Patent Publication Number: US-2013242504-A1

Title: Cooling an electronic assembly using position variable flow restrictors

Description:
BACKGROUND 
     Computer systems or servers, at a datacenter or other location, may be rack-mounted. Each rack (e.g., Electronics Industry Association standard racks) may house a number of computer systems or servers. The components of each computer system may dissipate significant amounts of heat during operation. Each computer system is typically cooled by fans that move cooling fluid, e.g., air, conditioned air, etc., across the heat dissipating components. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a detailed description of various examples of the invention, reference will now be made to the accompanying drawings in which: 
         FIG. 1  shows a schematic level diagram for a system for cooling a server that employs louvers in accordance with principles disclosed herein; 
         FIG. 2  shows a block diagram for a system for cooling a server that employs louvers in accordance with principles disclosed herein; 
         FIG. 3  shows a flow diagram for a method for cooling a server using louvers to direct airflow in accordance with principles disclosed herein; and 
         FIG. 4  shows a flow diagram for a method for cooling a server using louvers to direct airflow in accordance with various principles disclosed herein. 
     
    
    
     NOTATION AND NOMENCLATURE 
     Certain terms are used throughout the following description and claims to refer to particular system components. As one skilled in the art will appreciate, computer companies may refer to a component by different names. This document does not intend to distinguish between components that differ in name but not function. In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . .” Also, the term “couple” or “couples” is intended to mean either an indirect, direct, optical or wireless electrical connection. Thus, if a first device couples to a second device, that connection may be through a direct electrical connection, through an indirect electrical connection via other devices and connections, through an optical electrical connection, or through a wireless electrical connection. The recitation “based on” is intended to mean “based at least in part on.” Therefore, if X is based on Y, X may be based on Y and any number of additional factors. 
     DETAILED DESCRIPTION 
     The following discussion is directed to various implementations of a cooling system that employs individually positionable louvers to direct cooling fluid to an electronic assembly. The principles disclosed have broad application, and the discussion of any implementation is meant only to illustrate that implementation, and not intended to intimate that the scope of the disclosure, including the claims, is limited to that implementation. 
     Servers and other electronic assemblies are generally cooled using fans to move cool air across heat dissipating components. Data centers supporting a large number of servers can employ thousands of fans. Such systems are subject to a number of disadvantages. For example, fan inefficiencies accumulate as the number of fans increase, and fans always consume some power because they must be run at at least a nominal rate to prevent leakage current even when no cooling is needed. 
     The systems disclosed herein employ flow restrictors, such as louvers, to control airflow across server components. The flow restrictors can directly replace fans and be operated by a fan controller, and unlike fans, the flow restrictors do not present cumulative inefficiencies. Further, use of flow restrictors reduces system power consumption because the flow restrictors consume power only when changing position, and the power consumed is not dependent on the rate of airflow as with fans. Additionally, in some implementations, the flow restrictors require less space than fans. 
       FIG. 1  shows a schematic level diagram for a system for cooling a server  104  that employs louvers  112  in accordance with principles disclosed herein. The system  100  includes a plenum  102  and the server  104 . The plenum  102  provides pressurized cool air to an air inlet of the server  104 . For example, the temperature of the cool air provided via the plenum  102  may be lower than the temperature of the air flowing out of the server  104 . The pressurized cool air provided through the plenum  102  may be generated by a central computer room air conditioning system (not shown). Providing pressurized cool air from a central source improves overall cooling system efficiency because the larger fan at the air source moves air more efficiently than small fans disposed in the server  104 . 
     The server  104  includes an enclosure  114 , a plurality of louvers  112  or other airflow restrictors, a thermal controller  106 , thermal sensors  108 , and heat generating components  110 . The louvers  112  are slats, blades, fins, or the like that change position about an axis to vary the size of an air passage and/or the direction of airflow. The heat generating components may be, for example, electronic components, such as processor(s), memories, and/or various other integrated circuits, semiconductor devices, etc. that dissipate heat while operating. 
     The thermal sensors  108  are distributed about the interior of the server  104  to provide measurement of temperatures across different regions of the interior of the server  104 . The thermal sensors  108  may include any type of suitable temperature sensor, and may be integrated into or separate from any electronic component included in the server  104 . For example, a temperature sensor  108  may integrated with a processor and/or provided as a discrete device. While three temperature sensors  108  are illustrated in the server  104  as a matter of convenience, in practice, the server  104  may include two or more thermal sensors  108 . 
     The thermal sensors  108  are coupled to a thermal controller  106 . The thermal controller  106  controls the positioning of the louvers  112  in accordance with the temperature measurements provided by the thermal sensors  108  and/or other relevant information provided by the server  104 . The thermal controller  106  receives temperature measurements from the thermal sensors  108 , and determines from the measurements a level of cooling needed for each of multiple regions of the server  104 , where the regions correspond to areas having a temperature measured by one or more of the thermal sensors  108 . For example, one thermal region of the server  104  may be dedicated to a processor, and another thermal region of the server  104  may be dedicated to memory, etc. 
     The thermal controller  106  may include a processor that executes instructions retrieved from a computer-readable medium. Suitable processors may include, for example, one or more general-purpose microprocessors, digital signal processors, microcontrollers, or other devices capable of executing instructions retrieved from a computer-readable storage medium. Processor architectures generally include execution units (e.g., fixed point, floating point, integer, etc.), storage (e.g., registers, memory, etc.), instruction decoding, peripherals (e.g., interrupt controllers, timers, direct memory access controllers, etc.), input/output systems (e.g., serial ports, parallel ports, etc.) and various other components and sub-systems. In some implementations, the thermal controller  106  may be implemented via a server management system, such as an Integrated Lights-Out Baseboard Management Computer. 
     A processor may store data in and execute instructions retrieved from a non-transitory computer-readable storage medium. A non-transitory computer-readable storage medium may include volatile storage such as random access memory, non-volatile storage (e.g., a hard drive, an optical storage device (e.g., CD or DVD), FLASH storage, read-only-memory), or combinations thereof. In some implementations, a storage medium may be local to the processor. In other implementations, storage may be remote from the processor accessed via a network. 
     The thermal controller  106  generates signals that control the positions of the louvers  112 . Some implementations of the thermal controller  106  control the position of each louver  112  individually. The thermal controller  106  may generate signals that can be used to control the rotation rate of fans, i.e., the thermal controller  106  may be a fan controller. For example, the thermal controller  106  may generate pulse width modulated (PWM) signals, wherein the duty cycle of each signal corresponds to the rotation rate of a fan used to cool a portion of the server. The louvers  112  may replace fans in the server  104 , and the louvers  112  may apply the PWM fan control signals generated by the thermal controller  106  to determine louver position. For example, the degree to which a louver  112  is open may correspond to the duty cycle of the PWM fan control signal. Accordingly, in some implementations, a louver  112  may move to the closed position  112 B (blocking airflow therethrough) based on a 0% duty cycle PWM fan control signal and move to the fully open position  112 C based on a 100% duty cycle PWM fan control signal. 
     The thermal controller  106  may individually position the louvers  112  to provide a needed level of flow of cooled airflow to each region of the server  104 , and may also position the louvers  106  to direct cooled airflow within the server  104 . For example, the positioning of the louvers  112 A may direct cooled airflow to region  116  of the server  104  rather than region  118 . 
       FIG. 2  shows a block diagram for the system  100  for cooling a server  104  that employs louvers  112  in accordance with principles disclosed herein. As explained above, the thermal controller  106  receives temperature measurements  208  from the thermal sensors  108  which are distributed within the server  104 . The thermal controller  106  employs the temperature measurements  208  to determine what level of cooling is needed within the server  104  and positions the louvers  112  accordingly. 
     The thermal controller  106  also receives server information  202  from various components within the server  104 . The server information  202  includes non-temperature measurement information that is indicative of a need for cooling in a particular region of the server  104 . For example, the server information  202  may include clock rate information provided by a processor of the server  104 , bus utilization information, power consumption information, etc. that may be indicative of the level of cooling needed in a region of the server  104 . The thermal controller  106  may position the louvers  112  based on the server information  202 . 
     Based on the temperature measurements  208  provided by the thermal sensors  108  and/or the server information  202  indicative of needed level, degree, or amount of cooling, the thermal controller  106  generates the control signals  204 . The control signals  204  control louver motors  206  that move the louvers  112 . The louver motors  206  may be any type of actuators that can change the position of the louvers  112 . For example, a louver motor  206  may be a stepper motor used in conjunction with a shaft position encoder to position a louver  112  and feedback louver position information to the thermal controller  106 . In some implementations, each louver  112  is controlled by a separate and distinct louver motor  206 . As explained above, the thermal controller  106  may be a fan controller, and the control signals  204  maybe fan speed control signals, such as PWM signals having a duty cycle proportional to fan speed. The louver motors  206  and/or circuitry associated therewith may determine a requested louver position based on the fan control signals and/or convert the fan control signals into signals that move the louvers  112  into a requested position. 
       FIG. 3  shows a flow diagram for a method  300  for cooling a server using louvers  112  to direct airflow in accordance with principles disclosed herein. Though depicted sequentially as a matter of convenience, at least some of the actions shown can be performed in a different order and/or performed in parallel. Additionally, some implementations may perform only some of the actions shown. At least some of the operations of the method  300  can be performed by processor(s) executing instructions retrieved from a computer-readable medium. 
     In block  302 , the server  104  is operating. Components of the server  104  are dissipating heat, and cooling is provided to maintain the components of the server  104  within a predetermined operating temperature range. The inlets of the server  104  are coupled to the plenum  102 . The plenum  102  provides pressurized cooled air to the server  104 . The cooled air may be provided from a central source, such as a computer room air conditioner. 
     In block  304 , the temperature sensors  108  distributed about the interior of the server  104  measure the temperatures of components and/or air within the server. 
     In block  306 , based on the temperature measurements provided by the temperature sensors  108 , the thermal controller  106  determines a level of cooling need to maintain each portion of the server  104 , where the portions of the server are associated the distributed temperature sensors  108 , within the predetermined operating temperature limits. For example, portions of the server  104  having a temperature above an upper operating temperature limit may require an increase in flow of cooled air, and portions of the server  104  having a temperature below a lower operating temperature limit may require a reduction in flow of cooled air. 
     In block  308 , the thermal controller  106  positions the variable position flow restrictors (e.g., the louvers  112 ) within the server  104  to direct cooled air provided from the plenum  102  to the portions of the server  104  where cooling is needed. For example, the thermal controller  106  may adjust the positions of some of the flow restrictors  112  to increase the flow of cooled air to a portion of the server  104 , and may adjust the positions of other of the flow restrictors  112  to decrease the flow of cooled air to a different portion of the server  104 . 
       FIG. 4  shows a flow diagram for a method  400  for cooling a server using louvers to direct airflow in accordance with principles disclosed herein. Though depicted sequentially as a matter of convenience, at least some of the actions shown can be performed in a different order and/or performed in parallel. Additionally, some implementations may perform only some of the actions shown. At least some of the operations of the method  400  can be performed by processor(s) executing instructions retrieved from a computer-readable medium. 
     In block  402 , the server  104  is operating. Components of the server  104  are dissipating heat, and cooling is provided to maintain the components of the server  104  within a predetermined operating temperature range. The inlets of the server  104  are coupled to the plenum  102 . The plenum  102  provides pressurized cooled air to the server  104 . The cooled air may be provided from a central source, such as a computer room air conditioner. 
     In block  404 , the temperature sensors  108  distributed about the interior of the server  104  measure the temperatures of components and/or air within the server. 
     In block  406 , based on the temperature measurements provided by the temperature sensors  108 , the thermal controller  106  determines a level of cooling need to maintain each portion of the server  104  within the predetermined operating temperature limits. The thermal controller  106  determines the level of cooling needed by each portion of the server  104  based on temperature measurements provided by the temperature sensors  108  and/or based on other server operation information (e.g., clock rates, bus utilization, etc.) indicative of a level of cooling needed by a portion of the server  104 . 
     In block  408 , the thermal controller  106  generates control signals to adjust the cooling provided to portions of the server  104 . Some implementations of the thermal controller  106  are fan controllers that generate PWM fan speed control signals. The thermal controller generates the control signals based on the determined cooling needs of each region or portion of the server  104 . 
     In block  410 , the positions of the flow restrictors  112  within the server  104  are set in accordance with the control signals generated by the thermal controller  106 . The flow restrictors (e.g., the louvers  112 ) are set to direct cooled air provided from the plenum  102  to the portions of the server  104  where cooling is needed. For example, the thermal controller  106  may adjust the positions of some of the flow restrictors  112  to increase the flow of cooled air to a portion of the server  104 , and may adjust the positions of other of the flow restrictors  112  to decrease the flow of cooled air to a different portion of the server  104 . In some implementations, each flow restrictor  112  is opened in proportion to the duty cycle of the PWM control signal associated with the flow restrictor  112  (e.g., 100% duty cycle—fully open, 0% duty cycle—fully closed). 
     The above discussion is meant to be illustrative of the principles and various embodiments of the present invention. Numerous variations and modifications will become apparent to those skilled in the art once the above disclosure is fully appreciated. It is intended that the following claims be interpreted to embrace all such variations and modifications.