Liquid cooling system and a method for extracting heat from a server rack

Abstract

The present invention relates to a liquid cooling system (1) for extracting heat from a server arranged in a rack, wherein the liquid cooling system comprises: a circuit (20) comprising a plurality of channels configured to guide a flow of liquid; a first air-to-liquid heat exchanger (30) arranged on a first circuit (31) and configured to absorb heat from air within a cabinet housing the server by circulating the liquid through the first air-to-liquid heat exchanger; and a liquid cold-plate (40) arranged on a second circuit (41) and in thermal communication with a heat-intensity device of the server and configured for absorbing heat from the heat-intensity device, wherein the first circuit (31) is serially connected by a liquid channel (21) to the second circuit (41), wherein the liquid cold-plate (40) is downstream to the air-to- liquid heat exchanger (30) relative to the liquid flow.

Description

[0001] Liquid cooling system and a method for extracting heat from a server rack

[0002] Field of the Invention

[0003] The present invention relates to a system for extracting heat from a server. The invention also relates to a method of extracting heat from a server and how to control the system in order to maximize the heat output.

[0004] Background of the Invention

[0005] Whenever a computer such as a server performs data processing, computation and any other tasks, the computer hardware produces heat which requires cooling. It is estimated that data centres consume approximately 4% of the global energy consumption, where approximately half of the energy consumed in a data centre is used to cool the servers. Oftentimes, when a server is cooled the excess heat removed from the servers is vented into the atmosphere and lost.

[0006] It is estimated that 70-80% of the combined energy consumed by the computer hardware (which becomes heat) and the cooling systems can be reused as e.g., district heating. However, so far, no sustainable solutions have been implemented in a widespread manner.

[0007] US20200113083A1 describes a system and method for cooling heat-generating devices, wherein an air-to-liquid heat exchanger is configured to absorb heated air from a plurality of server chassis and provide cooled air back to the chassis while absorbing the heating into the liquid being fed back to a cooler. Furthermore, cooled liquid is also provided to a plurality of liquid cold plates each configured to provide cooling to heat-intensity devices.

[0008] Object of the Invention

[0009] One objective of the present disclosure is to achieve a system able to adequately cool one or more servers while providing a high temperature liquid output which temperature is adequately high in order to be reused. Hence, the objective is to provide a system with a sustainable design, which aids in reducing the environmental impact of data server cooling. A further objective of the invention is to provide a system which is modular and may be used for a plurality of different server configurations and sizes and / or enable a server rack to be progressively upgraded / filled with hardware while still being able to provide the high temperature liquid output.

[0010] Description of the Invention

[0011] One objective of the invention is achieved by a liquid cooling system for extracting heat from a server arranged in a rack, wherein the liquid cooling system comprises:

[0012] - a circuit comprising a plurality of channels configured to guide a flow of liquid;

[0013] - a first air-to-liquid heat exchanger arranged on a first circuit and configured to absorb heat from air within a cabinet housing the server by circulating the liquid through the first air-to-liquid heat exchanger; and

[0014] - a liquid cold-plate arranged on a second circuit and in thermal communication with a heat-intensity device of the server and configured for absorbing heat from the heat-intensity device, wherein the first circuit is serially connected by a liquid channel to the second circuit, wherein the liquid cold-plate is downstream to the air-to-liquid heat exchanger relative to the liquid flow.

[0015] The rack may comprise a plurality of servers, wherein each server may function as a database server, a web server, media-processing server, a computing server, a game server, email server, proxy server, scientific server, file server. Generally, a server may be contained in a single cabinet. However, a server may also require several cabinets, i.e., a distributed server. Furthermore, a single server cabinet may also house a plurality of server functions, e.g., by being configured to perform server virtualization.

[0016] Each server may comprise one or more heat-intensity devices such as a general processing unit (CPU), a graphics processing unit (GPU), field-programmable gate array (FPGA), neural processing unit (NPU), deep learning processor, accelerated processing unit (APU), chipset, data storage media such as randomaccess memory (RAM) or solid-state drives (SSD), and network and communication processors, among others. The circuit comprising a plurality of channels configured to guide a flow of liquid may comprise a circuit loop, wherein the circuit comprises a heat outlet configured for extracting a heated liquid from the circuit and a cooling inlet configured for transferring a cooled liquid to the circuit. In one aspect, a cooling unit may be connected to the cooling inlet and be configured to extract heat from and cool the liquid flowing through the circuit. The cooling unit may be a liquid-to- liquid heat exchanger configured for extracting heating from the liquid and transfer the heating to an output liquid.

[0017] In one aspect, the liquid cooling system may comprise a single air-to-liquid heat exchanger configured to absorb heating from the air within the one or more cabinets housing the servers. In this aspect, the heat exchanger may cover an entire side of the rack. In a further aspect, an air-to-liquid heat exchanger may be arranged in contact or the vicinity of each cabinet housing a server. In this aspect where multiple servers are arranged in a rack each comprising an air-to-liquid heat exchanger, the liquid flowing through each air-to-liquid heat exchangers may be configured to flow in parallel from a downstream to an upstream position of the first circuit.

[0018] In one aspect, the second circuit may comprise one or more manifolds configured to distribute the flow of liquid to two or more liquid cold-plates in thermal communication with heat-intensity devices. Le., the liquid cold-plates may be arranged in parallel relative to the flow of liquid. Preferably, a plurality of liquid cold-plates is connected to the manifold in order to provide cooling to a plurality of heat-intensity devices in a plurality of servers. In a further aspect, if a server in a cabinet comprises two, three or more heat-intensity devices e.g., two CPUs or two CPUs and a GPU or any other combination thereof, the liquid cold-plates may be serially connected so that only one inlet channel and one outlet channel must be provided to provide a flow of liquid into and out of the cabinet.

[0019] The liquid cold-plate may be a piece of metal configured for being coupled with a heat dissipating surface of the heat-intensity devices and configured to absorb heat from the heat-intensity devices. The liquid cold-plate may comprise internal channels and chambers comprising heat sinks configured to efficiently transfer heat to the liquid. In another aspect, the liquid cold-plate may comprise heat pipes configured to transfer the heat efficiently to the liquid.

[0020] One advantage of providing a manifold is that heat may be extracted from a plurality of heat-intensity devices at once, and hence the liquid cooling system can provide cooling and heat extraction from a plurality of servers in a rack. A further advantage is that the rack can be built and upgraded in an easy and modular manner simply by plugging further channels into the manifold, so that further liquid cold-plates are connected to the second circuit.

[0021] One advantage of serially connecting the first circuit by a liquid channel to the second circuit, is that the liquid first absorbs heating from the air by being circulated through the first air-to-liquid heat exchanger and then secondly absorbs heating from the liquid cold-plates by being circulated through the second circuit and flowing over the one or more liquid cold-plates, thus obtaining a higher output temperature compared to if the first and second circuit were arranged in parallel or not connected altogether, wherein the output temperature is measured downstream to the second circuit.

[0022] In one example, the first air-to-liquid heat exchanger may be supplied with a liquid at a low initial temperature (e.g., an ambient temperature of 18 to 25 degrees Celsius) and the first air-to-liquid heat exchanger may raise an intermediate temperature of the liquid to a medium level (e.g., 30-35 degrees Celsius) and then further heat absorption at the liquid cold-plates further raises the liquid temperature to a scalding level (e.g., 50-90 degrees Celsius), wherein the initial temperature and intermediate temperature are measured upstream and downstream to the first air-to-liquid heat exchanger, respectively. If the second circuit and consequently the liquid cold-plates were provided with a liquid with a lower input temperature (e.g., 15-25 degrees Celsius) measured upstream to the liquid cold-plates, the output temperature would not consistently reach a scalding or a high level of heating and thus the liquid is not heated sufficiently in order to be re-used as waste heat. Hence, an advantage of the liquid cooling system is that the high level of heating being extracted from the server and transferred into the liquid may be used as waste heat for heat demanding processes. The waste heat may be re-used either by transferring the heated liquid to the heat demanding process or by converting the heat stored in the heated liquid to another liquid or another medium such as a gas. Among others, the heat demanding processes may be for heat consumers in district heating, greenhouses, space heating, industrial manufacturing, etc.

[0023] A further advantage of heat extraction from both the air within the cabinets housing the servers and the heat-intensity devices is that the server hardware is cooled so that the server hardware achieves a long lifespan, can operate continuously with minimal downtime, and avoids thermal throttling which reduces performance.

[0024] In a further embodiment of the liquid cooling system, the first circuit comprises a first recirculation channel arranged between an upstream and a downstream position relative to the first air-to-liquid heat exchanger and wherein the first circuit comprises a first valve unit configured to adjust recirculation of the liquid through the first circuit.

[0025] The first valve unit may be configured to adjust the flow of liquid through one or more channels, e.g., a T-shaped joint, wherein the first recirculation channel may form a part of the T-shaped joint. In one aspect, the first valve unit may be a three-way valve. In a further aspect, the first valve unit may be two separate oneway valves arranged on two channels of a T-shaped joint, e.g., the first recirculation channel and a channel upstream to the first air-to-liquid heat exchanger.

[0026] One advantage of providing a gradual liquid recirculation to the flow of liquid through the first circuit is that the recirculated liquid decreases occurrence of cold and / or hot spots / pockets trapped within channels of the first circuit and / or the first air-to-liquid heat exchanger. One advantage of providing a greater degree of recirculation of the flow of liquid through the first circuit and the first air-to-liquid heat exchanger is that the intermediate temperature of the liquid measured downstream to the first air-to- liquid heat exchanger may reach an even higher temperature. Thus, if the air within the cabinet housing the servers is at a low temperature, the recirculation may ensure that the intermediate temperature is still high, so that the liquid which is transferred into the second circuit and out of the second circuit is at a high output temperature, so that it may be re-used as waste heat.

[0027] A further advantage of the first valve unit is that it enables the liquid to gradually or completely bypass the first air-to-liquid heat exchanger. In one scenario, the bypass may be favorable if the air within the cabinet does not require cooling; if the intermediate temperature of the liquid downstream to the first air-to-liquid heat exchanger is sufficiently high; and / or if the one or more heat-intensity devices require a higher-than-normal amount of cooling from the liquid cold-plates to e.g., protect the heat-intensity devices from damage due to overheating or prevent thermal throttling.

[0028] In a further embodiment of the liquid cooling system, the second circuit comprises a second recirculation channel arranged between an upstream and a downstream position relative to the liquid cold-plate and wherein the second circuit comprises a second valve unit configured to adjust recirculation of the liquid through the second circuit.

[0029] The second valve unit may be configured to adjust the flow of liquid through one or more channels, e.g., a T-shaped joint, wherein the second recirculation channel may form a part of the T-shaped joint. In one aspect, the second valve unit may be a three-way valve. In a further aspect, the second valve unit may be two separate one-way valves arranged on two channels of a T-shaped joint, e.g., the second recirculation channel and a channel upstream to the liquid cold-plate.

[0030] One advantage of providing a gradual liquid recirculation to the flow of liquid through the second circuit is that the recirculated liquid decreases occurrence of cold and / or hot spots / pockets trapped within channels of the second circuit and / or the one or more liquid cold-plates.

[0031] One advantage of providing a greater degree of recirculation of the flow of liquid through the second circuit and the one or more liquid cold-plates is that the output temperature of the liquid measured downstream to the liquid cold-plates may reach an even higher temperature. Thus, if the one or more heat-intensity devices are running at a lower temperature, the recirculation may ensure that the output temperature is still high so that the heated liquid or the heat which is extracted from the liquid cooling system may be re-used as waste heat.

[0032] A further advantage of the second valve unit is that it enables the liquid to gradually or completely bypass the one or more liquid cold-plates. In one example, the bypass may be favorable if the one or more heat-intensity devices do not require cooling.

[0033] In a further embodiment of the liquid cooling system, the first circuit and / or the second circuit comprises one or more pumps configured to adjust and / or maintain the flow of liquid through the circuit.

[0034] In one aspect, the one or more pumps may be arranged upstream to the first air- to-liquid heat exchanger and / or upstream to the one or more liquid cold-plates.

[0035] In one aspect, one or more pressure sensors may be arranged upstream and / or downstream to each pump, wherein the pressure sensors are configured to measure the pressure of the liquid and wherein the pressure of the liquid may be used to control a pumping speed of the one or more pumps. In a further aspect, pressure sensors arranged upstream and downstream to a pump may be used to determine a differential pressure, wherein the differential pressure may be used to control the pump.

[0036] One advantage of increasing the flow of liquid through the first circuit and / or the second circuit is that the heat absorption in the first air-to-liquid heat exchanger and / or the one or more liquid cold-plates is decreased for a given volume of liquid, respectively. Consequently, one advantage of decreasing the flow of liquid through the first circuit and / or the second circuit is that the heat absorption in the first air-to-liquid heat exchanger and / or the one or more liquid cold-plates is increased for a given volume of liquid, respectively.

[0037] A further advantage of increasing the flow of liquid is that the occurrence of cold and / or hot spots / pockets trapped within channels of the first and second circuits, the first air-to-liquid heat exchanger and the one or more liquid cold-plates may be reduced.

[0038] In a further embodiment of the liquid cooling system, the system comprises one or more temperature sensors configured for measuring a temperature of the liquid, one or more flow sensors configured for measuring a flow of the liquid, and a controller configured to adjust the first and / or second valve units and / or the one or more pumps, so that an output temperature of the liquid downstream to the liquid cold-plate is maximized while the heat-intensity device is sufficiently cooled.

[0039] In one aspect, the temperature sensors and / or the flow sensors may be arranged upstream and / or downstream to the one or more liquid cold-plates and / or the first air-to-liquid heat exchanger. Thus, the temperature sensors provide a measurement of the output temperature, measured downstream to the liquid cold plates; an intermediate temperature, measured downstream to the first air-to- liquid heat exchanger or upstream to the liquid cold-plates; or an initial temperature, measured upstream to the first air-to-liquid heat exchanger. Similarly, the flow sensors provide a measurement of the flow of the liquid at various positions along the circuit, the first circuit and / or the second circuit.

[0040] The one or more flow sensors may be used to adjust the speed of the one or more pumps to achieve an accurate control of the flow of liquid and in turn an optimal cooling of the server and / or optimal heat extraction.

[0041] In a further aspect, an air temperature sensor may be arranged inside the one or more cabinets housing the servers, wherein the air temperature sensor is configured to measure an air temperature. The cooling capacity of the first air-to- liquid heat exchanger may be controlled as a function of the air temperature, by e.g., increasing or decreasing the flow of liquid through the first air-to-liquid heat exchanger and / or increasing an airflow through the cabinet.

[0042] In one aspect, the controller may be implemented on a general processing unit, a computer, a microprocessor, a programmable system on a chip, or any other suitable processing unit.

[0043] The controller may implement a control loop to adjust the valve units and / or the one or more pumps based on a proportional, integral and / or derivative control algorithm or a combination thereof, e.g. a proportional-integral control algorithm or a proportional-integra-derivative control algorithm.

[0044] One advantage of providing a controller and adjusting the one or more valve units and / or the one or more pumps is that the intermediate temperature and / or the output temperature may be very precisely controlled, hence ensuring that the air within the cabinet and / or the heat-intensity devices are sufficiently cooled while an optimal amount of heat is extracted from the air and the heat-intensity devices. Thus, by being able to extract a great amount of heat from the servers, the heat can be re-used e.g., to deliver heating for an industrial plant, warm water supply, and / or district heating.

[0045] In one scenario, where one or more servers are not running at full capacity, the pumps may be adjusted to provide a lower flow of liquid so that the intermediate temperature and / or output temperature are still at a high level required in order to use the heated liquid as waste heat.

[0046] In a further embodiment of the liquid cooling system, the output temperature is in the range of 50 to 90 degrees Celsius, or 60 to 80 degrees Celsius, or 65 to 75 degrees Celsius.

[0047] One advantage of ensuring that the output temperature of the liquid is at least 50 degrees Celsius is that the liquid is warm enough to be re-used in an efficient manner. More preferably, if the output temperature is at least 60 degrees Celsius and up to 90 degrees Celsius, the re-use of the heated liquid may be very efficient and the re-use entails that the energy consumed on the heat extraction from the servers, essentially the server cooling, is more environmentally friendly because the extracted heat is not rejected into the atmosphere as waste heat.

[0048] In a further embodiment of the liquid cooling system, a second air-to-liquid heat exchanger is arranged on a circuit in parallel with the first air-to-liquid heat exchanger and is configured to cool a second rack.

[0049] In one aspect, the second air-to-liquid heat exchanger may be an in-row cooler arranged between two server racks and configured to absorb heating from the two adjacent racks.

[0050] The second air-to-liquid heat exchanger may be arranged in parallel to the first circuit or the first air-to-liquid heat exchanger by a cold liquid input and a warm liquid output of the second air-to-liquid heat exchanger being connected to an upstream position and a downstream position of the first circuit or the first air-to- liquid heat exchanger. In one aspect, the warm liquid output of the air-to-liquid heat exchanger may be connected to the one or more liquid cold-plates and / or it may be connected to the output liquid or the heat outlet, wherein this connection may be controlled by a valve unit, e.g., a three-way valve.

[0051] One advantage of arranging the first and second air-to-liquid heat exchangers in parallel is that an intermediate temperature of the liquid measured downstream to the two or more air-to-liquid heat exchangers is at a higher temperature compared to a single air-to-liquid heat exchanger.

[0052] In a further embodiment of the liquid cooling system, the first and / or second air- to-liquid heat exchanger is a rear-door cooler or computer room air-conditioning or in-row cooler or in-rack cooler or an aisle containment system, wherein the first and / or second air-to-liquid heat exchangers are configured to absorb heating from a plurality of servers arranged in a rack. A further objective of the invention is achieved by a method for extracting heat from a rack with a server, wherein the method comprises the steps of:

[0053] - providing a rack with a server, the rack comprising an air-to-liquid heat exchanger and the server comprising a heat-intensity device with a liquid coldplate;

[0054] - generating a liquid flow from the air-to-liquid heat exchanger through the liquid cold-plate; and

[0055] - adjusting the liquid flow to have a liquid temperature exiting the liquid cold-plate above 50 degrees Celsius.

[0056] The air-to-liquid heat exchanger may be configured to absorb heat from air within the rack and transfer the heat into a liquid. The liquid cold-plate may be configured to absorb heat from the heat-intensity device and transfer the heat into a liquid.

[0057] One advantage of generating the liquid flow from the air-to-liquid heat exchanger through the liquid cold-plate is that the temperature of the liquid exiting the liquid cold-plate is higher compared to if the air-to-liquid heat exchanger is arranged parallel to the liquid cold-plate or if the liquid does not flow through the air-to- liquid heat exchanger before flowing through the liquid cold-plate.

[0058] A further advantage of extracting heat from a server and the heat-intensity devices is that the server and the heat-intensity devices are cooled and thus may yield a higher computational performance, or a longer lifespan of the computer components may entail.

[0059] In one aspect, the liquid flow may be adjusted by decreasing or increasing the flowrate of the liquid flow so that a volume of the liquid absorbs heat over a longer or shorter period of time, respectively.

[0060] One advantage of adjusting the liquid flow to obtain a liquid temperature above 50 degrees Celsius is that heat energy in the liquid may be re-used for a variety of heating purposes, e.g., district heating or for industrial applications. Hence, an environmental impact of the heat extraction is lessened. In a further embodiment of the method, the method comprises a further step of:

[0061] - recirculating part of the liquid through the air-to-liquid heat exchanger and / or the liquid cold-plate.

[0062] Recirculation of a part of the liquid through the air-to-liquid heat exchanger and / or the liquid cold-plate may be achieved by providing at least one valve unit configured to recirculate a part of the liquid from a downstream position to an upstream position relative to the air-to-liquid heat exchanger and / or the liquid cold-plate, respectively.

[0063] One advantage of providing recirculation of a part of the liquid through the air-to- liquid heat exchanger and / or the liquid cold-plate is that the recirculated liquid decreases occurrence of cold and / or hot spots / pockets trapped in the air-to-liquid heat exchanger and / or the liquid cold-plate.

[0064] One further advantage of providing the recirculation of the liquid flow through the air-to-liquid heat exchanger and / or the liquid cold-plate is that the liquid temperature exiting the liquid cold-plate may reach an even higher temperature. Thus, if the one or more heat-intensity devices are running at a lower temperature, the recirculation may ensure that the liquid temperature is still high so that the liquid may be re-used as waste heat.

[0065] A further advantage of the recirculation of the liquid is that the recirculation may enable the flow of the liquid to be at a higher flow, while still ensuring that as much heat as possible is absorbed from the air within the rack and / or from the heat-intensity device.

[0066] In a further embodiment of the method, the method comprises a further step of:

[0067] - utilizing the liquid flow with the liquid temperature above 50 degrees Celsius for heating such as for heat consumers in district heating or industrial greenhouses or swimming pools or office installation or other industrial applications. One advantage of utilizing the heated liquid flow for heating is that an environmental impact of the heat extraction is lessened, and hence also the energy consumed on cooling the servers is lessened.

[0068] Description of the Drawing

[0069] Various examples are described hereinafter with reference to the figures. Like reference numerals refer to like elements throughout. Like elements will, thus, not be described in detail with respect to the description of each figure. It should also be noted that the figures are only intended to facilitate the description of the examples. They are not intended as an exhaustive description of the claimed invention or as a limitation on the scope of the claimed invention. In addition, an illustrated example need not have all the aspects or advantages shown. An aspect or an advantage described in conjunction with a particular example is not necessarily limited to that example and can be practiced in any other examples even if not so illustrated, or if not so explicitly described.

[0070] Exemplary embodiments of the invention are described in the figures, whereon:

[0071] Fig. 1 a illustrates one embodiment of a rack.

[0072] Fig. 1 b illustrates one embodiment of a liquid-cooler unit.

[0073] Fig. 2a illustrates one embodiment of a liquid cooling system.

[0074] Fig. 2b illustrates one further embodiment of a liquid cooling system.

[0075] Fig. 2c illustrates one further embodiment of a liquid cooling system.

[0076] Fig. 2d illustrates one further embodiment of a liquid cooling system.

[0077] Fig. 3a illustrates one embodiment of a method for extracting heat.

[0078] Fig. 3b illustrates one further embodiment of a method for extracting heat.

[0079] Detailed Description of the Invention

[0080] Exemplary examples will now be described more fully hereinafter with reference to the accompanying drawings. In this regard, the present examples may have different forms and should not be construed as being limited to the descriptions set forth herein. Accordingly, the examples are merely described below, by referring to the figures, to explain aspects. Throughout the specification, when an element is referred to as being “connected” to another element, the element is “directly connected” to the other element, “electrically connected”, “fluidic connected” or “communicatively connected” to the other element with one or more intervening elements interposed there between.

[0081] The terminology used herein is for the purpose of describing particular examples only and is not intended to be limiting. As used herein, the terms “comprises" "comprising" "includes" and / or "including" when used in this specification specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0082] Unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by those skilled in the art to which this invention pertains. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined in the present specification. Figure 1 a illustrates one embodiment of a rack 10 comprising a plurality of servers 11 housed in individual cabinets 14 in the rack 10. The air 13 within the cabinets 14 may be moved out of the cabinets 14 by fans 15 arranged in the cabinets 14. In another aspect, the one or more fans 15 may be arranged inside the one or more cabinets 14 so that a set of one or more fans each move air out of the cabinet 14 housing a server 11 .

[0083] The heating in the air 13 is absorbed into a liquid by a first air-to-liquid heat exchanger 30 arranged on the rack 10. The air-to-liquid heat exchanger 30 receives the liquid from a first circuit 31 connected to the liquid cooling system according to the present disclosure and transfers the heated liquid back to the first circuit 31. The first air-to-liquid heat exchanger may also comprise a plurality of fans 15 configured to move air from the cabinets 14 to pass over the heat exchanger. In another aspect, two or more air-to-liquid heat exchangers 30 may be arranged on the rack 10.

[0084] Figure 1b illustrates one embodiment of a liquid-cooler unit 45, the top illustration illustrates the unit as it is illustrated in the following figures and the bottom illustration illustrates the components of the unit.

[0085] The liquid-cooler unit 45 is connected to a second circuit 41 , wherein liquid is transferred to and away from the liquid-cooler unit 45 through the second circuit 41. The respective inlet and outlet to the liquid-cooler unit 45 may be provided with shut-off valves 45a enabling the liquid-cooler unit 45 to be easily serviced and / or replaced without requiring a drain of all liquid from the circuits.

[0086] The liquid-cooler unit 45 comprises one or more liquid cold-plates 40 configured to be in thermal communication with heat-intensity devices of the servers and configured to absorb heat from the heat-intensity devices. Each liquid cold-plate 40 may be connected via quick couplers 45c to a manifold 45b. The manifold 45b is configured to enable a plurality of liquid cold-plates 40 to be connected in parallel. The quick couplers 45c are configured to enable quick connection and disconnection of channels or tubes connecting the liquid cold-plates 40 to the manifold 45b. In one aspect, two or more liquid cold-plates 40 may be connected in series between two quick couplers 45c, so that a single pair of channels or tubing is provided into a cabinet in order to cool two or more heat-intensity devices.

[0087] Figure 2a illustrates one embodiment of a liquid cooling system 1 for extracting heat from a server 11 arranged in a rack 10 (as illustrated in fig. 1a), wherein the liquid cooling system comprises a circuit 20 comprising a plurality of channels configured to guide a flow of liquid. The circuit 20 comprises a liquid inlet 22 wherein liquid may be received into the circuit 20, and a liquid outlet 23 wherein liquid may be transferred out of the circuit 20. The circuit 20 may comprise a circuit pump 24 configured to maintain the flow of the liquid through the circuit 20.

[0088] The liquid cooling system 1 comprises a first air-to-liquid heat exchanger 30 arranged on a first circuit 31 and configured to absorb heat from air 13 within the cabinet 14 housing the server 11 (as illustrated in fig. 1 a). The first circuit 31 is connected to the circuit 20.

[0089] The liquid cooling system 1 comprises a liquid cooling unit 45 comprising one or more liquid-cold plates 40 (as illustrated in fig. 1b) arranged on a second circuit 41 and configured to absorb heat from one or more heat-intensity devices arranged in the one or more servers 11. The first circuit 31 is serially connected by a liquid channel 21 to the second circuit 41 , so that the one or more liquid cold-plates 40 are downstream to the air-to-liquid heat exchanger 30 relative to the flow of the liquid.

[0090] Figure 2b illustrates one further embodiment of the liquid cooling system 1 , wherein the first circuit 31 and / or the second circuit 41 comprises a pump 34, 44 configured to control the flow of the liquid through the respective circuits. Furthermore, the first circuit 31 comprises a first recirculation channel 32 and a first valve unit 33 configured to adjust an amount of liquid being recirculated from a downstream position to an upstream position relative to the air-to-liquid heat exchanger 30. The second circuit 41 may comprise a second recirculation channel 42 and a second valve unit 43 configured to adjust an amount of liquid being recirculated from a downstream position to an upstream position relative to the liquid cold-plates 40. The pumps 34, 44 may be configured to increase and / or decrease the flow of the recirculated liquid.

[0091] Figure 2c illustrates one further embodiment of the liquid cooling system 1 , wherein the circuit 20 comprises one or more temperature sensors 26, flow sensors 27 and / or pressure sensors 28 configured to measure the temperature, flow and pressure of the liquid flowing through the channels of the circuit 20.

[0092] The one or more sensors may be arranged to measure the temperature, flow and / or pressure of the liquid being received at the liquid inlet 22 and the liquid outlet 23. Furthermore, the sensors may also measure the flow and / or pressure upstream and downstream relative to the circuit pump 24 and / or the pumps 34, 44 in order to determine a differential pressure across the pumps, wherein the differential pressure may be used to control the pumps efficiently. Measurement of the flow of the liquid at two independent and spaced apart positions may be used to determine if a leak is occurring in the one or more circuits.

[0093] The first circuit 31 and the second circuit 41 may also comprise one or more temperature sensors 36, 46; flow sensors 37, 47 and / or pressure sensors 38, 48 configured to measure the temperature, flow and / or pressure of the liquid, respectively. Sensor measurements may be used to control the amount of recirculation through the first and / or second valve units 33, 43. Furthermore, the temperature measurements may be used to control the pumps 34, 44 so that the liquid flows at a slower speed which increases the heat absorption in the air-to- liquid heat exchanger 30 and / or the liquid cold-plates 40 and thus yields a higher temperature of the liquid which is transferred to the liquid outlet 23.

[0094] The liquid cooling system 1 may also comprise a bypass channel 51 configured to connect to a downstream position relative to the air-to-liquid heat exchanger 30 and an upstream position relative to the liquid cold-plates 40 so that the bypass channel 51 provides a flow of liquid from the air-to-liquid heat exchanger 30 directly to the liquid outlet 23. The bypass channel 51 comprises a bypass valve 53 configured to adjust the flow of liquid through the bypass channel 51. The bypass channel 51 may be used to bypass the liquid cold-plate 40 and / or to mix the higher temperature liquid flowing downstream from the liquid cold-plate 40 with a slightly lower temperature liquid flowing downstream from the air-to-liquid heat exchanger 30. One advantage of providing a bypass channel 51 is that the liquid cooling system 1 may be used for one or more racks 10 which do not comprise servers 11 with one or more heat-intensity devices.

[0095] A further advantage of the bypass channel 51 is that the liquid cooling system 1 may continue to circulate liquid for cooling and heat extraction through the one or more air-to-liquid heat exchangers 30,35. This may be useful in scenarios where the second circuit 41 is being serviced or the heat-intensity devices are not running and therefore do not require cooling by the liquid cold-plates 40.

[0096] A further advantage of providing a bypass channel 51 enabling an amount of the liquid flowing from the air-to-liquid heat exchanger 30 to be bypassed while a remaining amount flows to the liquid cold-plates is that the liquid cooling system 1 is more flexible. In one scenario, the air-to-liquid heat exchangers 30 may require a larger flow of liquid than the liquid cold-plates 40 require, then a part of the excess liquid flow from the air-to-liquid heat exchanger 30 may flow through the bypass channel 51.

[0097] Figure 2d illustrates one further embodiment of the liquid cooling system 1 , wherein the system comprises a second air-to-liquid heat exchanger 35 configured to absorb heating from a second rack. The second air-to-liquid heat exchanger 35 is arranged on an additional circuit 31a arranged in parallel to the first air-to-liquid heat exchanger 30, i.e., the two heat exchangers 30, 35 are connected to the same upstream position of the circuit 20 and the same downstream position of the liquid channel 21 wherein the upstream and downstream positions are relative to the heat exchangers 30, 35.

[0098] One advantage of providing a second air-to-liquid heat exchanger 35 in parallel to the first air-to-liquid heat exchanger is that the temperature of the liquid provided to the one or more liquid cold-plates 40 may be at a higher temperature and thus enabling the temperature of the liquid being transferred out of the liquid cold-plates 40 to be at a higher temperature. A further advantage is that a larger volume of liquid flows to the liquid cooling unit 45, ensuring that the flow of liquid may be as high as possible.

[0099] The flow of the liquid from the second air-to-liquid heat exchanger 35 may flow through the bypass channel 51 or the liquid channel 21 , the flow through one or both channels 21 , 51 is controlled by the bypass valve 53.

[0100] The one or more circuits 20, 31 , 31 a, 41 may comprise check valves 39, 49, 59 configured to block liquid from flowing from a downstream position to an upstream position. Le., the check valves 39, 49, 59 ensure that the liquid only flows in the intended direction. E.g., a third check valve 59 ensures that liquid downstream to the first air-to-liquid heat exchanger does not flow backwards to the second air-to-liquid heat exchanger 35; the first check valve 29 ensures that recirculated liquid does not flow into the liquid channel 21 and backwards from the liquid cold-plate to the first air-to-liquid heat exchanger 30 and / or the bypass channel 51 ; and a second check valve 49 ensures that liquid flowing from the bypass channel 51 to the liquid outlet 23 does not flow backwards to the liquid cold-plate 40 and / or the second valve unit.

[0101] Figure 3a illustrates one embodiment of a method 100 for extracting heat from a rack with a server, wherein the method comprises the steps of:

[0102] - providing 110 a rack with a server, the rack comprising an air-to-liquid heat exchanger and the server comprising a heat-intensity device with a liquid coldplate;

[0103] - generating 120 a liquid flow from the air-to-liquid heat exchanger through the liquid cold-plate; and

[0104] - adjusting 130 the liquid flow to have a liquid temperature exiting the liquid coldplate above 50 degrees Celsius.

[0105] Figure 3b illustrates further embodiments of the method 100, wherein the method comprises a further step of:

[0106] - recirculating 140 part of the liquid through the air-to-liquid heat exchanger and / or the liquid cold-plate. Furthermore, the method 100 may comprise a further step of:

[0107] - utilizing 150 the liquid flow with the liquid temperature above 50 degrees Celsius for heating such as for heat consumers in district heating or industrial greenhouses or swimming pools or office installation or other industrial applications.

Claims

CLAIMS1. A liquid cooling system (1 ) for extracting heat from a server (11) arranged in a rack (10), wherein the liquid cooling system comprises:- a circuit (20) comprising a plurality of channels configured to guide a flow of liquid;- a first air-to-liquid heat exchanger (30) arranged on a first circuit (31) and configured to absorb heat from air (13) within a cabinet (14) housing the server (11 ) by circulating the liquid through the first air-to-liquid heat exchanger; and- a liquid cold-plate (40) arranged on a second circuit (41 ) and in thermal communication with a heat-intensity device (12) of the server (11) and configured for absorbing heat from the heat-intensity device, wherein the first circuit (31) is serially connected by a liquid channel (21) to the second circuit (41 ), wherein the liquid cold-plate (40) is downstream to the air-to- liquid heat exchanger (30) relative to the liquid flow.

2. The liquid cooling system (1) according to claim 1 , wherein the first circuit (31) comprises a first recirculation channel (32) arranged between an upstream and a downstream position relative to the air-to-liquid heat exchanger (30) and wherein the first circuit comprises a first valve unit (33) configured to adjust recirculation of the liquid through the first circuit.

3. The liquid cooling system (1) according to claim 1 or 2, wherein the second circuit (41) comprises a second recirculation channel (42) arranged between an upstream and a downstream position relative to the liquid cold-plate (40) and wherein the second circuit comprises a second valve unit (43) configured to adjust recirculation of the liquid through the second circuit.

4. The liquid cooling system (1) according to any one of the preceding claims, wherein the first circuit (31) and / or the second circuit (41) comprises one or more pumps (34, 44) configured to adjust the flow of liquid through the circuit (31 , 41).

5. The liquid cooling system (1) according to any one of claims 2-4, wherein the system comprises one or more temperature sensors (26, 36, 46) configured for measuring a temperature of the liquid, one or more flow sensors (27, 37, 47)configured for measuring a flow of the liquid, and a controller (60) configured to adjust the valve units (33, 43) and / or the one or more pumps (34, 44), so that an output temperature of the liquid downstream to the liquid cold-plate (40) is maximized while the heat-intensity device (12) is sufficiently cooled.

6. The liquid cooling system (1) according to claim 5, wherein the output temperature is in the range of 50 to 90 degrees Celsius, or 60 to 80 degrees Celsius, or 65 to 75 degrees Celsius.

7. The liquid cooling system (1) according to any one of the preceding claims, wherein a second air-to-liquid heat exchanger (35) is arranged on an additional circuit (31 a) in parallel with the first air-to-liquid heat exchanger (30) and is configured to cool a second rack.

8. The liquid cooling system (1) according to any one of the preceding claims or claim 7, wherein the first and / or second air-to-liquid heat exchangers (30,35) is a rear-door cooler, or computer room air-conditioning, or in-row cooler or in-rack cooler, or an aisle containment system, wherein the first and / or second air-to- liquid heat exchangers are configured to absorb heating from a plurality of servers (11) arranged in the rack (10).

9. A method (100) for extracting heat from a rack (10) with a server (11), wherein the method comprises the steps of:- providing (110) a rack with a server (11 ), the rack comprising an air-to-liquid heat exchanger (30) and the server (11 ) comprising a heat-intensity device (12) with a liquid cold-plate (40);- generating (120) a liquid flow from the air-to-liquid heat exchanger (30) through the liquid cold-plate (40); and- adjusting (130) the liquid flow to have a liquid temperature, exiting the liquid cold-plate (40), above 50 degrees Celsius.

10. The method (100) according to claim 9, wherein the method comprises a further step of:- recirculating (140) part of the liquid through the air-to-liquid heat exchanger (30) and / or the liquid cold-plate (40).

11. The method (100) according to claim 9 or 10, wherein the method comprises a further step of:- utilizing (150) the liquid flow with the liquid temperature above 50 degrees Celsius for heating such as for heat consumers in district heating or industrial greenhouses or swimming pools or office installation or other industrial applications.

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