Refrigerant pumped active / passive cooling system

Abstract

A cooling system including an evaporator, a passive condenser, a heat exchanger, and a pump. The passive condenser is arranged in parallel with the heat exchanger with respect to the fluid flow of a primary cooling medium. When a secondary cooling medium is supplied to the heat exchanger, the heat exchanger receives at least a portion of the primary cooling medium in gas phase that was received by the passive condenser without the operation of any valve, and the heat exchanger supplies the primary cooling medium in liquid phase to the evaporator. On the other hand, when the secondary cooling medium is not supplied to the heat exchanger, the heat exchanger does not supply the primary cooling medium in liquid phase to the evaporator. The pump is arranged in a liquid line fluidly connecting the evaporator to the passive condenser and the heat exchanger, and is configured to pump the primary cooling medium in liquid phase to the evaporator.

Description

[Technical field]

[0001] The present invention relates to a cooling system, and to a system and method for controlling a cooling system, and in particular to a cooling system having both active and passive modes, particularly suitable for use in, for example, data center cooling systems. [Background technology]

[0002] Data centers often require large amounts of energy to operate: their servers generate large amounts of heat, which must be cooled. Summary of the Invention [Problem to be solved by the invention]

[0003] Therefore, more efficient cooling systems are desired to reduce energy usage in data centers. [Means for solving the problem]

[0004] In one aspect, the present invention relates to a cooling system including an evaporator, a passive condenser, a heat exchanger, a liquid line, and a pump. The evaporator contains a primary cooling medium and is configured to receive a process fluid. The evaporator is configured to extract heat from the process fluid upon receipt of the process fluid to cool the process fluid and cause the primary cooling medium to change phase from a liquid phase to a gas phase. The passive condenser includes an exterior surface and is fluidly coupled to the evaporator and configured to direct an airflow through the exterior surface. The passive condenser is configured to (i) receive the primary cooling medium in the gas phase from the evaporator, (ii) transfer heat from the primary cooling medium, (iii) cause the primary cooling medium to change phase from a gas phase to a liquid phase, and (iv) supply the primary cooling medium in the liquid phase to the evaporator upon directing the airflow through the exterior surface of the passive condenser. The heat exchanger is fluidly coupled to the evaporator and configured to selectively supply a secondary cooling medium. When the secondary cooling medium is supplied to the heat exchanger, the heat exchanger receives at least a portion of the gas phase primary cooling medium received by the passive condenser without the need to arrange and operate any valve between the evaporator and the passive condenser and between the evaporator and the heat exchanger, and the heat exchanger is configured to (i) receive the gas phase primary cooling medium from the evaporator, (ii) transfer heat from the primary cooling medium, (iii) change the phase of the primary cooling medium from the gas phase to a liquid phase, and (iv) supply the liquid phase primary cooling medium to the evaporator. On the other hand, when the secondary cooling medium is not supplied to the heat exchanger, the heat exchanger does not supply the liquid phase primary cooling medium to the evaporator. The liquid line fluidly connects the evaporator to each of the passive condenser and the heat exchanger to supply the liquid phase primary cooling medium from at least one of the passive condenser and the heat exchanger to the evaporator. The pump is arranged in the liquid line and configured to pump the liquid phase primary cooling medium to the evaporator. The passive condenser is positioned in parallel with the heat exchanger relative to the fluid flow of the primary cooling medium.

[0005] In another aspect, the present invention relates to a cooling system including an evaporator, a plurality of passive condensers, at least one heat exchanger, a liquid line, and a pump. The evaporator contains a primary cooling medium and is configured to receive a process fluid. The evaporator is configured to extract heat from the process fluid upon receipt of the process fluid to cool the process fluid and cause the primary cooling medium to change phase from a liquid phase to a gas phase. Each passive condenser includes an exterior surface and is fluidly coupled to the evaporator and configured to direct an airflow through the exterior surface. Each passive condenser is configured to (i) receive the primary cooling medium in a gas phase from the evaporator, (ii) transfer heat from the primary cooling medium, (iii) cause the primary cooling medium to change phase from a gas phase to a liquid phase, and (iv) supply the primary cooling medium in a liquid phase to the evaporator upon directing the airflow through the exterior surface of the passive condenser. The at least one heat exchanger is fluidly coupled to the evaporator and configured to selectively supply a secondary cooling medium. When the secondary cooling medium is supplied to the at least one heat exchanger, the at least one heat exchanger receives at least a portion of the primary cooling medium in the gas phase that the passive condenser received, without the need to place and operate any valves between the evaporator and the passive condenser and between the evaporator and the heat exchanger, so that the at least one heat exchanger (i) receives the primary cooling medium in the gas phase from the evaporator, (ii) transfers heat from the primary cooling medium, (iii) changes the phase of the primary cooling medium from the gas phase to a liquid phase, and (iv) supplies the primary cooling medium in the liquid phase to the evaporator. On the other hand, when the secondary cooling medium is not supplied to the at least one heat exchanger, the heat exchanger does not supply the primary cooling medium in the liquid phase to the evaporator. The liquid line fluidly connects the evaporator to each passive condenser of the multiple passive condensers and the at least one heat exchanger to supply the primary cooling medium in the liquid phase from at least one of the multiple passive condensers and the at least one heat exchanger to the evaporator. A pump is disposed in the liquid line and configured to pump the primary cooling medium in a liquid phase to the evaporator. At least one passive condenser of the plurality of passive condensers is disposed in parallel with the at least one heat exchanger relative to the fluid flow of the primary cooling medium.

[0006] These and other aspects of the invention will become apparent from the following disclosure. [Brief description of the drawings]

[0007] [Figure 1] FIG. 1 is an elevation view of a data center using a cooling system according to a preferred embodiment of the present invention; [Diagram 2] FIG. 1 is a schematic diagram illustrating a cooling system according to a preferred embodiment of the present invention operating in passive mode; [Diagram 3] Schematic diagram showing how the cooling system shown in Figure 2 operates in active mode. [Figure 4] FIG. 1 is a schematic diagram illustrating an air handler unit of a cooling system according to a preferred embodiment of the present invention. [Diagram 5] FIG. 5 is a schematic diagram showing a condensing unit used with the air handler unit shown in FIG. [Figure 6] FIG. 1 is an elevational view of a cooling system according to a preferred embodiment of the present invention; [Figure 7A] Diagram showing an example of a server rack cooled by a single-phase immersion cooling system used in combination with the cooling system shown in Figure 1. [Figure 7B] Diagram showing an example of a server rack cooled by a two-phase immersion cooling system used in combination with the cooling system shown in Figure 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] FIG. 1 illustrates a data center 100 having at least one cooling system 200 according to a preferred embodiment of the present invention. Although the cooling system 200 is illustrated and described in connection with the data center 100, the cooling system 200 is not limited to this application and may be used in other suitable cooling applications, such as cooling a stream of air heated by other heat sources. The racks 112 may carry electronic components, such as servers. The racks 112 may be arranged in rows to form aisles between the rows of racks. In this arrangement, one aisle is designated as a cold aisle and the other aisle is designated as a hot aisle. Cooled supply air 122 from the cooling system is directed into the cold aisle. The supply air 122 in the cold aisle then passes through the racks and into the hot aisle. As the air passes through the racks 112, it removes heat from the electronic components and cools them. This causes the air to become hot air, which then enters the hot aisle. This warm air is then returned to the cooling system 200 as warm return air 124. The supply air fan 126 (see FIG. 4) is used to draw the return air 124 from the data center 100 and pass it through the cooling system 200 (where the return air 124 is cooled), thereby returning the cooled return air 124 to the data center 100 as supply air 122.

[0009] The cooling system 200 can be divided into two parts, an indoor air handler 202 and an outdoor condensing unit 204. In this specification, the part of the cooling system 200 through which the return air 124 flows and which cools the return air 124 and returns it as the supply air 122 is referred to as the indoor air handler 202. The data center 100 shown in FIG. 1 is a multi-story data center 100 having multiple floors. In this embodiment, the data center 100 has three floors, a first floor 102, a second floor 104, and a third floor 106. The second floor 104 is higher than the first floor 102, and the third floor 106 is higher than both the first floor 102 and the second floor 104. In this embodiment, the first floor 102 is the first floor. Each of the first floor 102, the second floor 104, and the third floor 106 in this embodiment is provided with multiple racks 112 that accommodate electronic components. At least one indoor air handler 202 is located on each floor 102, 104, 106 to provide cooling for the electronic components located on the racks 112 on the corresponding floor.

[0010] The cooling system 200 of this embodiment has two modes, a passive mode and an active mode. The passive mode can also be called a saving mode. FIG. 2 is a schematic diagram showing the cooling system 200 in the passive mode, and FIG. 3 is a schematic diagram showing the cooling system 200 in the active mode. The cooling system 200 incorporates a capability of using a free cooling sink utilizing outside air (passive mode or saving mode) and a capability of performing active cooling when the free cooling sink utilizing outside air is not able to reduce the temperature enough to sufficiently remove the heat (active mode). This is achieved by providing two separate condensers 210 and 220 that operate in parallel. In this specification, one of the condensers is called a passive condenser 210 and is used in the passive mode (saving mode). The other condenser is called an active condenser 220 and is used in the active mode.

[0011] The cooling system 200 is used to cool a process fluid containing heat extracted from electronic components (e.g., servers) in a rack. The primary coolant loop 240 includes an evaporator 230 thermally coupled to the process fluid. In this embodiment, the process fluid is air, more specifically, the return air 124, and the evaporator 230 is a coil, preferably a single-pass flooded coil. However, any suitable coil may be used, such as a finned tube coil or a microchannel coil, as described, for example, in U.S. Patent Application Publication Nos. 2018 / 0038660 and 2021 / 0368647, the entire disclosures of which are incorporated herein by reference. In both passive and active modes, the return air 124 is directed over the outer surface of the evaporator 230 by the supply air fan 126. The evaporator 230 contains a primary cooling medium. The primary cooling medium may be any suitable refrigerant that changes phase from liquid to gaseous. Such a refrigerant may be, for example, R-134a, or may be a natural refrigerant such as water. In this specification, the primary cooling medium may be referred to as a refrigerant. When the warm return air 124 passes over the outer surface of the evaporator 230, the primary cooling medium in the evaporator 230 is vaporized. The phase change of the primary cooling medium from a liquid phase to a gas phase (vapor phase) cools the return air 124, and the return air 124 can be returned to the data center 100 as the cool supply air 122.

[0012] However, as described above and in more detail below, the process fluid may be any other suitable fluid. Examples of such suitable fluids include liquids such as water, water-glycol mixtures, and non-conductive fluids (dielectrics). In these embodiments, the evaporator 230 may also be any other suitable heat exchanger. Examples of such suitable heat exchangers include a plate heat exchanger, a coaxial heat exchanger, and a shell-and-tube heat exchanger.

[0013] The primary coolant circulates through a primary coolant loop 240 that includes an evaporator 230. The primary coolant loop 240 includes pipes, piping, conduits, etc., that fluidly connect the various components of the primary coolant loop 240, some of which are shown in Figures 4 and 5. Once the primary coolant is warmed in the evaporator 230 and in its vapor phase, it flows through a vapor line 250 to one of the two condensers 210, 220.

[0014] In the passive mode shown in FIG. 2, the vapor proceeds to a passive condenser 210. Like the evaporator 230, the passive condenser 210 in this embodiment is also a coil, preferably a single-pass coil, although any suitable coil can be used. Suitable coils can include, for example, tube coils (either finned or unfinned) or microchannel coils, such as those described in U.S. Patent Application Publication No. 2018 / 0038660. Scavenger air 206 flows over the exterior surface of the passive condenser 210 due to the suction of a scavenger fan 208 (see FIG. 1). In this embodiment, the scavenger air 206 is fresh air drawn from the outdoor environment surrounding the cooling system 200 (more specifically, the condensing unit 204). As the scavenger air 206 passes over the passive condenser 210, heat from the primary cooling medium contained in the passive condenser 210 is released to the scavenger air 206, causing the primary cooling medium to condense. This causes the primary cooling medium to change phase from gas to liquid. The primary cooling medium is then supplied to the evaporator 230 through the liquid refrigerant line 260. The scavenger air 206 is exhausted to the outside by the scavenger fan 208.

[0015] In the event that the outside air conditions are not sufficient to cool the return air 124 to the desired condition (e.g., the desired temperature) as the supply air 122, the cooling system 200 may operate in an active mode as shown in FIG. 3. In the active mode, the primary cooling medium in the vapor phase flows through the vapor line 250 to the active condenser 220 where it is condensed. The active condenser 220 is configured to selectively receive a secondary cooling medium. The active condenser 220 transfers heat from the primary cooling medium to the secondary cooling medium of the secondary cooling system 270. The secondary cooling medium may be any suitable refrigerant medium. Such suitable refrigerant medium may include, for example, chilled water or a vapor phase change refrigerant used in a direct expansion cooling system. In some embodiments, a water-glycol mixture may be used rather than water alone, i.e., a chilled water-glycol mixture may be used as the secondary cooling medium. The active condenser 220 may also be any suitable heat exchanger. Suitable heat exchangers include, for example, a plate heat exchanger, a coaxial heat exchanger, and a shell-and-tube heat exchanger. Thus, the active condenser 220 may be referred to herein as a heat exchanger (HX). When the heat of the primary cooling medium is released to (absorbed by) the secondary cooling medium, the primary cooling medium condenses from vapor to liquid. Thereafter, as in the case of the passive condenser 210, the primary cooling medium is supplied to the evaporator 230 through the liquid refrigerant line 260.

[0016] In this embodiment, the secondary refrigeration system 270 is a direct expansion (DX) refrigeration system utilizing a conventional refrigeration cycle, and the secondary refrigeration medium is any suitable refrigerant used in such systems. The secondary refrigeration system 270 includes a compressor 272 where the secondary refrigeration medium is increased in pressure and temperature before being cooled in a condenser 274. In this embodiment, the condenser 274 of the secondary refrigeration system 270 may also be cooled by the scavenger air 206 and may also be any suitable condenser, such as those described above with respect to the passive condenser 210. The secondary refrigeration medium then passes through an expansion valve 276 where the pressure and temperature are reduced before entering the active condenser 220.

[0017] The cooling system 200 preferably operates without using a valve for mode switching. In this embodiment, the passive condenser 210 and the active condenser 220 are arranged in parallel with each other with respect to the flow of the primary cooling medium. Then, the steam pipe 250 is branched so that the primary cooling medium in the gas phase leaving the evaporator 230 flows to one of the passive condenser 210 and the active condenser 220. The primary cooling medium in the gas phase naturally proceeds to the lower temperature of the two condensers 210, 220 and is condensed there. In the passive mode, the primary cooling medium in the gas phase proceeds to the passive condenser 210, and in the active mode, most of the primary cooling medium in the gas phase proceeds to the active condenser 220. Therefore, by operating the secondary cooling system 270 to cool the active condenser 220, the cooling system 200 automatically switches from the passive mode to the active mode, and when the operation of the secondary cooling system 270 is stopped, the cooling system 200 switches back to the passive mode. When the outside air temperature is not low enough to remove heat sufficiently, the secondary cooling system 270 is operated. Then, even if a valve is not arranged between the evaporator and the passive condenser or between the evaporator and the heat exchanger and is not operated, the active condenser 220 receives at least a part of the gas phase primary cooling medium that the passive condenser 210 received. In the passive mode, the secondary cooling system 270 is not operated, and the secondary cooling medium is not supplied to the active condenser 220. In addition, in the passive mode, the active condenser 220 does not supply the liquid phase primary cooling medium to the evaporator 230. On the other hand, in the active mode, a part of the primary cooling medium may be condensed in the passive condenser 210 as well.

[0018] As described above, the liquid phase primary cooling medium condensed by either the passive condenser 210 or the active condenser 220 is supplied to the evaporator 230 through the liquid refrigerant line 260. Both the passive condenser 210 and the active condenser 220 are fluidly coupled to a common liquid refrigerant line 260 (sometimes referred to as a liquid line). A pump 280 is disposed in the liquid refrigerant line 260 and configured to pump the liquid phase primary cooling medium to the evaporator. The use of the pump 280 allows the cooling system 200 to be used in configurations where natural circulation and gravity are not feasible (e.g., where the condenser cannot be installed at a sufficient height to provide a pressure head to support the flow of the primary cooling medium in the primary coolant loop 240). An example of such a configuration is the multi-story data center 100 shown in FIG. 1. The roof of the data center 100 may not have enough space or strength to support all of the condensing units 204 required to adequately cool the racks 112 of the data center 100. Thus, a condensing unit 204 comprising a passive condenser 210 and an active condenser 220 may be installed at a location on the ground, such as along the perimeter of the data center 100, in which case a pump 280 can supply a liquid phase primary cooling medium to an evaporator 230 located on a floor (e.g., the second floor 104 or the third floor 106) that is higher than the passive condenser 210 and the active condenser 220.

[0019] In the embodiment shown in Figures 2 and 3, the cooling system 200 includes one each of a passive condenser 210, an active condenser 220, and an evaporator 230. However, in some embodiments, multiples of each of these components may be used, such as the cooling system 200 shown in Figures 4 and 5. Figures 4 and 5 are schematic diagrams of a cooling system 200 having multiple passive condensers 210, multiple active condensers 220, and multiple evaporators 230. Figure 4 illustrates the indoor air handler 202 of the cooling system 200 of this embodiment, and Figure 5 illustrates the condensing unit 204.

[0020] The cooling system 200 may include multiple primary coolant loops 240. In this embodiment, the cooling system 200 includes two primary coolant loops 240, a first primary coolant loop 242 and a second primary coolant loop 244. As shown in FIG. 4, each of the first primary coolant loop 242 and the second primary coolant loop 244 includes at least one evaporator 230. In this embodiment, the first primary coolant loop 242 includes two first evaporators 232, and the second primary coolant loop 244 includes two second evaporators 234. The first evaporators 232 are arranged in parallel with the return air 124 and are connected to a first common steam pipe 252 and a first common liquid refrigerant line 262. Similarly, the second evaporator 234 is arranged in parallel with the return air 124 and is connected to a second common steam pipe 254 and a second common liquid refrigerant line 264. Each first evaporator 232 is disposed in series with one of the second evaporators 234 with respect to the return air 124. The return air 124 is directed to pass through the first evaporator 232 after passing through the second evaporators 234.

[0021] Condensing unit 204, as shown in FIG. 5, includes four circuits: a first circuit (CIRCUIT 1), a second circuit (CIRCUIT 2), a third circuit (CIRCUIT 3), and a fourth circuit (CIRCUIT 4). Although condensing unit 204 is described herein as having four circuits, any suitable number of circuits may be used. Additionally, while the components within each of the four circuits are described using specific components (e.g., passive condenser 210 and active condenser 220), it is contemplated that the scope of the present invention includes the use of these components in various arrangements and quantities.

[0022] 5, the first primary coolant loop 242 includes a plurality of first passive condensers 212. In this embodiment, the first primary coolant loop 242 includes six first passive condensers 212. The first passive condensers 212 are connected in parallel with each other, and the first evaporator 232 is fluidly connected to the first passive condensers 212 by a first common vapor line 252 and a first common liquid refrigerant line 262. Two first passive condensers 212 are disposed in each of the first, second, and third circuits.

[0023] The first primary coolant loop 242 further includes three first active condensers 222, one each in the first circuit, the second circuit, and the third circuit. In this embodiment, each secondary cooling system 270 includes two condensers 274 connected in parallel to each other. The condensers 274 are arranged in the same circuit as the corresponding first active condenser 222. Note that in FIG. 5, the compressors 272 are labeled, but the expansion valves 276 are not labeled for clarity. The first active condensers 222 are connected in parallel to each other and to the first passive condenser 212. The first evaporator 232 is also fluidly connected to each of the first active condensers 222 by the first common vapor line 252 and the first common liquid refrigerant line 262.

[0024] The second primary coolant loop 244 also includes a plurality of second passive condensers 214. In this embodiment, the second primary coolant loop 244 includes six second passive condensers 214. The second passive condensers 214 are connected in parallel with each other, and the second evaporator 234 is fluidly connected to the second passive condensers 214 by the second common vapor line 254 and the second common liquid refrigerant line 264. Two second passive condensers 214 are disposed in each of the first, second and third circuits.

[0025] In this embodiment, the second primary coolant loop 244 includes one second active condenser 224 that is arranged in parallel with six second passive condensers 214. The second active condenser 224 is also fluidly connected to the second evaporator 234 by a second common vapor line 254 and a second common liquid refrigerant line 264. The second active condenser 224 of the second primary coolant loop 244 is arranged in a fourth circuit. The fourth circuit includes a second active condenser 224 and a corresponding secondary cooling system 270, but does not include a second passive condenser 214. That is, each of the four circuits includes a secondary cooling system 270.

[0026] The first, second and third circuits have similar circuit arrangements. Therefore, the following description of the first circuit applies equally to the second and third circuits. The condensers 212, 214, 274 of the first circuit are arranged in two sets, a first set of condensers and a second set of condensers. Then, the scavenger air 206 sent by the scavenger fan 208 can pass over the outer surfaces of the condensers of each set. The first set of condensers and the second set of condensers are arranged in parallel with each other with respect to the air flow of the scavenger air 206. Each of the first set of condensers and the second set of condensers includes one first passive condenser 212 of the first primary coolant loop 242, one second passive condenser 214 of the second primary coolant loop 244 and one condenser 274 of the secondary cooling system 270.

[0027] These condensers 212, 214, 274 are arranged in series with respect to the airflow of the scavenger air 206. The suction of the scavenger fan 208 of the first circuit causes the scavenger air 206 to travel through these condensers as follows: The scavenger air 206, which is fresh air taken from the outdoor environment surrounding the condensing unit 204, first passes through the first passive condenser 212 of the first primary coolant loop 242. The scavenger air 206 then passes through the second passive condenser 214 of the second primary coolant loop 244. The scavenger air 206 then passes through the condenser 274 of the secondary cooling system 270 before being exhausted to the outside by the scavenger fan 208. Each scavenger fan 208 can be independently variable or at least variable for each circuit. By arranging the condensers 212, 214, 274 of the first circuit in this way, a counter-flow design can be implemented. The primary coolant in the first primary coolant loop 242 is colder than the primary coolant in the second primary coolant loop 244. Thus, the coldest scavenger air 206 passes through the coldest condenser (first passive condenser 212) first, and the scavenger air 206 warmed by the first passive condenser 212 passes through the warmer second passive condenser 214.

[0028] Similar to the cooling system 200 described above with reference to Figures 2 and 3, the cooling system 200 shown in Figures 4 and 5 also preferably switches between active and passive modes without using valves in the first and second primary coolant loops 242 and 244. Instead of using valves, the secondary cooling system 270 is operated to cool the first and / or second active condensers 222 and / or 224, so that the primary cooling medium in the gas phase naturally travels to the cooler active condenser (the first and / or second active condensers 222 and / or 224) and is condensed therein. That is, the cooling system 200 transitions from the passive mode to the active mode by thermodynamic forces.

[0029] When the outside temperature is low enough, all circuits can be operated in a passive mode and the speed of the scavenger fan 208 can be adjusted to help control the temperature of the supply air 122 to the desired set point. Then, when the maximum flow rate of the scavenger air 206 still causes the temperature of the supply air 122 to exceed the set point, at least one secondary cooling system 270 can be activated to provide a secondary cooling medium to at least one of the first active condenser 222 and the second active condenser 224. In the cooling system 200 shown in Figures 4 and 5, the secondary cooling systems 270 of each circuit can be activated in stages as needed to maintain the temperature of the supply air 122 at the set point. While there are various possible sequences for activating the secondary cooling systems 270 of each circuit, one approach is to activate the secondary cooling systems 270 in stages as needed, starting with the first circuit, followed by the second circuit, followed by the third circuit, followed by the fourth circuit, and so on. Thus, in this embodiment, the secondary cooling systems 270 of the first primary coolant loop 242 may be staged followed by the secondary cooling systems 270 of the second primary coolant loop 244. Then, when the temperature of the supply air 122 falls below a setpoint temperature, the secondary cooling systems 270 may be shut down, for example, in the reverse order that the circuits were staged.

[0030] Then, if the temperature of the supply air 122 falls below the set temperature even when all secondary cooling systems 270 (active cooling mode) are shut down and the fan speed of the scavenger fans 208 is minimized, the scavenger fans 208 can be shut down in stages as necessary to maintain the temperature of the supply air 122 at the set temperature. Then, when all but one of the scavenger fans 208 are shut down, only one of the first primary coolant loop 242 and the second primary coolant loop 244 can be operated. As described below, each of the first primary coolant loop 242 and the second primary coolant loop 244 includes a pump 280, i.e., the first primary coolant loop 242 includes a first pump 282 for supplying the liquid phase primary coolant to the first evaporator 232, and the second primary coolant loop 244 includes a second pump 284 for supplying the liquid phase primary coolant to the second evaporator 234. Thus, only one of the first primary coolant loop 242 and the second primary coolant loop 244 can be operated by operating only one of the first pump 282 and the second pump 284. When a pump 282, 284 is not operating, the corresponding loop 242, 244 is stopped operating.

[0031] The first pump 282 and the second pump 284 can also help regulate the cooling system 200. The first pump 282 can be configured to precisely control the liquid level (amount of primary cooling medium in liquid phase) in the first evaporator 232 to maintain the temperature of the vapor leaving the evaporator 232 at a desired temperature, and the second pump 284 can be configured to precisely control the liquid level in the second evaporator 234 to maintain the temperature of the vapor leaving the evaporator 234 at a desired temperature. For example, the first pump 282 and the second pump 284 can both be variable speed pumps, and the amount of primary cooling medium provided to the first evaporator 232 and the second evaporator 234 can be controlled by controlling the speed of the pumps 282, 284. Using the first pump 282 and the second pump 284 in this manner allows the primary cooling medium to be circulated through the first primary coolant loop 242 and the second primary coolant loop 244 efficiently over a wide range of heat loads and ambient conditions. Adjusting the speed of the pumps 282, 284 can be used to prevent too much liquid primary cooling medium from entering the evaporators 232, 234 (e.g., flooding the evaporators 232, 234 with liquid primary cooling medium), which may prevent vapor flow from the evaporators 232, 234. Additionally, adjusting the speed of the pumps 282, 284 can be used to prevent too little liquid primary cooling medium from entering the evaporators 232, 234 (e.g., starving the evaporators 232, 234), which may prevent effective and efficient condensation in the condensers 212, 214, 222, 224. These considerations and the speed control of pumps 282, 284 may be particularly important when the indoor air handler 202 is far from the condensing unit 204. This is because the greater the distance between the indoor air handler 202 and the condensing unit 204, the greater the amount of primary cooling medium used, exacerbating problems such as overflow described above.

[0032] Setting the speed of the pumps 282, 284, and therefore the liquid inflow to the evaporators 232, 234, can be done in a variety of approaches. For example, the speed of the pumps 282, 284 can be based on heat absorption in the evaporators 232, 234, heat rejection of the return air 124 / supply air 122, heat rejection in the condensers 212, 214, 222, 224, heat absorption by the scavenger air 206, or superheat of the vapor. Measuring these pump 282, 284 speed control factors can be done as described in U.S. Patent Application Publication No. 2021 / 0368647, the entire disclosure of which is incorporated herein by reference.

[0033] The cooling system 200 may be operated using a controller 290. In this embodiment, the controller 290 is a microprocessor-based controller including a processor 292 for performing the various functions described herein and a memory 294 for storing various data. The controller 290 may also be referred to as a CPU. In some embodiments, the control of the cooling system 200 may be effected by a set of instructions stored in the memory 294 and executed by the processor 292.

[0034] The controller 290 may be communicatively coupled to various temperature sensors ("TS") 296 that monitor the temperatures of various environments. The controller 290 is configured to receive temperature information (e.g., temperature) from the temperature sensors 296. For example, the temperature sensors 296 may be used to monitor the temperature of the supply air 122, as shown in FIG. 4, such that the temperature of the supply air 122, etc. may be transmitted from the temperature sensors 296 (and received by the controller 290). The temperature sensors 296 may also be used to monitor the temperature of the return air 124. Still other temperature sensors 296 may be used to monitor other conditions, for example, the temperature sensor 296 may be positioned to monitor the outside air temperature (the temperature of the scavenger air 206) as shown in FIG. 5. Other temperature sensors 296 and other sensors may also be used to measure various parameters of the cooling system 200 and each of the first primary coolant loop 242, the second primary coolant loop 244, and the secondary cooling system 270. For example, the loop sensors may measure the temperature and pressure of the primary coolant in each loop using temperature and pressure sensors.

[0035] The controller 290 may also be communicatively and operatively coupled to other components of the cooling system 200 such that the controller 290 can be used to control those components. For example, the supply air fan 126 and the scavenger fan 208 may be communicatively and operatively coupled to the controller 290 such that the controller 290 can be used to operate the supply air fan 126 and the scavenger fan 208 as described above. The controller 290 may also be communicatively and operatively coupled to the secondary cooling system 270 of each loop such that the controller 290 can be used to turn the secondary cooling system 270 on and off as described above. The controller 290 may also be communicatively and operatively coupled to the first pump 282 and the second pump 284 such that the controller 290 can be used to control the operation of the first pump 282 and the second pump 284, respectively, as described herein.

[0036] As described above, the first common liquid refrigerant line 262 may be supplied with the liquid phase primary cooling medium from both the first passive condenser 212 and the first active condenser 222. Similarly, the second common liquid refrigerant line 264 may be supplied with the liquid phase primary cooling medium from both the second passive condenser 214 and the second active condenser 224. As shown in FIG. 5, the first common liquid refrigerant line 262 includes a first pump 282, and the second common liquid refrigerant line 264 includes a second pump 284. The first pump 282 is disposed downstream of the first passive condenser 212 and the first active condenser 222, and the second pump 284 is disposed downstream of the second passive condenser 214 and the second active condenser 224. Moreover, the first pump 282 is disposed upstream of the first evaporator 232, and the second pump 284 is disposed upstream of the second evaporator 234. The first pump 282 is configured to pump the liquid phase primary cooling medium to the first evaporator 232, and the second pump 284 is configured to pump the liquid phase primary cooling medium to the second evaporator 234.

[0037] As described above and shown in FIG. 1, the condensing unit 204 is disposed at a lower position than the indoor air handler 202. Thus, the first passive condenser 212, the second passive condenser 214, the first active condenser 222, and the second active condenser 224 are disposed at a lower position than the first evaporator 232 and the second evaporator 234. More specifically, the condensers 212, 214, 222, and 224 each include an outlet 266 (see FIG. 5), each of which is fluidly connected to the first common liquid refrigerant line 262 or the second common liquid refrigerant line 264 to supply the primary cooling medium in a liquid phase. Additionally, the first evaporator 232 and the second evaporator 234 each include an inlet 268 (FIG. 4), each of which is fluidly connected to the first common liquid refrigerant line 262 or the second common liquid refrigerant line 264. Each inlet 268 is fluidly connected to a corresponding outlet 266 by the first common liquid refrigerant line 262 or the second common liquid refrigerant line 264 and configured to receive the primary cooling medium in a liquid phase. As shown in FIG. 1, the inlets 268 are located at a height higher than the outlets 266. In this configuration, natural circulation and gravity cannot generate sufficient pressure to deliver the primary cooling medium in a liquid phase from the condensers 212, 214, 222, 224. The inlets 268 of the first evaporator 232 and the second evaporator 234 are located at a height that does not allow sufficient gravity and natural circulation to move the primary cooling medium from the outlets 266 of the condensers 212, 214, 222, 224 to the inlets 268. Instead, a first pump 282 and a second pump 284 are utilized to provide pressure to deliver the primary cooling medium in a liquid phase. Thus, the use of the first pump 282 and the second pump 284 allows the cooling system 200 to employ configurations that would not be available if the cooling system 200 relied solely on natural circulation and gravity.

[0038] Other configurations are contemplated in which the inlets 268 of the first evaporator 232 and the second evaporator 234 are located at an elevation that does not provide sufficient gravity and natural circulation to move the primary cooling medium from the outlets 266 to the inlets 268 of the condensers 212, 214, 222, 224. In configurations that operate without pumps (e.g., the first pump 282 and the second pump 284), the maximum hydraulic force available to drive the liquid phase primary cooling medium to the evaporators 232, 234 is provided by the relative heights of the condensers 212, 214, 222, 224 with respect to the evaporators 232, 234, and more specifically, the height difference between the outlets 266 and the inlets 268. In order for natural circulation and gravity to circulate the primary coolant through the primary coolant loop 240, the fluid forces must be sufficient to overcome the flow resistance (pressure loss) of the primary coolant through the primary coolant loop 240 (e.g., the first primary coolant loop 242 and the second primary coolant loop 244, respectively). If the pressure (fluid force) available through the elevation difference is less than the pressure loss of the system (primary coolant loop 240), the system will not operate through natural circulation and gravity. In this situation, the options are to increase the size of the piping or to reduce the mass flow rate of the system. However, increasing the size of the piping increases the installation cost and requires a larger refrigerant charge. Also, reducing the mass flow rate reduces the heat removal performance of the system. Therefore, in this situation, the embodiment utilizing the pump 280 described herein is considered to be preferable.

[0039] The following table shows an example of a second primary coolant loop 244 with elevation differences that may be suitable for embodiments described herein. Table 1 shows the system pressure loss in feet (meters) for two different mass flow rates, one for 400 kW heat removal and the other for 300 kW heat removal. Straight piping has a pressure loss value per straight piping length, and other system components such as elbows, t-sections, condenser coils, and evaporator coils can also be converted to equivalent straight piping lengths in feet (m) (see, for example, Copper Development Association Inc. Design Handbook, Table 14.7). These are summed together to give the total equivalent straight piping length in feet (m) for the second primary coolant loop 244 shown in Table 1. The following example uses R134a as the primary coolant. The second common vapor line 254 has a diameter of 4 inches (10 cm) and the second common liquid refrigerant line 264 has a diameter of 2 inches (5 cm). Table 2 shows the hydraulic forces (maximum hydraulic forces) that can be achieved at various elevation differences.

[0040] [Table 1]

[0041] [Table 2]

[0042] As can be seen by comparing the maximum fluid forces (Table 2) and pressure losses (Table 1), natural circulation and gravity are sufficient to provide the necessary pressure to operate the system (second primary coolant loop 244) with an equivalent straight pipe length of 300 feet (91 m) when the vertical separation is 8 feet (2.4 m) or 10 feet (3.0 m). Similarly, natural circulation and gravity are sufficient to provide the necessary pressure to operate the system (second primary coolant loop 244) with an equivalent straight pipe length of 300 feet (91 m) and a mass flow rate of 300 kW heat removal when the vertical separation is 6 feet (1.8 m). On the other hand, when the maximum fluid forces are not sufficient, the embodiments described herein can be applied. As can be seen from Tables 1 and 2 above, for a 300 kW heat removal system, the embodiments described herein can be applied when the vertical separation is 4 feet (1.2 m) and the primary coolant loop 240 has a pressure drop of 150 feet (46 m) or more of equivalent straight pipe length. Similarly, for a 400 kW heat removal system, the embodiments described herein can be applied when the vertical separation is 6 feet (1.8 m) and the primary coolant loop 240 has a pressure drop of 225 feet (69 m) or more of equivalent straight pipe length, and more preferably when a safety factor of 0.5 PSI (3.4 kPa) is applied, the embodiments described herein can be applied regardless of the equivalent straight pipe length, as long as the vertical separation is 4 feet (1.2 m) or less, especially when a safety factor of 0.5 PSI (3.4 kPa) is applied.

[0043] Furthermore, when relying on natural circulation and gravity, in order to reduce pressure loss in the first common liquid refrigerant line 262 and the second common liquid refrigerant line 264 while appropriately arranging the condensers 212, 214, 222, 224 and the evaporators 232, 234, the piping size of the first common liquid refrigerant line 262 and the second common liquid refrigerant line 264 used by the system is considered to be relatively large, and as a result, the amount of primary cooling medium in the first primary coolant loop 242 and the second primary coolant loop 244 is considered to be relatively large. However, if the piping size without the pump 280 is approximately 2 1 / 8 inches (5.40 cm), by providing the pump 280, this can be reduced to approximately 1 3 / 8 inches (3.49 cm). If the corresponding size reduction is performed for the first common liquid refrigerant line 262 and the second common liquid refrigerant line 264, the refrigerant charge of the primary cooling medium can be reduced by up to 40% depending on the length of the interconnecting lines. The interconnecting lines are the portions of the vapor lines 252 , 254 and liquid refrigerant lines 262 , 264 between the indoor air handler 202 and the condensing unit 204 .

[0044] Another advantage of using a pump such as pump 280 is that a pumped system can facilitate integration of the indoor air handler 202 and the condensing unit 204 into a single unit that can be sized for road transport. FIG. 6 illustrates a cooling system 300 in a single unit sized for road transport. The cooling system 300 can be configured and operated similarly to the cooling system 200 described above. Note that in FIG. 6, like reference numbers refer to the same or similar components as the cooling system 200 described above, and therefore these components will not be described in detail here. Additionally, some components such as the secondary cooling system 270 have been omitted from this example for brevity, but the cooling system 300 can include any of the components described above. The use of pump 280 eliminates the need for a height difference between the passive condenser 210 and the evaporator 230 that would be required if natural circulation and gravity were used to drive the primary coolant through the primary coolant loop 240, allowing the passive condenser 210 to be located at a similar height to the evaporator 230. Thus, the overall height can be reduced to a height acceptable for road transport (e.g., 152 inches (386 cm)). Thus, the evaporator 230 and the passive condenser 210 can be positioned relative to each other such that the overall height of a single unit is 14 feet (4.27 m) or less, such as 13.5 feet (4.11 m) or less, or 13 feet (3.96 m) or less. Also, in these embodiments, the active condenser 220 can be positioned relative to the evaporator 230 and the passive condenser 210 such that the overall height can be acceptable for road transport.

[0045] The road transport of a single unit system (cooling system 300) may have the advantage that the unit may be preassembled as a single unit at a factory, reducing the amount of assembly required at the site where the cooling system 300 is to be used. That is, the cooling system 300 may be pre-filled and pre-tested to reduce installation time and improve quality control. The system may then be connected to the racks 112 to be cooled by suitable fluid conduits (e.g., in this embodiment, an air duct (not shown) to a room holding the racks 112). To this end, the cooling system 300 includes a process fluid inlet and a process fluid outlet. The process fluid inlet and process fluid outlet are fluidly connected to an evaporator 230 for supplying process fluid to the evaporator 230 and receiving cooled process fluid therefrom. In this embodiment, the cooling system 300 includes an air inlet 302 and a return air inlet 304, which may be connected to a duct for supplying supply air 122 and a duct for supplying return air 124.

[0046] The single unit system (cooling system 300) also provides other advantages, such as reduced charge of primary cooling medium (refrigerant) because the single unit system requires less piping (e.g., due to the elimination of interconnecting piping). The single unit system (cooling system 300) also allows for greater flexibility in configuring the data center 100, as various duct configurations can be more radically adapted to the layout and configuration of the data center 100 than piping such as the vapor piping 250 and liquid refrigerant line 260 described above. Additionally, by moving the indoor air handler 202 to a location outside the data center 100, additional floor space is available on each floor 102, 104, 106, which can be used for various purposes, such as adding additional racks 112.

[0047] 1 and 6, the primary coolant loop 240 (e.g., each of the first and second primary coolant loops 242 and 244) may also include a refrigerant receiver 246. The refrigerant receiver 246 is fluidly connected to the first and second common liquid refrigerant lines 262 and 264, respectively, at a location downstream of the outlets 266 of the condensers 212, 214, 222, and 224 and upstream of the first pump 282 or the second pump 284. Preferably, the refrigerant receiver 246 is positioned vertically below the bottom of the active condensers 222 and 224 such that the primary cooling medium in liquid phase naturally flows into the refrigerant receiver 246.

[0048] The refrigerant receiver 246 can be used when the primary coolant loop 240 is operating in an active mode. The first passive condenser 212 and the second passive condenser 214 may have a capacity that is significantly larger than the first active condenser 222 and the second active condenser 224. Therefore, during operation in an active mode, it is believed that there is an excess of primary cooling medium due to the small volume of the first active condenser 222 and the second active condenser 224. The refrigerant receiver 246 can then store the excess primary cooling medium and prevent it from flowing back into the first active condenser 222 and the second active condenser 224. If such a backflow occurs, the heat removal efficiency of the first active condenser 222 and the second active condenser 224 may be reduced. Thus, in some embodiments, when the primary coolant loops 240 (e.g., each of the first primary coolant loop 242 and the second primary coolant loop 244) are operating with at least one circuit in an active mode, excess primary coolant can be collected in the refrigerant receiver 246. The refrigerant receiver 246 is configured to receive excess primary coolant when the evaporator 230 is receiving the primary coolant in a liquid phase from at least one of the first active condenser 222 and the second active condenser 224.

[0049] The refrigerant receiver 246 may be any suitable refrigerant receiver, and may additionally or alternatively be oversized piping (e.g., an oversized section of the first common liquid refrigerant line 262 or the second common liquid refrigerant line 264) appropriately sized to hold the excess primary cooling medium.

[0050] In the above example, the process fluid cooled by the cooling system 200 is air (e.g., return air 124). The above describes directing air (process fluid) to the racks 112 housing electronic equipment, where the air is warmed and then directed to the evaporator 230 (return air 124) where it is cooled. However, the cooling system 200 described herein is not limited to cooling air, but can be used to cool any suitable fluid. For example, the process fluid can include liquids such as water, water-glycol mixtures, and non-conductive fluids (dielectrics). In the above embodiment in which air is the process fluid, a microchannel coil or a finned tube coil was suitable as the evaporator 230. However, in the case where the process fluid is a liquid rather than a vapor (gas), other suitable evaporators 230 can be used, such as, for example, a microchannel cold plate, a plate heat exchanger, a coaxial heat exchanger, or a shell-and-tube heat exchanger.

[0051] For example, if the process fluid is a liquid, the process fluid may be circulated through the process fluid loop by a pump. The process fluid may be configured to receive heat from a thermal load, such as electronic equipment housed in the rack 112. In some embodiments, the process fluid loop may include an air-to-liquid heat exchanger through which warmed air (e.g., air within the rack 112) may be passed to increase the temperature of the process fluid.

[0052] In another embodiment, the cooling system 200 can be used with an immersion cooling system. Figures 7A and 7B show an example of a rack 112 for use with an immersion cooling system. In Figure 7A, the servers 114 are immersed in the dielectric 132. When the servers 114 warm the dielectric 132, the dielectric 132 remains liquid (single phase). The warmed dielectric 132 is circulated as the process fluid 134 through the process fluid loop 130 to cool it and then returned to the rack 112 to further cool the servers 114.

[0053] In FIG. 7B, the server 114 is again immersed in the dielectric 132. In this example, however, the dielectric 132 cools the server 114 by two-phase cooling. When the server 114 heats the dielectric 132, the dielectric 132 changes phase to vapor. The dielectric vapor then rises to the top of the rack 112. At the top of the rack 112, a coil 136 is provided. A suitable process fluid 134 flows through the coil 136, which condenses the dielectric 132. Note that in other embodiments, rather than using a separate fluid as the process fluid 134, the vapor phase dielectric 132 can be used as the process fluid 134 and cooled directly by the evaporator 230.

[0054] In the embodiment described above, the server 114 is physically separate from the evaporator 230 and utilizes a process fluid loop 130 to transport heat from other information technology ("IT") equipment, such as the server 114, to the evaporator 230. However, the invention described herein is not so limited and the evaporator 230 can be any liquid-to-refrigerant heat exchanger that uses a circulating liquid (dielectric fluid or other fluid such as water) to transport heat from the IT equipment to a refrigerant contained in a two-phase thermosiphon loop. Other suitable such evaporators 230 can include, for example, a cold plate that is integrated with the server 114 or IT component to absorb heat directly from the component or chips within the component, or multiple cylindrical surfaces that are integrated directly into an immersion cooling system.

[0055] Although the present invention has been described through the description of specific exemplary embodiments, many other modifications and variations will become apparent to those skilled in the art based on the present disclosure. Therefore, it should be understood that the present invention can be implemented in a manner different from that specifically described herein. In other words, the exemplary embodiments of the present invention should be considered in all respects as merely illustrative and not limiting, and the scope of the present invention should be determined not by the above description but by the claims that can be supported in this specification and their equivalents. [Explanation of symbols]

[0056] 100 Data Centers 102 1st Floor 104 Second Floor 106 Third Floor 112 racks 114 Server 122 Air Supply 124 Return Air 126 Intake fan 130 Process Fluid Loop 132 Dielectric 134 Process Fluids 136 Coil 200, 300 Cooling System 202 Indoor Air Handler 204 Outdoor condensing unit 206 Scavenger Air 208 Scavenger Fan 210 Passive Condenser 212 First passive condenser 214 Secondary Passive Condenser 220 Active Condenser 222 First active condenser 224 Second active condenser 230 Evaporator 232 First Evaporator 234 Second Evaporator 240 Primary Coolant Loop 242 First Primary Coolant Loop 244 Second Primary Coolant Loop 246 Refrigerant Receiver 250 Steam piping 252 First common steam pipe 254 Second common steam pipe 260 Common liquid refrigerant line 262 First common liquid refrigerant line 264 Second common liquid refrigerant line 266 Condenser outlet 268 Evaporator inlet 270 Secondary Cooling System 272 Compressor 274 Condenser of secondary cooling system 276 Expansion valve 280 Pump 282 First Pump 284 Second Pump 290 Control Device 292 processor 294 Memory 296 Temperature Sensor 302 Air supply port 304 Return air port

Claims

1. an evaporator configured to contain a primary cooling medium and to receive a process fluid, the evaporator being configured to extract heat from the process fluid upon receipt thereof to cool the process fluid and cause a phase change of the primary cooling medium from a liquid phase to a gas phase; a passive condenser having an exterior surface and fluidly coupled to the evaporator and configured to have an airflow directed to the exterior surface, the passive condenser configured, when the airflow is directed to the exterior surface of the passive condenser, to (i) receive the primary cooling medium in a gas phase from the evaporator, (ii) transfer heat from the primary cooling medium, (iii) cause a phase change of the primary cooling medium from a gas phase to a liquid phase, and (iv) supply the primary cooling medium in a liquid phase to the evaporator; a heat exchanger fluidly coupled to the evaporator and configured to selectively receive a secondary cooling medium, (a) when the secondary cooling medium is supplied to the heat exchanger, the heat exchanger receives at least a portion of the primary cooling medium in the gas phase that was received by the passive condenser, without the need to place and operate any valves between the evaporator and the passive condenser and between the evaporator and the heat exchanger, so that the heat exchanger (i) receives the primary cooling medium in the gas phase from the evaporator, (ii) transfers heat from the primary cooling medium, (iii) changes the phase of the primary cooling medium from the gas phase to a liquid phase, and (iv) supplies the primary cooling medium in the liquid phase to the evaporator; (b) a heat exchanger configured such that, when the secondary cooling medium is not supplied to the heat exchanger, the heat exchanger does not supply the primary cooling medium in a liquid phase to the evaporator; a liquid line fluidly connecting the evaporator to each of the passive condenser and the heat exchanger for supplying the primary cooling medium in a liquid phase from at least one of the passive condenser and the heat exchanger to the evaporator; a pump disposed in the liquid line and configured to pump the primary cooling medium in a liquid phase to the evaporator; A cooling system comprising: A cooling system wherein the passive condenser is positioned in parallel with the heat exchanger relative to the fluid flow of the primary cooling medium.

2. The cooling system of claim 1 , wherein the process fluid is air.

3. The cooling system of claim 1 , wherein the process fluid is a liquid.

4. at least one electronic component cooled by a dielectric; A cooling system as claimed in claim 1 for cooling the dielectric; An electronic device system comprising:

5. The electronics system of claim 4 , wherein the process fluid is the dielectric.

6. 2. The cooling system of claim 1, wherein the secondary cooling medium is a refrigerant in a direct expansion cooling system comprising a compressor and an expansion valve.

7. The cooling system of claim 1 , wherein the secondary cooling medium is chilled water or a chilled water-glycol mixture.

8. 2. The cooling system of claim 1, wherein when the secondary cooling medium is supplied to the heat exchanger, a portion of the primary cooling medium is received by both the passive condenser and the heat exchanger to (i) transfer heat from the primary cooling medium, (ii) cause the primary cooling medium to change phase from a gas phase to a liquid phase, and (iii) supply the primary cooling medium in the liquid phase to the evaporator.

9. a refrigerant receiver configured to store excess primary cooling medium; The cooling system of claim 1 , wherein the refrigerant receiver is disposed in the liquid line at a location upstream from the pump and downstream from the heat exchanger.

10. The cooling system of claim 9 , wherein the refrigerant receiver is disposed at a height vertically below a bottom of the heat exchanger.

11. the evaporator comprising an inlet configured to receive the primary cooling medium in a liquid phase; the passive condenser comprising an outlet configured to supply the primary cooling medium in a liquid phase; the inlet of the evaporator is fluidly connected to the outlet of the passive condenser by the liquid line; 2. The cooling system of claim 1, wherein the inlet of the evaporator is located at a height that does not provide sufficient gravity and natural circulation to move the primary cooling medium from the outlet of the passive condenser to the inlet of the evaporator.

12. the evaporator comprising an inlet configured to receive the primary cooling medium in a liquid phase; the heat exchanger including an outlet configured to supply the primary cooling medium in a liquid phase; the inlet of the evaporator is fluidly connected to the outlet of the heat exchanger by the liquid line; 2. The cooling system of claim 1, wherein the inlet of the evaporator is located at a height that does not provide sufficient gravity and natural circulation to move the primary cooling medium from the outlet of the heat exchanger to the inlet of the evaporator.

13. the evaporator comprising an inlet configured to receive the primary cooling medium in a liquid phase; the passive condenser comprising an outlet configured to supply the primary cooling medium in a liquid phase; the inlet of the evaporator is fluidly connected to the outlet of the passive condenser by the liquid line; The cooling system of claim 1 , wherein the inlet of the evaporator is positioned higher than the outlet of the passive condenser.

14. the evaporator comprising an inlet configured to receive the primary cooling medium in a liquid phase; the heat exchanger including an outlet configured to supply the primary cooling medium in a liquid phase; the inlet of the evaporator is fluidly connected to the outlet of the heat exchanger by the liquid line; The cooling system of claim 1 , wherein the inlet of the evaporator is positioned higher than the outlet of the heat exchanger.

15. the evaporator comprising an inlet configured to receive the primary cooling medium in a liquid phase; the passive condenser comprising an outlet configured to supply the primary cooling medium in a liquid phase; the inlet of the evaporator is fluidly connected to the outlet of the passive condenser by the liquid line; 2. The cooling system of claim 1, wherein the outlet of the passive condenser is positioned no more than 6 feet (1.8 m) above the inlet of the evaporator.

16. a vapor line fluidly connecting the evaporator to each of the passive condenser and the heat exchanger for supplying the primary cooling medium in a vapor phase from the evaporator to at least one of the passive condenser and the heat exchanger; 16. The cooling system of claim 15, wherein the evaporator, the passive condenser, the heat exchanger, the liquid line, and the vapor line have an equivalent straight line length of 225 feet (69 m) or greater.

17. 17. The cooling system of claim 16, wherein the evaporator, the passive condenser, the heat exchanger, the liquid line, and the vapor line have an equivalent straight pipe length of 150 feet (46 m) or greater.

18. the evaporator comprising an inlet configured to receive the primary cooling medium in a liquid phase; the heat exchanger including an outlet configured to supply the primary cooling medium in a liquid phase; the inlet of the evaporator is fluidly connected to the outlet of the heat exchanger by the liquid line; 2. The cooling system of claim 1, wherein the outlet of the heat exchanger is positioned no more than 6 feet (1.8 m) above the inlet of the evaporator.

19. a vapor line fluidly connecting the evaporator to each of the passive condenser and the heat exchanger for supplying the primary cooling medium in a vapor phase from the evaporator to at least one of the passive condenser and the heat exchanger; 20. The cooling system of claim 18, wherein the evaporator, the passive condenser, the heat exchanger, the liquid line, and the vapor line have an equivalent straight pipe length of 225 feet (69 m) or greater.

20. 20. The cooling system of claim 19, wherein the evaporator, the passive condenser, the heat exchanger, the liquid line, and the vapor line have an equivalent straight pipe length of 150 feet (46 m) or greater.

21. The cooling system of claim 1 , wherein the evaporator is positioned higher than at least one of the passive condenser and the heat exchanger.

22. The cooling system of claim 1 , wherein the pump is a variable speed pump.

23. 23. The cooling system of claim 22, further comprising a controller operably coupled to the pump to control a speed of the pump.

24. the cooling system further comprising a temperature sensor; the controller is communicatively coupled to the temperature sensor to receive temperature information; The cooling system of claim 23 , wherein the controller is configured to control a speed of the pump based on the temperature information.

25. The cooling system of claim 1 , wherein the evaporator, the passive condenser, the heat exchanger, and the pump are integrated into a single unit.

26. 26. The cooling system of claim 25, wherein the evaporator and passive condenser are positioned relative to one another such that the overall height of the single unit is 14 feet (4.27 m) or less.

27. 26. The cooling system of claim 25, further comprising a process fluid inlet fluidly connected to the evaporator and a process fluid outlet fluidly connected to the evaporator.

28. 26. The cooling system of claim 25, wherein the process fluid inlet is a return air inlet connectable to a return air duct and the process fluid outlet is a supply air inlet connectable to a supply air duct.

29. a plurality of floors including a first floor and a second floor higher than the first floor; a plurality of racks for holding electronic components disposed on the second floor; 29. A cooling system according to claim 28; A multi-storey data centre comprising: the return air inlet is connected to the return air duct to receive air from the plurality of racks disposed on the second floor; A multi-floor data center, wherein the air intake is connected to the air intake duct to supply air to the plurality of racks arranged on the second floor.

30. a plurality of floors including a first floor and a second floor higher than the first floor; a plurality of racks for holding electronic components disposed on the second floor; A cooling system according to claim 1; A multi-storey data centre comprising: the evaporator is disposed on the second floor; The multi-floor data center, wherein the passive condenser and the heat exchanger are located below the second floor.

31. an evaporator configured to contain a primary cooling medium and to receive a process fluid, the evaporator being configured to extract heat from the process fluid upon receipt thereof to cool the process fluid and cause a phase change of the primary cooling medium from a liquid phase to a gas phase; a plurality of passive condensers each having an exterior surface, each passive condenser being fluidly coupled to the evaporator and each configured to have an airflow directed to the exterior surface, wherein when the airflow is directed to the exterior surface of the passive condenser, the passive condensers are configured to (i) receive the primary cooling medium in a gas phase from the evaporator, (ii) transfer heat from the primary cooling medium, (iii) cause the primary cooling medium to change phase from a gas phase to a liquid phase, and (iv) supply the primary cooling medium in a liquid phase to the evaporator; at least one heat exchanger fluidly coupled to the evaporator and configured to selectively receive a secondary cooling medium, (a) when the secondary cooling medium is supplied to the at least one heat exchanger, the at least one heat exchanger receives at least a portion of the primary cooling medium in the gas phase that was received by the passive condenser without the need to place and operate any valves between the evaporator and the passive condenser and between the evaporator and the heat exchanger, and the at least one heat exchanger (i) receives the primary cooling medium in the gas phase from the evaporator, (ii) transfers heat from the primary cooling medium, (iii) changes the phase of the primary cooling medium from the gas phase to a liquid phase, and (iv) supplies the primary cooling medium in the liquid phase to the evaporator; (b) a heat exchanger configured such that when the secondary cooling medium is not supplied to the at least one heat exchanger, the heat exchanger does not supply the primary cooling medium in a liquid phase to the evaporator; and a liquid line fluidly connecting the evaporator to each passive condenser of the plurality of passive condensers and the at least one heat exchanger for supplying the primary cooling medium in a liquid phase from at least one of the plurality of passive condensers and the at least one heat exchanger to the evaporator; a pump disposed in the liquid line and configured to pump the primary cooling medium in a liquid phase to the evaporator; A cooling system comprising: A cooling system, wherein at least one passive condenser of the plurality of passive condensers is disposed in parallel with the at least one heat exchanger relative to a fluid flow of the primary cooling medium.

32. 32. The cooling system of claim 31, wherein the multiple passive condensers are positioned in parallel with one another relative to the fluid flow of the primary cooling medium.

33. the evaporator comprising an inlet configured to receive the primary cooling medium in a liquid phase; each passive condenser of the plurality of passive condensers comprises an outlet configured to supply the primary cooling medium in a liquid phase; the inlet of the evaporator is fluidly connected to the outlet of each passive condenser of the plurality of passive condensers by the liquid line; 32. The cooling system of claim 31, wherein the inlet of the evaporator is positioned higher than the outlet of each passive condenser of the plurality of passive condensers.

34. the evaporator comprising an inlet configured to receive the primary cooling medium in a liquid phase; the at least one heat exchanger comprising an outlet configured to supply the primary cooling medium in a liquid phase; the inlet of the evaporator is fluidly connected to the outlet of the at least one heat exchanger by the liquid line; 32. The cooling system of claim 31, wherein the inlet of the evaporator is positioned higher than the outlet of the at least one heat exchanger.

35. 32. The cooling system of claim 31, wherein the secondary cooling medium is a refrigerant in a direct expansion cooling system comprising a compressor and an expansion valve.

36. 32. The cooling system of claim 31, wherein when the secondary cooling medium is supplied to the at least one heat exchanger, a portion of the primary cooling medium is received by each passive condenser of the plurality of passive condensers and the at least one heat exchanger to (i) transfer heat from the primary cooling medium, (ii) cause the primary cooling medium to change phase from a gas phase to a liquid phase, and (iii) supply the primary cooling medium in the liquid phase to the evaporator.

37. the cooling system further comprising a plurality of heat exchangers; 32. The cooling system of claim 31, wherein each heat exchanger of the plurality of heat exchangers is disposed in parallel with each passive condenser of the plurality of passive condensers relative to a fluid flow of the primary cooling medium.

38. the evaporator comprising an inlet configured to receive the primary cooling medium in a liquid phase; each heat exchanger of the plurality of heat exchangers comprising an outlet configured to supply the primary cooling medium in a liquid phase; the inlet of the evaporator is fluidly connected to the outlet of each heat exchanger of the plurality of heat exchangers by the liquid line; 38. The cooling system of claim 37, wherein the inlet of the evaporator is positioned higher than the outlet of each heat exchanger of the plurality of heat exchangers.

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