Abstract:
The present invention is a system that automatically controls the selection, start-up and operation of primary and secondary heating towers chosen from an array of heating towers having varying physical and thermal sizes. The automatic control is implemented via a programmable logic controllers (PLC). The PLC provides independent control for each heating tower irrespective of the tower being a primary or secondary heating source. Should the demand for heated water upon the primary heating tower increase to a rate that the primary tower cannot satisfy, the PLC maintains the operation of the primary tower and at the same time starts the secondary heating tower to meet the increased hot water demand. Once the demand has dropped to rates that the primary heating tower can once again maintain, the secondary tower is disabled.

Description:
This application is based on U.S. Provisional Application No. 60/274,454 filed on Mar. 9, 2001. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to heating towers that provide heated water to satisfy a predetermined flow demand and more particularly, to a system that selects primary and secondary heating towers from a plurality of heating towers to satisfy the flow demand. 
     2. Background of the Prior Art 
     Control systems that start-up, operation and shut-down heating towers are commonly used. The control technologies use electrical relays with discrete components, programable logic controllers (PLC) and computers. The systems developed to control the heating towers include the use of dedicated primary and secondary heating towers to satisfy flow demands at a predetermined temperature. Generally, the dedicated secondary heating tower starts and stops correspondingly with flow demand or based upon other predetermined parameters. Dedicated primary heating towers are not used as secondary heating towers even if the primary tower would be less expensive to operate as a secondary tower. Further, irrespective of the wear and time of operation on the dedicated primary towers, a dedicated secondary tower is not used as a replacement for the primary towers. 
     The problem with the prior art heating tower control systems is that the systems do not have the flexibility to select any available tower as either a primary tower or a secondary tower. Not having this flexibility increases the quantity of heating fuel ultimately used to heat liquids (water) required to satisfy flow demand rates. The increased fuel use results from less available turndown ratio for multiple heating towers (turndown being the additive capacity of all heating towers combined divided by the minimum fire capacity-low firing rate of the smallest heating tower). Also, the wear and fatigue that develops upon a primary heating tower in continuous use cannot but distributed to less used towers, but instead increases until the respective dedicated primary tower unexpectedly fails. 
     A need exists for a control system for heating towers that allows any tower of a plurality of heating towers to be selected as either a primary or secondary heating tower. The control system must be able to select single or multiple heating towers as being primary or secondary. Further, the selection of any heating tower for use must be based upon parameters that quantify heating tower wear. Also, the control system must be capable of starting and stopping secondary heating towers based upon flow demand thereby reducing cost for heating the liquid. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to overcome many of the disadvantages associated with control systems for heating towers. 
     A principle object of the present invention is to provide a system that independently controls heating towers irrespective of the tower being a primary or secondary heating source. A feature of the system is that no heating tower is permanently designated as primary or secondary. An advantage of the system is that the turndown ratio, being defined as the maximum high fire (the additive capacity of all heating towers combined)/the minimum fire capacity (low firing rate of the smallest heating tower), is increased thereby reducing fuel consumption when heating liquids (water) to satisfy flow demand. 
     Another object of the present invention is to alternate the selection of primary and secondary heating towers amongst all of the heating towers. A feature of the system is to shut down secondary heating towers when flow demand is such that only the primary heating tower need operate to satisfy the flow demand. An advantage of the system is that fuel consumption is reduced. Another advantage of the system is that operating wear is more evenly distributed amongst all the heating towers. 
     Still another object of the present invention is to select multiple primary and multiple secondary heating towers meet flow demand. A feature of the system selects the heating tower with the smallest heating capacity when satisfying flow demand. An advantage of the system is that operating costs are reduced when satisfying demand. 
     Yet another object of the present invention is to select primary and secondary heating towers with the least wear. A feature of the system is the collection of fatigue or wear parameters for each heating tower including but not limited to inoperable heating towers, running time, number of stops and starts, number of failures (unexpected shutdown), and the time of day with corresponding low and high flow demand. An advantage of the system is that the useful life of all the heating towers is increased. 
     Another object of the present invention is to maintain the operation of a selected primary tower while allowing multiple secondary to stop and start depending upon flow demand. A feature of the system is utilize a secondary heating tower that minimally meets flow demand which exceeds the capacity of the primary heating tower. An advantage of the system is that use of heating fuel to satisfy the flow demand is kept to a minimum. 
     Briefly, the invention provides a control system for multiple heating towers comprising means for selecting at least one of a plurality of heating towers as a primary heating tower; means for starting said selected primary heating tower; means for operating said selected primary heating tower; means for operating at least one of a plurality of heating towers as a secondary heating tower; means for starting said selected secondary heating tower when predetermined demand parameters are required of said selected primary heating tower; and means for operating said selected secondary heating tower. 
     Further, the invention provides a method for heating liquids and distributing operating wear amongst a plurality of heating towers, said method comprising the steps of determining operable heating towers form a plurality of heating towers; determining initial flow demand; determining the temperature that the initial flow demand is to be heated; selecting at least one primary heating tower from said operable heating towers, said selected primary heating tower satisfying initial flow demand at said determined temperature; starting said selected primary heating tower; operating said selected primary heating tower; determining when flow demand has increased beyond the heating capacity of said primary heating tower; selecting at least one secondary heating tower from said operable heating towers, said selected secondary heating tower satisfying increased flow demand at said determined temperature; starting said selected secondary heating tower; and operating said selected secondary heating tower. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other objects, advantages and novel features of the present invention, as well as details of an illustrative embodiment thereof, will be more fully understood from the following detailed description and attached drawings, wherein: 
     FIG. 1 is a flowchart of a system for selecting at least one primary heating tower from a plurality of heating towers in accordance with the present invention. 
     FIG. 2 is a continuation of the flowchart depicted in FIG. 1 in accordance with the present invention. 
     FIG. 3 is a continuation of the flowchart depicted in FIG. 2 in accordance with the present invention. 
     FIG. 4 is a continuation of the flowchart depicted in FIG. 3 in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention is directed to a control system for multiple heating towers and a method for heating liquids and distributing operating wear amongst a plurality of heating towers. The control system may be configured from a myriad of technologies including but not limited to electrical relays, programable logic controllers (PLC&#39;s) and computers. These technologies may control separately or in combination to select, start and operate primary and secondary heating towers. Referring now to FIGS. 1-4, a flowchart of a system for multiple heating towers selects at least one primary heating tower from a plurality of heating towers is depicted. At the start  10 , a person determines customer demand by reading meters  12  that provide continuous measurements of outgoing water flow, or by reviewing instruments  14  that provide water level change in water storage tanks. 
     At decision block  16 , the person decides whether a primary heating tower is to be manually selected. If not, the controlling technology (a PLC for purposes of this Description) is to select the primary heating tower and proceeds to block  22 ; if so, the person starts and operates the selected heating tower via the PLC at  18 , whereupon, the selection procedure ends at  20  and the PLC continuous operating the selected primary heating tower. The starting and operating control circuitry and corresponding methods of control, are well known to those of ordinary skill in the art and need not be detailed in this description. At block  22 , the system examines all heating towers and determines which heating towers are operable and inoperable. The information as to which heating towers are inoperable, is entered via discrete components into the PLC database at block  24 . The database having already been provided with information as to all of the plurality of heating towers, the system will readily determine which heating towers are operable. The PLC then determines the total running hours of operation for each operable heating tower at block  26 ; the hours of operation being input into the PLC data base at block  28  via an electronic timing device, well known to those of ordinary skill, or via manual entry on a periodic bases. 
     At block  30 , the system determines the number of stop and starts of each operable heating tower. The start and stop information being provided to the PLC database at block  32  by one of a myriad components including but not to start-stop buttons, control relays in motor or solenoid circuits, or fuel circuit components that shut off gas flow to the heating towers. At block  34 , the system determines the number of failures (unexpected heater tower shutdowns) past and/or present of each operable heating tower. The failure information being manually entered into the PLC database at block  36 . At block  38 , the system determines the time of day via an internal clock, whereupon, the system at decision block  40  decides if a low flow time of day is present. If not, the system at decision block  42  decides if a high flow time of day is present. If neither a low or high flow time of day is present, the system utilizes flow demand information from the PLC database at block  44 . If either a low or high flow time of day is present, the system preemptively sets a corresponding low or high flow demand rate at blocks  46  and  48 , respective. 
     At block  50 , the system determines the operable heating towers that have the capacity to supply heated liquid (water) at the required flow demand rates at a predetermined temperature. The capacity of each of the plurality of heating tower having been manually entered into the database of the PLC at block  52 . At decision block  54 , the system reviews the capacity of all operable heating towers and decides if more than one heating tower is required to satisfy flow demand. If not, the system at decision block  56  decides if more than one tower has the required capacity, if not, that heating tower is selected as the primary heating tower at block  58 , the heating tower being started and operated via typical circuitry at block  90 . If more than one heating tower has the required capacity, the system at block  60  determines which of the towers has the least running hours. 
     At decision block  62 , the system decides if other towers having sufficient capacity have less than 100 (a number that can vary) hours more run time than the tower with the least running hours. If no other towers has less than 100 hours more run time, the tower with the least running time is selected as the primary heating tower at block  64 , the heating tower being started and operated at block  92 . If there are other towers having less than 100 hours, the system determines at block  66  which of those same towers has the least number of stop and starts. At decision block  68 , the system decides if any of those same towers have less than 20 (a number that can vary) stop-starts more than the tower with the least stop-starts. If no other towers has less than 20 more stop-starts, the system selects the tower with the least stop-starts as the primary heating tower at block  70 , the heating tower being started and operated at block  94 . If there is more than one tower having less than 20 more stop-starts, than the system determines at block  72  which of those same towers has the least number of failures. The tower with the least number of failures is selected as the primary heating tower at block  74 , the heating tower being started and operated at block  96 . 
     The system then reads flow demand at block  75  and proceeds to decision block  77  and decides if flow demand has increased beyond the capacity of the primary heater. If not, the system decides at decision block  79  if flow demand has reduced below the need for multiple heating towers for longer than 10 minutes. If yes, the smallest primary heater is shut down at block  85  and the system control returns to the read flow demand block  75 . If the primary heater should not be shut down, the system returns to block  75  and reads flow demand. At decision block  77 , if flow demand has increased beyond the capacity of the primary heater, the system proceeds to block  83  and determines demand deficiency required to be satisfied by secondary heating tower heating capacity by subtracting maximum heating capacity of the selected primary heating towers from measured output demand for the selected primary heating towers. 
     At decision block  54 , if more than one heating tower is required to satisfy flow demand, the system determines at block  76 , which inoperable heating towers are set for maintenance repair via manual input to the system at  78 . Those heating towers not being scheduled for maintenance repair are considered capable of being started. At block  80 , the system selects the largest heating tower capable of being started as a primary heating tower. At decision block  82 , the system decides if only one more heating tower is required to satisfy flow demand. If so, the system at block  84 , selects the smallest heating tower that, when added to the capacity of the largest heating tower selected, satisfies the flow demand. Both the largest and the smallest heating towers are considered primary heating towers. If at least 2 more heating towers are required to satisfy flow demand, the system selects the next largest heating tower as an additional primary tower at block  98 . The system then returns to decision block  82  to determine once again if only one more heating tower need be selected to satisfy flow demand. Upon selecting the required quantity of primary heating towers to satisfy flow demand, the system then reads flow demand at block  75  and proceeds to decision block  77  to repeat the steps detailed, supra. 
     After the system determines demand deficiency at block  83 , the system proceeds to decision block  100  and after reviewing the capacity of all remaining operable heating towers, decides if more than one heating tower is required to satisfy flow demand. If not, the system at decision block  102  decides if more than one tower has the required capacity, if not, that heating tower is selected as the secondary heating tower at block  104 , the heating tower being started and operated via typical circuitry at block  152 . If more than one heating tower has the required capacity, the system at block  106  determines which of the towers has the least running hours. 
     At decision block  108 , the system decides if other towers having sufficient capacity have less than 100 (a number that can vary) hours more run time than the tower with the least running hours. If no other towers has less than 100 hours more run time, the tower with the least running time is selected as the primary heating tower at block  110 , the heating tower being started and operated at block  154 . If there are other towers having less than 100 hours, the system determines at block  112  which of those same towers has the least number of stop and starts. At decision block  114 , the system decides if any of those same towers have less than 20 (a number that can vary) stop-starts more than the tower with the least stop-starts. If no other towers has less than 20 more stop-starts, the system selects the tower with the least stop-starts as the primary heating tower at block  116 , the heating tower being started and operated at block  156 . If there is more than one tower having less than 20 more start-stops, than the system determines at block  118  which of those same towers has the least number of failures. The tower with the least number of failures is selected as the secondary heating tower at block  120 , the heating tower being started and operated at block  158 . 
     The system then reads flow demand at block  122  and proceeds to decision block  124  and decides if flow demand has increased beyond the capacity of the secondary heater. If not, the system decides at decision block  126  if flow demand has reduced below the need for multiple heating towers for more than 10 minutes. If so, the smallest secondary heater is shut down at block  132  via components in a shutdown circuit (well known to those of ordinary skill) and the system returns to the read flow demand block  75 . If the secondary heater should not be shut down, the system returns to block  122  and reads flow demand. At decision block  124 , if flow demand has increased beyond the capacity of the secondary heater, the system proceeds to block  130  and determines demand deficiency required to be satisfied by another secondary heating tower by subtracting maximum heating capacity of the selected primary and secondary heating towers from measured output demand for the selected primary and secondary heating towers. The system then returns to decision block  100  to repeat the selection steps. 
     At decision block  100 , if more than one heating tower is required to satisfy flow demand, the system determines at block  134 , which inoperable heating towers are set for maintenance repair via manual input to the system at  136 . Those heating towers not being scheduled for maintenance repair are considered capable of being started. At block  138 , the system selects the largest heating tower capable of being started as a secondary heating tower. At decision block  140 , the system decides if only one more heating tower is required to satisfy flow demand. If so, the system at block  142 , selects the smallest heating tower that, when added to the capacity of the largest heating tower selected, satisfies the flow demand. Both the largest and the smallest heating towers are considered secondary heating towers. If at least 2 more heating towers are required to satisfy flow demand, the system selects the next largest heating tower as an additional secondary tower at block  150 . The system then returns to decision block  140  to determine once again if only one more heating tower need be selected to satisfy flow demand. Upon selecting the required quantity of secondary heating towers to satisfy flow demand, the system then reads flow demand at block  122  and proceeds to decision block  124  to repeat the steps detailed, supra. 
     While the invention has been described with reference to the details of the embodiment, these details are not intended to limit the scope of the invention as defined in the appended claims.