Abstract:
A heat balancing system for a natural draft gas burning appliance having a flue. When the appliance is in a standby mode, a main burner is shut off and the pilot light remains on. Temperature in the heat exchanger (e.g., temperature of water in a heater tank) may be decreased or increased, respectively, by opening or closing a damper in a flue as needed. If opening the damper does not sufficiently reduce the temperature of the heat exchanger, then the pilot light may be shut off to further reduce the temperature. The pilot light may be turned on again to bring up the temperature. There may be a control or controller to operate the damper to maintain the temperature of the exchanger within a certain range. Electrical power may be provided for the system from a power line, a storage device, or other source.

Description:
[0001]    This application is a continuation-in-part of U.S. patent application Ser. No. 12/553,795, filed Sep. 3, 2009, and entitled “A Damper Control System”. U.S. patent application Ser. No. 12/553,795, filed Sep. 3, 2009, is hereby incorporated by reference. 
         [0002]    U.S. patent application Ser. No. 11/276,121, filed Feb. 15, 2006, and entitled “Appliance Control with Automatic Damper Detection”, is a related application. U.S. patent application Ser. No. 11/276,121, filed Feb. 15, 2006, is hereby incorporated by reference. 
     
    
     BACKGROUND 
       [0003]    The present invention pertains to devices for building control systems and particularly damper control devices. More particularly, the invention pertains to damper control devices for fuel fired appliances. 
       SUMMARY 
       [0004]    The invention is a heat balancing system for a natural draft gas burning appliance having a flue. When the appliance is in a standby mode, a main burner is shut off and the pilot light remains on. Blocking the flue may cause significant heat rise in a water tank (e.g., water heater) due to heat from the pilot light. Temperature in the heat exchanger (e.g., temperature of water in a heater tank) may be maintained by opening and closing a damper in a flue as needed. If opening the damper does not sufficiently reduce the temperature of the heat exchanger, then the pilot light may be shut off to further reduce the temperature. The temperature of the exchanger may fall further than desired due to a lack of heat in the stand-by mode. Thus, the pilot light may be turned on again to bring up the temperature. There may be a control or controller to operate the damper to maintain the temperature of the exchanger within a certain range. The damper may be operated as completely open and closed, or partially open and closed. 
         [0005]    Electrical power may be provided from line power, a storage device or other source for the control or controller, an electrical drive for the damper, pilot light shut-off valve, and other like items as needed for the heat exchanger. In the case of the storage device, it may be recharged with a light- or heat-to-electric converter. The light or heat may be provided by the pilot light. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0006]      FIG. 1  is a diagram of cutaway side view of an illustrative fuel fired appliance; 
           [0007]      FIG. 2  is a diagram of an illustrative controller for operating and/or controlling the appliance of  FIG. 1 ; 
           [0008]      FIG. 3  is a flow diagram showing temperature control using basic open and closed positions of a damper; 
           [0009]      FIG. 4  is a flow diagram showing temperature control using variable positions of the damper; 
           [0010]      FIG. 5  is a flow diagram showing heating water in a heater tank with just a pilot light; and 
           [0011]      FIG. 6  is a flow diagram showing a recharge with over-temperature protection. 
       
    
    
     DESCRIPTION 
       [0012]    Flue dampers may greatly improve the efficiency of natural draft gas burning appliances. However, when used with a standing pilot system, blocking the flue may cause excessive heat rise in the heat exchanger due to heat from the pilot. This phenomenon appears especially true in water heaters. Blocking the flue on a standing pilot water heater may result in excessive water temperature eventually causing a relief valve or a high limit switch to open. 
         [0013]      FIG. 1  is cutaway view of an illustrative example of a natural gas burning appliance such as a water heater  10 . The illustrative water heater  10  may incorporate a tank  12 , an insulating layer  14 , an external shell  16 , a heater  18 , and a controller  50 . Tank  12  may hold water that is to be heated and be constructed of steel or other heat conducting material. Tank  12  may have an inner surface  22 , an input supply tube or dip tube  24 , an output conduit or pipe  26 , a drainage valve  28 , a rust inhibiting liner  30 , and an outer surface  32 . 
         [0014]    Insulating layer  14  may be located between outer surface  32  of tank  12  and external shell  16 . Insulating layer  14  may limit or otherwise minimize the heat loss of the heated water from passing from tank  12  to the outside world. Bonded to the inside of inner surface  22  may be a rust inhibiting liner  30 . In addition, tank  12  may have a sacrificial anode rod (not illustrated) to keep tank  12  from corroding, and have flue baffling which is designed to optimize heat exchange between combustion by-products and water. It may be like a secondary heat exchanger. 
         [0015]    Tank  12  may also have a top surface  34  and a bottom surface  36 . Dip tube  24  and output pipe  26  may pass through top surface  34 . Output pipe  26  may extend through top surface  34  to a second predetermined distance from bottom surface  36 . This second predetermined distance may be fairly close to top surface  34 . 
         [0016]    Heater  18  may heat tank  12  and tank  12  may heat water inside it. Temperature of the water in tank  12  may be detected by one or more temperature sensors  42  and  44 , which are connected to controller  50 . Heater  18  may have one or more gas-fired burners  38  and a pilot  40  located in a combustion chamber  43 . 
         [0017]    The heat output of heater  18  may be controlled by burner orifice size, gas pressure, and/or time. To produce heat in the gas-fired water heater, gas may flow into burner  38  in the combustion chamber  43  through the gas-flow valve, where pilot source  40  ignites the gas. Pilot  40  may also produce heat resulting in heating the water or keeping it hot. The gas may continue to burn until the supply of gas is terminated. The burner  38  and pilot  40 , which are situated in combustion chamber  43 , may be in fluid communication with an exhaust outlet, such as a flue  41 . The flue  41  may be coupled to a vent pipe  45  that vents combustion gases exiting from the combustion chamber  43  to the atmosphere (e.g., outside of the building). 
         [0018]    In some cases, the combustion gases may be vented via flue  41  and vent pipe  45  through natural convection. Alternatively, a fan or like (not shown) may be provided to help force the combustion gases through the flue  41  and vent pipe  45  to the atmosphere. In either case, during off-cycle periods, the water heater  10  may lose heat through the flue  41  and vent pipe  45  to the atmosphere by natural convection and conduction. To help reduce these losses, a damper  49  may be installed either at the flue  41  exit or in the vent pipe  45 . 
         [0019]    In some cases, one or more electric motor controlled dampers may be used. The damper  49  shown in  FIG. 1  may be one such electric motor controlled damper. The damper  49  may be controlled by a controller  50  or the like via wiring  53 . In some cases, the damper  49  may be controlled to open when combustion of either burner  38  and/or pilot  40  in the combustion chamber  43  starts, and close immediately or sometime after combustion stops. This may help minimize the off-cycle heat losses that may occur through natural convection through the vent pipe  45  to the atmosphere. 
         [0020]      FIG. 2  is a block diagram of a control or controller  50 . A user interface  55  of controller  50  may be for control, entry, observing a display, and so forth. User interface  55  may be utilized for installing a program or function in controller  50  to control burner  38 , pilot  40  and damper  49  control in appliance  10 . An input  56  to controller  50  may be for receiving tank  12  water temperature indications from sensors  42  and  44 . An input  57  to controller  50  may be for receiving a damper  49  position in flue  41  or vent pipe  45 . An input  58  to controller  50  may be for receiving a tank temperature setpoint. An output  51  from controller  50  may be for controlling pilot  40 . An output  52  from controller may be for controlling damper  49 . An output  54  may be for controlling burner  38 . 
         [0021]    The present approach may solve the problem of excessive heat rise in an appliance, for example, a water heater, by controlling the damper based on the temperature of a medium. In the case of a water heater, water temperature may be monitored. When the appliance off-state or off-cycle (i.e., the burner is not running or the main fuel valve is closed) temperature is seen to be rising, or when it exceeds a threshold, the damper may be opened by some amount to allow heat loss up the flue. Instead of water temperature; air temperature, a temperature of the heat exchanger itself, or some other temperature indication may be used. 
         [0022]    One way to control heat rise is to cut a relief area in the damper plate to allow heat to escape. While effective, the relief area should be fine-tuned to each appliance and even to different installations. In addition, a relief area may directly reduce the effectiveness of the damper&#39;s impact on efficiency. It is likely that many installations will have more relief area than required to maintain a constant temperature or keep from resulting in a dropping temperature. Heat rise may be controlled also by making the damper smaller than necessary so that the relief area is the distance between the damper and the flue (circular dimension) and not a notch in the center of the damper. 
         [0023]    A water heater control may be capable of measuring water temperature in the tank and be in control of the flue damper. It may be in direct control of the damper or it may provide signals to a separate damper controller. During the off-cycle, a situation may be that the pilot is burning, the main fuel (e.g., gas) valve is off, and the damper is closed. In some cases, this situation may lead to heating of the water due to the pilot flame, particularly in significantly energy efficient or small water heaters. The control or controller may continue to monitor water temperature. If the water temperature is approaching some first threshold value, then the damper may be opened to allow heat to escape up the flue. Once the temperature comes down below a second threshold value, the damper may be closed again. The first threshold value is greater than the second threshold value. 
         [0024]    Alternatively, the control may partially open the damper in an attempt to balance heat loss and maintain a somewhat constant water temperature. In this case, the damper may be continually adjusted to basically maintain a setpoint temperature in the off-cycle. 
         [0025]    The present approach may be extended further to encompass intermittent pilot systems as well. Using the fact that the pilot may be capable of adequately warming the heat exchanger (e.g., the tank of a water heater) with the damper closed, a control may light the pilot to satisfy light heating demands and leave the main fuel valve closed. More than needed heat may be balanced by using the damper or cycling the pilot. In flame-powered systems, the control may be required to periodically light the pilot to recharge batteries or capacitors via thermocouples, solar cells, or other heat or light to electric energy converters. In this case, the damper may be used to guard against overheating the appliance during the battery or capacitor recharge phase. 
         [0026]    One may have a standing pilot and millivolt (mV) damper control strategy for prevention of tank failure due to overheating. Flue dampers have not been successfully applied to smaller fossil fuel water heaters due to hazards of overheating. Sizing a pilot may require a minimum orifice opening to pass agency testing when running at reduced rates to ensure that the main burner light is off. If one wishes to apply a damper to the fossil fuel appliance, one will likely compromise appliance optimization in order to prevent heat build up in the flue chamber during a standby mode with the pilot operating. This heat build-up may eventually blow the temperature and pressure relief (T&amp;P) valve or a high temperature limit. 
         [0027]    Because many manufacturers may prefer a standing pilot approach that does not require additional outside electricity to be introduced, and can be used in existing systems which utilize metal flue piping (i.e., no need to convert to PVC as it may be very expensive). The algorithm herein may allow manufacturers to maximize insulation on a tank to reduce standby losses, and yet prevent a water vessel from becoming overheated due to the minimum orifice size needed for the standing pilot application. The secondary effect of this system may be an increase in efficiency by ensuring that heat from the standing pilot has an opportunity to be transferred into the tank without overheating it. 
         [0028]    One may have an intermittent pilot and millivolt damper control strategy for optimization of heat transfer of the pilot during long standby periods without over-temping the tank. Again, many manufacturers may prefer a standing pilot system that does not require additional outside electricity to be introduced or new flue piping added. The algorithm herein may allow manufacturers to maximize insulation on a tank to reduce standby losses, prevent a water vessel from becoming overheated due to the minimum size orifice needed for the standing pilot application, introduce intermittent spark as an approach to relight the pilot when tank is at setpoint during standby, and also use short pulse burns with the pilot to keep the tank at setpoint for long periods of time without the need to fire the main burner. 
         [0029]      FIG. 3  is a flow diagram showing temperature control using basic discrete open and closed positions of a damper. At symbol  73  may be a question of whether the main burner is on (or there is a request to turn the main burner on). If the answer is yes, the damper is opened at symbol  74 . If the answer is no, then a question of whether the temperature is greater than a desired temperature may be asked at symbol  75 . If the answer is yes, then the damper is opened at symbol  74 . If the answer is no, then the damper is closed at symbol  76 . The positions of the damper may be fed from symbols  74  and  76  to symbol  73 . 
         [0030]      FIG. 4  is a flow diagram showing temperature control using variable or partially open and partially closed positions of the damper. At symbol  78  may be a question of whether the main burner is on (or there is a request to turn the main burner on). If the answer is yes, then the damper may be opened completely at symbol  83 . If the answer is no, then a question of whether the temperature is greater than a desired may be asked at symbol  79 . If the answer is yes, then the opening of the damper may be increased at symbol  81 . If the answer is no, then the opening of the damper may be decreased at symbol  82 . 
         [0031]      FIG. 5  is a flow diagram showing controlling heating water in the heater tank with just a pilot light. A question of whether the temperature of the water in a heater tank is greater than desired is asked at symbol  61 . If the answer is yes, then a question of whether the damper is open  100  percent may be asked at symbol  62 . If the answer is yes, then the pilot may be shut off at symbol  63 . If the answer is no, then the damper may be opened at symbol  64 . If the answer to the question at symbol  61  is no, then a question of whether the damper is closed  100  percent may be asked at symbol  65 . If the answer is yes, then the pilot may be turned on at symbol  66 . If the answer is no, then the damper may be closed at symbol  67 . Indications of the status of the pilot light and the damper may be fed to symbol  61  via lines  68 . 
         [0032]      FIG. 6  is a flow diagram showing a recharge with over-temperature protection. A question of whether the temperature of the water in the heater tank is greater than desired may be asked at symbol  69 . If the answer is yes, then the damper may be opened at symbol  70 . If the answer is no, then a question of whether there should be a recharge may be asked at symbol  71 . If the answer is yes, then the pilot may be lighted at symbol  72 . If the answer is no, then the pilot may be shut off and the damper be closed at symbol  77 . The status of the pilot light and the damper may be fed to symbol  71  via lines  80 . 
         [0033]    In the present specification, some of the matter may be of a hypothetical or prophetic nature although stated in another manner or tense. 
         [0034]    Although the present system has been described with respect to at least one illustrative example, many variations and modifications will become apparent to those skilled in the art upon reading the specification. It is therefore the intention that the appended claims be interpreted as broadly as possible in view of the prior art to include all such variations and modifications.