Abstract:
A rack mount assembly measurement tool, for determining physical values including air flow and heat loads, includes a front assembly and a rear duct assembly that are non-intrusively and releasably mounted on the front and rear of such rack mount enclosure. Physical values are sensed at multiple vertical locations to enable a determination of overall and localized heat loads within the enclosure. Front sensor values are collected and wirelessly transmitted from the front assembly to a receiver/processor supported on the rear duct, which generates computed values that are displayed in addition to the sensed values.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention pertains to heat flow measurement equipment and more particularly to a method and apparatus for non-invasively measuring the heat flow associated with a rack mounted assembly of electronic equipment. 
       BACKGROUND AND SUMMARY 
       [0002]    The present invention is related to application Ser. No. 11/834,752, filed Aug. 7, 2007 and entitled “Bidirectional and Expandable Heat Flow Measurement Tool for Units of Air Cooled Electrical Equipment” which is directed to ascertaining conditions related to individual electronic components, such as servers. The measurement tool illustrated and described is mounted sequentially at the front and then at the back of the device under test to obtain air pressure and temperature values, which in turn enable the air flow and rate of heat dissipation to be determined. This measurement tool also presents a marginal surface, which engages the device, that is compliant to allow any cables to remain connected to the device and continue device operation during test. 
         [0003]    At the rack level it is also necessary to obtain data regarding physical conditions to assist installation and determine whether subsequent operating conditions comply with the design requirements. The problems encountered by the assembly of numerous devices at the rack level differs from those for an individual device and requires different solutions. 
         [0004]    As individual electronic components are improved, the power consumption is usually reduced; however, since the concentration of components is rapidly increased, the concentration of power and the requirement to dissipate heat from a given space is increased. The number of components concentrated in a given space rises faster than the power requirements diminish. Adequate heat sink capability and air flow capacity must be increased commensurate with the increase in power. To assure adequate heat dissipation, water cooling is also employed to assist heat dissipation. The use of water cooling also introduces a further level of concern when employed with electronic equipment. 
         [0005]    To comply with data center owner&#39;s preferences or outright requirements, it is necessary that any equipment or system test be effected non-invasively and be non-disruptive with respect to operating equipment. No customer or user is likely to allow equipment to be turned off to obtain information such as an inline power measurement. In the rack mount environment, it is also necessary that the heat dissipation capability be determined with rack covers in place so that this second order effect is included in the determination of the effectiveness of the overall system. Similarly, the equipment utilized for testing must be designed and used in a manner that imposes minimal additional effect on the system subject to investigation. 
         [0006]    In a rack mount enclosure it has been found that a vertical temperature gradient through the height of the rack enclosure air input opening must be accommodated to obtain an accurate determination of localized heat dissipation in addition to overall air flow and heat dissipation values. The temperature must be observed at multiple vertically spaced locations calculated to accurately represent the variation of temperature over the height of the enclosure opening. It is also preferable practice to obtain sensed values, such as temperature simultaneously at both the inlet and outlet locations of the system. 
         [0007]    At the outlet of the cabinet, the air flow may be collected and routed through a single duct for sensing air pressure and temperature (to obtain respectively a calculated air flow and temperature difference). Such an approach materially adds to the air pressure drop of the system and results in undesirable vector effects at the exit caused by a large volume of air being turned 90 degrees approaching the single outlet. Air resistance can be reduced to obtain a more accurate and representative value of air flow and mean air temperature, while accommodating the vertical temperature gradient, by employing multiple exit ducts vertically spaced through the height of the rack enclosure outlet opening. The outlet air flow is further stabilized by the use of horizontal flow partitioners between adjoining exit ducts. The measurement of the quantity of heat removed from the enclosure can be made with greater accuracy by also determining the relative humidity at the locations at which temperature is determined to obtain the specific heat in the air volume passing through the enclosure. 
         [0008]    When used with a rack enclosure assembly that includes water cooling, the relative humidity sensed at the locations at which the temperature is determined can also provide a determination of the absolute humidity entering and leaving the enclosure. A rise of absolute humidity between the rack enclosure inlet and outlet air openings can be used to initiate a signal calling for a check of the integrity the water cooling system. 
         [0009]    In the environment wherein enclosures are used to house units of identical blower or fan cooled devices, the use of known device fan or blower rotational speeds (RPM) can be utilized in the calculation of rack enclosure air flow and heat dissipation values. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is an elevation of the rear duct with the conduit and tube portions leading from the sensors shown in phantom view. 
           [0011]      FIG. 2  is a section view taken along line II-II of  FIG. 1 . 
           [0012]      FIG. 3  is a partial rear elevation of the rear duct showing the detail of one of the three pitot assemblies. 
           [0013]      FIG. 4  is an interrupted, partial isometric view, partially in phantom view, of the measurement tool front assembly. 
           [0014]      FIG. 5  is an isometric view of a typical rack mount enclosure assembly. 
           [0015]      FIG. 6  shows the rack mount assembly of  FIG. 5  with the measurement tool rear duct assembly and front assembly attached thereto and including the front assembly wireless transmitter and rear duct wireless receiver/processor assembly. 
           [0016]      FIG. 7  shows details of the wireless receiver/processor carried by the rear duct assembly. 
           [0017]      FIG. 8  is a flow chart that shows the processor sequence that generates and displays values such as air flows and heat loads. 
           [0018]      FIG. 9  illustrates an alternative embodiment wherein a front frame is shown which is utilized in conjunction with rear frame of  FIGS. 1 and 2 . 
           [0019]      FIG. 10  is a section view taken along line XX of  FIG. 9 . 
       
    
    
     DETAILED DESCRIPTION 
       [0020]      FIG. 1  illustrates the rear duct assembly  10  of the present invention and  FIG. 2  is a section view of the rear duct assembly of  FIG. 1  taken along line II-II. The duct assembly  10  includes an end wall  12  with contiguous side walls  13 , top wall  14  and bottom wall  15 . The end wall  12  includes integral upper, middle and lower duct portions  18 ,  19  and  20  respectively. Also formed integral with the end wall  12  and side walls  13  are a pair of flow partitioners  22  and  23  which are horizontal panels that divide the air passing through the assembly  10  into upper, middle and lower flow paths. The duct assembly, as illustrated, is formed of a closed cell plastic material, but could be constructed of any material that would confine and direct the air flow while possessing a low specific heat to enable the temperature of air passing through the assembly to quickly stabilize to the temperatures at the entry and exit of the system. For example, the assembly could be a flexible material formed over a tubular frame which could be hinged to enable greater flexibility to accommodate variations in rack dimensions. 
         [0021]    As shown, the duct assembly  10  includes a continuous, readily compressible foam strip  26  along the distal edges of side walls  13 , top wall  14  and bottom wall  15  that serves as a gasket to seal the assembly against the marginal wall surfaces which surround a rack enclosure rear opening when the duct assembly  10  is secured thereto. Flexible marginal flaps  28  are secured at the edges of the top wall, bottom wall and side walls of the duct assembly  10 . Each of the flaps  28  includes a continuous flexible magnet  29  which adheres the respective flap to a rack wall surface when the duct assembly  10  is installed in the operating position, to thereby attach and secure the rear duct assembly. 
         [0022]    Temperature is sensed within each of the upper, middle, and lower duct portions  18 ,  19  and  20  by a thermocouple  30  supported on the respective tube branch  31 . Also mounted on each of the tube branches  31  is a relative humidity sensor  32 . The wire leads for each of the thermocouples and relative humidity sensors enters the respective tube branch  31  through an opening or openings therein and extends up the integral vertical tube  34  (which is shown in phantom view, save for the uppermost portion which emerges through the top wall). 
         [0023]    The air pressure sensing structure is more clearly shown in  FIG. 3 , which is a partial elevation which shows the side of the upper duct portion  18  opposite the side shown in the elevation of  FIG. 1 . Air pressure is sensed using pitot openings  35  in an “H” shaped tube assembly  36  where the end of each leg is closed and supported in the upper or lower wall forming the respective duct portion  18 . The pitot tube assembly  36  includes a single outlet in the form of a tube which extends horizontally through the duct portion  18  side wall and upward through top wall  14  such that an independent tube  38  extends from each of the “H” shaped pitot assemblies resident in an associated duct portion  18 ,  19  or  20 . Also visible in  FIG. 3  is the branched tube  34  which serves as a conduit for the leads from thermocouples  30  and relative humidity sensors  32  mounted on integral branch tubes  31 . 
         [0024]      FIG. 4  is a partial isometric view (which is interrupted and partly in phantom view) of a front, entry air temperature and relative humidity sensing assembly  40  for a rack mount enclosure. An angle frame element  42  has a magnet  43  secured to the lower surface of the horizontal portion  44  which enables the assembly to be firmly, but releasably secured to a steel rack enclosure door. The vertical flange  45  includes a clamp  46  for securing the conduit tube  48  and precluding rotation of the tube relative to the assembly frame  42 . The clamp  46  is secured to the tube  48  by turning thumb screw  49  and urging the flanges  50  toward one another. 
         [0025]    The vertical conduit tube has three parallel branches  52 , each of which supports a thermocouple  53  for temperature sensing and a relative humidity sensor  54 . Leads from the sensors  53  and  54  enter the conduit through openings in the branch tube on which it is supported and, as a part of a cable  56  in the vertical conduit tube  48 , extend from the upper end of the conduit. The cables  56  are attached to the wireless transmitter  58  which is secured to and supported on the upper surface of the horizontal portion  44  of angle frame  42 . The conduit branches  52  are separated by a distance substantially the same as the vertical spacing between the adjacent temperature sensors  30  supported on the rear duct assembly  10  of  FIG. 1 . This spacing enables the temperature and relative humidity sensed at sites located at the front and rear of the rack mount enclosure to be respectively at the same height. 
         [0026]      FIG. 5  illustrates a typical rack enclosure  60  which includes a body portion  61  with open front and rear surfaces. At the rear a planar rear door  62  is often mounted which includes a perforated steel or louvered steel surface to present a minimal obstruction to air flow. One option is to not mount a rear door and thereby minimize or virtually eliminate air flow restriction. The front door  64  may be a planar member, similar to that shown as the rear door of  FIG. 5 , which has extensive louvered or perforate surface areas or may be of a convex configuration as shown in  FIG. 1  wherein one or more of the front surfaces  65 ,  66  and  67  include substantial perforate surfaces to afford minimal air flow resistance. The convex structure also offers the opportunity to utilize extensive open areas with an internal baffle structure to create large inlet air passages and minimize air flow resistance while precluding line of sight access through the door. As illustrated in  FIG. 5 , the front door is convex with a front surface  66  that is entirely removed except for marginal flange surfaces  68 . A vertical column is mounted within the door which divides the air flow, interrupts the line of sight into the enclosure, and provides the opportunity to present a rigid flow directing surface on the center column outwardly facing surface and a sound attenuating surface facing the rack mount enclosure. 
         [0027]    When operating to determine physical characteristics such as heat flow, the apparatus including the duct assembly of  FIG. 1  and the entry air sensing assembly of  FIG. 4  are mounted respectively at the rear wall outlet and the front door air entry of the rack mount assembly such as that of  FIG. 5 . The entry air sensing assembly of  FIG. 4  is magnetically attached by securing the magnet  43  to the door upper surface  70  ( FIG. 5 ). To minimize the intrusion into the inlet air flow path, the inlet air assembly  40  is attached to the rack mount enclosure door  64  with the vertically extending conduit  48  adjacent the door flange  71  and the conduit branches  52  extending across the opening in door surface  66 . Thus, only the conduit branches and the sensor elements which they support are disposed in the air flow path. 
         [0028]    The duct assembly  10  of  FIG. 1  is mounted at the rear surface of the rack mount assembly  60  with the flexible gasket material abutting the rack rear door or the rack mount cabinet marginal wall portions or flanges if a rear door is not present. The duct assembly  10  is secured to the rack mount cabinet  60  by the continuous magnets  29  in the flexible flaps  28  that overlie the steel cabinet surface portions. The temperature and relative humidity sensor leads are wired directly to the processor and display unit  72  mounted on the duct assembly top wall  14 . Likewise, the tubes connected to the pitot openings  35  within the duct portions are connected to the processor  72  to enable the average pressure encountered in each duct portion to be simultaneously sensed. The wireless connection between the processor  72  and the wireless transmitter  58  enables the simultaneous determination of inlet and outlet temperatures and relative humidities and the pressure differential to optimize the accuracy of the heat flow determination. 
         [0029]      FIG. 7  shows the wireless receiver and calculation unit  72  which is mounted on the rear duct assembly  10 . Calculation unit  72  receives entry air temperature and relative humidity values wirelessly from the sensor and transmitter  58 . All sensors could be directly wired to the calculation unit  72 , but use of a wireless connection from the front sensors makes the installation of the equipment more flexible and adaptable to rack assemblies of varying size and inlet air opening configuration. Sensed values of rear exit air temperature and relative humidity are received from wires connecting sensors in the ducts which extend to the calculation unit through the conduit  34  which is attached at the opening  74 . The tubes  38  from the respective pitot assemblies in the duct portions  18 ,  19  and  20  are connected to calculation unit  72  through the individual openings  76 . The receiver and calculation unit  72  includes a display screen  78  which displays the sensed measurements and calculated results derived therefrom. The screen  78  also includes “touch screen” controls for turning the equipment on and off and making necessary adjustments such as the duration of the time out period cycles of calculation and the refresh of the displayed results. 
         [0030]      FIG. 8  is a flow chart showing the sequence of operations within the calculation unit  72  which generate and display measurements and results based on values sensed within the rack enclosure front input air flow and the rear exhaust air flow. At box  81  inlet air characteristics are sensed including temperature and relative humidity at each of the top, middle and bottom locations and wirelessly transmitted from the transmitter  58  mounted on the front assembly  40  to the receiver and calculation unit  72  mounted on the rear duct assembly  10 . At box  82  inlet air characteristics, including relative humidity, temperature and pressure sensed at each of the top, middle and bottom duct portions  18 ,  19  and  20  are received at the receiver and calculation unit  72 . At box  83  the air flow rates at the top, middle and bottom are calculated using the sensed AP multiplied by (p, which is the factor representing the air flow which occurs per unit of the pressure difference sensed. The temperature differences between inlet and outlet air flows are determined at box  84 . At box  75 , the heat loads within the top, middle and bottom air flows are established using the air flow, specific heat (C p ), density (p) and temperature difference. Finally, the total heat loads and air flows are determined (box  86 ) and all measured and calculated values are displayed (box  87 ). Before recycling the calculation cycle and refreshing the display of the measured and calculated values, a time out or wait time is interposed (box  88 ). 
         [0031]      FIGS. 9 and 10  illustrate an alternative structure for sensing the air temperature and relative humidity of the entry air at the front of the rack mount enclosure.  FIG. 9  is a front elevation of the front frame  90  and  FIG. 10  is a section view taken along line XX on  FIG. 9 . A rectangular tubular frame  91  supports the front wall  92 , top wall  93 , bottom wall  94 , and side walls  95 ,  96 . Front wall  92  surrounds an opening, defined by edge surfaces  97 , and provides an enlarged open area calculated to cause minimal resistance to air flow to the front openings of the a rack mount enclosure to which the front frame  90  is attached. Side walls  95  and  96  are secured about the vertical elements of frame  91  respectively and are spring biased toward one another such that the terminal edge flap portions  98  are clamped against the side wall surfaces of a rack mount enclosure to which the front frame  90  is to be attached. Similarly, the top wall  93  and bottom wall  94  are pivotally secured to the horizontal portions of tubular frame  91  and are spring biased toward one another to enable the edge flap portions  98  to be clamped against the upper and lower wall surfaces of a rack mount enclosure to which the frame is to be secured. A flexible web portion  100  is connected between the walls and the edge of the adjoining top or bottom wall to close the openings between adjoining wall portions while allowing the limited pivotal motion of the respective wall with respect to the tubular frame  91 . A tubular conduit member  101  is secured to the tubular frame  91  between the top and bottom horizontal portions. Tubular conduit  101  includes branches  102  which support relative humidity sensors  103  and thermocouples  104  for sensing temperature. The tubular conduit  101  supplies a conduit for the cables  105  which lead from the sensors to the wireless transmitter unit  58  (mounted on the top wall). Flow partitioners  106  are supported on tubular frame  91  and positioned between adjacent locations at which temperature and relative humidity are sensed. The flow partitioners  106  are also positioned to be substantially aligned with the flow partitioners  22 ,  23  carried by the rear duct assembly  10  ( FIGS. 1 and 2 ) when both front and rear assemblies are mounted on a rack mount enclosure. 
         [0032]    The use of the front frame of  FIGS. 9 and 10  with the rear duct assembly  10  of  FIGS. 1 and 2  enables both the inlet air flow and the outlet air flow to be stratified vertically to enhance vertical isolation of air flows and implement better analysis of variations of heat loads within the rack mount enclosure. 
         [0033]    The foregoing description of embodiments of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. It is intended that the scope of the invention be limited not by this detailed description, but rather by the claims appended hereto.