Abstract:
New data center heat removal systems and methods allow a combination of active and passive thermal processes for removing heat from and cooling air in data center environments. Systems and methods include a data center heat removal system including an adjustable thermal feed cold air intake system, a distribution system for cold and warm air including one or more hot aisles and one or more cold aisles, and a convection system to draw cool air through data center equipment using a naturally-occurring convection processes to expel hot air. Misters, cooling elements, and/or freezer boxes may further cool the intake of air. A controller is programmed to efficiently manage and control the climate (e.g., temperature, humidity, air flow, pressure, air quality, etc.) within a data center to minimize the use for energy for air distribution and cooling.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
       [0001]    This is a conversion of, and claims a benefit of priority under 35 U.S.C. §119 from Provisional Application No. 62/098,176, entitled “DATA CENTER HEAT REMOVAL SYSTEMS AND METHODS,” filed Dec. 30, 2014, which is hereby fully incorporated by reference in its entirety, including appendices. 
     
    
     COPYRIGHT NOTICE 
       [0002]    A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by any one of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever. 
       TECHNICAL FIELD 
       [0003]    This disclosure relates generally to data centers. More particularly, this disclosure relates to new, improved systems and methods for cooling data center servers and removal of heat from data centers. 
       BACKGROUND 
       [0004]    A data center is a facility used to house computer systems and associated components such as air conditioning systems. Large scale data centers can include hundreds of servers and can require as much energy as a small town to power the data center computer equipment and cooling equipment. 
         [0005]    As such, energy usage consumed by data centers is a major cost consideration. Energy costs in data centers arise from computing, networking activities, and power transformations that use energy and, as a byproduct, generate heat. However, a majority of energy costs is associated with the removal of heat from the data center. Active heat management equipment (i.e., air conditioning systems) is substantially less than 100% efficient, which means heat monitoring and management equipment adds to the data center heat removal problems because they generate heat through their own operation. 
         [0006]    In a conventional data center environment, desired temperatures are maintained using heating, ventilation, air conditioning (HVAC). Typically, the ambient temperature is monitored by a thermostat, which turns the heat or air conditioning on and off to maintain the temperature set by the thermostat. 
       SUMMARY OF THE DISCLOSURE 
       [0007]    Embodiments provide systems and methods to allow a combination of active and passive thermal data center processes for removing heat from data center environments having computing equipment, networking equipment, and/or power distribution systems. 
         [0008]    In some embodiments, a data center heat removal system may include an adjustable thermal feed cold air intake system, a distribution system for cold and warm air including one or more hot aisles and one or more cold aisles, and a convection system to draw cool air through data center equipment using a naturally-occurring convection processes to expel hot air. That is, some embodiments utilize passive pressure differences to expel hot air and bring in cool air, either alone or in combination with active use of fans or other air circulation devices. In addition, some embodiments may use heat exchangers. 
         [0009]    In some embodiments, these components are interchangeable and modular and are the basis of a novel solution that provides an efficient method of removing heat from a data center. 
         [0010]    Embodiments utilize natural convection for heat removal from a data center including using the pressure differential between a hot aisle and a cold aisle. Embodiments may also use cold air from misters and/or freezer boxes for the intake of cold air. Some embodiments may use a natural process to form two distinct pressure regions in the data center. Some embodiments may use natural processes to maximize the air pressure differential between the cold aisle input of an individual server and its output to the warm aisle. Some embodiments allow natural process-driven multi-stage air cooling. 
         [0011]    Advantageously, embodiments efficiently manage the climate (which can include temperature, humidity, air flow, and air quality, etc.) within a data center and minimize the use for energy for air distribution. Some embodiments minimize the use of active heat management equipment that generates heat through their own operation. Some embodiments minimize and eliminate the use of moving cooling parts. Some embodiments minimize maintenance costs associated with server heating and cooling. Some embodiments manage the costs of computing services. 
         [0012]    In some embodiments, a system for data center heat removal includes an adjustable pressure feed cold air intake system; one or more heat exchangers; a distribution system for cold and warm air (cool aisles and warm aisles); and a convection system to draw cool air through data center equipment along with embedded server fans. The system further may make use of naturally-occurring convection processes to expel hot air, thus creating a relative vacuum to draw in cool air (and may optimally use an adjustable fan for disposing of warm air). Thus, embodiments may include a sealed warm low pressure area and a cold pressure area. 
         [0013]    Some embodiments may automatically utilize convection for cooling. Some embodiments are designed to allow multi-stage cooling. Some embodiments utilize pressure to expel hot air and draw in cool air. Numerous additional embodiments are also possible. 
         [0014]    These, and other, aspects of the disclosure will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following description, while indicating various embodiments of the disclosure and numerous specific details thereof, is given by way of illustration and not of limitation. Many substitutions, modifications, additions and/or rearrangements may be made within the scope of the disclosure without departing from the spirit thereof, and the disclosure includes all such substitutions, modifications, additions and/or rearrangements. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    The drawings accompanying and forming part of this specification are included to depict certain aspects of the disclosure. It should be noted that the features illustrated in the drawings are not necessarily drawn to scale. A more complete understanding of the disclosure and the advantages thereof may be acquired by referring to the following description, taken in conjunction with the accompanying drawings in which like reference numbers indicate like features. 
           [0016]      FIG. 1  depicts a diagram illustrating an exemplary data center heat removal system configured for a data center and having a chilling unit according to some embodiments. 
           [0017]      FIG. 2  is a perspective view of an exemplary server pod of a data center implementing an exemplary data center heat removal system disclosed herein. 
           [0018]      FIG. 3  is a block diagram of an exemplary arrangement of a chilling unit according to some embodiments. 
           [0019]      FIGS. 4-7  are views of an exemplary chilling unit according to some embodiments. 
           [0020]      FIG. 8  is a block diagram illustrating an exemplary data center heat removal system configured to maintain a desired temperature in a data center according to some embodiments. 
           [0021]      FIG. 9  is a logical control diagram for an exemplary data center heat removal system according to some embodiments. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]    Following is a description of one exemplary data center environment in which a heat removal system may be implemented according to some embodiments.  FIG. 1  depicts a diagram schematically illustrating a layout of a data center heat removal system according to some embodiments. In the example of  FIG. 1 , a data center heat removal system for a data center  100  includes a chilling unit  102 . As will be described in greater detail below, the chilling unit  102  may include a housing, one or more fans or similar devices configured for drawing in air from outside the data center, one or more misters for cooling the air, and one or more chiller units for further reducing the air temperature. 
         [0023]    The data center  100  may include one or more server pods  106   a  and  106   b . The server pods  106   a  and  106   b  may be embodied as self-contained rooms or enclosures that have walls  107 , doors  116   a ,  116   b ,  116   c ,  116   d , and ceilings (not shown). The server pods  106   a  and  106   b  are configured to house one or more banks of servers  108   a ,  108   b  and  108   c , and  108   d , respectively. The server banks  108   a ,  108   b  and  108   c , and  108   d  may comprise racks of servers mounted on above each other. It is noted that while two server pods are illustrated, in practice, a data center may employ many more. Thus, the figures are by way of example only. 
         [0024]    The server pods  106   a  and  106   b  include openings  112  for drawing in cool air from the chilling unit  102  via one or more “cold aisles”  115 . Additional cold aisles may be formed between other server pods, in the example where the data center includes numerous server pods. The server pods  106   a  and  106   b  may further be configured such that banks of servers  108   a  and  108   b  (and similarly, server banks  108   c  and  108   d ) are separated by a “hot aisle”  110   a  and  110   b , respectively. In operation, cold air is drawn in from the cold aisle(s)  115  and flows across the server banks  108   a  and  108   b  (and similarly, server banks  108   c  and  108   d ), where the air is heated by the servers. The heated air, isolated in the hot aisles  110   a  and  110   b , is then drawn up and out through vents  117   a  and  117   b  in the ceiling of the respective pods  106   a  and  106   b . The heated air escaping from the hot aisles  110   a  and  110   b  will yield lower pressure in the hot aisles  110   a  and  110   b , causing cool air to be drawn from the cold aisle(s)  115 . The air circulation can be controlled by varying the volume of air allowed through the supply side or through the exhaust side or both (described in detail below). 
         [0025]    Accordingly, air heated by the server banks  108   a ,  108   b  and  108   c , and  108   d  will rise to the top of the pods  106   a  and  106   b  via natural convection and be vented through vents  117   a  and  117   b . Some embodiments provide a sealed hood for the hot air flows (see e.g., the hood  211  shown in  FIG. 2 ). In some embodiments, additional fans may be provided in or in conjunction with the vents  117   a  and  117   b  to assist in drawing out the heated air and/or to maintain a desired pressure differential. 
         [0026]    As illustrated by the exemplary flow lines in  FIG. 1  (represented by lines  114   a  and  114   b ), air flows from the chilling unit  102  into one or more cold aisles  115 , from which they are drawn into the server pods  106   a  and  106   b  via openings  112 . Inside the server pods  106   a  and  106   b , internal fans of the servers (not shown) may draw the air across the servers and out into the hot aisles  110   a  and  110   b . From the hot aisles  110   a  and  110   b , the heated air is vented through the vents  117   a  and  117   b.    
         [0027]    In some embodiments, the vents  117   a  and  117   b  may be provided with or associated with fans that draw air up into them. In some embodiments, the fans are coupled to or controlled by one or more pressure sensors, which can be utilized to ensure that the pressure in the hot aisles  110   a  and  110   b  is lower than the pressure in the cold aisles  115 . For example, if the pressure in the hot aisle  110   a  or  110   b  is detected as being the same or higher than the pressure in the cold aisle  115 , the respective fans may be operated at a higher speed to draw more air in the hot aisles  110   a  and  110   b  up for venting through the vents  117   a  and  117   b . This ensures that a desired pressure differential, and/or a desired air flow rate, can be maintained or otherwise controlled. 
         [0028]      FIG. 2  is a perspective view illustrating an exemplary server pod of a data center that houses a plurality of server banks (now shown). For clarity, only one server pod is shown. The data center of  FIG. 2  may be an embodiment of the data center  100  shown in  FIG. 1 . In this example, a server pod  206   a  and an adjacent server pod (not shown) are separated by cold aisle  215 . The sides of the server pod  206   a  include screened openings  212  for admitting cool air into the server pods  206   a . As illustrated, the server pod  206   a  includes an access door  216   a  defining an opening to the hot aisle (not shown) inside the server pod  206   a . In the example illustrated, the server pod hot aisle (inside the server pod  206   a ) extends from the ceiling of the server pod  206   a  to the ceiling of the data center via an enclosure or hood  211 . The cold aisle  215  is pressurized with cool air which is then drawn through the racks of the server pod  206   a , as illustrated by arrows  214 . The air is then drawn out the top of the server pod  206   a  via the enclosed or sealed hood  211 . 
         [0029]    As described above with respect to  FIG. 1 , a data center heat removal system may include one or more chilling units, such as the chilling unit  102 .  FIG. 3  is a block diagram of one exemplary arrangement of a chilling unit  300 , which may be used in a data center according to some embodiments. The chilling unit  300  may include a structure or housing for housing the various components of the chilling unit, described below. In one example, a housing may comprise a shipping container housing, being approximately 20 feet long, 7′10″ tall, and 7′8″ wide according to one non-limiting example. Other types and sizes are may also be used. 
         [0030]    In the exemplary chilling unit  300  shown in  FIG. 3 , the direction of air flow through the chilling unit  300  is shown by the arrows at each end of the chilling unit  300 . Ambient air enters the chilling unit  300  at a first end  301  (as shown by the arrow  303 ) and exits at a second end  305  into the data center (as shown by the arrow  307 ). In the example illustrated in  FIG. 3 , the chilling unit  300  includes a first fan unit  314 , a first filter  312 , a second fan unit  310 , a mister  308 , a chiller unit  306 , a third fan unit  304 , and a second mister  302 . In some embodiments, each of the components may be configured to extend across a cross section of the container. Further, in some embodiments, one or more of the components may not be necessary. For example, in some embodiments, the chiller unit  306  may not be required by a data center heat removal system disclosed herein (e.g., the data center  100  shown in  FIG. 1 ) where the air outside a data center configured with the data center heat removal system is usually at a sufficiently cool temperature (e.g., depending upon the climate, location, and/or altitude at which the data center is located) that artificial cooling may not be necessary. Furthermore, in some embodiments, the humidity of the air may be such that only one mister is needed. 
         [0031]    In some embodiments, the number and configuration of fan units in the chilling unit  300  may be chosen based on air flow requirements, as desired. In some embodiments, the fan units  314 ,  310 , and  304  may each include four 44″ drum fans capable of moving approximately 72,000 CFM of air. The control of the fan units is described in detail below. The filter units  312  may be implemented as four-stage Hepa filters in some embodiments. 
         [0032]    In some embodiments, the chiller unit  306  may be configured to include chillers on both sides of the chilling unit  300 , with coils that extend to meet each other at 45 degrees from the sides. In some embodiments, the coil units may be hinged such that, when not in use, they can swing to the sides of the chilling unit using motors. 
         [0033]    In some embodiments of a data center heat removal system, various types of sensors can be placed in a data center to sense various conditions in the data center. In some embodiments, the sensed conditions are stored in a database and are used by a control system to control the operation of the components of the chilling unit and associated fans, vents, etc. (described below). The control system may be associated with the chilling unit  300  or the data center itself, or both. The sensors may include temperature sensors, humidity sensors, air flow sensors, pressure sensors, and/or other types of environmental sensors. In some embodiments, each chilling unit  300  may provide up to 60,000 CFM of air to the data center at or under 78 degrees. In other embodiments, each chill unit  300  may provide more or less capacity, as desired. 
         [0034]    While the chilling unit  300  is pressurizing the data center, the variable speed ceiling fans (e.g., for the vents  117   a  and  117   b  of  FIG. 1  or the hood  211  of  FIG. 2 ) of the data center may be adjusted to keep the pressure in the hot aisles at lower than the cool side of the system. When the temperature is below a threshold value (e.g., 65 degrees), one of the fans may be slowed or shut off to decrease the pressure and the ceiling fan will slow to reduce amount of air that is being released. 
         [0035]      FIGS. 4-7  are views of an exemplary chilling unit according to some embodiments. Other configurations and layouts are also possible. In  FIGS. 4-7 , the housing walls are hidden to show the chilling unit components inside the housing.  FIG. 4  is an isometric view of a chilling unit.  FIG. 5  is a top view of the chilling unit shown in  FIG. 4 .  FIG. 6  is a side view of the chilling unit shown in  FIG. 4 .  FIG. 7  is an end view of the chilling unit shown in  FIG. 4 . 
         [0036]    As mentioned above, in some embodiments, a chilling unit can be housed using a standard shipping container. A typical shipping container is comprised of a steel box having doors at one end. Although a standard shipping container works well as a chilling unit housing, a customized housing can also be used. In one example, a standard 20 foot freezer shipping container is used. In this example, an intake area (described below) is formed at one end of the container. 
         [0037]    As shown in  FIGS. 4-7 , a chilling unit  400  includes a housing  410  having doors  412  at one end. During use of the chilling unit  400 , the doors  412  are opened, or completely removed. In  FIGS. 4-6 , the direction of air flow through the chilling unit  400  is from right to left. 
         [0038]    At the right end of the chilling unit  400  are a plurality of vents  414  that form openings in the housing  410  to allow air to be drawn into the chilling unit  400  from outside. In the example shown in  FIG. 4 , the vents  414  are formed on the end, and on 3 sides of the housing  410 . Downstream from the vents  414  are one or more fans  416 . In the example shown in  FIGS. 4-7 , four fans are arranged to substantially cover the cross-sectional area of the housing  410 . More or fewer fans could be used. As described in more detail below, the fans  416  may be single or variable speed, and may be controlled together or independently. The fans  416  draw air into the chilling unit  400  via the vents  414 , and force the air through filter(s)  418 . In one example, the fans  416  are 42 inch drum fans, each capable of moving 18,200 cubic feet per minute (CFM) of air. In the example of  FIGS. 4-7 , four fans are placed in the intake side. In other examples (e.g.,  FIG. 3 ), four more fans are placed on the exhaust end of the housing  410 . In one example, the filters are 3-stage heap filters angled at 45 degrees from both sides to provide more surface area. 
         [0039]    Downstream from the filters  418  is a mister  420 . In the example shown, the mister  420  comprises a series of mister nozzles near the top of the housing  410  pointing downward. When the mister  420  is activated, a fine mist  422  of water is sprayed downward as the air flows through the chilling unit  400 . Depending on the temperature and relative humidity, the mister  420  can lower the temperature of the air by approximately 10 degrees. 
         [0040]    Downstream from the mister  420  are mister cooling elements  424 . For clarity, the mister cooling elements  424  are not shown in  FIG. 4 , but are shown in  FIGS. 5-6 . The mister cooling elements  424  are made of a metal material and help to cool the air even further by providing a surface for mist condensation. As the air flows through the mister cooling elements  424 , the air is not only cooled by evaporating mist, but also by passing through the mister cooling elements  424 . The mister cooling elements  424  can be any configuration that allows air to flow through, while providing a metal surface for mist condensation. Examples of the mister cooling elements  424  can include coils, a metal grate or mesh, etc., as one skilled in the art would understand. 
         [0041]    Downstream from the mister  420  and the mister cooling elements  424  are a pair of chillers  426  mounted on opposite walls of the housing  410 . The chillers  426  can be conventional off-the-shelf air-conditioning or freezer units configured to chill the air. If the air needs to be further cooled, one or more of the chillers  426  can be turned on.  FIGS. 5-6  also show freezer elements such as freezer coils  428  disposed within the housing  410  between the chillers  426 . The freezer elements  428  are extensions of piping from the chillers  426  extending into the chiller unit  400  to improve heat transfer with the air. In one example, the freezer elements  428  are configured to extend out at a 45 degree angle from the sides of the housing  410 . In one example, the freezer elements  428  are movable to automatically swing back against the interior wall of the housing  410  when not in use. 
         [0042]    Note that the configuration of a chilling unit can take on many configurations, as desired. For example, the chilling unit  300  shown in  FIG. 3  has three sets of fans and two sets of misters. Depending on various factors, such as local climate, data center size, cost limitations, etc., a chilling unit can be configured in such a way as to balance desired performance and cost. 
         [0043]    As mentioned above, the temperature of a data center can be controlled and maintained by sensing various conditions in the data center and controlling various components of a system accordingly.  FIG. 8  is a block diagram illustrating a system  800  that is configured to maintain a desired data center temperature in the most energy efficient manner possible. The system  800  has a controller  810  capable of interfacing and controlling the various components of the system  800 . The controller  810  may be comprised of a single device that interfaces with the components of the system  800 , or may include multiple devices working together. For example, a data center may have separate fan controllers, chiller controllers, etc. In one example, a web-based application runs on a server  812  and controls the operation of the controller  810 . One or more client devices  814  can be used by a technician to configure and monitor the controller via the web-based application. 
         [0044]    The system  800  uses a plurality of sensors  816  to sense various conditions in the data center. The sensors may include temperature sensors, humidity sensors, air flow sensors, and/or pressure sensors, and any other desired sensors. The temperature sensors may sense the temperature in the hot isles, cold isles, server pods, chilling units, exhaust vents, individual servers, etc. The ambient temperature can also be sensed outdoors or at the intake portion of the chilling unit. Similarly, humidity sensors can also sense the humidity anywhere in the data center, as desired. Pressure sensors sense air pressure at various places in the data center. By monitoring the air pressure throughout the data center, a desired air flow through the system can be maintained. In one example, the air pressure is sensed in the cold isles, hot isles, and exhaust vents. The system  800  may also use any other type of sensor desired. 
         [0045]    The system  800  controls the operation of the fans  818  of the system to maintain a desired air flow throughout the system. For example, a data center may have fans in the chilling units (e.g., fans  416  in  FIG. 4 ) and in the exhaust vents (e.g., vents  117   a  and  117   b  in  FIG. 1 ). The controller  810  controls whether the fans are on or off, as well as controlling their speed, when variable speed fans are used. The controller  810  is capable of determining how to most efficiently use the fans to maintain a desired air flow, and thus temperature. For example, if a given amount of air flow is needed to maintain a target temperature, the controller can selectively activate individual fans, and control them at desired speed(s) to achieve a desired airflow using the least amount of electricity possible. 
         [0046]    The system  800  can also control the opening and closing of vents  820  in the system, if the system is equipped with closable vents. For example, the intake vents of the chilling units may include louvers that can be opened and closed by the controller  810 . Similarly, the exhaust vents can be opened and closed by the controller  810 . The vents  820  can not only be opened and closed, but can be opened a desired amount, to further control the amount of air flow through the vents  820 . 
         [0047]    The system  800  also controls the operation of the misters  822  (e.g., misters  420  in  FIG. 4 ) of the system to lower the air temperature in the system. As described above, activating the misters  822  can, under the right conditions, lower the air temperature by approximately 10 degrees. The misters  822  have the most effect in low-humidity conditions. By knowing the humidity of the air, the controller  810  can determine when activating the misters  822  will have a beneficial effect. 
         [0048]    The system  800  also controls the operation of the chiller units  824  (e.g., chillers  426  in  FIG. 4 ) of the system to lower the air temperature. By activating the chiller units  824 , the air temperature can be significantly lowered to help achieve a desired air temperature. 
         [0049]    The controller  810  may also control various other components, as desired. In addition, the controller  810  and web-based application can monitor, log, and report various aspects of the operation of the system  800 . The system  800  may include monitors, visual indicators, alarms, etc., either via client devices or standalone indicators and devices, to allow users or technicians to monitor the operation of the system  800 . 
         [0050]    The system  800  is controlled to achieve a desired target temperature in the server pods in the most efficient manner possible. The dominate factor that determines the cost of cooling a data center of electricity usage. The various components of the system  800  that contribute to lowering air temperatures each use different amounts of electricity. Therefore, the controller  810  is configured to achieve and maintain a target temperature by controlling the system components in such a way that electricity usage is minimized. 
         [0051]    A goal of the controller is to maintain a desired target temperature, using the least possible amount of electricity. When the chiller units may use significantly more power than the fans and misters, the controller will try to maintain the desired target temperature without using the chiller units, or at least minimizing the use of the chiller units. Similarly, the controller will selectively activate and control the speed of the fans to achieve a desired airflow using the least amount of power. 
         [0052]    In one example, the controller  810  uses an algorithm to control the system. The algorithm may, when possible, maintain a desired target temperature without using the chiller units  824 . For example, under the right conditions, the desired target temperature can be maintained by controlling the activation and speed of the fans  818  alone. Under the right conditions (e.g., a relatively low humidity level), the misters  822  may be used with the fans. Use of the misters  822  may allow fans usage to be reduced, further lowering power usage. 
         [0053]    The control algorithm, via the sensors, knows the conditions (e.g., temperature, humidity, air pressure differentials) in the system, and can control the system accordingly. For example, assume that an X degree temperature drop is needed. Knowing the outside ambient air temperature, the various temperatures in the system, and the relative air pressures in the system, the controller can determine that Y cubic feet of air flow is needed to reach the desired target temperature. The controller then selectively activates and controls the speed of the fans in the system to achieve the determined air flow rate. The controller also takes into account how activation of the misters will affect the air temperature, and thus the desired air flow rate. When the sensed conditions indicate that use of the misters would be beneficial, the misters will be activated. As a result, the controller can maintain the desired target temperature using a combination of fans and the misters in the most efficient way possible, preferably without relying on the chiller units. If the outside ambient temperature is high enough (perhaps 78 degrees, in one example), the desired target temperature may not be achievable with fans and mister alone. When that is the case, the controller will turn on one or more of the chiller units to bring the air temperature down to the desired target level. 
         [0054]      FIG. 9  is a logical control diagram illustrating an example of the control of the fans (e.g., fans  416  in  FIG. 4 ) in a chilling unit based on a sensed condition. In the example illustrated in  FIG. 9 , the controller controls the amount of air flow through the system based on the temperature of the air at the intake of the chilling unit. In general, cooler air requires less air flow to cool the data center, while warmer air requires more air flow to cool the data center. 
         [0055]    As shown in  FIG. 9 , the controller obtains a temperature reading from one or more temperature sensors. The temperature sensor(s) may be located at the intake of the chilling unit, outside of the chilling unit, or at any other suitable location. In this example, if the sensor reports an air temperature of approximately 50 degrees Fahrenheit, the controller sends a digital signal to the chilling unit fans to run at 50 CFM/kW. As indicated by the air flow rate values in  FIG. 9 , the desired flow rate also depends on the amount of power being consumed in the data center, in this example, 50 CFM/kW. In other words, when more power is being consumed by the data center, more heat is generated, and therefore, more air flow is needed. The desired flow rate can be achieved by selectively activating fans, as well as setting the speed of the activated fans. In some examples, the air flow rate may be fine-tuned by also controlling exhaust fans. If the sensor reports an air temperature of approximately 70 degrees Fahrenheit, the controller sends a digital signal to the chilling unit fans to run at 126 CFM/kW. If the sensor reports an air temperature of approximately 90 degrees Fahrenheit, the controller sends a digital signal to the chilling unit fans to run at 225 CFM/kW. 
         [0056]    Other components of the system (e.g., misters, coolers, etc.) can be controlled in a similar manner based on any desired sensed conditions, as one skilled in the art would understand. Also note that the activation of different components of the system may affect each other. For example, if the misters are activated, a lower air flow rate may be desired, compared to a desired air flow rate without the misters. 
         [0057]    Note that it is important to not only lower the temperature of a data center to a desired level, but to not let the temperature drop too far below the desired level. The reliability of some server equipment relies on a relatively constant temperature. Therefore, in some conditions (e.g., winter months), the outside ambient air will be cool enough that the controller will restrict air flow to keep the air temperature up to the desired target value. 
         [0058]    The systems described above can be built into a new data center or retrofitted into an existing data center. In an example where a system is retrofitted into an existing data center, one or more chilling units can each be installed in an opening formed in a data center wall, as illustrated in  FIG. 1 . In each hot isle, an exhaust vent/hood (e.g., vents  117   a  and  117   b  in  FIG. 1 ) is created to draw hot air out of the data center. A controller and various sensors (e.g., temperature, humidity, and/or pressure, etc.) can also be installed to monitor and control the operation of the system. 
         [0059]    These, and other, aspects of the disclosure and various features and advantageous details thereof are explained more fully with reference to the exemplary, and therefore non-limiting, embodiments illustrated herein. It should be understood, however, that the detailed description and the specific examples, while indicating the preferred embodiments, are given by way of illustration only and not by way of limitation. Descriptions of known programming techniques, computer software, hardware, operating platforms and protocols may be omitted so as not to unnecessarily obscure the disclosure in detail. Various substitutions, modifications, additions and/or rearrangements within the spirit and/or scope of the underlying inventive concept will become apparent to those skilled in the art from this disclosure. 
         [0060]    Some embodiments described herein can be implemented in the form of control logic in software or hardware or a combination of both. The control logic may be stored in an information storage medium, such as a computer-readable medium, as a plurality of instructions adapted to direct an information processing device to perform a set of steps disclosed in the various embodiments. Based on the disclosure and teachings provided herein, a person of ordinary skill in the art will appreciate other ways and/or methods to implement the invention. 
         [0061]    It is also within the spirit and scope of the invention to implement in software programming or code the steps, operations, methods, routines or portions thereof described herein, where such software programming or code can be stored in a computer-readable medium and can be operated on by a processor to permit a computer to perform any of the steps, operations, methods, routines or portions thereof described herein. The invention may be implemented by using software programming or code in one or more control systems, by using application specific integrated circuits, programmable logic devices, field programmable gate arrays, optical, chemical, biological, quantum or nanoengineered systems, components and mechanisms, various types of sensors including temperature, humidity, and/or pressure sensors may be used. The functions of the invention can be achieved by various means including distributed, or networked systems, hardware components, and/or circuits. In another example, communication or transfer (or otherwise moving from one place to another) of data may be wired, wireless, or by any other means. 
         [0062]    A “computer-readable medium” may be any medium that can contain, store, communicate, propagate, or transport the program for use by or in connection with the instruction execution system, apparatus, system or device. The computer readable medium can be, by way of example only but not by limitation, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, system, device, propagation medium, or computer memory. Such computer-readable medium shall be machine readable and include software programming or code that can be human readable (e.g., source code) or machine readable (e.g., object code). Examples of non-transitory computer-readable media can include random access memories, read-only memories, hard drives, data cartridges, magnetic tapes, floppy diskettes, flash memory drives, optical data storage devices, compact-disc read-only memories, and other appropriate computer memories and data storage devices. In an illustrative embodiment, some or all of the software components may reside on a single server computer or on any combination of separate server computers. As one skilled in the art can appreciate, a computer program product implementing an embodiment disclosed herein may comprise one or more non-transitory computer readable media storing computer instructions translatable by one or more processors in a computing environment. 
         [0063]    A “processor” includes any, hardware system, mechanism or component that processes data, signals or other information. A processor can include a system with a central processing unit, multiple processing units, dedicated circuitry for achieving functionality, or other systems. Processing need not be limited to a geographic location, or have temporal limitations. For example, a processor can perform its functions in “real-time,” “offline,” in a “batch mode,” etc. Portions of processing can be performed at different times and at different locations, by different (or the same) processing systems. 
         [0064]    Those skilled in the art will appreciate that a suitable control system can include a central processing unit (“CPU”), at least one read-only memory (“ROM”), at least one random access memory (“RAM”), at least one hard drive (“HD”), and one or more input/output (“I/O”) device(s). The I/O devices can include a keyboard, monitor, printer, electronic pointing device (for example, mouse, trackball, stylus, touch pad, etc.), or the like. In embodiments of the invention, the control system can have access to at least one database over a network connection. 
         [0065]    ROM, RAM, and HD are computer memories for storing computer-executable instructions executable by the CPU or capable of being compiled or interpreted to be executable by the CPU. Suitable computer-executable instructions may reside on a computer readable medium (e.g., ROM, RAM, and/or HD), hardware circuitry or the like, or any combination thereof. Within this disclosure, the term “computer readable medium” is not limited to ROM, RAM, and HD and can include any type of data storage medium that can be read by a processor. Examples of computer-readable storage media can include, but are not limited to, volatile and non-volatile computer memories and storage devices such as random access memories, read-only memories, hard drives, data cartridges, direct access storage device arrays, magnetic tapes, floppy diskettes, flash memory drives, optical data storage devices, compact-disc read-only memories, and other appropriate computer memories and data storage devices. Thus, a computer-readable medium may refer to a data cartridge, a data backup magnetic tape, a floppy diskette, a flash memory drive, an optical data storage drive, a CD-ROM, ROM, RAM, HD, or the like. 
         [0066]    As used herein, the terms “comprises,” “comprising,” “includes,” “including,” “has,” “having,” or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a process, product, article, or apparatus that comprises a list of elements is not necessarily limited only those elements but may include other elements not expressly listed or inherent to such process, product, article, or apparatus. 
         [0067]    Furthermore, the term “or” as used herein is generally intended to mean “and/or” unless otherwise indicated. For example, a condition A or B is satisfied by any one of the following: A is true (or present) and B is false (or not present), A is false (or not present) and B is true (or present), and both A and B are true (or present). As used herein, including the accompanying appendices, a term preceded by “a” or “an” (and “the” when antecedent basis is “a” or “an”) includes both singular and plural of such term, unless clearly indicated otherwise (i.e., that the reference “a” or “an” clearly indicates only the singular or only the plural). Also, as used in the description herein and in the accompanying appendices, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise. 
         [0068]    Additionally, any examples or illustrations given herein are not to be regarded in any way as restrictions on, limits to, or express definitions of, any term or terms with which they are utilized. Instead these examples or illustrations are to be regarded as being described with respect to one particular embodiment and as illustrative only. Those of ordinary skill in the art will appreciate that any term or terms with which these examples or illustrations are utilized encompass other embodiments as well as implementations and adaptations thereof which may or may not be given therewith or elsewhere in the specification and all such embodiments are intended to be included within the scope of that term or terms. Language designating such non-limiting examples and illustrations includes, but is not limited to: “for example,” “for instance,” “e.g.,” “in one embodiment,” and the like. 
         [0069]    Those skilled in the art of the invention will recognize that the disclosed embodiments have relevance to a wide variety of areas in addition to the specific examples described above. For example, although the examples above are described in the context of data centers, some embodiments disclosed herein can be adapted or otherwise implemented to work in other types of environments, circumstances, etc. In this context, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of this disclosure. Accordingly, the scope of the present disclosure should be determined by the following claims and their legal equivalents.