Patent Publication Number: US-2019182990-A1

Title: Rack cooling system

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to U.S. Provisional Patent Application No. 62/598,103 filed Dec. 13, 2017, the contents of which are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to the field of heat dissipation, and more particularly to a cooling system. 
     BACKGROUND OF THE INVENTION 
     With the increasing development and popularization of science and technology, various electronic computing devices such as network storage devices or servers have been essential parts of people&#39;s daily lives. Generally, these electronic computing devices are stored in a rack that is made of cold-rolled steel or alloy. Consequently, these electronic computing devices are protected from electromagnetic interference and arranged in an orderly and neat manner. Moreover, the electronic computing devices in the rack can be easily maintained or repaired in the future. 
     With the advent of big data and the Internet era, the processing power of the electronic computing device is increasing and the amount of the generated heat is large. It is important to effectively dissipate the heat from the electronic computing devices in the rack so as to increase the performance and the use lives of these electronic computing devices. In views of the power-saving benefit, it is important to achieve the proper heat dissipation efficacy with less power consumption. 
       FIG. 5  schematically illustrates the architecture of a conventional rack cooling system. As shown in  FIG. 5 , the conventional rack cooling system  7  comprises plural cold plates  71 , a manifold device  72 , a coolant distribution unit (CDU)  75  and a chiller  76 . The manifold device  72  comprises a first fluid manifold  77  and a second fluid manifold  78 . The plural cold plates  71  correspond to plural electronic computing devices  8  in a rack (not shown). For example, each cold plate  71  is in contact with the heat source of the corresponding electronic computing device  8 . Each cold plate  71  comprises a cold plate inlet  711  and a cold plate outlet  712 . The first fluid manifold  77  comprises a first manifold inlet  771  and plural first manifold outlets  772  corresponding to the plural cold plates  71 . The second fluid manifold  78  comprises plural second manifold inlets  781  corresponding to the plural cold plates  71  and a second manifold outlet  782 . The coolant distribution unit  75  comprises a first coolant distribution unit inlet  751 , a first coolant distribution unit outlet  752 , a second coolant distribution unit inlet  753  and a second coolant distribution unit outlet  754 . The chiller  76  comprises a chiller inlet  761  and a chiller outlet  762 . 
     The cold plate inlet  711  of each cold plate  71  is in fluid communication with the corresponding first manifold outlet  772  of the first fluid manifold  77 . The cold plate outlet  712  of each cold plate  71  is in fluid communication with the corresponding second manifold inlet  781  of the second fluid manifold  78 . The first coolant distribution unit inlet  751  of the coolant distribution unit  75  is in communication with the second manifold outlet  782  of the second fluid manifold  78 . The first coolant distribution unit outlet  752  of the coolant distribution unit  75  is in communication with the first manifold inlet  771  of the first fluid manifold  77 . In other words, a first fluid loop is defined by the plural cold plates  71 , the manifold device  72  and the coolant distribution unit  75  collaboratively. 
     A first fluid medium (not shown) is filled in the first fluid loop. In the rack cooling system  7 , the manifold device  72  is used for connecting associated conduits, homogenizing the first fluid medium and transferring the first fluid medium. The coolant distribution unit  75  is capable of uniformly or intelligently transferring the first fluid medium to the cold plates  71  through the first fluid manifold  77  of the manifold device  72  according to the practical requirements. 
     The chiller inlet  761  of the chiller  76  is in fluid communication with the second coolant distribution unit outlet  754  of the coolant distribution unit  75 . The chiller outlet  762  of the chiller  76  is in fluid communication with the second coolant distribution unit inlet  753  of the coolant distribution unit  75 . That is, a second fluid loop is defined by the chiller  76  and the coolant distribution unit  75  collaboratively. Moreover, a second fluid medium (not shown) is filled in the second fluid loop. The chiller  76  may be considered as a back-end heat dissipation mechanism for removing the heat from the first fluid medium that is transferred through the first fluid loop. That is, the first fluid medium in the first fluid loop and the second fluid medium in the second fluid loop exchange heat in the coolant distribution unit  75 , wherein the first fluid medium and the second fluid medium are not mixed together. 
     The operations of the conventional rack cooling system  7  will be described as follows. When the first fluid medium flows through the cold plate  71  along the first fluid loop, the first fluid medium is heated by the heat source of the electronic computing device  8  corresponding to the cold plate  71 . Then, the heated first fluid medium is transferred to the coolant distribution unit  75  through the second fluid manifold  78  of the manifold device  72 . When the second fluid medium flows through the coolant distribution unit  75  along the second fluid loop, the second fluid medium is heated by the first fluid medium that is introduced into the coolant distribution unit  75 . After the heated second fluid medium is outputted from the coolant distribution unit  75 , the second fluid medium is transferred to the chiller  76  through the chiller inlet  761 . Consequently, the second fluid medium is cooled down. After the second fluid medium is cooled down, the second fluid medium is transferred to the coolant distribution unit  75  again. Since the first fluid medium flowing into the coolant distribution unit  75  along the first fluid loop exchanges heat with the second fluid medium, the first fluid medium is cooled down. After the first fluid medium is cooled down, the first fluid medium is transferred to the cold plate  71  again through the first fluid manifold  77  of the manifold device  72 . The above steps are repeatedly done to circulate the first fluid medium along the first fluid loop and circulate the second fluid medium along the second fluid loop. Since the heat of the electronic computing device  8  is dissipated to the low-temperature site, the efficacy of reducing the temperature of the first fluid medium is enhanced. 
     However, as the science and technology change very quickly, the racks  8  for storing the electronic computing devices have diversified specifications and designs according to different requirements. Even if the racks comply with the same specifications, the heat dissipation demands are not always identical. As known, the conventional rack cooling system  7  is monotonous and lacks elastic changes. For example, the racks belonging to some specifications have insufficient power dissipation capability. Although the racks belonging to some other specifications have sufficient power dissipation capability, these racks are not power-saving. In other words, the conventional rack cooling system  7  needs to be further improved. 
     SUMMARY OF THE INVENTION 
     For solving the drawbacks of the conventional technologies, the present invention provides a rack cooling system. The rack cooling system has the elastically-changed architecture. Consequently, the rack cooling system can be applied to the racks with different heat dissipation demands while achieving the power-saving efficacy. 
     In accordance with an aspect of the present invention, there is provided a rack cooling system for a rack. Moreover, plural electronic computing devices are installed in the rack. The rack cooling system includes plural cold plates corresponding to the plural electronic computing devices, a radiator, a coolant distribution unit, at least one fan and a manifold device. A fluid medium flows through the radiator to exchange heat. After the fluid medium is introduced into the coolant distribution unit, the fluid medium is distributed by the coolant distribution unit. The at least one fan is used for driving an airflow. The manifold device is connected between the plural cold plates, the radiator and the coolant distribution unit. The fluid medium is circulated through the plural cold plates, the radiator, the coolant distribution unit and the manifold device. Consequently, the heat from the plural electronic computing devices is dissipated away. 
     In an embodiment, the manifold device includes a first fluid manifold and a second fluid manifold. The first fluid manifold includes a first manifold inlet and plural first manifold outlets corresponding to the plural cold plates. The second fluid manifold includes a second manifold outlet and plural second manifold inlets corresponding to the plural cold plates. 
     In an embodiment, each of the plural cold plates includes a cold plate inlet and a cold plate outlet. The cold plate inlet is in fluid communication with the corresponding one of the plural first manifold outlets. The cold plate outlet is in fluid communication with the corresponding one of the plural second manifold inlets. After the fluid medium is outputted from the cold plate through the cold plate outlet, the fluid medium is transferred to the second fluid manifold through the corresponding one of the plural second manifold inlets. After the fluid medium is outputted from the first fluid manifold through the corresponding one of the plural first manifold outlets, the fluid medium is transferred to the cold plate through the cold plate inlet. 
     In an embodiment, the radiator includes a radiator inlet and a radiator outlet, and the coolant distribution unit includes a first coolant distribution unit inlet and a first coolant distribution unit outlet. The radiator inlet is in fluid communication with the second manifold outlet. The radiator outlet is in fluid communication with the first coolant distribution unit inlet. The first coolant distribution unit outlet is in communication with the first manifold inlet. After the fluid medium is outputted from the second fluid manifold through the second manifold outlet, the fluid medium is transferred to the radiator through the radiator inlet. After the fluid medium is outputted from the radiator through the radiator outlet, the fluid medium is transferred to the coolant distribution unit through the first coolant distribution unit inlet. After the fluid medium is outputted from the coolant distribution unit through the first coolant distribution unit outlet, the fluid medium is transferred to the first fluid manifold through the first manifold inlet. 
     In an embodiment, the radiator includes a radiator inlet and a radiator outlet, and the coolant distribution unit includes a first coolant distribution unit inlet and a first coolant distribution unit outlet. The radiator inlet is in fluid communication with the first coolant distribution unit outlet. The radiator outlet is in fluid communication with the first manifold inlet. The first coolant distribution unit inlet is in communication with the second manifold outlet. After the fluid medium is outputted from the second fluid manifold through the second manifold outlet, the fluid medium is transferred to the coolant distribution unit through the first coolant distribution unit inlet. After the fluid medium is outputted from the coolant distribution unit through the first coolant distribution unit outlet, the fluid medium is transferred to the radiator through the radiator inlet. After the fluid medium is outputted from the radiator through the radiator outlet, the fluid medium is transferred to the first fluid manifold through the first manifold inlet. 
     In an embodiment, the rack cooling system further includes a chiller with a chiller inlet and a chiller outlet, and the coolant distribution unit includes a second coolant distribution unit inlet and a second coolant distribution unit outlet. The chiller inlet is in fluid communication with the second coolant distribution unit outlet. The chiller outlet is in fluid communication with the second coolant distribution unit inlet. After an additional fluid medium is outputted from the coolant distribution unit through the second coolant distribution unit outlet, the additional fluid medium is transferred to the chiller through the chiller inlet. After the additional fluid medium is outputted from the chiller through the chiller outlet, the additional fluid medium is transferred to the coolant distribution unit through the second coolant distribution unit inlet. 
     Preferably, the at least one fan is arranged near the radiator, or the at least one fan is arranged near the plural cold plates. 
     After the fluid medium is outputted from one of the plural cold plates and before the fluid medium is introduced into the radiator, the fluid medium has a first average temperature. After the fluid medium is outputted from the radiator and before the fluid medium is transferred to the one of the plural cold plates, the fluid medium has a second average temperature. Consequently, the first average temperature is higher than the second average temperature. 
     After the fluid medium is outputted from one of the plural cold plates and before the fluid medium is introduced into the coolant distribution unit, the fluid medium has a first average temperature. After the fluid medium is outputted from the coolant distribution unit and before the fluid medium is transferred to the one of the plural cold plates, the fluid medium has a second average temperature. Consequently, the first average temperature is higher than the second average temperature. 
     In an embodiment, each of the plural electronic computing devices is a server or a network storage device. 
     In an embodiment, the radiator is a condenser. 
     Due to the arrangement of the radiator, the rack cooling system of the present invention has the elastically-changed architecture. Consequently, the rack cooling system can be applied to the racks with different heat dissipation demands while achieving the power-saving efficacy. 
     The above objects and advantages of the present invention will become more readily apparent to those ordinarily skilled in the art after reviewing the following detailed description and accompanying drawings, in which: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  schematically illustrates the architecture of a rack cooling system according to a first embodiment of the present invention; 
         FIG. 2  schematically illustrates the architecture of a rack cooling system according to a second embodiment of the present invention; 
         FIG. 3  schematically illustrates the architecture of a rack cooling system according to a third embodiment of the present invention; 
         FIG. 4  schematically illustrates the architecture of a rack cooling system according to a fourth embodiment of the present invention; and 
         FIG. 5  schematically illustrates the architecture of a conventional rack cooling system. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  schematically illustrates the architecture of a rack cooling system according to a first embodiment of the present invention. As shown in  FIG. 1 , the rack cooling system  1  comprises plural cold plates  11 , a manifold device  12 , a system cooling unit  13  and a coolant distribution unit (CDU)  15 . The manifold device  12  comprises a first fluid manifold  17  and a second fluid manifold  18 . The plural cold plates  11  correspond to plural electronic computing devices  8  in a rack (not shown). For example, the electronic computing devices  8  are servers or network storage devices. Each cold plate  11  is in contact with the heat source of the corresponding electronic computing device  8 . Preferably but not exclusively, the cold plate  11  and the corresponding electronic computing device  8  are included in the same chassis (not shown). Each cold plate  11  comprises a cold plate inlet  111  and a cold plate outlet  112 . The first fluid manifold  17  comprises a first manifold inlet  171  and plural first manifold outlets  172  corresponding to the plural cold plates  11 . The second fluid manifold  18  comprises plural second manifold inlets  181  corresponding to the plural cold plates  11  and a second manifold outlet  182 . The coolant distribution unit  15  comprises a coolant distribution unit inlet  151  and a coolant distribution unit outlet  152 . 
     In the first embodiment, the system cooling unit  13  comprises a radiator  19  and a fan  10 . Preferably but not exclusively, the radiator  19  is a condenser. The condenser is a heat exchanger for transforming gas or vapor into liquid so as to provide cooling efficacy. In addition, the heat from the heat pipe (not shown) of the condenser can be quickly radiated to the ambient air of the radiator  19 . Consequently, the heat is dissipated away. The fan  10  is used for driving the airflow W 1  to remove heat from the ambient air of the radiator  19 . Preferably but not exclusively, the fan  10  is arranged near the radiator  19 . The radiator  19  comprises a radiator inlet  191  and a radiator outlet  192 . 
     The cold plate inlet  111  of each cold plate  11  is in fluid communication with the corresponding first manifold outlet  172  of the first fluid manifold  17 . The cold plate outlet  112  of each cold plate  11  is in fluid communication with the corresponding second manifold inlet  181  of the second fluid manifold  18 . The radiator inlet  191  of the radiator  19  is in fluid communication with the second manifold outlet  182  of the second fluid manifold  18 . The radiator outlet  192  of the radiator  19  is in fluid communication with the coolant distribution unit inlet  151  of the coolant distribution unit  15 . The coolant distribution unit outlet  152  of the coolant distribution unit  15  is in communication with the first manifold inlet  171  of the first fluid manifold  17 . In other words, a fluid loop is defined by the plural cold plates  11 , the manifold device  12 , the radiator  19  and the coolant distribution unit  15  collaboratively. 
     Preferably but not exclusively, the relationship of each fluid communication may be established through the connection of an associated conduit (not shown). Moreover, a fluid medium (not shown) is filled in the fluid loop. The fluid medium is a liquid medium, a gaseous medium or the mixture of the liquid medium and the gaseous medium. In the rack cooling system  1 , the manifold device  12  is used for connecting associated conduits, homogenizing the fluid medium and transferring the fluid medium. After the fluid medium is introduced into the coolant distribution unit  15 , the fluid medium is distributed by the coolant distribution unit  15 . For example, the fluid medium is uniformly or intelligently transferred from the coolant distribution unit  15  to the cold plates  11  through the first fluid manifold  17  of the manifold device  12  according to the practical requirements. Preferably but not exclusively, the coolant distribution unit  15  is capable of monitoring the heat dissipation performance in real time and automatically adjusting the optimal heat dissipation performance. 
     The operations of the rack cooling system  1  according to the first embodiment of the present invention will be described as follows. When the fluid medium flows through the cold plate  11 , the fluid medium is heated by the heat source of the electronic computing device  8  corresponding to the cold plate  11 . After the fluid medium is outputted from the cold plate  11  through the cold plate outlet  112 , the fluid medium is transferred to the second fluid manifold  18  through the corresponding second manifold inlet  181 . After the fluid medium is outputted from the second fluid manifold  18  through the second manifold outlet  182 , the fluid medium is transferred to the radiator  19  through the radiator inlet  191 . As mentioned above, the fluid medium flowing into the radiator  19  exchanges heat with the radiator  19 , and thus the fluid medium is cooled down. At the same time, the fan  10  of the system cooling unit  13  drives the airflow W 1  to remove the heat from the ambient air of the radiator  19 . After the fluid medium is cooled down by the radiator  19 , the fluid medium is outputted from the radiator  19  through the radiator outlet  192 . Then, the fluid medium is transferred to the coolant distribution unit  15  through the coolant distribution unit inlet  151 . After the fluid medium is outputted from the coolant distribution unit  15  through the coolant distribution unit outlet  152 , the fluid medium is transferred to the first fluid manifold  17  through the first manifold inlet  171 . After the fluid medium is outputted from the first fluid manifold  17  through the first manifold outlet  172 , the fluid medium is transferred to the cold plate  11  again through the corresponding cold plate inlet  111 . The above steps are repeatedly done to circulate the fluid medium along the fluid loop. Since the heat of the electronic computing device  8  is dissipated to the low-temperature site, the efficacy of reducing the temperature of the fluid medium is enhanced. 
     For example, after the fluid medium is outputted from the cold plate  11  and before the fluid medium is introduced into the radiator  19 , the fluid medium has an average temperature T 11 . After the fluid medium is outputted from the radiator  19  and before the fluid medium is transferred to the cold plate  11 , the fluid medium has an average temperature T 12 . Consequently, the average temperature T 12  is lower than the average temperature T 11 . 
     In comparison with the conventional rack cooling system  7 , the chiller of the rack cooling system  1  of the first embodiment does not consume much energy. In other words, the rack cooling system of the present invention has the power-saving benefit. In addition, the rack cooling system of this embodiment is suitably installed in the rack with lower heat dissipation demand. 
       FIG. 2  schematically illustrates the architecture of a rack cooling system according to a second embodiment of the present invention. As shown in  FIG. 2 , the rack cooling system  2  comprises plural cold plates  21 , a manifold device  22 , a first system cooling unit  23 , a second system cooling unit  24  and a coolant distribution unit (CDU)  25 . The manifold device  22  comprises a first fluid manifold  27  and a second fluid manifold  28 . The plural cold plates  21  correspond to plural electronic computing devices  8  in a rack (not shown). For example, the electronic computing devices  8  are servers or network storage devices. Each cold plate  21  is in contact with the heat source of the corresponding electronic computing device  8 . Preferably but not exclusively, the cold plate  21  and the corresponding electronic computing device  8  are included in the same chassis (not shown). Each cold plate  21  comprises a cold plate inlet  211  and a cold plate outlet  212 . The first fluid manifold  27  comprises a first manifold inlet  271  and plural first manifold outlets  272  corresponding to the plural cold plates  21 . The second fluid manifold  28  comprises plural second manifold inlets  281  corresponding to the plural cold plates  21  and a second manifold outlet  282 . The coolant distribution unit  25  comprises a first coolant distribution unit inlet  251 , a first coolant distribution unit outlet  252 , a second coolant distribution unit inlet  253  and a second coolant distribution unit outlet  254 . 
     In the second embodiment, the first system cooling unit  23  comprises a radiator  29  and a fan  20 . For example, the radiator  29  is a condenser. Preferably but not exclusively, the second system cooling unit  24  comprises a chiller  26 . The condenser is a heat exchanger for transforming gas or vapor into liquid so as to provide cooling efficacy. In addition, the heat from the heat pipe (not shown) of the condenser can be quickly radiated to the ambient air of the radiator  29 . Consequently, the heat is dissipated away. The fan  20  is used for driving the airflow W 2  to remove heat from the ambient air of the radiator  29 . Preferably but not exclusively, the fan  20  is arranged near the radiator  29 . The radiator  29  comprises a radiator inlet  291  and a radiator outlet  292 . The chiller  26  comprises a chiller inlet  261  and a chiller outlet  262 . 
     The cold plate inlet  211  of each cold plate  21  is in fluid communication with the corresponding first manifold outlet  272  of the first fluid manifold  27 . The cold plate outlet  212  of each cold plate  21  is in fluid communication with the corresponding second manifold inlet  281  of the second fluid manifold  28 . The radiator inlet  291  of the radiator  29  is in fluid communication with the second manifold outlet  282  of the second fluid manifold  28 . The radiator outlet  292  of the radiator  29  is in fluid communication with the first coolant distribution unit inlet  251  of the coolant distribution unit  25 . The first coolant distribution unit outlet  252  of the coolant distribution unit  25  is in communication with the first manifold inlet  271  of the first fluid manifold  27 . In other words, a first fluid loop is defined by the plural cold plates  21 , the manifold device  22 , the radiator  29  and the coolant distribution unit  25  collaboratively. 
     Preferably but not exclusively, the relationship of each fluid communication may be established through the connection of an associated conduit (not shown). Moreover, a first fluid medium (not shown) is filled in the first fluid loop. The first fluid medium is a liquid medium, a gaseous medium or the mixture of the liquid medium and the gaseous medium. In the rack cooling system  2 , the manifold device  22  is used for connecting associated conduits, homogenizing the first fluid medium and transferring the first fluid medium. After the first fluid medium is introduced into the coolant distribution unit  25 , the first fluid medium is distributed by the coolant distribution unit  25 . For example, the first fluid medium is uniformly or intelligently transferred from the coolant distribution unit  25  to the cold plates  21  through the first fluid manifold  27  of the manifold device  22  according to the practical requirements. Preferably but not exclusively, the coolant distribution unit  25  is capable of monitoring the heat dissipation performance in real time and automatically adjusting the optimal heat dissipation performance. 
     The chiller inlet  261  of the chiller  26  is in fluid communication with the second coolant distribution unit outlet  254  of the coolant distribution unit  25 . The chiller outlet  262  of the chiller  26  is in fluid communication with the second coolant distribution unit inlet  253  of the coolant distribution unit  25 . That is, a second fluid loop is defined by the chiller  26  and the coolant distribution unit  25  collaboratively. Moreover, a second fluid medium (not shown) is filled in the second fluid loop. The second fluid medium is a liquid medium, a gaseous medium or the mixture of the liquid medium and the gaseous medium. The chiller  26  may be considered as a cooling mechanism for removing the heat from the first fluid medium that is transferred through the first fluid loop. That is, the first fluid medium in the first fluid loop and the second fluid medium in the second fluid loop exchange heat in the coolant distribution unit  25 , wherein the first fluid medium and the second fluid medium are not mixed together 
     The operations of the rack cooling system  2  according to the second embodiment of the present invention will be described as follows. When the first fluid medium flows through the cold plate  21  along the first fluid loop, the first fluid medium is heated by the heat source of the electronic computing device  8  corresponding to the cold plate  21 . After the heated first fluid medium is outputted from the cold plate  21  through the cold plate outlet  212 , the first fluid medium is transferred to the second fluid manifold  28  through the corresponding second manifold inlet  281 . After the first fluid medium is outputted from the second fluid manifold  28  through the second manifold outlet  282 , the first fluid medium is transferred to the radiator  29  through the radiator inlet  291 . As mentioned above, the first fluid medium flowing into the radiator  29  exchanges heat with the radiator  29 , and thus the first fluid medium is cooled down in a first stage. At the same time, the fan  20  of the first system cooling unit  23  drives the airflow W 2  to remove the heat from the ambient air of the radiator  29 . After the first fluid medium is cooled down by the radiator  29  in the first stage, the first fluid medium is outputted from the radiator  29  through the radiator outlet  292 . Then, the first fluid medium is transferred to the coolant distribution unit  25  through the first coolant distribution unit inlet  251 . 
     Similarly, when the second fluid medium flows through the coolant distribution unit  25  along the second fluid loop, the second fluid medium is heated by the first fluid medium that is introduced into the coolant distribution unit  25 . After the heated second fluid medium is outputted from the coolant distribution unit  25  through the second coolant distribution unit outlet  254 , the second fluid medium is transferred to the chiller  26  through the chiller inlet  261 . Consequently, the second fluid medium is cooled down. After the second fluid medium is cooled down, the second fluid medium is outputted from the chiller  26  through the chiller outlet  262 . Moreover, the cooled second fluid medium is transferred to the coolant distribution unit  25  again through the second coolant distribution unit inlet  253 . Since the first fluid medium flowing into the coolant distribution unit  25  along the first fluid loop exchanges heat with the second fluid medium, the first fluid medium is cooled down in a second stage. 
     After the first fluid medium is cooled down in the second stage, the first fluid medium is outputted from the coolant distribution unit  25  through the coolant distribution unit outlet  252 . Then, the first fluid medium is transferred to the first fluid manifold  27  through the first manifold inlet  271 . After the first fluid medium is outputted from the first fluid manifold  27  through the first manifold outlet  272 , the first fluid medium is transferred to the cold plate  21  again through the corresponding cold plate inlet  211 . The above steps are repeatedly done to circulate the first fluid medium along the first fluid loop and circulate the second fluid medium along the second fluid loop. Since the heat of the electronic computing device  8  is dissipated to the low-temperature site, the efficacy of reducing the temperature of the first fluid medium is enhanced. 
     For example, after the fluid medium is outputted from the cold plate  21  and before the fluid medium is introduced into the radiator  29 , the first fluid medium has an average temperature T 21 . After the first fluid medium is outputted from the radiator  29  and before the first fluid medium is transferred to the coolant distribution unit  25 , the first fluid medium has an average temperature T 22 . After the first fluid medium is outputted from the coolant distribution unit  25  and before the first fluid medium is transferred to the cold plate  21 , the first fluid medium has an average temperature T 23 . Consequently, the average temperature T 23  is lower than the average temperature T 22 , and the average temperature T 22  is lower than the average temperature T 21 . 
     In comparison with the conventional rack cooling system  7 , the rack cooling system  2  of the second embodiment is further equipped with the first system cooling unit  23 . After the heated first fluid medium is outputted from the cold plate  21 , the first fluid medium is cooled down in the first stage. Consequently, the heat dissipation loading and the power consumption amount of the second system cooling unit  24  are reduced. In other words, the rack cooling system  2  of this embodiment is suitably installed in the rack with higher heat dissipation demand. Preferably but not exclusively, the heat dissipation capacity of the first system cooling unit  23  takes about  20  percent of the overall heat dissipation capacity, and the heat dissipation capacity of the second system cooling unit  24  takes about  80  percent of the overall heat dissipation capacity. 
       FIG. 3  schematically illustrates the architecture of a rack cooling system according to a third embodiment of the present invention. As shown in  FIG. 3 , the rack cooling system  3  comprises plural cold plates  31 , a manifold device  32 , a first system cooling unit  33 , a second system cooling unit  34  and a coolant distribution unit (CDU)  35 . The manifold device  32  comprises a first fluid manifold  37  and a second fluid manifold  38 . The plural cold plates  31  correspond to plural electronic computing devices  8  in a rack (not shown). For example, the electronic computing devices  8  are servers or network storage devices. Each cold plate  31  is in contact with the heat source of the corresponding electronic computing device  8 . Preferably but not exclusively, the cold plate  31  and the corresponding electronic computing device  8  are included in the same chassis (not shown). Each cold plate  31  comprises a cold plate inlet  311  and a cold plate outlet  312 . The first fluid manifold  37  comprises a first manifold inlet  371  and plural first manifold outlets  372  corresponding to the plural cold plates  31 . The second fluid manifold  38  comprises plural second manifold inlets  381  corresponding to the plural cold plates  31  and a second manifold outlet  382 . The coolant distribution unit  35  comprises a first coolant distribution unit inlet  351 , a first coolant distribution unit outlet  352 , a second coolant distribution unit inlet  353  and a second coolant distribution unit outlet  354 . 
     In the third embodiment, the first system cooling unit  33  comprises a radiator  39  and a fan  30 . For example, the radiator  39  is a condenser. Preferably but not exclusively, the second system cooling unit  34  comprises a chiller  36 . The condenser is a heat exchanger for transforming gas or vapor into liquid so as to provide cooling efficacy. In addition, the heat from the heat pipe (not shown) of the condenser can be quickly radiated to the ambient air of the radiator  39 . Consequently, the heat is dissipated away. The fan  30  is used for driving the airflow W 3  to remove heat from the ambient air of the radiator  39 . Preferably but not exclusively, the fan  30  is arranged near the radiator  39 . The radiator  39  comprises a radiator inlet  391  and a radiator outlet  392 . The chiller  36  comprises a chiller inlet  362  and a chiller outlet  362 . 
     The cold plate inlet  311  of each cold plate  31  is in fluid communication with the corresponding first manifold outlet  372  of the first fluid manifold  37 . The cold plate outlet  312  of each cold plate  31  is in fluid communication with the corresponding second manifold inlet  381  of the second fluid manifold  38 . The first coolant distribution unit inlet  351  of the coolant distribution unit  35  is in fluid communication with the second manifold outlet  382  of the second fluid manifold  38 . The first coolant distribution unit outlet  352  of the coolant distribution unit  35  is in communication with the radiator inlet  391  of the radiator  39 . The radiator outlet  392  of the radiator  39  is in fluid communication with the first manifold inlet  371  of the first fluid manifold  37 . In other words, a first fluid loop is defined by the plural cold plates  31 , the manifold device  32 , the coolant distribution unit  35  and the radiator  39  collaboratively. 
     Preferably but not exclusively, the relationship of each fluid communication may be established through the connection of an associated conduit (not shown). Moreover, a first fluid medium (not shown) is filled in the first fluid loop. The first fluid medium is a liquid medium, a gaseous medium or the mixture of the liquid medium and the gaseous medium. In the rack cooling system  3 , the manifold device  32  is used for connecting associated conduits, homogenizing the first fluid medium and transferring the first fluid medium. After the first fluid medium is introduced into the coolant distribution unit  35 , the first fluid medium is distributed by the coolant distribution unit  35 . For example, the first fluid medium is uniformly or intelligently transferred from the coolant distribution unit  35  to the radiator  39  according to the practical requirements. Preferably but not exclusively, the coolant distribution unit  35  is capable of monitoring the heat dissipation performance in real time and automatically adjusting the optimal heat dissipation performance. 
     The chiller inlet  361  of the chiller  36  is in fluid communication with the second coolant distribution unit outlet  354  of the coolant distribution unit  35 . The chiller outlet  362  of the chiller  36  is in fluid communication with the second coolant distribution unit inlet  353  of the coolant distribution unit  35 . That is, a second fluid loop is defined by the chiller  36  and the coolant distribution unit  35  collaboratively. Moreover, a second fluid medium (not shown) is filled in the second fluid loop. The second fluid medium is a liquid medium, a gaseous medium or the mixture of the liquid medium and the gaseous medium. The chiller  36  is considered as a cooling mechanism for removing the heat from the first fluid medium that is transferred through the first fluid loop. That is, the first fluid medium in the first fluid loop and the second fluid medium in the second fluid loop exchange heat in the coolant distribution unit  35 , wherein the first fluid medium and the second fluid medium are not mixed together. 
     The operations of the rack cooling system  3  according to the third embodiment of the present invention will be described as follows. When the first fluid medium flows through the cold plate  31  along the first fluid loop, the first fluid medium is heated by the heat source of the electronic computing device  8  corresponding to the cold plate  31 . After the heated first fluid medium is outputted from the cold plate  31  through the cold plate outlet  312 , the first fluid medium is transferred to the second fluid manifold  38  through the corresponding second manifold inlet  381 . After the first fluid medium is outputted from the second fluid manifold  38  through the second manifold outlet  382 , the first fluid medium is transferred to the coolant distribution unit  35  through the first coolant distribution unit inlet  351 . Similarly, when the second fluid medium flows through the coolant distribution unit  35  along the second fluid loop, the second fluid medium is heated by the first fluid medium that is introduced into the coolant distribution unit  35 . After the heated second fluid medium is outputted from the coolant distribution unit  35  through the second coolant distribution unit outlet  354 , the second fluid medium is transferred to the chiller  36  through the chiller inlet  361 . Consequently, the second fluid medium is cooled down. After the second fluid medium is cooled down, the cooled second fluid medium is outputted from the chiller  36  through the chiller outlet  362 . Moreover, the second fluid medium is transferred to the coolant distribution unit  35  again through the second coolant distribution unit inlet  353 . Since the first fluid medium flowing into the coolant distribution unit  35  along the first fluid loop exchanges heat with the second fluid medium, the first fluid medium is cooled down. 
     Moreover, after the first fluid medium flowing along the first fluid loop is cooled down by the coolant distribution unit  35 , the first fluid medium is outputted from the coolant distribution unit  35  through the coolant distribution unit outlet  352 . Then, the first fluid medium is transferred to the radiator  39  through the radiator inlet  391 . After the first fluid medium is outputted from the radiator  39  through the radiator outlet  39 , the first fluid medium is transferred to the first fluid manifold  37  through the first manifold inlet  371 . After the first fluid medium is outputted from the first fluid manifold  37  through the first manifold outlet  372 , the fluid medium is transferred to the cold plate  31  again through the corresponding cold plate inlet  311 . The above steps are repeatedly done to circulate the first fluid medium along the first fluid loop and circulate the second fluid medium along the second fluid loop. Since the heat of the electronic computing device  8  is dissipated to the low-temperature site, the efficacy of reducing the temperature of the first fluid medium is enhanced. As mentioned above, the radiator  39  has the ability to reduce the temperature of the ambient air. Moreover, the fan  30  is cooperatively used to drive the airflow W 3 . Since the overall temperature of the environment around the rack cooling system  3  is reduced, the efficacy of dissipating the heat of the air is achieved. 
     For example, after the first fluid medium is outputted from the cold plate  31  and before the first fluid medium is introduced into the coolant distribution unit  35 , the fluid medium has an average temperature T 31 . After the first fluid medium is outputted from the coolant distribution unit  35  and before the first fluid medium is transferred to the cold plate  31 , the first fluid medium has an average temperature T 32 . Consequently, the average temperature T 32  is lower than the average temperature T 31 . 
     In comparison with the conventional rack cooling system  7 , the rack cooling system  3  of the third embodiment is further equipped with the first system cooling unit  33  to cool the ambient air. In other words, the rack cooling system  3  of this embodiment is suitably installed in the rack with higher heat dissipation demand. Preferably but not exclusively, the heat dissipation capacity of the first system cooling unit  33  takes about  20  percent of the overall heat dissipation capacity, and the heat dissipation capacity of the second system cooling unit  34  takes about  80  percent of the overall heat dissipation capacity. 
       FIG. 4  schematically illustrates the architecture of a rack cooling system according to a fourth embodiment of the present invention. 
     As shown in  FIG. 4 , the rack cooling system  4  comprises plural cold plates  41 , a manifold device  42 , a radiator  49 , a system cooling unit  44  and a coolant distribution unit (CDU)  45 . The manifold device  42  comprises a first fluid manifold  47  and a second fluid manifold  48 . The plural cold plates  41  correspond to plural electronic computing devices  8  in a rack (not shown). For example, the electronic computing devices  8  are servers or network storage devices. Each cold plate  41  is in contact with the heat source of the corresponding electronic computing device  8 . Preferably but not exclusively, the cold plate  41  and the corresponding electronic computing device  8  are included in the same chassis (not shown). Each cold plate  41  comprises a cold plate inlet  411  and a cold plate outlet  412 . The first fluid manifold  47  comprises a first manifold inlet  472  and plural first manifold outlets  472  corresponding to the plural cold plates  41 . The second fluid manifold  48  comprises plural second manifold inlets  481  corresponding to the plural cold plates  41  and a second manifold outlet  482 . The coolant distribution unit  45  comprises a first coolant distribution unit inlet  451 , a first coolant distribution unit outlet  452 , a second coolant distribution unit inlet  453  and a second coolant distribution unit outlet  454 . 
     For example, the radiator  49  is a condenser. Preferably but not exclusively, the system cooling unit  44  comprises a chiller  46 . The condenser is a heat exchanger for transforming gas or vapor into liquid so as to provide cooling efficacy. In addition, the heat from the heat pipe (not shown) of the condenser can be quickly radiated to the ambient air of the radiator  49 . Consequently, the heat is dissipated away. The radiator  49  comprises a radiator inlet  491  and a radiator outlet  492 . The chiller  46  comprises a chiller inlet  461  and a chiller outlet  462 . 
     The cold plate inlet  411  of each cold plate  41  is in fluid communication with the corresponding first manifold outlet  472  of the first fluid manifold  47 . The cold plate outlet  412  of each cold plate  41  is in fluid communication with the corresponding second manifold inlet  481  of the second fluid manifold  48 . The first coolant distribution unit inlet  451  of the coolant distribution unit  45  is in fluid communication with the second manifold outlet  482  of the second fluid manifold  48 . The first coolant distribution unit outlet  452  of the coolant distribution unit  45  is in communication with the radiator inlet  491  of the radiator  49 . The radiator outlet  492  of the radiator  49  is in fluid communication with the first manifold inlet  471  of the first fluid manifold  47 . In other words, a first fluid loop is defined by the plural cold plates  41 , the manifold device  42 , the coolant distribution unit  45  and the radiator  49  collaboratively. 
     Preferably but not exclusively, the relationship of each fluid communication may be established through the connection of an associated conduit (not shown). Moreover, a first fluid medium (not shown) is filled in the first fluid loop. The first fluid medium is a liquid medium, a gaseous medium or the mixture of the liquid medium and the gaseous medium. In the rack cooling system  4 , the manifold device  42  is used for connecting associated conduits, homogenizing the first fluid medium and transferring the first fluid medium. After the first fluid medium is introduced into the coolant distribution unit  45 , the first fluid medium is distributed by the coolant distribution unit  45 . For example, the first fluid medium is uniformly or intelligently transferred from the coolant distribution unit  45  to the radiator  49  according to the practical requirements. Preferably but not exclusively, the coolant distribution unit  45  is capable of monitoring the heat dissipation performance in real time and automatically adjusting the optimal heat dissipation performance. 
     The chiller inlet  461  of the chiller  46  is in fluid communication with the second coolant distribution unit outlet  454  of the coolant distribution unit  45 . The chiller outlet  462  of the chiller  46  is in fluid communication with the second coolant distribution unit inlet  453  of the coolant distribution unit  45 . That is, a second fluid loop is defined by the chiller  46  and the coolant distribution unit  45  collaboratively. Moreover, a second fluid medium (not shown) is filled in the second fluid loop. The second fluid medium is a liquid medium, a gaseous medium or the mixture of the liquid medium and the gaseous medium. The chiller  46  may be considered as a cooling mechanism for removing the heat from the first fluid medium that is transferred through the first fluid loop. That is, the first fluid medium in the first fluid loop and the second fluid medium in the second fluid loop exchange heat in the coolant distribution unit  45 , wherein the first fluid medium and the second fluid medium are not mixed together. 
     The operations of the rack cooling system  4  according to the fourth embodiment of the present invention will be described as follows. When the first fluid medium flows through the cold plate  41  along the first fluid loop, the first fluid medium is heated by the heat source of the electronic computing device  8  corresponding to the cold plate. After the heated first fluid medium is outputted from the cold plate  41  through the cold plate outlet  412 , the first fluid medium is transferred to the second fluid manifold  48  through the corresponding second manifold inlet  481 . After the first fluid medium is outputted from the second fluid manifold  48  through the second manifold outlet  482 , the first fluid medium is transferred to the coolant distribution unit  45  through the first coolant distribution unit inlet  451 . Similarly, when the second fluid medium flows through the coolant distribution unit  45  along the second fluid loop, the second fluid medium is heated by the first fluid medium that is introduced into the coolant distribution unit  45 . After the heated second fluid medium is outputted from the coolant distribution unit  45  through the second coolant distribution unit outlet  454 , the second fluid medium is transferred to the chiller  46  through the chiller inlet  461 . Consequently, the second fluid medium is cooled down. After the second fluid medium is cooled down, the cooled second fluid medium is outputted from the chiller  46  through the chiller outlet  462 . Moreover, the second fluid medium is transferred to the coolant distribution unit  45  again through the second coolant distribution unit inlet  453 . Since the first fluid medium flowing into the coolant distribution unit  45  along the first fluid loop exchanges heat with the second fluid medium, the first fluid medium is cooled down. 
     After the first fluid medium flowing along the first fluid loop is cooled down by the coolant distribution unit  45 , the first fluid medium is outputted from the coolant distribution unit  45  through the coolant distribution unit outlet  452 . Then, the first fluid medium is transferred to the radiator  49  through the radiator inlet  491 . After the first fluid medium is outputted from the radiator  49  through the radiator outlet  49 , the first fluid medium is transferred to the first fluid manifold  47  through the first manifold inlet  471 . After the first fluid medium is outputted from the first fluid manifold  47  through the first manifold outlet  472 , the fluid medium is transferred to the cold plate  41  again through the corresponding cold plate inlet  411 . The above steps are repeatedly done to circulate the first fluid medium along the first fluid loop and circulate the second fluid medium along the second fluid loop. Since the heat of the electronic computing device  8  is dissipated to the low-temperature site, the efficacy of reducing the temperature of the first fluid medium is enhanced 
     In the fourth embodiment, the rack cooling system comprises plural fans  9  corresponding to the plural electronic computing devices  8 . For example, the plural fans  9  are arranged near the plural electronic computing devices  8 . The airflow W 4  driven by each fan  9  facilitates removing at least a portion of the heat from the corresponding plural electronic computing device  8 . Consequently, the ambient air is heated. As mentioned above, the radiator  49  is capable of reducing the temperature of the ambient air. Consequently, the temperature of the heated airflow is reduced by the radiator  49 . Since the overall temperature of the environment around the rack cooling system  4  is reduced, the efficacy of dissipating the heat of the air is achieved. 
     For example, after the first fluid medium is outputted from the cold plate  41  and before the first fluid medium is introduced into the coolant distribution unit  45 , the fluid medium has an average temperature T 41 . After the first fluid medium is outputted from the coolant distribution unit  45  and before the first fluid medium is transferred to the cold plate  41 , the first fluid medium has an average temperature T 42 . Consequently, the average temperature T 42  is lower than the average temperature T 41 . 
     In comparison with the conventional rack cooling system  7 , the rack cooling system  4  of the fourth embodiment is further equipped with the radiator  49  and the plural fans  9  to cool the ambient air. In other words, the rack cooling system  4  of this embodiment is suitably installed in the rack with higher heat dissipation demand. 
     While the invention has been described in terms of what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention needs not be limited to the disclosed embodiments. On the contrary, it is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims which are to be accorded with the broadest interpretation so as to encompass all modifications and similar structures.