Active / passive cooling system

Abstract

The present invention relates to a cooling assembly comprising an evaporator containing a primary cooling medium, a passive condenser, a heat exchanger, and a flow control valve controlling the flow of the primary cooling medium into the evaporator. When a secondary cooling medium is provided to the heat exchanger, the primary cooling medium in the gas phase switches from being received by the passive condenser to the heat exchanger without operating any valves located between the evaporator and the passive condenser and between the evaporator and the heat exchanger. The primary cooling medium circulates between the evaporator and the passive condenser and between the evaporator and the heat exchanger by natural circulation and gravity without the need to provide a pump in the flow path of the primary cooling medium between the heat exchanger and the evaporator and between the passive condenser and the evaporator to circulate the primary cooling medium.

Description

[0001] This application is a divisional application of the invention patent application entitled "Active / Passive Cooling System", with an international application date of July 29, 2022, international application number PCT / US2022 / 038815, and national application number 202280054974.0. Technical Field

[0002] This invention relates to cooling systems and systems and methods for controlling them. In particular, this invention relates to a cooling system that has both active and passive modes. For example, a particularly suitable application is in data center cooling systems. Background Technology

[0003] Data centers typically require a significant amount of energy to operate. The servers in these data centers generate substantial heat that needs to be cooled. To reduce energy consumption in data centers, more efficient cooling systems are needed.

[0004] Heat pipes and thermosiphons are devices that transfer energy from a high-temperature evaporator section to a low-temperature condenser section through the evaporation and condensation of a closed volume of refrigerant. The refrigerant is transferred from the condenser section to the evaporator section by gravity or capillary force. Heat pipes have been used as indirect energy savers for data center cooling. In these devices, for example, hot air from the data center is recirculated through the evaporator section of the heat pipe, where the closed refrigerant is evaporated by the heat from the data center, thus cooling the data center air. Cooler ambient air is blown to the condenser section of the heat pipe, where the refrigerant vapor is condensed, and the heat from the data center is expelled. In some applications, the ambient air is first adiabatically cooled by an evaporative cooler before passing through the condenser section of the heat pipe to provide a lower radiator temperature. In another configuration, the condenser section of the heat pipe can be sprayed with water while ambient air passes through its surface, thereby providing a radiator temperature close to the ambient wet-bulb temperature.

[0005] In these implementations, heat pipes and thermosiphons are limited by ambient temperature conditions and may not provide sufficient heat dissipation when ambient temperatures are high. One solution to this limitation is a pumped refrigerant system that combines a mechanical cooling system, such as a direct expansion (DX) cooling system (active mode), with an approximate passive mode similar to thermosiphon operation. These systems include a pump that moves liquid refrigerant from the condenser to the evaporator. By using the pump, the refrigerant flow can be controlled independently of the pressure drop in the evaporator and condenser, as well as the effects of gravity. This approach is approximately passive because the pump requires only a small amount of power to transfer a large amount of heat. In a pumped refrigerant system, the pump can be shut off, and the compressor and expansion valve can be integrated into the system refrigerant flow via operating valves to allow the system to function as a direct expansion cooling system.

[0006] System design constraints in direct expansion systems typically require moderate pressure drops in the evaporator and condenser sections to provide a uniform refrigerant flow through multiple parallel evaporator and condenser loops. It is precisely because of these pressure drops that a pump is needed to circulate the refrigerant fluid when the system operates in near-passive mode. Since the refrigerant loop includes the compressor system, the refrigerant volume also needs to include oil for lubrication. Various design and operational constraints exist for pumped refrigerant systems, such as best practices for refrigerant velocity (i.e., so-called "oil management") to ensure that oil does not become trapped in the various pipe lengths of the system and reliably returns to the required compressor. These oil management constraints become problematic when operating in pumped mode (near-passive mode) because the flow paths and velocities in pumped mode may not be consistent with the rules required in DX mode. For example, the volume of refrigerant needed for proper operation within the system may also differ significantly between pumped mode and DX mode due to different available superheat and subcooling levels, as well as coil overflow levels.

[0007] Therefore, there is a need for cooling systems that further reduce energy consumption, as well as cooling systems that do not require oil management in passive or near-passive modes. Summary of the Invention

[0008] In one aspect, the present invention relates to a cooling system comprising an evaporator containing a primary cooling medium, a passive condenser, and a heat exchanger. The evaporator is configured to receive a process fluid and, upon receiving the process fluid, change the phase of the primary cooling medium from liquid to gas. The passive condenser has an outer surface and is fluidly coupled to the evaporator. The passive condenser is configured to have an airflow guided on its outer surface. When the airflow is guided on the outer surface of the passive condenser, the passive condenser is configured to (i) receive the gaseous primary cooling medium from the evaporator, (ii) transfer heat from the primary cooling medium, (iii) change the phase of the primary cooling medium from gas to liquid, and (iv) supply the liquid phase of the primary cooling medium to the evaporator. The heat exchanger is fluidly coupled to the evaporator and is configured to have a secondary cooling medium selectively supplied thereto. When the secondary cooling medium is supplied to the heat exchanger, the primary cooling medium in the gaseous phase is switched from being received by the passive condenser to being supplied to the heat exchanger without operating any valves located between the evaporator and the passive condenser, or between the evaporator and the heat exchanger. The heat exchanger is configured to (i) receive the gaseous primary cooling medium from the evaporator, (ii) transfer heat from the primary cooling medium, (iii) change the phase of the primary cooling medium from gas to liquid, and (iv) supply the liquid-phase primary cooling medium to the evaporator. When the heat exchanger does not accept the secondary cooling medium, it does not supply the liquid-phase primary cooling medium to the evaporator. The primary cooling medium circulates between the evaporator and the passive condenser, and between the evaporator and the heat exchanger, by natural circulation and gravity, without the need for pumps to circulate the primary cooling medium in its flow path between the heat exchanger and the evaporator, and between the passive condenser and the evaporator.

[0009] In another aspect, the present invention relates to a method for cooling a process fluid. The method includes guiding the process fluid through an evaporator to transfer heat from the process fluid to a primary cooling medium contained in the evaporator and to change the primary cooling medium from a liquid phase to a gas phase, and selectively utilizing one of a heat exchanger and a passive condenser to change the primary cooling medium from a gas phase to a liquid phase. Each of the heat exchanger and the passive condenser is coupled to the evaporator to receive the gaseous primary cooling medium from the evaporator and to supply the liquid primary cooling medium to the evaporator. The method also includes circulating the primary cooling medium between the evaporator and at least one of the heat exchanger and the passive condenser by natural circulation. One of the heat exchanger and the passive condenser is selected to not operate any valves in the connection between the evaporator and the passive condenser, or in the connection between the evaporator and the heat exchanger.

[0010] These and other aspects, objects, features, and advantages of the invention will become apparent from the following detailed description of illustrative embodiments thereof, which will be read in conjunction with the accompanying drawings. Attached Figure Description

[0011] Figure 1This is a front view of a data center using a cooling system according to a preferred embodiment of the present invention.

[0012] Figure 2 It is along Figure 1 The middle 2-2 line is cut off Figure 1 The diagram shows a cross-sectional view of the cooling system.

[0013] Figure 3 This is a schematic diagram of an airflow cooling assembly operating in passive mode according to a preferred embodiment of the present invention.

[0014] Figure 4 yes Figure 3 The diagram shows the airflow cooling assembly operating in active mode.

[0015] Figure 5A Showing what can be used Figure 3 The microchannel cooling coil of the airflow cooling assembly shown. Figure 5B It is along Figure 5A The line 5B-5B is cut off. Figure 5A The image shows a cross-sectional view of the microchannels in the microchannel cooling coil.

[0016] Figure 6 This is a schematic diagram of a cooling system, which has... Figure 3 The diagram shows multiple loops of an airflow cooling assembly operating in passive mode.

[0017] Figure 7 yes Figure 6 The diagram shows a cooling system in which one of the airflow cooling component loops operates in active mode.

[0018] Figure 8 yes Figure 6 The diagram shows a cooling system in which all airflow cooling component loops operate in active mode.

[0019] Figure 9 It is a description Figure 4 The flowchart shows the operation method of the cooling system.

[0020] Figure 10 This is a schematic diagram of an air handling unit of a cooling assembly according to a preferred embodiment of the present invention.

[0021] Figure 11 Is with Figure 10 A schematic diagram of a condenser unit used in conjunction with the air handling unit shown.

[0022] Figure 12 This is a schematic diagram of a cooling assembly according to a preferred embodiment of the present invention.

[0023] Figure 13A and 13B Through with Figure 12 The example shown is a server rack cooled by an immersion cooling system used in conjunction with cooling components. Figure 13A This illustrates a single-phase immersion cooling system. Figure 13B This illustrates a two-phase immersion cooling system.

[0024] Figure 14 This is a schematic diagram of an airflow cooling assembly operating in passive mode according to a second preferred embodiment of the present invention.

[0025] Figure 15 yes Figure 14 The diagram shows the airflow cooling assembly operating in active mode.

[0026] Figure 16 This is a schematic diagram of an alternative configuration of the airflow cooling assembly in the second embodiment, which operates in passive mode.

[0027] Figure 17 yes Figure 16 The diagram shows the airflow cooling assembly operating in active mode.

[0028] Figure 18 yes Figure 16 A schematic diagram of another configuration of the airflow cooling assembly shown.

[0029] Figure 19 This is a schematic diagram of a cooling system, which has... Figure 14 and Figure 15 The circuit of the airflow cooling assembly shown Figure 18 The circuit of the airflow cooling assembly is shown.

[0030] Figure 20 This is a schematic diagram of another cooling system operating in near-passive mode.

[0031] Figure 21 yes Figure 20 The diagram shows the cooling system operating in active mode. Detailed Implementation

[0032] Figure 1 A data center 100 is shown having a cooling system 110 according to a preferred embodiment of the present invention. Figure 2 It is along Figure 1A cross-sectional view of the cooling system 110 taken from line 2-2. Although the cooling system 110 is shown and described with reference to data center 100, the cooling system 110 is not limited to this application and can be used for other suitable air-cooling applications. Electronic components such as servers can be mounted on racks 102, and in data center 100, these racks 102 can be arranged in rows, forming aisles 104, 106 between them. One aisle 104 is a cold aisle, and the other aisle 106 is a hot aisle. Cooling supply air 112 from the cooling system is directed into the cold aisle 104. The supply air 112 then passes through the racks from the cold aisle 104 and enters the hot aisle 106. As the air passes through the racks 102, it draws heat from the electronic components, cools them, and causes hot air to enter the hot aisle 106. This air is then directed back to the cooling system 110 as hot return air 114. Air supply fan 116 is used to draw return air 114 from data center 100, pass the return air 114 through cooling system 110, cool the return air 114 at cooling system 110, and then return the now cooled return air 114 to data center 100 as supply air 112. The portion of cooling system 110 through which the return air 114 flows, is cooled, and returns as supply air 112 is referred to herein as internal air processor 132.

[0033] Cooling system 110 uses at least one airflow cooling assembly to cool return air 114. The airflow cooling assembly described in the following embodiments may also be referred to as an airflow cooling assembly loop or loop. Figure 3 and Figure 4 An airflow cooling assembly 200 according to a first embodiment of the present invention is shown. The airflow cooling assembly 200 has two modes: a passive mode and an active mode. The passive mode can also be referred to as a saving mode. Figure 3 This is a schematic diagram of the airflow cooling assembly 200 in passive mode. Figure 4 This is a schematic diagram of the airflow cooling assembly 200 in active mode. The airflow cooling assembly 200 incorporates the efficiency of a thermosiphon, which has the ability to provide active cooling when the available ambient free-cooling heat sink is not at a sufficiently low temperature to provide adequate heat dissipation. This is achieved by including two independent condensers 214, 216 in the loop 200, one (condenser 214) for passive mode and the other (condenser 216) for active mode.

[0034] The airflow cooling assembly 200 circulates the main cooling medium 202 through the main coolant circuit 210. The main cooling medium 202 circulates through the main coolant circuit 210 via natural circulation and gravity circulation, eliminating the need for pumps and compressors. The main cooling medium 202 can be any suitable refrigerant that changes the phase from liquid to gas. As will be discussed further below, the main coolant circuit 210 requires no moving parts. As a result, for example, the range of refrigerants suitable as the main cooling medium 202 is greatly expanded compared to direct expansion (DX) cooling systems, and suitable refrigerants include natural refrigerants such as water.

[0035] The main coolant circuit 210 includes an evaporator 212, within which the main cooling medium 202 is contained. In this embodiment, the evaporator 212 is a coil, and preferably a single-pass overflow coil. Any suitable coil can be used, including, for example, microchannel coils, such as those described further below, or finned tube coils. In passive and active modes, return air 114 is directed by a blower fan 116 to the outer surface of the evaporator 212. As the hot return air 114 passes over the outer surface of the evaporator 212, it causes the main cooling medium 202 in the evaporator 212 to evaporate. The phase change of the main cooling medium 202 from liquid phase 204 to gas phase (or vapor phase) 206 cools the return air 114, allowing it to return to the data center 100 as cold supply air 112. The vapor 206 then rises through vapor line 222 to one of the two condensers 214, 216.

[0036] In passive mode, such as Figure 3 As shown, vapor 206 travels to the passive condenser 214 in the main coolant circuit 210. Like the evaporator 212, the passive condenser 214 in this embodiment is a coil, preferably a single-pass coil, and any suitable coil can be used, including, for example, microchannel coils, such as those further described below, or tube coils (finned and unfinned). A scavenging fan 120 (see...) Figure 1 and Figure 2 The scavenging air 118 is drawn over the outer surface of the passive condenser 214. In this embodiment, the scavenging air 118 is ambient air drawn in from the outdoor environment surrounding the cooling system 110. As the scavenging air 118 passes over the passive condenser 214, the heat contained in the main cooling medium 202 within the passive condenser 214 is released into the scavenging air 118, condensing the vapor 206 into liquid 204. Gravity then causes the main cooling medium 202, now in the liquid phase 204, to flow downwards along the liquid refrigerant line 224 and return to the evaporator 212. The scavenging air 118 is discharged to the outside via the scavenging fan 120.

[0037] When ambient air conditions are insufficient to cool the return air 114 to the conditions (e.g., temperature) required for the supply air 112, the airflow cooling assembly 200 can... Figure 4 The system operates in the active mode shown. In active mode, the vapor 206 of the primary cooling medium 202 condenses in the active condenser 216. In this embodiment, the active condenser 216 may also be referred to herein as a heat exchanger (HX). In the active condenser 216, heat is transferred from the primary cooling medium 202 to the secondary cooling medium 208 of the secondary cooling system 230. The secondary cooling medium 208 can be any suitable refrigerant medium, including, for example, cooling (or cooling) water or vapor-changing refrigerant used in direct expansion cooling systems. The active condenser 216 can be any suitable heat exchanger, including, for example, a plate heat exchanger, a coaxial heat exchanger, or a shell-and-tube heat exchanger. As the heat of the primary cooling medium 202 is dissipated by the secondary cooling medium 208, the primary cooling medium 202 condenses from vapor 206 into liquid 204. Similar to the passive condenser 214, gravity then causes the primary cooling medium 202, now in the liquid phase 204, to flow down the liquid refrigerant line 224 and back to the evaporator 212.

[0038] In this embodiment, the secondary cooling system 230 is a direct expansion (DX) cooling system 230 using a conventional refrigeration cycle, and the secondary cooling medium 208 is any suitable refrigerant used in such systems. The direct expansion cooling system 230 includes a compressor 232 to increase the pressure and temperature of the refrigerant 208 before it is cooled in the condenser 234. In this embodiment, the condenser 234 of the direct expansion cooling system 230 may also be cooled by scavenging gas 118 (see...). Figure 1 and Figure 2 The refrigerant 208 then passes through the expansion valve 236, reducing its pressure and temperature, before flowing into the active condenser 216.

[0039] Even in active mode, the airflow cooling assembly 200 operates without the need for pumps, oil, or compressors in the main coolant circuit 210. The airflow cooling assembly 200 operates even without valves to switch between modes. Instead, the vapor 206 of the main cooling medium 202 naturally travels to the cooler of the two condensers 214, 216 for condensation. Therefore, by activating the auxiliary cooling system 230 to cool the active condenser 216, the airflow cooling assembly 200 automatically switches from passive to active mode (assuming the temperature in the active condenser 216 is lower than the temperature in the passive condenser 214), and by deactivating the auxiliary cooling system 230, the circuit 200 returns to passive mode. The controller 240 can be used to activate and deactivate the auxiliary cooling system 230, as described below. Another advantage of the airflow cooling assembly 200, due to the absence of moving parts, is the elimination of oil, allowing the main cooling medium 202 to flow outside the refrigerant velocity typically required to entrain and maintain oil circulation within the main circuit 210.

[0040] Although the condensers 214 and 216 of the airflow cooling assembly 200 are in Figure 3 and Figure 4 The condensers 214 and 216 are shown in parallel, but they can also be arranged in series, so that the outlet of one of the active or passive condensers 214 and 216 is located upstream of and supplies the inlet of the other condenser 214 and 216. The main coolant circuit 210 may also include a trap 218 and / or a check valve 220 after each of the condensers 214 and 216. The trap 218 and check valve 220 prevent the main cooling medium 202 from flowing backward through condensers 214 and 216 that are not currently operating in a given mode. Other suitable valves or methods can be used to prevent backflow. Such valves or traps are optional because including the trap 218 and check valve 220 increases the pressure drop in the system, thereby inhibiting the natural circulation of the main cooling medium 202 in the main circuit 210.

[0041] Vent lines 226 may be located after the trap 218 of each condenser 214, 216 and connected to the inlet of the respective condenser 214, 216. These vent lines 226 allow any gas entrained in the liquid 204 of the main cooling medium 202 to escape to the vapor side of the loop, thereby helping the liquid flow to the evaporator 212 by gravity.

[0042] Bubbles formed during the evaporation of the main cooling medium 202 in evaporator 212 may carry liquid as they rise in the channels of evaporator 212. The entrained liquid return line 228 can be located at the outlet of evaporator 212 and connected to the inlet manifold of evaporator 212, allowing the entrained liquid to return to the evaporator inlet manifold without having to flow back into the boiling flow path in evaporator 212.

[0043] Because the airflow cooling assembly 200 of this embodiment operates in a natural circulation manner with the aid of gravity, the evaporator 212 is positioned below the level of the condensers 214, 216 to allow the main cooling medium 202 (liquid 204) that is condensed by gravity to return to the evaporator 212. It is desirable to keep the main cooling medium 202 in the liquid phase 204 along the entire length of the evaporator 212. The height of the condensers 214, 216 above the evaporator is therefore preferably high enough to provide sufficient head from the main cooling medium 202 in the liquid phase 204 to overcome the pressure drop of the evaporator 212. Although the evaporator 212 may be flush with the liquid and vapor headers of the evaporator 212 located in the same horizontal plane, the evaporator 212 may also preferably be inclined at an angle α relative to the horizontal plane, with the vapor header of the evaporator 212 higher than the liquid header to facilitate vapor discharge. The passive condenser 214 may also preferably be inclined at an angle β relative to the horizontal plane, with the liquid header of the passive condenser 214 lower than the vapor header to facilitate condensate flow by gravity. The tilt angle (angle β) of the passive condenser is preferably sufficient to provide an unobstructed discharge path and eliminate the backflow of the main cooling medium 202 in the passive condenser 214.

[0044] As described above, the evaporator 212 and the passive condenser 214 can be microchannel coils. Figure 5A A microchannel coil 300 is shown, which can be used as the evaporator 212 and passive condenser 214 in this embodiment. Using the microchannel coil 300 has many advantages, including, for example, the high internal surface area of ​​the microchannel coil 300 facilitates heat transfer. Furthermore, compared to, for example, a finned tube coil, the microchannel coil 300 significantly reduces the volume of the primary cooling medium 202 required in the primary coolant circuit 210. This reduction in the volume of the primary cooling medium 202 is beneficial for many reasons, including cost reduction and a reduction in potential greenhouse gas emission sources when using certain refrigerants. The microchannel coil 300 has a liquid side 302 and a vapor side 304. Figure 5A As shown, when the microchannel coil 300 is used as an evaporator 212, the flow of the main cooling medium 202 is from the liquid side 302 to the vapor side 304 (from left to right), while when the microchannel coil 300 is used as a passive condenser 214, the flow is reversed (from right to left).

[0045] The microchannel coil 300 has a liquid manifold 310 and a vapor manifold 320 connected by multiple microchannel extruders 330. Along Figure 5A The cross-section of the microchannel extruder cut from line 5B-5B is shown in the figure. Figure 5B As shown. The microchannel extruder 330 has an outer surface 332 and includes a plurality of microchannels 334, 336. Figure 5B As shown, the airflow is along direction A (in Figure 5AThe microchannels (both inside and outside the page) are guided on the outer surface 332 of the microchannel extruder 330. The main cooling medium 202 flows through the microchannels 334 and 336. Each of the multiple microchannel extruders 330 is mechanically brazed to aluminum fins 340 positioned between the microchannel extruders 330 to facilitate heat transfer.

[0046] The liquid manifold 310 includes a liquid connection 312 that connects the liquid manifold 310 to the liquid refrigerant line 224. Similarly, the vapor manifold 320 also includes at least one vapor connection 322 that connects the vapor manifold 320 to the vapor line 222. Having multiple vapor connections 322 may be advantageous when using a microchannel coil as the evaporator 212. In this embodiment, three vapor connections 322 are shown. Using multiple vapor connections 322 reduces the vapor back pressure in the vapor manifold 320 and promotes natural circulation in the main refrigerant circuit 210. When multiple vapor connections 322 are used for the evaporator 212, a corresponding number of vapor connections 322 can be used for both the passive condenser 214 and the active condenser 216, resulting in multiple vapor lines 222 connected to the vapor connections 322. Another consideration for steam pipe 222 and steam connection 322 is the use of large-diameter pipes, thereby reducing the back pressure of the steam and promoting natural circulation in the main coolant circuit 210. For example, when R410a is used as the main cooling medium 202, the dimensions of steam pipe 222 can be set to allow the velocity of the main cooling medium 202 in the gas phase 206 to be preferably less than 1000 fpm, more preferably less than 600 fpm. These manifold design features are not limited to microchannel coils but can also be applied to other evaporators and condensers, including finned tube coils.

[0047] As described above, the cooling system 110 of the present invention may include a plurality of airflow cooling component circuits 200. For example, Figure 1 and Figure 2 The cooling system 110 shown has four airflow cooling component loops 200. In the following discussion of the multiple loops, the same references used above will be used. Figure 3 and Figure 4 The same reference numerals are discussed, and letters are added after the reference numerals to indicate different circuits. For example, the letter "a" is attached to a component of the first airflow cooling assembly circuit 200a, the letter "b" is attached to a component of the second airflow cooling assembly circuit 200b, and so on.

[0048] A pair of evaporators 212a, 212b are arranged in parallel with another pair of evaporators 212, 212d relative to the airflow of return air 114. Evaporators 212a, 212b, 212c, 212d within each pair are arranged in series. In the first pair, return air 114 is directed through the first evaporator 212a of the pair before being directed through the second evaporator 212b. Similarly, in the second pair, return air 114 is directed through the first evaporator 212c of the pair before being directed through the second evaporator 212d. Corresponding passive condensers 214a, 214b, 214c, 214d are similarly arranged in pairs (first pair 214a, 214b and second pair 214c, 214d), with the first pair connected in parallel to the second pair, and each condenser in the pair arranged in series. In the first pair, the scavenging gas 118 is guided through the first condenser 214a of the pair before being guided through the second condenser 214b of the pair, and in the second pair, it is guided through the first condenser 214c of the pair before being guided through the second condenser 212d of the pair.

[0049] exist Figure 1 and Figure 2 In one configuration of the cooling system 110 shown, the cooling system 110 can be 32 feet long ( Figure 1 ) and 10 feet 2 inches wide ( Figure 2 The footprint is enclosed, with a total height (excluding the scavenging fan 120) of 12 feet 8 inches. In this example, 88 square feet of coil area (evaporator 212) is available for the cooling process. A design flow rate of 44,000 scfm and 348 kW is possible at a nominal 500 fpm through evaporator 212, resulting in a peripheral watt capacity of 107 kW / m. The coil length of evaporator 212 can be easily extended to further increase airflow, thereby increasing the capacity of cooling system 110 without increasing its width, thus enabling a larger peripheral watt capacity. Cooling system 110 can be divided into two parts: an internal air handler 132 and a condenser unit 134. Figure 1 and Figure 2 As shown, evaporators 212a, 212b, 212c, 212d and supply air fan 116 are located in the internal air processor 132. The remaining components of the airflow cooling assembly 200, including subsystem 230 and scavenging fan 120, are located in the condenser unit 134. Figure 1 In the diagram, the condenser unit 134 is shown adjacent to the internal air processor 132, but it can be located in any suitable location, including, for example, on the roof of the data center 100 (e.g., on the top of the building that houses the rack 102).

[0050] Any suitable configuration of multiple airflow cooling component loops 200 can be used. For example, Figure 6 This is a schematic diagram of another arrangement of a cooling system 110 having multiple airflow cooling component circuits 200. Figure 6 In the configuration shown, the cooling system 110 has four airflow cooling component loops 200. The evaporators 212e, 212f, 212g, and 212h of each loop 200 are arranged in series with respect to the return air 114; however, as described above, the evaporators 212e, 212f, 212g, and 212h can also be arranged in parallel. The return air is first guided through the evaporator 212e of the first loop, then sequentially through the evaporator 212f of the second loop, the evaporator 212g of the third loop, and the evaporator 212h of the fourth loop. Figure 6 In the configuration shown, all four passive condensers 214e, 214f, 214g, and 214h are arranged in parallel with respect to scavenging gas 118. However, as mentioned above, the passive condensers 214e, 214f, 214g, and 214h can also be arranged in series. Each condenser 234e, 234f, 234g, and 234h for the auxiliary cooling system 230 (a direct expansion cooling system in this embodiment) is arranged in series with the corresponding passive condensers 214e, 214f, 214g, and 214h in the scavenging gas 118.

[0051] Typically, the internal temperature of each airflow cooling component loop 200 will be isothermal, but each of the four airflow cooling component loops 200 will operate at different temperatures and pressures. The temperature of the main cooling medium 202 in the first loop will be the hottest because the air entering the evaporator 212e of the first loop will be the warmest (the initial temperature of the return air 114). The air entering the evaporators 212f, 212g, and 212h subsequently becomes colder than the air in the previous loops due to the cooling generated by the previous loops. When the ambient air temperature is lower than the temperature of each airflow cooling component loop 200, energy in the main cooling medium can be transferred from the return air 114 to the scavenging air 118 in passive mode, and all four loops operate in passive mode, as... Figure 6 As shown.

[0052] Each loop can be selectively operated in either passive or active mode. Figure 7 The operation of the cooling system 110 is shown, with the fourth circuit in active mode and the other three circuits in passive mode. Figure 8This shows that all four loops are in active mode. Controller 240 can be used to operate cooling system 110. In this embodiment, controller 240 is a microprocessor-based controller that includes a processor 242 for performing various functions discussed further below and a memory 244 for storing various data. Controller 240 may also be referred to as a CPU. In one embodiment, control of cooling system 110 can be achieved through a series of instructions stored in memory 244 and executed by processor 242.

[0053] The controller 240 is communicatively coupled to a temperature sensor (“TS”) 122. In this embodiment, the temperature sensor 122 is used to monitor the temperature of the supply air 112, thereby allowing the temperature sensor 122 to send (and the controller 240 to receive) the temperature of the supply air 112. The loop sensor 250 can also be used to measure various parameters of each airflow cooling assembly loop 200. For example, the loop sensor 250 can use the temperature sensor (“TS”) 252 and the pressure sensor (“PS”) 254 respectively to measure the temperature and pressure of the main cooling medium 202 in each loop. Preferably, the temperature and pressure sensors 252 and 254 are located in the liquid refrigerant line 224 to monitor the temperature and pressure of the liquid phase 204 of the main cooling medium 202.

[0054] The controller 240 can also be communicatively connected to other components of the cooling system 110 and used to control these components. For example, the supply air fan 116 and the scavenging air fan 120 can be communicatively connected to the controller 240, so the controller 240 can be used to direct the return air 114 and the scavenging air 118 to the evaporators 212e, 212f, 212g, 212h and the condensers 214e, 214f, 214g, 214h respectively, and to increase or decrease the airflow. The controller 240 can also be communicatively connected to the auxiliary cooling systems 230e, 230f, 230g, 230h of each loop, and is used to turn the auxiliary cooling systems 230e, 230f, 230g, 230h on or off (start or stop).

[0055] Figure 9 It is a flowchart showing how to control Figure 6 and Figure 7An example of the cooling system 110 shown. In step S405, controller 240 directs return air 114 to evaporators 212e, 212f, 212g, 212h. Supply air temperature sensor 122 is used to measure the temperature of supply air 112, and in step S410, controller 240 receives the temperature of supply air 112. Controller 240 then compares the measured temperature of supply air 112 with a setpoint in step S415. The setpoint can be provided to controller 240 using any suitable method or device. For example, controller 240 can be communicatively coupled to a user interface through which a user can provide the desired temperature of supply air 112, and controller 240 can receive the desired temperature of supply air 112 as the setpoint. If the temperature of supply air 112 is equal to the setpoint (or within an appropriate operating range of the setpoint), control system 240 returns to step S405 to continue monitoring the temperature of supply air 112.

[0056] If the temperature of the supply air 112 is too low (below the setpoint or operating range), the controller 240 checks in step S420 whether any of the loops 200 are operating in active mode. For example, when the controller starts or stops the auxiliary cooling system 230 for the loop, the controller 240 can store the loop mode in memory 244. The controller 240 can then query memory 244 to determine the mode of any loop. The controller 240 can store other suitable parameters in memory 244, such as the flow rate of scavenging air 118 (e.g., the speed and number of operating scavenging fans 120), and the controller 240 can check and change these parameters in a similar manner. If the controller 240 determines (in step S420) that no loop 200 is in active mode, the controller 240 reduces the airflow of scavenging air 118 in step S425 to continue monitoring the temperature of the supply air 112 before returning to step S405. If any changes are made to the cooling system 110 in step S425 (or any other steps discussed herein), the controller 240 may delay monitoring the temperature of the supply air 112 to allow the changes to affect the temperature of the supply air 112.

[0057] If, in step S420, the controller 240 determines that at least one loop 200 is in active mode, then in step S430, the controller 240 disables the auxiliary cooling system 230 in one of the loops 200. For example, as Figure 7 As shown, the fourth loop operates in active mode. If the supplied air temperature is too low in this configuration, the controller 240 will disable the auxiliary cooling system 230h of the fourth loop, returning the fourth loop to passive mode, as shown. Figure 6As shown. Preferably, controller 240 disables the secondary cooling system 230 of the loop operating in active mode, where the evaporator 212 is located upstream relative to the return air 114. Controller 240 then returns to step S405 to continue monitoring the temperature of the supply air 112.

[0058] If the temperature of the supply air 112 is too high (above the setpoint or operating range), the controller 240 first checks in step S435 whether the airflow of the scavenging air 118 can be increased. If the airflow of the scavenging air 118 can be increased (the scavenging air 118 is not at its maximum airflow), the controller 240 increases the airflow of the scavenging air 118 in step S440 before returning to step S405. The controller 240 can increase the airflow of the scavenging air 118 by any suitable means, including, for example, by increasing the speed of the scavenging fan 120. If the airflow of the scavenging air 118 cannot be increased (the scavenging air 118 is at its maximum airflow), then in step S445, the controller 240 checks whether all loops 200 are in active mode. If all loops 200 are in active mode, such as... Figure 8 As shown, cooling system 110 operates at its maximum cooling capacity, and controller 240 returns to step S405. If at least one loop is in passive mode, controller 240 will activate the auxiliary cooling system 230 of one of loops 200 in step S450. For example, as Figure 6 As shown, if all loops are operating in passive mode, controller 240 will activate the auxiliary cooling system 230 of one of the loops 200, such as the auxiliary cooling system 230h of the fourth loop. Preferably, controller 240 will activate the auxiliary cooling system 230 of the loop operating in passive mode, whose evaporator 212 is located downstream of the return air 114. Controller 240 then returns to step S405 to continue monitoring the temperature of the supply air 112.

[0059] For data center cooling systems, an efficiency of 65% or higher is typically desired in energy-saving mode (passive mode in this embodiment). In passive mode, the refrigerant is at nearly the same pressure throughout the main coolant loop 210, and the internal temperature is isothermal. Based on energy balance requirements, if the heat transfer constraints of the passive condenser 214 and evaporator 212 are the same (the airflow on the outer surfaces of the condenser 214 and evaporator 212 is the same, and the surface characteristics of the outer surfaces of the condenser 214 and evaporator 212 are the same), the refrigerant will be present at a temperature equal to the average temperature of the inlets of the evaporator 212 and the passive condenser 214, and in a non-ideal case, the net efficiency of a single loop 200 will be less than 50%. However, with unbalanced airflow on the outer surfaces of the condenser 214 and evaporator 212, heat exchange efficiency can be achieved when measured at a evaporator size greater than 50%.

[0060] By using multiple loops 200 with air flowing counter-currently to the main coolant loop 210, the efficiency of each loop will have an additive effect, and an efficiency greater than that of a single loop can be achieved. For example, if two loops 200 are used, each with an efficiency of 50%, where scavenging air 118 flows in series through the first loop and then through the second loop, and return air 114 flows in the opposite direction (through the second loop and then through the first loop), an efficiency greater than 70% can be achieved. However, if the efficiency of a single loop 200 drops to 39%, three loops 200, instead of two, can be positioned in counter-current flow to achieve a net efficiency greater than 70%. The calculations above use scavenging air 118 delivered at 10000 cfm at a temperature of 70°F and return air 114 delivered at 5000 cfm at a temperature of 100°F.

[0061] The following examples (cases 1 to 6) were used to evaluate the efficiency of a single loop 200. The results of these evaluations are shown in Table 1 below. In the following cases, an unbalanced airflow was used, where the scavenging fan 120 was selected to provide a scavenging air 118 to return air 114 airflow ratio of at least 2:1, based on the nominal 500 fpm surface velocity of the return air 114 on the evaporator 212. However, in the following experimental cases, a flow ratio closer to 2.2:1 was achieved, where the total airflow through the evaporator 212 was 5000 scfm, while the total airflow through the passive condenser 214 was 11000 scfm. The surface velocity through the passive condenser 214 was 500 fpm.

[0062] Case 1 (Case 1) uses finned tube (“FT”) coils for evaporator 212 and passive condenser 214. Evaporator 212 has an overflow two-row, one-way coil, while passive condenser 214 has a three-row, one-way coil. In a typical tube arrangement, both coils use half-inch tubes with 10 fins per inch. Each coil is 5 feet long. Both evaporator 212 and passive condenser 214 are mounted at a 15-degree angle relative to the horizontal plane to facilitate vapor discharge and gravity flow of condensate. The lower end of passive condenser 214 is mounted 2 feet above the upper discharge port of evaporator 212. The vapor and liquid lines between the coils are enlarged, using 1 1 / 8-inch tubes for liquid refrigerant line 224 and 2 1 / 8-inch tubes for vapor line 222, thus not restricting refrigerant flow and affecting final performance. R410a is used as the refrigerant.

[0063] The second scenario (Scenario 2) is the same as the first scenario, but uses an overflow microchannel coil (MC) instead of a finned tube coil as the evaporator 212. Using a microchannel coil significantly reduces the required refrigerant charge because the internal volume of the microchannel coil is significantly reduced (by more than 47%) compared to a half-inch tube coil. Each microchannel extrusion 330 has a width of 38 mm and contains 28 microchannels 334, 336. The 26 internal microchannels 334 have a width of 0.92 mm, and the two external microchannels 336 (see...) Figure 5B The radius of the rounding of the microchannel extruder 330 is 0.55 mm, and the total width is 0.94 mm. The total height of the microchannel extruder 330 is 1.8 mm, and the outer wall thickness t is 0.35 mm. The inner wall thickness of the microchannel 334 is 0.40 mm. 67 microchannel extruders 330 are used, each with a length of 1.57 m. A single liquid connector 312 with an outer diameter of 22.2 mm and a single vapor connector 322 with an outer diameter of 25 mm are used.

[0064] The third scenario (Scenario 3) is the same as the second scenario, but a microchannel coil (MC) is used instead of a finned tube coil as the passive condenser 214. The microchannel coil of the passive condenser 214 is designed to be similar to the microchannel coil of the evaporator 212 (as described above in Scenario 2), but the passive condenser 214 uses 100 microchannel extrusions 330, each extrusion having a length of 1.57 m.

[0065] Case 4 is the same as Case 3, but uses three vapor pipes 222 and vapor connection 322 instead of one (MC Mod). The configurations of loop 200 in Cases 3 and 4 were also evaluated in cases with a higher temperature difference between evaporator 212 and passive condenser 214 (Case 5 and 6, respectively). The temperature difference between evaporator 212 and passive condenser 214 in Cases 5 and 6 was increased by increasing the temperature of return air 114 by 20°F to 25°F, relative to Cases 3 and 4. Table 1 below shows the results for each case, where "Evap" refers to evaporator 212 and "Cond" refers to passive condenser 214.

[0066] Table 1

[0067]

[0068] As can be seen from Table 1 above, by comparing Case 1 and Case 2, using a microchannel coil instead of a finned tube coil in evaporator 212 had the most significant impact on performance, increasing the heat exchange efficiency from 34% to 57%. Changing the passive condenser 214 to a microchannel coil had almost no impact on the performance results under normal conditions (compare Case 2 and Case 3). Modifying evaporator 212 and passive condenser 214 to have additional vapor connections 322 resulted in a 3% efficiency gain under normal conditions (compare Case 3 and Case 4). As the temperature difference between evaporator 212 and passive condenser 214 increased, the efficiency decreased (compare Case 3 and 4 with Case 5 and 6 respectively), but having multiple vapor connections 322 resulted in a smaller efficiency decrease, and the total power transfer increased significantly to close to 50 kW.

[0069] Using the characteristics of R410a and its known heat transfer rate, the mass flow rate of the main cooling medium 202 can be calculated based on the specific heat of the vapor and liquid. In the case of the microchannel evaporator 212, the heat flux limit is in the range of 20 kW. Using the enthalpy difference between the liquid and vapor of R410a, a mass flow rate of 387 kg / hr and a heat transfer rate of 5.88 m³ / h are calculated. 3 The flow rate is 4.2 m / s. Using a single 7 / 8 inch tube with an inner diameter, the gas velocity is 4.2 m / s. Adding two additional vapor connections to the coil increases the capacity by 50 kW and generates a velocity of 3.1 m / s. Therefore, for practical purposes, when using R410a, the pipe connection size is preferably below approximately 4 m / s for the maximum velocity. For a heat exchange rate of 50 kW, the vapor velocity inside the microchannel extruder 330 is 2.1 m / s. The dimensions for other refrigerants will vary depending on their density and viscosity, but can be determined experimentally.

[0070] In each of cases 1 through 6, a plate heat exchanger is used as the active condenser 216. The active condenser 216 is arranged in parallel with the passive condenser 214, and cooling water is used as the secondary cooling medium 208. In active mode, efficiency and maximum power data closely simulate air-to-air data, confirming the superiority of the microchannel evaporator 212 over the finned tube evaporator 212, and the increase in total capacity after adding additional manifold connections to the microchannels for steam transport.

[0071] Another cooling system 110, such as Figure 10 and Figure 11 As shown. Figure 10 and Figure 11 The features and components of the cooling system 110 shown above are the same as those above. Figure 1-9 Similar to what is discussed in the text. Figure 10 and Figure 11The same reference numerals are used to describe components that are the same as or similar to those described above, and detailed descriptions of these components are omitted in the following discussion. Figure 10 The internal air processor 132 is shown. Figure 11 The condenser unit 134 of the cooling system 110 of this embodiment is shown.

[0072] and Figure 1 The cooling system 110 shown is the same. Figure 10 and Figure 11 The cooling system 110 shown includes a plurality of evaporators 212, which in this embodiment are four evaporators 212i, 212j, two first evaporators 212i, and two second evaporators 212j. The first evaporators 212i are arranged in parallel with each other relative to the return air 114 and are connected to a first common vapor line 262 and a first common liquid refrigerant line 266. Similarly, the second evaporators 212j are arranged in parallel with each other relative to the return air 114 and are connected to a second common vapor line 264 and a second common liquid refrigerant line 268. As described above, each of the first common liquid refrigerant line 266 and the second common liquid refrigerant line 268 is analogous to a vapor line 222 and a liquid refrigerant line 224, respectively. Each first evaporator 212i is arranged in series with one of the second evaporators 212j relative to the return air 114. The return air 114 is directed through the first evaporators 212i before being directed through the second evaporators 212j.

[0073] Figure 11 The condenser unit 134 shown includes four loops: a first loop (loop 1), a second loop (loop 2), a third loop (loop 3), and a fourth loop (loop 4). In the following discussion of each of these loops, the references above will be used. Figure 3 and Figure 4 The same reference numerals are discussed, and reference characters are appended to the reference numerals to indicate different loops. Reference character "c1" is appended to components of the first loop. Reference character "c2" is appended to components of the second loop. Reference character "c3" is appended to components of the third loop. Reference character "c4" is appended to components of the fourth loop. However, reference characters relating to specific loops are omitted if the discussion of components is general to any loop. Although the condensing unit 134 is described herein as having four loops, any suitable number of loops can be used. Furthermore, although specific components (e.g., passive condenser 214 and active condenser 216) are described in each of these four loops, various arrangements of these components are considered to be within the scope of the invention.

[0074] Furthermore, in each of the first, second, and third loops, two passive condensers 214 are associated with a first evaporator 212i (part of the first thermosiphon loop 200i), and two passive condensers 214j are associated with a second evaporator 212j (part of the second thermosiphon loop 200j). These condensers 214 will also have an "i" or "j" appended to the reference numerals to indicate which loop the passive condenser 214 is located in. For example, 214ic1 is used to specify one of the two passive condensers 214 in the first loop, both of which are part of the first thermosiphon loop 200i.

[0075] like Figure 11 As shown, a first evaporator 212i is connected in parallel to six passive condensers 214i. Two of the six passive condensers 214i are located in each of the first, second, and third loops. A first thermosiphon loop 200i includes an active condenser 216c4 connected in parallel with the six passive condensers 214i. The active condenser 234c4 of the first thermosiphon loop 200i is located in a fourth loop. In this embodiment, the fourth loop includes the active condenser 216c4 and its corresponding secondary cooling system 230c4, but does not include any passive condensers 214. A scavenging fan 120c4 is configured to direct scavenging air 118 to the outer surface of the condenser 234c4 of the secondary cooling system 230c4.

[0076] The second evaporator 212j is also connected in parallel to six passive condensers 214j. Two of the six passive condensers 214j are located in each of the first, second, and third loops. The second thermosiphon loop 200j includes three active condensers 216j. One of each of the three active condensers 216jc1, 216jc2, and 216jc3 is located in each of the first, second, and third loops. Therefore, each of the four loops includes a secondary cooling system 230. In this embodiment, each of the secondary cooling systems 230c1, 230c2, 230c3, and 230c4 includes two condensers 234 connected in parallel with each other. In other embodiments, the precooler 124 (see...) Figure 12 This can be used to cool the scavenging gas 118 before it passes through the passive condenser 214j of the second thermosiphon circuit 200j. In this case, the active condensers 216jc1, 216jc2, and 216jc3 in the second thermosiphon circuit 200j can be omitted.

[0077] The arrangement of each of the first, second, and third loops is similar to that of each other. The following description of the first loop also applies to the second and third loops. The condensers 214ic1, 214jc1, and 234c1 in the first loop are arranged in two groups: a first condenser group 272c1 and a second condenser group 274c1. The first condenser group 272c1 and the second condenser group 274c1 are arranged in parallel with each other relative to the airflow of scavenging gas 118. Each of the first condenser group 272c1 and the second condenser group 274c1 includes one of each of the passive condenser 214jc1 of the second thermosiphon circuit 200j, the passive condenser 214ic1 of the first thermosiphon circuit 200i, and the condenser 234c1 of the auxiliary cooling system 230. The condensers 214jc1, 214ic1, and 234c1 are arranged in series with respect to the airflow of scavenging gas 118. Scavenging air 118 is drawn through each condenser by scavenging fan 120c1 of the first loop, as described below. Scavenging air 118 is ambient air drawn in from the outdoor environment surrounding condensing unit 134 and first passes through the passive condenser 214jc1 of the second thermosiphon loop 200j. Next, scavenging air 118 passes through the passive condenser 214ic1 of the first thermosiphon loop 200i. Then, scavenging air 118 passes through the condenser 234c1 of the auxiliary cooling system 230 before being discharged to the outside by scavenging fan 120. Each scavenging fan 120 can be independently variable or at least variable between different loops.

[0078] The arrangement of condensers 214jc1, 214ic1, and 234c1 in the first loop allows for a counter-current design. The main cooling medium 202 in the second thermosiphon loop 200j is colder than the main cooling medium 202 in the first thermosiphon loop 200i. Therefore, the coldest scavenging gas 118 first passes through the coldest condenser 214jc1, and then, after being heated by the passive condenser 214jc1 of the second thermosiphon loop 200j, the scavenging gas 118 passes through the warmer passive condenser 214ic1 of the first thermosiphon loop 200j.

[0079] Figure 10 and Figure 11 The cooling system 110 shown, like the cooling system 110 described above, does not use valves in the first thermosiphon circuit 200i and the second thermosiphon circuit 200j to switch between active and passive modes. Instead, by activating the auxiliary cooling system 230 to cool the active condenser 216, the vapor 206 of the main cooling medium 202 naturally travels to the cooler active condenser 216 for condensation, and the airflow cooling assembly 100 thermally transitions from passive to active mode.

[0080] Figure 10 and Figure 11The cooling system 110 shown can be controlled in a similar manner to the cooling system 110 described above, for example, using a reference. Figure 9 The process shown and described. The temperature of the supply air 112 can be controlled to a set point (see step S415). First, if the temperature of the supply air 112 is higher than the set point, the controller 240 for controlling the cooling system 110 will increase the flow rate of the scavenging air 118, for example, by increasing the fan speed of the scavenging fan 120 (see step S440). If the temperature of the supply air 112 is lower than the set point, the controller 240 will decrease the flow rate of the scavenging air 118 (for example, by decreasing the fan speed of the scavenging fan 120) (see step S425).

[0081] If the temperature of the supply air 112 is higher than the set point and the flow rate of the scavenging air 118 is at its maximum value, the controller 240 will activate the auxiliary cooling system 230 (see step S450). Figure 10 and Figure 11 In the cooling system 110 shown, the controller 240 can gradually activate the secondary cooling system 230 via a loop as needed to maintain the temperature of the supply air 112 at a set point. Although the secondary cooling system 230 of the loop can be activated in different sequences, one approach is to activate the secondary cooling system 230 sequentially in the order of the first loop, second loop, third loop, and fourth loop as needed. Therefore, in this embodiment, the secondary cooling system 230 of the second thermosiphon loop 200j can be activated sequentially before the secondary cooling system 230c4 of the first thermosiphon loop 200i. If the temperature of the supply air 112 is lower than the set point, the controller 240 can then deactivate the secondary cooling system 230, for example, in the reverse order of loop activation (see step S430).

[0082] If the temperature of the air supply 112 is below the setpoint, and all auxiliary cooling systems 230 (active cooling mode) are shut down, and the scavenging fan 120 is operating at its minimum speed, the controller 240 may gradually shut down the scavenging fan 120 as needed to maintain the air supply 112 at the setpoint. With all but one of the scavenging fans 120 shut down, the controller 240 may operate only one of the first thermosiphon circuit 200i and the second thermosiphon circuit 200j. This can be achieved by closing the flow control valve 276 of the deactivated circuit (discussed further below), which may, for example, be the second thermosiphon circuit 200j.

[0083] Even when some or all of the active condensers 216 are operating, thus the system operates in active mode, the inventors unexpectedly discovered some savings even in active mode (cooling from the main cooling medium 202 of the passive condenser 214), as shown in the test results in Table 2 below. Table 2 shows the test results for a nominal heat load of 350 kW on the evaporator 212. For the conditions in the table below, at least one loop of the first thermosiphon loop 200i and the second thermosiphon loop 200j operates in active mode. The test was conducted for various ambient air (scavenging air 118) temperatures, and the heat dissipation from both the active condenser 216 and the passive condenser 214 was measured. The active mode of the loops was gradually activated and deactivated based on the ambient air temperature, but at the highest ambient air temperature, all secondary cooling systems 230 were operating.

[0084] Table 2

[0085]

[0086] In Table 2 above, use the following equation (1) to calculate the heat dissipation.

[0087]

[0088] In equation (1), V is the volume of air (e.g., supply air 112) passing through the condenser or evaporator in actual cubic feet per minute, and T is... I T is the temperature of the air entering the condenser or evaporator (e.g., return air 114), measured in Fahrenheit. O The temperature of the air leaving the condenser or evaporator (e.g., supply air 112) is measured in Fahrenheit. a It is a coefficient based on altitude. Altitude coefficient (f) a The following equation (2) can be used to calculate, where A is the altitude in feet.

[0089] f a =(1-(6.8754×10) -6 A) -5.2559 (2)

[0090] Although the valve is not used for switching between modes, it can be used to help regulate the cooling system 110. In this embodiment, a flow control valve 276 is placed at the inlet of each evaporator 212 in the first common liquid refrigerant line 266 and the second common liquid refrigerant line 268. Any suitable valve can be used as the flow control valve 276, but in this embodiment, the flow control valve 276 is a shut-off valve operated by a stepper motor. Here, the flow control valve 276 allows continuous regulation of the flow rate through the plug or disc of the flow control valve 276, and the plug or disc is operated by a stepper motor. The flow control valve 276 includes a closed position and multiple open positions, each with a different opening area. The multiple open positions thus allow different amounts of the main cooling medium 202 in the liquid phase 204 to flow through the flow control valve 276 based on the opening area of ​​that position.

[0091] Flow control valve 276 is used to precisely control the liquid level (the amount of main cooling medium 202 in liquid phase 204) in evaporator 212 and maintain the vapor 206 leaving evaporator 212 at the desired temperature. The inventors have discovered that using flow control valve 276 allows the main cooling medium 202 to circulate efficiently through the first thermosiphon loop 200i and the second thermosiphon loop 200j by natural circulation and gravity over a wide range of heat loads and ambient air conditions. Flow control valve 276 can be used to prevent excessive liquid 204 from entering evaporator 212 (e.g., causing evaporator 212 to overflow), which inhibits the outflow of vapor 206 from evaporator 212. Furthermore, flow control valve 276 can be used to prevent too little liquid 204 from entering evaporator 212 (e.g., causing evaporator 212 to become depleted), which inhibits effective and efficient condensation in condensers 214, 216. With the internal air processor 132 and condenser unit 134 separated, this consideration, and therefore the use of the flow control valve 276, may be particularly relevant, as the greater distance requires a larger amount of main cooling medium 202, which further exacerbates the aforementioned problems, such as overflow.

[0092] Various methods can be used to position the flow control valve 276, thereby setting the amount of liquid 204 flowing into the evaporator 212. For example, the position of the flow control valve 276 can be based on heat absorption in the evaporator 212, heat dissipation from the return air 114 / supply air 112, heat dissipation from the condensers 214, 216, heat absorption from the scavenging air 118, or superheating of the vapor 206. As described above, the controller 240 is communicatively coupled to various sensors, such as loop sensors 250 (e.g., temperature sensor 252 and pressure sensor 254) located in the first thermosiphon loop 200i and the second thermosiphon loop 200j, or temperature sensors for monitoring the temperatures of the supply air 112, return air 114, and scavenging air 118. Using the outputs from these sensors (inputs to the controller), the controller 240 can determine the appropriate position of the flow control valve 276 and appropriately drive the stepper motor of the flow control valve 276.

[0093] When controlling the flow control valve 276 based on heat absorption in the evaporator 212, the heat absorption can be determined based on the temperature rise across the evaporator 212. One way to determine the temperature rise is to measure the temperature of the main cooling medium 202 at the inlet (or another suitable location at the bottom of the evaporator 212) and the temperature of the main cooling medium 202 at the outlet (or another suitable location at the top of the evaporator 212). Another way to determine the temperature rise is to measure the temperature of the supply air 112 at the bottom third (the third closest to the inlet) and the top third (the third closest to the outlet) of the evaporator 212. The temperature rise can then be determined by taking the difference between the measured temperatures and comparing that difference to a setpoint. If the difference is lower than the setpoint, the controller 240 controls the stepper motor to move the flow control valve 276 in the closing direction to reduce the flow of liquid 204 into the evaporator 212. If the temperature is higher than the set point, the controller 240 controls the stepper motor to move the flow control valve 276 in the opening direction to increase the flow rate of liquid 204 entering the evaporator 212.

[0094] Another method for controlling the flow control valve 276 is to measure the heat discharged from the return air 114 / supply air 112. When controlling the flow control valve 276 based on the heat discharged from the return air 114 / supply air 112, a temperature sensor can be used to measure the temperature of the return air 114 before it reaches the evaporator 212, and then again after it passes through the evaporator 212. The controller 240 can then be used to calculate the heat discharged in the thermosiphon loop (e.g., the first thermosiphon loop 200i or the second thermosiphon loop 200j) based on the measured temperature and flow rate of the return air 114 / supply air 112. The controller then sets the position of the flow control valve 276 in the thermosiphon loops 200i, 200j based on a curve or lookup table as a function of the heat absorbed in the thermosiphon loops 200i, 200j. Different curves or values ​​can be used for different operating modes, such as curves when each loop operates in active mode.

[0095] When the flow control valve 276 is controlled based on the heat dissipation in condensers 214 and 216, the heat dissipation can be determined based on the temperature drop in each of condensers 214 and 216. Similar to measuring the temperature rise, as described above, one way to determine the temperature drop is to measure the temperature of the main cooling medium 202 at the inlet (or another suitable location at the top of condensers 214 and 216) and the temperature of the main cooling medium 202 at the outlet (or another suitable location at the bottom of condensers 214 and 216). Another way to determine the temperature rise is to measure the temperature of the scavenging air 118 exiting the top third (the third of condensers 214 and 216 near the inlet) and the temperature of the scavenging air 118 exiting the bottom third (the third of condensers 214 and 216 near the outlet). The temperature drop can then be determined by measuring the difference between these temperatures. The temperature drop of each condenser 214, 216 can be used to calculate the total heat dissipated by the condensers 214, 216 in the thermosiphon loop (e.g., the first thermosiphon loop 200i or the second thermosiphon loop 200j). The controller 240 then sets the position of the flow control valve 276 in the thermosiphon loops 200i, 200j as a function of the heat dissipation in those loops, based on a curve or lookup table. As mentioned above, different curves or values ​​can be used for different operating modes, such as the curve when each loop operates in active mode. In this case, as mentioned above, the flow control valve 276 can be adjusted to be more open for more heat dissipation, or more closed for less heat dissipation. Alternatively, instead of using the controller 240 to calculate the heat dissipation, the temperature drop can be used directly as the basis for the curve or lookup table.

[0096] Another method to determine the heat dissipated by condenser unit 134 is to measure the heat absorbed by scavenging gas 118. When controlling flow control valve 276 based on the heat absorption of scavenging gas 118, a temperature sensor can be used to measure the temperature of scavenging gas 118 before it reaches condensers 214, 216, 234 and after it passes through condensers 214, 216, 234. Controller 240 can then be used to calculate the amount of absorption in the thermosiphon loop (e.g., first thermosiphon loop 200i or second thermosiphon loop 200j) based on the measured temperature and flow rate of scavenging gas 118, and the controller then sets the position of flow control valve 276 in thermosiphon loops 200i, 200j as a function of the heat absorbed in the thermosiphon loops 200i, 200j, in a manner similar to that discussed above for controlling flow control valve 276 based on heat dissipation in condensers 214, 216.

[0097] When the flow control valve 276 is controlled based on a predetermined value (setpoint) of superheated steam 206, if the superheat temperature of steam 206 rises above the setpoint, the flow control valve 276 can be opened to allow more condensate 204 to enter the evaporator 212, thereby reducing the superheat temperature of steam 206. Similarly, if the superheat temperature of steam 206 drops below the setpoint, the flow control valve 276 can be closed to reduce the flow rate of condensate 204 entering the evaporator 212, thereby increasing the superheat temperature of steam 206. Loop sensors 250, such as temperature sensor 252 and pressure sensor 254, can be located at the outlet of evaporator 212. Such sensors 250 can also be suitably located in the evaporator 212 itself or in the steam line leading to condensers 214, 216. Controller 240 then calculates the superheat based on temperature and pressure measurements and compares it to the setpoint (e.g., a predetermined (desired) level). Controller 240 then adjusts the flow control valve 276 as described above. In any control method, once a measured or calculated value exceeds a setpoint, adjustment should not be made immediately; instead, the controller 240 may adjust the flow control valve 276 only when the flow exceeds and falls below the upper and lower threshold temperatures (or values) of the setpoint, respectively. Although the invention is described in terms of control based on the setpoint herein, those skilled in the art will understand that such operations are included in this description.

[0098] As with any cooling system 110 described herein, the speed of the supply air fan 116, which drives the airflow (return air 114) through the evaporator 212, can be varied. The supply air fan 116 can be located downstream of the evaporator 212 (in the direction of travel of the return air 114 / supply air 112), such as... Figure 10 As shown. Alternatively, the air supply fan 116 can be located upstream of the evaporator 212, as shown. Figure 1As shown, the supply air fan 116 can also be referred to as a return air fan. In one example, the airflow of return air 114 / supply air 112 can be driven by the requirements of data center 100. Data center 100 may have a controller (not shown), referred to herein as a building management system (BMS), which is separate from the controller 240 for cooling system 110. The BMS determines the appropriate speed of the supply air fan 116 based on the needs within data center 100. These needs may vary from data center to data center. The BMS may send supply air fan speed signals to the controller 240 for cooling system 110, and the controller 240 may adjust the supply air fan 116 (e.g., the speed and number of operating supply air fans 116) to match the signals given by the BMS.

[0099] For example, if the BMS signal is absent, another way to control the supply air fan 116 in the cooling system 110 is to control the supply air fan 116 to the return air temperature setpoint of the return air 114. The controller 240 can adjust the flow rate of the return air 114 / supply air 112 by adjusting the speed of the supply air fan 116 (or the number of operating supply air fans 116) to maintain the temperature of the return air 114 at the return air temperature setpoint. If the temperature of the return air 114 is higher than the return air temperature setpoint, the speed (or number) of the supply air fan 116 is increased. If the temperature of the return air 114 is lower than the return air temperature setpoint, the speed (or number) of the supply air fan 116 is decreased.

[0100] The fluid cooled by the cooling system 110 described herein may be referred to as process fluid 142. In the above embodiment, the process fluid 142 cooled by the cooling system 110 is air. In the preceding discussion, the air (process fluid 142) is directed to the rack 102 containing the electronic components and heated before being directed to the evaporator 212 (return air 114) for cooling. However, the cooling system 110 described herein is not limited to cooling air and can be used to cool any suitable fluid. Process fluid 142 may include, for example, liquids such as water, mixtures of water and ethylene glycol, and non-conductive fluids (dielectrics).

[0101] In the above embodiments, the process fluid 142 is air, and the evaporator 212 is suitably a microchannel coil or a finned tube coil. When the process fluid 142 is a liquid rather than vapor (gas), other suitable evaporators 212 can be used, including, for example, plate heat exchangers, coaxial heat exchangers, or shell-and-tube heat exchangers. Figure 12A cooling system 110 is shown, wherein an evaporator 212 is suitably designed to cool a process fluid 142 as a liquid. The process fluid 142 circulates in a process fluid loop 140 via a pump 144. This embodiment includes a first evaporator 212k and a second evaporator 212l arranged in series in the process fluid loop 140. The process fluid 142 is heated by a heat load, such as a server 103 in rack 102 (see...). Figure 13A and 13B Then, the process fluid 142 is cooled by the first evaporator 212k and the second evaporator 212l before returning to cool the server 103.

[0102] In this embodiment, the second evaporator 212l is fluidly connected to the passive condenser 214 (passive condenser 214l) and the active condenser 216 (active condenser 216l), as described above. Figure 3 and Figure 4 The first evaporator 212k operates in the same manner as loop 200. The first evaporator 212k is fluidly connected to the passive condenser 214 (passive condenser 214k), which is downstream of the passive condenser 214k relative to the airflow direction of the scavenging gas 118 between the condenser 234 and the passive condenser 214k in the auxiliary cooling system 230. Similar to the embodiments discussed above, the first evaporator 212k can also be fluidly connected to the passive condenser 214k and the active condenser 216 (active condenser 216k), as described above. Figure 3 and Figure 4 The circuit 200 described herein operates in the same manner. The condenser unit 134 of this embodiment may also include an adiabatic precooler 124 to precool the scavenging gas 118 before it passes through any of the condensers 214, 234. Any suitable adiabatic precooler 124 may be used, including, for example, the Munters FA6 manufactured by Munters Corporation of Buena Vista, Virginia, USA. TM Evaporative humidifier / cooler.

[0103] As described above, the process fluid 142 can be heated by a heat load, such as a server 103 located in a rack 102 of the data center 100. Figure 12 The cooling system 110 shown may be suitable for use with the immersion cooling system of server 103. Figure 13A and 13B An example of rack 102 used in an immersion cooling system is shown. Figure 13A In this configuration, server 103 is submerged in dielectric 146. Server 103 heats dielectric 146, but dielectric 146 remains liquid (single phase). The heated dielectric 146 circulates as process fluid 142 through process fluid loop 140 to be cooled and returns to rack 102 for further cooling of server 103.

[0104] exist Figure 13B In this configuration, server 103 is also immersed in dielectric 146. In this case, dielectric 146 cools server 103 through two-phase cooling. Server 103 heats dielectric 146, and dielectric 146 transforms into vapor (gas). The dielectric vapor rises to the top of rack 102. The top of rack 102 includes coil 148. A suitable process fluid 142 flows through coil 148 and condenses dielectric 146. In another embodiment, dielectric 146 in the gas phase can be directly cooled by a second evaporator 212l and a first evaporator 212k, which serve as process fluid 142, instead of using another fluid.

[0105] In the above embodiments, server 103 is physically separated from the first evaporator 212k and the second evaporator 212l, and process fluid loop 140 is used to transfer heat from server 103 or other information technology (“IT”) equipment. However, the invention described herein is not limited thereto; evaporator 212 can be any liquid-refrigerant heat exchanger in which a circulating liquid (dielectric fluid, water, or other fluid) transfers heat from the IT equipment to a refrigerant integrated with a two-phase thermosiphon loop. Other suitable evaporators 212 include, for example, cold plates integrated into server 103 or IT components to absorb heat directly from the components and / or chips therein, or multiple tubular surfaces directly integrated into an immersion cooling system.

[0106] A second preferred embodiment of the airflow cooling component circuit 500, for example... Figure 14 and 15 As shown. In this embodiment, the evaporator 512 and the passive condenser 514 are combined in an integral heat exchanger 510, which operates as a heat pipe. The evaporator 512 is the lower part of the integral heat exchanger 510 and may also be referred to as the evaporator section 512. Similarly, the passive condenser 514 is the upper part of the integral heat exchanger 510 and may also be referred to as the condenser section. As in the first embodiment, any suitable heat exchanger can be used, including finned tube coils or microchannel coils. In this embodiment, the integral heat exchanger 510 is shown as a finned tube coil having a tube 516 connecting two fixed manifolds, a top manifold 522, and a bottom manifold 524. As described below, gravity also plays a role in the cooling process; therefore, the tube 516 is preferably oriented vertically, more preferably vertically.

[0107] The airflow cooling assembly 500 operates in passive mode, such as... Figure 14As shown. Hot return air 114 is directed to the evaporator section 512 of the integral heat exchanger 510. The main cooling medium 202 contained within tube 516 changes from liquid phase 204 to gas phase 206, absorbing heat from the return air 114 and thus cooling the return air 114. As the main cooling medium 202 evaporates, the vapor 206 rises in tube 516 to the condenser section 514 of the heat exchanger. In passive mode, scavenging air 118 is directed to the condenser section 514. Heat is discharged from the main cooling medium 202 to the scavenging air 118, condensing the main cooling medium from gas phase 206 to liquid phase 204. Then, the liquid 204 of the main cooling medium 202 is drawn back down along the side of tube 516 to the evaporator section 512 with the aid of gravity.

[0108] Airflow cooling assembly 500 operating in active mode, such as Figure 15 As shown. Similar to the airflow cooling assembly 200 of the first embodiment, the evaporator 512 of the airflow cooling assembly 500 is also connected to the second condenser, namely the active heat exchanger condenser 216. A vapor pipe 526 connects the top manifold 522 of the integral heat exchanger 510 to the active condenser 216. The vapor 206 of the main cooling medium 202 travels through the vapor pipe 526 to the active condenser 216. As in the first embodiment, heat is discharged from the main cooling medium 202 at the active condenser to the secondary cooling medium 208 of the secondary cooling system 230, causing the main cooling medium 202 to change from vapor 206 to liquid 204. The condensed liquid 204 then travels by gravity through the liquid refrigerant line 528 to the bottom manifold 524, establishing a recirculated refrigerant flow.

[0109] Similar to the first embodiment, the airflow cooling assembly 500 in this embodiment operates without the need for pumps, oil, compressors, or even valves to switch between modes. Instead, by activating the secondary cooling system 230 to cool the active condenser 216, the vapor 206 of the primary cooling medium 202 naturally travels to the cooler active condenser 216 for condensation, and the airflow cooling assembly 500 automatically switches from passive to active mode. Furthermore, a controller 240 communicatively connected to temperature sensors 122, 252 can be used to control the airflow cooling assembly 500 of this embodiment.

[0110] As described above, microchannel coils can be used instead of the finned tube coils used in the integral heat exchanger 510. However, the total available heat flux may be limited in passive mode, which depends solely on the heat pipe operation, because the condensed liquid and the evaporated gas flow in opposite directions to each other in the small channels of the microchannel extruder. Figure 16 and Figure 17Another configuration of the second embodiment is shown, including a second passive condenser 530 (a third condenser). In this embodiment, the third condenser 530 is a microchannel coil positioned in series with the condenser portion 514 of the integrated heat exchanger 510 relative to the scavenging gas 118. Preferably, the third condenser 530 is positioned upstream of the condenser portion 514 of the integrated heat exchanger. The third condenser 530 has a vapor manifold 532 and a liquid manifold 534. The vapor manifold 532 of the third condenser is connected to the top manifold 522 of the integrated heat exchanger 510 via a vapor pipe 526.

[0111] In passive mode (e.g.) Figure 16 As shown, the vapor 206 of the primary cooling medium 202 flows through the vapor pipe 526 and enters the third heat exchanger, where a large portion of the primary cooling medium 202 will condense. Similar to the passive condenser 214 of the first embodiment, a scavenging gas 118 is driven across the outer surface of the third condenser 530, and the heat contained in the primary cooling medium 202 within the third condenser 530 is released to the scavenging gas 118, thereby condensing the vapor 206 into liquid 204. The liquid 204 of the primary cooling medium 202 then travels by gravity through the liquid refrigerant line 528 to the bottom manifold 524 as a recirculated refrigerant stream.

[0112] In active mode (e.g.) Figure 17 As shown, in the embodiment described above, vapor 206 flows naturally to the cooler active condenser 216 for condensation, and in active mode, the flow rate of the main cooling medium 202 through the third condenser 530 is minimal (if any). Similar to the first embodiment, it may be beneficial to include a vapor trap (not shown) and / or a check valve 220 in the liquid refrigerant line 528 to prevent reverse flow of the main cooling medium 202 through condensers 216, 530 that are not currently operating in the given mode.

[0113] The second passive condenser 530 can also be used in configurations without an active condenser 216, such as... Figure 18 As shown. This configuration has only a passive mode, but the evaporator 512 is still connected to two condensers, namely the condenser section 514 of the integral heat exchanger 510 and the second passive condenser 530.

[0114] Similar to the airflow cooling assembly 200 of the first embodiment, the cooling system 110 may include multiple airflow cooling assemblies 500 of the second embodiment. For example, the cooling system 110 may include two circuits 500a and 500b, such as... Figure 19 As shown. The first loop 500a is similar to Figure 18 The configuration shown is similar, but without the active condenser 216; the second loop 500b is similar. Figure 14 and 15The configuration shown is modified, but with microchannel coils for the integral heat exchanger 510b. In this configuration, two evaporators 512a, 512b are arranged in series with respect to the return air 114. The integral heat exchanger 510b of the second loop 500b (with an active condenser 216) is located upstream of the integral heat exchanger 510a of the first loop 500a.

[0115] Figure 20 and Figure 21 Another cooling system 110 is shown, having two airflow cooling component circuits 600, a first airflow cooling component circuit 600a and a second airflow cooling component circuit 600b, but any number of circuits, including a single circuit, may be used. As discussed above, a letter is appended after the reference numerals to indicate the circuit in which the component resides. In this cooling system 110, return air 114 is directed through two cooling coils 612a, 612b arranged in parallel with respect to the return air 114, but the cooling coils 612a, 612b may also be arranged in parallel. As the return air 114 flows through the cooling coils 612, heat is transferred from the return air to the main cooling medium 602 contained within the main coolant circuit 610, thereby heating the main cooling medium 602. Any suitable main cooling medium 602 may be used, including, for example, water or a mixture of water and ethylene glycol.

[0116] The heat absorbed by the main cooling medium 602 is then discharged at the second coil 614 in thrift mode or at the heat exchanger 616 in active mode. The main cooling medium 602 is circulated through the main coolant circuit 610 by pump 618 and reaches the second coil 614 or the heat exchanger 616. The diversion valve 620 selectively directs the pumped main cooling medium 602 to the second coil 614 or the heat exchanger 616 according to the mode.

[0117] Figure 20The cooling system 110 in energy-saving mode is shown. Energy-saving mode is used when the ambient air temperature is lower than the temperature of the main cooling medium 602 after it has absorbed heat from the return air 114 (e.g., measured at a point in the main coolant circuit 610 after cooling coil 612), as in the passive mode discussed in the embodiments above. As in the embodiments discussed above, a predetermined temperature difference can be applied to determine when to use energy-saving mode or active mode. In energy-saving mode, the diverter valve 620 directs the main cooling medium 602 from cooling coil 612 to the second coil 614 to cool the main cooling medium 602. The scavenging fan 120 directs scavenging air 118 across the outer surface of the second coil 614. The heat in the main cooling medium 602 is then expelled from the main cooling medium 602 and absorbed by the scavenging air 118. The main cooling medium 602 then returns to cooling coil 612. Cooling coil 612 and second coil 614 can be any suitable coil, including finned tube coils or microchannel coils. The expansion tank 622 can be located upstream of the pump 618 and downstream of the cooling coil 612.

[0118] Figure 21 The cooling system 110 in active mode is shown. Similar to the active mode discussed above, the active mode of this embodiment is used when the ambient temperature is higher than or within a predetermined temperature range after the main cooling medium 602 absorbs heat from the return air 114. In active mode, the diversion valve 620 directs the main cooling medium 602 from the cooling coil 612 to the heat exchanger 616 to cool the main cooling medium 602. The heat in the main cooling medium 602 is then discharged from the main cooling medium 602 and absorbed by the secondary cooling medium 208 of the secondary cooling system 230. As discussed in the embodiments above, the secondary cooling system 230 can be any suitable cooling system, including a direct expansion cooling system. The main cooling medium 602 then returns to the cooling coil 612.

[0119] Although the invention has been described in certain specific exemplary embodiments, many additional modifications and variations will be apparent to those skilled in the art from this disclosure. Therefore, it should be understood that the invention can be practiced in ways other than those specifically described. Accordingly, exemplary embodiments of the invention should be considered illustrative rather than restrictive in all respects, and the scope of the invention is determined by any of the claims supported by this application and its equivalents, rather than by the foregoing description.

Claims

1. A cooling system, comprising: An evaporator comprising a main cooling medium, the evaporator being configured to receive a process fluid and, upon receiving the process fluid, to change the phase of the main cooling medium from liquid to gas. A passive condenser fluidly connected to the evaporator, the passive condenser being configured to receive cooling air, wherein, when the passive condenser receives cooling air, the passive condenser is configured to (i) receive a gaseous primary cooling medium from the evaporator, (ii) transfer heat from the primary cooling medium, (iii) change the phase of the primary cooling medium from gas to liquid, and (iv) supply a liquid-phase primary cooling medium to the evaporator. A first heat exchanger, fluidly connected to the evaporator and configured to have a first secondary cooling medium supplied thereto, wherein, when the first secondary cooling medium is supplied to the first heat exchanger, the first heat exchanger is configured to (i) receive a gaseous primary cooling medium from the evaporator, (ii) transfer heat from the primary cooling medium, (iii) change the phase of the primary cooling medium from gas to liquid, and (iv) supply a liquid-phase primary cooling medium to the evaporator; and A second heat exchanger, fluidly connected to the evaporator and configured to selectively supply a second secondary cooling medium thereto, such that: (a) When the second auxiliary cooling medium is supplied to the second heat exchanger, without operating any valves located between the evaporator and the passive condenser, and between the evaporator and the second heat exchanger, at least some of the gaseous main cooling medium is switched from being received by the passive condenser to the second heat exchanger, and the second heat exchanger is configured to (i) receive the gaseous main cooling medium from the evaporator, (ii) transfer heat from the main cooling medium, (iii) change the phase of the main cooling medium from gas to liquid, and (iv) supply the liquid main cooling medium to the evaporator; and (b) When the second auxiliary cooling medium is not supplied to the second heat exchanger, the second heat exchanger does not supply the liquid-phase main cooling medium to the evaporator. Where there is no pump in the flow path of the main cooling medium between the passive condenser and the evaporator, between the first heat exchanger and the evaporator, and between the second heat exchanger and the evaporator to circulate the main cooling medium, the main cooling medium circulates between the evaporator and the passive condenser, between the evaporator and the first heat exchanger, and between the evaporator and the second heat exchanger by natural circulation and gravity.

2. The cooling system according to claim 1, wherein, The second auxiliary cooling medium is the refrigerant of a direct expansion cooling system, which includes a compressor and an expansion valve.

3. The cooling system according to claim 2, wherein, The first cooling medium is water.

4. The cooling system according to claim 2, wherein, The first auxiliary cooling medium is the refrigerant of a direct expansion cooling system, which includes a compressor and an expansion valve.

5. The cooling system according to claim 1, wherein, The passive condenser and the first heat exchanger are arranged in parallel with respect to the flow of the main cooling medium.

6. The cooling system according to claim 1, wherein, The passive condenser and the second heat exchanger are arranged in parallel with respect to the flow of the main cooling medium.

7. The cooling system according to claim 1, wherein, The first heat exchanger and the second heat exchanger are arranged in parallel with respect to the flow of the main cooling medium.

8. The cooling system according to claim 1, wherein, The process fluid is air.

9. The cooling system according to claim 1, wherein, The process fluid is a liquid.

10. The cooling system of claim 1, further comprising a flow control valve positioned in a flow path between the first heat exchanger and the evaporator, in a flow path between the second heat exchanger and the evaporator, and in a flow path between the passive condenser and the evaporator, the flow control valve having a plurality of open positions and configured to control the flow rate of the liquid phase main cooling medium to the evaporator.

11. The cooling system of claim 10, further comprising a controller configured to control the position of the flow control valve between the plurality of open positions.

12. The cooling system of claim 1, further comprising a controller configured to selectively control the supply of a second auxiliary cooling medium to the second heat exchanger.

13. An electronic system comprising: At least one electronic component cooled by a dielectric; and The cooling system according to claim 1, wherein the cooling system cools the dielectric.

14. The electronic system according to claim 13, wherein, The process fluid is the dielectric.

15. A cooling system, comprising: An evaporator comprising a main cooling medium, the evaporator being configured to receive a process fluid and, upon receiving the process fluid, to change the phase of the main cooling medium from liquid to gas. A passive condenser fluidly connected to the evaporator, the passive condenser being configured to receive cooling air from a cooling gas stream, wherein, when the passive condenser receives cooling air, the passive condenser is configured to (i) receive a gaseous primary cooling medium from the evaporator, (ii) transfer heat from the primary cooling medium, (iii) change the phase of the primary cooling medium from gas to liquid, and (iv) supply a liquid-phase primary cooling medium to the evaporator; A precooler, located upstream of the passive condenser in the cooling airflow, is configured to cool the cooling air before it is received by the passive condenser; and A heat exchanger, fluidly connected to the evaporator and configured to selectively supply a secondary cooling medium thereto, such that: (a) When the secondary cooling medium is supplied to the heat exchanger, without operating any valves located between the evaporator and the passive condenser and between the evaporator and the heat exchanger, at least some of the gaseous primary cooling medium is switched from being received by the passive condenser to the heat exchanger, and the heat exchanger is configured to (i) receive the gaseous primary cooling medium from the evaporator, (ii) transfer heat from the primary cooling medium, (iii) change the phase of the primary cooling medium from gas to liquid, and (iv) supply the liquid primary cooling medium to the evaporator; and (b) 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. Where there is no pump in the flow path of the main cooling medium between the evaporator and the passive condenser and between the heat exchanger and the evaporator to circulate the main cooling medium, the main cooling medium circulates between the evaporator and the passive condenser and between the evaporator and the heat exchanger by natural circulation and gravity.

16. The cooling system according to claim 15, wherein, The precooler is an adiabatic precooler.

17. The cooling system according to claim 15, wherein, The precooler is an evaporative precooler.

18. The cooling system of claim 15, further comprising a flow control valve positioned in a flow path between the heat exchanger and the evaporator and in a flow path between the passive condenser and the evaporator, the flow control valve having a plurality of open positions and configured to control the flow rate of the liquid phase primary cooling medium to the evaporator.

19. The cooling system of claim 18, further comprising a controller configured to control the position of the flow control valve between the plurality of open positions.

20. The cooling system of claim 15 further includes a controller configured to selectively control the supply of a secondary cooling medium to the heat exchanger.

21. The cooling system according to claim 15, wherein, The process fluid is air.

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