Abstract:
A data center having multiple rows of computer racks for holding heat-generating computer equipment is cooled by a liquid overfeed air conditioning unit that provides supply air at a temperature of about forty degrees Fahrenheit (40° F. or lower). The air conditioning unit is positioned outside the data center. Ducting from the heat exchanger outlet of the unit is connected to supply registers mounted in aisles that are provided between the rows of computer racks so that very cold supply air enters the space between the racks. Each computer rack includes vertically spaced compartments that house computer components to be cooled. At least one circulation fan is associated with each compartment and causes supply air to flow through the compartment to cool the components. The supply air gradually warms as it flows through successive compartments and is approximately 72° Fahrenheit when it reaches a return register in the ceiling of the data center. The use of a high temperature differential conserves energy, reduces noise, increases usable data center floor space, and maintains proper data system component operating temperatures.

Description:
BACKGROUND OF INVENTION 
     1. Field of the Invention 
     This invention relates, generally, to highly efficient air conditioning systems for data centers. More particularly, it relates to a system that includes a liquid overfeed air conditioning unit that supplies conditioned air to the data center at temperatures of forty-five degrees Fahrenheit and below. 
     2. Description of the Prior Art 
     Data centers are buildings that house large numbers of file servers, data processors, or other heat-generating computer components. Typically, the interior of a data center is filled with multiple rows of cabinet-like equipment called racks that are arranged in parallel relation to one another throughout the entire extent of the data center. An aisle for service personnel is provided between each row of racks and at each end of the building. Each rack houses multiple, vertically spaced components. In this way, a very large number of file servers or other components can be placed in a data center. 
     The heat collectively generated by very large numbers of densely packed components within a data center is sufficient to cause catastrophic failure of the file servers. Accordingly, even the earliest data centers were air conditioned twenty four hours per day, every day of the year. These early data centers utilized common window units, but these proved inadequate as computer componentd evolved and consumed higher levels of energy, thereby creating more heat. 
     Modern data centers employ packaged chilled water or direct expansion (DX) air conditioning units positioned inside the data center. Such units represent a substantial improvement over window units but they have a number of drawbacks. For example, they are placed inside the data center and thus reduce the number of racks that can be housed therein. Moreover, they cool the supply air to about fifty five degrees. This type of cooling was acceptable before components were packed as densely as they are today. Many densely populated data centers throughout the world have components that are now operating under thermal stress, or very near their highest acceptable operating temperatures. As data centers are being converted or renovated to house as many components as possible at the greatest possible density, it is clear that a revolutionary new way of cooling data centers is required. 
     However, even though the data center industry is alarmed over the current situation, and has been for several years, no one has come forward with a solution to the problem. 
     Accordingly, it may be concluded that the solution to the problem was not obvious to those of ordinary skill in the data center field at the time the present invention was made. 
     SUMMARY OF INVENTION 
     The longstanding but heretofore unfulfilled need for an improved apparatus and method for cooling data centers is now met by a new, useful, and nonobvious apparatus for cooling a data center of the type including a plurality of rows of computer racks. The invention includes at least one liquid overfeed air conditioning unit disposed externally to the data center. Each row of computer racks has an aisle on its opposite sides so that data center personnel may walk between the rows. At least one conditioned air supply register is disposed in at least one of the aisles and at least one air conditioning duct provides fluid communication between the heat exchanger outlet of the liquid overfeed air conditioning unit and said at least one register. 
     In this way, supply air at a temperature of forty-five degrees Fahrenheit or lower is supplied to the interior of the data center by the liquid overfeed air conditioning unit and its associated distribution ducts. Moreover, the flow rate of supply air into the interior of the data center is reduced relative to a flow rate of supply air produced by a chilled water or a direct expansion air conditioning unit due to the increased work capacity of the lower temperature air. Noise reduction within the interior of said data center is therefore achieved and electrical energy is conserved because the liquid overfeed air conditioning system requires less energy relative to a chilled water or a direct expansion air conditioning system. 
     Each of the computer racks includes a plurality of vertically spaced apart components. The racks are open on their front and back so that conditioned air can flow therethrough from one aisle to another. Circulation fans are mounted so that supply air is drawn into cooling relation to each component through the substantially open front of the rack, flows past the heat-generating equipment, acquiring heat therefrom, and into the aisle adjacent the back of the rack. 
     The primary object of this invention is to provide an enhanced means for cooling computer components housed in a data center. 
     A closely related object is to provide efficient means for producing and delivering conditioned supply air to the interior of a data center having a temperature of forty-five degrees Fahrenheit and below. 
     A more specific object is to cool components housed in a data center with a liquid overfeed air conditioning system. 
     Additional important objects are to conserve data center floor space, electrical energy and attenuate noise by reducing the flow rate of supply air into a data center, said reduced flow rate being made possible by the reduced temperature of supply air provided by the liquid overfeed air conditioning unit relative to the temperature of supply air provided by chilled water and direct expansion air conditioning units. 
     Yet another object is to reduce the chances that computer equipment within the data center will be exposed to condensation or frost. 
     These and other important objects, advantages, and features of the invention will become clear as this description proceeds. 
     The invention accordingly comprises the features of construction, combination of elements, and arrangement of parts that will be exemplified in the description set forth hereinafter and the scope of the invention will be indicated in the claims. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     For a fuller understanding of the nature and objects of the invention, reference should be made to the following detailed description, taken in connection with the accompanying drawings, in which: 
     FIG. 1 is a diagrammatic side elevational view of a. prior art data center of the type that relies upon wall DX air conditioning units typically providing supply air temperatures of approximately 55° F. to 60° F.; 
     FIG. 2 is a diagrammatic side elevational view of a prior art data center of the type that employs a chilled water or DX system that is mounted within the data center and which typically provides supply air temperatures of approximately 55° F. to 60° F.; 
     FIG. 3 is a diagrammatic side elevational view of a data center cooled in accordance with the teachings of this invention and which is provided with supply air temperatures of less than 45° F.; 
     FIG. 4 is a diagrammatic side elevational view showing the interior of a single rack and depicting the temperature gradient at various heights throughout the rack in a typical densely populated data center cooled by the present invention; and 
     FIG. 5 is a top plan diagrammatic view of a data center cooled by the novel air conditioning method of this invention. 
    
    
     DETAILED DESCRIPTION 
     Referring initially to FIG. 1, it will there be seen that the reference numeral  10  denotes a prior art data center as a whole. A plurality of computer racks, collectively denoted  12 , are disposed in equidistantly spaced, parallel rows within data center  10 . Cables, collectively denoted  14 , provide both high and low voltage to each rack. Advantageously, such cables  14  are positioned beneath a false or raised floor  16 , thereby keeping aisles  18  clear so that service personnel can walk between the racks  12  as needed. 
     A window or wall-mounted air conditioner  20  is provided to perform the cooling function. Cool air is supplied at a supply air outlet as indicated by directional arrow  22  and return air is denoted by directional arrow  24 . It is apparent from a cursory inspection of FIG. 1 that the computer racks nearest air conditioner unit  20  will be cooled to a greater extent than the racks furthest from unit  20 . 
     FIG. 2 depicts, schematically, a second generation data center  10   a . The FIG. 2 data center is currently in widespread use and represents the current state of the art in data centers. Window or wall-mounted air conditioning unit  20  is eliminated and replaced by multiple floor-mounted units  26  having evaporator coil  28  and fan  30 . 
     Air conditioning unit  26  may be of the chilled water or direct expansion type and is capable of delivering supply air  22  at temperatures as low as about fifty-five degrees. 
     Advantageously, an open-grille grating or floor register  32  is placed in each aisle  18  so that supply air  22  is discharged by fan  30  into space  34  below raised floor  16 . Supply air  22  thus escapes from space  34  by flowing through the floor registers, collectively denoted  32 . Floor registers  32  are made of a strong material to support service personnel, not shown, who may need to walk in aisles  18  between racks  12  to perform service and maintenance functions. The flow of supply air  22  through floor registers  32  and upwardly between racks  12  of each row is collectively denoted  22  and return air flow to return air register  24  is denoted by directional arrows  24  as in the prior art system of FIG.  1 . 
     The advantages of the FIG. 2 prior art system over the FIG. 1 prior art system are clear. Air conditioning unit  26 , which is of the chilled water or direct expansion type as aforesaid, operates at a higher efficiency than a wall or window-mounted unit  20 . It also has a longer operating life and is more reliable. Moreover, the utilization of the space below raised floor  16  as a means for delivering cool supply air to each aisle  18  represents a significant improvement over the FIG. 1 system. 
     However, there are two major drawbacks of the FIG. 2 system. Floor unit  26  supplants at least one computer rack  12 , thereby reducing the revenue generated by data center  10   a  relative to data center  10 . Secondly, it provides supply air  22  at about the same temperature provided by the wall or window-mounted air conditioning unit  20 . Specifically, as already mentioned, floor unit  26  is a chilled water or direct expansion system; accordingly, the temperature of the supply air is about fifty-five to sixty degrees Fahrenheit (55° F.-60° F.) under optimal climate conditions. Significantly, both chilled water and direct expansion systems employ large amounts of fan brake horsepower. Specifically, the power consumption of a chilled water system is about 1.1 kilowatts per ton and the power consumption of a direct expansion system is about 1.3 kilowatts per ton. 
     Thus, although the FIG. 2 system represents a significant advance over the FIG. 1 system, the increased power consumption and concomitant heat generation of modern file servers, plus the increased density of such file servers in modern data centers, places maximum stress on FIG. 2 systems. This is the system now in use throughout the world, and such data centers are at a crisis point because their ability to cool has been maximized and the number of heat generating components in racks  12  is increasing as technology advances. 
     The preferred embodiment of the present invention is schematically depicted in FIG.  3  and is denoted by the reference numeral  40  as a whole. It is similar to first generation data center  10  at least to the extent that it provides an external air conditioning unit, here denoted  42  as a whole, and thus does not supplant any computer racks  12  from the data center. It provides a flow of supply air  22  through floor registers  32  that are positioned in every other aisle so that said supply air flows through the racks in the direction indicated by the directional arrows collectively denoted  22 . The temperature of supply air produced by unit  42  is much colder than that of the air conditioning units of the prior art data centers. 
     Unit  42 , which includes fan  44  and cooling coil  46 , includes a liquid overfeed refrigeration system capable of delivering supply air as cold as thirty-five degrees Fahrenheit (35° F.) in ideal climate conditions. Under some climate conditions, the supply air temperature may be as high as forty-five degrees Fahrenheit (45° F.). This range of 35° F.-45° F. compares favorably with the supply air range of 55° F. -60° F. of chilled water and direct expansion systems. 
     The provision of supply air  22  at a significantly colder temperature accomplishes the important object of providing a data center that is adequately cooled even when densely packed with modern high power consumption electronic components. It simultaneously enables a significant reduction in brake horsepower of fan  44  because the colder supply air of the FIG. 3 embodiment circulates through the data center at a slower rate than the warmer supply air of the prior art. This accomplishes the objective of reducing the power consumption of a data center air conditioning unit. It also accomplished the objective of reducing the noise within a data center. 
     Liquid overfeed systems have been used commercially only in those environments requiring intense cold, such as in meatpacking plants and blast freezers. They have not been used in data center applications because the conventional wisdom has been that temperatures below fifty degrees Fahrenheit (50° F.) should be avoided in data centers. It has been thought that sub fifty-degree temperatures could cause static electricity to build up within the data center, could cause condensation or even frost formation, and would prove unacceptably uncomfortable to service and maintenance personnel. 
     These problems have been solved by the structure disclosed in FIGS. 3 and 4. As disclosed in FIG. 4, a small circulating fan, or series of fans, is positioned in air circulating relation to each component in each computer rack  12 . In this particular example, supply air  22  at forty-two degrees Fahrenheit (42° F.) flows upwardly through each floor register  32  (positioned in alternate aisles as aforesaid) and is driven by circulating fan  50  into cooling relation to lowermost compartment  66  that is occupied by twelve (12) file servers or other components in this example. Air entering compartment  66  through front opening  57  thereof has a temperature of about forty-five degrees Fahrenheit (45° F.), and the air exiting said compartment through rear opening  57 A has a temperature of about forty-eight degrees Fahrenheit (48° F.) due to the heat generated by the twelve (12) servers therein. 
     Each compartment  66 ,  68 ,  70 ,  72  has an open or substantially open face  57 ,  59 ,  61 , and  63 , respectively, and an open or substantially open back face  57   a ,  59   a ,  61   a , and  63   a , respectively. Supply air drawn sequentially into compartments  66 ,  68 ,  70 , and  72  by circulating fans  50 ,  52 ,  54 , and  56 , respectively, flows through each of said compartments, cooling the components therein. 
     Since warm air rises, air flowing out of compartment  66  has been heated by the components therein to about forty-eight degrees Fahrenheit (48° F.). This air-warming process continues as fans  52 ,  54 , and  56  sequentially pull air into their respective compartments  68 ,  70 ,  72 . Specifically, in this example, air enters compartment  68  at fifty-three degrees Fahrenheit (53° F.) and exits said compartment at fifty-six degrees Fahrenheit (56° F.). It then enters compartment  70  at sixty degrees Fahrenheit (60° F.) and exits said compartment at sixty-three degrees Fahrenheit (63° F.). It flows into upper compartment  72  at sixty eight degrees Fahrenheit (68° F.) and exits said compartment  72  at seventy-two degrees Fahrenheit (72° F.). 
     Note that fans  50 ,  52 ,  54 , and  56  recirculate much more air than is supplied by outside unit  42 . About ninety per cent (90%) of server ventilation fan  44  is recirculated air from said compartments. 
     In summary, there is a three or four degree rise in temperature for each circulation of a compartment such as compartments  66 ,  68 ,  70 , and  72 , attributable to heat generated by the components therein. It will also be observed that there is a four or five degree increase in temperature between supply air exiting a compartment and entering the next adjacent compartment disposed upwardly thereof. This gradual rise in temperature is attributed to the fact that the air exiting uppermost compartment  72  is about seventy-two degrees Fahrenheit (72° F.). That relatively warm air flows into return air grill  74 . Thus, there is a thirty degree Fahrenheit (30° F.) temperature rise in each of the aisles  18  between contiguous racks  12 , i.e., from floor  16  to ceiling  76 . The relatively warm air in each aisle thus elevates the temperature of the air as it exits each compartment. Service and maintenance personnel who must enter the data center are therefore not subjected to the intense cold of a meat locker. Furthermore, the rate of supply air flow, expressed in cubic feet per minute (cfm), produced by liquid overfeed unit  42 , is slower than that of chilled water and direct expansion systems, thereby further moderating the interior climate of the data center and reducing the noise level therein. Moreover, condensation and frost are not problems and static electricity buildup has not been deemed a significant problem. 
     A top plan view of data center  40  equipped with the novel invention is provided in FIG.  5 . In this particular example, four liquid overfeed air conditioning units, collectively denoted  42 , are mounted outside the center on the ground. However, units  42  could also be roof-mounted. In either case, the ducting has sufficient cross sectional area to avoid any significant pressure drop throughout the length thereof. 
     This innovative system overcomes a pressing problem faced by today&#39;s data centers. It greatly reduces the temperature of the supply air, resulting in a higher temperature differential and increased system efficiency relative to water-cooled or DX cooing systems. This also allows the components to operate at a lower temperature which increases the effective life of such components. The innovative system also conserves energy, reduces noise levels, and does not occupy valuable space within the interior of a data center. 
     It will thus be seen that the objects set forth above, and those made apparent from the foregoing description, are efficiently attained. Since certain changes may be made in the above construction without departing from the scope of the invention, it is intended that all matters contained in the foregoing description or shown in the accompanying drawings shall be. interpreted as illustrative and not in a limiting sense. 
     It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween. 
     Now that the invention has been described,