Cooling arrangement for autonomous cooling of a rack

Abstract

A cooling arrangement for autonomous cooling of a rack hosting components and fans comprises a closed loop and an open loop. Liquid cooling is used in the closed loop to transfer heat from heat-generating units of the components to a primary side of a liquid-to-liquid heat exchanger. An air-to-liquid cooling unit is used in the open loop to absorb heat expelled from the rack by the fans. A liquid from a cold supply line is first heated to some degree in the air-to-liquid cooling unit before reaching a secondary side of the liquid-to-liquid heat exchanger. The primary side being hotter than the secondary side, heat is transferred from the primary side to the secondary side of the liquid-to-liquid heat exchanger. The liquid is expelled at a higher temperature from the secondary side to a hot return line.

Claims

1. A cooling arrangement for autonomous cooling of a rack hosting a plurality of components and at least one fan, characterized in that the cooling arrangement comprises: a first closed loop comprising: a plurality of liquid cooling units thermally coupled to a plurality of heat-generating units of the plurality of components, each of the plurality of heat-generating units corresponding to one of the plurality of components and each of the plurality of liquid cooling units being thermally coupled to one of the plurality of heat-generating units and comprising a first liquid channel adapted for transferring heat from the corresponding one of the plurality of heat-generating units to a first liquid flowing in the corresponding first liquid channel, a first primary side of a first liquid-to-liquid heat exchanger, the first primary side being fluidly connected to the first liquid channel of each of the plurality of liquid cooling units, and a first pump fluidly connected between the first primary side of the first liquid-to-liquid heat exchanger and each of the plurality of liquid cooling units, the first pump being adapted for causing the first liquid to flow within the first closed loop; a first open loop comprising: a first air-to-liquid heat exchanger mounted to the rack so that heated air expelled from the rack by the at least one fan flows through the first air-to-liquid heat exchanger, the first air-to-liquid heat exchanger being adapted to receive a second liquid from a first cold supply line, and a first secondary side of the first liquid-to-liquid heat exchanger, the first secondary side being thermally coupled to the first primary side for transfer of heat from the first primary side to the first secondary side when a temperature of the first primary side is higher than a temperature of the first secondary side, the first secondary side being fluidly connected to the first air-to-liquid heat exchanger, the first secondary side being adapted for receiving the second liquid from an outlet of the first air-to-liquid heat exchanger and returning the second liquid to a first hot return line.

2. The cooling arrangement of claim 1, wherein the first cold supply line is adapted for being connected to a cold outlet of a dry cooler and the first hot return line is adapted for being connected to a hot inlet of the dry cooler.

3. The cooling arrangement of claim 1, wherein: the first liquid channel of each of the plurality of liquid cooling units extends between a first liquid inlet and a first liquid outlet of the corresponding one of the plurality of liquid cooling units; the first primary side of the first liquid-to-liquid heat exchanger comprises a second liquid inlet fluidly connected to the first liquid outlet of each of the plurality of liquid cooling units, the first primary side further comprising a second liquid outlet fluidly connected to the first liquid inlet of each of the plurality of liquid cooling units; the first air-to-liquid heat exchanger comprises a third liquid inlet adapted to receive the second liquid from the first cold supply line, the first air-to-liquid heat exchanger further comprising a third liquid outlet; and the first secondary side of the first liquid-to-liquid heat exchanger comprises a fourth liquid inlet fluidly connected to the third liquid outlet of the first air-to-liquid heat exchanger and a fourth liquid outlet adapted for returning the second liquid to the first hot return line.

4. The cooling arrangement of claim 3, wherein the rack has a generally rectangular perimeter, the first air-to-liquid heat exchanger being positioned on a first side of the rack, the cooling arrangement further comprising a subframe adapted to be mounted on a second side of the rack perpendicular to the first side, the subframe being configured to receive: the first liquid-to-liquid heat exchanger; the first pump being connected to the second liquid inlet of the first primary side of the first liquid-to-liquid heat exchanger; a first valve within a connection extending from the first liquid outlet of each of the plurality of liquid cooling units to the first pump; a second valve within a fluid connection extending from the second liquid outlet of the first primary side of the first liquid-to-liquid heat exchanger to the first liquid inlet of each of the plurality of liquid cooling units; a third valve within a fluid connection extending from the third liquid outlet of the first air-to-liquid heat exchanger to the fourth liquid inlet of the first secondary side of the first liquid-to-liquid heat exchanger; and a fourth valve within a fluid connection extending from the fourth liquid outlet of the first secondary side of the first liquid-to-liquid heat exchanger to the first hot return line.

5. The cooling arrangement of claim 3, further comprising: a second closed loop comprising: a plurality of second liquid channels of the plurality of liquid cooling units, each of the plurality of second liquid channels being comprised by one of the plurality of liquid cooling units and being adapted for transferring heat from the heat-generating unit to a third liquid flowing in the second liquid channel of the corresponding one of the plurality of liquid cooling units; a second primary side of a second liquid-to-liquid heat exchanger, the second primary side being fluidly connected to each of the plurality of second liquid channels of the plurality of liquid cooling units, and a second pump fluidly connected between the second primary side of the second liquid-to-liquid heat exchanger and each of the plurality of liquid cooling units, the second pump being adapted for causing the third liquid to flow within the second closed loop; and a second open loop comprising: a second air-to-liquid heat exchanger mounted to the rack so that air having flowed through the first air-to-liquid heat exchanger flows through the second air-to-liquid heat exchanger, the second air-to-liquid heat exchanger being adapted to receive a fourth liquid from the first cold supply line or from a second cold supply line, and a second secondary side of the second liquid-to-liquid heat exchanger, the second secondary side being thermally coupled to the second primary side for transfer of heat from the second primary side to the second secondary side when a temperature of the second primary side is higher than a temperature of the second secondary side, the second secondary side being fluidly connected to the second air-to-liquid heat exchanger, the second secondary side being adapted for returning the fourth liquid to the first hot return line or to a second hot return line.

6. The cooling arrangement of claim 5, wherein: each of the plurality of the second liquid channels of each of the plurality of the liquid cooling units extends between a fifth liquid inlet and a fifth liquid outlet of the corresponding one of the plurality of liquid cooling units; the second primary side of the second liquid-to-liquid heat exchanger comprises a sixth liquid inlet fluidly connected to the fifth liquid outlet of each of the plurality of liquid cooling units, the second primary side further comprising a sixth liquid outlet fluidly connected to the fifth liquid inlet of each of the plurality of liquid cooling units; the second air-to-liquid heat exchanger comprises a seventh liquid inlet adapted to receive the fourth liquid from the first cold supply line or from the second cold supply line, the second air-to-liquid heat exchanger further comprising a seventh liquid outlet; and the second secondary side of the second liquid-to-liquid heat exchanger comprises an eighth liquid inlet fluidly connected to the seventh liquid outlet of the second air-to-liquid heat exchanger and an eighth liquid outlet adapted for returning the second liquid to the first hot return line or to the second hot return line.

7. The cooling arrangement of claim 6, wherein the rack has a generally rectangular perimeter, the first air-to-liquid heat exchanger being positioned on a first side of the rack, the cooling arrangement further comprising a subframe adapted to be mounted on a second side of the rack perpendicular to the first side, the subframe being configured to receive: a first module comprising: the first liquid-to-liquid heat exchanger; the first pump being connected to the second liquid inlet of the first primary side of the first liquid-to-liquid heat exchanger; a first valve within a connection extending from the first liquid outlet of each of the plurality of liquid cooling units to the first pump; a second valve within a fluid connection extending from the second liquid outlet of the first primary side of the first liquid-to-liquid heat exchanger to the first liquid inlet of each of the plurality of liquid cooling units; a third valve within a fluid connection extending from the third liquid outlet of the first air-to-liquid heat exchanger to the fourth liquid inlet of the first secondary side of the first liquid-to-liquid heat exchanger; and a fourth valve within a fluid connection extending from the fourth liquid outlet of the first secondary side of the first liquid-to-liquid heat exchanger to the first hot return line; and a second module comprising: the second liquid-to-liquid heat exchanger; the second pump being connected to the sixth liquid inlet of the second primary side of the second liquid-to-liquid heat exchanger; a fifth valve within a connection extending from the fifth liquid outlet of each of the plurality of liquid cooling units to the second pump; a sixth valve within a fluid connection extending from the sixth liquid outlet of the second primary side of the second liquid-to-liquid heat exchanger to the fifth liquid inlet of each of the plurality of liquid cooling units; a seventh valve within a fluid connection extending from the seventh liquid outlet of the second air-to-liquid heat exchanger to the eighth liquid inlet of the second secondary side of the second liquid-to-liquid heat exchanger; and an eighth valve within a fluid connection extending from the eighth liquid outlet of the second secondary side of the second liquid-to-liquid heat exchanger to the first hot return line or to the second hot return line.

8. The cooling arrangement of claim 7, wherein: the first closed loop and the first open loop are taken out of service by closing the first, second, third and fourth valves and by turning off the first pump; and the second closed loop and the second open loop are taken out of service by closing the fifth, sixth, seventh and eighth valves and by turning off the second pump.

9. The cooling arrangement of claim 7, wherein: the first closed loop and the first open loop are configured to provide sufficient cooling for maintaining a temperature of the at least one component to less than a safe temperature threshold when the second closed loop and the second open loop are taken out of service; the second closed loop and the second open loop are configured to provide sufficient cooling for maintaining the temperature of the plurality of components to less than the safe temperature threshold when the first closed loop and the first open loop are taken out of service.

10. The cooling arrangement of claim 5, wherein the second liquid-to-liquid heat exchanger is a plate heat exchanger.

11. The cooling arrangement of claim 1, wherein the first liquid-to-liquid heat exchanger is a plate heat exchanger.

12. The cooling arrangement of claim 1, wherein: the rack comprises a plurality of server housings, each of the server housing hosting at least one component; the at least one fan comprises at least one fan mounted in each of the server housings; the first open loop comprises a plurality of air-to-liquid heat exchangers mounted to the rack so that heated air expelled by the at least one fan of each server housing flows through a corresponding one of the plurality of air-to-liquid heat exchangers; each of the plurality of air-to-liquid heat exchangers is adapted to receive liquid from the first cold supply line; and the first secondary side of the first liquid-to-liquid heat exchanger is fluidly connected to each of the plurality of air-to-liquid heat exchangers.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) For a better understanding of the present technology, as well as other aspects and further features thereof, reference is made to the following description which is to be used in conjunction with the accompanying drawings, where:

(2) FIG. 1 is a highly schematic perspective view of a server rack on which three (3) air-to-liquid heat exchangers are mounted;

(3) FIG. 2 is a schematic diagram of a single-flow air-to-liquid heat exchanger;

(4) FIG. 3 is a visual representation of a stratified temperature pattern of an airflow expelled from the single-flow air-to-liquid heat exchanger of FIG. 2;

(5) FIG. 4 is a schematic diagram of a multi-flow air-to-liquid heat exchanger;

(6) FIG. 5 is a schematic side-view of the multi-flow air-to-liquid heat exchanger of FIG. 4;

(7) FIG. 6 is a top plan schematic representation of a water block;

(8) FIG. 7 is a highly schematic representation of a pair of air-to-liquid heat exchangers assembled in an anti-parallel configuration in accordance with an embodiment of the present technology;

(9) FIG. 8 is a rear perspective view of a server rack having an autonomous and redundant cooling arrangement including a pair of closed loops and a pair of open loops in accordance with an embodiment of the present technology;

(10) FIG. 9 is a partial, front perspective view of the server rack of FIG. 8;

(11) FIG. 10 is a side elevation view of the server rack of FIGS. 8 and 9 in accordance with an embodiment of the present technology;

(12) FIG. 11 is a highly schematic illustration of a cooling arrangement having a closed loop including a liquid cooling unit and an open loop including air-to-liquid heat exchangers;

(13) FIG. 12 is a schematic block diagram of a manifold connection between a plurality of water blocks, a pump and a liquid-to-liquid heat exchanger;

(14) FIG. 13 is another side elevation view of the server rack of FIGS. 8 and 9 showing a removal of a module in accordance with an embodiment of the present technology; and

(15) FIG. 14 is a visual representation of a homogeneous temperature pattern of an airflow expelled from dual-flow air-liquid heat exchangers assembled in an anti-parallel configuration in accordance with an embodiment of the present technology.

(16) It should also be noted that, unless otherwise explicitly specified herein, the drawings are not to scale.

DETAILED DESCRIPTION

(17) The examples and conditional language recited herein are principally intended to aid the reader in understanding the principles of the present technology and not to limit its scope to such specifically recited examples and conditions. It will be appreciated that those skilled in the art may devise various arrangements that, although not explicitly described or shown herein, nonetheless embody the principles of the present technology.

(18) Furthermore, as an aid to understanding, the following description may describe relatively simplified implementations of the present technology. As persons skilled in the art would understand, various implementations of the present technology may be of a greater complexity.

(19) In some cases, what are believed to be helpful examples of modifications to the present technology may also be set forth. This is done merely as an aid to understanding, and, again, not to define the scope or set forth the bounds of the present technology. These modifications are not an exhaustive list, and a person skilled in the art may make other modifications while nonetheless remaining within the scope of the present technology. Further, where no examples of modifications have been set forth, it should not be interpreted that no modifications are possible and/or that what is described is the sole manner of implementing that element of the present technology.

(20) Moreover, all statements herein reciting principles, aspects, and implementations of the present technology, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof, whether they are currently known or developed in the future.

(21) An aspect of the present technology introduces a cooling arrangement for autonomous cooling of a rack, for example a server rack, hosting at least one heat generating component and at least one fan. The cooling arrangement comprises a closed loop and an open loop. The closed loop provides liquid cooling for the heat generating component. The open loop provides cooling for air expelled from the rack by the at least one fan. A cold liquid, for example water, is fed to the open loop and is brought to a warm temperature by the air expelled by the rack. The warm liquid is then fed to a heat exchanger at a junction between the open loop and the closed loop. A hotter liquid of the closed loop is cooled by thermal transfer from the closed loop to the open loop in the heat exchanger. The liquid from the open loop, which has increased in temperature, is expelled from the open loop.

(22) With these fundamentals in place, we will now consider some non-limiting examples to illustrate various implementations of aspects of the present technology.

(23) FIG. 7 is a highly schematic representation of a pair of air-to-liquid heat exchangers assembled in an anti-parallel configuration in accordance with an embodiment of the present technology. A cooling arrangement 300 that may be mounted on a rack hosting electronic equipment and at least one fan, for example the server rack 10 having the fans 12, comprises at least a pair of air-to-liquid heat exchangers, for example and without limitation, a pair of single-flow heat exchangers 100 as introduced in the description of FIG. 2. With continued reference to FIG. 7, also considering FIGS. 1 and 2, an air-to-liquid heat exchanger 100.sub.A is shown in dotted lines and another air-to-liquid heat exchanger 100.sub.B is shown in solid lines. On FIG. 7, the air-to-liquid heat exchangers 100.sub.A and 100.sub.B are shown as being mounted at an offset from one another; this illustration is solely intended to render visible various parts of the air-to-liquid heat exchangers 100.sub.A and 100.sub.B. In a practical application, the air-to-liquid heat exchangers 100.sub.A and 100.sub.B may be aligned so that there is no discernable offset therebetween.

(24) The air-to-liquid heat exchanger 100.sub.A is mounted to the server rack 10 so that heated air expelled from the server rack 10 by the one or more fans 12 flows through the air-to-liquid heat exchanger 100.sub.A. The air-to-liquid heat exchanger 100.sub.A comprises a frame 102.sub.A, a liquid inlet 106.sub.A mounted to the frame 102.sub.A for receiving liquid from a cold supply line, a liquid outlet 108.sub.A mounted to the frame 102.sub.A for returning liquid to a hot return line, and a continuous internal conduit 104.sub.A. The continuous internal conduit 104.sub.A forms a plurality of interconnected parallel sections 110.sub.A (only some are shown) extending within the frame 102.sub.A. Examples of the cold supply line and of the hot return line are shown on later Figures.

(25) The continuous internal conduit 104.sub.A connects the liquid inlet 106.sub.A to the liquid outlet 108.sub.A. In more details, a one of the plurality of interconnected parallel sections 110.sub.A is connected to the liquid inlet 106.sub.A. Then, each one of the plurality of interconnected parallel sections 110.sub.A except a last one is connected to a next one of the plurality of interconnected parallel sections 110.sub.A via one of a plurality of U-shaped sections 112.sub.A of the continuous internal conduit 104.sub.A. The last one of the plurality of interconnected parallel sections 110.sub.A is connected to the liquid outlet 108.sub.A.

(26) The air-to-liquid heat exchanger 100.sub.B is mounted to the air-to-liquid heat exchanger 100.sub.A so that air having flowed through the air-to-liquid heat exchanger 100.sub.A flows through the air-to-liquid heat exchanger 100.sub.B. The air-to-liquid heat exchanger 100.sub.B comprises a frame 102.sub.B, a liquid inlet 106.sub.B mounted to the frame 102.sub.B and adapted to receive liquid from the same cold supply line or from another cold supply line, a liquid outlet 108.sub.B mounted to the frame 102.sub.B and adapted to return liquid to the same hot return line or to another hot return line, and a continuous internal conduit 104.sub.B forming a plurality of interconnected parallel sections 110.sub.B (only some are shown) extending within the frame 102.sub.B.

(27) The continuous internal conduit 104.sub.B connects the liquid inlet 106.sub.B to the liquid outlet 108.sub.B. In more details, a one of the plurality of interconnected parallel sections 110.sub.B is connected to the liquid inlet 106.sub.B. Then, each one of the plurality of interconnected parallel sections 110.sub.B except a last one is connected to a next one of the plurality of interconnected parallel sections 110.sub.B via one of a plurality of U-shaped sections 112.sub.B of the continuous internal conduit 104.sub.B. The last one of the plurality of interconnected parallel sections 110.sub.B is connected to the liquid outlet 108.sub.B. The air-to-liquid heat exchangers (100.sub.A, 100.sub.B) are assembled in an anti-parallel configuration in the sense that liquid flows in opposite directions in their respective liquid parallel sections (110.sub.A, 110.sub.B).

(28) FIG. 7 illustrates a particular configuration in which the liquid inlet 106.sub.A and the liquid outlet 108.sub.A are connected on opposite sides of the frame 102.sub.A, the continuous internal conduit 104.sub.A forming an even number of interconnected parallel sections 110.sub.A while the continuous internal conduit 104.sub.B forms an even number of interconnected parallel sections 110.sub.B. Likewise, the liquid inlet 106.sub.B and the liquid outlet 108.sub.B are connected on opposite sides of the frame 102.sub.B. As illustrated, the interconnected parallel sections 110.sub.A and 110.sub.B extend horizontally. This is just one of many possible configurations. For instance, the interconnected parallel sections 110.sub.A and 110.sub.B may extend vertically. Some other configurations will be illustrated hereinbelow.

(29) The air-to-liquid heat exchangers 100.sub.A and 100.sub.B are mounted to the server rack 10 so that the frame 102.sub.A is parallel and adjacent to the frame 102.sub.B. One of the plurality of interconnected parallel sections 110.sub.A of the continuous internal conduit 104.sub.A nearest to the liquid inlet 106.sub.A is proximate one of the plurality of interconnected parallel sections 110.sub.B of the continuous internal conduit 104.sub.B nearest to the liquid outlet 108.sub.B. Otherwise stated, among the plurality of interconnected parallel sections 110.sub.A, the one interconnected parallel section 110.sub.A that is closest to the liquid inlet 106.sub.A is also the one interconnected parallel section 110.sub.A that is closest to the one interconnected parallel section 110.sub.B that is closest to the liquid outlet 108.sub.B.

(30) The one of the plurality of interconnected parallel sections 110.sub.A of the continuous internal conduit 104.sub.A nearest to the liquid inlet 106.sub.A and the one of the plurality of interconnected parallel sections 110.sub.B of the continuous internal conduit 104.sub.B nearest to the liquid outlet 108.sub.B may be directly facing each other when viewed in a general direction of an airflow expelled from the server rack 10. Alternatively, one of these parallel sections 110.sub.A or 110.sub.B may be positioned slightly higher or lower than the other. Precise placement of the one of the plurality of interconnected parallel sections 110.sub.A of the continuous internal conduit 104.sub.A nearest to the liquid inlet 106.sub.A in relation to the proximate one of the plurality of interconnected parallel sections 110.sub.B of the continuous internal conduit 104.sub.B nearest to the liquid outlet 108.sub.B may depend on the construction of the air-to-liquid heat exchangers 100.sub.A and 100.sub.B and on manufacturing tolerances. Minor variations on the placement of the parallel sections 110.sub.A and 110.sub.B within the cooling arrangement 300 are not expected to have a significant impact on the cooling performance.

(31) Given any one of these configurations, a topmost strata of the airflow expelled from the server rack 10 flows within the air-to-liquid heat exchanger 100.sub.A around its topmost interconnected parallel sections 110.sub.A in which the liquid flowing through the continuous internal conduit 104.sub.A is coolest, being closest to the liquid inlet 106.sub.A. The topmost strata of the airflow then flows within the air-to-liquid heat exchanger 100.sub.B around its topmost interconnected parallel sections 110.sub.B in which the liquid flowing through the continuous internal conduit 104.sub.B is warmest, being closest to the liquid outlet 108.sub.B. Conversely, a bottommost strata of the airflow expelled from the server rack 10 flows within the air-to-liquid heat exchanger 100.sub.A around its bottommost interconnected parallel sections 110.sub.A in which the liquid flowing through the continuous internal conduit 104.sub.A is warmest, being closest to the liquid outlet 108.sub.A. The bottommost strata of the airflow then flows within the air-to-liquid heat exchanger 100.sub.B around its bottommost interconnected parallel sections 110.sub.B in which the liquid flowing through the continuous internal conduit 104.sub.B is coolest, being closest to the liquid inlet 106.sub.B. An equivalent result may be obtained by positioning the liquid inlet 106.sub.A and the liquid outlet 108.sub.B at the bottom of the cooling arrangement 300, also positioning the liquid outlet 108.sub.A and the liquid inlet 106.sub.B at the top of the cooling arrangement 300. Rotating the cooling arrangement 300 so that the interconnected parallel sections 110.sub.A and 110.sub.B extend vertically is also contemplated.

(32) This effect is spread to all strata of the airflow, each of which gradually receive less cooling from the air-to-liquid heat exchanger 100.sub.A along their distribution from the topmost strata toward the bottommost strata, gradually receiving more cooling from the air-to-liquid heat exchanger 100.sub.B along the same distribution.

(33) FIG. 8 is a rear perspective view of a server rack having an autonomous and redundant cooling arrangement including a pair of closed loops and a pair of open loops in accordance with an embodiment of the present technology. FIG. 9 is a partial, front perspective view of the server rack of FIG. 8. FIG. 10 is a side elevation view of the server rack of FIGS. 8 and 9 in accordance with an embodiment of the present technology. FIG. 11 is a highly schematic illustration of a cooling arrangement having a closed loop including a liquid cooling unit and an open loop including air-to-liquid heat exchangers. A server rack 500 has a plurality of server housings 502 (three are shown), each of which includes at least one fan 12 (FIG. 1). Each server housing 502 may host a plurality of components 254, for example servers, network switches, power distribution units and other electric or electronic devices, mounted via the front of the server rack 500 in respective stages 498 of the server housings 502. One or more processors 252 or other heat-generating units, such as graphical processor units, random-access memory devices, hard disk drives, may be mounted on each component 254. A water block 250 or another cooling unit, for example a heat pipe, may be mounted on each heat-generating unit. A cooling arrangement 350 is mounted on the rack 500. The cooling arrangement 350 provides autonomous cooling for the rack 500. In a datacenter, a plurality of cooling arrangements 350 may independently provide cooling for a plurality of corresponding racks 500.

(34) The cooling arrangement 350 as shown comprises two closed loops 510.sub.A and 510.sub.B operatively and fluidly connected to two corresponding open loops 540.sub.A and 540.sub.B. In the non-limiting embodiment of FIGS. 8, 9 and 10, the rack 500 has a generally rectangular perimeter. Most components of the open loops 540.sub.A and 540.sub.B are mounted on a rear side of the rack 500. Most components of the closed loops 510.sub.A and 510.sub.B are mounted in a subframe 504 mounted on a lateral side of the rack perpendicular to the rear side.

(35) The cooling arrangement 350 includes two closed loops 510.sub.A and 510.sub.B and two open loops 540.sub.A and 540.sub.B for redundancy purposes. Each pair comprising one closed loop 510.sub.A or 510.sub.B and one corresponding open loop 540.sub.A or 540.sub.B may provide sufficient cooling capacity to maintain all components 254 hosted in the rack 500 to less than a safe temperature threshold when the other closed loop and the other open loop are taken out of service, so to provide full and complete cooling redundancy for the rack 500. Cooling arrangements including only one closed loop and one open loop, or including two closed loops and only one open loop, or including one closed loop and two open loops, are also contemplated in applications where redundancy is a less important concern.

(36) The two closed loops 510.sub.A and 510.sub.B are substantially identical and the closed loop 510.sub.A will first be described. The closed loop 510.sub.A comprises at least one liquid cooling unit, for example a water block 250, thermally coupled to a heat-generating unit, for example a processor 252 of at least one component 254, for example a server, mounted in the rack 500. Each water block 250 comprises a liquid channel 264 in which a liquid, for example water, may flow. Heat generated by the processor 262 is transferred to the liquid flowing in the liquid channel 264. The closed loop 510.sub.A comprises a primary side 512.sub.A of a liquid-to-liquid heat exchanger 514.sub.A. In an embodiment, the liquid-to-liquid heat exchanger 514.sub.A is a plate heat exchanger. The primary side 512.sub.A is fluidly connected to the liquid channel 264 of the at least water block 250. A pump 516.sub.A is fluidly connected between the at least one water block 250 and the primary side 512.sub.A of the liquid-to-liquid heat exchanger 514.sub.A. The pump 516.sub.A maintains a flow of the liquid circulating within the closed loop 510.sub.A. Positioning the pump 516.sub.A at the level of the subframe 504 for serving one rack 500 allows to easily manage a flow rate of the cooling liquid in the water blocks 250.

(37) In more details, the primary side 512.sub.A of the liquid-to-liquid heat exchanger 514.sub.A comprises a liquid inlet 518.sub.A fluidly connected to the liquid outlet 268 of the water block 250, via the pump 516.sub.A, and a liquid outlet 520.sub.A fluidly connected to the liquid inlet 260 of the water block 250. As shown on FIG. 6, the liquid channel 264 extends between the liquid inlet 260 and the liquid outlet 268 of the water block 250. A valve 522.sub.A is provided within the connection that extends from the liquid outlet 268 of the water block 250 to the pump 516.sub.A. Another valve 524.sub.A is provided within the connection that extends from the liquid outlet 520.sub.A of the primary side 512.sub.A to the liquid inlet 260 of the water block 250. The valves 522.sub.A and 524.sub.A may be closed when it is desired to take the closed loop 510.sub.A out of service, for example for maintenance purposes. The pump 516.sub.A should be turned off when the valves 522.sub.A and 524.sub.A are closed.

(38) The primary side 512.sub.A of the liquid-to-liquid heat exchanger 514.sub.A may be connected to a plurality of water blocks 250 that are each thermally coupled to a corresponding processor 252 or other heat-generating unit. FIG. 12 is a schematic block diagram of a manifold connection between a plurality of water blocks, a pump and a liquid-to-liquid heat exchanger. Within the closed loop 510.sub.A, a manifold 526.sub.A includes a multi-port inlet 528.sub.A having a plurality of ports 530.sub.A connectable to the liquid outlets 268 of a plurality of water blocks 250 and one port 532.sub.A connectable to the valve 522.sub.A for delivering hot liquid from the water blocks 250 to the primary side 512.sub.A of the liquid-to-liquid heat exchanger 514.sub.A via the pump 516.sub.A. The manifold 526.sub.A also includes a multi-port outlet 534.sub.A having a port 536.sub.A for receiving, via the valve 524.sub.A, liquid having been cooled by the liquid-to-liquid heat exchanger 514.sub.A. The multi-port outlet 534.sub.A also includes a plurality of ports 538.sub.A for delivering this liquid to the liquid inlets 260 of the water block 250.

(39) The closed loop 510.sub.B is constructed in the same manner as the closed loop 510.sub.A and includes the same or equivalent components. Within the closed loop 510.sub.B, a respective primary side of a respective liquid-to-liquid heat exchanger 514.sub.B, for example another plate heat exchanger, is fluidly connected to the liquid inlet 258 and to the liquid outlet 270 of each water block 250, a respective pump 516.sub.B ensuring a flow of liquid in the liquid channel 266 of each water block 250. Within the closed loop 510.sub.B, the respective liquid-to-liquid heat exchanger 514.sub.B comprises a liquid inlet and a liquid outlet as described hereinabove. The closed loop 510.sub.B also comprises a respective manifold as present in the closed loop 510.sub.A. Respective valves 522.sub.B and 524.sub.B similar to those present in the closed loop 510.sub.A may be closed when it is desired to take the closed loop 510.sub.B out of service.

(40) The first and second open loops 540.sub.A and 540.sub.B as illustrated respectively comprise first and second dual-flow air-to-liquid heat exchangers 300.sub.A and 300.sub.B. These dual-flow air-to-liquid heat exchangers 300.sub.A and 300.sub.B represent a modest increase in size, particularly an increased thickness, when compared to the single-flow heat exchangers 100 used in the configuration of FIG. 7. They however provide a large increase in cooling efficiency while remaining significantly thinner than the multi-flow air-to-liquid heat exchanger 200 of FIG. 4. Although FIG. 8 shows the dual-flow air-to-liquid heat exchangers 300.sub.A and 300.sub.B, mounting first and second single-flow heat exchangers 100.sub.A and 100.sub.B on the server rack 500, as a part of the cooling arrangement 350, is also contemplated.

(41) The fan or fans 12 contained within each server housing 502 provide forced air cooling to the equipment mounted in the server housings 502 and generate an airflow directed toward the corresponding pair of dual-flow air-to-liquid heat exchangers 300.sub.A and 300.sub.B. Each one of the first and second dual-flow air-to-liquid heat exchangers 300.sub.A and 300.sub.B may be configured for reducing a temperature of the air expelled from the corresponding server housing 502 to less than a maximum rated air temperature to maintain a safe operating temperature of the corresponding server housing 502 on which it is mounted when the other one of the first and second dual-flow air-to-liquid heat exchangers 300.sub.A and 300.sub.B is taken out of service for maintenance or as a result from an equipment failure. Redundancy of the forced air cooling may be obtained by providing at least two fans 12 in each server housing 502, the at least two fans 12 receiving electrical power from two distinct electrical sources.

(42) FIG. 10 also shows that the air-to-liquid heat exchangers 300.sub.A, 300.sub.B may be mounted on the server rack 500 by use of a pair of hinges 506 mounted on a lateral side of the first frame 302.sub.A, the hinges 506 being adapted for pivotally mounting the air-to-liquid heat exchangers 300.sub.A, 300.sub.B on the rack 10. Optionally, additional hinges may be installed between the two hinges 506 as shown. The particular configuration of FIG. 10 shows that the hinges 506 are located on the same side of the air-to-liquid heat exchangers 300.sub.A, 300.sub.B where the liquid inlets 306.sub.A, 306.sub.B and the liquid outlets 308.sub.A, 308.sub.B are also located. This configuration facilitates pivoting of the air-to-liquid heat exchangers 300.sub.A, 300.sub.B about the hinges 506. Mounting the cooling arrangement 300 of FIG. 7 on a rack using the hinges 506 is also contemplated. It may be noted that, in some implementations the fans 12 installed in each server housing may be mounted on a fan plate (not shown) physically connected to the server rack 500 by use of additional hinges (not shown) that may be located on a same side as the hinges 506 or on an opposite side. When the hinges of the fan plate and the hinges 506 are on the same side and share a common pivot axis, the fan plate and the air-to-liquid heat exchangers 300.sub.A, 300.sub.B may be configured to rotate independently or as a single block. Mounting the air-to-liquid heat exchangers 300.sub.A, 300.sub.B on the rack 500 using the hinges 506 allows access to the fans 12 for maintenance purposes. Rotating the fan plate in this manner may be useful in providing access to network connectivity devices, hard disk drives, electrical connections and hydraulic connections within the rack 500.

(43) Also shown on FIG. 10 is a temperature sensor 508 mounted on an external face 326.sub.B of the dual-flow second air-to-liquid heat exchanger 300.sub.B. The temperature sensor 508 may measure and transmit a temperature of air having flowed through the first and second dual-flow air-to-liquid heat exchangers 300.sub.A, 300.sub.B to a remote monitoring device (not shown). The server rack 500 may comprise a plurality of additional sensors (not shown) for providing various temperature, liquid flow, and pressure measurements to the remote monitoring device, the temperature sensor 508 and these additional sensors sharing a common communication link (not shown) for forwarding their measurements to the remote monitoring device. A position of the temperature sensor 508 on the external face 326.sub.B of the second dual-flow air-to-liquid heat exchanger 300.sub.B may vary horizontally and/or vertically, given that the temperature of the air having flowed through the first and second dual-flow air-to-liquid heat exchangers 300.sub.A, 300.sub.B substantially homogeneous, as will be illustrated on FIG. 14. Mounting the temperature sensor 508 on an external face of the second air-to-liquid heat exchanger 100.sub.B of the cooling arrangement 300 is also contemplated.

(44) On FIGS. 8 and 10, a liquid inlet 306.sub.A and a liquid outlet 308.sub.A are connected on a same side of a frame 302.sub.A, and a liquid inlet 306.sub.B and a liquid outlet 308.sub.B are connected on a same side of the frame 302.sub.B. Additionally, the liquid inlets 306.sub.A and 306.sub.B are located on a same side of the cooling arrangement 350. An alternate configuration in which the liquid inlets 306.sub.A and 306.sub.B are located on opposite sides of the cooling arrangement 350 is also contemplated.

(45) As best seen on FIG. 10, in a particular non-limiting configuration, the first dual-flow air-to-liquid heat exchanger 300.sub.A comprises a first continuous internal conduit 304.sub.A forming a first plurality of interconnected parallel sections (not shown) and a third continuous internal conduit 314.sub.A forming a third plurality of interconnected parallel sections (not shown). The first and third pluralities of interconnected parallel sections extend within the first frame 302.sub.A. The first and third continuous internal conduits 304.sub.A and 314.sub.A connect the first liquid inlet 306.sub.A to the first liquid outlet 308.sub.A. Likewise, the second dual-flow air-to-liquid heat exchanger 300.sub.B comprises a second continuous internal conduit 304.sub.B forming a second plurality of interconnected parallel sections (not shown) and a fourth continuous internal conduit 314.sub.B forming a fourth plurality of interconnected parallel sections (not shown), the second and fourth pluralities of interconnected parallel sections extending within the second frame 302.sub.B. The second and fourth continuous internal conduits 304.sub.B and 314.sub.B connect the second liquid inlet 306.sub.B to the second liquid outlet 308.sub.B.

(46) As illustrated, a first portion of the first plurality of interconnected parallel sections is located in a first plane 316.sub.A within the first frame 302.sub.A and a second portion of the first plurality of interconnected parallel sections is located in a second plane 318.sub.A within the first frame 302.sub.A, the second plane 318.sub.A being parallel to the first plane 316.sub.A. Conversely, a first portion of the third plurality of interconnected parallel sections is located in the second plane 318.sub.A within the first frame 302.sub.A and a second portion of the third plurality of interconnected parallel sections is located in the first plane 316.sub.A within the first frame 302.sub.A. The third continuous internal conduit 314.sub.A and the first continuous internal conduit 304.sub.A, both change between the first plane 316.sub.A and the second plane 318.sub.A at a crossing point 324.sub.A. Variants of the first dual-flow air-to-liquid heat exchanger 300.sub.A may include one or more crossing points 324.sub.A and may alternatively have no such crossing point.

(47) Likewise, a first portion of the second plurality of interconnected parallel sections is located in a third plane 316.sub.B within the second frame 302.sub.B and a second portion of the second plurality of interconnected parallel sections is located in a fourth plane 318.sub.B within the second frame 302.sub.B, the fourth plane 318.sub.B being parallel to the third plane 316.sub.B. Conversely, a first portion of the fourth plurality of interconnected parallel sections is located in the fourth plane 318.sub.B within the second frame 302.sub.B and a second portion of the fourth plurality of interconnected parallel sections is located in the third plane 316.sub.B within the second frame 302.sub.B. The fourth continuous internal conduit 314.sub.B and the second continuous internal conduit 304.sub.B, both change between the third plane 316.sub.B and the fourth plane 318.sub.B at a crossing point 324.sub.B. Variants of the second dual-flow air-to-liquid heat exchanger 300.sub.B may include one or more crossing points 324.sub.B and may alternatively have no such crossing point. The first and second dual-flow air-to-liquid heat exchangers 300.sub.A, 300.sub.B of the cooling arrangement 350 may have different numbers of crossing points 324.sub.A or 324.sub.B.

(48) In the open loop 540.sub.A, the air-to-liquid heat exchanger 300.sub.A is fed via a cold supply line 320.sub.A with cold liquid from an external source to reduce a temperature of the air expelled from the rack 500 by the fans 12. The air-to-liquid heat exchanger 300.sub.B in the open loop 540.sub.B is either fed by the cold supply line 320.sub.A or by another cold supply line (not shown). A temperature of the liquid flowing out of the liquid outlets 308.sub.A and 308.sub.B is modestly increased by the transfer of heat from the air expelled from the server rack 500; for explanation purposes, the liquid flowing out of the open loops 540.sub.A and 540.sub.B may be characterized as a ‘warm’ liquid. In contrast, the liquid flowing out of the water blocks 250 has a considerably higher temperature. As a result, the warm liquid at the output of the open loops 540.sub.A and 540.sub.B is used to provide cooling to the closed loops 510.sub.A and 510.sub.B. To this end, the closed loops 510.sub.A and 510.sub.B are respectively thermally connected to the open loops 540.sub.A and 540.sub.B.

(49) As best seen on FIG. 10, the liquid inlet 306.sub.A of each air-to-liquid heat exchanger 300.sub.A is connected to the first cold supply line 320.sub.A and the liquid outlet 308.sub.A of the air-to-liquid heat exchanger 300.sub.A is connected to a first warm liquid line 322.sub.A. Although not shown, the liquid inlet 306.sub.B of air-to-liquid heat exchanger 300.sub.B may be connected to the first cold supply line 320.sub.A or to another cold supply line (not shown). The liquid outlet 308.sub.B of air-to-liquid heat exchanger 300.sub.B is connected to a second warm liquid line (not shown) similar to the first warm liquid line 322.sub.A. As shown on FIG. 11, the first and second warm liquid lines respectively deliver the warm liquid from the liquid outlets 308.sub.A and 308.sub.B to secondary sides of the liquid-to-liquid heat exchangers 514.sub.A and 514.sub.B. The first warm liquid line 322.sub.A is fluidly connected via a valve 570.sub.A to a liquid inlet 542.sub.A of a secondary side 544.sub.A of the liquid-to-liquid heat exchanger 514.sub.A.

(50) The primary side 512.sub.A and the secondary side 544.sub.A of the liquid-to-liquid heat exchanger 514.sub.A are thermally coupled for transfer of heat from the primary side 512.sub.A to the secondary side 544.sub.A when a temperature of the first primary side 512.sub.A is higher than a temperature of the secondary side 544.sub.A. In operation, the primary side 512.sub.A receives the hot liquid from one or more water blocks 250 and its temperature is significantly higher than that of the warm liquid received in the secondary side 544.sub.A. Therefore, the liquid-to-liquid heat exchanger 514.sub.A transfers heat from its primary side 512.sub.A to the secondary side 544.sub.A. The warm liquid received at the liquid inlet 542.sub.A of the secondary side 544.sub.A is heated before being expelled from the secondary side 544.sub.A via a liquid outlet 546.sub.A. The heated liquid flows from the liquid outlet 546.sub.A via a valve 572.sub.A and leaves the open loop 540.sub.A via a hot return line 550.sub.A. The open loop 540.sub.A may be taken out of service by closing the valves 570.sub.A and 572.sub.A. The open loop 540.sub.B is constructed in the same manner; it can also be taken out of service by closing valves 570.sub.B and 572.sub.B. It may be noted that the air-to-liquid heat exchangers 300.sub.A may be substituted with the air-to-liquid heat exchangers 100.sub.A; the same is true for the air-to-liquid heat exchangers 300.sub.B that may be substituted with the air-to-liquid heat exchangers 100.sub.B. For example and without limitation, in the open loop 540.sub.A, water may be received on the cold supply line 320.sub.A at 30 degrees. The water is heated by the dual-flow air-liquid heat exchangers 300.sub.A to a temperature of 34.5 degrees in the first warm liquid line 322.sub.A. In the same example, water is supplied by the primary side 512.sub.A of the liquid-to-liquid heat exchanger 514.sub.A to the water blocks 250 at 40 degrees, the water reaching a temperature of 50 degrees when returning to the primary side 512.sub.A. Thermal exchange from the primary side 512.sub.A to the secondary side 544.sub.A of the liquid-to-liquid heat exchanger 514.sub.A causes the water in the open loop 540.sub.A to reach a temperature of 45 degrees in the hot return line 550.sub.A while causing the water in the closed loop 510.sub.A to reach the above-mentioned temperature of 40 degrees at the liquid inlet 518.sub.A of the primary side 512.sub.A. It may be noted that, in cold climates, the high temperature of the liquid flowing in the hot return line 550.sub.A could be considered for heat recovery purposes.

(51) Although not shown on FIG. 11, two distinct pumps may be mounted in series for redundancy and/or for increasing the flow of the liquid circulating within the closed loop 510.sub.A. Likewise, two liquid-to-liquid heat exchangers may be mounted so that their primary sides are connected in series or in parallel within the closed loop 510.sub.A and so that their secondary sides are connected in series or in parallel within the open loop 540.sub.A. The use of two liquid-to-liquid heat exchangers allows extracting more thermal energy from the water blocks 250 within the closed loop 510.sub.A.

(52) Also not shown on FIG. 11, the closed loop 510.sub.B and the open loop 540.sub.B are connected in a similar manner as expressed in the discussion of the closed loop 510.sub.A and the open loop 540.sub.A. The heated liquid flowing from the liquid outlet of the secondary side of the liquid-to-liquid heat exchanger 514.sub.B, at the junction of the closed loop 510.sub.B and the open loop 540.sub.B, may leave the cooling arrangement via the hot return line 550.sub.A or via another hot return line. It may be noted that although the above description of FIGS. 8-11 indicates that the open loop 510.sub.A is only connected to the closed loop 510.sub.A and that the open loop 540.sub.B is only connected to the closed loop 510.sub.B, other configurations are also contemplated. For example and without limitation, the liquid outlets 308.sub.A and 308.sub.B of the air-to-liquid heat exchangers 300.sub.A and 300.sub.B could all be connected to common same warm liquid line 322.sub.A feeding both secondary sides of the liquid-to-liquid heat exchangers 514.sub.A and 514.sub.B. Configurations having distinct numbers of open loops and distinct numbers of closed loops are also contemplated; in an embodiment, the number of open loops may differ from the number of closed loops.

(53) In the non-limiting configuration of FIGS. 8, 9 and 10, the liquid-to-liquid heat exchangers, the pumps and the valves included in the closed loops, the valves in fluidic connection between the air-to-liquid heat exchangers and the liquid-to-liquid heat exchangers are all located within the subframe 504. FIG. 13 is another side elevation view of the server rack of FIGS. 8 and 9 showing a removal of a module in accordance with an embodiment of the present technology. The components contained in the subframe 504 may be grouped in two modules 552.sub.A and 552.sub.B. The module 552.sub.A contains the liquid-to-liquid heat exchanger 514.sub.A, the pump 516.sub.A, the valves 522.sub.A, 524.sub.A, 570.sub.A and 572.sub.A, and tubing connection these various components. The module 552.sub.B contains the liquid-to-liquid heat exchanger 514.sub.B, the pump 516.sub.B, the valves 522.sub.B, 524.sub.B, 570.sub.B and 572.sub.B, and tubing connection these various components. When all valves contained in one of the modules 552.sub.A or 552.sub.B are closed, and as the corresponding pump 516.sub.A or 516.sub.B is turned off, that module 552.sub.A or 552.sub.B may be removed from the subframe 504 for maintenance purposes, as shown on FIG. 13. It may be noted that, in some embodiments, the valves 522.sub.A, 524.sub.A, 570.sub.A and 572.sub.A (resp. 522.sub.B, 524.sub.B, 570.sub.B and 572.sub.B) are fixed parts of the tubing connections beyond the module 552.sub.A (resp. 552.sub.B), and in this case, the module 552.sub.A (resp. 552.sub.B) should be drained from its liquid before it may be removed from the subframe 504.

(54) Various embodiments may comprise the inclusion of additional redundant components for enhanced cooling reliability. For example, in a non-limiting embodiment, the liquid-to-liquid heat exchanger 514.sub.A (resp. 514.sub.B) of the module 552.sub.A (resp. 552.sub.B) may be replaced by two liquid-to-liquid heat exchangers 514.sub.A (resp. 514.sub.B) fluidly connected either in series or in parallel configurations. In the same or another embodiment the pump 516.sub.A (resp. 516.sub.B) of the module 552.sub.A (resp. 552.sub.B) may be replaced by a pair of two pumps 516.sub.A (resp. 516.sub.B) fluidly connected in series. The pumps of the pair may be electrically connected to distinct and independent electrical sources for redundancy purposes. One pump of the pair may run while the other is off. In the same or another embodiment, each valve 522.sub.A, 524.sub.A, 570.sub.A and 572.sub.A (resp. 522.sub.B, 524.sub.B, 570.sub.B and 572.sub.B) may be replaced by a pair of valves fluidly connected in series for security purposes, a first valve of each pair belonging to the module 552.sub.A (resp. 552.sub.B), a second valve of the pair staying attached to the piping beyond the first valve. In the same or another embodiment, the modules 552.sub.A and 552.sub.B may be connected to the same closed loop 510.sub.A and to the same open loop 540.sub.A by means of T-piping elements located outside the modules 552.sub.A and 552.sub.B. In such an embodiment, the two modules 552.sub.A and 552.sub.B may be fluidly connected in parallel regarding the closed loop 510.sub.A and the open loop 540.sub.A. Finally, in the same or another embodiment, a same liquid may be used in the closed loops 510.sub.A and 510.sub.B and in the open loops 540.sub.A and 540.sub.B, for example water. In such an embodiment, the closed loop 510.sub.A (resp. 510.sub.B) may initially be filled in liquid using a pressure regulator (not shown) installed in the module 552.sub.A (resp. 552.sub.B) and connected between the closed loop 510.sub.A (resp. 510.sub.B) and the open loop 540.sub.A (resp. 540.sub.B). The open loops 540.sub.A and 540.sub.B may thus become a liquid source for the closed loops 510.sub.A and 510.sub.B when needed. In a similar way, a pressure relief valve (not shown) may be installed in the module 552.sub.A (resp. 552.sub.B) and connected between the closed loop 510.sub.A (resp. 510.sub.B) and the open loop 540.sub.A (resp. 540.sub.B). In case of an excessive pressure in the closed loop 510.sub.A (resp. 510.sub.B), the liquid may be expelled into the open loop 540.sub.A (resp. 540.sub.B). It may be noted that other piping elements may be present in the modules 552.sub.A and 552.sub.B. Though not shown in the different Figures, filters may be disposed in various piping, check valves may be placed after the pumps 516.sub.A and 516.sub.B, and expansion tanks may be used to attenuate variations of pressure in the closed loops 510.sub.A and 510.sub.B.

(55) One or two external pumps of one or two pumping substations (not shown) provide a continuous flow of cold liquid delivered to the cooling arrangement 350 via the cold supply line or lines 320.sub.A and 320.sub.B, and retrieve heated liquid from the cooling arrangement 350 via the hot return line or lines. The external pumps ensure a continuous flow of the liquid between the cooling arrangement 350 and a cold outlet and a hot inlet of further cooling equipment, for example a dry cooler (not shown), located outside of the data center.

(56) FIG. 14 is a visual representation of a homogeneous temperature pattern of an airflow expelled from dual-flow air-liquid heat exchangers assembled in an anti-parallel configuration in accordance with an embodiment of the present technology. A diagram 400 illustrates a temperature of a flow of air determined in a simulation environment, before and after passing through the cooling arrangement 350. The air flows in the direction of arrows 402 and 404. In a first zone 406 upstream of the cooling arrangement 350, a temperature of the airflow is high due to the generation of heat in the server rack 10, being for example at about 40 degrees. The temperature of the airflow is substantially uniform within the first zone 406. Cold water is received at the top of the first dual-flow air-liquid heat exchanger 300.sub.A, at a temperature of about 25 degrees. Upper strata 410 of the air flowing downstream of the first dual-flow air-liquid heat exchanger 300.sub.A are cooled to about 30 degrees. A temperature of the water flowing through the first dual-flow air-liquid heat exchanger 300.sub.A increases as it passes through the various interconnected parallel sections 110.sub.A, being continuously exposed to the 40 degrees airflow. The water reaches about 33 degrees the bottom of the first dual-flow air-liquid heat exchanger 300.sub.A. Consequently, the airflow between the first and second dual-flow air-liquid heat exchangers 300.sub.A, 300.sub.B has a stratified, heterogeneous temperature profile in which lower strata 412 of the air flowing downstream of the first dual-flow air-liquid heat exchanger 300.sub.A are only cooled to about 37 degrees.

(57) The same airflow immediately reaches the second dual-flow air-liquid heat exchanger 300.sub.B. Cold water is received at the bottom of the second dual-flow air-liquid heat exchanger 300.sub.B, also at a temperature of about 25 degrees. Lower strata 412 of the airflow, which have been cooled to a limited extent to about 37 degrees when flowing through the dual-flow first air-liquid heat exchanger 300.sub.A, receive maximum cooling from the dual-flow second air-liquid heat exchanger 300.sub.B and reach a temperature of about 30 degrees. Upper strata 410 of the airflow, which have been cooled to a larger extent to about 30 degrees when flowing through the first dual-flow air-liquid heat exchanger 300.sub.A, receive a modest level of cooling from the second dual-flow air-liquid heat exchanger 300.sub.B to also reach a temperature of about 29 degrees. As a result, the same airflow having passed through the second dual-flow air-liquid heat exchanger 300.sub.B has a substantially homogeneous temperature profile and all strata of the airflow expelled from the cooling arrangement 350 in a zone 408 are at a substantially uniform temperature of about 30 degrees. The water also reaches about 29 degrees the top of the second dual-flow air-liquid heat exchanger 300.sub.B.

(58) Referring again to FIG. 3, the diagram 150 illustrates results obtained when using the single-flow heat exchanger 100. In contrast, the diagram 400 illustrates results obtained when using a pair of dual-flow heat exchangers 300.sub.A, 300.sub.B. These results are not directly comparable due to the respective cooling capacities of these different heat exchangers. However, while the numerical absolute temperature values shown on FIGS. 3 and 14 cannot be directly compared, the difference in the airflow temperature patterns is striking: while FIG. 3 shows an important stratification of the temperature pattern, FIG. 14 shows uniformity and homogeneity of the temperature in all strata of the airflow expelled from the cooling arrangement 350. It may be noted that using a pair of single-flow heat exchangers mounted in anti-parallel fashion would arguably produce a lesser decrease of the airflow temperature, but would nevertheless provide homogeneity of the temperature in all strata of the resulting airflow. In contrast, using a single dual-flow heat exchanger would still result in a stratified, heterogeneous temperature profile of the resulting airflow.

(59) In summary, the cooling configuration illustrated on the various view of FIGS. 8 to 12 fluidly connects in series the air-to-liquid heat exchangers 100.sub.A and 100.sub.B, or 300.sub.A and 300.sub.B, of the rack 500 to the secondary sides of the liquid-to-liquid heat exchangers 514.sub.A and 514.sub.B mounted to the same rack 500. This configuration may be compared to a more traditional cooling arrangement in which the cooling needs of a plurality of racks are served by larger components, including a dedicated pumping sub-station for air-to-liquid heat exchangers, further outside cooling equipment (e.g. dry coolers), further including dedicated pumping sub-stations for liquid cooling within the racks, and large liquid-to-liquid heat exchangers.

(60) Experimentations were made using the present cooling configuration, in which water was used as a cooling liquid. These experimentations have shown a 50% reduction of a number of piping lines within a data center. As illustrated in the example of FIG. 11, a temperature difference between the cold supply line 320.sub.A and the hot return line 550.sub.A was equal to about 15 degrees, which compares to a typical difference of about 5 degrees obtained using a conventional configuration and is indicative of a far better heat transfer performance. Given this increase of the temperature gradient between the cold supply line 320.sub.A and the hot return line 550.sub.A, the flow of water required to cool the rack 500 was reduced so the nominal diameter of the cold supply line 320.sub.A and of the hot return line 550.sub.A was reduced from 4 inches to 2.5 inches. The thermal efficiency of dry coolers used as external cooling units receiving the return water from the hot return line 550.sub.A and returning cold water via the cold supply line 320.sub.A was increased by more than 33% and it was possible to operate such dry coolers without adding any evaporative cooling A total number of pumping stations was reduced by 25%. Capital expenses required to provide the same cooling capacity as when using a conventional configuration were reduced by 25%, despite the fact that traditional polyvinyl chloride (PVC) piping was replaced with stainless steel and copper piping for enhanced reliability. Operating expenses in terms of electrical power required to drive various pumps and fans was reduced by more than 50%.

(61) The present technology is amenable to implementations in data centers and other computing facilities in which various racks having distinct ratios of air-cooling and liquid-cooling capabilities. In many implementations, impacts of eventual cooling equipment failures are constrained to a single rack and are limited by the redundancy of many components.

(62) While the above-described implementations have been described and shown with reference to particular steps performed in a particular order, it will be understood that these steps may be combined, sub-divided, or re-ordered without departing from the teachings of the present technology. At least some of the steps may be executed in parallel or in series. Accordingly, the order and grouping of the steps is not a limitation of the present technology.

(63) It should be expressly understood that not all technical effects mentioned herein need to be enjoyed in each and every embodiment of the present technology.

(64) Modifications and improvements to the above-described implementations of the present technology may become apparent to those skilled in the art. The foregoing description is intended to be exemplary rather than limiting. The scope of the present technology is therefore intended to be limited solely by the scope of the appended claims.