Patent Publication Number: US-2013244563-A1

Title: Integrated building based air handler for server farm cooling system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of and claims priority to U.S. patent application Ser. No. 13/230,809 filed Sep. 12, 2011 entitled, INTEGRATED BUILDING BASED AIR HANDLER FOR SERVER FARM COOLING SYSTEM, which is a continuation in part (CIP) of and claims priority to U.S. patent application Ser. No. 12/500,520 filed Jul. 9, 2009 entitled, INTEGRATED BUILDING BASED AIR HANDLER FOR SERVER FARM COOLING SYSTEM, all of which are incorporated herein by reference in their entireties. 
     TECHNICAL FIELD 
     The present disclosure relates generally to cooling systems. 
    
    
     BACKGROUND 
     The rapid growth of Internet services such as Web email, Web search, Web site hosting, and Web video sharing is creating increasingly high demand for computing and storage power from servers in data centers. While the performance of servers is improving, the power consumption of servers is also rising despite efforts in low power design of integrated circuits. For example, one of the most widely used server processors, AMD&#39;s Opteron processor, runs at up to 95 watts. Intel&#39;s Xeon server processor runs at between 110 and 165 watts. Processors are only part of a server, however; other parts in a server such as storage devices consume additional power. 
     Servers are typically placed in racks in a data center. There are a variety of physical configurations for racks. A typical rack configuration includes mounting rails to which multiple units of equipment, such as server blades, are mounted and stacked vertically within the rack. One of the most widely used 19-inch rack is a standardized system for mounting equipment such as 1U or 2U servers. One rack unit on this type of rack typically is 1.75 inches high and 19 inches wide. A rack-mounted unit that can be installed in one rack unit is commonly designated as a 1U server. In data centers, a standard rack is usually densely populated with servers, storage devices, switches, and/or telecommunications equipment. One or more cooling fans may be mounted internally within a rack-mounted unit to cool the unit. In some data centers, fanless rack-mounted units are used to increase density and to reduce noise. 
     Rack-mounted units may comprise servers, storage devices, and communication devices. Most rack-mounted units have relatively wide ranges of tolerable operating temperature and humidity requirements. For example, the system operating temperature range of the Hewlett-Packard (HP) ProLiant DL365 G5 Quad-Core Opteron processor server models is between 50° F. and 95° F.; the system operating humidity range for the same models is between 10% and 90% relative humidity. The system operating temperature range of the NetApp FAS6000 series filers is between 50° F. and 105° F.; the system operating humidity range for the same models is between 20% and 80% relative humidity. There are many places around the globe such as parts of the northeast and northwest region of the United States where natural cool air may be suitable to cool servers such as the HP ProLiant servers and the NetApp filers during certain periods of a year. 
     The power consumption of a rack densely stacked with servers powered by Opteron or Xeon processors may be between 7,000 and 15,000 watts. As a result, server racks can produce very concentrated heat loads. The heat dissipated by the servers in the racks is exhausted to the data center room. The heat collectively generated by densely populated racks can have an adverse effect on the performance and reliability of the equipment installed in the racks, since they rely on the surrounding air for cooling. Accordingly, heating, ventilation, air conditioning (HVAC) systems are often an important part of the design of an efficient data center. 
     A typical data center consumes 10 to 40 megawatts of power. The majority of energy consumption is divided between the operation of servers and HVAC systems, HVAC systems have been estimated to account for between 25 to 40 percent of power use in data centers. For a data center that consumes 40 megawatts of power, the HAVC systems may consume 10 to 16 megawatts of power. Significant cost savings can be achieved by utilizing efficient cooling systems and methods that reduce energy use. For example, reducing the power consumption of HVAC systems from 25 percent to 10 percent of power used in data centers translates to a savings of 6 megawatts of power which is enough to power thousands of residential homes. The percentage of power used to cool the servers in a data center is referred to as the cost-to-cool efficiency for a data center. Improving the cost-to-cool efficiency for a data center is one of the important goals of efficient data center design. For example, for a 40 megawatt data center, the monthly electricity cost is about $1.46 million assuming 730 hours of operation per month and $0.05 per kilowatt hour. Improving the cost to cool efficiency from 25% to 10% translates to a saving of $219,000 per month or $2.63 million a year. 
     In a data center room, server racks are typically laid out in rows with alternating cold and hot aisles between them. All servers are installed into the racks to achieve a front-to-back airflow pattern that draws conditioned air in from the cold rows, located in front of the rack, and ejects heat out through the hot rows behind the racks. A raised floor room design is commonly used to accommodate an underfloor air distribution system, where cooled air is supplied through vents in the raised floor along the cold aisles. 
     A factor in efficient cooling of data center is to manage the air flow and circulation inside a data center. Computer Room Air Conditioners (CRAC) units supply cold air through floor tiles including vents between the racks. In addition to servers, CRAC units consume significant amounts of power as well. One CRAC unit may have up to three 5 horsepower motors and up to 150 CRAC units may be needed to cool a data center. The CRAC units collectively consume significant amounts of power in a data center. For example, in a data center room with hot and cold row configuration, hot air from the hot rows is moved out of the hot row and circulated to the CRAC units. The CRAC units cool the air. Fans powered by the motors of the CRAC units supply the cooled air to an underfloor plenum defined by the raised sub-floor. The pressure created by driving the cooled air into the underfloor plenum drives the cooled air upwardly through vents in the subfloor, supplying it to the cold aisles where the server racks are facing. To achieve a sufficient air flow rate, hundreds of powerful CRAC units may be installed throughout a typical data center room. I-However, since CRAC units are generally installed at the corners of the data center room, their ability to efficiently increase air flow rate is negatively impacted. The cost of building a raised floor generally is high and the cooling efficiency generally is low due to inefficient air movement inside the data center room. In addition, the location of the floor vents requires careful planning throughout the design and construction of the data center to prevent short circuiting of supply air. Removing tiles to fix hot spots can cause problems throughout the system. 
     SUMMARY 
     The present teaching relates to cooling systems. 
     In one example, an air handler building structure is disclosed, which includes a floor, a plurality of lateral walls, a roof, and one or more openings located either on the roof or on at least one of the lateral walls. The lateral walls include a lower and an upper lateral walls opposing to each other having different respective heights determined in accordance with a ratio. The roof has a pitch consistent with the ratio associated with the lower and upper lateral walls. The shape of the building structure allows air within the building structure to rise via natural convection. In addition, a first dimension along a first direction defined between the lower and upper lateral walls relative to a second dimension along a second direction perpendicular to the first direction is such that the building structure provides access to outside natural air via one or more openings on the lower lateral wall. 
     In another example, a server cooling system is disclosed, which includes a first space defined by a floor, one or more lateral walls, and a ceiling, having a plurality of servers installed therein, and second space defined by the ceiling and a roof. One or more openings are located on at least one of the ceiling, the roof, and at least one of the one or more lateral walls. The server cooling system also includes an air inlet coupled with a first lateral wall and operable to allow outside natural air to enter, one or more air-handling units coupled with the air inlet to draw the outside natural air and to provide air to the first space, and an air outlet coupled with a second lateral wall and operable to allow air in the second space to exit. The server cooling system further includes a control system configured to control the one or more air-handling units to provide air to the first space in accordance with temperatures measured within and outside of the first space. 
     In still another example, a server cooling system is disclosed, which includes a first space defined by a floor, a plurality of lateral walls, and a ceiling, and a second space defined by the ceiling and a sloped roof constructed in accordance with a pitch. One or more openings are located on at least one of the roof, the ceiling, and at least one of the lateral walls, that enable outside natural air to enter the first space and air in the second space to exit by natural convection. The server cooling system also includes an interior space inside the first space, that is substantially enclosed and engaging the ceiling, and a rack engaging the interior space in a substantially sealed manner and having a plurality of rack-mounted servers mounted thereon. Respective front faces of the rack-mounted servers interface with the first space respective back faces of the rack-mounted servers interface with the interior space. Each rack-mounted server includes one or more fans installed therein operable to draw air from the first space through its front face and expel heated air to the interior space through its back face. 
     In yet another example, an air handler building structure is disclosed, which includes a floor, a plurality of lateral walls, a roof portion, a protruding portion, and one or more openings located on at least one of the roof portion, at least one of the lateral walls, and the protruding portion. The roof portion has opposing sides, each having a pitch. The protruding portion extends above the roof portion. In addition, the shape of the building structure allows outside natural air to enter through one or more openings on at least one of the lateral walls via natural convection and exit through one or more openings on at least one of the roof portion and the protruding portion. 
     The following detailed description together with the accompanying drawings will provide a better understanding of the nature and advantages of various embodiments of the present invention. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram showing an exemplary, server cooling system; 
         FIG. 2  is a diagram showing an example server cooling system wherein the server cooling system comprises an attic space; 
         FIG. 3  is a diagram showing an example server cooling system wherein air is re-circulated inside the example server cooling system; 
         FIG. 4  is a diagram showing an example server cooling system with a hot row enclosure and a cold row enclosure; 
         FIG. 5  is a diagram showing an example server cooling system with a hot row enclosure and a cold row enclosure wherein air is re-circulated inside the a server cooling system; 
         FIG. 6  is a diagram showing an example server cooling system with a single-sloped roof; 
         FIG. 7  is a diagram showing a top view of an example server cooling system with a single-sloped roof; 
         FIG. 8  is a diagram showing an example server cooling system with a gable roof; 
         FIG. 9  is a diagram showing an example server cooling system with an air mixing chamber; 
         FIGS. 10A and 10B  are diagrams showing an example air handler building structure; 
         FIG. 11  is a diagram showing an example server cooling system; 
         FIG. 12  is a diagram showing another example server cooling system; 
         FIG. 13  illustrates a cross-section of an other example of an air handler building structure; and 
         FIG. 14  illustrates a cross section of yet another exemplary air handler building structure. 
     
    
    
     DESCRIPTION OF EXAMPLE EMBODIMENT(S) 
     The following example embodiments and their aspects are described and illustrated in conjunction with apparatuses, methods, and systems which are meant to be illustrative examples, not limiting in scope. 
       FIG. 1  illustrates an example server cooling system comprising lateral walls  100 , a floor  102 , a roof  104 , an enclosure  106 , and a server rack  108 . The lateral walls  100 , the floor  102  and the roof  104  define an inside space  118 . Floor  102  may or may not be a raised sub-floor. There may be valved openings  110  on the roof  104  and valved openings  114  on the lateral walls  100 . The valved openings may be connected to a control system which is operable to selectively open or close each valved opening. The enclosure  106  may have a frame, panels, doors, and server rack ports. A server rack port is an opening in the enclosure  106  that can be connected to one or more server racks  108 . The enclosure  106  may be made of a variety of materials such as steel, composite materials, or carbon materials that create a housing defining an interior space  116  that is substantially sealed from the inside space  118 . The enclosure  106  comprises at least one server rack port that allows one or more rack-mounted units installed in the server rack  108  to interface with the interior space  116 . In one implementation, the a server rack port is an opening configured to substantially conform to the outer contours of, and accommodate, a server rack  108 . One or more edges of the server rack port may include a gasket or other component that contacts the server rack  108  and forms a substantially sealed interface. The server rack  108  may be removably connected to the enclosure  106  through the server rack port in a substantially sealed manner. In some embodiments, one or more rack-mounted units are installed in the server rack  108  such that respective front faces of the rack-mounted units interface with the inside space  118 , and that respective back faces of the rack-mounted units interface with the interior space  116  defined by the enclosure  106 . An example rack-mounted unit may be a server blade, data storage array or other functional device. A front-to-back air flow through the rack-mounted units installed in the server rack  108  draws cooling air from the inside space  118  and expels heated air to the interior space  116 . 
     The enclosure  106  may be connected to valved openings  110  on the roof  104  through a connector  112  on a top side of the enclosure. In some embodiments, the connector  112  may be made of metal ducts. In other embodiments, the connector  112  may be made of soft and flexible materials so that the enclosure may be removably connected to the valved openings  110 . In some embodiments, the enclosure  106  may be mounted directly to the floor  102 . In other embodiments, the enclosure  106  may have wheels on the bottom side and may be easily moved around in a data center. 
     In some embodiments, the server rack  108  may be sparsely populated with servers and other equipment. Since servers and other equipment are stacked vertically within the rack, the scarcity may create open gaps to the interior space  116 . Air may leak from the interior space  116  through the open gaps. To prevent air leakage, the gaps may be blocked by panels mounted to the server rack  108  that prevent air from escaping and entering the enclosure  106  through the gaps. 
     In some embodiments, one or more air handling units  122  may draw external cool air into the inside space  118 . The cool air enters the server cooling system through valved openings  114  on the lateral walls  100 . One or more fans draw the cool air from the inside space  118  through the front faces of the one or more rack-mounted units and expel heated air through the back faces of the one or more rack-mounted units to the interior space  116 . The heated air passes through the connector  112  and leaves the interior space  116  through the valved openings  110  on the roof  110 . In some embodiments, the cooling fans mounted internally within the rack-mounted units installed in the rack  108  draw the cool air from the inside space  118  and expel heated air to the interior space  116 ; no additional air handling units, in one implementation, are need to cool the rack-mounted units. In other embodiments where fanless rack-mounted units are installed in the rack  108 , one or more fans may be installed on one side of the rack  108  to draw air through the rack-mounted units from the inside space  118  to the interior space  116  to cool the rack-mounted units installed in the rack  108 . 
     In some embodiments, there may be valved openings  120  on the enclosure  116 . A control system is operably connected to the valved openings  120 , the valved openings  110  on the roof  104 , and the valved openings  114  on the lateral walls  100 . The control system is operable to selectively activate each of the valved openings based on temperatures observed within and outside the inside space  118  to achieve one or more desired air flows. When the air external to the inside space  118  is not suitable to be introduced to the inside space  118 , the control system closes the valved openings  110  and  114 , and opens up the valved openings  120 . To cool air in the inside space  118 , one or more cooling units may be used. In some embodiments, the cooling units may be evaporative coolers which are devices that cool air through the simple evaporation of water. Compared with refrigeration or absorption air conditioning, evaporative cooling may be more energy efficient. Cooling air is drawn from the inside space  118  through the rack-mounted units and heated air is expelled to the interior space  116  defined by the enclosure  106 . Heated air inside the enclosure  106  is exhausted to the inside space  118  through the valved openings  120 . In some embodiments, one or more fans may be used to exhaust the heated air out of the enclosure  106 . 
     In other embodiments, one or more cooling units may be used while external air is introduced to the inside space  118 . The control system may open the valved openings  110 ,  114 , and  120  simultaneously. Evaporative cooling units may be used in close proximity to the valved openings  114  so that the external air may be cooled while being introduced to the inside space  118 . 
     In yet other embodiments, the control system may open the valved openings  110 , and close valved openings  114  and  120  when the difference in temperature between the outside and the insider space reaches certain configurable threshold values. In other embodiments, the control system may close valved openings  110 , and open up valved openings  114  and  120 . To cool the air in the inside space  120 , one or more evaporative cooling units may be placed in the inside space  120  to provide cooling. 
     In some embodiments, the roof  104  comprises a single-sloped roof which may be easy to manufacture and install. In other embodiments, other types of roof configurations, such as a gable roof, may be used. The lateral walls  100 , the floor  102 , and the roof  104  may be pre-manufactured in a factory and assembled on the construction site where a data center is to be built. Pre-manufactured units may significantly reduce the cost to build a data center. One of the cost advantages of the integrated building based air handler for server farm cooling system is the convenience and low cost of pre-manufacture parts of the system and the ease of installation of pre-manufactured parts in a data center. 
     In some embodiments, the integrated building based air handler for server farm cooling system illustrated in  FIG. 1  obviates the need for raised subfloors, CRAC units and water chillers. A large number of parts of the cooling system may be pre-manufactured and easily assembled. Natural cool air may be used to cool the servers. Cooling fans installed internally within the servers may provide the needed air flow to draw cooling air to cool the servers; CRAC units and raised subfloors may no longer be needed. Efficient evaporative coolers may replace the water chillers which are costly to install and operate. Overall, the cooling systems described herein may significantly reduce the construction cost, and electricity power and water usage, of server farm deployments. 
       FIG. 2  illustrates another example server cooling system comprising lateral walls  200 , a floor  202 , a roof  204 , an enclosure  206 , a server rack  208 , and a ceiling  210 . The example cooling system in  FIG. 2  is similar to that in  FIG. 1  except that the ceiling  210  and the roof  204  define an attic space  220 . The lateral walls  200 , the floor  202  and the ceiling  210  define an inside space  218 . One or more valved openings  222  are coupled to the ceiling  210 . There may be valved openings  224  on the roof  204  and valved openings  214  on the lateral walls  200 . The enclosure  206  is operably connected to the attic space  220  through a connector  212 . 
     In some embodiments, one or more air handling units  226  may draw external cool air into the inside space  218 . One or more fans draw the cool air from the inside space  218  through the front faces of the one or more rack-mounted units installed in the rack  208  and expel heated air through the back faces of the rack-mounted units to the interior space  216 . The heated air passes through the connector  212  and enters the attic space  220 . In some embodiments, the cooling fans mounted internally within the rack-mounted units installed in the rack  208  draw the cooling air to the interior space  216  and no additional air handling units are needed. In other embodiments where fanless rack-mounted units are installed in the rack  208 , one or more fans may be installed on one side of the rack  208  to draw air from the inside space to the interior space  216  to cool the rack-mounted units installed in the server rack  208 . Heated air rises to the attic space  220  and is exhausted out of the cooling system through the valved openings  224 . 
       FIG. 3  illustrates another example server cooling system comprising lateral walls  300 , a floor  303 , a roof  304 , an enclosure  306 , a server rack  308 , and a ceiling  310 . The lateral walls  300 , the floor  302  and the ceiling  310  define an inside space  318 . The roof  304  and the ceiling  310  define an attic space  330 . One or more valved openings  322  are coupled to the ceiling  310 . There may be valved openings  324  on the roof  304  and valved openings  314  on the lateral walls  300 . The enclosure  306  is operably connected to the attic space  320  through a connector  312 . The example cooling system in  FIG. 3  is similar to that in  FIG. 2  except that external air may not be introduced into the inside space  318  and that heated air in the attic space  330 , at some points in time, may not be exhausted to the outside of the example server cooling system; rather, the heated air may be mixed into the inside space  318  as needed to maintain a desired operating temperature. 
     In one embodiment, the valved openings  322 ,  324 , and  314  are connected to a control system which is operable to selectively activate each of the valved openings based on temperatures observed within and outside the inside space  318 . When the external air is not suitable to be introduced to the inside space  318 , the control system closes the valved openings  314  and  324 , and opens up the valved openings  322 . To cool air in the inside space  318 , one or more cooling units may be used. In some embodiments, the cooling units may be evaporative coolers. Cooling air is drawn from the inside space  318  through the rack-mounted units and the heated air is expelled to the interior space  316  defined by the enclosure  306 . Heated air inside the enclosure  306  is exhausted to the attic space  320  through the connector  312  and re-circulated to the inside space  318  through the valved openings  322  coupled to the ceiling  310 . In some embodiments, one or more fans may be used to exhaust the heated air out of the enclosure  306  to the attic space  320  and/or re-circulate at least some of the heated air to the inside space  318 . 
     In other embodiments, one or more cooling units may be used while the external air is introduced to the inside space  318 . The control system may open the valved openings  314 ,  322 , and  324  simultaneously or at selected times individually. Evaporative cooling units may be used in close proximity to the valved openings  314  so that external air may be cooled while being introduced to the inside space  318 . 
     In yet other embodiments, the control system may open up the valved openings  314  and  322 , and close the valved openings  324 . Evaporative cooling units may be used in close proximity to the valved openings  314  and/or the valved openings  322  to provide efficient cooling in the inside space  318 . In other embodiments, the control system may close valved openings  314 , and open up valved openings  322  and  324 . In one embodiment, the control system may close valved openings  314  and  322 , and open up the valved openings  324 . The control system monitors the temperatures within the inside space  318 , within the attic space  320  and the temperature outside. When the difference among the three observed temperatures reaches one or more configurable threshold vales, the control system may selectively open up or close each valved opening. 
       FIG. 4  illustrates another example server cooling system comprising lateral walls  400 , a floor  402 , a roof  404 , a hot row enclosure  406 , a server rack  408 , a cold row enclosure  410 , and a ceiling  424 . The example cooling system in  FIG. 4  is similar to that in  FIG. 3  except that one or more cold row enclosures are used to provide efficient cooling of servers installed in the rack  408 . 
     The lateral walls  400 , the floor  402  and the ceiling  424  define an inside space  418 . The ceiling  424  and the roof  404  define an attic space  420 . In some embodiments, one or more valved openings  426  may be coupled to the ceiling  424 . In some other embodiments, the hot row enclosure  406  comprises at least one server rack port that allows one or more rack-mounted units to interface with a hot row interior space  416 . The cold row enclosure  410  also comprises at least one server rack port that allows one or more rack-mounted units to interface with a cold row interior space  422 . The server rack  408  may be removably connected to the hot row enclosure  406  through the server rack port in a substantially sealed manner. The server rack  408  may also be removably connected to the cold row enclosure  410  through the server rack port in a substantially sealed manner. In some embodiments, the rack-mounted units are installed in the server rack  408  such that respective front faces of the rack-mounted units interface with the cold row interior space  422 , and that respective back faces of the rack-mounted units interface with the hot row interior space  416 . In some embodiments, the hot row enclosure  406  may be operably connected to the attic space  420  through a connector  412 . In some other embodiments, the cold row enclosure may comprise a fan unit  430  to draw air from the cold row interior space  422  through the front faces of the rack-mounted units installed in the rack  408  to cool the rack-mounted units; the heated air is ejected to the hot row interior space  416  through the back faces of the rack-mounted units. 
     In some embodiments, one or more air handling units  432  may draw external cool air into the inside space  418 . The cool air enters the server cooling system through valved openings  414  on the lateral walls  400 . The one or more fans  430  draw the cool air from the inside space  418  to the cold row interior space  422  through one or more openings on the cold row enclosure  410 . In some embodiments, each cold row enclosure  410  may be operably connected to the valved openings  414  so that the external cool air may be drawn to the cold row interior space  422 . In some other embodiments, the cooling fans mounted internally within the rack-mounted units draw the cool air from the cold row interior space  422 . The cool air flows through the front faces of the one or more rack-mounted units installed in the rack  408  and expel heated air through the back faces of the one or more rack-mounted units to hot row interior space  416 . The heated air passes through the connector  412  and enters the attic space  420 . In some embodiments, the heated air inside the attic space  420  may be exhausted out of the cooling system through the valved openings  428 . 
     In some embodiments where fanless rack-mounted units are installed in the rack  408 , one or more fans may be installed on one side of the rack  408  to draw air from the inside space  418  to the interior space  416  to cool the rack-mounted units installed in the rack  408 . In other embodiments, the one or more fans  422  may provide the needed power for the cool air to flow from the cold row interior space  422  to the hot row interior space  416 . 
       FIG. 5  illustrates another example server cooling system comprising lateral walls  500 , a floor  502 , a roof  504 , a hot row enclosure  506 , a server rack  508 , a cold row enclosure  510 , and a ceiling  524 . The lateral walls  500 , the floor  502  and the ceiling  524  define an inside space  51 . The ceiling  524  and the roof  504  define an attic space  520 . The example cooling system in  FIG. 5  is similar to that in  FIG. 4  except that external air may not be introduced into the inside space  518  and that heated air in the attic space  520  may not be exhausted to the outside of the example server cooling system. 
     In some embodiments, one or more valved openings  526  may be coupled to the ceiling  524 . The valved openings  514 ,  528 , and  526  are operably connected to a control system which is operable to selectively activate each of the valved openings based on temperatures observed within and outside the inside space  518  and/or the attic space  520 . When the external air is not suitable to be introduced to the inside space  518 , the control system closes the valved openings  514  and  528 , and opens up the valved openings  526 . To cool air in the inside space  518 , one or more cooling units  532  may be used. In some embodiments, the cooling units  532  may be evaporative coolers. Cooling air is drawn from the inside space  518  to the cold row interior space  522 . In some embodiments, one or more fans  530  may be used to draw cooling air into the cold row enclosure  510 . The cooling air is drawn from the cold row interior space  522  through the rack-mounted units installed in the rack  508 ; the heated air is expelled to the hot row interior space  516  defined by the enclosure  506 . Heated air enters the attic space  520  through the connector  512  and is re-circulated to the inside space  518  through the valved openings  526  coupled to the ceiling  524 . In some embodiments, one or more fans may be used to exhaust the heated air out of the enclosure  506  to the attic space  520  and re-circulated to the inside space  518   
       FIG. 6  illustrates a three dimensional view of an example server cooling system comprising lateral walls  600 , a floor  602 , a roof  604 , an enclosure  606 , a server rack  608 , and a ceiling  610 . The lateral walls  600 , the floor  602  and the ceiling  610  define an inside space  618 . The roof  604  and the ceiling  610  define an attic space  620 . The enclosure  606  defines an interior space  616 . One or more valved openings  622  are coupled to the ceiling  610 . There may be valved openings  624  on the roof  604  and valved openings  614  on the lateral walls  600 . The enclosure  606  is operably connected to the attic space  620  through a connector  612 . In some embodiments, one or more rack-mounted units are installed in the rack  608  such that respective front faces of the rack-mounted units interface with the inside space  618 , and that respective back faces of the rack-mounted units interface with the interior space  616 . In some embodiments, external cool air may be drawn into the inside space  618  through valved openings  614 . The cool air may be drawn from the inside space  618  by cooling fans mounted internally within the rack-mounted units installed in the rack  608 ; the heated air is ejected into the interior space  616  and enters the attic space  620  through the connector  612 . In other embodiments where fanless rack-mounted units are installed in the rack  608 , one or more fans may be used to draw cooling air from the inside space  618  to the interior space  616 . In some embodiments, the air handling units  626  may be used to draw external cool air to the inside space  618  through valved openings  614 . The valved openings  614 ,  624 , and  622  are operably connected to a control system which is operable to selectively activate each of the valved openings based on temperatures observed within and outside the inside space  618  and/or the attic space  620 . When the external air is not suitable to be introduced to the inside space  618 , the control system closes the valved openings  614  and  624 , and opens up the valved openings  622 . To cool air in the inside space  618 , one or more cooling units may be used. In some embodiments, the cooling units may be evaporative coolers. The cooled air is drawn from the inside space  618  through the rack-mounted units and installed in the rack  608 ; the heated air is expelled to the interior space  616 . Heated air enters the attic space  620  through the connector  612  and is re-circulated to the inside space  618  through the valved openings  622  coupled to the ceiling  610 . In some embodiments, one or more fans may be used to exhaust the heated air out of the enclosure  606  to the attic space  620  and re-circulate the air to the inside space  618   
       FIG. 7  illustrates a top view of an example cooling system. The lateral walls  700  and a ceiling or roof define an inside space  718 . An enclosure  706  defines an interior space  716 . The enclosure may be connected to one or more racks  708  in a substantially sealed manner. One or more rack-mounted units each comprising one or more cooling fans are installed in the rack  708 . One or more valved openings  714  on the lateral walls  700  allow outside cool air to enter the inside space  718 . The cool air is drawn from the inside space by the cooling fans mounted internally within the rack-mounted units installed in the server racks, and the heated air is ejected to the interior space  716 . In some embodiments, one or more air handling units  726  may draw external cool air to the inside space  718 . In one embodiment, the cooling system measures 60 feet wide, 255 feet long, and 16 feet high. Four enclosures are installed in the cooling system. Eight racks are connected to each enclosure on each side in a substantially sealed manner. Each rack comprises 16 1U servers. The lateral wails, the ceiling, the roof, and the enclosures may be pre-manufactured and installed on the construction site of the data center. Comparing with other data center designs, the example cooling system may easier to install and more efficient to operate. 
       FIG. 8  illustrates another example server cooling system comprising lateral walls  800 , a floor  802 , a roof  804 , an enclosure  806 , a server rack  808 , and a ceiling  810 . The lateral walls  800 , the floor  802  and the ceiling  810  define an inside space  818 . The roof  804  and the ceiling  810  define an attic space  820 . One or more valved openings  822  are coupled to the ceiling  810 . There may be valved openings  824  on the roof  804  and valved openings  814  on the lateral walls  800 . The example server cooling system in  FIG. 8  is similar to the one in  FIG. 2  except that a gable roof  804  is used instead of a single-sloped roof  204 . A gabled roof may provide better air circulation in the attic space  818 . However, the cost of building a gable roof may be higher than that of building a single-sloped roof. 
       FIG. 9  illustrates another example server cooling system comprising lateral walls  900 , a floor  902 , a roof  904 , an enclosure  906 , a server rack  908 , a ceiling  910 , and outside walls  930 . The example server cooling system in  FIG. 9  is similar to the one in  FIG. 8  except that the roof  904 , the floor  902 , the lateral walls  900 , and the outside walls  930  define a mixing space  928 . The lateral walls  900 , the floor  902  and the ceiling  910  define an inside space  918 . The roof  904  and the ceiling  910  define an attic space  920 . In some embodiments, outside cool air may be drawn into the mixing space  928  through valved openings  914  on the outside walls  930 . The cool air is drawn to the inside space  918  by one or more air handling units  926  coupled to the lateral wails  900 . One or more rack-mounted units each comprising a cooling fan are installed in the rack  908 . The cooling fans mounted internally within the rack-mounted units draw cooling air from the inside space  918  through the rack-mounted units and eject heated air to the interior space  916 . The heated air enters the attic space  920  through one or more connectors  912  which operably connect the interior space  916  to the attic space  920 . In some embodiments, the heated air in the attic space  920  is exhausted to the outside through one or more valved openings  924 . In other embodiments, the heated air is drawn to the mixing space  928  through one or more valved openings  922  and is mixed with the outside cool air. In yet other embodiments, the valved openings  914 ,  922 , and  924  may be operably connected to a control system which is operable to selectively activate each valved openings. When the external air is not suitable to be introduced to the inside space  918 , the control system closes valved openings  914  and  924  and opens valved openings  922 . Heated air in the attic space  920  is re-circulated to the mixing space  928  and is re-circulated to the inside space  918 . In other embodiments, the control system monitors the temperature in the inside space  918 , the attic space  920 , the mixing space  928 , and the temperature outside. When the difference in temper among the observed temperatures reaches one or more threshold values or other dynamic or predetermined levels, the control system may selectively open or close each valved opening. To cool the air in the inside space, one or more cooling units may be used. In some embodiments, the cooling units are installed within the mixing space  928 . In other embodiments, the cooling units are installed within the inside space  918 . In one embodiment, the cooling units are evaporative coolers. 
       FIGS. 10A and 10B  illustrate an example of an air handler building structure  1000 , including a floor  1002 , a plurality of lateral walls  1004 , and a roof  1006 . In this example, the building structure  1000  may be pre-manufactured in a factory and assembled on the construction site where a data center is to be built. As describe before, pre-manufactured units may significantly reduce the cost of the building structure  1000 . One of the cost advantages of the air handier building structure  1000  for a server cooling system is the convenience and low cost of pre-manufacture parts of the system and the ease of installation of pre-manufactured parts in a data center. The material of the building structure  1000  includes, but is not limited to, steel, composite material, carbon material, or any other suitable material. 
     The floor  1002  in this example is a non-raised floor, which has a relative low initial construction cost compared with a raised floor. It is understood that raised floor may be partially or completely used in the building structure  1000  in other examples. The plurality of lateral walls  1004  include a lower lateral wall  1004 - a  and an upper lateral wall  1004 - b  opposing to each other having different respective heights determined in accordance with a ratio. As shown in  FIG. 10B , which is the top-view of the building structure  1000 , the plurality of lateral walls  1004  may also include two other lateral walls  1004 - c ,  1004 - d  substantially perpendicular to the lower and upper lateral walls  1004 - a ,  1004 - b . The roof  1006  may be constructed in accordance with a pitch consistent with the ratio associated with the lower and upper lateral walls  1004 - a ,  1004 - b . In other words, the roof  1006  is a sloped roof with a pitch of 1:x, where x is substantially larger than one, so that snow builds up and melts on the roof  1006 , with the heat from the interior of the building structure  1000  accelerates the snow-melting process. In one example, x equals to 6 (e.g., the pitch may be 2:12). In this example, the roof  1006  is a single-sloped roof (also known as a shed roof). It is understood that, in other examples, such as in  FIGS. 8 and 9 , the roof  1006  may be a gable roof or any other suitable type of roof. 
     One or more openings  1008 , such as valved openings, may be located on different parts of the building structure  1000 , such as on one or more lateral walls  1004  and the roof  1006 . In this example, the lower lateral wall  1004 - a  has one or more openings  1008 - a  through which outside natural air may enter the building structure  1000 . In one example, the lower lateral wall  1004 - a  may be substantially louvered to facilitate the outside natural air to enter the building structure  1000 . In this example, the upper lateral wall  1004 - b  may have one or more openings  1008 - b  through which air in the building structure  1000  can exit. In one example, a portion of the upper lateral wall  1004 - b  that is above the height of the lower lateral wall  1004 - a  may be substantially louvered to allow air to exit the building structure  1000 . Optionally, the roof  1006  may also include one or more openings  1008 - c  through which air in the building structure  1000  can exit. It is understood that, although  FIG. 10A  shows openings  1008 - b ,  1008 - c  on both the upper lateral wall  1004 - b  and the roof  1006 , this configuration may not be necessary in other examples. As long as there are openings above the height of the openings  1008 - a  on the lower lateral wall  1004 - a , air in the building structure  1000  can exit the building structure  1000  via natural convection. 
     Referring now to  FIG. 10B , a first dimension L 1  along a first direction is defined between the lower and upper lateral walls  1004 - a ,  1004 - b , and a second dimension L 2  along a second direction is defined perpendicular to the first direction, in this example, between the other two lateral walls  1004 - c ,  1004 - d . As shown in  FIG. 10B , L 1  is smaller than L 2 . The relative length of L 1  and L 2  is designed such that the building structure  1000  provides access to outside natural air via the one or more openings  1008 - a  on the lower lateral wall  1004 - a  by increasing the area-volume-ratio of the building structure  1000 . In one example, L 2  may be twice of L 1 . Accordingly, the shape of the building structure  1000  allows air within the building structure  1000  to rise via natural convection. In other words, the building structure  1000  is designed to take advantage of the warm air&#39;s tendency to rise to achieve “free cooling.” This natural “drafting” enhances the mechanically induced movement of air and therefore reduces the overall power for cooling. With the design in this example, the building structure  1000  itself serves well as an air handler even without the traditional mechanical cooling system (i.e., by “free cooling”). 
     As shown in  FIG. 10A , the building structure  1000  may include a ceiling  1010  that divides the interior of the building structure  1000  into a first space  1012  and a second space  1014 . In this example, the first space  1012 , which may be used for installing servers of a data center, is defined between the floor  1002  and the ceiling  1010 ; the second space  1014 , as an attic space, is defined between the ceiling  1010  and the roof  1006 . The ceiling  1010  may have one or more openings  1008 - d  located at different regions of the ceiling  1010 . In this example, at least one opening  1008 - d  is located near the openings  1008 - a  on the lower lateral wall  1004 - a  where the outside natural air enters the building structure  1000 . With such configuration, the outside natural air enters the first space  1012  through the openings  1008 - a  on the lower lateral wall  1004 - a  and exits the first space  1012 , by natural convection, through the openings  1008 - d  on the ceiling  1010  to enter the second space  1014 . The air in the second space  1014  then exits, by natural convection, through the openings  1008 - b  on the portion of the upper lateral wall  1004 - b  above the ceiling  1010  and/or the openings  1008 - c  on the roof  1006 . The air in the second space  1014  may also enter the first space  1012  through the openings  1008 - d  on the ceiling  1010  near the lower lateral wall  1004 - a  and may be mixed with the natural air entered the first space  1012 . 
       FIG. 11  illustrates an example of a server cooling system  1100 . In this example, the system  1100  includes a first space  1102  defined by a floor  1104 , one or more lateral walls  1106 , and a ceiling  1108 . A plurality of servers  1110  may be installed in the first space  1102 . The system  1100 , in this example, also includes a second space  1112 , as an attic space, defined by the ceiling  1108  and a roof  1114 . One or more openings  1116 , such as valved openings, may be located on at least one of the ceiling  1108 , the roof  1114  and at least one of the lateral walls  1106 . In this example, the first lateral wall (e.g., a lower lateral wall)  1106 - a  has one or more openings  1116 - a ; the ceiling  1108  has one or more openings  1116 - d , including at least one opening  1116 - d  near the lower lateral wall  1106 - a ; a portion of a second lateral wall (e.g., an upper lateral wall)  1106 - b  above the ceiling  1108  (in the second space  1112 ) and/or the roof  1114  include one or more openings  1116 - b ,  1116 - c , respectively. The openings  1116 , as described above, are used to realize the movement of air between the outside space, the first space  1102 , and the second space  1112 . 
     In this example, the system  1100  includes an air inlet  1118  coupled with the first lateral wall  1106 - a  and operable to allow outside natural air to enter the first space  1102 . The air inlet  1118 , in this example, includes one or more louvered openings  1116 - a  on the first lateral wall  1106 - a . The system  1100  may also include an air outlet  1120  coupled with the second lateral wall  1106 - b  and operable to allow air in the second space  1112  to exit. The air outlet  1120 , in this example, includes one or more louvered openings  1116 - b  on the second lateral wall  1106 - b . The system  1100  may further include one or more air-handling units  1122  coupled with the air inlet  1118  to draw the outside natural air and to provide air to the first space  1102 . The air-handling units  1122  include, for example, a fan  1122 - a , an evaporative cooling unit  1122 - b  configured to generate evaporative cooling air based on the outside natural air, and in some embodiments a filter  1122 - c  configured to filter the outside natural air entering the first space  1102 . The fan  1122 - a  may be a speed controlled fan and is designed to keep air turbulence high, which helps mitigate temperature gradients and induces mixing. Optionally, the system  1100  may also include one or more uninterruptible power supply (UPS) systems utilizing kinetic stored energy. 
     In this example, the system  1100  also includes a control system  1124  configured to control the one or more air-handling units  1122  to provide air to the first space  1102  in accordance with temperatures measured within and outside of the first space  1102 . The control system  1124  may include one or more devices such as a microprocessor, microcontroller, digital signal processor, or combinations thereof capable of executing stored instructions and operating upon stored data. Control system arrangements are well known to those having ordinary skill in the art, for example, in the form of embedded system, laptop, desktop, tablet, or server computers. 
     The control system  1124  may include or couple to one or more sensors (not shown) to monitor the environmental metrics such as temperature and humidity within and outside the first space  1102 . For example, temperature sensors may be deployed at different locations in the first space  1102 , the second space  1112 , and space outside the server cooling system  1100  to provide real-time temperatures of various locations. In one example, hot aisle (hot row enclosure) temperature of the server racks in the first  1102  may be used to regulate speed controlled fans; cold aisle (cold row enclosure) temperature of the server racks in the first  1102  and outside air temperature and humidity may be used to provide an indication of outdoor and return air mixing efficiencies. Dew point sensors and/or humidity sensors may also be provided in the air inlet  1118  and the air-handling units  1122  to monitor the humility of the air entering the first space  1102 . It is understood that, although the control system  1124  in  FIG. 11  is installed in the second space  1112 , it may be installed in other places within the server cooling system  1100  or outside the server cooling system  1100 . In this example, the control system  1124  is operatively coupled to the air-handling units  1122  and other components of the server cooling system  1100 , such as but not limited to an air-exchanging unit  1126 , which may be coupled to the openings  1214 - d  on the ceiling  1108  near the first lateral wall  1106 - a  and may be configured to draw air from the second space  1112  into the first space  1102  in order to mix with the outside natural air entering the first space  1102 . The connections between the control system  1124  and other components of the system  1100  may be achieved using any known wire or wireless communication techniques. 
     Depending on the measured temperatures within and outside of the first space  1102 , the control system  1124  may control the operations of the air-handling units  1122  in conjunction with other components of the server cooling system  1100  in, for example three different working modes at three different temperature ranges. 
     In a first range, which is an optimal working temperature range for the servers  1110 , the control system  1124  may control the air-handling units  1122  in conjunction with the air-exchanging unit  1126  to directly provide the outside natural air into the first space  1102  to achieve the so called “free cooling.” Specifically, in this mode, the control system  1124  may turn off the evaporative cooling unit  1122 - b  and turn on the fan  1122 - a  to directly draw the outside natural air into the first space  1102  without extra cooling. Optionally, the control system  1124  may also turn on the filter  1122 - c  to filter the incoming natural air. In this mode, the control system  1124  may further turn off the air exchanging unit  1126  to stop mixing the incoming natural air in the first space  1102  with the heated air from the second space  1112 , which may increase the temperature in the first space  1102 . In one example, the first range is substantially between 70° F. and 85° F. 
     In a second range, which is lower than the first range, the control system  1124  may control the air-handling units  1122  in conjunction with the air-exchanging unit  1126  to provide air to the first space  1102  based on a mixed outside natural air and air exhausted from the servers  1110  through one or more openings  1116 - d  on the ceiling  1108  near the air inlet  1118 . Specifically, in this mode, the control system  1124  may turn off the evaporative cooling unit  1122 - b  and turn on the fan  1122 - a  to draw the outside natural air into the first space  1102 . Optionally, the control system  1124  may turn on the filter  1122 - c  to filter the incoming natural air. In this mode, the control system  1124  may turn on the air-exchanging unit  1126  to draw the air exhausted through the servers  1110  into the second space  1112  to the first space  1102  in order to heat up the incoming natural air in the first space  1102 . In this example, the air-exchanging unit  1126  may include a damper, a return fan coupled with the openings  1106 - d , and a recirculation fan to help blend the mixing air, preventing any temperature or humidity gradients. In one example, the second range is about below 70° F. 
     In a third range, which is higher than the first range, the control system  1124  may control the air-handling units  1122  in conjunction with the air-exchanging unit  1126  to provide evaporative cooling air to the first space  1102  based on the outside natural air drawn from the air inlet  1118  through saturated media. Specifically, in this mode, the control system  1124  may turn on both the evaporative cooling unit  1122 - b  and the fan  1122 - a  to draw the outside natural air into the first space  1102  and cool it down by evaporative cooling. Optionally, the control system  1124  may turn on the filter  1122 - c  to filter the incoming natural air. In this mode, the control system  1124  may turn off the air-exchanging unit  1126  to stop mixing the incoming natural air in the first space  1102  with the heated air from the second space  1112 . Optionally, a dew point sensor may be used in conjunction with the evaporative media of the evaporative cooling unit  1122 - b  to ensure additional moisture is not added to already saturated air. In one example, the second range is substantially between 85° F. and 110° F. 
     It is noted that in any temperature range, the control system  1124  may be further configured to selectively activate one or more of the openings  1116 - a  on the first lateral wall  1106 - a  to control the amount of the outside natural air drawn into the first space  1102  based on the temperatures measured within and outside of the first place  1102 . In addition, when the measured temperature is above 110° F., additional mechanical cooling units and air-conditioning units may be turned on to provide extra cooling. 
     The first space  1102  of the system  1100  may further include at least one substantially enclosed interior space  1128  engaging the ceiling  1108  and open to the second space  1112  and at least one rack  1130  engaging the interior space  1128  in a substantially sealed manner and having the plurality of servers  1110  mounted thereon. The interior space  1128  may be defined by an enclosure having a frame, panels, doors, and rack ports. The enclosure of the interior space  1128  may be made of a variety of materials such as steel, composite materials, or carbon materials. The enclosure creates a housing defining the interior space  1128  that is substantially sealed from the first space  1102 . The enclosure of the interior space  1128  includes at least one rack port that allows one or more servers  1110  installed in the racks  1130  to interface with the interior space  1128 . One or more edges of the rack port may include a gasket or other component that contacts the rack  1130  and forms a substantially sealed interface. The rack  1130  may be removably connected to the enclosure of the interior space  1128  through the rack port in a substantially sealed manner. 
     In this example, one or more servers  1110  are installed in the racks  1130  such that respective front faces of the servers  1110  interface with the first space  1102 , and that respective back faces of the servers  1110  interface with the interior space  1128 . In this example, each rack-mounted server  1110  may include one or more fans  1132  therein operable to draw air from the first space  1102  through its front face and expel heated air to the interior space  1128  through its back face. 
     The server cooling system  1100  can maintain a properly mixed server supply air in an optimal working temperature range, for example between 70° F. and 85° F. and in a non-condensing relative humidity range, for example below 85%. 
       FIG. 12  illustrates another example of a server cooling system  1200 . The system  1200  includes a first space  1202  defined by a floor  1204 , a plurality of lateral walls  1206 , and a ceiling  1208 , and a second space  1210  defined by the ceiling  1208  and a sloped roof  1212  constructed in accordance with a pitch. One or more openings  1214 , such as valved openings, may be located on at least one of the roof  1212 , the ceiling  1208 , and at least one of the lateral walls  1206 , that enable outside natural air to enter the first space  1202  and air in the second space  1210  to exit by natural convection. The system  1200  may also include at least one interior space  1216  inside the first space  1202 , that is substantially enclosed and engaging the ceiling  1208 , and at least one rack  1218  engaging the interior space  1216  in a substantially sealed manner and having a plurality of servers  1220  mounted thereon. In this example, one or more servers  1220  are installed in the racks  1218  such that respective front faces of the servers  1220  interface with the first space  1202 , and that respective back faces of the servers  1220  interface with the interior space  1216 . In this example, each rack-mounted server  1220  may include one or more fans  1222  therein operable to draw air from the first space  1202  through its front face and expel heated air to the interior space  1216  through its back face. 
     The building structure in  FIG. 12  is similar to that in  FIGS. 10A and 10B , which is designed to take advantage of natural convention to enhance the mechanically induced movement of air and therefore reduce the overall energy necessary for cooling the servers. The example server cooling system  1200  in  FIG. 12  is similar to that in  FIG. 11  except that system  1200  does not include the external air-handling units and air exchanging units such as fans and evaporative cooling unit. The air circulation is induced by the internal fans  1222  of the servers  1220  and the natural convection enhanced by the special designed building structure. Accordingly, the total energy consumption of the system  1200  in  FIG. 12  may be further reduced compared with the system  1100  in  FIG. 1 . 
       FIG. 13  illustrates a cross-section of another exemplary air handler building structure  1300 . The air handler building structure  1300  is similar to air handler building structure  1000 , including a floor  1302 , a plurality of lateral walls  1304 . The floor  1302  in this exemplary embodiment can be a non-raised floor. It is understood that a raised floor may be partially or completely used in the building structure  1300  in other embodiments. 
     The air handler building structure  1300  has two roof portions  1306 , symmetrically placed on either side of a protruding portion  1322 . The protruding portion  1307  is higher than the highest part of the roof portions  1306 , and placed above the center of the building in cross-section. The roof portions  1306 , and the protruding portion  1322  extend along the air handler building structure  1300  in a direction perpendicular to the cross-section in  FIG. 13 . 
     The protruding portion  1322  has lateral walls  1324  and roof portions  1326 . The lateral walls  1304 ,  1324  and the roof portions  1306 ,  1326  are constructed in a similar manner to lateral walls  1004  and the roof portions  1006 . 
     The roof portions  1306 , like the roof portions  1006  may be constructed in accordance with a pitch of 1:x, where x is substantially larger than one, so that snow builds up and melts on the roof  1006 , with the heat from the interior of the building structure  1300  accelerating the snow-melting process. In one example, x equals to 6. 
     One or more openings  1308 , such as valved openings, may be located on different parts of the building structure  1300 , such as on one or more lateral walls  1304  and the roof portions  1306 . In this example, the lower lateral wall  1304 - a  has one or more openings  1308 - a  through which outside natural air may enter the building structure  1300 . In one example, the lateral wall  1304  may be substantially louvered to facilitate the outside natural air to enter the building structure  1300 . In this example, the lateral walls  1324  of the protruding portion  1312  may have one or more openings  1308 - b  through which air in the building structure  1300  can exit. In one example, a portion of the lateral walls  1324  are above the height of the lateral wall  1304  may be substantially louvered to allow air to exit the building structure  1300 . Optionally, the roof portions  1306  may also include one or more openings  1308 - c  through which air in the building structure  1300  can exit. It is understood that, although  FIG. 13  shows openings  1308 - c  on the roof portion  1306 , this configuration may not be necessary in other examples. As long as there are openings  1308  above the height of the openings  1308 - a  on the lateral wall  1304 , air in the building structure  1300  can exit the building structure  1300  via natural convection. 
     The additional height of the one or more openings  1308 - b  on the lateral walls  1324  above the height of the openings  1308 - a  on the lateral wall  1304  increases the natural convection in the building structure  1300  over that of the building structure  1000 . 
     As shown in  FIG. 13 , the building structure  1300  may include a ceiling  1310  that divides the interior of the building structure  1300  into a first space  1312  and a second space  1314 . In this example, the first space  1312 , which may be used for installing servers of a data center, is defined between the floor  1302  and the ceiling  1310 ; the second space  1314 , as an attic space, is defined between the ceiling  1310  and the roof  1306  and the protruding portion  1322 . The ceiling  1310  may have one or more openings  1308 - d  located at different regions of the ceiling  1310 . In this example, at least one opening  1308 - d  is located near the openings  1308 - a  on the lower lateral wall  1304 - a  where the outside natural air enters the building structure  1300 . With such configuration, the outside natural air enters the first space  1312  through the openings  1308 - a  on the lateral wall  1304  and exits the first space  1312 , by natural convection, through the openings  1308 - d  on the ceiling  1310  to enter the second space  1314 . The air in the second space  1314  then exits, by natural convection, through the openings  1308 - b  on the protruding portion  1322  above the ceiling  1310  and/or the openings  1308 - c  on the roof portion  1306 . The air in the second space  1314  may also enter the first space  1312  through the openings  1308 - d  on the ceiling  1310  near the lateral wall  1304 - a  and may be mixed with the natural air entered into the first space  1312 . 
       FIG. 14  illustrates a cross-section of an other example of an air handler building structure  1400  that is similar to the building structure  1300  but without the ceiling  1310  and opening  1308 - d . (other features have the same labels as in  FIG. 13 ) The natural convection draws air through openings  1308 - a  which rises through the building structure  1400  and out through openings  1308 - b.    
     The various examples of the building structures and server cooling systems disclosed herein can achieve an almost 100% uptime availability, for example, 99.98% uptime availability for a data center facility, for example, having a 9.0 MW critical load. The various examples of the building structures and server cooling systems disclosed herein can allow for free cooling, for example, 99% of the year via the building structures&#39; unique shape and orientation, as well as server physical configuration. Also, the various examples of the building structures and server cooling systems disclosed herein can achieve about 2% annualized “cost to cool” with evaporative cooling, where “cost to cool” is the energy (kW) expended to remove the heat generated by the data center load as a percentage of the data center load itself. Further, the various examples of the building structures and server cooling systems disclosed herein can save, for example, about 36 million gallons of water used for cooling compared with conventional water-cooled chiller plant designs with comparable IT loads. The various examples of the building structures and server cooling systems disclosed herein can achieve high efficiency to a target power usage effectiveness (PUE) of, for example, less than about 1.11, such as 1.08. Moreover, the various examples of the building structures and server cooling systems disclosed herein can achieve about 40% reduction in data center electricity consumption relative to industry-typical legacy data centers. For example, for a data center with a 9 MW of critical load, various examples of the building structures and server cooling systems disclosed herein can reduce energy consumption of 8.6 to 18.9 million KWh per year compared with conventional collocated facilities. Because water-cooled chiller may not be required in the exemplary server cooling systems disclosed herein, there may be zero data center-related wastewater generated by the server cooling systems, which equals to a reduction of about 8 million gallons of sewer discharge per year compared with conventional water-cooled chiller plant design. Furthermore, the various examples of the building structures and server cooling systems disclosed herein can reduce the construction cost compared with traditional designs, for example, to no more than $5M per MW and reduce the construction time to, for example, less than 6 months. In one example, the various examples of the building structures and server cooling systems disclosed herein can maintain the following room environmental requirements: room temperature of 55° F.-90° F., no higher than 85% non-condensing relative humidity, pressure of ±0.1 inches H 2 O, and 5.4° F. per hour of rate of temperature change. The various examples of the building structures and server cooling systems disclosed herein can withstand 100-year temperature and humidity conditions and extremely low winter temperatures while maintaining server room environmental requirements. 
     Exemplary Results 
       
     
       
         
           
               
               
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 2005 
                 2006 
                 2006 
                 2007 
                 2010 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Type of System 
                 Standard CRAC: 
                 Water cooled site 
                 Air cooled 
                 Modular, tuned 
                 Yahoo! 
               
               
                   
                 no economizing; 
                 built chiller plant; 
                 chiller plant; 
                 chiller plant; 
                 Compute 
               
               
                   
                 DX cooling system 
                 standard CRAC; 
                 AHU with outside 
                 next-gen AHU 
                 Coop 
               
               
                   
                   
                 no economizing 
                 economizing 
                 with outside 
               
               
                   
                   
                   
                   
                 air economizing 
               
               
                 Site Example 
                 Yahoo! 
                 Yahoo! 
                 Yahoo! existing 
                 Quincy, WA 
                 Lockport, 
               
               
                   
                 colocation site in 
                 colocation site in 
                 data center facility 
                 Phase 1 
                 NY 
               
               
                   
                 Santa Clara, CA 
                 Santa Clara, CA 
                 in Wenatchee, WA 
               
               
                 KW per ton AHU 
                 0.50 
                 0.50 
                 0.40 
                 0.35 
                 0.10 
               
               
                 KW per ton CHW 
                 NA 
                 0.75 
                 1.15 
                 0.68 
                 0.03 
               
               
                 KW per ton CHW 
                   
                   
                 0.10 
                 0.06 
                 0 
               
               
                 during free cooling 
               
               
                 KW per ton DX 
                 1.38 
                 NA 
                 NA 
                 NA 
                 NA 
               
               
                 EXAMPLE electro/ 
                 5,000 
                 5,000 
                 5,000 
                 5,000 
                 5,000 
               
               
                 mechanical load KW 
               
               
                 Tonnage requirement 
                 1,420 
                 1,420 
                 1,420 
                 1,420 
                 1,420 
               
               
                 KW AHU (max) 
                 710 
                 710 
                 566 
                 497 
                 142 
               
               
                 KW AHU best 
                 N/A 
                 N/A 
                 142 
                 85 
                 0 
               
               
                 (free cooling) 
               
               
                 KW AHU average 
                 719 
                 710 
                 355 
                 291 
                 71 
               
               
                 KW heat removal max 
                 1,960 
                 1,065 
                 1,633 
                 965 
                 42 
               
               
                 (DX or CHW) 
               
               
                 KW heat removal best 
                 — 
                 — 
                 142.05 
                 85.23 
                 0 
               
               
                 (free cooling) 
               
               
                 KW heat removal 
                 1,960 
                 1,065 
                 968 
                 568 
                 21 
               
               
                 average 
                   
                   
               
               
                 Total cooling load 
                 2,670 
                 1,775 
                 1,313 
                 859 
                 92 
               
               
                 KW per MW DC load 
               
               
                 % of Total Cooling 
                 53% 
                 36% 
                 26% 
                 17% 
                 2% 
               
               
                   
               
            
           
         
       
     
     TABLE 1 is a breakdown of the progression of cooling efficiency over time by using at least some of the examples of the building structures and server cooling systems disclosed herein. In TABLE 1 AHU represents air handling units, CHW represents chilled water, and DX represents direct expansion. For example, by applying at least some of the examples of the building structures and server cooling systems disclosed herein, the average power used in AHU has been reduced from 710 KW to 71 KW. As another example, using at least some of the exemplary disclosed embodiments, the percentage of the total cooling have been reduced over the years from 53% in 2005, as typical industry standard, to only 2% in the most recent experiment via YAHOO!&#39;s Compute Coop in 2010. This represents a substantial improvement. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                   
                   
                 Yahoo! 
               
               
                   
                 Yahoo! 
                   
                 Compute 
               
               
                   
                 Colocation 
                 Yahoo! 
                 Coop (YCC) 
               
               
                   
                 Data Center 
                 Data Center 
                 Data Center 
               
               
                   
                 Facility - 
                 Facility- 
                 Facility - 
               
               
                   
                 Santa Clara, CA 
                 Quincy, WA 
                 Lockport, NY 
               
               
                   
                 (2006) 
                 (2007) 
                 (2010) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 True server load 
                 140 
                 89 
                 89 
               
               
                 (watts): equivalent 
               
               
                 performance - 2 
               
               
                 CPU cores, 4 GB 
               
               
                 RAM; 1 80 GB HD 
               
               
                 Power supply 
                 215 
                 93 
                 93 
               
               
                 efficiency loss 
               
               
                 (watts) 
               
               
                 Dist/server voltage 
                 222 
                 — 
                 — 
               
               
                 transformation 
               
               
                 loss (watts) 
               
               
                 UPS efficiency 
                 252 
                 99 
                 97 
               
               
                 loss (watts) 
               
               
                 Medium voltage 
                 257 
                 101 
                 99 
               
               
                 transformation 
               
               
                 loss (watts) 
               
               
                 Total power per 
                 257 
                 101 
                 99 
               
               
                 example server 
               
               
                 (watts) 
               
               
                 KW cost to power 
                 6,438 
                 2,529 
                 2,489 
               
               
                 25,000 servers 
               
               
                 (without cooling) 
               
               
                 KW cost to cool 
                 2,265 
                 434 
                 46 
               
               
                 servers 
                   
                   
                   
               
               
                 Total KW cost for 
                 8,722 
                 2,963 
                 2,535 
               
               
                 25,000 servers 
               
               
                 Total KW power 
                   
                 5,759 
                 6,187 
               
               
                 savings versus 
               
               
                 Santa Clara CoLo 
               
               
                 PUE 
                 1.62 
                 1.27 
                 1.08 
               
               
                   
               
            
           
         
       
     
     TABLE 2 is a breakdown of the progression of electrical efficiency over time by using at least some of the examples of the building structures and server cooling systems disclosed herein. In TABLE 2, PUE represents power usage effectiveness, which is obtained by measuring the system utility power input and the critical power consumption as close as possible to the server loads. This information may be read and collected from the installed Electrical Power Monitoring System (EPMS) using power circuit monitors. Since all data centers in TABLE 2 may extensively utilize outside air cooling methods, data may be collected on a monthly basis and annualized to account for variables such as weather, operating hours, etc. PUE can be calculated using the following: 
     
       
         
           
             
               P 
                
               
                   
               
                
               U 
                
               
                   
               
                
               E 
             
             = 
             
               
                 Total 
                  
                 
                     
                 
                  
                 Facility 
                  
                 
                     
                 
                  
                 Power 
               
               
                 IT 
                  
                 
                     
                 
                  
                 Equipment 
                  
                 
                     
                 
                  
                 Power 
               
             
           
         
       
     
     where, IT Equipment Energy is the comprehensive energy use associated with all of the IT equipment such as computer, storage and network equipment along with supplemental equipment; Total Facility Energy is all facility energy use including IT equipment energy, electrical distribution losses, cooling system energy, fuel usage, and other miscellaneous energy use. 
     TABLE 2 shows that YAHOO!Lockport, N.Y. facility has a 70% improvement over the YAHOO!Santa Clara, Calif. co-location facility when improvements in all components in electrical efficiency path are included. For example, by applying at least some of the examples of the building structures and server cooling systems disclosed herein, PUE has been further reduced from 1.62 to 1.08, compared with an industry average of 2.0. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 3 
               
               
                   
                   
               
               
                   
                 Yahoo! 
                   
                 Yahoo! 
               
               
                   
                 Colocation 
                   
                 Compute 
               
               
                   
                 Data Center 
                 Yahoo! 
                 Coop (YCC) 
               
               
                   
                 Facility - 
                 Data Center 
                 Data Center 
               
               
                   
                 Santa 
                 Facility - 
                 Facility - 
               
               
                   
                 Clara, CA 
                 Quincy, WA 
                 Lockport, NY 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 PUE 
                 1.62 
                 1.27 
                 1.08 
               
               
                 Relative 
                 26,541,307 
                 12,094,773 
                 — 
               
               
                 energy savings 
               
               
                 for a 9 MW 
               
               
                 YCC plant 
               
               
                 (kWh/year) 
               
               
                 Average annual 
                 14,863 
                 6,773 
                 — 
               
               
                 carbon savings 
               
               
                 (tons CO 2 ) 
               
               
                   
               
            
           
         
       
     
     TABLE 3 shows the energy and carbon savings utilizing at least some of the examples of the building structures and server cooling systems disclosed herein. In addition, minimized use of evaporative cooling as compared to standard cooling methods may yield a 99% reduction in water use at the facility (and a corresponding reduction in wastewater outflow) as compared to a traditional data center that uses water cooled chillers. The carbon savings below assumes an average U.S. carbon intensity of 0.56 tons CO 2 /MWh. In other examples, the actual carbon reductions may be much lower by virtue of how clean electricity is in all three sites (0.31 tons CO 2 /MWh for Santa Clara, and close to zero for both WA state and NY state). 
     Two example YAHOO!data center facilities disclosed in TABLES 1-3 are described in details below. 
     YAHOO!Data Center Facility—WA 
     Site Description. The existing installation at Wenatchee has proven to be the most efficient YAHOO!data center prior to 2010. Located in central Washington, the site was selected for its climate, with the existing building optimized to take advantage of outside air economization. Air handling units (AHU) discharge into a traditional raised floor plenum, distributing supply air to the servers. 
     Installation Date: 2006 
     Electrical: 4.8 MW, N+1 critical infrastructure with 4,800 KW static battery UPS and 4×2 MW diesel generator back up.
 
Cooling System: Air Cooled Chillers and AHUs with outside air economizing.
 
     Designed Target PUE: 1.25. 
     YAHOO!Compute Coop (YCC) Data Center Facility—Lockport, N.Y. 
     Site Description: The innovative design and installation of the YAHOO!Compute Coop at Lockport is the most efficient of all YAHOO!data centers to date. Located in Lockport, N.Y., the greenfield site was selected for its cold climate; its unique design exclusively incorporates outside air economization, significantly reducing supply fan horsepower. 
     Installation Date: 2010. 
     Electrical: 9 MW, N+1 critical infrastructure with line interactive UPS systems using kinetic stored energy and diesel generator backup. Primary UPS systems are deployed in 200 KW modules, allowing systems to be taken offline when not in use.
 
Cooling System: YAHOO!Compute Coop integrated building system cooling with evaporative cooling.
 
     Designed Target PUE: 1.08-1.11. 
     The deployment of at least some of the examples of the building structures and server cooling systems disclosed herein has evidence to prove their effectiveness. Innovative building structures and server cooling systems disclosed herein can reduce risk aversion within the data center industry (both data center designers and IT equipment manufacturers) for other innovations that relate to free cooling, chiller-less data centers, and broader temperature ranges—as well as experimenting with designing data centers with closer attention to maximizing the use of local climate conditions. 
     The present invention has been explained with reference to specific embodiments. For example, while embodiments of the present invention have been described with reference to specific components and configurations, those skilled in the art will appreciate that different combination of components and configurations may also be used. For example, raised subfloors, CRAC units, water chiller, or humidity control units may be used in some embodiments. Seismic control devices and electrical and communication cable management devices may also be used in some embodiments. Other embodiments will be evident to those of ordinary skill in the art. It is therefore not intended that the present invention be limited, except as indicated by the appended claims.