Abstract:
A method of controlling air circulation in a data center system. The data center system includes: a cold aisle; a hot aisle including a floor element and a ceiling element; a server rack comprising a controller and servers separating the cold aisle from the hot aisle; and an air conditioning unit. The method includes: toggling, by the controller, the hot aisle between: (a) a first configuration in which the ceiling element is opened and the floor element is closed and (b) a second configuration in which the ceiling element is closed and the floor element is opened, wherein the first configuration enables circulation of air from the from the hot aisle to the cold aisle via the air conditioning unit, and wherein the second configuration enables circulation of air from the from the hot aisle to the cold aisle without the circulated air passing through the air conditioning unit.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a data center system in which hot and cold aisles are separated by server racks. 
         [0002]    The present invention further relates to a server rack for such a data center system. 
         [0003]    The present invention yet further relates to a method of controlling the temperature in a data center. 
       BACKGROUND 
       [0004]    Data centers are large computer rooms that are organized in so-called hot aisles and cold aisles. Server racks separate the hot aisles from the cold aisles, with the servers in the server racks typically arranged to draw cold air from the cold aisles to cool the servers in the racks and expel the heated air into the hot aisles. A computer room air conditioning (CRAC) unit draws in air from the hot aisles, typically through ceiling tiles of the computer room and returns the cooled air to the cold aisles via perforated floor tiles and/or grates in the cold aisles. The conduits required for the air flow from and to the CRAC unit are typically defined by a suspended ceiling and a raised floor, as is well-known per se. 
         [0005]    Data centers require large amounts of energy to operate. A substantial part of this energy is being consumed by the CRAC unit. As is well-known, the efficiency of air conditioning units such as CRAC units depends on the temperature of the inbound air, i.e. the air drawn from the hot aisles. In case of low server activity, the air of the associated hot aisle may have a relatively low temperature, which therefore negatively impacts on the efficiency of the CRAC unit. This is undesirable, as this pushes up the energy consumption of the data center as a whole, which not only increases the operation cost of the data center but also increases the risk of black-outs if the energy demand of the data center cannot be met, which is highly undesirable. It is therefore desirable to try and improve the energy efficiency of data centers. 
         [0006]    U.S. Pat. No. 8,156,753 B2 discloses a data center cooling solution providing techniques for using baffles, doors and roof sections to prevent warm air from being entrained into a cold aisle in a data center, wherein the data center generally contains an air cooling system and a raised floor structure. The raised floor structure is configured to deliver cool air into the data center through a plurality of grates and perforated tiles in the floor. Electronic equipment racks are disposed around the grates and perforated tiles, such that the front faces of the equipment racks face the grates and perforated tiles. A collection of baffles, doors or roof sections inhibit the mixing of the cool air delivered by the air cooling system and the warm air exhausted by the electronic equipment. This improves cooling of the servers and therefore increases the temperature gradient between the hot aisles and cold aisles. However, this solution does not address the problem of CRAC inefficiency if this temperature gradient is small, e.g. because of low server activity. 
         [0007]    US 2011/0303406 A1 discloses a computer room air-conditioning system including a temperature detection unit which is provided for each of a front and a back of each rack, and which measures air temperatures at the front and the back of the rack. A control device for acquiring a measured temperature by each temperature detection unit and for performing control based on the measured temperature is also present. With the configuration, the control device includes a temperature difference calculation unit for calculating a temperature difference between cool air at the front and warm air at the back of each rack based on each measured and acquired temperature; and a heating element, i.e. server, cooling control unit for controlling by adjustment an amount of flow of cool air from the underfloor space to the computer room based on the calculated temperature difference. This improves the energy efficiency of the data center because the air flow to and from the CRAC unit is reduced for small temperature gradients. Nevertheless, this still requires the CRAC unit to operate at reduced efficiency, albeit at reduced air volumes. 
       BRIEF SUMMARY OF THE INVENTION 
       [0008]    The present invention seeks to provide a data center system that can be operated at further improved energy efficiency. 
         [0009]    The present invention further seeks to provide a server rack for use in such a data center system. 
         [0010]    The present invention yet further seeks to provide a method of controlling the temperature in a data center. 
         [0011]    According to an aspect of the present invention, there is provided data center system comprising a cold aisle comprising a first perforated floor element; a hot aisle comprising a second perforated floor element and a ceiling element that each can be opened and closed; a server rack comprising a plurality of servers separating the cold aisle from the hot aisle; an air conditioning unit having an input coupled to the hot aisle via the ceiling element and an output coupled to the cold aisle via the first perforated floor element; and a controller arranged to toggle the data center system between a first configuration in which the ceiling element is opened and the second perforated floor element is closed; and a second configuration in which the ceiling element is closed and the second perforated floor element is opened. 
         [0012]    In this system, the air conditioning (AC) unit can be bypassed if there is no need to feed the air from the hot aisle to the AC unit. In this bypass mode, the air from the hot aisle is recirculated to the cold aisle via the raised floor including the first perforated floor element and the adjustable second perforated floor element. The floor elements may for instance be tiles. This has the advantage that the AC unit can be kept in a standby mode in situations where the AC unit would otherwise have operated at reduced efficiency, thus improving the energy efficiency of the data center system. 
         [0013]    The controller may be arranged to toggle between the first configuration and the second configuration upon the temperature in the cold aisle reaching a defined threshold, such as 28° C. If the temperature in the cold aisle exceeds this defined threshold, cooling of the servers in the server racks may be compromised, such that upon reaching this temperature the AC unit should be included in the recirculation loop to ensure that the air temperature in the cold aisle does not exceed this temperature. 
         [0014]    Alternatively or additionally, the controller may be arranged to toggle between the first configuration and the second configuration upon the temperature in the hot aisle reaching a defined further threshold, such as 45° C. This further threshold may be selected based on the efficiency characteristics of the AC unit, such that the AC unit is only activated when it can operate in a sufficiently efficient manner. 
         [0015]    The server rack may comprise a temperature sensor coupled to the controller, said controller being responsive to said temperature sensor, which may be located at the front of the server rack to sense the temperature in the cold aisle or at the back of the server rack to sense the temperature in the hot aisle. The server rack may comprise a pair of such temperature sensors, i.e. a temperature sensor at the front of the rack and a further temperature sensor at the back of the rack, with the controller being responsive to each of said temperature sensors. 
         [0016]    In a particularly advantageous embodiment, the controller is integrated in the server rack, such that no separate controllers have to be provided in the data center system, thus reducing implementation complexity. 
         [0017]    The data center system may comprise a plurality of server racks separating the hot aisle from the cold aisle. The data center system may further comprise a plurality of said controllers, wherein each of said server racks comprises one of said controllers, and wherein the ceiling element and the second perforated floor element are responsive to each individual controller. This has the advantage each server rack can trigger the activation of the AC unit, for instance when it is detected that the servers in a particular rack switch to a mode of high activity, thereby providing a more fine-grained level of control over the temperature in the data center. 
         [0018]    According to another aspect of the present invention, there is provided a server rack for use in the data center system according to an embodiment of the present invention, the server rack comprising a controller arranged to toggle the data center system between a first configuration in which the ceiling element is opened and the second perforated floor element is closed; and a second configuration in which the ceiling element is closed and the second perforated floor element is opened. 
         [0019]    The server rack may further comprise at least one temperature sensor coupled to the controller for sensing the temperature in the hot aisle or cold aisle, as previously explained. 
         [0020]    In accordance with yet another aspect of the present invention, there is provided a method of controlling the temperature in a data center system comprising a cold aisle comprising a first perforated floor element; a hot aisle comprising a second perforated floor element and a ceiling element that each can be opened and closed; a server rack comprising a plurality of servers separating the cold aisle from the hot aisle; and an air conditioning unit having an input coupled to the hot aisle via the ceiling element and an output coupled to the cold aisle via the first perforated floor element; the method comprising recirculating air from the hot aisle to the cold aisle via the second perforated tile and the first perforated tile whilst keeping the ceiling element closed; and upon a parameter indicative of server activity reaching a defined threshold, recirculating air from the hot aisle to the cold aisle via the ceiling element and the air conditioning unit whilst keeping second perforated tile closed. This ensures an energy efficient operation of such a data center, as explained in more detail above. 
         [0021]    In an embodiment, the method further comprises generating a control signal at the server rack to control said recirculation. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]    Preferred embodiments of the present invention will now be described, by way of example only, with reference to the following drawings, in which: 
           [0023]      FIG. 1  schematically depicts a data center system according to an embodiment of the present invention in a first configuration; 
           [0024]      FIG. 2  schematically depicts a data center system according to an embodiment of the present invention in a second configuration; 
           [0025]      FIG. 3  schematically depicts an aspect of a data center system according to an embodiment of the present invention; and 
           [0026]      FIG. 4  shows a flow chart of a method of controlling the temperature in a data center according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0027]    It should be understood that the Figures are merely schematic and are not drawn to scale. It should also be understood that the same reference numerals are used throughout the Figures to indicate the same or similar parts. 
         [0028]    In the context of the present application, where embodiments of the present invention constitute a method, it should be understood that such a method is a process for execution by a computer, i.e. is a computer-implementable method. The various steps of the method therefore reflect various parts of a computer program, e.g. various parts of one or more algorithms. 
         [0029]      FIG. 1  schematically depicts a data center system according to an embodiment of the present invention in a first configuration. The data center system is placed in a computer room  10  having a raised floor  20  and a ceiling  30  such as a suspended ceiling. The clearance  26  between the raised floor  20  and the floor of the computer room  10  defines a first conduit and the clearance  36  between the ceiling  30  and the ceiling of the computer room  20  defines a second conduit. The first conduit is used to transport cool air produced by the air conditioning unit  70  to the cold aisles  40  through first perforated floor elements  22  in the raised floor  20 . The second conduit is used to transport hot air from the hot aisles  50  through ceiling elements  32  to the air conditioning unit  70  for cooling. The air circulated in this manner is indicated by the solid arrows in  FIG. 1 . It is noted for the avoidance of doubt that the air conditioning unit  70  may be placed in any suitable location, e.g. inside or outside the computer room  10 . 
         [0030]    As is well-known per se, rows of server racks  60  separate the cold aisles  40  from the hot aisles  50 . The server racks typically comprise one or more servers  62  having a front panel facing a cold aisle  40  and a back panel facing a hot aisle  50 . Each server  62  typically comprises at least one fan that forces air from the cold aisle  40  through the server  62  towards the hot aisle  50  in order to cool the one or more processing elements and other elements generating heat in the server  62 . This is indicated by the solid arrows through the server racks  60 . 
         [0031]    In accordance with an embodiment of the present invention, the hot aisles further comprise a configurable second perforated floor element  24  that forms part of the raised floor  20 . The configurable second perforated floor element  24  can be switched between a first configuration in which the perforations are closed, as shown in  FIG. 1 , and a second configuration in which the perforations are opened, as will be explained in more detail later. Similarly, the ceiling elements  32  are configurable ceiling elements that can be switched between a first configuration in which the ceiling element is opened, as shown in  FIG. 1 , and a second configuration in which the ceiling element is closed, as will be explained in more detail later. 
         [0032]    The specific implementation of the first and second perforated floor elements  22  and  24  and the ceiling element  32  is not particularly limited. Any suitable implementation may be chosen. For instance, the first and second perforated floor elements  22  and  24  may be perforated floor tiles, grates and so on. Similarly, the ceiling element  32  may be a perforated ceiling tile, a grate forming part of the ceiling  30 , or may be a valve-like element mounted on a single server rack  60  or on opposing server racks  60 , with the valve being arranged to expose an opening in the ceiling  30  in the first configuration and cover this opening in the second configuration of the ceiling element  30 . It should be understood that any element that can be used to configurably cover and uncover an opening in the raised floor  20  and the ceiling  30  may be used for such a purpose. 
         [0033]    The data center system further comprises a plurality of temperature sensors for monitoring the temperature in at least one of the cold aisles  40  and the hot aisles  50 . For instance, in an embodiment, the data center system may comprise a temperature sensor  66  in each of the cold aisles  40 . In an alternative embodiment, the data center system may comprise a temperature sensor  68  in each of the hot aisles  50 . In yet another embodiment, which is shown in  FIG. 1 , the data center system may comprise a temperature sensor  66  in each of the cold aisles  40  as well as a temperature sensor  68  in each of the hot aisles  50 . The temperature sensors are coupled to a controller  64  arranged to toggle the second perforated floor element  24  and the ceiling element  32  between the first configuration in which the ceiling element  32  is opened and the second perforated floor element  24  is closed and the second configuration in which the ceiling element  32  is closed and the second perforated floor element  24  is opened. The first configuration is shown in  FIG. 1  and the second configuration is shown in  FIG. 2 . 
         [0034]    In the second configuration shown in  FIG. 2 , the air conditioning unit  70  is bypassed and the air forced through the server racks  60  by the fans in the servers  62  from a cold aisle  40  to a hot aisle  50  is recirculated through a configurable second perforated floor element  24  into the first conduit  26  and into a cold aisle  40  through a first perforated floor element  22 . 
         [0035]    The switching between the first configuration in  FIG. 1  and the second configuration in  FIG. 2  is performed to avoid the air conditioning unit  70  operating at reduced efficiencies, which for instance occurs if the air temperature of the air transported from the hot aisles  50  to the air conditioning unit  70  is below a certain temperature, e.g. 45° C. This may indicate that the servers  62  operate below full capacity, such that the cooling of the servers  62  in the server racks  60  is less critical, such that less cold air, i.e. the air from the hot aisles  50  may be used to cool the servers  62  without having to cool this air using the air conditioning unit  70 . If this is the case, the data center system is configured as shown in  FIG. 2 , in which the air conditioning unit  70  is bypassed and the air from the hot aisles  50  is fed back to the cold aisles  40  through the opened second perforated floor element  24  and the first perforated floor element  22 . 
         [0036]    To this end, the controllers  64  may directly or indirectly control the second perforated floor element  24  and the ceiling element  32  in response to one or more temperature sensors  68  in the hot aisles  50 , as indicated by the dashed arrows in  FIG. 1  and  FIG. 2 . In an embodiment, the controllers  64  of the server racks  60  backing the hot aisle  50  are in direct control of the second perforated floor elements  24  and the ceiling elements  32  of the hot aisles  50 . 
         [0037]    The controllers  64  may be interconnected by a network (not shown for the sake of clarity) that is further conductively coupled to the second perforated floor elements  24  and the ceiling elements  32 . Upon one of the controllers  64  signaling that the temperature in a hot aisle  50  has reached a critical value, i.e. a defined threshold, the ceiling elements  32  will be switched to an opened state and the second perforated floor elements  24  will be switched to a closed state as shown in  FIG. 1  such that the air from the hot aisles  50  is fed to the air conditioning unit  70 . 
         [0038]    In the absence of such a signal on the network, the ceiling elements  32  will be switched to a closed state and the second perforated floor elements  24  will be switched to an opened state as shown in  FIG. 2  such that the air from the hot aisles  50  is fed back into the cold aisles  40 , bypassing the air conditioning unit  70 . In an embodiment, the air conditioning unit  70  is also responsive to the control signal generated by the controllers  64  such that upon detection of the control signal the air conditioning unit  70  may switch from a standby to an active mode. 
         [0039]    In another embodiment, which is particularly preferable, each of the controllers  64  is responsive to a temperature sensor  66  in one of the cold aisles  40 , such that the controllers  64  can switch from the second configuration in  FIG. 2  in which the air conditioning unit  70  is bypassed to the first configuration in  FIG. 1  in which the air conditioning unit  70  is included in the air flow from the hot aisles  50  to the cold aisles  40 . This is for instance advantageous if the servers  62  must be cooled by air not exceeding a defined further temperature in order to guarantee that the servers  62  will not overheat. In an embodiment, this defined further temperature threshold may be 28° C. 
         [0040]    In yet another embodiment, the each of controllers  64  may be responsive to a temperature sensor  66  in one of the cold aisles  40  as well as to a temperature sensor  68  in one of the hot aisles  50  such that the configuration of the data center system may be switched between the first configuration of  FIG. 1  and the second configuration of  FIG. 2  when at least one of the temperature sensors  66  and  68  indicates that the aforementioned defined temperature threshold has been reached, such that the air conditioning unit  70  can be activated and included in the air recirculation path from the hot aisles  50  and the cold aisles  40  as explained in more detail above. 
         [0041]    At this point, it is noted that in the above detailed description, the controllers  64  and temperature sensor  66  and/or temperature sensor  68  are shown as forming part of a server rack  60 . It should however be understood that this is by way of non-limiting example only. It is equally feasible to provide at least one of the controller  64 , the temperature sensor  66  and/or temperature sensor  68  as separate components of the data center system without departing from the teachings of the present invention. 
         [0042]      FIG. 3  schematically depicts an aspect of the data center system according to an embodiment of the present invention. The data center system may comprise a network  80  connecting the various controllers  64  of the server racks  60  to a master controller  90  that controls the he ceiling elements  32  and the second perforated floor elements  24  in the hot aisles  50 , and may additionally control the air conditioning unit  70  in another embodiment. The master controller may toggle the ceiling elements  32  and the second perforated floor elements  24  in the hot aisles  50  between the first configuration and the second configuration in the presence or absence of a control signal from the controllers  64  signaling that the temperature in one of the hot aisles  50  and/or one of the cold aisles  40  has reached a defined threshold, as previously explained. 
         [0043]      FIG. 4  schematically depicts an embodiment of the method of the present invention. Upon initialization of the data center system in step  110 , it is checked in step  120  if the temperature in the cold aisles  40  and/or the hot aisles  50  is below a defined threshold. Preferably, it is checked if the temperature in the cold aisles  40  is below a defined threshold, e.g. 28° C. If this is the case, the method proceeds to step  130  in which the ceiling elements  32  and the second perforated floor elements  24  are switched to the second configuration in which the ceiling elements  32  are closed and the second perforated floor elements  24  are opened to bypass the air conditioning unit  70 . If this is not the case, the method proceeds to step  140  in which the ceiling elements  32  and the second perforated floor elements  24  are switched to the first configuration in which the ceiling elements  32  are opened and the second perforated floor elements  24  are closed to include the air conditioning unit  70  in the air recirculation from the hot aisles  50  to the cold aisles  40 . It is checked in step  150  if operation of the data center system is to continue. If so, the method returns to step  110 . Otherwise, the method terminates in step  160 . In an embodiment, the decision making process in step  120  is triggered by a control signal generated at the server rack  60  to control said recirculation, as has been explained in more detail above. 
         [0044]    In the above detailed description, the controllers  64  are responsive to one of more temperature sensors  66  and/or  68 . However, it should be understood that alternative embodiments in which the controllers  64  are responsive to another parameter indicative of server activity are equally feasible. For instance, the controllers  64  may monitor the activity or power consumption of the servers  62  in an associated server rack  60 , and generate the control signal to toggle the configuration of the data center system between the first configuration and the second configuration upon the activity or power consumption of the servers  62  reaching a defined threshold instead. Other suitable parameters will be apparent to the skilled person. 
         [0045]    While particular embodiments of the present invention have been described herein for purposes of illustration, many modifications and changes will become apparent to those skilled in the art. Accordingly, the appended claims are intended to encompass all such modifications and changes as fall within the true spirit and scope of this invention.