Abstract:
An arrangement of apparatus for the measurement of the quantity amount of ice in an ice thermal storage system having a storage tank with a storage fluid and a cooling coil assembly therein, and the method for measuring such ice quantity, which apparatus includes a means to provide an uplift force to the coil assembly and, means for measurement of the vertical displacement of the coil in the storage tank and means for relating the vertical displacement of the cooling coil assembly to the quantity of ice on the cooling coil assembly, and further noting a specific uplifting force assembly for use in such storage tanks.

Description:
This application is a continuation-in-part of U.S. patent application Ser. No. 09/603,400, filed on Jun. 26, 2000, now U.S. Pat. No. 6,298,676 and entitled “Ice Thermal Storage Control”, the complete disclosure of which is herein incorporated by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to ice thermal storage systems and more particularly teaches an improved method and apparatus for measuring the amount of ice present on an ice thermal storage heat exchanger, such as a tubular coil assembly. 
     Ice thermal storage equipment of the type which forms ice during off peak energy periods and then makes the ice available as a supply of cold or low temperature fluid for space conditioning, and the like, is known in the art. The ice thermal storage equipment may be broadly classified as internal melt systems and external melt systems. One form of thermal storage equipment and external melt system transfers a coolant liquid, such as brine or ethylene glycol solution, through a coil assembly immersed in a tank of storage liquid to be frozen, which liquid may for example be water. The coil assembly is usually a serpentine configuration of bent tubing with multiple tube runs nested in the tank and storage liquid. Multiple coil assemblies are usually packed in parallel within the tank. The coil assemblies are connected between inlet and outlet headers for receipt and discharge of the coolant liquid from and to one or more heat exchangers or chillers, which cool the coolant fluid during the ice production cycle. Although the use of the coolant liquid has been noted as a brine solution, it is noted that the coolant liquid could be a refrigerant, such as R-22 or ammonia. 
     During the ice-production cycle, coolant liquid, such as brine, at a temperature below the solidification point of the storage liquid within the pool is continuously produced by mechanical refrigeration or other means in a heat exchanger, sometimes referred to as a chiller. The low-temperature coolant is transferred to an inlet header, through the coil assemblies and discharged from the outlet header for return to the chiller. The storage liquid in the tank is frozen on the tube outer walls in the form of surrounding envelopes and gradually develops as a substantial thickness of frozen liquid, usually ice. There is a volume of the storage liquid in the tank, which remains as a liquid. During recovery of the stored thermal energy, the chilled storage liquid is withdrawn from the tank and communicated to a downstream cooling coil or heat exchanger for use in cooling operations, such as air conditioning or food processing. Thereafter, the spent or warmed storage liquid is returned to the tank to be cooled and further used for cooling operations. 
     Efforts have been made to measure or quantify the degree of freezing of the liquid in the tank. The underlying reasons for the desire to quantify the frozen liquid is to know the amount of stored cooling capacity that exists in the tank. One method of ice build up measurement positions a coil on springs and employs load cells to sense the uplifting force of the coils, which are restrained from vertical movement. The intent of this apparatus is to relate the uplifting force to the quantity of ice on the coil. The precise structure and schematic drawings are not available in a published format for this load cell system. 
     Current means used to measure or monitor the ice build up on the coil assemblies in the tank liquid pool have included visual inspection of the ice at the surface, which is not considered to be efficient or measurable. Another ice-measurement method uses a fluid level monitor, which operates on the principle that a pound of ice occupies more volume than a pound of water. These devices are not relied upon in cases where the hydraulic system is not a closed loop. In addition, ice thickness measurements are provided in an external-melt system by utilization of electronic probes noting the change in conductivity on the tubes as the ice develops. However, the probes used in this method have proven to be fragile. 
     SUMMARY OF THE INVENTION 
     The present invention provides a method for identifying the amount of ice build up in a storage tank and thus, the available cooling capacity, and apparatus for measuring the ice build up in a pool of liquid by means providing an uplifting force and a displacement sensing arrangement. More specifically, it is desired to measure the mass of ice formed in a liquid pool of an ice-thermal storage system. The mass of ice is measured as a function of the vertical movement of the surface of the coil assembly. The vertical movement may be measured electronically or manually. 
     The ice mass measurement allows the ice-forming or chilling cycle to be stopped at the one hundred percent of the design or any desired ice mass in the tank, which enhances the cooling operation of the thermal storage system. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     In the several figures of the drawing, like reference numerals identify like components, and in those drawings: 
     FIG. 1 is an oblique view in partial section illustrating an exemplary prior art coil assembly in a thermal storage tank; 
     FIG. 2 is an end view of stacked coil assemblies and their headers with the spring assembly interposed between the top two coil assemblies; 
     FIG. 3 is an exemplary schematic of a control circuit for the ice thermal storage system; 
     FIG. 4 is an enlarged view of the placement of the spring assemblies on a support channel for the ice coils in the storage tank; 
     FIG. 5 illustrates a partially exploded elevational view of the housing for a coil spring assembly; 
     FIG. 6 is a phantom outline illustration of the elevational view in FIG. 5; 
     FIG. 7 is an exploded view of the coil spring assembly in FIG. 5; 
     FIG. 8 is a partially exploded view of the spring assembly of FIG. 5 with Belleville washers; 
     FIG. 9 is a phantom outline illustration of the elevational view in FIG. 8; 
     FIG. 10 is a schematic outline of an exemplary ice thermal storage unit; 
     FIG. 11 graphically illustrates the percentage of ice in the storage tank as a function of the vertical coil movement in inches; and, 
     FIG. 12 is an enlarged view of the placement of the spring assemblies between brackets at the comers between individual coil assemblies. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A basic or exemplary thermal storage unit  10  is shown in FIG. 10 with chamber  14  of storage tank  12  filled with a storage fluid, such as water. A coil arrangement  16  is nested in chamber  14  and is coupled to a glycol chiller or direct refrigerant system  18 . In an external melt system a chilled coolant fluid, such as ethylene glycol, is communicated through coils  16  for chilling and freezing the storage fluid in chamber  14 . Ice water pump  26  is connected to pool  14  by conduit  28  for communication of the chilled storage fluid in chamber  14  to a cooling coil  30  through conduit  22  for utilization of the stored cooling capacity for a low temperature air mixing terminal unit  20 . The spent cooling fluid from cooling coil  30  is recirculated to chamber  14  through return conduit  24 . Cooling coil  30  may be a heat exchange unit for an air conditioning unit, as an example. System  10  in FIG. 10 is merely an exemplary illustration of the use and operation of a thermal storage unit. 
     Coil arrangement  16  in FIG. 10 is noted as a single serpentine coil or flow path in chamber  14  with wide vertical gaps between the adjacent horizontal runs of the coil. However, exemplary tubes  32  of a typical coil arrangement  16 , as shown in FIGS. 1 and 2, have a more usual arrangement of a tight array of tubes  32  extending between headers  46  and  48 . Coil arrangements  16  are generally designed with an ice mass or volume that is considered to be a design or desired ice buildup. 
     In FIG. 1, each vertical coil arrangement  16  has lower tube bundle  40  and upper tube bundle  42 , although it is known that the number of vertical tube bundles may be greater than two. Tube bundles  40  and  42  in FIG. 1 are each nested in coil frame arrangement  44  with upper coil header  46 , lower coil header  48 , and, vertical framing members  50  and  52  as noted. The noted framing with headers  46  and  48 , and vertical framing members  50  and  52  provides structure to the ordered array of tube bundles within chamber  14  of tank  12 . Tube spacers, not shown but known in the art, are positioned between the adjacent tubes  32  within each bundle to maintain the horizontal and vertical location of tubes  32  within tube bundles  40  and  42 . 
     Coil stacks  51  and  53  in FIG. 2 each have three tube bundles  40 ,  42  and  43  vertically stacked. More specifically, each pair of tube bundles  40 ,  42  and  43  of coil stacks  51  and  53  is coupled by splice plates  55  and  57 . Each tube bundle  40 ,  42  or  43  has first vertical support  50  and second vertical support  52  as well as upper coil header  46  and lower coil header  48  horizontally extending between first and second vertical supports  50  and  52 . In this illustration, spring assembly  70  is shown at an outer corner of tube bundle  43  of first coil stack  51  and second spring assembly  72  is noted at the outer corner of tube bundle  43  of second coil stack  53 , which spring assemblies  70  and  72  are nested on comers or corner brackets of respective vertical supports  50  and  52 . Spring assemblies  70  and  72  provide a force directing tube bundles  43  vertically upward, which tube bundles are free to move vertically at least at one end of tube bundle  43 . 
     The arrangement of spring assemblies  70  and  72  are more clearly illustrated in FIG. 4 with spring and channel arrangement  60 . In this figure, channel or I-beam  62  may be provided as a support for spring assemblies  70  and  72 , which channel  62  has upper surface  64 , a first end  66  and a second end  68 . A first spring assembly  70  is positioned on upper surface  64  at first end  66  and a second spring assembly  72  is positioned on upper surface  64  at second end  68 . The corner bracket or lower edge of vertical frame member  50  or  52  of tube bundle  43  is positioned on the respective upper ends  74  and  76  of spring assemblies  70  and  72 . Channel  62  is provided in this figure as support for springs  70  and  72 . Within the context of FIG. 2, this arrangement could be provided for support at the base of coil stacks  51  and  53 , which might be the bottom of tank chamber  14  in an alternative arrangement. It is thus apparent that the location of springs  70  and  72  may be located to support any number of the tube bundles in a coil stack arrangement having vertical freedom above such springs. 
     The specific structure of spring assemblies  70  and  72  is illustrated in FIGS. 5,  6  and  7 , which shows spring assembly  70  in exploded views. As spring assemblies  70  and  72  are similar only spring assembly  70  will be described but the description will be applicable to spring assembly  72 . Spring assembly  70  is a stacked arrangement of components. Lower housing  78  has first metal pipe segment  84  with passage  81 , and second metal pipe segment  82  with passage  89 , and an insulator collar  80  between insulator cores  83  and  85 . Insulator core  83  mates with passage  81  and second insulator core  85  mates with passage  89  to capture collar  80  between upper housing segment  82  and lower housing segment  84 . Annular disc  87  with aperture  91  is positioned between third housing segment  93  with passage  95  and second housing segment  82 . Second insulator core  85  has aperture  79  alignable with disc aperture  91 . Coil spring  88  is positioned about rod  86  and extends to passage  95  in lower housing  78 . Upper housing  90  has upper pipe segment  92  with passage  94  and lower pipe segment  101  with passage  103 . Insulator core  105  has passage  107 , second upper insulator core  109  has passage  111 , and second insulator collar  113  is positioned between insulator cores  105  and  109 . Insulator core  105  is mated into passage  94  of pipe segment  92  and lower insulator core  109  is mated with passage  103  of lower pipe segment  101  with collar  113  secured between segments  92  and  101 . Second annular disc  115  has aperture  117  alignable with insulator core aperture  111  and mates with rod  86 . Annular disc  115  is secured to the bottom of housing segment  101  for bearing against spring  88  with rod  86  movable in the aligned apertures  111 ,  117  and  107 . In this illustrated arrangement of spring  70 , lower housing  78  and upper housing  90  are shown as generally cylindrical with round cross-sections, but housing shape is not a limitation. 
     An alternative spring arrangement  100  is illustrated in FIGS. 8 and 9 within upper housing  90  and lower housing  78  of spring assembly  70 . In this arrangement, a plurality of Belleville washers are stacked on rod  86  in passage  95  to provide the uplifting force against disc  115  and upper housing segment  90  similar to the uplifting force of coil spring  88 . Other uplifting means may provide the uplifting force to be applied to the tube bundles of coil assembly  16 , such as pneumatic, hydraulic or elastomeric apparatus. 
     FIG. 12 illustrates an alternative arrangement of spring assembly  70  where upper corner bracket  162  and lower corner bracket  164  are utilized to constrain and support spring assembly  70 . Framing members  50  in this figure have front face  166  and side face  168 . Angle bracket  170  is formed around lower header  48  at lower end  172  of the upper framing member  50  and angle bracket  174  is formed around upper header  46  at upper end  176  of the lower framing member  50 . Upper corner bracket  162  has vertical wall  178  and horizontal wall  180 , which are joined at junction  182 . Vertical wall  178  is secured to front face  166  of upper framing member  50  and angle bracket  170  by means known in the art such as brazing, welding or riveting. Similarly, lower corner bracket  64  has vertical wall  184  and horizontal wall  186 , which are joined at junction  188 . Vertical wall  184  is secured to front face  166  of lower member  50  in proximity to angle bracket  174 . 
     In this figure, spring-assembly lower segment  84 , insulator  80 , second segment  82 , upper segment  92 , second insulator  113  and lower segment  101  are all noted with a rectangular shape in contrast to the circular shape of the elements in FIGS. 5 and 6. However, shape is not a limitation to the function and operation of the various segments of spring assembly  70 . 
     In this alternative arrangement, coil spring assembly  70  is positioned and operable between upper-bracket horizontal wall  180  and lower-bracket horizontal wall  186 . A similar upper and lower bracket arrangement would be provided at the opposite ends of headers  46  and  48  for coil assembly  72 , which is similar to coil assembly  70 , and thus has not been specifically described. The assembly in FIG. 12 is similar to the assembly in FIG. 4, but is horizontally displaced to reduce the vertical height of a coil assembly such as the assembly shown in FIG.  2 . Further, it is recognized that lower bracket  164  could be mounted in chamber  14  on the floor or base of storage tank  12  in the case where there is a single coil assembly in tank  12 . 
     In FIG. 1, sensor  130  is noted as mounted at upper edge  132  of tank  12 . Sensor  130  is utilized to note the upward movement of coil assembly  42  as ice is developed on tube  32 . The upward movement is the result of a balance of forces from at least the following force components: (1) the weight of coil assembly  16  above spring assemblies  70  and  72 , whether such coil assembly is one or more tube bundles; (2) the weight of the cooling fluid in tubes  32  of the coil assembly above spring assemblies  70  and  72 ; (3) the upwardly directed force from spring assemblies  70  and  72 ; (4) the weight of the ice formed on tubes  32  of the coil assembly  16  above spring assemblies  70  and  72 ; and, (5) the buoyant force from the ice formed on tubes  32  of coil assembly  16 . It is recognized that these forces will be dependent upon the storage fluid in chamber  14  continuously covering coil assembly  16 , and that these resultant forces will vary with the mass of fluid in the tubes  32  and the amount of ice formed on tubes  32 . The tube bundle, or bundles,  40 ,  42  and  43  above spring assemblies  70  and  72  must be free to move vertically. Typically this may be accommodated by various means including flexible connections at headers  46  and  48 , or by measurement at a single end of the tube bundle under consideration. 
     Sensor  130  is not an active element in thermal storage unit  10 , but merely monitors the upward shift or displacement of coil assembly  16 , which is translated into a percentage of ice growth in tank  12 . The specific type of sensor  130  is a design choice, but an example of such a sensor is a displacement transducer Series  240  from Trans-Tek Incorporated. Further, the upward displacement may be measured manually for conversion to a percentage of ice buildup in chamber  14  by such means as a nomograph, a chart, or a graphical illustration. 
     An example of such graphical conversion chart is noted in FIG. 11 where the percentage of ice growth, as compared to the full design capacity, is noted as a function of the displacement of coil assembly  16 . The correlative nature between vertical movement of coil assembly  16  and the growth of ice as a percentage of theoretical or design ice capacity is noted in FIG.  11 . In this graphical display, movement of coil assembly 16 up to 0.35 inch from a zero or reference position is correlated to the expected rate of growth of ice per inch of coil assembly rise. In this case, the change in position of the free-floating coil assembly  16  from its reference or as-assembled position is being monitored by sensor  130 . The specific amount of change in coil position for each coil design and tank structure may vary but can be calibrated. The change in vertical position of coil assembly is a reflection of the buoyancy associated with the quantity of the ice growth from the storage liquid in chamber  14 . 
     In the operation of the exemplary external melt system of FIG. 10, thermal storage system  10  has an ice buildup cycle and an ice melt cycle for recovery of the stored thermal energy. As noted above, an external melt cycle chilled fluid from chamber  14  would be transferred by pump  26  to a downstream cooling coil  30  and thereafter returned to chamber  14  for reuse. During the ice buildup cycle there is a buoyancy effect upon coil assembly  16  as the density of the ice is less than the density of the water. This buoyancy effect acts in combination with the springs to produce vertical movement of the coil assembly  16 . 
     In the present case, a single coil assembly  16 , and more specifically tube bundle or bundles  40 ,  42  and  43 , is constrained against horizontal movement, but rests on calibrated spring assemblies  70 ,  72  allowing it to move vertically. In FIG. 1, the vertical movement is monitored by a calibrated transducer  130 , which communicates an output signal over a line  140  to a signal receiver, such as central processing unit, CPU,  142  in FIG.  3 . CPU  142  is operable to receive the signal from transducer  130  and compare it to empirical data indicative of the percentage of ice buildup in tank  12 . Further, CPU  142  may provide an output signal to a controller  144  over line  146 , which may provide direct control to refrigeration system  18  over line  150  to initiate ice buildup or shut down refrigeration system  18  after the desired ice buildup in tank  12 . In this exemplary control arrangement, it is considered that the empirical data for the control cycle is available and provided to control device  142 , which data may be calculated or experimental. 
     The style of spring assembly  70  and  72  may utilize coil springs as shown in FIGS. 5,  6  and  7 , or Belleville washers as shown in FIGS. 8 and 9, but the output signals for CPU  142  will require calibration for the style of spring assembly, the specific transducer assembly  130  and the amount of expected displacement of coil assembly  16 . The specific signal receiver and control circuit can be varied to accommodate available equipment, and the circuit of FIG. 3 is merely exemplary and not a limitation. Alternatively, the amount of vertical displacement may be measured manually and the relationship to the amount of ice buildup in chamber  14  may be directly compared to empirical data and read from a nomogram, chart or graph. 
     While only specific embodiments of the invention have been described and shown, it is apparent that various alterations and modifications can be made therein. It is, therefore, the intention in the appended claims to cover all such modifications and alterations as may fall with the scope and spirit of the invention.