Abstract:
A cooling system and method for cooling devices housed in a data center. A cabinet housing a set of condenser coils is located within the data center positioned on its floor and including fans for drawing air passed the condenser coils and exiting the device angularly to the floor of the data center. The present invention also contemplates the use of redundant compressors and condensers, a system that includes a secondary evaporator coil and configuration which enables the device, under certain conditions, to bypass its compressor.

Description:
TECHNICAL FIELD 
       [0001]    The present invention involves a cooling system and method for its operation used for cooling devices in a data center. Data centers are rooms that contain electronic systems generally arranged on racks, the standard rack being defined by the EIA as an enclosure approximately 78″ high, 24″ wide and 40″ deep. These racks are employed to house printed circuit board-based devices which, under normal operation, can generate significant amounts of heat. For the proper operation of such devices and for maintaining them throughout their normal life cycle, proper temperature and humidity must be maintained. 
       BACKGROUND OF THE INVENTION 
       [0002]    Historically, computer room air conditioning (CRAC) systems were manufactured by those who supplied residential and commercial air conditioning systems, generally. The design philosophy was to build such systems at the lowest possible cost, that is, the cost of manufacturing being more important than the operational cost of the system. These CRAC systems were built to do as much work as possible while occupying the smallest possible space within the data center. Energy consumption in running these systems was less of a consideration than the floor space that the units would occupy in a typical data center location. 
         [0003]    These design considerations have changed considerably over time as computing systems of the type typically located within a data center consume considerable amounts of energy while generating heat necessitating CRAC systems of greater efficiency. With the increasing popularity of the Internet, data centers are now considered to be the number one energy consumer in the United States. 
         [0004]    There have been three fundamental CRAC system designs referred to, for the sake of simplicity, as CRAC 1 , CRAC 2  and CRAC 3 . 
         [0005]    CRAC 1  is a split refrigeration system with outdoor air cooled condensing. This system is characterized by having two main components, namely, the CRAC unit itself located inside of the data center and a condenser located external thereto. The indoor unit houses the systems&#39; compressors, evaporators, controls and cooling fans. The outdoor unit houses the condenser and condenser fans which inter-connect to the indoor unit with piping through which the refrigerant travels. 
         [0006]    The CRAC 2  system also employs two main components, namely, the CRAC units located within the data center and heat exchanger components located external thereto. The indoor unit houses the compressor, condenser, evaporator, system controls and cooling fans. The outdoor unit is composed of a heat exchanger from which heat from the system is rejected as well as pumps used to move heat transfer fluid from the indoor to outdoor units. This design can also have an optional heat exchanger located in series with the indoor heat exchangers. When the fluid temperature from the outdoor heat exchanger is below the return air temperature, a valve opens allowing the heat transfer fluid to pass through the lead heat exchanger. The fluid removes heat from the return air stream. 
         [0007]    CRAC 3  systems employ CRAC units located in the data center and fluid chillers located external thereto. The indoor unit houses the indoor heat exchanger, indoor fan systems and controls. The outside unit is composed of either a self-contained refrigeration system which chills the heat transfer fluid which is usually air cooled or a split chiller system which is composed of a compressor, evaporator, fluid cooled condenser and fluid cooled heat exchanger. 
         [0008]    Regardless of the system type, the design philosophy in sizing and installing CRAC systems in a data center is quite consistent from installation to installation. The typical installation involves adding a sufficient number of units to meet the anticipated heat load of the facility and one additional unit for redundancy. Thus, as facilities grow, more indoor and outdoor units are added to the system noting that, typically, each CRAC unit operates independently of other units. Thus, the control valves of each unit are turned on and off independently of other units to meet and maintain building loads. Indoor fans never shut off to maintain the load imposed upon the facility. Centrifugal fans are commonly employed for supply side air. Small fans are employed even though smaller fans are generally more inefficient than those which are larger. Regardless of fan type, current CRAC installations are based upon a “one load, one system” methodology. Such installations exhibit the same efficiency when operating under normal or emergency conditions. These systems do not integrate redundancy in the form of additional heat exchange area in order to make them more efficient. Parameters seldom change dramatically unless loads change dramatically. The redundancy of this type of system is based upon adding units which are brought on line as needed. 
         [0009]    It is quite apparent that previously suggested CRAC systems made no attempt to maximize operating efficiencies as most prior designs were created well before energy became as expensive as it is today and before the explosive use of Internet-based communications and information downloading created such a severe impact upon energy usage and resultant heat generation. 
         [0010]    Thus, it is an object of the present invention to provide CRAC systems having several unique and innovative design criteria to make such systems much more efficient to operate while maximizing their ability to effectively cool a data center both under ordinary conditions and when emergencies require supplemental cooling capacity. 
         [0011]    It is yet a further object of the present invention to provide a data center cooling system which, depending upon environmental conditions, can transfer coolant while bypassing the systems&#39; compressor. 
         [0012]    Although the discussion which appears below reveals a unique system capable, under certain conditions, to provide coolant to condenser coils without use of a compressor, the present invention is not the first instance in which compressor-free cooling has been suggested. In this regard, reference is made to  FIG. 1  representing a schematic drawing of such a system commercially available from Trane Co. Specifically, when water returning from cooling tower  11  is colder than the chilled water circulating through cooling load  12 , refrigerant pressure within condenser  13  is slightly lower than that in evaporator  14 . This pressure differential drives the refrigerant vapor “boiled off” in evaporator  14  to condenser  13 , where it condenses and flows by gravity back to evaporator  14 . As long as the proper pressure difference exists between evaporator  14  and condenser  13 , refrigerant flow and consequent “free cooling” continues. According to its manufacture, the system shown in  FIG. 1  is capable of refrigerant-migration “free cooling” up to as much as 40% of the chiller&#39;s design tonnage. Since the chiller and “free cooling” cycle cannot operate simultaneously, free cooling of this type can only be used when the cooling capacity of water tower  11  is sufficient to meet the entire building load. As “free cooling” capacity is available only when the ambient wet bulb temperature is below 50 degrees F., accessories such as chilled water pumps, condenser water pumps and cooling tower fans must continue to operate in their conventional manner while the chiller operates in the “free cooling mode.” This minimizes the energy savings from such a system which is realized only from its ability to bypass its compressor. 
       SUMMARY OF THE INVENTION 
       [0013]    As a first embodiment, the present invention involves a cooling system for cooling devices housed in a data center, the device comprising a cabinet, a set of evaporator coils, an inlet and outlet and at least one fan for drawing air from within the data center through said cabinet and for movement of the air over said evaporator coils to the data center heat loads. The improvement comprises angling the air flow emanating from the cabinet proximate 45° to 70° to the plane of the flooring. 
         [0014]    As a second embodiment, the invention is directed to a cooling system for cooling a data center to a predetermined temperature and humidity, the cooling system comprising a set of evaporator coils and a fan for moving air within the data center passed the set of evaporator coils. At least two sets of compressors, two sets of condensers and two independent control systems are located external to the data center and positioned in parallel to provide coolant to the set of evaporator coils. 
         [0015]    The third embodiment involves a cooling system comprising a compressor, a condenser, coolant, pump and primary evaporator coil for cooling. The improvement comprises a secondary evaporator coil in series with the primary evaporator coil, the secondary evaporator coil being a flooded coil piped to the condenser. 
         [0016]    As yet another embodiment, the invention involves a cooling system comprising a compressor, condenser, condensable coolant, pump and evaporator coils. The improvement comprises a measurement device and actuator wherein when the measurement device measures the wet-bulb temperature and when it is no greater than a preselected value, the compressible coolant is circulated by the pump between the condenser and evaporator coils while bypassing the compressor. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0017]      FIG. 1  is a schematic depiction of a commercially available chiller of the prior art. 
           [0018]      FIG. 2  is a side view of a portion of the present invention showing evaporator coils and fans to be housed in a cabinet used for cooling an appropriate data center according to the present invention. 
           [0019]      FIG. 3  is a schematic view of a system according to the present invention including two circuits provided for redundancy and for increased efficiency. 
           [0020]      FIG. 4  is a schematic view of a part time economizing system using a scavenger coil in series with main evaporator coils to increase efficiency of the present invention. 
           [0021]      FIG. 5  is yet another schematic view of an economizing circuit similar to that depicted in  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0022]    Turning first to  FIG. 2 , housing  20  is depicted with its side walls removed for illustrative purposes. Frame members  21  support sets of evaporator coils  22  receiving coolant from compressors and related hardware located external to the data center being cooled. 
         [0023]    In operation, ambient air within the data center is drawn through open top  25  passed sets of evaporator coils  22  through the use of prop or axial fans  23 . Ideally, multiple fans are employed sufficient to maintain a positive static pressure within a space beneath the flooring. Although not shown, cool air created by housing  20  is discharged proximate racks of circuit boards and similar solid state devices through openings strategically located proximate thereto. 
         [0024]    A feature of the present invention is the orientation of fans  23  in directing cooled air in the direction of arrows  24 . CRAC units of the prior art generally employ centrifugal fans that blow air directly at the floor. This increases the static pressure load on the fans as the air is forced to change direction by 90 degrees upon impacting the floor. The present invention employs prop or axial fans  23  directing air discharge as shown by arrows  24  by mounting the fans at a 20 to 45 degree angle from vertical or 45 to 70 degree angle proximate to the plane of the floor. This provides a much improved approach angle of the cold air discharge relative to the floor and reduces the pressure drop characterized by prior systems. All such expedients are considered to be embraced within the present invention. Sufficient fans are employed for maintaining static pressure and air flow within the space noting that output can be varied to maintain the required static pressure via static pressure sensors. 
         [0025]    Yet a further embodiment of the present invention can be appreciated by reference to  FIG. 3 . In its basic terms, system  30  is composed of two simple circuits, operating in parallel. Specifically, parallel condensers  31 A and  31 B as well as parallel compressors  34 A and  34 B operate externally to the data center each set operating in conjunction with pumps  35 A and  35 B, respectively, to supply coolant to expansion valves  36  and onto evaporators  32 A/ 32 B and  33 A/ 33 B, located within the data center. Redundant condensers and evaporators are operated together at part load while increasing the heat exchange surface area resulting in a decrease in the temperature differences within the system; that is, the temperature difference between the coolant temperature and the air temperature flowing over the coil. By decreasing this temperature difference, pressures are generally higher on the evaporator side and lower on the condenser side of the system thereby decreasing the compression ratio of the coolant and reducing the energy the compressors consume to compress the coolant gas. 
         [0026]    A main function of the present system is that it allows for reduced compression operation. Compression ratio is a reference to the difference between the suction and the discharge pressures measured in absolute pressure. There are several main reasons why the present invention can accomplish reduced compression where others cannot. 
         [0027]    As background, typical systems compression ratios are derived by the use and control of the condensing pressure. Typical systems control the condensing pressure buy either staging the condenser fans off and on to meet a set point of condensing pressure or speed control fans to meet that specific point. The present system utilizes a unique form of control to allow for reduced compression. Instead of turning fans on and off or slowing them down to meet a specific point, the present system utilizes a variable set point. Ideally, this set point establishes a condensing temperature that is 8 degrees F. higher than the wet bulb temperature. Condensers are controlled to match loads in ton and to match a true constant set point. 
         [0028]    It should be noted that every major compressor manufacturer establishes proper operational conditions for its products. It is common for manufacturers to state that a compression ratio of 1.5 to 1 is the lowest allowable compression ratio as anything less is not warrantable. Increased mass flow rate is the main reason manufacturers do not want lower compression rations. As compression ratios decrease, a machine&#39;s capability of pumping refrigerant increases. As an example, at a 2 to 1 compression ratio, a machine may be capable of pumping 50 tons of coolant while at a 1.5 to 1 compression ratio a machine may be capable of pumping 75 tons of coolant and at 1.05 to 1, that same machine may be capable of pumping 100 tons of coolant. As the mass flow rates increase thru the compressor restriction, friction increases as well, as much as double in some cases. This causes a higher amount of wear and tear on machine parts as gas flows thru the compressor ports, pipe and valves. 
         [0029]    The present system commonly operates at compression ratios of 1.05 to 1-1.51 to 1 and in most cases it operates well under a manufacture&#39;s published allowable compression ratio for long periods of time. This is done by not exceeding the machine&#39;s designed mass flow rate rather than compression ratio. This is achieved by reducing the speed of the compressor to only allow the machine to pump coolant to match its maximum mass flow rate. 
         [0030]    To enable the present system to perform at reduced compression levels, it must be able to compensate for what normal systems cannot do. Low compression ratios create lower flow rates through typical metering devices. Every metering device is rated based on pressure differential across its valve. For example, a common metering device may be rated at 15 tons under common conditions, but as a system&#39;s compression ratio or pressure differential drops, that same valve may be only rated for 5 to 10 tons. 
         [0031]    Ideally, metering valves used herein are rated and designed at a 1.3 to 1 compression ratio. These metering valves are provided with a constant pressure differential by amplifying liquid pressure entering the valve with the use of a liquid coolant pump and speed control. Pump speed is varied to maintain a constant pressure drop across the metering devices. 
         [0032]    Yet a further embodiment of the present invention can be appreciated by reference to  FIG. 4 . Specifically, system  40  is depicted whereby coolant from pump  42  located externally to the data center urges coolant through a separate evaporator coil  44  which is called a “scavenger coil.” The scavenger coil is located in series with main evaporator coils  43  through which air flows in the direction of arrows  45  for cooling the data center. Vapor condenser  41  is also located externally to the data center to complete the circuit. 
         [0033]    Again referring to  FIG. 4 , scavenger coil  44  is a flooded coil that is piped directly back to condenser  41 . When the coolant temperature is lower than the return air temperature, bypass valve  47  opens allowing coolant into the scavenger coil where it removes heat from the data center. The coolant then returns directly back to condenser  41 , via flash vessel  33  without moving through a compressor, thus enhancing system efficiency. As condenser  41  still uses energy to remove heat and pumps use energy to pump coolant, some energy is still employed to operate system  40 . However, energy usage is far more efficient than in a typical vapor compressor cycle. 
         [0034]    As is quite apparent, coolant from the pump goes through an entirely separate cooling coil called the scavenger coil (SC) in series with the main evaporator coils. This SC coil is a flooded coil that is direct piped back to the condenser. When the condensing liquid temperature is lower than the return air temperature a valve opens allowing refrigerant into the scavenger coil where it removes heat and goes directly back to the condenser to extract the heat from the room. If, for example, the return air temperature is 68° F. and the condensing liquid temperature is 65° F., heat from the return air is absorbed into the refrigerant (hot goes to cold). The larger the differential is between the return air temperature and the refrigerant temperature, the more energy is removed with this coil. Since a BTU is a BTU the condensers still use energy to remove the heat and the pumps use energy to pump the refrigerant there still is energy used. This energy usage is far more efficient than a typical vapor compressor cycle. 
         [0035]    To summarize, coolant pump  42  pumps liquid refrigerant to feed devices  49  and into the scavenger coils  44 . Inside the scavenger coils, the liquid refrigerant removes heat while still in a semi liquid form. Liquid refrigerant leaves the scavenger coils and flows to flash vessel  46 . Vapor leaves flash vessel  46  and enters the condenser  41  to be condensed. Flash vessels  46  level is approximately 2 feet below condenser  41  outlet for purposes of maintaining a proper liquid trap. Flash vessel  46  maintains a liquid level based on the weight of the refrigerant and acts as an expansion tank. 
         [0036]    The present system is also designed, under certain conditions, to allow for “free cooling.” This means that the system operates under the physics of a thermo-siphon or through migration cooling as was suggested when discussing  FIG. 1 . However, in this instance, when the wet bulb temperature is less than approximately 41-45 degrees F., the “free cooling” cycle operates. Instead of operating with gravity controlling the flow rate as in the prior art, the present system employs a pump to ensure there is enough of a pressure difference to allow the coolant to flow through the metering valve and the evaporator where it is boiled off and routed through a motorized valve to the condenser where it condenses without moving through a compression cycle. If the system detects a lack of movement of the coolant or if a pulse is detected indicating a break in natural migration from the condenser to the evaporator, the compressor is activated by a sensor enabling the system to operate normally. 
         [0037]    To fully appreciate the system architecture of the present invention, as its preferred embodiment, reference is made to  FIG. 5 . It is noted that system  50  is, in effect, one system having two circuits. Multiple evaporator coils  51  and  52  are located within the data center to be cooled. A first circuit comprised of compressor  53 , condenser  54 , expansion receiver  55 , pump  56  and metering valves  57  is employed in conjunction with parallel elements comprised of compressor  58 , condenser  59 , expansion receiver  60 , pump  61  and metering valves  62 . Both circuits work together but are capable of working independently in case of system failures or emergencies. Each air handling unit has both circuits operating in parallel comprised of the same components as in any typical refrigeration system. The systems can be expanded to meet growing loads. Indoor and outdoor units can be added as demand or as planned expansion requires. Further, through the use of pumps  56  and  61  together with metering valves  57  and  62 , economizing can be carried out as explained above, by circulating coolant without use of compressors  53  and  58  if outdoor wet bulb temperatures so dictate. 
         [0038]    What was discussed above represents examples of various embodiments of the present invention. It is assumed that other embodiments will be readily apparent to those skilled in the art. It is intended that the specification is to be considered illustrative of the present invention, the scope of which is to be limited only by the claims.