Patent Publication Number: US-9894807-B2

Title: Changeable, airflow venting cover assembly for an electronics rack

Description:
BACKGROUND 
     The power dissipation of integrated circuit chips, and the modules containing the chips, continues to increase in order to achieve increases in processor performance. This trend poses cooling challenges at both the rack and data center levels. Increased airflow rates are needed to effectively cool higher power components and to control the temperature of egressing air exhausted into the computer center. 
     In many large server applications, processors along with their associated electronics (e.g., memory, disk drives, power supplies, etc.) are packaged in removable drawer configurations stacked within a rack or frame. In other cases, the electronics may be in fixed locations within the rack or frame. Typically, the components are cooled by air moving in airflow paths, usually front-to-back, impelled by one or more air moving devices (e.g., axial or centrifugal fans). In some cases it may be possible to handle increased power dissipation within a single drawer or subsystem by providing greater airflow, through the use of a more powerful air moving device(s) or by increasing the rotational speed (i.e., RPMs) of an existing air moving device. However, this approach may be problematic at the rack or data center level. 
     BRIEF SUMMARY 
     In one aspect, the shortcomings of the prior art are overcome and additional advantages are provided through the provision of an apparatus comprising a changeable cover assembly sized to cover, at least in part, an air outlet side of an electronics rack. The changeable cover assembly facilitates redirecting and venting airflow passing therethrough egressing from the air outlet side of the electronics rack, and includes, for instance: a frame with at least one opening through which air egressing from the air outlet side of the electronics rack passes; and at least one vent cover coupled to the frame and overlying, at least in part, the at least one opening in the frame to facilitate redirecting and venting the air passing therethrough. The at least one vent cover is changeable to change a direction of the vented air egressing from the cover assembly. 
     In another aspect, an apparatus is provided which includes an electronics rack and a changeable cover assembly. The electronics rack has an air inlet side and air outlet side respectively facilitating ingress and egress of air through the electronics rack. The changeable cover assembly is coupled to the electronics rack at the air outlet side thereof, and facilitates redirecting and venting airflow passing therethrough egressing from the air outlet side of the electronics rack. The changeable cover assembly includes, for instance: a frame with at least one opening through which air egressing from the air outlet side of the electronics rack passes; and at least one vent cover coupled to the frame and overlying, at least in part, the at least one opening in the frame to facilitate redirecting and venting the air passing therethrough, the at least one vent cover being changeable to change a direction of the vented air egressing from the changeable cover assembly. 
     In a further aspect, a method is provided which includes: providing a changeable cover assembly sized to cover, at least in part, an air outlet side of an electronics rack, the changeable cover assembly, when positioned at the air outlet side of the electronics rack, facilitating redirecting and venting airflow passing therethrough egressing from the air outlet side of the electronics rack, and the providing including, for instance: providing a frame with at least one opening through which air egressing from the air outlet side of the electronics rack passes; and providing at least one vent cover coupled to the frame and overlying, at least in part, the at least one opening in the frame to facilitate redirecting and venting the air passing therethrough, the at least one vent cover being changeable to change a direction of the vectorized air egressing from the changeable cover assembly. 
     Additional features and advantages are realized through the techniques of the present invention. Other embodiments and aspects of the invention are described in detail herein and are considered a part of the claimed invention. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       One or more aspects of the present invention are particularly pointed out and distinctly claimed as examples in the claims at the conclusion of the specification. The foregoing and other objects, features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  depicts one embodiment of a conventional, raised-floor layout of an air-cooled data center; 
         FIG. 2  depicts one embodiment of an air-cooled electronics rack, which may be fitted with a changeable cover assembly, in accordance with one or more aspects of the present invention; 
         FIG. 3  is a cross-sectional, side elevational view of one embodiment of an air-cooled electronics rack to employ a changeable cover assembly, in accordance with one or more aspects of the present invention; 
         FIG. 4A  is a cross-sectional, side elevational view of an apparatus comprising the air-cooled electronics rack of  FIG. 3 , and a changeable cover assembly disposed at the air outlet side thereof, in accordance with one or more aspects of the present invention; 
         FIG. 4B  is a cross-sectional, side elevational view of the apparatus of  FIG. 4A , with one or more vent covers of the changeable cover assembly shown reversed, in accordance with one or more aspects of the present invention; 
         FIG. 5  is an exploded view of one embodiment of a changeable cover assembly, in accordance with one or more aspects of the present invention; 
         FIG. 6A  is a cross-sectional, elevational view of an apparatus comprising the air-cooled electronics rack of  FIG. 3 , and another embodiment of a changeable cover assembly disposed at the air outlet side thereof, in accordance with one or more aspects of the present invention; 
         FIG. 6B  depicts the apparatus of  FIG. 6A , with the vent cover of the changeable cover assembly shown reversed, in accordance with one or more aspects of the present invention; 
         FIG. 7A  depicts a more detailed embodiment of the changeable cover assembly of  FIGS. 6A and 6B , in accordance with one or more aspects of the present invention; 
         FIG. 7B  is an exploded view of the changeable cover assembly of  FIG. 7A , in accordance with one or more aspects of the present invention; 
         FIG. 7C  depicts a frame-side view of the changeable cover assembly of  FIG. 7A , illustrating in greater detail one embodiment of the frame thereof, in accordance with one or more aspects of the present invention; 
         FIG. 8A  depicts an alternate embodiment of a changeable cover assembly for an air outlet side of an air-cooled electronics rack, with multiple adjustable louvers of the vent cover shown depicted at a first orientation, in accordance with one or more aspects of the present invention; 
         FIG. 8B  depicts the changeable cover assembly of  FIG. 8A , with the multiple adjustable louvers thereof depicted transitioned to a second orientation, in accordance with one or more aspects of the present invention; 
         FIG. 9A  depicts one embodiment of a process for automatically controlling the adjustable louver orientation within a changeable cover assembly such as depicted in  FIGS. 8A &amp; 8B , in accordance with one or more aspects of the present invention; 
         FIG. 9B  depicts another embodiment of a process for automatically controlling the adjustable louver orientation within a changeable cover assembly such as depicted in  FIGS. 8A &amp; 8B , in accordance with one or more aspects of the present invention; 
         FIG. 10A  depicts one embodiment of an apparatus comprising the air-cooled electronics rack of  FIG. 3 , and another embodiment of a changeable cover assembly, shown coupled to the air-outlet side of the electronics rack, in accordance with one or more aspects of the present invention; 
         FIG. 10B  depicts an alternate embodiment of the apparatus of  FIG. 10A , in accordance with one or more aspects of the present invention; and 
         FIG. 10C  depicts a further alternate embodiment of the apparatus of  FIG. 10A , in accordance with one or more aspects of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Recent trends in addressing data center operating costs have placed increased focus on improving overall operating efficiencies, including cooling efficiencies. A significant contributor in this regard is associated with the supply of ambient cool air and the subsequent removal of egressing heated air generated within the data center&#39;s electronics racks, or information technology (IT) infrastructure. Note that electronics rack, rack unit, rack, IT infrastructure are used interchangeably herein, and unless otherwise specified, include any housing, frame, support, structure, compartment, etc. having one or more heat generated components of a computer system, electronics system, IT system, etc. Note also that reference is made below to the drawings, which are not drawn to scale to facilitate an understanding of the invention, where the same reference numbers used throughout different figures designate the same or similar components. 
     By way of example, one embodiment of an air cool data center is depicted in  FIG. 1 . As shown, in a raised floor layout of an air-cooled data center  100 , multiple electronics racks  110  may be disposed in one or more rows. A computer installation such as depicted may house several hundred, or even several thousand processors. In the arrangement of  FIG. 1 , chilled air enters the computer room via floor vents from a supply air plenum  145  defined between a raised floor  140  and a base or sub-floor  165  of the room. Cooled air is taken in through the front, or air inlet sides  111 , of the electronics racks and expelled through the back, or air outlet sides  112 , of the electronics racks. Each electronics rack  110  may have one or more air-moving devices (e.g., axial or centrifugal fans) to provide forced inlet-to-outlet airflow to cool the electronic components within the rack. Supply air plenum  145  provides conditioned and cooled air to the air-inlet sides of the electronics racks via perforated floor tiles  160  disposed (in one embodiment) in a “cold” air aisle of the data center. The conditioned and cooled air is supplied to plenum  145  by one or more air-conditioning units  150 , which may also be disposed within data center  100 . Room air is taken into each air-conditioning unit  150  near an upper portion thereof. In the depicted embodiment, this room air comprises in part exhausted air from the “hot” air aisles of the data center defined by opposing air outlet sides  112  of electronics racks  110 . 
     Due to ever increasing airflow requirements through the electronics racks, and the limits of air distribution within the typical computer room installation, such as the above-described, raised-floor environment of  FIG. 1 , or alternatively, a non-raised-floor environment, recirculation problems within the room may occur. Recirculation can occur because the conditioned air supplied may be only a fraction of the airflow rate forced through the electronics racks by the air moving devices disposed within the racks. This can be due, for example, to limitations on diffuser flow rates. The remaining fraction of the supply of inlet side air may be made up by ambient room air through recirculation, for example, from the air outlet side of the rack unit to the air inlet side. This re-circulating flow is often very complex in nature, and can lead to significantly higher rack inlet temperatures than might be expected. 
     Recirculation of hot exhaust air from the hot aisle of the computer room installation to the cold aisle can be detrimental to the performance and reliability of the computer system(s), or electronic system(s), within the rack(s). Data center equipment is typically designed to operate with rack air inlet temperatures in the 15-35° C. range. For a layout such as depicted in  FIG. 1 , however, temperatures can range from 15-20° C. at the lower portion of the rack, close to the cool air floor vents, to as much as 32-42° C. at the upper portion of the electronics rack, where hot air can form a self-sustaining recirculation loop. Since the allowable rack heat load is limited by the rack inlet air temperature at the “hot” part, this temperature distribution correlates to an inefficient utilization of available air conditioning capability. Computer installation equipment almost always represents a high capital investment to the customer. Thus, it is of significant importance, from a product reliability and performance view point, and from a customer satisfaction and business perspective, to better facilitate airflow control within a data center. 
     Data center designers have implemented cold aisle/hot aisle layouts to compartmentalize airflow requirements within a data center. Although theoretically optimized, such an implementation has been problematic given that airflow recirculation issues may occur, and given the heterogeneous nature of installed IT or rack content within the data center. As one solution, various attempts have been made to implement cold aisle/hot aisle containment structures, such as containment barriers at the end of a cold aisle or hot aisle extending upwards, for instance, to the ceiling of the data center. Although proving to be effective, concerns remain with respect to a data center with heterogeneous IT content. For instance, IT content can vary between racks, from racks with relatively inherently low velocity horizontal air flow to those with high velocity variably directed airflow, each exiting into a hot aisle of a data center. By definition, the exiting air may be either in the same or in opposing directions, depending on the equipments&#39; location, with the worst case scenario being when high velocity horizontal airflow from one side of a hot aisle adversely effects airflow through an opposing rack by impinging on a lower velocity airflow emanating from the opposing electronics rack, possibly negatively effecting its operational characteristics. To address these deficiencies, and to assist in both optimizing data center layouts and airflow containment designs, the ability to changeably redirect, or vectorize, airflows exiting an electronics rack into, for instance, a hot aisle of a data center, is disclosed herein in order to assist in improving control of overall data center airflow efficiency. 
       FIG. 2  depicts one embodiment of an apparatus comprising an electronics rack  110  with an air exhaust door  210  mounted at a vertical hinge edge  211  to the electronics rack, for instance, at the air outlet side  112  of the electronics rack, where cool airflow  201  ingresses via air inlet side  111  of electronics rack  110  and heated exhaust air  202  egresses via air outlet side  112  thereof. In this embodiment, air exhaust door  210  is sized to substantially cover air outlet side  112  of electronics rack  110 . As shown, air exhaust door  210  includes, in addition to hinge edge  211 , a vertically extending latch edge  212  located opposite to hinge edge  211 , and an inner side (not shown) and an outer side  214 , which are opposite main sides of air exhaust door  210 . In the embodiment depicted, the inner side of air exhaust door  210  is disposed closer to air outlet side  112  of electronics rack  110 , with air exhaust door  210  mounted to the rack via top and bottom hinge brackets  230  and hinge pins  231  located at or adjacent to hinge edge  211  of air exhaust door  210 . As illustrated, hinge pins  231  may be positioned close to outer side  214  of air exhaust door  210  so that the hinge axis is out from electronics rack  110  to, at least in part, minimize or even eliminate outward swing of air exhaust door  210  past the sides of electronics rack  110  as the air exhaust door is rotated between closed and opened positions. A door latch mechanism  215  may be disposed (in one embodiment) at or adjacent to latch edge  212 , and be configured to facilitate latching of air exhaust door  210  to electronics rack  110  when in the closed position, as illustrated in  FIG. 2 . Perforated screens may be provided at either the inner side or the outer side  214  of air exhaust door  210 , through which the heated exhaust air  202  flows laterally out. 
     By way of further example,  FIG. 3  depicts a more detailed embodiment of an apparatus  300  comprising an electronics rack  310 , with an air inlet side  311  and an air outlet side  312  into which cool airflow  301  ingresses and heated exhaust airflow  302   a ,  302   b ,  302   c  egresses, respectively. As illustrated in  FIG. 3 , electronics rack  310  may include different electronic, IT infrastructure, components, subsystems, etc., in different regions of the rack. For instance, a lowermost region  320  may comprise a cooling subsystem with, for instance, a liquid-to-air heat exchanger or radiator, a central region  330 , with one or more electronic subsystems to be cooled, such as multiple System Z® Enterprise Class™ (z EC or zEnterprise®) servers offered by International Business Machines Corporation of Armonk, N.Y., USA, and an uppermost region  340 , with, for instance, input/output systems for electronics rack  310 . As illustrated by the different number and differently sized airflow arrows through the rack  310 , the different regions  320 ,  330  &amp;  340  may have different egressing airflow  302   a ,  302   b ,  302   c  characteristics at air outlet side  312  of electronics rack  310 . For instance, in one example, lowermost region  320  and middle region  340  may have localized, higher temperature, higher velocity airflow exhaust than, for example, uppermost region  340 . Note that differently manufactured electronics racks, or different generations of the same electronics rack, may have significantly different rack-level airflow patterns due to different heterogeneous or mixed flow characteristics of the racks&#39; contents. 
     Given the unique airflow requirements of different electronics racks from, for instance, different manufactures, or from the same manufacture, but different generations, the primary airflow direction through the electronics rack, and the primary direction of air egress from the electronics racks may differ with, for instance, some designs providing a straight-through egress of airflow as depicted in  FIG. 3  and other designs establishing, for instance, a downward airflow egress direction. The result is an observed uncontrollable, non-uniform distribution of exhaust airflow into the data center, with localized higher temperatures, as well as regions of higher velocity exhaust airflow, that together raise significant potential customer issues due to the data center cooling impact of the non-uniform, non-controllable nature of the airflow distribution. 
     Generally stated, disclosed herein therefore is an apparatus and method of fabrication which includes a changeable cover assembly sized to cover, at least in part, an air outlet side of an electronics rack. The changeable cover assembly is designed or configured to facilitate redirecting or vectorizing airflow passing therethrough egressing from the air outlet side of the electronics rack. The redirecting, or vectorizing, of the airflow includes, for instance, redirecting at least a portion of the airflow egressing from the air outlet side of the electronics rack to a desired, non-horizontal exhaust orientation. 
     The changeable cover assembly includes, for instance, a frame with at least one opening through which air egressing from the air outlet side of the electronics rack passes, and at least one vent cover coupled to the frame and overlying, at least in part, the at least one opening in the frame to facilitate redirecting and venting the air passing through the changeable cover assembly. The at least one vent cover is designed to be changeable or reconfigurable to allow changing of the direction of vented air egressing from the changeable cover assembly. For instance, the vent cover(s) may be configured to be reversible relative to the frame in order to allow a technician to change the direction of the vented air. In one implementation, the vent cover(s) includes multiple fixed louvers having, at least in part, a common orientation relative to the frame. Reversing of the direction of the vented air may include, for instance, turning upside down one or more vent covers of the assembly to change the direction of the vented air egressing from the changeable cover assembly. Note that, in certain embodiments, the changeable cover assembly may be sized to fully or substantially cover the air outlet side of the electronics rack. 
     In certain implementations, the vent cover(s) may include multiple adjustable louvers which facilitate redirecting or vectorizing the air passing through the opening(s) in the frame. The multiple adjustable louvers may have, at least in part, a common adjustable orientation relative to the frame, and may be manually or automatically adjustable, for instance, via a controller or control system coupled to the multiple adjustable louvers. The control system may be disposed, for instance, within the electronics rack, or elsewhere within the data center housing the rack. In certain implementations, the control system may automatically adjust the common orientation of the multiple adjustable louvers based on one or more sensed parameters associated with, for instance, the electronics rack or the data center housing the electronics rack. The one or more sensed parameters may be, for example, one or more sensed temperatures or power levels, as explained further below. 
     In one implementation, the changeable cover assembly may include multiple vent covers coupled to the frame and overlying the one or more openings in the frame to redirect or vectorize the air passing therethrough. In these implementations, the at least one vent cover is a vent cover(s) of the multiple vent covers. By way of example, the at least one vent cover may be reversible relative to the frame to selectively change the direction of the vented air egressing from that section of the changeable cover assembly. In another example, two or more vent covers of the multiple vent covers may be differently configured to facilitate differently redirecting the air passing therethrough in different directions. In certain implementations, two or more of the vent covers may be differently sized, with one or more of the vent covers being changeable to change the direction of the vented air. For instance, one vent cover could define one or more fixed air exhaust channels relative to the frame, and the other could have changeable air exhaust channels. In another embodiment, each vent cover of the multiple vent covers could receive a respective percentage of the air passing through the at least one opening in the frame, and each may be changeable to independently change the direction of the vented air egressing therefrom. 
     In one or more other implementations, the frame and the at least one vent cover may define at least one air exhaust plenum at the air outlet side of the electronics rack, with the at least one air exhaust plenum redirecting air egressing from the air outlet side of the electronics rack by, for instance, substantially 90° to exit upwards, perpendicular to an upper surface of the electronics rack, or downwards, perpendicular to a lower surface of the electronics rack. By way of further example, the frame and the vent cover(s) may define multiple air exhaust plenums at the air outlet side of the electronics rack, with the multiple air exhaust plenums each redirecting a portion of the air egressing from the air outlet side of the electronics rack by substantially 90°. In these configurations, the vent cover may be changeable by reversing the vent cover, so as to change the direction of egressing airflow from the one or more air exhaust plenums, or may be changeable by changing the vent cover used in the changeable cover assembly by, for instance, coupling a different vent cover to the frame of the changeable cover assembly, which defines a different configuration of the one or more air exhaust plenums defined by the changeable cover assembly. 
     In one or more implementations, the cover assembly may further include at least one electromagnetic compatibility (EMC) screen, for instance, within the at least one opening of the frame, such that the at least one vent cover overlies the at least one EMC screen. As noted, the cover assembly may be sized to substantially cover the air outlet side of the electronics rack, and the frame may be a door frame hingedly mountable to the electronics rack at the air outlet side thereof. Additionally, in one or more implementations, an acoustically-absorptive material may be associated with the at least one vent cover, for instance, disposed on inner surfaces thereof, and be selected to attenuate noise emanating from the electronics rack through the at least one opening in the frame when the cover assembly is coupled to the air outlet side of the electronics rack. 
     Advantageously, disclosed herein are various changeable cover assembly designs for, for instance, the air outlet side of an electronics rack. The changeable cover assemblies disclosed controllably redirect or vectorize air egressing from the electronics rack in a desired manner for a particular data center implementation, and/or for a particular electronics rack design. In one or more implementations, a fixed louver, reversible vent cover design is disclosed, wherein airflow can be directed, for instance, either at an upward angle or a downward angle relative to horizontal, as selected by the data center operator. Selecting a downward air flow direction may enable commonality with certain legacy rack systems, while reducing the downward airflow for a push pull system upgrade due to downwardly directed airflow. Selecting an upward airflow direction may enable airflow optimization within a data center that has a hot aisle containment construction. Multi-piece, changeable cover assembly designs are presented herein, which facilitate addressing human factor requirements, for instance, with respect to single-person assembly lift weight recommendations. Further, a sectional vent cover approach may be employed to address human factor requirements with respect to single person lift weight recommendations on the vent cover itself. For instance, the concepts disclosed herein may be executed with a single-piece, or multi-piece, fixed or variable louver design. Alternatively, a variable or adjustable louver design could be manually, or automatically, implemented, for instance, via server feedback control based on environmental operating parameters. The changeable cover assembly approach disclosed herein may be extended, in one or more embodiments, to a chimney-type form to redirect airflow into, for instance, a data center&#39;s return air plenum located above, or even below the electronics rack. 
       FIGS. 4A-10C  depict various examples of the above-summarized aspects of the present invention. Referring initially to  FIGS. 4A &amp; 4B , wherein one embodiment of an apparatus  400  is shown comprising a changeable cover assembly  401  coupled to an air outlet side  312  of electronics rack  310 , such as the above-described electronics rack  310  of  FIG. 3 . In the embodiment depicted in  FIGS. 4A &amp; 4B , changeable cover assembly  401  is sized and configured by way of example to fully or substantially cover air outlet side  312  of electronics rack  310 , such that substantially all air egressing from electronics rack  310  passes through changeable cover assembly  401 . Thus, in one embodiment, cover assembly  401  has substantially the same height and width as electronics rack  310  at air outlet size  312  thereof. 
     In the implementation of  FIGS. 4A &amp; 4B , changeable cover assembly  401  includes a frame  410  and multiple vent covers  420 ,  430  overlying one or more openings (not shown) in frame  410 . Airflow egressing from air outlet side  312  of electronic rack  310  passes through the one or more openings in frame  410 , and is redirected or vectorized into multiple airflow channels or pathways through the vent covers  420 ,  430 . Note that  FIGS. 4A &amp; 4B  depict a two-vent cover implementation, but that in other embodiments, three or more vent covers could be coupled together, and to frame  410  to define changeable cover assembly  401 . In the two-vent cover example of  FIGS. 4A &amp; 4B , upper vent cover  420  may be reversible, as illustrated in  FIGS. 4A &amp; 4B , with vent cover  430  being fixed (that is, in one example). By way of example only, vent cover  420  includes multiple fixed louvers  421 , which in  FIG. 4A , are oriented at an approximate 40° angle downwards from horizontal, and in  FIG. 4B , are angled approximately 40° upwards from horizontal, that is, when the vent cover  420  is reversed by flipping the vent cover upside-down. Note that the 40° angle of the louvers is presented by way of example only. Various angles may be implemented in combination with a changeable cooling assembly such as described herein, for instance, in order to optimize the assembly&#39;s application to the particular IT content of the electronics rack. Note also that in three dimensions, vent covers  420 ,  430  may have various shapes, such as trapezoidal, rhombus, rectangular, curvilinear, semispherical, etc., as desired for a particular application to define the desired airflow channels or pathways. Note further that, airflow egressing from different regions of the air outlet side of the electronics rack may be isolated and separately directed by the changeable cover assembly  401 , for instance, through the configuration of frame  410  and the use of different vent covers  420 ,  430 . 
     In the embodiment depicted in  FIGS. 4A &amp; 4B , vent covers  420 ,  430  each include respective fixed louvers  421 ,  431 . The multiple fixed louvers  421  of vent cover  420  are disposed substantially parallel and spaced so as to define parallel airflow channels  424 , through which egressing airflow  302  is vented in substantially parallel airflow paths, in a downward manner in the configuration of  FIG. 4A , and when reversed, in an upward manner, as illustrated in  FIG. 4B . In one embodiment, fixed louvers  421  may comprise one or more surfaces with acoustic material  423  coupled thereto. The acoustic material is a noise-reducing material which is selected and positioned to attenuate noise emanating from the electronics rack, through the one or more openings in the frame of the changeable cover assembly, that is, when the cover assembly is operatively coupled to the electronics rack, as illustrated in  FIGS. 4A &amp; 4B . In this manner, the changeable cover assembly  401  may comprise a changeable acoustic cover assembly for the electronics rack. 
     By way of further example, vent cover  430  is configured with airflow channels defined between respective airflow structures  431 ,  432 , which together direct egressing airflow  303  in different directions so as to intersect upon being vented from the cover assembly, for instance, to reduce momentum of the egressing airflow upon leaving apparatus  400 , with the resulting exiting exhaust air  303  being substantially horizontally directed. Note that this particular configuration of vent cover  430  is presented by way of example only, and may be advantageously employed to optimize, for instance, radiator efficiency in a specific system design such as depicted in  FIG. 3 , wherein the lowermost region  320  includes a radiator of the cooling system. As with vent cover  420 , one or more surfaces of vent cover  430  may have acoustic material  433  coupled thereto to attenuate noise emanating from the electronics rack. 
     Note that  FIGS. 4A &amp; 4B  are provided as one example only of a changeable cover assembly, in accordance with one or more aspects of the present invention. In this cover assembly implementation, the assembly is changeable, and in particular, vent cover  420  is changeable, by being configured to allow for the vent cover to be readily reversed, such that a data center operator may control whether for a particular rack or for a particular location within the data center, exhausting airflow from the electronics rack is directed downwards or upwards. Depending upon the electronics rack implementation, and desired egressing airflow control, various numbers of vent covers and various configurations of vent covers may be provided and combined. Note that coupling of the vent cover(s) to the frame of the changeable cover assembly may be accomplished using a variety of approaches. In one approach, gravity via fixed mounting pins may be used. Alternatively, one or more fasteners may be employed, particularly for use within a data center within a high seismic activity region. 
     By way of further example,  FIG. 5  depicts a changeable cover assembly  500  implemented as a door assembly to be hingedly mounted to, for instance, an air outlet side of an electronics rack, such as electronics rack  310  described above in connection with  FIG. 3 . In this configuration, cover assembly  500  includes a frame  510 , designed as a door frame with one or more openings  511  through which air egressing from an air outlet side of an electronics rack passes when changeable cover assembly  500  is hingedly mounted to the electronics rack. By way of example, frame  510  may be sized with a height and width substantially matching a height and width of the air outlet side of the electronics rack model to which the frame is to be hingedly mounted. Hinges  512  may be provided along a hinge edge  508  of frame  510 , and a door latch mechanism  513  may be disposed (in one embodiment) adjacent to a latch edge  509  of frame  510 , which is opposite to hinge edge  508  of frame  510 . Latch mechanism  513  is configured to facilitate latching of frame  510  to the respective electronics rack when in closed position. One or more perforated screens (not shown) may be provided within the one or more openings  511  of frame  510 . For instance, one or more electromagnetic compatibility (EMC) screens (not shown) may be provided to attenuate electromagnetic noise. Note that frame  510  may include one or more crossbars  514  for enhanced frame rigidity, as well as to provide one or more surfaces for vent covers of changeable cover assembly  500  to seal to in order, for instance, to separate or isolate air egressing from a lowermost region of the associated electronics rack from, for example, a central or uppermost region of the electronics rack. In this manner, different airflow zones at the air outlet side of the electronics rack may be separately handled by the changeable cover assembly  500 . 
     As illustrated, changeable cover assembly  500  further includes multiple vent covers  515 ,  520  &amp;  530 , which may be differently configured, as illustrated. The number and particular configuration of each vent cover  515 ,  520 ,  530  may be tailored to airflow characteristics of a particular type of electronics rack, or a particular manufacturer&#39;s rack design. That is, depending upon the component IT content within the rack, different egressing airflow characteristics may be obtained from the lower to the upper regions of the one or more openings  511  in frame  510 . In the example illustrated, upper vent cover  515  may be configured as a cap, and allow for lateral egress of exhaust airflow, while vent cover  520  may include multiple fixed louvers  521  defining multiple substantially parallel airflow channels therethrough. In this configuration, vent cover  520  is reversible, such that egressing airflow  522  through vent cover  520  may be directed either upwards (as shown), or downwards, upon upside-down reversal of the vent cover. Vent cover  530  may be similar to vent cover  430  described above in connection with  FIGS. 4A &amp; 4B , and be provided to align to, for instance, a radiator section of an electronics rack in a lowermost region of the rack. Vent cover  530  may include one or more airflow-directing structures  531  which direct egressing airflow substantially laterally outward by mixing airflow from two or more airflow channels, in a manner similar to that described above in connection with  FIGS. 4A &amp; 4B . One or more of the surfaces of vent covers  415 ,  420 ,  430  may include acoustically absorptive material  523 ,  533 , as desired to, for instance, attenuate noise emanating from the electronics rack through the air outlet side of the electronics rack. 
     With vent covers  515 ,  520 ,  530  configured as depicted in  FIG. 5 , vent cover  530  in the lowermost region of the door assembly may be, for instance, integrated or permanently affixed to frame  510  so as to overlie the lowermost opening  511  in the frame and seal to frame  510  and crossbar  514  to separate airflow egressing from the lowermost region of the associated electronics rack from airflow egressing from the central and uppermost regions of the electronics rack when changeable cover assembly  500  is hingedly mounted to the air outlet side of the electronics rack. Further, as noted, vent cover  520  may be configured to be reversible relative to the frame to allow, for instance, a data center operator to change a direction of vented air egressing from at least a portion of the cover assembly by, for instance, flipping the vent cover  520  upside-down in order to direct the egressing airflow either upward or downward, depending on the orientation of louvers  521  of vent cover  520 . Note that in one implementation, upper vent cover  515  could be attached to middle vent cover  520  prior to coupling of the vent covers  515 ,  520  to frame  510 . 
       FIGS. 6A &amp; 6B  depict an alternate embodiment of an apparatus  600  comprising an electronics rack  310 , such as described above in connection with  FIG. 3 , and a changeable cover assembly  601 , in accordance with one or more aspects of the present invention. In one implementation, cover assembly  601  could be secured via one or more fasteners (not shown) to air outlet side  312  of electronics rack  310  in order for substantially all air egressing from the air outlet side of the electronics rack to pass therethrough. Alternatively, changeable cover assembly  601  could be configured as a changeable cover assembly door configured to mount to electronics rack  310  and be rotatable between an opened position (not shown) and a closed position, illustrated by way of example in  FIGS. 6A &amp; 6B . In the illustrated configuration, changeable cover assembly  601  includes a frame  610 , designed with one or more openings (not shown) through which air egressing from the air outlet side of electronics rack  310  passes when the frame  610  of changeable cover assembly  601  is mounted to electronics rack  310 . As illustrated, the height and width of frame  610  may be sized to substantially match a height and width of the air outlet side of electronics rack  310  to which frame  610  is mounted. If configured as a door assembly, hinges (not shown) may be provided along a hinge edge of frame  610 , and a door latch mechanism (not shown) may be disposed along an opposite latch edge of frame  610 , in a manner similar to that described above in connection with the embodiment of  FIG. 5 . One or more perforated screens (not shown) may be provided within the one or more openings in frame  610 . For instance, one or more electromagnetic compatibility (EMC) screens (not shown) may be provided within the one or more openings in frame  610  to attenuate electromagnetic noise. 
     Changeable cover assembly  601  further includes a vent cover  620 , which is reversible and has a plurality of louvers  621  oriented, at least in part, in a common direction from, for instance, horizontal. By way of specific example, the multiple louvers  621  could be oriented at approximately 40° angle from horizontal, with the angle being depicted downward in  FIG. 6A , and upward in  FIG. 6B , depending on the particular orientation of vent cover  620 . As illustrated, multiple parallel airflow channels  622  are defined between louvers  621  of vent cover  620  in order to facilitate redirecting and venting airflow  302  egressing from air outlet side  312  of electronics rack  310  in a desired direction, that is, downward or upward, depending (for instance) on the location of electronics rack  310  within a data center and/or depending upon the particular air-cooling configuration of the data center, as to whether downward or upward redirecting, or vectorizing, of airflow  302  is desired. As with the prior embodiments, one or more surfaces of the changeable cover assembly  601 , and in particular of the vent cover  620 , may include acoustically-absorptive material  623  as desired, to attenuate noise emanating from the electronics rack through the air outlet side of the electronics rack. By way of example, one or more surfaces of louvers  621  may include the acoustically-absorptive material  623 . In one implementation, vent cover  620  may be secured via fasteners to frame  610 , or via other mechanical coupling approaches. If desired, frame  610  may include one or more crossbars (not shown) to which reversible vent cover  620  may seal to, for instance, to maintain separate airflow egressing from one or more regions of electronics rack  310  from one or more other regions of the electronics rack. By way of example, airflow egressing from the lowermost region  320  of electronics rack  310  could be segregated from airflow egressing from the central and/or uppermost  330 ,  340  regions of electronics rack  310 . 
     By way of further explanation,  FIGS. 7A-7C  depict in greater detail one embodiment of the changeable cover assembly  601  of  FIGS. 6A &amp; 6B . 
     Referring collectively to  FIGS. 7A-7C , in one or more embodiments, changeable cover assembly  601  may be implemented as a door assembly to be hingedly mounted to, for instance, air outlet side  312  of electronics rack  310  of  FIGS. 6A &amp; 6B . In this configuration, changeable cover assembly  601  includes frame  610 , designed as a door frame with one or more openings  611  through which air egressing from the air outlet side of the electronics rack passes when changeable cover assembly  601  is hingedly mounted to the electronics rack. That is, frame  610  may be sized with a height and a width substantially matching the height and width of the air outlet side of the electronics rack model to which the frame is to be hingedly mounted. 
     Hinges  612  may be provided along a hinge edge  608  of frame  610 , and a door latch mechanism  613  may be disposed (in one embodiment) adjacent to a latch edge  609  of frame  610 , which is opposite to hinge edge  608  of frame  610 . Latch mechanism  613  may be configured to facilitate latching of frame  610  to the electronics rack when in closed position, and to allow pivotable opening of the changeable cover assembly  601  when desired, for instance, to access the air outlet side of the electronics rack. One or more perforated screens  614  may be provided within the opening(s)  611  of frame  610 . For instance, one or more electromagnetic compatibility (EMC) screens  614  may be provided to attenuate electromagnetic noise associated with the electronics rack. 
     Further, one or more localized, perforated brackets  614 ′ may be provided within one or more openings  611  of changeable door assembly  601  in order to add localized airflow impedance to further customize airflow balance through the changeable door assembly where desired. The localized, perforated bracket  614 ′ may allow for a lower airflow rate through that region compared with, for instance, the airflow rate through an adjacent region of the respective opening  611  having only perforated screen  614 . 
     Reversible vent cover  620  may be reversibly mounted to frame  610  using, for instance, one or more mechanical fasteners, or other mechanical coupling means. In  FIGS. 7A &amp; 7B , louvers  621  of vent cover  620  are illustrated (by way of example only) in an upward orientation, similar to that depicted in  FIG. 6B . Perforated panels  625  may be provided at the upper surface and lower surface of reversible vent cover  620  to, for instance, minimize airflow impedance at the upper and lower regions of the reversible vent cover  620 . 
     As discussed in connection with  FIGS. 6A &amp; 6B , the multiple louvers  621  may be, in one embodiment, multiple fixed louvers, which facilitate redirecting and venting of air passing through opening(s)  611  in frame  610  so as to, for instance, vectorize the egressing air into multiple parallel airflow paths with a substantially common orientation, such as either upward or downward relative to horizontal, as described above in connection with  FIGS. 6A &amp; 6B . For instance, depending upon the location of the associated electronics rack within the data center, or the particular airflow configuration of the data center, it may be desirable for an operator to customize the airflow egressing from the electronics rack by orienting the reversible vent cover in a manner for the airflow to egress at an upward angle relative to horizontal, or at a downward angle relative to horizontal. In addition, and as noted, one or more surfaces of vent cover  620  may include acoustically-absorptive material  623  to facilitate attenuating noise emanating from the electronics rack through the air outlet side of the electronics rack. 
       FIGS. 8A &amp; 8B  depict a further variation on the changeable cover assembly  601  of  FIGS. 7A-7C , wherein the changeable cover assembly  601 ′ includes multiple moveable or adjustable louvers  621 ′ within vent cover  620 ′. In one or more implementations, changeable cover assembly  601 ′ is similar to changeable cover assembly  601  of  FIGS. 7A-7C , including having a frame  610  configured and sized to hingedly mount to an air outlet side of the electronics rack. In such an embodiment, latch mechanism  613  may be provided to facilitate latching of frame  610  to the respective electronics rack when in closed position. 
     As illustrated in  FIGS. 8A &amp; 8B , in one embodiment, the multiple adjustable louvers  621 ′ may be collectively adjusted upward or downward, relative to horizontal, in order to change the direction of airflow  302 ′ egressing from the changeable cover assembly  601 ′. Multiple adjustable louvers  621 ′ facilitate redirecting and venting of the airflow passing through the one or more openings in frame  610  and have, at least in part, a common, adjustable orientation relative to the frame, or relative to horizontal, where the frame is assumed to be vertically coupled to an air outlet side of an electronics rack. The louvers could be manually adjusted by, for instance, allowing an operator access to an actuator bar  812  coupled to the adjustable louvers  621 ′. Alternatively, an automatic adjustment system  800  may be coupled to adjustment louvers  621 ′, and include, for instance, a control system  810 , an actuator  811 , one or more moveable coupling linkages, and one or more actuator bars  812 , coupling movement of actuator  811  to the multiple adjustable louvers  621 ′ under control of control system  810 . In this manner, control system  810  may be configured or programmed to dynamically or periodically adjust orientation of the multiple adjustable louvers  621 ′ based on one or more sensed parameters associated with the electronics rack to which changeable cover assembly  601 ′ is mounted, or associated with, for instance, the data center housing the electronics rack. For instance, orientation of the multiple adjustable louvers  621 ′ may be automatically controlled in order to adjust the redirecting of airflow  302 ′ egressing from the changeable cover assembly in a manner best suited for the current conditions within the electronics rack or data center housing the electronics rack. 
     In one implementation, adjustable louvers  621 ′ may each have respective hinge points or pins  814  within vent cover  620 ′, about which the louvers pivot, depending on the position of one or more actuator bars  812 . In one implementation, actuator  811  is an actuator cylinder, however, different forms of actuators could be employed in a changeable cover assembly  601 ′ such as described herein. For instance, linear or rotary actuators could alternatively be used, as well as other forms of linkages. Automatic, individual control of each adjustable louver  621 ′ could, in one embodiment, be implemented by one skilled in the art using a rotary-type actuator. Note that, in one or more implementations, control system  810  could be implemented within the associated electronics rack, or could reside at another location within the data center housing the electronics rack. 
       FIGS. 9A &amp; 9B  depict two examples of control processes which could be programmed into control system  810  of a changeable cover assembly  601 ′, such as depicted in  FIGS. 8A &amp; 8B . 
     Referring first to  FIG. 9A , in one embodiment, the control system processing  900  receives as input multiple sensed temperatures, including, for instance, an upper-level room temperature, a mid-level room temperature, and a lower-level room temperature, from upper-level room temperature sensor  901 , mid-level room temperature sensor  902 , and lower-level room temperature sensor  903 . Depending on the implementation, multiple temperature sensors may be provided at each of the different levels within the data center, or may be disposed, for instance, at different regions of the data center, or different regions of the associated electronics rack. The control system  900 , which in one embodiment may be a power thermal control system, may be programmed to adjust the adjustable louver orientations based on one or more predetermined set points. The particular set point(s) will vary by facility, depending on the room air-conditioning system and specific system layouts of the data center floor. Once determined, the control system  900  controls the louver actuator(s)  910 , to collectively or separately adjust the multiple adjustable louvers dependent, for example, on the values of the sensed parameters. 
       FIG. 9B  depicts an alternate control process, wherein the control system process  900  monitors the system environment and workload of the associated electronics rack to, for instance, obtain a maximum acoustic attenuation, based on predetermined reliability temperature limits. For instance, the control system may initially control fan/blower speed  928  until a preset lower limit is reached. If the temperature reliability limits have not been reached, the louvers can then be actuated via control of the louver actuator  910  to close the louvers to further improve acoustic performance to the system. Closing of the louvers could entail orienting louvers in a more downward position or a more upward position, dependent, for instance, on the room air-conditioning system and rack layout of the data center. In this control implementation, control system process  900  may receive sensed parameters, such as processor power  920 , processor temperature  922 , inlet rack temperature  924 , and one or more other rack temperatures via one or more other rack temperature sensors  926 . The sensed parameter information may be employed by the control system process  900  being configured or programmed to automatically adjust fan/blower speed  928  and/or control the louver actuator  910 , to (for instance) balance airflow recirculation with noise attenuation within the data center. 
       FIGS. 10A-10C  depict further variations on a changeable cover assembly, in accordance with one or more aspects of the present invention. 
     Referring first to the embodiment of  FIG. 10A , an apparatus  1000  is illustrated which includes, by way of example, electronics rack  310  of  FIG. 3  and a changeable cover assembly  1001 . Changeable cover assembly  1001  is sized to cover, at least in part, air outlet side  312  of electronics rack  310 . In one or more implementations, changeable cover assembly  1001  substantially completely covers the air outlet side of electronics rack  310 , and may be configured, for instance, as a door assembly to be hingedly mounted to the electronics rack, as in certain of the embodiments described above. In the implementation of  FIG. 10A , changeable cover assembly  1001  includes a frame  610 , such as described above in connection with  FIGS. 7A-7C , and a vent cover  1020  which is configured to detachably couple to frame  610  so as to be, for instance, readily reversible to direct egressing airflow  1030  either upwards, as shown in  FIG. 10A , or downwards, in an alternate data center implementation, where egressing airflow is exhausted through one or more air exhaust plenums located below the electronics rack  310 . As depicted, vent cover  1020  defines (in the example of  FIG. 10A ) an air exhaust plenum  1021  which redirects the exhausting airflow from electronics rack  310  substantially 90° to exit via an overhead airflow exhaust chimney  1040 , which may, in one embodiment, be disposed in close proximity to changeable cover assembly  1001 , or be coupled to the changeable cover assembly so as to form, for instance, an air-tight seal. Note that the cover assembly is changeable by, for example, changing the orientation of the vent cover  1020 , or alternatively, by changing the vent cover itself, for instance, to an embodiment such as depicted in  FIG. 10C . 
     In  FIG. 10B , an apparatus  1000 ′ is depicted, which includes electronics rack  310  and changeable cover assembly  1001 . In this embodiment, electronics rack  310  is provided with an opening  1005  in an upper surface thereof to allow for a portion  1031  of the egressing airflow to directly exit from electronics rack  310  into an enlarged, overhead airflow exhaust chimney  1040 ′. As in the embodiment of  FIG. 10A , overhead airflow exhaust plenum  1040 ′ may be disposed in close proximity to electronics rack  310  and changeable cover assembly  1001 , or alternatively, may be coupled thereto to establish an air-tight seal between the chimney and electronics rack  310  and changeable cover assembly  1001 . This configuration may be advantageous with an electronics rack  310  such as described above in connection with  FIG. 3 , wherein a lower volume of airflow egresses from the uppermost region of the electronics rack compared to, for instance, the central and lowermost regions. With the higher rate of airflow exhausting from the central and lower regions, airflow  1031  exhausting from the upper region of electronics rack  310  could be inhibited by a strong exhausting airflow  1030  within airflow exhaust plenum  1021  of vent cover  1020 . 
       FIG. 10C  depicts a further embodiment of an apparatus  1000 ″, in accordance with one or more aspects of the present invention. As shown, apparatus  1000 ′ is similar to that described above in connection with  FIG. 10B , with the exception that the changeable cover assembly  1001 ′ includes a vent cover  1020 ′ which comprises an outer vent cover  1023  and an inner vent cover  1024  defining an outer air exhaust plenum  1021 ′ and an inner air exhaust plenum  1022 , respectively. In this manner, airflow  1030  exhausting from the lowermost region  320  of electronics rack  310  may be redirected to pass through outer air exhaust plenum  1021 ′, and be substantially isolated from the higher airflow exiting from the central region  330  of the electronics rack  310 , that is, in the rack embodiment described herein by way of example. As illustrated, air exhaust  1032  exiting from the central region of electronics rack  310  is redirected within the inner air exhaust plenum  1022  to exit towards the overhead airflow exhaust chimney  1040 ′ of the data center housing apparatus  1000 ″. As with the changeable cover assembly  1001  embodiment of  FIGS. 10A &amp; 10B , changeable cover assembly  1001 ′ may be, for instance, reversed to redirect airflow exhausting from the electronics rack in a downward manner, depending upon the data center&#39;s airflow exhaust configuration. Further, as with the changeable cover assembly embodiments described above, one or more surfaces of the changeable cover assembly, for instance, one or more surfaces of vent covers  1023 ,  1024  may comprise an acoustically-absorptive material (not shown) to attenuate noise emanating from the electronics rack through the air outlet side of the electronics rack. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprise” (and any form of comprise, such as “comprises” and “comprising”), “have” (and any form of have, such as “has” and “having”), “include” (and any form of include, such as “includes” and “including”), and “contain” (and any form contain, such as “contains” and “containing”) are open-ended linking verbs. As a result, a method or device that “comprises”, “has”, “includes” or “contains” one or more steps or elements possesses those one or more steps or elements, but is not limited to possessing only those one or more steps or elements. Likewise, a step of a method or an element of a device that “comprises”, “has”, “includes” or “contains” one or more features possesses those one or more features, but is not limited to possessing only those one or more features. Furthermore, a device or structure that is configured in a certain way is configured in at least that way, but may also be configured in ways that are not listed. 
     The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below, if any, are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present invention has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. The embodiment was chosen and described in order to best explain the principles of one or more aspects of the invention and the practical application, and to enable others of ordinary skill in the art to understand one or more aspects of the invention for various embodiments with various modifications as are suited to the particular use contemplated.