Abstract:
A control system for a solid fuel combustion appliance, e.g., a wood burning stove, includes a temperature sensor for sensing an output temperature of the appliance. A controller receives the output temperature and controls a damper associated with air flow through the stove to maintain a predetermined temperature. The system also includes a detector that senses certain conditions of the solid fuel, e.g., wood, that is burned by the stove. When additional fuel is added to the appliance, the system temporarily encourages initial combustion of the new fuel, before returning to maintaining the predetermined temperature.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of provisional patent application No. 61/351,477, filed Jun. 4, 2010, which is hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to computerized control systems and methods for solid fuel combustion appliances, e.g., wood stoves. 
     2. Description of the Related Art 
     Wood burning stoves have a long and distinguished history for providing heating for houses and enclosures of every sort. The efficiency of such stoves has been steadily increasing in recent years, especially with the addition of catalysts to lower the burning temperature of the solid fuel. However, there still remains the possibility of higher efficiency and greater temperature control over such stoves. 
     BRIEF SUMMARY 
     The application describes a control system for a solid fuel combustion appliance. The appliance includes a housing defining a combustion chamber and an inlet, an outlet, and an opening, each in fluidic communication with the combustion chamber. The appliance also includes an inlet damper movable between a plurality of positions for controlling airflow into the inlet. The system includes a drive mechanism operatively connected to the inlet damper for controlling the position of the inlet damper. An exhaust temperature sensor measures the temperature of air exhausted through the outlet. The system also includes a detector for signaling a certain condition of the solid fuel in the combustion chamber. A controller is in communication with the drive mechanism, the exhaust temperature sensor, and the detector. The controller controls the drive mechanism to position the inlet damper to maintain a predetermined temperature of airflow through the outlet. The controller also controls the drive mechanism to position the inlet damper at a predetermined position for a predetermined period of time in response to the detector signaling the certain condition of the solid fuel in the combustion chamber regardless of the predetermined temperature. 
     As such, the control system regulates the temperature output of the stove utilizing precise control over the inlet damper. Furthermore, when the user adds new fuel, e.g., wood, to the combustion chamber, the control system automatically controls the inlet damper to ensure that the new fuel is quickly ignited so that its rate of burn can also be precisely controlled. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other advantages of the disclosed subject matter will be readily appreciated, as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein: 
         FIG. 1  is a perspective view of an exemplary solid fuel combustion appliance for use with the control system and method; 
         FIG. 2  is an cross-sectional view of an exemplary solid fuel combustion appliance; and 
         FIG. 3  is an electrical block diagram of the control system. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to the Figures, wherein like numerals indicate like parts throughout the several views, a control system  10  is shown herein. 
     The control system  10  is preferably used in conjunction with a solid fuel combustion appliance  12 , as shown in  FIG. 1 . The appliance  12  may be alternatively referred to as a stove, a fireplace, a burner, or other name as appreciated by those skilled in the art. The solid fuel (not shown) burned with the appliance  12  may be wood, biomass, coal, charcoal, or other solid known to those skilled in the art. The solid fuel may be in log, pellet, chip, powder, briquette, or other suitable form known to those skilled in the art and typically dependent on the specific design and configuration of the appliance  12 . 
     Referring now to  FIG. 2 , the appliance  12  includes a housing  14  defining a combustion chamber  16 . The combustion chamber  16  may also be referred to by those skilled in the art as a “firebox”. The housing  14  defines an inlet  18  and an outlet  20 , each in fluidic communication with the combustion chamber  16 . The inlet  18  supplies air to the combustion chamber  16  while the outlet  20  serves to exhaust combustion gases. In the illustrated embodiment, a chimney  21  is fluidically connected to the outlet  20  to exhaust the combustion gases to atmosphere, outside of a structure (not shown) where the appliance  12  is located, as is well known to those skilled in the art. 
     The housing  14  may further define an opening  22  in fluidic communication with the combustion chamber  16 . The opening  22  may be utilized to add the solid fuel to the combustion chamber  16 . In the illustrated embodiment, as shown in  FIG. 1 , a door  24  is operatively connected to the housing  14 . For instance, the door  24  may be connected to the housing  14  with hinges (not shown). The door  24  is preferably positionable in a plurality of positions including a closed position to block the opening  22 . The opening  22  may be completely or at least partially blocked by the door  24  depending on the design and configuration of the appliance  12 . 
     In one embodiment, the door  24  is manually opened by a user for adding solid fuel to the combustion chamber  16 . In other embodiments, the solid fuel may be added automatically. For instance, an auger (not shown) may feed the solid fuel, especially in pellet form, through the opening  22  and to the combustion chamber  16 . 
     Referring again to  FIG. 2 , the appliance  12  further includes an inlet damper  26 . The inlet damper  26  is in fluidic communication with the inlet  18  and movable between a plurality of positions for controlling the flow of air into the inlet  18  and, as such, controlling the flow of air into the combustion chamber  16 . The appliance  12  may also include an outlet damper (not shown) for closing off the outlet  20 , e.g., when the appliance  12  is not in use. 
     The appliance  12  may also include a catalyst  28  fluidically disposed between the combustion chamber  16  and the outlet  20 . As such, combustion gases pass through the catalyst  28  prior to being exhausted through the outlet. Those skilled in the art realized that the catalyst  28 , often referred to as a catalytic converter, changes the rate of the chemical reaction, which, in this case, is the combustion or burning of the solid fuel. In particular, the catalyst  28  of the combustion appliance  12  lowers the temperature at which smoke can catch fire. The appliance  12  may further include a catalyst damper  30  to allow the combustion gases to pass through the catalyst  28  or to bypass the catalyst  28 . 
     The appliance  12  may also include a fan  32  for blowing air from the combustion chamber to a space outside the housing  14 . That is, the fan  32  may blow heated air from inside the housing  14  to outside the housing  14 . Control of the fan  32  will be described in further detail hereafter. 
     Referring now to  FIG. 3 , the control system  10  includes a controller  40 . The controller  40  controls various aspects of the combustion performed by the solid fuel combustion appliance  12  as described herein. In the illustrated embodiment, the controller  40  is programmable and executes a software program. The controller  40  may be implemented as a microcontroller, microprocessor, application specific integrated circuit, or other suitable device or combination of devices capable of performing the functions described herein. The control system  10  may also include an analog-to-digital converter (“ADC”) and a digital-to-analog converter (“DAC”) for converting signals as is well known to those skilled in the art. The ADC and DAC may be integrated with the controller  40  or separate therefrom. 
     The control system  10  includes at least one temperature sensor  42 . The at least one temperature sensor  42  may be implemented as a thermocouple, a resistive temperature detector (“RTD”), infrared thermometer, or other suitable device as appreciated by those skilled in the art. The at least one temperature sensor  42  is in communication with the controller  40 . Typically, the at least one temperature sensor  42  is electrically connected to the ADC which produces a digital value corresponding to the measured temperature to the controller  40 . Of course, other techniques for transferring temperature data from the temperature sensor  42  to the controller  40  are realized by those skilled in the art. 
     In one embodiment, the at least one temperature sensor  42  is implemented as an exhaust temperature sensor  42   a . The exhaust temperature sensor  42   a  measures the temperature of air exhausted through the outlet  20 . In the illustrated embodiment, the exhaust temperature sensor  42   a  is disposed in the chimney  21  adjacent the outlet  20 . However, other suitable locations for positioning the exhaust temperature sensor  42   a  will be realized by those skilled in the art. 
     In another embodiment, the at least one temperature sensor  42  is implemented as the exhaust temperature sensor  42   a  and a catalyst temperature sensor  42   b . The catalyst temperature sensor  42   b  measures the temperature of air passing through the catalyst  28 . Accordingly, the catalyst temperature sensors  42   b  is disposed adjacent to the catalyst  28  or integrated within the catalyst  28 . 
     The control system  10  also includes a drive mechanism  44  operatively connected to the inlet damper  26 . The drive mechanism  44  controls the position of the inlet damper  26 . As just one example, the drive mechanism  44  may control the position of the inlet damper  26  at five degree increments (e.g., 0% open, 5% open, 10% open, . . . 95% open, 100% open). The drive mechanism  44  is preferably a motor (not separately numbered) having a mechanical linkage (not shown) to the damper  26 . However, other devices may be implemented as the drive mechanism  44 . The drive mechanism  44  is in communication with the controller  40  such that the controller  40  issues commands and/or signals to the drive mechanism  44  for controlling the position of the inlet damper  26 . 
     The control system  10  may further include a detector  46  for signaling a certain condition of the solid fuel in the combustion chamber  16 . The detector  46  is in communication with the controller  40  such that the controller  40  receives a signal when the certain condition of the solid fuel is ascertained. In the illustrated embodiment, the certain condition is the addition of solid fuel. 
     The detector  46  of the illustrated embodiment is implemented as a switch  48  electrically connected to the controller  40 . In one technique, the switch  48  is coupled to the housing  14  to operatively engage the door  24  to signal when the door  24  has been opened and reclosed. The opening and reclosing of the door  24  thus signals the addition of solid fuel to the combustion chamber  16 . In another technique, the switch  48  is disposed in a position allowing the user to manually depress the switch  48 , thus signaling the addition of solid fuel to the combustion chamber  16 . In yet another technique, the switch  48  is operatively connected to the auger to sense when the auger is adding solid fuel to the combustion chamber  16 . 
     The detector  46  may be implemented with devices other than the switch  48  in other embodiments. In one example, an optical device (not shown) may be utilized to sense when the door  24  is opened and reclose or when additional solid fuel is added to the combustion chamber  16 . In another example, a capacitive sensor (not shown) may be implemented to sense the amount of solid fuel in the combustion chamber  16  and thus determine whether additional sold fuel has been added. 
     The controller  40  may also be in communication with the fan  32  for controlling operation of the fan  32 . For example, the controller  40  may operate a relay (not shown) for turning the fan  32  on and off. Alternatively, the controller  40  may be electrically connected to a motor (not shown) of the fan  32  to more precisely control the speed of the fan  32 , and thus the airflow produced by the fan  32 . 
     The control system  10  of the illustrated embodiment further includes an annunciator  50  in communication with the controller  40 . The annunciator  50  may be implemented as any device capable of providing information to the user. For instance, the annunciator  50  may be implemented as a light, a display, and/or a speaker. Those skilled in the art will realize other techniques to implement the annunciator  50 . 
     The control system  10  may further include a remote control device  52  in communication with the controller  40  such that commands and/or data may be sent back-and-forth between the remote control device  52  and the controller  40 . The communications between the controller  40  and the remote control device  52  may be implemented via radio frequency (RF) signals, optical signals (e.g., infrared or ultraviolet), or a combination of RF and optical signals. Those skilled in the art realize other techniques for facilitating communications between the remote control device  52  and the controller  40 . 
     The remote control device  52  allows the user to control operation of the controller  40  and to receive information from the controller  40 . The remote control device  52  of the illustrated embodiment includes a plurality of pushbuttons  54  for receiving input from the user and a display  56  for providing information to the user. Of course, other techniques for receiving input from the user and providing information to the user may alternatively be implemented. 
     In addition to or as a substitute to the remote control device  52 , the control system  10  may also include pushbuttons, switches, keypads, or other controls (none of which are shown) electrically connected to the controller  40 . For instance, DIP switches (not shown) may be mounted on a printed circuit board (not shown) which also supports the controller  40 . 
     In the illustrated embodiment, the controller  40  operates an automatic mode or a manual mode. In the automatic mode, the controller  40  generally attempts to control for output temperature of the combustion. In the illustrated embodiment, the mode of the controller  40  is controlled utilizing the remote control device  52 . 
     In one aspect of automatic mode, the controller  40  controls the drive mechanism  44  to position the inlet damper  26  to maintain a predetermined temperature of airflow through the outlet  20 . The predetermined temperature may actually be a range of temperatures. For instance, in one implementation, the predetermined temperature may range from 260° C. to 280° C. As such, the controller  40  may incrementally close the inlet damper  26  as the temperature rises and approaches or exceeds 280° C. to reduce the amount of air, and consequently oxygen, that is available to the fire. Likewise, the controller  40  may incrementally open the inlet damper  26  as the temperature falls and approaches or passes 260° C. The control of the temperature of airflow through the outlet  20  may be implemented with a proportional-integral (PI) or proportional-integral-derivative (PID) techniques, or other suitable techniques. 
     When additional solid fuel is added to the combustion chamber  16 , it is advantageous to provide for maximum airflow to the combustion chamber  16  in order to fully ignite and envelop the additional solid fuel. As such, in automatic mode, the controller  40  preferably reacts to the certain condition of the solid fuel sensed by the detector  46 . Specifically, the controller  40  does not strictly control for temperature when new solid fuel is added to the combustion chamber  16 . Instead, in response to the certain condition of the solid fuel, the controller  40  controls the drive mechanism  44  to position the inlet damper  26  at a predetermined position for a predetermined period of time regardless of the predetermined temperature. In the illustrated embodiment, the controller  40  controls the drive mechanism  44  to position the inlet damper  26  at a fully open position for about one minute. After the predetermined period of time has expired, the controller  40  returns to controlling for the predetermined temperature of airflow through the outlet  20 . 
     The controller  40  may also provide for other control techniques in automatic mode. In another aspect of the automatic mode, the controller  40  controls the drive mechanism  44  based on temperature of the room, i.e., the area outside of the appliance  12  itself. This is accomplished with a thermostat (not shown) or other device in communication with the controller  40 . Furthermore, the controller  40  may also provide for different conditions of the solid fuel. For instance, the controller  40  may include a “wet wood” automatic mode. In this mode, the controller  40  will control for a higher temperature output due to the wet nature of the solid fuel. 
     The predetermined temperature of airflow may be controlled by the user. For instance, in a “long-burn” automatic mode, the predetermined temperature is set very low, but still high enough to support combustion. In another instance, in a “high output” automatic mode, the predetermined temperature is at or near a maximum safe operating temperature. 
     In the manual mode, the user may control some or all of the control elements of the system  10  manually. In the illustrated embodiment, the user may utilize the remote control device  52  to manually open and close the inlet damper to maintain control over the temperature output from the appliance  12 . 
     In the illustrated embodiment, the controller  40  receives both the temperature of the air passing through the outlet  20  and the temperature of the air passing through the catalyst  28 . By analyzing these two temperatures, the controller  40  determines when the solid fuel is expiring. Specifically, when both temperatures fall by a predetermined amount for a predetermined period of time, the controller  40  ascertains that the solid fuel is near the end of its combustible life. In response to the solid fuel expiring, the controller  40  communicates the expiration via the annunciator  50 . For instance, in one embodiment, the controller  40  may activate an LED (not shown) affixed to the housing 
     The present invention has been described herein in an illustrative manner, and it is to be understood that the terminology which has been used is intended to be in the nature of words of description rather than of limitation. Obviously, many modifications and variations of the invention are possible in light of the above teachings. The invention may be practiced otherwise than as specifically described within the scope of the appended claims.