator  25  in this period to 100%. Further, when the number of the operating nodes in a certain period is 75% of all the nodes included in the calculator  25 , the main controller  35  sets the operating rate of the calculator  25  in this period to 75%. Furthermore, when the number of the operating nodes in a certain period is 50% of all the nodes included in the calculator  25 , the main controller  35  sets the operating rate of the calculator  25  in this period to 50%. 
         [0102]    Here, for the convenience of description, it is assumed that, at step S 21 , the daily operation plan is drafted, and data on the operation plan is input to the main controller  35  by the operator. Further, at step S 22 , the main controller  35  determines the operating rate of that day (one day). 
         [0103]    Subsequently, proceeding to step S 23 , the main controller  35  detects the temperature T 1  of the cooling water fed into the calculator  25 , the flow rate Q of the cooling water, and the temperature T 2  of the cooling water discharged from the calculator  25 , based on the outputs of the temperature sensors  31   a  and  31   b  and the flow sensor  32 . 
         [0104]    Subsequently, proceeding to step S 24 , the main controller  35  calculates the instantaneous calorific value E′ of the calculator  25  using the above-described equation (1). 
         [0105]    Subsequently, proceeding to step S 25 , the main controller  35  calculates a ratio of the instantaneous calorific value E′ of the calculator  25  to the maximum calorific value E 0  of the calculator  25  (E(=(E/E 0 )×100%)) and then sets the operating condition based on the value of the ratio E of the instantaneous calorific value E′ to the maximum calorific value E 0 . However, the maximum calorific value E 0  is the calorific value of the calculator  25  when the calculator  25  is operated at the operating rate determined at step S 22 . Further, the operating condition is set using the table of  FIG. 4 . 
         [0106]    For example, it is assumed that the operating rate of that day determined at step S 22  is 100%. In this case, when the value of E is 57.5% or /less (E≦57.5%), the main controller  35  sets the operating condition of the pump  13  to 70% (=0.7×1×100). Further, when the value of E ranges from 57.5% to 75% (57.5%&lt;E≦75%), the main controller  35  sets the operating condition of the pump  13  to 85% (=0.85×1×100). Further, when the value of E exceeds 75% (75%&lt;E), the main controller  35  sets the operating condition of the pump  13  to 100% (=1×1×100). 
         [0107]    Further, for example, it is assumed that the operating rate determined at step S 22  is 75%. In this case, when the value of E is 57.5% or less (E≦57.5%), the main controller  35  sets the operating condition of the pump  13  to 52.5% (=0.7×0.75×100). Further, when the value of E ranges from 57.5% to 75% (57.5%≦E≦75%), the main controller  35  sets the operating condition of the pump  13  to 63.8% (=0.85×0.75×100). Further, when the value of E exceeds 75% (75%&lt;E), the main controller  35  sets the operating condition of the pump  13  to 75% (=1×0.75×100). 
         [0108]    Furthermore, for example, it is assumed that the operating rate determined at step S 22  is 50%. In this case, when the value of E is 57.5% or less (E≦57.5%), the main controller  35  sets the operating condition of the pump  13  to 35% (=0.7×0.5×100). Further, when the value of E ranges from 57.5% to 75% (57.5%&lt;E≦75%), the main controller  35  sets the operating condition of the pump  13  to 42.5% (=0.85×0.5×100). Further, when the value of E exceeds 75% (75%&lt;E), the main controller  35  sets the operating condition of the pump  13  to 50% (=1×0.5×100). 
         [0109]    Subsequently, proceeding to step S 26 , the main controller  35  operates the pump  13  under the set operating condition. Thereafter, proceeding to step S 27 , the main controller  35  determines whether to read the operation plan or not. When the period (one day) set in the operation plan is not yet completed (“NO” at step S 27 ), the above-described steps are repeated starting from step S 23 . Meanwhile, when it is determined, at step S 27 , that the period (one day) set in the operation plan has been completed (“YES” at step S 27 ), the main controller  35  returns to step S 21  and reads the operation plan for a next period to repeat the above-described steps. 
         [0110]      FIG. 11  is a view illustrating an energy saving effect when the operating rate of the calculator  25  is 100%. In this case, compared to the cooling apparatus of  FIG. 1 , the power consumption of the pump  13  is reduced by 15% at the medium load and by 30% at the low load. 
         [0111]      FIG. 12  is a view illustrating an energy saving effect when the operating rate of the calculator  25  is 75%. In this case, compared to the cooling apparatus of  FIG. 1 , the power consumption of the pump  13  is reduced by 25% at the high load, by 36.2% at medium load, and reduced by 47.5% at the low load. 
         [0112]      FIG. 13  is a view illustrating an energy saving effect when the operating rate of the calculator  25  is 50%. In this case, compared to the cooling apparatus of  FIG. 1 , the power consumption of the pump  13  is reduced by 50% at the high load, reduced by 57.5% at the medium load, and reduced by 65% at the low load. 
         [0113]    As described above, according to the present exemplary embodiment, the maximum operating rate of the calculator  25  is determined for each period according to the operation plan, the maximum calorific value for each period is calculated according to the maximum operating rate of the calculator  25 , and the operating condition of the chiller unit  11  (pump  13 ) is determined according to the result of the calculation. Accordingly, the present exemplary embodiment is capable of further saving energy compared to the first exemplary embodiment. Further, the user of the calculator  25  may send any job to the calculator  25  as long as he or she is within the section allocated to the user, and does not need to consider the operating rate of the CPU. 
         [0114]    Although the present exemplary embodiment has been described based on a case where an operation plan is input to the cooling apparatus of the first exemplary embodiment so as to operate a data processing system, the present exemplary embodiment may be configured to input the operation plan to the cooling apparatus of the second exemplary embodiment so as to operate the data processing system. 
         [0115]    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 illustrating 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.