Active / passive cooling system

Abstract

A cooling assembly includes an evaporator containing a primary cooling medium, a passive condenser, a heat exchanger, and a flow control valve that controls the flow of the primary cooling medium into the evaporator. When the secondary cooling medium is provided to the heat exchanger, the primary cooling medium in the gas phase is switched from being received by the passive condenser to the heat exchanger without operating any valves between the evaporator and the passive condenser and between the evaporator and the heat exchanger. 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 without providing a pump in the flow path of the main cooling medium between the heat exchanger and the evaporator and between the passive condenser and the evaporator to circulate the main cooling medium.

Description

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

[0002] The present invention relates to cooling systems and systems and methods for controlling them. In particular, the present invention relates to a cooling system having both an active mode and a passive mode. For example, a particularly suitable application is in a data center cooling system. Background Art

[0003] Data centers typically require a lot of energy to run. The servers in these data centers generate a lot of heat that needs to be cooled. In order to reduce the energy use of data centers, more efficient cooling systems are needed.

[0004] Heat pipes and thermosyphons are devices that transfer energy from a high temperature evaporator section to a low temperature condenser section by 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 forces. Heat pipes have been used as indirect economizers for data center cooling. In these devices, for example, hot air from a data center is recirculated through the evaporator section of a heat pipe where the closed refrigerant is evaporated by the heat from the data center, thereby 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 removed. In some applications, the ambient air is first adiabatically cooled with an evaporative cooler before passing through the condenser section of the heat pipe to provide a lower temperature heat sink. In another configuration, the condenser section of the heat pipe can be sprayed with water while ambient air passes over its surface to provide a heat sink temperature close to the ambient wet bulb temperature.

[0005] In these embodiments, heat pipes and thermosyphons are limited by ambient temperature conditions and may not provide adequate heat removal when ambient temperatures are high. One such 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 approximately passive mode similar to the operation of a thermosyphon. These systems include a pump that moves the liquid refrigerant from the condenser to the evaporator. By using a pump, the flow of the refrigerant can be controlled independently of the pressure drops across the evaporator and condenser and the effects of gravity. This approach is approximately passive because the pump only requires a small amount of power to transfer a large amount of thermal energy. In a pumped refrigerant system, the pump can be turned off and, by operating the valves, the compressor and expansion valve can be integrated into the system refrigerant flow to allow the system to act as a direct expansion cooling system.

[0006] System design constraints in direct expansion systems typically require moderate pressure drops in the evaporator and condenser portions of the system to provide uniform refrigerant flow through the multiple parallel evaporator and condenser circuits of the system. It is because of these pressure drops that a pump is required to circulate the refrigerant fluid when the system is operating in a near-passive mode. Since the refrigerant circuit includes a compressor system, the refrigerant volume also needs to include oil for lubrication. There are various design and operating constraints on pumped refrigerant systems, such as best practices for refrigerant velocity (so-called "oil management") to ensure that oil is not trapped in the various pipe lengths of the system and reliably returns to the compressor where it is needed. These oil management constraints become a problem when operating in pumping mode (near-passive mode) because the flow paths and flow rates of the pumping mode may not be consistent with the rules required for the DX mode. For example, the refrigerant volumes required for correct operation within the system may also be very different during pumping mode and DX mode due to different available superheat and subcooling levels and coil flooding levels.

[0007] Therefore, there is a need for cooling systems that further reduce energy usage, and cooling systems that do not require oil management in passive or near-passive mode. Summary of the invention

[0008] In one aspect, the present invention relates to a cooling system, including an evaporator, a passive condenser and a heat exchanger containing a main cooling medium. The evaporator is configured to receive a process fluid, and when receiving the process fluid, the phase of the main cooling medium is changed from liquid to gas. The passive condenser has an outer surface and is fluidly connected 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 main cooling medium in gas phase 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 main cooling medium in liquid phase to the evaporator. The heat exchanger is fluidly connected to the evaporator and is configured to have a secondary cooling medium selectively provided thereto. When the secondary cooling medium is provided to the heat exchanger, the main cooling medium in gas phase is switched 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 heat exchanger is configured to (i) receive a primary cooling medium in a gas phase 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 primary cooling medium in a liquid phase to the evaporator. When the heat exchanger does not receive the secondary cooling medium, the heat exchanger does not supply the primary cooling medium in a liquid phase 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 providing a pump in a 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.

[0009] In another aspect, the present invention relates to a method for cooling a process fluid. The method includes directing the process fluid through an evaporator to transfer heat from the process fluid to a primary cooling medium contained in the evaporator and changing the primary cooling medium from a liquid phase to a gas phase, and selectively using 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 connected to the evaporator to receive the primary cooling medium in a gas phase from the evaporator and supply the primary cooling medium in a liquid phase 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 valve in the connection between the evaporator and the passive condenser and the connection between the evaporator and the heat exchanger.

[0010] These and other aspects, objects, features and advantages of the present invention will become apparent from the following detailed description of illustrative embodiments thereof, which is to be read in connection with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0012] Figure 2 is along Figure 1 Intercepted from the 2-2 line Figure 1 Cross-sectional view of the cooling system shown.

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

[0014] Figure 4 yes Figure 3 Schematic diagram of an airflow cooling assembly operating in active mode.

[0015] Figure 5A Shown can be used Figure 3 Microchannel cooling coils of the airflow cooling assembly shown. Figure 5B is along Figure 5A The line 5B-5B in Figure 5A A cross-sectional view of the microchannels of the microchannel cooling coil shown in FIG.

[0016] Figure 6 is a schematic diagram of a cooling system having Figure 3 Airflow cooling multiple circuits of a component shown operating in passive mode.

[0017] Figure 7 yes Figure 6 Schematic diagram of a cooling system shown with one airflow cooling assembly loop operating in active mode.

[0018] Figure 8 yes Figure 6 Schematic diagram of the cooling system shown with all airflow cooling component circuits operating in active mode.

[0019] Fig. 9 Is a description Figure 4 A flow chart of a method of operating a cooling system is shown.

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

[0021] Fig.11 is with Fig.10 A schematic diagram of a condensing unit for use with an air handling unit is shown.

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

[0023] Fig.13A and 13B is through Fig.12 An example of a cooling assembly shown being used in conjunction with an immersion cooling system to cool a server rack. Fig.13A A single-phase immersion cooling system is shown, Fig. 13B A two-phase immersion cooling system is shown.

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

[0025] Fig.15 yes Fig.14 Schematic diagram of an airflow cooling assembly operating in active mode.

[0026] Fig.16 is a schematic diagram of an alternative configuration of the airflow cooling assembly of the second embodiment operating in a passive mode.

[0027] Fig.17 yes Fig.16 Schematic diagram of an airflow cooling assembly operating in active mode.

[0028] Fig.18 yes Fig.16 A schematic diagram of another configuration of an airflow cooling assembly is shown.

[0029] Fig.19 is a schematic diagram of a cooling system having Fig.14 and Fig.15 The airflow cooling circuit shown in the figure and Fig.18 The airflow shown cools the circuit of the assembly.

[0030] Fig. 20 is a schematic diagram of another cooling system operating in a nearly passive mode.

[0031] Fig.21 yes Fig. 20 Schematic diagram of the cooling system shown operating in active mode. DETAILED DESCRIPTION

[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 is along Figure 12-2. Although the cooling system 110 is shown and described with reference to the 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 the data center 100, these racks 102 can be arranged in rows to form aisles 104, 106 therebetween. One aisle 104 is a cold aisle, while the other aisle 106 is a hot aisle. Cooled 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 extracts heat from the electronic components, cools them, and causes hot air to enter the hot aisle 106. The air is then directed back to the cooling system 110 as hot return air 114. The supply air fans 116 are used to draw return air 114 from the data center 100, pass the return air 114 through the cooling system 110, cool the return air 114 at the cooling system 110, and then return the now cooled return air 114 to the data center 100 as the supply air 112. The portion of the cooling system 110 through which the return air 114 flows, is cooled, and is returned as the supply air 112 is referred to herein as an interior air handler 132.

[0033] The cooling system 110 uses at least one airflow cooling assembly to cool the 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 The airflow cooling assembly 200 according to the 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 may also be referred to as a conservation mode. Figure 3 is a schematic diagram of the airflow cooling assembly 200 in passive mode, Figure 4 is a schematic diagram of an airflow cooling assembly 200 in active mode. The airflow cooling assembly 200 combines the efficiency of a thermosyphon with the ability to provide active cooling when the available ambient free cooling heat sink is not at a low enough temperature to provide adequate heat rejection. This is accomplished by including two separate condensers 214, 216 in the loop 200, one (condenser 214) for passive mode and the other (condenser 216) for active mode.

[0034] The air flow cooling assembly 200 circulates a primary cooling medium 202 through a primary coolant loop 210. The primary cooling medium 202 circulates through the primary coolant loop 210 by natural circulation and gravity without the need for a pump and a compressor. The primary cooling medium 202 can be any suitable refrigerant that changes phase from a liquid to a gas. As will be discussed further below, the primary coolant loop 210 does not require any moving parts. As a result, for example, the available range of refrigerants suitable as the primary cooling medium 202 is greatly expanded compared to a direct expansion (DX) cooling system, and suitable refrigerants include natural refrigerants such as water.

[0035] The primary coolant loop 210 includes an evaporator 212, and the primary cooling medium 202 is contained within the evaporator 212. In this embodiment, the evaporator 212 is a coil, and preferably a single-pass flooded coil. Any suitable coil may be used, including, for example, microchannel coils, such as those described further below, or fin tube coils. In both passive and active modes, the return air 114 is directed onto the outer surface of the evaporator 212 by the supply fan 116. As the hot return air 114 passes over the outer surface of the evaporator 212, it evaporates the primary cooling medium 202 in the evaporator 212. The phase change of the primary cooling medium 202 from the liquid phase 204 to the 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 the vapor pipe 222 to one of the two condensers 214, 216.

[0036] In passive mode, Figure 3 As shown, vapor 206 travels to passive condenser 214 in primary coolant loop 210. As with evaporator 212, passive condenser 214 of this embodiment is a coil, preferably a single pass coil, and any suitable coil may be used, including, for example, microchannel coils, such as those described further below, or tube coils (finned and unfinned). Scavenging fan 120 (see Figure 1 and Figure 2 ) draws the sweep air 118 across the outer surface of the passive condenser 214. In this embodiment, the sweep air 118 is ambient air drawn from the outdoor environment surrounding the cooling system 110. As the sweep air 118 passes through the passive condenser 214, heat from the primary cooling medium 202 contained in the passive condenser 214 is released to the sweep air 118, condensing the vapor 206 into a liquid 204. Gravity then causes the primary cooling medium 202, now in the liquid phase 204, to flow downwardly along the liquid refrigerant line 224 and back to the evaporator 212. The sweep air 118 is exhausted to the exterior by the sweep air fan 120.

[0037] When the 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 may be Figure 4 206 is operated in the active mode shown. In the active mode, the vapor 206 of the main cooling medium 202 is condensed in the active condenser 216. In this embodiment, the active condenser 216 may also be referred to as a heat exchanger (HX) in this article. In the active condenser 216, heat is transferred from the main 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 change refrigerant used in a direct expansion cooling system. 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. When the heat of the main cooling medium 202 is discharged by the secondary cooling medium 208, the main cooling medium 202 condenses from the vapor 206 to the liquid 204. As with the passive condenser 214, gravity then causes the main cooling medium 202, which is now in the liquid phase 204, to flow down along the liquid refrigerant line 224 and return to the evaporator 212.

[0038] In this embodiment, the secondary cooling system 230 is a direct expansion (DX) cooling system 230 using a common refrigeration cycle, and the secondary cooling medium 208 is any suitable refrigerant used in such a system. The direct expansion cooling system 230 includes a compressor 232 to increase the pressure and temperature of the refrigerant 208 before the refrigerant 208 is cooled in the condenser 234. In this embodiment, the condenser 234 of the direct expansion cooling system 230 can also be cooled by the sweep gas 118 (see Figure 1 and Figure 2 ). The refrigerant 208 then passes through the expansion valve 236 , reducing its pressure and temperature, and then flows 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 loop 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 to condense. Therefore, by starting the secondary cooling system 230 to cool the active condenser 216, the airflow cooling assembly 200 automatically switches from passive mode to active mode (assuming that the temperature in the active condenser 216 is lower than the temperature in the passive condenser 214), and by deactivating the secondary cooling system 230, the loop 200 returns to the passive mode. As described below, the controller 240 can be used to activate and deactivate the secondary cooling system 230. Another advantage of the airflow cooling assembly 200, due to the absence of moving parts, is that no oil is required, allowing the main cooling medium 202 to flow outside the refrigerant velocity, which is usually required to entrain and keep the oil circulating in the main loop 210.

[0040] Although the condensers 214, 216 of the airflow cooling assembly 200 are Figure 3 and Figure 4 214, 216, but the condensers 214, 216 may also be arranged in series, so that the outlet of one of the active or passive condensers 214, 216 is located upstream of and supplies the inlet of the other of the condensers 214, 216. The main coolant loop 210 may also include a trap 218 and / or a check valve 220 after each of the condensers 214, 216. The trap 218 and the check valve 220 prevent the main cooling medium 202 from flowing in reverse through the condensers 214, 216 that are not currently operating in a given mode. Other suitable valves or methods may be used to prevent reverse flow. Such a valve or trap is optional because including the trap 218 and the check valve 220 will increase the pressure drop of the system, thereby inhibiting the natural circulation flow of the main cooling medium 202 in the main loop 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 primary cooling medium 202 to escape to the vapor side of the loop, thereby assisting the flow of liquid to the evaporator 212 by gravity.

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

[0043] Because the airflow cooling assembly 200 of the present embodiment operates in a natural circulation mode with the help of gravity, the evaporator 212 is placed at a level lower than the condensers 214, 216 to allow gravity to help the condensed primary cooling medium 202 (liquid 204) return to the evaporator 212. It is desirable to keep the primary cooling medium 202 in the liquid phase 204 over 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 pressure head from the primary cooling medium 202 in the liquid phase 204 to overcome the pressure drop of the evaporator 212. Although the evaporator 212 can be flush with the liquid and vapor headers of the evaporator 212 located in the same horizontal plane, the evaporator 212 can also be preferably tilted 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 can also be preferably tilted 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 the flow of condensed liquid by gravity. The passive condenser's tilt angle (angle β) is preferably sufficient to provide an unobstructed drainage path and eliminate backflow of the primary cooling medium 202 in the passive condenser 214 .

[0044] As described above, the evaporator 212 and the passive condenser 214 may be microchannel coils. Figure 5A A microchannel coil 300 is shown which may be used as the evaporator 212 and passive condenser 214 of the present embodiment. Using the microchannel coil 300 has many advantages including, for example, that the high internal surface area of ​​the microchannel coil 300 facilitates heat transfer. Additionally, the microchannel coil 300 greatly reduces the volume of the primary cooling medium 202 required in the primary coolant loop 210 as compared to, for example, a fin tube coil. This reduction in the volume of the primary cooling medium 202 is beneficial for a number of reasons including a reduction in cost and, when certain refrigerants are used, a reduction in potential sources of greenhouse gas emissions. The microchannel coil 300 has a liquid side 302 and a vapor side 304. As shown in FIG. Figure 5A As shown, when the microchannel coil 300 is used as an evaporator 212, the flow of the primary 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 opposite (from right to left).

[0045] The microchannel coil 300 has a liquid header 310 and a vapor header 320 connected by a plurality of microchannel extrusions 330. Figure 5A The cross section of the microchannel extrusion taken along line 5B-5B in FIG. Figure 5B As shown. The microchannel extrusion 330 has an outer surface 332 and includes a plurality of microchannels 334, 336. Figure 5B As shown, the airflow is in direction A (in Figure 5AThe primary cooling medium 202 flows through the microchannels 334, 336. Each of the plurality of microchannel extrusions 330 is mechanically brazed to aluminum fins 340 positioned between the microchannel extrusions 330 to facilitate heat transfer.

[0046] The liquid header 310 includes a liquid connection 312 that connects the liquid header 310 to the liquid refrigerant line 224. Similarly, the vapor header 320 also includes at least one vapor connection 322 that connects the vapor header 320 to the vapor tube 222. In the case of using a microchannel coil as the evaporator 212, it may be beneficial to have multiple vapor connections 322. In this embodiment, three vapor connections 322 are shown. The use of multiple vapor connections 322 reduces the vapor back pressure in the vapor header 320 and promotes natural circulation flow in the main coolant loop 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 tubes 222 connecting the vapor connections 322. Another consideration for the steam pipe 222 and the steam connection 322 is to use large diameter pipes to reduce the back pressure of the steam and promote natural circulation flow in the main coolant loop 210. For example, when R410a is used as the main cooling medium 202, the size of the 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 header design features are not limited to microchannel coils, but can also be applied to other evaporators and condensers including fin tube coils.

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

[0048] A pair of evaporators 212a, 212b is arranged in parallel with another pair of evaporators 212, 212d relative to the airflow of the return air 114. The evaporators 212a, 212b, 212c, 212d in each pair are arranged in series. In the first pair, the return air 114 is directed through the first evaporator 212a in the pair before being directed through the second evaporator 212b in the pair. Similarly, in the second pair, the return air 114 is directed through the first evaporator 212c in the pair before being directed through the second evaporator 212d in the pair. The corresponding passive condensers 214a, 214b, 214c, 214d are similarly arranged in pairs (a first pair 214a, 214b and a second pair 214c, 214d), wherein the first pair is in parallel with the second pair, and each condenser in the pair is arranged in series. In the first pair, the purge air 118 is directed through the first condenser 214a of the pair before being directed through the second condenser 214b of the pair, and in the second pair, is directed through the first condenser 214c of the pair before being directed 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 may be 32 feet long ( Figure 1 ) and 10 feet 2 inches wide ( Figure 2 ) has an enclosed footprint and an overall height (excluding the scavenging fan 120) of 12 feet 8 inches. In this example, there are 88 square feet of coil area (evaporator 212) available for the cooling process. At a nominal 500 fpm through the evaporator 212, a design flow rate of 44,000 scfm and 348 kW is possible, resulting in a perimeter watt capacity of 107 kW / m. The coil length of the evaporator 212 can be easily extended to further increase the airflow, thereby increasing the capacity of the cooling system 110 without increasing its width, thereby making a larger perimeter watt capacity possible. The cooling system 110 can be divided into two sections, the interior air handler 132 and the condensing unit 134. As Figure 1 and Figure 2 As shown, the evaporators 212a, 212b, 212c, 212d and the supply air fan 116 are located in the interior air handler 132. The remaining components of the airflow cooling assembly 200, including the subsystem 230 and the scavenging fan 120, are located in the condensing unit 134. Figure 1 In FIG. 1 , condensing unit 134 is shown adjacent to interior air handler 132 , but it may be located in any suitable location, including, for example, on top of a roof of data center 100 (eg, a building housing racks 102 ).

[0050] Any number of suitable configurations of multiple airflow cooling assembly circuits 200 may be used. For example, Figure 6 FIG. 1 is a schematic diagram of another arrangement of a cooling system 110 having multiple airflow cooling component loops 200. Figure 6 In the configuration shown, the cooling system 110 has four airflow cooling assembly circuits 200. The evaporators 212e, 212f, 212g, 212h of each circuit 200 are arranged in series with respect to the return air 114, but as described above, the evaporators 212e, 212f, 212g, and 212h may also be arranged in parallel. The return air is first directed through the evaporator 212e of the first circuit, and then directed through the evaporator 212f of the second circuit, the evaporator 212g of the third circuit, and the evaporator 212h of the fourth circuit. Figure 6 In the configuration shown, all four passive condensers 214e, 214f, 214g, 214h are arranged in parallel with respect to the purge gas 118, but as described above, the passive condensers 214e, 214f, 214g and 214h can also be arranged in series. Each condenser 234e, 234f, 234g, 234h for the secondary cooling system 230 (in this embodiment, a direct expansion cooling system) is arranged in series with respect to the purge gas 118 with the passive condenser 214e, 214f, 214g, 214h of the corresponding circuit.

[0051] Typically, the internal temperature of each airflow cooling assembly loop 200 will be isothermal, but each of the four airflow cooling assembly loops 200 will operate at different temperatures and pressures. The temperature of the primary 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, 212h then becomes cooler than the air in the previous loop due to the cooling generated by the previous loop. When the ambient air temperature is lower than the temperature of each airflow cooling assembly loop 200, the energy in the primary cooling medium can be transferred from the return air 114 to the scavenging air 118 in a passive mode, with all four loops operating in a passive mode, such as Figure 6 shown.

[0052] Each circuit can selectively operate in passive or active mode. Figure 7 1 shows the operation of the cooling system 110, wherein the fourth circuit is in active mode and the other three circuits are in passive mode, Figure 8All four circuits are shown in active mode. A controller 240 can be used to operate the cooling system 110. In this embodiment, the 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. The controller 240 may also be referred to as a CPU. In one embodiment, control of the cooling system 110 can be achieved by a series of instructions stored in the memory 244 and executed by the processor 242.

[0053] The controller 240 is communicatively coupled to the 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 air flow cooling assembly loop 200. For example, the loop sensor 250 can use a temperature sensor ("TS") 252 and a pressure sensor ("PS") 254 to measure the temperature and pressure of the primary cooling medium 202 in each loop. Preferably, the temperature and pressure sensors 252, 254 are located in the liquid refrigerant pipeline 224 to monitor the temperature and pressure of the liquid 204 phase of the primary cooling medium 202.

[0054] The controller 240 may also be communicatively coupled 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 may be communicatively coupled to the controller 240, so that the controller 240 may 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 increase or decrease the airflow. The controller 240 may also be communicatively coupled to the secondary cooling systems 230e, 230f, 230g, 230h of each circuit and used to turn on or off (activate or deactivate) the secondary cooling systems 230e, 230f, 230g, 230h.

[0055] Fig. 9 is a flow chart showing how to control Figure 6 and Figure 7An example of a cooling system 110 shown in FIG. 4 is shown in FIG. 405 . In step S405 , the controller 240 directs the return air 114 to the evaporators 212e, 212f, 212g, 212h. The supply air temperature sensor 122 is used to measure the temperature of the supply air 112, and the controller 240 receives the air temperature of the supply air 112 in step S410. The controller 240 then compares the measured temperature of the supply air 112 with the set point in step S415. The set point can be provided to the controller 240 using any suitable method or device. For example, the controller 240 can be communicatively coupled to a user interface through which a user can provide a desired temperature of the supply air 112, and the controller 240 can receive the desired temperature of the supply air 112 for use as a set point. If the temperature of the supply air 112 is equal to the set point (or within an appropriate operating range of the set point), the control system 240 returns to step S405 to continue monitoring the temperature of the supply air 112.

[0056] If the temperature of the supply air 112 is too low (below the set point or the temperature of the operating range), the controller 240 checks in step S420 whether any of the circuits 200 is operating in the active mode. For example, when the controller activates or deactivates the secondary cooling system 230 for the circuit, the controller 240 can store the mode of the circuit in the memory 244. The controller 240 can then query the memory 244 to determine the mode of any circuit. The controller 240 can store other suitable parameters in the memory 244, such as the flow rate of the scavenging air 118 (e.g., the speed and number of scavenging fans 120 running), for example, and the controller 240 can also check and change these parameters in a similar manner. If the controller 240 determines (in step S420) that no circuit 200 is in the active mode, the controller 240 reduces the airflow of the scavenging air 118 in step S425 before returning to step S405 to continue monitoring the temperature of the supply air 112. If any changes are made to the cooling system 110 in step S425 (or any other step 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 the controller 240 determines in step S420 that at least one circuit 200 is in the active mode, the controller 240 deactivates the secondary cooling system 230 in one of the circuits 200 in step S430. Figure 7 As shown, the fourth circuit operates in active mode. If the temperature of the supply air is too low in this configuration, the controller 240 will deactivate the auxiliary cooling system 230h of the fourth circuit, returning the fourth circuit to passive mode, such as Figure 6Preferably, the controller 240 will deactivate the secondary cooling system 230 of the circuit operating in the active mode, the evaporator 212 of which is located most upstream relative to the return air 114. The 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 set point 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 in any suitable manner, including, for example, by increasing the speed of the scavenging air fan 120. If the airflow of the scavenging air 118 cannot be increased (the scavenging air 118 is at its maximum airflow), in step S445, the controller 240 checks whether all circuits 200 are in active mode. If all circuits 200 are in active mode, such as Figure 8 As shown, the cooling system 110 operates at its maximum cooling capacity and the controller 240 returns to step S405. If at least one circuit is in the passive mode, the controller 240 will start the secondary cooling system 230 of one of the circuits 200 in step S450. For example, Figure 6 As shown, if all circuits are operated in the passive mode, the controller 240 will start the secondary cooling system 230 of one of the circuits 200, such as the secondary cooling system 230h of the fourth circuit. Preferably, the controller 240 will start the secondary cooling system 230 of the circuit operating in the passive mode, whose evaporator 212 is located most downstream relative to the return air 114. The controller 240 then returns to step S405 to continue monitoring the temperature of the supply air 112.

[0059] For data center cooling systems, it is generally desirable to have an efficiency of 65% or more in an economizer mode (passive mode in this embodiment). In passive mode, the refrigerant is at nearly the same pressure at all locations within the main coolant loop 210, and the internal temperature is isothermal. Based on the energy balance requirements, if the heat transfer constraints of the passive condenser 214 and the evaporator 212 are the same (the air flow on the outer surfaces of the condenser 214 and the evaporator 212 are the same and the surface features of the outer surfaces of the condenser 214 and the evaporator 212 are the same), the refrigerant will exist at a temperature equal to the average temperature of the inlet of the evaporator 212 and the passive condenser 214, and in non-ideal conditions, the net efficiency of a single loop 200 will be less than 50%. However, in the case of unbalanced airflow on the outer surfaces of the condenser 214 and the evaporator 212, heat exchange efficiencies can be achieved when measured on an evaporator size greater than 50%.

[0060] By using multiple loops 200 with air flowing countercurrent to the flow in 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%, with the scavenge air 118 flowing in series through the first loop and then through the second loop, and the return air 114 flowing 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 can be positioned countercurrently instead of two to achieve a net efficiency greater than 70%. The above calculations used scavenge air 118 delivered at 10,000 cfm at a temperature of 70°F and return air 114 delivered at 5,000 cfm at a temperature of 100°F.

[0061] The following examples (cases 1 through 6) were used to evaluate the efficiency of a single loop 200. The results of these evaluations are shown in Table 1 below. The following cases used unbalanced airflow, where the scavenging fan 120 was selected to provide an airflow ratio of at least 2:1 of scavenging air 118 to return air 114 based on a nominal 500 fpm face velocity of the return air 114 on the evaporator 212. However, in the following experimental case, a flow ratio closer to 2.2:1 was achieved, where the total airflow through the evaporator 212 was 5000 scfm, and the total airflow through the passive condenser 214 was 11,000 scfm. The face velocity through the passive condenser 214 was 500 fpm.

[0062] The first case (Case 1) uses finned tube ("FT") coils for the evaporator 212 and the passive condenser 214. The coils for the evaporator 212 are flooded two-row one-pass coils, while the coils for the passive condenser 214 are three-row one-pass coils. In a typical tube arrangement, both coils use half-inch tubes and have 10 fins per inch. Each coil is 5 feet long. Both the evaporator 212 and the passive condenser 214 are mounted at an angle of 15 degrees relative to the horizontal plane to facilitate vapor discharge and condensate flow by gravity. The lower end of the passive condenser 214 is mounted 2 feet above the upper discharge port of the evaporator 212. The vapor and liquid lines between the coils are oversized, using 1 1 / 8 inch tubes for the liquid refrigerant line 224 and 2 1 / 8 tubes for the vapor line 222, so as not to inhibit the refrigerant flow and affect the final performance. R410a is used as the refrigerant.

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

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

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

[0066] Table 1

[0067]

[0068] As can be seen from Table 1 above, by comparing Case 1 and Case 2, using microchannel coils instead of fin tube coils in the evaporator 212 has the most significant impact on performance, increasing the heat exchange efficiency from 34% to 57%. Changing the passive condenser 214 to a microchannel coil has little effect on the performance results under normal conditions (compare Case 2 and Case 3). Modifying the evaporator 212 and passive condenser 214 to have an additional vapor connection 322 results in a 3% efficiency gain under normal conditions (compare Case 3 and Case 4). When the temperature difference between the evaporator 212 and the passive condenser 214 increases, the efficiency decreases (compare Cases 3 and 4 with Cases 5 and 6, respectively), but having multiple vapor connections 322 results in a smaller efficiency decrease, and the total power transfer is greatly increased to nearly 50kW.

[0069] Using the properties of R410a and the known heat transfer rate, the mass flow rate of the primary cooling medium 202 can be calculated based on the specific heats of the vapor and liquid. In the case of the microchannel evaporator 212, the limit of the heat flux is in the range of 20kW. Using the enthalpy difference between the liquid and vapor of R410a, a mass flow rate of 387kg / hr and 5.88m 3 / h flow rate. Using the inner diameter of a single 7 / 8 inch tube, the velocity of the gas is 4.2 m / s. Adding two additional vapor connections to the coil increases the capacity by 50 kW and produces a velocity of 3.1 m / s. Therefore, for practical purposes, when using R410a, the pipe connections are preferably sized so that the maximum velocity is less than about 4 m / s. For a heat exchange rate of 50 kW, the vapor flow rate inside the microchannel extrusion 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 to 6, a plate heat exchanger was used as the active condenser 216. The active condenser 216 was arranged in parallel with the passive condenser 214, and cooling water was used as the secondary cooling medium 208. In the active mode, the efficiency data and the maximum power data closely mimicked the air-to-air data, confirming the superiority of the microchannel evaporator 212 over the fin-tube evaporator 212, and the increase in total capacity after adding additional header connections to the microchannels for vapor transport.

[0071] Another cooling system 110 such as Fig.10 and Fig.11 shown. Fig.10 and Fig.11 The features and components of the cooling system 110 shown in FIG. Figure 1-9 Similar to what discussed in . Fig.10 and Fig.11The same reference numerals are used to describe the same and like components as those described above, and a detailed description of these components is omitted in the following discussion. Fig.10 An internal air handler 132 is shown, Fig.11 The condensing unit 134 of the cooling system 110 of the present embodiment is shown.

[0072] and Figure 1 Like the cooling system 110 shown, Fig.10 and Fig.11 The cooling system 110 shown includes a plurality of evaporators 212, in this embodiment 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 tube 262 and a first common liquid refrigerant line 266. Likewise, 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 tube 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 similar to the vapor tube 222 and the 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 evaporator 212i before being directed through the second evaporator 212j.

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

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

[0075] like Fig.11 As shown, the 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. The first thermosyphon loop 200i includes an active condenser 216c4 connected in parallel with the six passive condensers 214i. The active condenser 234c4 of the first thermosyphon loop 200i is located in the 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 condenser 214. The scavenging fan 120c4 is configured to direct the scavenging air 118 onto 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, 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, 230c4 includes two condensers 234 connected in parallel to each other. In other embodiments, the precooler 124 (see Fig.12 ) can be used to cool the purge gas 118 before it passes through the passive condenser 214j of the second thermosyphon loop 200j. In this case, the active condensers 216jc1, 216jc2, 216jc3 in the second thermosyphon loop 200j can be omitted.

[0077] The arrangement of each of the first, second and third loops is similar to each other. The following description of the first loop is also applicable to the second and third loops. The condensers 214ic1, 214jc1, 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 air flow of the 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 thermosyphon loop 200j, the passive condenser 214ic1 of the first thermosyphon loop 200i and the condenser 234c1 of the auxiliary cooling system 230. The condensers 214jc1, 214ic1, 234c1 are arranged in series relative to the air flow of the scavenging gas 118. The scavenging air 118 is drawn through each condenser by the scavenging fan 120c1 of the first circuit, as described below. The scavenging air 118 is ambient air drawn from the outdoor environment surrounding the condensing unit 134 and first passes through the passive condenser 214jc1 of the second thermosyphon circuit 200j. Next, the scavenging air 118 passes through the passive condenser 214ic1 of the first thermosyphon circuit 200i. The scavenging air 118 then passes through the condenser 234c1 of the secondary cooling system 230 before being discharged to the outside by the scavenging fan 120. Each scavenging fan 120 can be independently variable or at least variable between different circuits.

[0078] This arrangement of the condensers 214jc1, 214ic1, 234c1 in the first circuit allows a counter-flow design. The main cooling medium 202 in the second thermosyphon circuit 200j is cooler than the main cooling medium 202 in the first thermosyphon circuit 200i. Therefore, the coldest purge gas 118 first passes through the coldest condenser 214jc1, and then after being heated by the passive condenser 214jc1 of the second thermosyphon circuit 200j, the purge gas 118 passes through the warmer passive condenser 214ic1 of the first thermosyphon circuit 200j.

[0079] Fig.10 and Fig.11 The cooling system 110 shown, like the cooling system 110 described above, does not use valves in the first thermosyphon loop 200i and the second thermosyphon loop 200j to switch between active and passive 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 to condense, and the airflow cooling assembly 100 is thermally transitioned from the passive mode to the active mode.

[0080] Fig.10 and Fig.11The cooling system 110 shown may be controlled similarly to the cooling system 110 described above, for example using reference Fig. 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 above 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 below the set point, the controller 240 will reduce the flow rate of the scavenging air 118 (e.g., reduce the fan speed of the scavenging fan 120) (see step S425).

[0081] If the temperature of the supply air 112 is above the set point and the flow rate of the scavenging air 118 is at its maximum value, the controller 240 will activate the secondary cooling system 230 (see step S450). Fig.10 and Fig.11 In the cooling system 110 shown, the controller 240 can gradually start the auxiliary cooling system 230 by loop as needed to maintain the temperature of the supply air 112 at the set point. Although the auxiliary cooling systems 230 of the loops can be gradually started in different orders, one method is to gradually start the auxiliary cooling systems 230 in the order of the first loop, the second loop, the third loop, and the fourth loop as needed. Therefore, in this embodiment, the auxiliary cooling system 230 of the second thermosyphon loop 200j can be gradually started before the auxiliary cooling system 230c4 of the first thermosyphon loop 200i. If the temperature of the supply air 112 is lower than the set point, the controller 240 can then deactivate the auxiliary cooling system 230 (see step S430), for example, in the reverse order of the loop gradual start.

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

[0083] Even when some or all of the active condensers 216 are operating, so that the system is operating in active mode, the inventors have unexpectedly discovered that there are some savings even in active mode (cooling of the primary cooling medium 202 from the passive condensers 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 of the first thermosyphon loop 200i and the second thermosyphon loop 200j was operated in active mode. The test was conducted for a variety of ambient air (scavenging air 118) temperatures, and the heat rejection from both the active condensers 216 and the passive condensers 214 was measured. The active mode of the loops was gradually turned on and off based on the ambient air temperature, but at the highest ambient air temperature, all of the secondary cooling systems 230 were operating.

[0084] Table 2

[0085]

[0086] In Table 2 above, heat rejection is calculated using the following equation (1).

[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 I is the temperature of the air (e.g., return air 114) entering the condenser or evaporator in degrees Fahrenheit, T O is the temperature of the air (e.g., supply air 112) leaving the condenser or evaporator in degrees Fahrenheit, a It is a factor based on the altitude. a ) can be calculated using equation (2) below, 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 to switch between modes, the valve 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 stop valve operated by a stepper motor. Here, the flow control valve 276 allows continuous regulation of the flow through the plug or disk of the flow control valve 276, and the plug or disk is operated by a stepper motor. The flow control valve 276 includes a closed position and a plurality of open positions, each open position having a different opening area. The plurality of open positions therefore 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 ​​the position.

[0091] The flow control valve 276 is used to precisely control the liquid level (the amount of primary cooling medium 202 in the liquid phase 204) in the evaporator 212 and maintain a desired temperature of the vapor 206 leaving the evaporator 212. The inventors have discovered that the use of the flow control valve 276 allows the primary cooling medium 202 to be efficiently circulated through the first thermosyphon loop 200i and the second thermosyphon loop 200j by natural circulation and gravity over a wide range of heat loads and ambient air conditions. The flow control valve 276 can be used to prevent too much liquid 204 from entering the evaporator 212 (e.g., flooding the evaporator 212), which would inhibit the vapor 206 from flowing out of the evaporator 212. In addition, the flow control valve 276 can be used to prevent too little liquid 204 from entering the evaporator 212 (e.g., starving the evaporator 212), which would inhibit effective and efficient condensation in the condensers 214, 216. This consideration, and therefore the use of the flow control valve 276, may be particularly relevant where the interior air handler 132 and condensing unit 134 are separated, as the greater distance requires a greater amount of primary cooling medium 202, further exacerbating the above-mentioned problems, such as flooding.

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

[0093] When the flow control valve 276 is controlled 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 of the evaporator 212 (or another suitable location at the bottom of the evaporator 212) and the temperature of the main cooling medium 202 at the outlet of the evaporator 212 (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 leaving the bottom third of the evaporator 212 (the third of the evaporator 212 near the inlet) and the temperature of the supply air 112 leaving the top third of the evaporator 212 (the third of the evaporator 212 near the outlet). The temperature rise can then be determined by taking the difference between the measured temperatures and comparing the difference to the set point. If the difference is lower than the set point, 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 above the set point, the controller 240 controls the stepper motor to move the flow control valve 276 in an opening direction to increase the flow of the liquid 204 entering the evaporator 212 .

[0094] Another method of controlling the flow control valve 276 is to measure the heat rejected by the return air 114 / supply air 112. When the flow control valve 276 is controlled based on the heat rejected by the return air 114 / supply air 112, a temperature sensor may be used to measure the temperature of the return air 114 before the return air 114 reaches the evaporator 212, and then to measure the temperature of the return air again after passing through the evaporator 212. The controller 240 may then be used to calculate the amount of heat rejected in the thermosyphon loop (e.g., the first thermosyphon loop 200i or the second thermosyphon 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 thermosyphon loop 200i, 200j as a function of the heat absorbed in the thermosyphon loop 200i, 200j based on a curve or lookup table. Different curves or values ​​may be used for different operating modes, such as a curve when each loop is operated in an active mode.

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

[0096] Another method of determining the heat rejected by the condensing unit 134 is to measure the heat absorbed by the purge gas 118. When the flow control valve 276 is controlled based on the heat absorption of the purge gas 118, a temperature sensor may be used to measure the temperature of the purge gas 118 before the purge gas 118 reaches the condenser 214, 216, 234 and after passing through the condenser 214, 216, 234. The controller 240 may then be used to calculate the absorption amount in the thermosyphon loop (e.g., the first thermosyphon loop 200i or the second thermosyphon loop 200j) based on the measured temperature and flow rate of the purge gas 118, and the controller may then set the position of the flow control valve 276 in the thermosyphon loop 200i, 200j as a function of the heat absorbed in the thermosyphon loop 200i, 200j based on a curve or lookup table in a manner similar to that discussed above for controlling the flow control valve 276 based on the heat rejection in the condenser 214, 216.

[0097] When the flow control valve 276 is controlled based on a predetermined value (set point) of the superheated vapor 206, if the superheat temperature of the vapor 206 rises above the set point, the flow control valve 276 can be opened to allow more condensed liquid 204 to enter the evaporator 212, thereby reducing the superheat temperature of the vapor 206. Similarly, if the superheat temperature of the vapor 206 decreases below the set point, the flow control valve 276 can be closed, reducing the flow of condensed liquid 204 entering the evaporator 212, thereby increasing the superheat temperature of the vapor 206. Loop sensors 250, such as temperature sensors 252 and pressure sensors 254, can be located at the outlet of the evaporator 212. Such sensors 250 can also be appropriately located in the evaporator 212 itself or in the vapor lines leading to the condensers 214, 216. The controller 240 then calculates the superheat based on the temperature and pressure measurements and compares it to the set point (e.g., a predetermined (desired) level). The controller 240 then adjusts the flow control valve 276 as described above. In any control method, once the measured or calculated value exceeds the set point, adjustments may not be made immediately; instead, when passing through an upper threshold temperature (or value) and a lower threshold temperature (or value) above and below the set point, respectively, the controller 240 may adjust the flow control valve 276. Although the present invention is described in terms of set point based control herein, one of ordinary skill in the art will understand that these operating bands are included in such descriptions.

[0098] As with any of the cooling systems 110 described herein, the speed of the supply air fan 116 that drives the airflow (return air 114) across the evaporator 212 can vary. 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 Fig.10 Alternatively, the air supply fan 116 may be located upstream of the evaporator 212, as shown in FIG. Figure 1As shown, the supply fans 116 may also be referred to as return air fans. In one example, the airflow of the return air 114 / supply air 112 may be driven by the requirements of the data center 100. The 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 the cooling system 110. The BMS determines what the speed of the supply fans 116 should be based on the needs in the data center 100. These needs may vary from data center to data center. The BMS may send a supply fan speed signal to the controller 240 for the cooling system 110, and the controller 240 may adjust the supply fans 116 (e.g., the speed and number of supply fans 116 that are running) to match the signal given by the BMS.

[0099] Another way to control the supply air fan 116 in the cooling system 110, for example if the BMS signal is not present, is to control the supply air fan 116 to a return air temperature set point of the temperature 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 supply air fans 116 operated) to maintain the temperature of the return air 114 at the return air temperature set point. If the temperature of the return air 114 is above the return air temperature set point, the speed (or number) of the supply air fan 116 is increased. If the temperature of the return air 114 is below the return air temperature set point, 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 a process fluid 142. In the above-described embodiments, the process fluid 142 cooled by the cooling system 110 is air. In the previous discussion, the air (process fluid 142) is directed to the racks 102 containing the electronic devices and is heated before being directed to the evaporator 212 (return air 114) to be cooled. However, the cooling system 110 described herein is not limited to cooling air and may be used to cool any suitable fluid. The process fluid 142 may include, for example, liquids such as water, water and ethylene glycol mixtures, and non-conductive fluids (dielectrics).

[0101] In the above-described embodiment, where the process fluid 142 is air, the evaporator 212 is suitably a microchannel coil or a finned tube coil. In the case where the process fluid 142 is a liquid rather than a vapor (gas), other suitable evaporators 212 may be used, including, for example, a plate heat exchanger, a coaxial heat exchanger, or a shell and tube heat exchanger. Fig.12The cooling system 110 is shown in which the evaporator 212 is suitably designed to cool a process fluid 142 as a liquid. The process fluid 142 is circulated in a process fluid loop 140 by 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 a rack 102 (see FIG. 1 ). Fig.13A and 13B ). The process fluid 142 is then 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 2121 is fluidly connected to the passive condenser 214 (passive condenser 2141) and the active condenser 216 (active condenser 2161), and is similar to the above-mentioned Figure 3 and Figure 4 The first evaporator 212k is fluidly connected to the passive condenser 214 (passive condenser 214k), and the passive condenser 214 is located downstream of the passive condenser 214l with respect to the air flow direction of the scavenging air 118 between the condenser 234 of the secondary cooling system 230 and the passive condenser 214l. As in the embodiment discussed above, the first evaporator 212k can also be fluidly connected to the passive condenser 214k and the active condenser 216 (active condenser 216k) to be similar to the above embodiment. Figure 3 and Figure 4 The condensing unit 134 of this embodiment may also include an adiabatic precooler 124 to precool the purge gas 118 before it passes through either 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, process fluid 142 may be heated by a heat load, such as servers 103 located in racks 102 of data center 100 . Fig.12 The cooling system 110 shown in FIG. 1 may be suitable for use with an immersion cooling system for the server 103 . Fig.13A and 13B An example of a rack 102 used in an immersion cooling system is shown. Fig.13A In the embodiment, the server 103 is submerged in the dielectric 146. The server 103 heats the dielectric 146, but the dielectric 146 remains liquid (single phase). The heated dielectric 146 circulates as the process fluid 142 through the process fluid loop 140 to be cooled and returned to the rack 102 to further cool the server 103.

[0104] exist Fig. 13B , the servers 103 are also immersed in the dielectric 146. In this case, the dielectric 146 cools the servers 103 by two-phase cooling. The servers 103 heat the dielectric 146, and the dielectric 146 changes phase to vapor (gas). The dielectric vapor rises to the top of the rack 102. The top of the rack 102 includes a coil 148. A suitable process fluid 142 passes through the coil 148 and condenses the dielectric 146. In another embodiment, the dielectric 146 in the gas phase can be directly cooled by the second evaporator 212l and the first evaporator 212k as the process fluid 142, instead of using another fluid.

[0105] In the above-described embodiment, the server 103 is physically separated from the first evaporator 212k and the second evaporator 212l, and the process fluid loop 140 is used to transfer heat from the server 103 or other information technology ("IT") equipment. However, the invention described herein is not limited to this, and the 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 the refrigerant integrated into a two-phase thermosyphon loop. Such other suitable evaporators 212 include, for example, a cold plate integrated into the server 103 or IT component to directly absorb heat from the component and / or the chips therein, or a plurality of tubular surfaces directly integrated into an immersion cooling system.

[0106] A second preferred embodiment of the airflow cooling assembly circuit 500 is as follows Fig.14 and 15 As shown. In this embodiment, the evaporator 512 and the passive condenser 514 are combined in the 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 portion 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 portion. As with the first embodiment, any suitable heat exchanger may be used, including a fin tube coil or a microchannel coil. In this embodiment, the integral heat exchanger 510 is shown as a fin tube coil having a tube 516 connecting two fixed headers, a top header 522 and a bottom header 524. As described below, gravity also plays a role in the cooling process, and therefore, the tube 516 is preferably oriented upright, more preferably vertically.

[0107] The airflow cooling assembly 500 operating in the passive mode is as follows Fig.14As shown. The hot return air 114 is directed to the evaporator portion 512 of the integral heat exchanger 510. The primary cooling medium 202 contained within the tubes 516 changes from a liquid phase 204 to a vapor phase 206, extracting heat from the return air 114, and thereby cooling the return air 114. As the primary cooling medium 202 evaporates, the vapor 206 rises in the tubes 516 to the condenser portion 514 of the heat exchanger. In the passive mode, the sweep air 118 is directed to the condenser portion 514. Heat is rejected from the primary cooling medium 202 to the sweep air 118, condensing the primary cooling medium from the vapor phase 206 to the liquid phase 204. The liquid 204 of the primary cooling medium 202 is then drawn down the sides of the tubes 516 back to the evaporator portion 512 with the help of gravity.

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

[0109] Also like the first embodiment, the airflow cooling assembly 500 of 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 to condense, and the airflow cooling assembly 500 automatically switches from the passive mode to the active mode. In addition, the controller 240 that can be communicatively coupled to the temperature sensors 122, 252 can be used to control the airflow cooling assembly 500 of this embodiment.

[0110] As described above, microchannel coils may be used in place of fin tube coils for integral heat exchanger 510. However, the total heat flux available may be limited in passive mode, which depends solely on heat pipe operation, because condensing liquid and evaporating gas flow counter to each other in the small channels of the microchannel extrusion. Fig.16 and Fig.17Another configuration of the second embodiment is shown, including a second passive condenser 530 (third condenser). In this embodiment, the third condenser 530 is a microchannel coil positioned in series with the condenser portion 514 of the integral heat exchanger 510 relative to the purge gas 118. Preferably, the third condenser 530 is positioned on the upstream side of the condenser portion 514 of the integral heat exchanger. The third condenser 530 has a vapor header 532 and a liquid header 534. The vapor header 532 of the third condenser is connected to the top header 522 of the integral heat exchanger 510 through a vapor pipe 526.

[0111] In passive mode (such as Fig.16 ), the vapor 206 of the primary cooling medium 202 will flow through the vapor tube 526 and enter the third heat exchanger, where most of the condensation of the primary cooling medium 202 will occur. As with the passive condenser 214 of the first embodiment, the purge gas 118 is driven across the outer surface of the third condenser 530, and the heat of the primary cooling medium 202 contained in the third condenser 530 is released to the purge gas 118, thereby condensing the vapor 206 into liquid 204. The liquid 204 of the primary cooling medium 202 then travels to the bottom header 524 through the liquid refrigerant line 528 with the help of gravity as a recirculating refrigerant stream.

[0112] In active mode (such as Fig.17 530 for condensation, and in the active mode, the flow of the primary cooling medium 202 through the third condenser 530 is minimal (if any). As with 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 avoid reverse flow of the primary cooling medium 202 through the condenser 216, 530 that is not currently operating in a given mode.

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

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

[0115] Fig. 20 and Fig.21 Another cooling system 110 is shown having two airflow cooling component loops 600, a first airflow cooling component loop 600a and a second airflow cooling component loop 600b, although any number of loops, including a single loop, may be used. As discussed above, a letter is appended after the reference numeral to designate the loop in which the component is located. In this cooling system 110, the return air 114 is directed through two cooling coils 612a, 612b arranged in parallel relative to the return air 114, although 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 primary cooling medium 602 contained within the primary coolant loop 610, thereby heating the primary cooling medium 602. Any suitable primary cooling medium 602 may be used, including, for example, water or a mixture of water and ethylene glycol.

[0116] The heat absorbed by the primary cooling medium 602 is then rejected at the second coil 614 in economizing mode or at the heat exchanger 616 in active mode. The primary cooling medium 602 is circulated through the primary coolant loop 610 by a pump 618 and reaches the second coil 614 or the heat exchanger 616. The diverter valve 620 selectively directs the pumped primary cooling medium 602 to the second coil 614 or the heat exchanger 616 depending on the mode.

[0117] Fig. 20The cooling system 110 is shown in a conservation mode. When the ambient air temperature is lower than the temperature of the primary cooling medium 602 after absorbing heat from the return air 114 (e.g., measured at a point in the primary coolant loop 610 after the cooling coil 612), the conservation mode is used, just like the passive mode discussed in the above embodiments. As with the embodiments discussed above, a predetermined temperature differential can be applied to determine when to use the conservation mode or the active mode. In the conservation mode, the diverter valve 620 directs the primary cooling medium 602 from the cooling coil 612 to the secondary coil 614 to cool the primary cooling medium 602. The scavenging fan 120 directs the scavenging air 118 across the outer surface of the secondary coil 614. The heat in the primary cooling medium 602 is then discharged from the primary cooling medium 602 and absorbed by the scavenging air 118. The primary cooling medium 602 is then returned to the cooling coil 612. The cooling coil 612 and the secondary coil 614 can be any suitable coils, including, for example, fin tube coils or microchannel coils. An expansion tank 622 may be located upstream of the pump 618 and after the cooling coil 612 .

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

[0119] Although the present invention has been described in some specific exemplary embodiments, many additional modifications and variations will be apparent to those skilled in the art based on this disclosure. Therefore, it should be understood that the present invention can be practiced in a manner different from that specifically described. Therefore, the exemplary embodiments of the present invention should be considered in all aspects to be illustrative and not restrictive, and the scope of the present invention is determined by any claims supported by the present application and its equivalents, rather than by the foregoing description.

Claims

1. A cooling system, comprising: an evaporator containing a primary cooling medium, the evaporator being configured to receive a process fluid and, when receiving the process fluid, change a phase of the primary cooling medium from a liquid to a gas; a passive condenser fluidly coupled to the evaporator, the passive condenser configured to receive cooling air, wherein when the passive condenser receives cooling air, the passive condenser is configured to (i) receive a primary cooling medium in a gas phase 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 primary cooling medium in a liquid phase to the evaporator; a first heat exchanger fluidly coupled to the evaporator and configured to have a first secondary cooling medium provided thereto, wherein when the first secondary cooling medium is provided to the first heat exchanger, the first heat exchanger is configured to (i) receive a primary cooling medium in a gas phase 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 primary cooling medium in a liquid phase to the evaporator; and a second heat exchanger fluidly coupled to the evaporator and configured to have a second secondary cooling medium selectively provided thereto such that: (a) when the second secondary cooling medium is supplied to the second heat exchanger, without operating any valves between the evaporator and the passive condenser and between the evaporator and the second heat exchanger, at least some of the primary cooling medium in vapor phase 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 primary cooling medium in vapor phase 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 primary cooling medium in liquid phase 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 main cooling medium in liquid phase to the evaporator, In the case 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 secondary cooling medium is a refrigerant of a direct expansion cooling system, and the direct expansion cooling system includes a compressor and an expansion valve.

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

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

5. The cooling system according to claim 1, wherein: The passive condenser is arranged in parallel with the first heat exchanger relative to the flow of the primary cooling medium.

6. The cooling system according to claim 1, wherein: The passive condenser is arranged in parallel with the second heat exchanger relative to the flow of the primary 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 primary 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. An electronic system comprising: at least one electronic component cooled by a dielectric; and The cooling system of claim 1, wherein the cooling system cools the dielectric.

11. The electronic system according to claim 10, wherein: The process fluid is the dielectric.

12. The cooling system according to claim 1 further includes a flow control valve, which is positioned in the flow path between the first heat exchanger and the evaporator, in the flow path between the second heat exchanger and the evaporator, and in the flow path between the passive condenser and the evaporator, and the flow control valve has a plurality of opening positions and is configured to control the flow of the liquid phase main cooling medium into the evaporator.

13. The cooling system of claim 12, further comprising a controller configured to control a position of the flow control valve between the plurality of open positions.

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

15. A cooling system comprising: an evaporator containing a primary cooling medium, the evaporator being configured to receive a process fluid and, when receiving the process fluid, change a phase of the primary cooling medium from a liquid to a gas; a passive condenser fluidly coupled to the evaporator, the passive condenser configured to receive cooling air from the cooling air stream, wherein when the passive condenser receives the cooling air, the passive condenser is configured to (i) receive a primary cooling medium in a gas phase 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 primary cooling medium in a liquid phase to the evaporator; a precooler located in the cooling air flow upstream of the passive condenser, the precooler being configured to cool the cooling air before the cooling air is received by the passive condenser; and a heat exchanger fluidly coupled to the evaporator and configured to have a secondary cooling medium selectively provided thereto such that: (a) when the secondary cooling medium is supplied to the heat exchanger, without operating any valves between the evaporator and the passive condenser and between the evaporator and the heat exchanger, at least some of the primary cooling medium in vapor phase is switched from being received by the passive condenser to being received by the heat exchanger, and the heat exchanger is configured to (i) receive the primary cooling medium in vapor phase 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 primary cooling medium in liquid phase to the evaporator; and (b) when the secondary cooling medium is not supplied to the heat exchanger, the heat exchanger does not supply the primary cooling medium in liquid phase to the evaporator, In the case 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 according to claim 15 further includes a flow control valve, which is positioned in the flow path between the heat exchanger and the evaporator and in the flow path between the passive condenser and the evaporator, and the flow control valve has a plurality of opening positions and is configured to control the flow of the liquid phase main cooling medium into the evaporator.

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

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

21. The cooling system of claim 15, wherein: The process fluid is air.

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