Abstract:
A system for operating a cooling loop associated with a space and including at least one cooling coil and cooling fluid supply, the system including: a grain sensor positioned with respect to the space and providing a value indicative of the amount of moisture in the space; at least one pump fluidly coupled across the coil; at least one flow limiter fluidly coupled to the coil and limiting a flow of cooling fluid between the cooling fluid supply and the coil; and at least one controller electrically coupled to the flow limiter; wherein, the at least one controller selectively operates the flow limiter responsive to the value indicative of the amount of moisture in the space and the pump re-circulates cooling fluid independent of the cooling fluid supply dependently upon the flow limiter.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This is a continuation of U.S. patent application Ser. No. 12/315,190, filed Nov. 8, 2009, entitled “System and Method for Operating a Cooling Loop”, which claims priority to U.S. Provisional Patent Application No. 61/004,523, filed Nov. 28, 2007, entitled “System and Method for Operating a Cooling Loop”, the entireties of which are expressly incorporated herein by reference. 
     
    
     BACKGROUND 
     Field of the Invention 
       [0002]    The present invention relates generally to heating and cooling systems, and more particularly to heating and cooling systems incorporating a cooling coil and their operation. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0003]    Understanding of the present invention will be facilitated by consideration of the following detailed description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings, in which like numerals refer to like parts and in which: 
           [0004]      FIG. 1  illustrates a schematic representation of a system incorporating a cooling coil; 
           [0005]      FIG. 2  illustrates a schematic representation of a system incorporating a cooling coil according to an embodiment of the present invention; and 
           [0006]      FIG. 3  illustrates a schematic representation of a system incorporating a cooling coil according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0007]    It is to be understood that the figures and descriptions of the present invention have been simplified to illustrate elements that are relevant for a clear understanding of the present invention, while eliminating, for purposes of clarity, many other elements found in typical heating and cooling systems. However, because such elements are well known in the art, and because they do not facilitate a better understanding of the present invention, a discussion of such elements is not provided herein. The disclosure herein is directed to all such variations and modifications known to those skilled in the art. 
         [0008]      FIG. 1  shows a schematic representation of a chilled water system  10 . System  10  receives chilled water via a supply line  12 , and returns water that has been used to cool air  14  via line  16 . Chilled water supply line  12  and chilled water return line  16  are interconnected via cooling coil  18 . Basically, chilled water is supplied to system  10  via supply line  12 . Supplied chilled water circulates through coil  18 , where an air/water heat exchange occurs, leading to air  18  forced through coil  14  being cooled and the supplied chilled water being warmed. The warmed chilled water from coil  18  is returned for re-chilling by line  16 . Chilled air  14  may be supplied to a space  30 , such as a conventional space within a building serviced by system  10 . Chilled water supply and return lines, and cooling coils, are well known to those possessing an ordinary skill in the pertinent arts. 
         [0009]    Water flow through coil  18  is controlled via valve  20 . While valve  20  is shown to be in line  14 , it may be analogously situated in line  12 . Either way, valve  20  may be used to throttle chilled water flow through coil  18 , thereby controlling the cooling of air  14 . The position of valve  20 , and hence amount of cooling provided to air  14 , is controlled by temperature controller  24 , which is responsive to a conventional control algorithm (e.g., proportional-integral, or proportional- integral-derivative) and a temperature transmitter or sensor  22  and setpoint supplied by a setpoint generator  28 . Temperature transmitter  22  provides a signal indicative of the temperature of air  14  after cooling by coil  18 . Setpoint generator  28  provides a signal or value indicative of a temperature setpoint responsively to a percent relative humidity sensor  26 . Sensor  26  provides a signal indicative of the percent relative humidity of space  30 . 
         [0010]    Controller  24  compares the temperature of air  14  to the setpoint, and modulates the position of valve  20  accordingly. In essence, if air  14  is too warm, valve  20  may be opened to provide more chilled water through coil  18 , thereby providing more cooling. If air  14  is too cold, valve  20  may be partially closed, to provide less chilled water through coil  18 , thereby providing less cooling. By way of non-limiting example only, a typical setpoint for air  14  temperature may be around  52  degrees Fahrenheit to around  58  degrees Fahrenheit, depending upon the relative humidity of space  30  and operator preference. Air  14  may be reheated prior to introduction to space  30 , to around 70 degrees Fahrenheit to around  72  degrees Fahrenheit, depending upon operator preference. 
         [0011]    Such a configuration may be subject to certain shortcomings. For example, as chilled water flow through coil  18  lessens, flow may become laminar in nature. In such an event, heat exchange with air  14  may become significantly reduced, and a threshold condition effected between where proper air  14  cooling does and doesn&#39;t occur. This leads to inefficient cycling of system  10 . 
         [0012]    Referring now to  FIG. 2 , there is shown a schematic representation of a system  100  according to an embodiment of the present invention. Like elements in  FIGS. 1 and 2  have been labeled with like reference for non-limiting sake of explanation. 
         [0013]    System  100  additionally includes a coil re-circulating line  105 . While line  105  is shown in conjunction with a single coil  18 , it may analogously be coupled across a plurality of cooling coils, for example. Either way, recirculating line  105  connects chilled water return line  16  to chilled water supply line  12 . In the illustrated embodiment of  FIG. 2 , recirculating line  105  connects to return line  116  upstream from valve  20 . 
         [0014]    In the embodiment of  FIG. 2 , recirculating line  105  includes a serially coupled pump  110  and check valve  120 . Pump  110  serves to reintroduce warmed chilled water from coil  18  return line  14  to supply line  12 , and coil  18 . Pump  110  operates responsively to variable frequency drive (VFD)  130 . Pump  110  and drive  130  may, in certain embodiments, be selected to provide around 120% of the full- load, design coil flow of coil  18 . Check valve  120  serves to prevent chilled water from supply line  12  bypassing coil  18 . 
         [0015]    For non-limiting purposes of explanation only, it should be understood that cooling coils have a design temperature differential (ΔT design ) between the chilled water supply line  12  and chilled water return line  16 . The ΔT design  of a cooling coil is function of the original design of the entire chilled water system. An exemplary ΔT design  of a cooling coil may be around  10  degrees Fahrenheit to around  15  degrees Fahrenheit. Coil  18  operates efficiently (e.g., may be characterized as efficiently exchanging heat between chilled water and air) at ΔT design . As the actual temperature differential across a cooling coil (ΔT actual ) varies from ΔT design  though, the coil efficiency may degrade. This may result from a number of factors, including the occurrence of laminar flow through coil  18 , for example. 
         [0016]    Referring still to  FIG. 2 , system  100  also includes temperature transmitters or sensors  140 ,  150 . Temperature transmitters  140 ,  150  may take the form of commercially available platinum tip resistance temperature detectors (RTD&#39;s), for example. Temperature transmitter  140  provides a signal indicative of the temperature of water in chilled water return line  16 , after passing through cooling coil  18 . Temperature transmitter  150  provides a signal indicative of the temperature of water in chilled water supply line  12 , prior to passing through cooling coil  18 . While temperature transmitter  150  is shown in the embodiment of  FIG. 2  downstream from recirculating line  105 , it may optionally be positioned upstream from recirculating line  105  in supply line  12 . 
         [0017]    System  100  also includes a temperature controller  160  coupled to temperature transmitters  140 ,  150 . Controller  160  determines an actual temperature differential ΔT actual  across coil  18  and compares it to ΔT design  of coil  18 . Where controller  160  determines ΔT actual &lt;ΔT design , it may signal VFD  130  to slow pump  110 . Conversely, where controller  160  determines ΔT actual &gt;ΔT design , it may signal VFD  130  to speed pump  110 . In certain embodiments, controller  160  may take the form of a commercially available, digital proportional-integral controller. 
         [0018]    Referring still to  FIG. 2 , system  200  also includes a space sensor  170 . Space sensor  170  detects the relative humidity of space  30  (analogously to sensor  26 ), and additionally the temperature of space  30 . Space sensor  170  is coupled to a grain controller  180 . 
         [0019]    Grain controller  180  serves to calculate the absolute humidity in space  30  responsively to sensor  170 , such as by using a conventional psychometric-based approach. The absolute humidity may be expressed in grains of moisture/pound of dry air, for example. Regardless, grain controller  180  utilizes the determined absolute humidity of space  30 , together with a predetermined desired absolute humidity, to establish a setpoint for controller  24 . By way of non-limiting example, the desired absolute humidity may be around 64.5 grains of moisture/pound of dry air. Where the controller  180  determined absolute humidity is greater than 64.5 grains of moisture/pound of dry air, it may increase the temperature setpoint of controller  24 . Analogously, where the controller  180  determined absolute humidity is less than 64.5 grains of moisture/pound of dry air, it may decrease the temperature setpoint of controller  24 . As will be understood by those possessing an ordinary skill in the pertinent arts, the absolute humidity of space  30  is temperature independent, whereas the relative humidity of space  30  utilized in system  10  to determine a setpoint is temperature dependent. 
         [0020]    In certain embodiments of the present invention, space sensor  170  may take the form of a temperature and humidity transmitter, such as those commercially available via Rotronic Instrument Corp., of Huntingdon, N.Y., and controller  180  may take the form of a commercially available, digital proportional-integral controller. 
         [0021]    Controller  24  may throttle valve  20  in a manner analogous to system  10  responsively to air  14  temperature as determined by sensor  14  and the setpoint provided by grain controller  180 . In certain embodiments of the present invention, temperature transmitter  22  may take the form of a commercially available platinum tip RTD&#39;s, and controller  24  may take the form of a commercially available, digital proportional-integral controller. 
         [0022]    Referring now to  FIG. 3 , there is shown a schematic representation of a system  200  according to an embodiment of the present invention. Like elements in  FIGS. 1 ,  2  and  3  have been labeled with like reference for non-limiting sake of explanation. 
         [0023]    Different from the embodiment of  FIG. 2 , system  200  includes an additional valve  210 . Controller  160  throttles flow through recirculating line  105  to achieve a similar result as the embodiment of  FIG. 2 . 
         [0024]    It will be apparent to those skilled in the art that modifications and variations may be made without departing from the spirit or scope of the invention.