Abstract:
In a fuel-fired water heater with a standing pilot burner and a motorized flue damper, a specially designed controller is utilized to prevent overheating of water stored in the tank portion of the water heater caused by the hot combustion gases continuously generated by the pilot burner during standby periods of the water heater in which its main fuel burner is not being fired. The controller has a selectively variable water temperature control set point temperature and is operable to sense both ambient temperature and the tank water temperature and to open the flue damper and/or keep it open, after the main burner is off, in response to the presence for a predetermined continuous time period of a predetermined relationship of at least the selected temperature control set point temperature and the sensed ambient temperature

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The present application claims the benefit of the filing date of provisional U.S. patent application No. 61/720,906 filed Oct. 31, 2012. The entire disclosure of the provisional application is hereby incorporated herein by this reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    In a representatively illustrated embodiment thereof, this invention provides a standing pilot type fuel-fired water heater having incorporated therein a specially designed control algorithm which prevents overheating of water stored in the tank portion of the water heater during non-firing periods of the water heater&#39;s main burner. 
         [0003]    Fuel-fired water heaters typically have a main fuel burner which is ignited by a smaller pilot burner in response to a sensed demand for heating water stored in a tank portion of the water heater. During “standby” periods of the water heater (when its main burner is not firing), a damper in the flue portion of the water heater is normally held in a closed position and opened upon a subsequent firing of the main burner. 
         [0004]    When the water is provided with a “standing” pilot burner, whose flame burns continuously, the possibility exists that the tank water may be undesirably overheated by the hot combustion products continuously generated by the pilot burner. In view of this possibility, a need exists for control apparatus and methods for preventing such overheating. It is to this need that the present invention is primarily directed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]      FIG. 1  is a schematic illustration of a representative fuel-fired, standing pilot type water heater embodying principles of the present invention; and 
           [0006]      FIG. 2  is a logic flow chart functionally illustrating a specially designed flue damper control algorithm operatively incorporated in the water heater. 
       
    
    
     DETAILED DESCRIPTION 
       [0007]    Fuel-fired liquid heating apparatus is schematically depicted in  FIG. 1  and is representatively a fuel-fired water heater  10 , but could alternatively be another type of fuel-fired liquid heating apparatus, such as a boiler, without departing from principles of the present invention. Water heater  10  has the usual insulated tank  12  in which water  14  to be heated may be stored. Underlying the tank  12  is a combustion chamber  16  in which main and pilot burners  18 , 20  are disposed. Pilot burner  20  is a “standing” pilot burner which burns continuously and serves to ignite the main burner  18  when a controller  22  having a pre-programmed microprocessor  23  therein senses that the temperature of the water  14  is below a set point temperature of the controller  22  and responsively opens a main burner fuel supply valve  24 . Fuel (representatively gas) supplied to the main burner  18  is then ignited by the standing pilot flame  26 . 
         [0008]    During standby periods of the water heater  10  (when the main burner  18  is not firing), the standing pilot burner flame  26  continues to create hot combustion gases  28  that rise through a flue  30  communicating with the combustion chamber  16 , the flue  30  having a motor-driven damper  32  positioned in an upper end portion thereof for rotation between a solid line closed position and a dotted line open position. During water heater standby periods the damper  32  is normally motor-driven to and held in its solid line closed position in a suitable known manner by operation of the controller  22  which regulates the position of the damper  32 . 
         [0009]    Particularly when the ambient temperature externally adjacent the water heater  10  is at a high level, the potential exists for the hot standing pilot burner gases  28  to cause undesirable overheating of the tank water  14  when the water heater  10  is in a standby mode with the damper  32  closed. To combat this potential tank water overheating problem the controller  22  has a specially designed combination sensed water/ambient temperature-based damper control algorithm built into its microprocessor portion  23 . In addition to operating the main burner  18  in the usual manner to maintain the tank water  14  at a predetermined set point temperature, the controller  22  senses excessive tank water temperature during standby periods and responsively opens the flue damper  32  to allow pilot burner flame combustion gases  28  to more readily escape through the flue and thereby prevent tank water overheating during water heater standby periods. 
         [0010]    According to an aspect of the present invention, the controller  22 , via a suitable temperature sensor  34 , also monitors the ambient temperature externally adjacent the water heater  10  and transmits a sensed ambient temperature signal to the controller  22  which utilizes such signal, along with the sensed tank water temperature, in the previously mentioned algorithm to prevent overheating of the tank water  14  during standby periods of the water heater  10 . 
         [0011]    The functions of the combination water/ambient temperature-utilizing algorithm are depicted in the logic flow chart of  FIG. 2  to which reference is now made. In the following description of the  FIG. 2  algorithm, various illustrative numerical values and ranges are utilized for descriptive purposes. It is to be understood, however, that such values and ranges are utilized by way of non-limiting example only, and that other numerical values and ranges could be utilized if desired without departing from principles of the present invention. 
         [0012]    Upon a start-up of the water heater  10  at step  40 , at which a controller water temperature set point is selected, a transfer is made from step  40  to step  42  at which a query made as to whether the selected set point is less than 110° F. If it is, a transfer is made to step  44  at which a temperature parameter T Threshold  is set to 115° F. and a transfer is made to step  46 . If the query answer at step  42  is no, a transfer is made from step  42  to step  48  at which a query is made as to whether the selected set point is less than 130° F. and greater than or equal to 110° F. If it is, a transfer is made to step  50  at which T Threshold  is set to 120° F. and a transfer is made to step  52 . If the query answer at step  48  is negative, a transfer is made from step  48  to step  54  at which a query is made as to whether the selected set point is less than 140° F. and greater than or equal to 130° F. If it is, a transfer is made to step  56  at which T Threshold  is set to 125° F. and a transfer is made to step  52 . 
         [0013]    If the query answer at step  54  is negative, a transfer is made from step  54  to step  58  at which a query is made as to whether the selected set point is greater than or equal to 140° F. If it is, a transfer is made to step  60  at which T Threshold  is set to 130° F. When the query answer at step  58  is negative a transfer is also made to step  52 . 
         [0014]    If the selected set point temperature is less than 110° F., the algorithm has transferred to step  46  and operates to monitor the ambient temperature T Amb.  and responsively control the damper  32  to prevent overheating of the tank water  14 . Specifically, at step  46  a query is made as to whether T Amb.  has been greater than T Threshold  continuously for at least a predetermined time (for example, five minutes) as measured by a clock portion of the controller  22 . If the query answer at step  46  is yes, a transfer is made to step  62  at which the damper  32  is opened if the transfer to step  62  occurs during a standby period during which the damper  32  is closed, or the damper  32  is kept open after the main burner  18  is shut down to initiate a standby period. On the other hand, if the query answer at step  46  is no, a transfer is made from step  46  to step  64  at which the damper  32  is closed if open during a standby period, or kept closed after main burner shutdown initiates a standby period. 
         [0015]    After a transfer is made from step  46  to step  62  or step  64 , the clock is reset, and the ambient/threshold temperature-based monitoring is continued at step  46  which may subsequently switch the damper control from step  62  to step  64 , or from step  64  to step  62 , as necessary depending on the sensed ambient temperature and elapsed clock time. 
         [0016]    If the selected set point temperature is such that a transfer has been made to step  52  (via step  48 ,  54  or  58 ), the algorithm operates to monitor both the ambient temperature T Amb.  and the tank water temperature T Tank  and responsively control the damper  32  to prevent overheating of the tank water  14 . A query is made at step  52  as to whether both the sensed ambient temperature T Amb  and sensed tank water temperature T Tank  have been greater than T Threshold  continuously for at least a predetermined time as measured by the clock portion of the controller  32 . If this query answer is yes, a transfer is made from step  52  to step  62  at which the damper  32  is opened if the transfer to step  62  occurs during a standby period during which the damper  32  is closed, or the damper  32  is kept open after the main burner  18  is shut down to initiate a standby period. On the other hand, if the query answer at step  52  is no, a transfer is made from step  52  to step  64  at which the damper  32  is closed if open during a standby period, or kept closed after main burner shutdown initiates a standby period. 
         [0017]    After a transfer is made from step  52  to step  62  or step  64 , the clock is reset, and the ambient/tank water/threshold temperature-based monitoring is continued at step  52  which may subsequently switch the damper control from step  62  to step  64 , or from step  64  to step  62 , as necessary depending on the sensed ambient temperature, tank water temperature and elapsed clock time. 
         [0018]    As can be seen from the foregoing, the present invention uniquely provides for the control of a flue damper in a standing pilot type fuel-fired water heater based on various combinations of selected water heater set point temperature, sensed ambient temperature and sensed tank water temperature to prevent overheating of the water heater tank water during standby periods of the water heater. 
         [0019]    The foregoing detailed description is to be clearly understood as being given by way of illustration and example only, the spirit and scope of the present invention being limited solely by the appended claims.