Abstract:
A heating system has a heating unit with a combustion chamber for burning wood pellets or other pelletized fuel. The heating unit is controlled by a process control module that automatically keeps all operating functions within predetermined limits for safe, efficient and easy operation. The unit also includes a combustion air distribution assembly with a stir shaft that rotates within the combustion chamber and introduces combustion air through orifices along the length of the shaft to enhance fuel combustion. A thermo cycle plumbing assembly serves as a safety feature by preventing overheating in the event of a power failure or pump failure. Also included in the unit is a removable insulated firebox burn chamber that provides a high temperature combustion atmosphere and a heat/particulate recovery module which provides maximum heating efficiency and reduces emissions, meeting EPA requirements and contributing to a cleaner environment.

Description:
This application is entitled to and hereby claims the priority of U.S. provisional application, Ser. No. 60/929,931, filed Jul. 18, 2007. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is related to the field of wood burning heaters and, more particularly, to an automatically controlled outdoor heating unit that uses wood pellets or other pelletized fuel. 
     2. Description of the Related Art 
     Free standing outdoor wood burning heaters have been available for a number of years. The heater set forth by the present inventor in U.S. Pat. No. 4,360,003 uses wood logs or sections thereof as fuel and has a combustion chamber to burn the wood. The heat generated by the burning wood is transferred to water in a tank that substantially surrounds the combustion chamber. The hot water is then utilized for household use or to provide heat for a home heating system. 
     With the availability of a wider range of pelletized fuels in recent years, as well as advances in control systems, a need exists for an improved heating unit that is able to utilize these pelletized fuels and provide improved performance features through the use of an automatic control system. A further need is for a unit that is more environmentally friendly by virtue of its use of a by-product or waste product as fuel and also by its greater ability of particulate recovery resulting in significantly reduced emissions. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing, the present invention is directed to a heating system having a heating unit with a combustion chamber for burning wood pellets or other pelletized material as fuel. Heat from the combustion chamber is transferred to water in a water tank that substantially surrounds the combustion and related recovery chambers to provide hot water for household purposes or heat for a home heating system. 
     The heating unit is controlled by a process control module that is programmable to keep all operating functions within predetermined limits for safe, efficient and easy operation. With this control module, the operation of the heating unit is automatic, including the rates at which fuel and combustion air are introduced into the combustion chamber. 
     The heating unit further includes a combustion air distribution assembly having a stir shaft that rotates within the combustion chamber and introduces combustion air through orifices along the length of the shaft to optimize combustion of the fuel. The shaft is mounted within a removable insulated firebox burn chamber that provides a high temperature combustion atmosphere and is insulated sufficiently to maintain the heat necessary for a re-firing with minimal emissions produced when the unit cycles on. 
     A heat/particulate recovery module having a heat exchanger assembly with a plurality of heat recovery plates in spaced vertical relationship is placed in the combustion chamber directly over the firebox. The plates take off the heat generated by the combustion chamber and are filled with a liquid, preferably water, which is pumped to the lowermost plate and then moves to the remaining recovery plates and finally into a water tank. The recovery module also serves to remove emission particulates from the burned fuel by slowing the exhaust gases to a velocity so that the particulates will accumulate onto the top of the water-filled heat recovery plates and are not exhausted into the atmosphere. 
     A safety mechanism is also provided in the form of a thermo cycle plumbing assembly. Whenever a power failure or a pump failure occurs, the heat recovery module will continue to operate without overheating. The physics by which hot water taken from the coldest portion of the water tank rises through the heat recovery module to the upper and hottest portion of the tank and is fed through the thermo cycle plumbing assembly provides an effective safety feature. 
     In accordance with the foregoing, one object of the present invention is to provide an outdoor heating unit with a combustion chamber that uses wood pellets or other pelletized fuel as the heat source. 
     Another object of the present invention is to provide an outdoor heating unit controlled by a process control module so that operation of the unit is automatic, including the rates at which fuel and combustion air are introduced into the firebox burn chamber. 
     A further object of the present invention is to provide an outdoor heating unit that has a specially designed combustion air distribution assembly with a stir shaft that rotates in the combustion chamber and introduces combustion air through orifices along the length of the shaft to optimize combustion of the fuel. 
     Still another object of the present invention is to provide an outdoor heating unit having a specially designed, removable insulated firebox burn chamber that provides a high temperature combustion atmosphere and is insulated sufficiently to maintain the heat necessary for a re-firing with minimal emissions produced when the unit cycles on. 
     A still further object of the present invention is to provide an outdoor heating unit having a heat/particulate recovery module consisting of a heat exchanger assembly placed in the firebox that provides additional heat transfer above the combustion chamber for maximum heating efficiency while also slowing the exhaust gases to a velocity at which the particulates accumulate in the recovery module and are not exhausted into the atmosphere. 
     Yet another object of the present invention is to provide an outdoor heating unit which includes a safety mechanism in the form of a thermo cycle plumbing assembly that ensures that whenever a power failure or a pump failure occurs, the heat recovery module will continue to operate without overheating. 
     A still yet further object of the present invention is to provide a heating unit with automatic operation that provides the consumer with safety, efficiency and convenience. 
     Still yet another object of the present invention is to provide a heating unit that is not complex in structure and which can be manufactured at a reasonable cost but yet efficiently combusts a range of relatively inexpensive renewable energy sources to provide a cost-efficient and environmentally friendly hot water for home use. 
     These together with other objects and advantages which will become subsequently apparent reside in the details of construction and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawings forming a part hereof, wherein like numerals refer to like parts throughout. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an automatically controlled outdoor pelletized bio-fuel burning hydronic heating unit and fuel storage bin system in accordance with the present invention. 
         FIG. 2  is a left side view of the heating unit and fuel storage bin of  FIG. 1 . 
         FIG. 3  is a front view of the heating unit of  FIG. 1 . 
         FIG. 4  is a rear view of the heating unit of  FIG. 1 . 
         FIG. 5  is a cutaway side view of the heating unit and fuel storage bin as shown in  FIG. 2 , showing the combustion chamber with firebox burn chamber, combustion air distribution assembly, and heat/particulate recovery module. 
         FIG. 6  is a cutaway front view of the heating unit as shown in  FIG. 3 , showing the firebox burn chamber and heat/particulate recovery module. 
         FIG. 7A  is an end view of the firebox burn chamber and combustion air distribution assembly of the heating unit as shown in  FIG. 5 . 
         FIG. 7B  is a side view of the firebox burn chamber and combustion air distribution assembly as shown in  FIG. 7A . 
         FIG. 8A  is a perspective view of the heat/particulate recovery module of  FIG. 5 . 
         FIG. 8B  is a side view of the heat/particulate recovery module of  FIG. 8A . 
         FIG. 9  is an isolated view of the feed auger assembly of  FIG. 5 . 
         FIG. 10  is a rear view of the heating unit of  FIG. 1 , shown with the housing removed. 
         FIG. 11  is an isolated, exploded view of the combustion air distribution assembly. 
         FIG. 12A  is a rear view of the heating unit as in  FIG. 10 , and further showing water transport piping and water flow direction. 
         FIG. 12B  is a cutaway side view of the heating unit and fuel storage bin as shown in  FIG. 5 , further showing the water flow direction through the heat/particulate recovery module. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In describing a preferred embodiment of the invention illustrated in the drawings, specific terminology will be resorted to for the sake of clarity. However, the invention is not intended to be limited to the specific terms so selected, and it is to be understood that each specific term includes all technical equivalents which operate in a similar manner to accomplish a similar purpose. 
     As shown in  FIGS. 1-4 , the present invention is directed to an automatically controlled outdoor pelletized bio-fuel burning hydronic heating unit and fuel storage bin system generally designated by reference numeral  10 . The system  10  includes a heating unit generally designated by reference numeral  12  and a fuel storage bin generally designated by reference numeral  14 . The heating unit  12  releases exhaust to the environment through a smoke stack  16  and is enclosed within an outdoor weather-resistant insulated housing  18  that contains a combustion chamber generally designated by reference numeral  30 . 
     Access to the interior of the combustion chamber  30  is provided through an access door  19  on the front of the heating unit  12 . Access to the interior of the plumbing and electrical housing  18  is provided through an access door  22  on the rear of the heating unit. Accessible from outside the housing is a process control module  20  (see  FIG. 2 ) by which the heating unit  12  may be programmed and controlled. As a non-pressurized hydronic heater, the condenser stack  17  condenses the steam generated when the water is heated and returns the condensate to the water tank  31 . This prevents excess water use. 
     As shown in  FIGS. 5 ,  6 ,  7 A and  7 B, the combustion chamber  30  contains an insulated firebox burn chamber  34  having a combustion air distribution assembly, generally designated by reference numeral  32 , mounted therein. A heat/particulate recovery module generally designated by reference numeral  36 , shown in isolation in  FIGS. 8A and 8B , is mounted inside the combustion chamber  30  above the firebox burn chamber  34  as shown in  FIGS. 5 and 6 . Heat from the combustion chamber  30  is transferred to a water tank  31  that substantially surrounds the combustion chamber  30  to provide hot water for household purposes or heat for a home heating system. 
     A fuel auger assembly generally designated by reference numeral  40 , shown in isolation in  FIG. 9 , augers pelletized fuel flowing by gravity from the bottom  15  of the fuel storage bin  14  into the firebox burn chamber  34  where the fuel is ignited and the combustion process begins. To assist in combustion, a combustion air blower assembly generally designated by reference numeral  42 , shown in  FIGS. 5 and 10 , directs a flow of air into a combustion air/power transmission device  44  coupled to the combustion air distribution assembly  32 . 
     The combustion air distribution assembly  32 , shown in exploded view in  FIG. 11 , includes a stir shaft generally designated by reference numeral  48  having an insert rod  50  and a sleeve  52  that runs the length of the removable firebox  34 . The sleeve  52  is provided with a plurality of orifices  54  along its length through which combustion air is blown. A stir shaft drive assembly, generally designated by reference numeral  60 , attached to the combustion air/power transmission device  44  rotates the stir shaft  48  within the firebox burn chamber  34  so that combustion air being blown into the chamber through the stir shaft orifices  54  is distributed throughout the firebox burn chamber  34  to provide complete combustion of the fuel. Preferably, the stir shaft  48  is easily removable for maintenance convenience. 
     The insulated firebox burn chamber  34  shown in  FIGS. 7A and 7B  provides a high temperature combustion atmosphere and is sufficiently insulated to maintain the heat necessary to reinitiate combustion when the unit cycles on while, at the same time, producing minimal emissions. Like the stir shaft  48 , the firebox is also preferably easily removable for maintenance ease. 
     The heat/particulate recovery module  36  includes a heat exchanger assembly having a plurality of water-filled heat recovery plates  70  mounted vertically within the combustion chamber  30  as shown in  FIGS. 5 and 6 . In the preferred embodiment shown, there are five heat recovery plates  70 , although a greater or fewer number of such plates may also be used. Water is pumped by a circulating pump  88  from the heated location of the lowermost water-filled heat recovery plate  71  into the remaining recovery plates, four in this instance, and finally into a water tank  31  from which the heated water is directed to a heated location through a water supply line  87 . After passing through the heated location, a baseboard home heating system, for example, the water returns to the heating unit through a water line  85  and water return  81 . 
     The heat/particulate recovery module  36  has two functions. First, with the lowermost heat recovery plate  71  directly over the combusting fuel and the remaining plates  70  in spaced relationship thereto to systematically absorb the heat being generated, the module  36  provides additional heat transfer from the combustion chamber  30  for maximum heating efficiency. Second, the heat/particulate recovery module  36  removes emission particulates from the burned fuel by slowing the exhaust gases to a velocity at which the particulates will “fall out” of the air flow and accumulate onto the tops of the recovery plates rather than being exhausted into the atmosphere through the smoke stack  16 . 
     The present invention further includes a safety feature in the form of a thermo cycle plumbing assembly generally designated by reference numeral  80 , shown in  FIG. 10 . Whenever a power failure or a pump failure occurs, the thermo cycle plumbing assembly  80  enables the heat/particulate recovery module  36  to continue to operate without overheating. This continued operation is made possible by the physics of hot water rising. 
     More particularly, as shown in  FIGS. 12A and 12B , during a power interruption hot water rises from the coldest bottom portion of the water tank and is then fed through the thermo cycle plumbing assembly  80  and water return  81  to the heat/particulate recovery module  36 . The water moves upwardly through the module  36  from the lowermost recovery plate  71  to the uppermost, and hottest, portion of the water tank  31 . Rather than passing into the supply line  87  and to the heated location, however, the water continues to cycle through the heating unit, returning through the thermo cycle plumbing assembly  80  to the heat/particulate recovery module  36  in a circulating loop that prevents excessive heat buildup in a particular area that might damage the heating unit or create a safety concern. Once power is restored, the heated water is again pumped through the water supply line  87  to the heated location and then back to the heating unit through the water return line  85  as previously described. 
     The process control module  20  with process control relay  21  provides for automatic operation of the heating unit  12 , being programmable to control both the rate at which augered fuel is fed into the firebox burn chamber  34  and the rate at which the combustion air is introduced into the firebox burn chamber  34  for optimum burning, efficiency, safety and ease of operation. 
     In addition, the control module  20  receives inputs from various sensors including a low water sensor  82  and a water tank temperature sensor  84 . If the control module receives a signal from the low water sensor indicating that a low water condition exists in the water tank  31 , for example, the control module will automatically lock out the feed auger assembly  40  and the combustion air blower assembly  42 , and energize an automatic water fill valve  86  that is connected to the pressurized water fill line  89  to prevent overheating of the heating unit. Once the low water condition in the water tank  31  has been remedied, the control module returns the heating unit to normal operation. 
     The heating unit is designed to burn wood pellets or any of the variously known fuel pellets that are available on the market today. The heating unit may also be configured to burn bin run corn grain. These fuels are readily available, renewable energy sources which is an important consideration in reducing fossil fuel consumption as well as greenhouse gases. A further advantage of these renewable energy sources is that the composition and packaging of the fuel makes it convenient for the consumer to use. 
     The automatic process control system of the present invention provides the benefit of efficient, user-friendly operation, eliminating the need for the user to make manual adjustments while the unit is operating. In addition, the combustion chamber design provides a very high degree of heating efficiency as well as effective particulate recovery, resulting in reduced emissions which protects the environment. The heating unit is designed to meet the 2010 Environmental Protection Agency requirements for efficiency and emissions standards that apply to automatically fed bio-fuel outdoor heating appliances, as described in ASTM standard E2618 (ASTM E6.54.08 Standard Test Method for Measurement of Particulate Emissions and Heating Efficiency of Outdoor Solid Fueled-Fired Hydronic Heating Appliances). 
     The foregoing descriptions and drawings should be considered as illustrative only of the principles of the invention. The invention may be configured in a variety of shapes and sizes and is not limited by the dimensions of the preferred embodiment. Numerous applications of the present invention will readily occur to those skilled in the art. Therefore, it is not desired to limit the invention to the specific examples disclosed or the exact construction and operation shown and described. Rather, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.