Abstract:
In a data center including hot and cold aisles, the flow rate of airflow from the cold aisle through servers to the hot aisle depends on the flow resistance of different servers. As servers may have different cooling needs, an airflow throttling mechanism is coupled to each server to individually adjust the flow resistance through each server based on the amount of cooling airflow needed by a server. Hence, servers use the amount of cooling airflow they need, reducing the overall airflow needs, which reduces the central fan requirements, of the data center.

Description:
BACKGROUND 
     This invention relates generally to efficient cooling of computing devices within a data center. 
     Heat removal is an important consideration in computer system and data center design. As the number of computing assets deployed in a data center increases, heat generated by electronic components in the computing assets during operation also increases. Because the reliability of computing assets used by the data center decreases if they operate at a high temperature over time, a portion of the data center&#39;s power is used for cooling electronics in the computing assets. However, as the number of computing assets included in a data center increases, a greater portion of the power consumed by the data center is used to cool electronics within the computing assets. 
     Conventionally, computing assets in a data center are individually equipped with cooling systems to dissipate heat produced during operation. Commonly, each server includes a fan for dissipating heat generated during operation. However, these internal fans generally consume about 10%-15% of the power used by the computing assets, and also produce heat during operation, limiting their effectiveness. Additionally, a room in the data center housing the computing assets may also be cooled using methods such as air conditioning, using additional power for cooling. 
     SUMMARY 
     Airflow through an individual server in a data center is regulated by modifying the resistance of the airflow through the individual server based on the temperature of components within the server. For example, a throttling mechanism is included in or coupled to a server and modifies the resistance of airflow through the server based on server temperature. This regulates the amount of cooling airflow passing through a server based on the amount of cooling needed by the server, which reduces the overall airflow, and central fan requirements, of the data center. In various embodiments, active or passive throttling mechanisms controlled by the temperature of components within a server are used to regulate air flow through the server. 
     A data center includes a cold aisle that receives cold air, where the cold aisle is connected to one side of a set of servers. A hot aisle adjacent to another side of the servers has a pressure less than the pressure of the cold aisle, causing cold air to flow from the cold aisle through the servers, cooling the electronic components in the servers while heating the air flow. In an embodiment, a cold air supply unit that is external to the cooling system, such as a fan, supplies the cold air to the cold aisle and causes the pressure difference. Additionally, the hot aisle may include one or more exhaust units that are external to the servers. 
     An airflow throttling mechanism is coupled to each of the servers and regulates the amount of air flowing through a server based on the temperature of one or more components within the server. For example, as the temperature of a processor in a server increases, the airflow throttling mechanism decreases the flow resistance of air travelling through the server. This increases the amount of air flowing through the server to allow the server to be more effectively cooled. If the temperature of the processor in the server decreases, the airflow throttling mechanism increases the flow resistance of air travelling through the server, reducing the amount of air flowing through the server. 
     In one embodiment, a sensor monitors the temperature of a server component, such as a processor or a heat sink coupled to the processor, and adjusts the airflow throttling mechanism accordingly. For example, if the temperature of the server component reaches a threshold value, the sensor communicates a control signal to the airflow throttling mechanism to increase the amount of air travelling through the server. If the temperature of the server component reaches a different threshold value, the sensor may communicate a different control signal to the airflow throttling mechanism to decrease the amount of air travelling through the server. 
     In one embodiment, a cooling system includes a server having an air input opening for receiving cool air and an output opening to exhaust heated air generated by the operation of the servers. Also included in the system is an air throttling element configured to control cooling airflow through the server. In some embodiments, the air throttling element is actuated by temperature, resulting in throttling, and thus, closure of airflow through the air conduction channel at low temperature, e.g., when the servers are off or in a low activity state. In some embodiments, the air throttling element includes air baffles that are able to expand in response to elevated temperature to open a ventilation flap located at the air output opening. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an overhead view of a data center for cooling servers without relying on internal fans in accordance with an embodiment of the invention. 
         FIG. 2  is a side view of a data center for cooling servers without relying on internal fans showing airflow throughout the data center in accordance with an embodiment of the invention. 
         FIG. 3A  is side view of an airflow throttling mechanism for regulating airflow through a server in an open state in accordance with an embodiment of the invention. 
         FIG. 3B  is side view of an airflow throttling mechanism for regulating airflow through a server in a closed state in accordance with an embodiment of the invention. 
     
    
    
     The figures depict various embodiments of the present invention for purposes of illustration only. One skilled in the art will readily recognize from the following discussion that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the invention described herein. 
     DETAILED DESCRIPTION 
     Data Center Architecture Utilizing Server Airflow Throttling 
     An example data center  100  cooling one or more servers  105  is illustrated in  FIG. 1 . In one embodiment, a cold aisle  110  is adjacent to a first side of a partition  102  and a hot aisle  120  is adjacent to a second side of the partition  102 . In an embodiment, the partition  102  includes one or more servers  105  oriented so that a first side of the one or more servers  105  is adjacent to the cold aisle  110  and a second side of the one or more servers  105  is adjacent to the hot aisle  120 . The cold aisle  110  includes a cold air supply  115  while, in an embodiment, the hot aisle  120  includes one or more exhaust units  125 . Additionally, one or more sensors  117  are proximate to a server  105 , are included in the cold aisle  110 , and/or are included in the hot aisle  120 . 
     The partition  102  includes one or more openings though which air is able to flow. In an embodiment, the partition  102  comprises a rack or other structure to which one or more devices, such as one or more servers  105  or other electronic devices, may be attached. For example, the one or more servers  105  are mounted to one or more racks and may have different sizes, such as 1.5-2 rack units (“U”). The partition  102  is designed to increase airflow through the servers  105  that are included within the partition  102 . For example, the partition  102  includes a server rack that is designed to increase the amount of air directed through the servers  105  included in the rack. 
     A server  105  has one or more input openings on a first side and one or more output openings on a second side. A server  105  is oriented so the one or more input openings are adjacent to the cold aisle  110  and the one or more output openings are adjacent to the hot aisle  120 . Air from the cold aisle  110  enters the server  105  via the one or more input openings, travels through the server  105  and exits the server through the one or more output openings into the hot aisle  120 . Hence, the input and output openings allow air to travel through the server  105  to cool components included in the server  105 . 
     Cold air is supplied to the cold aisle  110  from a cold air supply  115 , such as a large fan or other air distribution device. In an embodiment, the cold air supply  115  is coupled to a cooling system, further described below in conjunction with  FIG. 2 . As used herein, “cold air” may refer to air having a temperature less than an ambient air temperature, air having a temperature below a specified temperature, or air having a lower relative temperature than air in a different region. For example, air included in the cold aisle  110 , referred to as “cold air,” has a first temperature, while air included in the hot aisle  120 , referred to as “hot air,” has a second temperature that is higher than the first temperature. In different embodiments, the position of the cold air supply  115  relative to the cold aisle  110  may differ. For example, the cold air supply  115  may be positioned above, below, or to the side of the cold aisle  110 . Additionally, in some embodiments, multiple cold air supplies  115  provide cold air to the cold aisle  110  and may have different positions relative to the cold aisle  110 . For example, cold air supplies  115  are positioned above and below or below and to the side of the cold aisle  110 . For purposes of illustration,  FIG. 1  shows an implementation with a cold air supply  115  positioned above the cold aisle  110 . As a result of the cold air supply  115 , the cold aisle  110  has a higher pressure than a hot aisle  120 , and this pressure difference causes cold air to flow from the higher pressure cold aisle  110  through the one or more input openings of a server  105  or the partition  102  to the lower pressure hot aisle  120 . 
     In an embodiment, the partition  102  is configured so that air flow paths external to the servers  105  are substantially blocked such that the airflow path of least resistance from the cold aisle  110  to the hot aisle  120  is through the servers  105 . Configuring the partition  102  so that the airflow path of least resistance is through the servers  105  allows more efficient server  105  cooling by increasing the amount of air passing through the servers  105 . In another embodiment, the partition  102  blocks substantially all airflow from the cold aisle  110  to the hot aisle  120  except for the airflow through the servers  105 , so that substantially all of the airflow from the cold aisle  110  to the hot aisle  120  is through the servers  105 . To facilitate airflow from the cold aisle  110  to the hot aisle, in one embodiment the cold aisle  110  may be pressurized while the hot aisle  120  is depressurized to facilitate airflow from the cold aisle  110  to the hot aisle  120 . As the cold air passes through the server  105 , it flows over components within the server  105 , dissipating heat generated from operation of the electric components in the servers  105 . 
     An airflow throttling mechanism  130  is coupled to each of the one or more servers  105  and regulates the amount of air flowing through the server  105  based on the temperature of one or more components within the server  105 . For example, as the temperature of a processor in a server increases, the airflow throttling mechanism  130  decreases the flow resistance of air travelling through the server  105 . This increases the amount of air flowing through the server  105  to increase cooling of components in the server  105 . If the temperature of the processor, or of another component in the server  105 , decreases, the airflow throttling mechanism  130  increases the flow resistance of air travelling through the server  105  to reduce the amount of air flowing through the server  105 . 
     For example, the airflow throttling mechanism  130  comprises a ventilation flap coupled to a thermodynamically actuated baffle coupled to a component included in the server. For example, the thermodynamically actuated baffle is coupled to a processor or to a heat sink of a processor included in the sever  105 . As the temperature of the component increases, the ventilation flap is repositioned to increase the amount of air flowing out of an output opening of the server  105 . For example, the thermodynamically actuated baffle expands as the temperature of the component increases, moving the ventilation flap from a closed position blocking the output opening of the server  105  to an open position. Similarly, as the temperature of the component decreases, the thermodynamically actuated baffle contracts, moving the ventilation flap from an open position to a closed position blocking air from flowing out of the server  105  via the output opening. Alternatively, the ventilation flap may be positioned to block air from flowing into the server  105  via an input opening or to allow air to flow into the server  105  via the input opening based on the temperature of the component coupled to the thermodynamically actuated baffle, as described above. 
     In different embodiments, the cold air supply  115  may statically or dynamically control the amount of air supplied to the cold aisle  110  to modify the airflow through the servers  105 . In an embodiment where the air supply is statically controlled, the cold air supply  115  is louver-based and supplies cold air in different directions, at different flow rates, and/or at different temperature levels. In an alternative embodiment, the cold air supply  115  dynamically modifies the airflow supplied to the cold aisle  110  by changing the speed of one or more supply fans, repositioning one or more air supply louvers (or otherwise redirecting the airflow), or changing the temperature to which the airflow is cooled. Modifying the supply fan speed, supply louver position, and/or air temperature allows the cold air supply  115  to more suitably cool the servers  105  included in the partition  102 . Hence, implementations of the cold air supply  115  allow non-uniform air flow and/or air temperature throughout the cold aisle  110 , enabling different locations within the cold aisle  110 , such as locations proximate to different servers  105 , to have a different air flow rate and/or a different air temperature. Additionally, the air flow from the cold air supply  115  may be determined or modified based on the size of the servers  105  being cooled. 
     After flowing through the servers  105 , cold air enters the hot aisle  120  because it has a lower pressure than the cold aisle  110 . Because the air extracts heat from components within one or more servers  105 , when passing from the cold aisle  110  to the hot aisle  120 , the air temperature increases so that air in the hot aisle  120  has a higher temperature than air in the cold aisle  110 . In an embodiment, the hot aisle  120  includes one or more exhaust units  125 , such as exhaust fans, which extract air from the hot aisle  120 . While  FIG. 1  shows an example hot aisle  120  with two exhaust units  125 , in other embodiments, the hot aisle may include a different number of exhaust units  125 . In an embodiment, the exhaust unit  125  is coupled to a cooling system, further described below in conjunction with  FIG. 2 , so that air flows from the hot aisle  120  into the one or more exhaust units  125  and into the cooling system, where it is cooled and recirculated into the cold aisle  110  via the cold air supply  115 . Alternatively, cold air enters the hot aisle  120  and is directed outside of the data center  100 . 
     The data center  100  also includes one or more sensors  117  in locations where air flows from the cold aisle  110  to the hot aisle  120 . The sensors  117  monitor air flow, air temperature, air humidity, absolute air pressure, differential air pressure, or any other data that describes air flow or air temperature, and combinations thereof. In an embodiment, the sensors  117  are placed in locations where airflow is likely to be less than other locations, such as a ceiling or a wall where the partition  102  abuts another surface, so that the temperature of the sensor locations is likely to be higher than other locations. For example, sensors  117  are placed in corners of the cold aisle  110  to monitor airflow through the corners, the temperature of the corners, the pressure difference between the cold aisle  110  and the hot aisle  120  or another value characterizing air flow through the sensor location. In another embodiment, sensors  117  are positioned at locations within the cold aisle  110 , at locations within the hot aisle  120 , at locations within one or more servers  105  or in any combination of the above-described locations. 
     The sensors  117  communicate with a control system  119  coupled to, or included in, the cooling system and/or the cold air supply  115  to modify how air is cooled by the cooling system or how cold air is supplied to the cold aisle  110  by the cold air supply  115 . The control system  119  generates a control signal responsive to data from one or more sensors  117  to modify operation of the cooling system and/or the cold air supply  115 . For example, responsive to detecting a temperature reaching a threshold value, an air flow reaching a threshold flow rate, or a pressure difference between the cold aisle  110  and the hot aisle  120  falling below a threshold value, a sensor  117  communicates with the control system  119 , which generates a control signal increasing the rate at which the cold air supply  115  supplied to the cold aisle  110  or modifying the direction in which cold air is supplied to the cold aisle  110  by the cold air supply  115 . Hence, the sensors  117  and control system  119  implement a feedback loop allowing the data center  100  to modify how cold air flows through the servers  105  responsive to changes in the data center environment, improving the cooling efficiency. 
       FIG. 2  is a side view of the airflow in data center  100  that is capable of cooling the servers  105  without depending on fans within the servers  105 , according to one embodiment. The arrows indicate the flow of air throughout the data center  100 . As illustrated, a cooling system  210  is coupled to a cold air supply  115  and to an exhaust unit  125 . While  FIG. 2  shows a single cold air supply  115  and a single exhaust unit  125 , other embodiments may have multiple cold air supplies  115  and/or multiple exhaust units  125 . 
     The cooling system  210  comprises a Heating, Ventilating and Air Conditioning (“HVAC”) system, which extracts heat from air. For example, the cooling system  210  uses free-air cooling, such as air-side or liquid-side economization to cool the air. In an embodiment, the cooling system  210  includes secondary cooling systems, such as an evaporative cooling system, an absorption cooling system, an adsorption cooling system, a vapor-compression cooling system, or another cooling system to extract heat from air. In another embodiment, the cooling system  210  also modifies the humidity of the cool air to improve reliability and/or longevity of the servers  105  being cooled. For example, the cooling system  210  produces cold air having a humidity within a specified range, such as 20% to 60% humidity, to the cold aisle  110 . 
     In one embodiment, the cooling system  210  receives heat from the exhaust units  125  included in the hot aisle  120 , cools and dehumidifies the received air, and supplies the cooled and dehumidified air to the cold air supply  115 , where it is supplied to the cold aisle  110 . In this embodiment, the cooling system  210  is a closed system, which recirculates air from the hot aisle  120  to the cold aisle  110  once the air is cooled and dehumidified. As illustrated by the arrows in  FIG. 2 , the cooled air travels from the cooling system  210  to the cold air supply  115 , which supplies the cold air to the cold aisle  110 . In an embodiment, the cold air supply  115  comprises one or more fans or one or more air nozzles, one or more air jets, or other device for directing air flow. 
     Cooled air from the cold air supply  115  enters the cold aisle  110 . Because the cold aisle  110  has a higher pressure than the hot aisle  120 , and the partition  102  includes one or more openings for air flow, the cold air flows from the cold aisle  110  to the lower pressure hot aisle  120 . To flow from the cold aisle  110  to the hot aisle  120 , the cold air passes through the openings in the partition  102 , so that the cold air is drawn through the partition  102 . In an embodiment, the partition  102  includes one or more servers  105  that have one or more input openings on a first side adjacent to the cold aisle  110  and one or more output openings on a second side adjacent to the hot aisle  120 . The input openings allow cold air to enter the server  105 , travel through the server  105 , flowing over components within the server  105 . After traveling through the server  105 , the output openings enable air to exit the server  105  into the hot aisle  120 . 
     As described above in conjunction with  FIG. 1 , an airflow throttling mechanism  130  may be coupled to each of the one or more servers  105 . An airflow throttling mechanism  130  regulates the resistance to air flow through a server  105  coupled to the airflow throttling mechanism  130  based on the temperature of one or more components within the server  105 . For example, as the temperature of a processor in a server  105  increases, the airflow throttling mechanism  130  decreases the flow resistance of air travelling through the server  105 , allowing more air to travel through the server  105 . For example, the airflow throttling mechanism  130  removes an obstruction from an input opening of the server  105  or from an output opening of the server  105  to increase air flow through the server  105 . As another example, the airflow throttling mechanism  130  obstructs, or partially obstructs, the input opening or the output opening of the server  105  when the temperature of a component in the server  105  decreases or reaches a minimum value. Obstructing the input opening or the output opening reduces the air flow through the server  105  by increasing the resistance to air flow. Examples of an airflow throttling mechanism  130  are further described below in conjunction with  FIGS. 3A and 3B . 
     As cool air travels through the partition  102  and/or a server  105  from the cold aisle  110  to the hot aisle  120 , a portion of the air travels across, or through, one or more sensors  117  which monitor attributes of the airflow, such as air temperature, air humidity, absolute air pressure of the cold aisle  110  or of the hot aisle  120 , or a pressure difference between the cold aisle  110  and the hot aisle  120 . The sensors  117  communicate the monitored attributes to a control system, which is coupled to or included in, the cold air supply  115  or the cooling system  210 . The control system generates a control signal modifying operation of the cold air supply  115  and/or the cooling system  210  to modify the cold air supplied to the cold aisle  110 . For example, responsive to a sensor  117  detecting a temperature above a threshold value, an air flow below a threshold flow rate or a pressure difference between the cold aisle  110  and the hot aisle  120  falling below a threshold value, the control system generates a control signal increasing the rate or direction at which the cold air supply  115  supplies cold air to the cold aisle  110  or generates a control signal directing cold air from the cold air supply  115  towards certain areas in the cold aisle  110  needing increased cooling. For example, the control signal causes the cold air supply  115  to move cold air towards a region of the partition  102  where a sensor  117  indicates a temperature above a threshold value or an airflow rate below a threshold value. Alternatively, the control system generates a control signal causing the cooling system  210  to further reduce the temperature of the air provided to the cold aisle  110 . 
     One or more exhaust units  125  are included in the hot aisle  120  to extract air from the hot aisle  120  and to direct air from the hot aisle  120  to the cooling system  210 , where the air is again cooled. Hence, the one or more exhaust units  125  implement a closed-loop where air is cooled by the cooling system  210  and recirculated to the cold aisle  110  via the cold air supply  115 . Because the pressure differential between cold aisle  110  and hot aisle  120  causes air to flow through the partition  102 , and electronic devices included in the partition  102 , electronic devices included in the data center  100  are cooled without relying on air moving devices, such as fans, operating at individual electronic devices. Additionally, reducing the use of locally-implemented air moving devices reduces power consumption of the electronic devices, making the data center  100  more power efficient. 
     Server Airflow Throttling System 
     An example airflow throttling mechanism  130  is shown in  FIGS. 3A and 3B .  FIG. 3A  shows the airflow throttling mechanism  130  in an “open” state, while  FIG. 3B  shows the airflow throttling mechanism  130  in a “closed” state. As shown in  FIGS. 3A and 3B , cool air enters an input  370  of the airflow throttling mechanism  130 , which may be aligned with an input of a server  105  coupled to the airflow throttling mechanism  130  or included in the airflow throttling mechanism  130 . A processor  330  is included in the server  105 , and a heat sink  320  is coupled to the processor  330 . The heat sink  320  collects heat generated during processor operation. In the example of  FIGS. 3A and 3B , the airflow throttling mechanism  130  includes a thermodynamically actuated baffle  340  coupled to a ventilation flap  360 . 
     When the server  105  is operating, the processor  330  generates heat that is transferred to the heat sink  320 . The thermodynamically actuated baffle  340  may expand as the heat sink  320  increases in temperature, which moves the ventilation flap  360  to an “open” position away from an output opening  380  of the server  105  or of the airflow throttling mechanism  130  as shown in  FIG. 3A . While the ventilation flap  360  is in the open position, air may freely flow from the input  370  of the airflow throttling mechanism  130 , through the server  105  and out of the other end the server  105  and airflow throttling mechanism  130  via the output opening  380 , drawing heat away from the processor  330 . The air flow is depicted by the arrows in  FIG. 3A . 
     When the processor  330  is off or in a low activity state, as shown in  FIG. 3B , less heat is generated and absorbed by the heat sink  320 . The lower heat sink temperature causes the thermodynamically actuated baffle  340  to contract, moving the ventilation flap  360  to a “closed” state blocking the output opening  380 . Hence, the closed state of the ventilation flap  360  prevents air from flowing through the server  105  and exiting through the output opening  380 . Hence, the airflow throttling mechanism  130  regulates air flow through a server  105  based on the temperature of components in the server  105 , increasing or decreasing the air flow depending on the need to cool components in the server  105 . 
     For example, when the heat sink  320  reaches a maximum temperature, the thermodynamically actuated baffle  340  expands and positions the ventilation flap  360  in the open state to cool the processor  330 . When the heat sink  320  reaches a minimum temperature, the thermodynamically actuated baffle  340  contracts and positions the ventilation flap  340  in the closed state to prevent air from flowing through the server  105 . Alternatively, the thermodynamically actuated baffle  340  dynamically repositions the ventilation flap  360  as the heat sink temperature changes, allowing the ventilation flap  360  have a range of positions based on the heat sink  320  temperature. 
     While  FIGS. 3A and 3B  show a passive airflow throttling mechanism  130  using expansion and contraction of a thermodynamically actuated baffle  340  to modify air flow through the server  150 , in other embodiments the airflow throttling mechanism  130  may use active components to reposition the ventilation flap  360  or otherwise block the input  370  or output  380  of the airflow throttling mechanism  130  and/or of the server  105 . For example, a sensor measures the temperature of the heat sink  320  and generates a control signal for a servo motor, which repositions the ventilation flap  360  based on the control signal. 
     Summary 
     The foregoing description of the embodiments of the invention has been presented for the purpose of illustration; it is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Persons skilled in the relevant art can appreciate that many modifications and variations are possible in light of the above disclosure. 
     Some portions of this description describe the embodiments of the invention in terms of algorithms and symbolic representations of operations on information. These algorithmic descriptions and representations are commonly used by those skilled in the data processing arts to convey the substance of their work effectively to others skilled in the art. These operations, while described functionally, computationally, or logically, are understood to be implemented by computer programs or equivalent electrical circuits, microcode, or the like. Furthermore, it has also proven convenient at times, to refer to these arrangements of operations as modules, without loss of generality. The described operations and their associated modules may be embodied in software, firmware, hardware, or any combinations thereof 
     Any of the steps, operations, or processes described herein may be performed or implemented with one or more hardware or software modules, alone or in combination with other devices. In one embodiment, a software module is implemented with a computer program product comprising a computer-readable medium containing computer program code, which can be executed by a computer processor for performing any or all of the steps, operations, or processes described. 
     Embodiments of the invention may also relate to an apparatus for performing the operations herein. This apparatus may be specially constructed for the required purposes, and/or it may comprise a general-purpose computing device selectively activated or reconfigured by a computer program stored in the computer. Such a computer program may be stored in a tangible computer readable storage medium, which include any type of tangible media suitable for storing electronic instructions, and coupled to a computer system bus. Furthermore, any computing systems referred to in the specification may include a single processor or may be architectures employing multiple processor designs for increased computing capability. 
     Embodiments of the invention may also relate to a computer data signal embodied in a carrier wave, where the computer data signal includes any embodiment of a computer program product or other data combination described herein. The computer data signal is a product that is presented in a tangible medium or carrier wave and modulated or otherwise encoded in the carrier wave, which is tangible, and transmitted according to any suitable transmission method. 
     Finally, the language used in the specification has been principally selected for readability and instructional purposes, and it may not have been selected to delineate or circumscribe the inventive subject matter. It is therefore intended that the scope of the invention be limited not by this detailed description, but rather by any claims that issue on an application based hereon. Accordingly, the disclosure of the embodiments of the invention is intended to be illustrative, but not limiting, of the scope of the invention, which is set forth in the following claims.