Abstract:
A multi-oil fired furnace having a heat exchanger that extends rearwardly of the combustion chamber and utilizes laminar air flow around the combustion chamber to minimize the width and height dimensions of the cabinet shell for the furnace. The heat exchanger includes an exhaust header having a central opening and a cluster of concentrically arranged exhaust tubes connected to the combustion chamber. A vertical baffle forces the flow of air through a central opening that is concentric with the combustion chamber into a group of horizontal baffles directing the air into a generally laminar flow pattern against the outer surface of the combustion chamber before being discharged from the cabinet shell in a selected one or more of three possible directions. The fan control switch is mounted on a mounting plate that is welded to the combustion chamber to provide a planar contact surface for the switch mechanism.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims domestic priority on U.S. Provisional Patent Application Serial No. 60/333,860, filed on Nov. 28, 2001, the contents of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates generally to an furnace and associated heat exchanger that are arranged in a generally linear configuration and, more particularly, to a heat exchanger that can be positioned behind the furnace to extract heat therefrom for dispersion into the surrounding environment or to a remote location. 
     Generally, multi-oil furnaces, sometimes referred to as a used-oil fired furnace because of the primary utilization thereof to burn used oil removed from automobiles and the like as well as standard grades of fuel oils, utilize an air-to-air heat exchanger with a blower than moves ambient air through the furnace structure and/or around the combustion chamber to transfer heat generated within the combustion chamber to a remote location for desired utilization thereof. An efficient air-to-air heat exchanger is shown and described for multi-oil furnaces in U.S. Pat. No. 5,494,025, issued to Benjamin K. Smoker and David J. Yoder on Feb. 27, 1996. This heat exchanger generally surrounds the burner chamber by circulating the combustion gases from the rear of the furnace by an upper set of conduits leading to a header in front of the furnace and then through a lower set of conduits to the rear of the furnace again where the gases are exhausted from the furnace. The ambient ventilation air is passed vertically through the assembly to absorb heat from the conduits and the burner chamber before being discharged from the furnace. 
     The heat exchanger described in U.S. Pat. No. 5,494,025 requires a cabinet shell having a height greater than the height of the burner chamber due to the upper and lower banks of conduits transferring the combustion gases around the burner chamber to exchange heat with the ambient ventilation air. Likewise, the width of the cabinet shell is required to be greater than the width of the burner chamber. In some installations, the height and/or width requirements will not permit the utilization of a cabinet shell that is significantly greater than the corresponding dimensions of the burner chamber. 
     Accordingly, it would be desirable to provide a multi-oil furnace that orients the air-to-air heat exchanger substantially rearwardly of the burner chamber so as to minimize the height and/or width dimensions of the furnace cabinet shell. 
     The thermostat controls for the switch associated with the operation of the fan is conventionally mounted on the circular combustion chamber to sense the temperature of the burner chamber. The switch is operable to start the motion of the fan to push room air through the heat exchanger when the combustion chamber has obtained a high enough temperature to expel warm air through the heat exchanger. Other thermostatic switches control the operation of the burner and are conventionally mounted in close proximity to the fan switch, but are operable to sense the temperature within the cabinet shell of the furnace. These other thermostatic switches are operable to shut down the burner in the event the temperatures get too high, such as could result if there is a failure in the fan to blow the cooling room air through he heat exchanger, and to control the ability to re-start the burner only when the temperature has sufficiently cooled. 
     The mounting of a flat fan control switch device on the outer circumference of a circular chamber results in a linear contact between the switch and the burner chamber. Tolerances to establish a properly operable switch in such circumstances are difficult to maintain. Since the fan switch will not start the operation of the fan until a minimum temperature setting has occurred, a fan control switch device that falls outside the acceptable tolerances can result in a premature shut down of the burner, because the temperature in the cabinet shell has increased above the maximum permissible by the other thermostatic switches without causing activation of the fan due to the improper sensing of the temperature of the combustion chamber. 
     Accordingly, an improved mounting for the fan control switch would be desirable to improve the operational performance of the furnace. 
     SUMMARY OF THE INVENTION 
     It is an object of this invent ion to provide a heat exchanger for a multi-oil furnace that overcomes the aforementioned disadvantages of the known heat exchangers. 
     It is another object of this invention to provide a heat exchanger for a multi-oil fired furnace that does not require a large cabinet shell to encase the heat exchanger and combustion chamber of the furnace. 
     It is still another object of this invention to provide a multi-oil furnace with a heat exchanger that enables the combustion chamber of the furnace to have a diameter and length to avoid impingement, metal deterioration, and carbonization from the operation thereof. 
     It is a feature of this invention that the heat exchanger does not restrict the diameter of the combustion chamber of a multi-oil furnace with respect to the overall size of the cabinet shell that encompasses the furnace and heat exchanger. 
     It is an advantage of this invention that the heat exchanger configuration extends the operative life of the combustion chamber because of the lack of restriction on the diameter of the combustion chamber. 
     It is another feature of this invention that the heat exchanger is formed with a plurality of exhaust tubes positioned behind the combustion chamber to transfer heat from the exhausted combustion gases to room air being circulated through the cabinet shell. 
     It is another advantage of this invention that the positioning of exhaust tubes in line with the combustion chamber reduces the height and width of the cabinet shell needed to house the heat exchanger for a multi-oil furnace. 
     It is still another feature of this invention that the exhaust tubes are connected to an exhaust header to collect the exhausted combustion gases before being discharged from the furnace. 
     It is still another advantage of this invention that the provision of an exhaust header rearwardly of the combustion chamber enables the combustion gases to be discharged from either side of the furnace. 
     It is still another feature of this invention that the exhaust header is provided with multiple discharge outlets for selective use to discharge the combustion gases from the furnace. 
     It is still another object of this invention to enhance the exchange of heat from the combustion chamber to room air being circulated through the cabinet shell. 
     It is yet another feature of this invention that the combustion chamber is provided with horizontal baffles to direct room air into a generally laminar flow over the surface of the combustion chamber. 
     It is still another feature of this invention that the room air is forced through a vertical baffle opening concentric with the combustion chamber before being engaged by the horizontal baffles directing room air along the surface of the combustion chamber. 
     It is yet another object of this invention to control the flow path of the room air through the cabinet shell in a manner to maximize the transfer of heat from the combustion process to the room air. 
     It is a further feature of this invention that room air is directed through a central opening through the exhaust header to cause room air to be circulated between exhaust tubes extending between the combustion chamber and the exhaust header, before being forced through an annular opening in a vertical baffle around the combustion chamber and into engagement with horizontal baffles to direct the room air into a laminar flow pattern along the surface of the combustion chamber. 
     It is a further advantage of this invention that the heat exchanger configuration causes room air to be circulated more equally to prolong the life of the heat exchanger due to stresses resulting from unequal heat distribution. 
     It is a further object of this invention to provide an improved mounting of the fan control switch on the combustion chamber to enhance the sensing of the temperature of the combustion chamber. 
     It is yet another advantage of this invention that the control of the operation of the blower fan to move room air through the heat exchanger is improved. 
     It is still a further feature of this invention that the fan control switch is mounted on a linear plate welded to the top of the combustion chamber for a consistent planar contact between the fan control switch and the combustion chamber. 
     It is a further advantage of this invention that the sensing of the temperature of the combustion chamber is sensed more accurately for the controlling of the operation of the blower fan on a multi-oil fired furnace. 
     It is still a further advantage that the contact between the fan control switch and the combustion chamber is planar, rather than linear, due to the welding of a mounting plate on the combustion chamber and forming an integral part thereof. 
     It is yet a further object of this invention to provide a heat exchanger for use with a multi-oil furnace which is durable in construction, inexpensive of manufacture, carefree of maintenance, facile in assemblage, and simple and effective in use. 
     It is still another object of this invention to provide a mounting for a fan control switch for use on a multi-oil fired furnace which is durable in construction, inexpensive of manufacture, carefree of maintenance, facile in assemblage, and simple and effective in use. 
     These and other objects, features, and advantages are accomplished according to the instant invention by providing a multi-oil fired furnace having a heat exchanger that extends rearwardly of the combustion chamber and utilizes laminar air flow around the combustion chamber to minimize the width and height dimensions of the cabinet shell for the furnace. The heat exchanger includes an exhaust header having a central opening and a cluster of concentrically arranged exhaust tubes connected to the combustion chamber. A vertical baffle forces the flow of air through a central opening that is concentric with the combustion chamber into a group of horizontal baffles directing the air into a generally laminar flow pattern against the outer surface of the combustion chamber before being discharged from the cabinet shell in a selected one or more of three possible directions. The fan control switch is mounted on a mounting plate that is welded to the combustion chamber to provide a planar contact surface for the switch mechanism. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The advantages of this invention will become apparent upon consideration of the following detailed disclosure of the invention, especially when taken in conjunction with the accompanying drawings wherein: 
     FIG. 1 is an upper left, front perspective view of a multi-oil furnace incorporating the principles of the instant invention; 
     FIG. 2 is an upper right, front perspective view of the multi-oil furnace shown in FIG. 1; 
     FIG. 3 is a left side elevational view of the multi-oil furnace shown in FIG. 1, a central portion of the cabinet shell being broken away to depict the location of the cupped target of the burner chamber, the burner assembly being removed for purposes of clarity; 
     FIG. 4 is a cross-sectional view taken along lines  4 — 4  of FIG. 3 to depict the rear wall of the burner chamber; 
     FIG. 5 is a front elevational view of the multi-oil furnace shown in FIGS. 1-3, typical threaded mounting rods used in the installation of the multi-oil furnace being depicted at the top of the cabinet shell; 
     FIG. 6 is an exploded diagrammatic upper left, front perspective view of the multi-oil furnace similar to that depicted in FIG. 1, but having the majority of the cabinet shell broken away to depict the interior of the furnace, portions of the combustion gas exhaust tubes being broken away for clarity; 
     FIG. 7 is an upper left, rear perspective view of the heat exchanger and combustion chamber incorporating the principles of the instant invention, the shell of the multi-oil furnace being removed for purposes of clarity; 
     FIG. 8 is an upper right, front perspective view of the heat exchanger and combustion chamber shown in FIG. 7; 
     FIG. 9 is a schematic upper left front perspective view of the multi-furnace incorporating the principles of the instant invention with a portion of the cabinet shell at the front of the furnace being broken away to depict the fan control switch and the thermostatic switches monitoring the temperature of the air within the cabinet shell; and 
     FIG. 10 is an enlarged detail view of the fan control and thermostatic switches mounted on the combustion chamber as depicted in FIG.  9 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to FIGS. 1-6, a multi-oil furnace incorporating the principles of the instant invention can best be seen. Any left and right references used herein are determined by standing at the front of the furnace facing the multi-oil burner mounted on the access door. The general configuration of the burner chamber and burner are shown and described in detail in U.S. Pat. No. 5,531,212, issued on Jul. 2, 1996, to Benjamin K. Smoker, et al, entitled “Multi-Oil Furnace”; and in U.S. Pat. No. 5,409,373, issued on Apr. 25, 1995, to Frederick W. Phillips, et al, entitled “Burner Housing for Multi-Oil Furnaces”, the contents of both of these patents being incorporated herein by reference. As best seen in FIGS. 4 and 5, the typical installation of a multi-oil furnace incorporating the principles of the instant invention is from the ceiling of a housing structure. Accordingly, the cabinet shell  12  is provided with a plurality of connector mounts  18  in the top surface thereof for engagement with threaded rods  19  to suspend the furnace  10  from an elevated structure (not shown). 
     More specifically, the cabinet shell  12  of the multi-oil furnace  10  has a front door  13  on which is mounted a burner assembly  15  for pivotal movement about a generally vertical axis  16  to permit the burner assembly  15  to open away from the front door  13  for service and cleaning in a conventional manner. The front door  13  of the cabinet shell  12  is also pivotally mounted on the cabinet shell  12  by hinges  14  to permit the opening of the front door  13  for service and cleaning of the burner chamber  20 . The burner chamber  20 , which is best seen in FIG. 6, is generally cylindrical in shape and terminates at a back wall  22  on which is mounted a cupped ceramic target  23  to deflect the combustion gases outwardly around the edges of the target  23  to double back around the flame F generated by the burner assembly  15 . The net result is that a greater burning efficiency is accomplished before the combustion gases are drawn out of the burner chamber  20  into the heat exchanger  30 . 
     The back wall  22  of the burner chamber  20  is provided with a circular array of combustion gas exhaust tubes  25  that are uniformly distributed around the circumference of the target  23 . The exhaust tubes  25  are open to the burner chamber  20  and serve to provide conduits for the escape of the combustion gases created in the burner chamber  20 . The exhaust tubes  25  extend rearwardly from the back wall  22  of the burner chamber  20  through the heat exchanger  30  into a header  27  positioned at the rear of the cabinet shell  12 . The header  27  is essentially a hollow box-like structure that is in flow communication with the full circular array of exhaust tubes  25  leading from the back wall  22  of the burner chamber  20 . The header  27  collects the combustion gases from the exhaust tubes  25  and discharges the combustion gases through a discharge opening  28  which can be located on either side of the cabinet shell  12  which is connected to an exhaust device (not shown) to remove the combustion gases to the atmosphere. 
     With the above-described arrangement of components, the heated combustion gases generated by the flame F from the burner assembly  15  are doubled back by the ceramic or stainless steel target  23  and then reversed in direction to discharge from the burner chamber  20  through the rearwardly leading exhaust tubes  25  into the header  27  for ultimate discharge from the furnace  10 . The exhaust tubes  25  extending between the back wall  22  of the burner chamber  20  and the header  27  are individual, discreet tubes  25  passing through and forming part of the heat exchanger  30 . Thus, air can circulate between the exhaust tubes  25  to absorb heat therefrom, as will be described in greater detail below. The exhaust tubes  25  are sealed against both the back wall  22  and the header  27  to prevent any intermingling of the combustion gases with the ambient environment air that would cause contamination thereof. 
     As best seen in FIGS. 6-8, the header  27  is formed with a sealed circular opening  29  passing completely through the header  27 . The circular opening  29  is positioned within the interior circumference of the circular array of the exhaust tubes  25  where the exhaust tubes  25  engage the header  27 . The opening  29  is sealed with respect to the header  27  so that the combustion gases collected therein do not pass into or through the opening  27 , but extends completely through the header  27 . Rearwardly of the header  27 , the rear wall of the cabinet shell  12  is formed with an opening (not shown) that is in register with the circular opening  29  through the header  27 . A blower  32  is supported on the rear wall of the cabinet shell  12  to blow ambient environment air from the surrounding structure through the opening  29  in the header  27  to absorb heat from the heat exchanger  30 . In the alternative, the blower  32  could be conveying air from a remote source for heating in the heat exchanger  30  and return to the remote source. 
     The heat exchanger  30  is formed within the cabinet shell  12  primarily rearwardly of the burner chamber  20 , but also extends around the outer periphery  20   a  of the burner chamber  20  to collect heat therefrom before passing through the selected heated air discharge opening  35 - 37  located forwardly on the cabinet shell, as will be described in greater detail below. Ambient air from the surrounding environment is blown through the opening  29  in the header  27  into the heat exchanger  30 . The orientation of the opening  29  and the velocity provided to the air blown therethrough, primarily pushes the ambient air directly against the back wall  22  of the burner chamber  20 . From the back wall  22 , the air deflects in all directions and passes through the circular array of exhaust tubes  25 , extending around and between the exhaust tubes  25  to absorb heat therefrom. 
     The cabinet shell  12  is preferably formed with a divider wall  38  that aligns with the back wall  22  of the burner chamber  20 . The divider wall  38  preferably has an opening  39  concentric with the burner chamber  20  to define an annular gap around the exterior of the burner chamber  20  to force the ambient air to circulate around the burner chamber  20  before being discharged through the heated air discharge opening  35 - 37 . Preferably, the space in the cabinet shell  12  surrounding the burner chamber  20  is be divided into passageways by horizontally, extending baffles  40  that are either welded to or supported on the burner chamber  20 . The horizontal baffles  40  intercept the majority of the air forced through the annular opening  39  and direct the movement of the ambient air into a generally laminar flow path along the exterior of the burner chamber  20  to increase the transfer of heat from the burner chamber  20  to the ambient air before being discharged from the furnace  10  through the heated air discharge opening  35 - 37 . 
     As best seen in FIG. 5, the cabinet shell  12  is provided with three alternate discharge openings  35 - 37 , one  35  on the left side of the cabinet shell  12 , one  36  on the opposite right side of the cabinet shell  12 , and the third  37  on the bottom surface of the cabinet shell  12 , that can be used to direct the discharge of warmed ambient air from the cabinet shell  12 . Each discharge opening  35 - 37  is divided into two individual openings, for example  36   a ,  36   b , to provide a number of selectable options for the discharge of warmed ambient air. Because of the size of the blower fan  32 , any two of the individual openings, depicted in FIGS. 1,  3  and  5  as individual openings  35   a ,  35   b , of the total of six such openings around the three sides of the cabinet shell  12  can be used to discharge warmed ambient air. 
     Using more than two of the individual openings can lead to an overworked and burned-out fan motor  32 . Those individual openings, depicted in FIG. 2 as  36   a ,  36   b , not utilized to discharge warmed ambient air will be covered with a blank  34  to prevent the discharge or air therefrom. Accordingly, the warmed ambient air could be selectively discharged all from the right side of the cabinet shell  12 , the left side, or the bottom, as depicted in FIG.  5 . One of the individual openings could be opened on any two of the sides for discharge of heated air simultaneously in different directions from the cabinet shell  12 . 
     In operation, the multi-oil furnace  10  is mounted for operation, such as by suspending the furnace  10  by threaded rods  19  interconnecting an elevated structure (not shown) and the connector mounts  18  on the top of the cabinet shell  12 . A supply of oil, such as used automotive oils, food service cooking oils or agricultural oils, is connected to the burner assembly in a conventional manner, such as is described in U.S. Pat. No. 5,531,212. Electrical power is provided through the junction box  17  coupled with an external source of electricity to provide electrical power to the burner assembly  15  to ignite the oil delivered to the burner assembly  15  and provide the flame F. The flame F is directed toward the cupped ceramic target  23  mounted on the rear wall  22  of the burner chamber  20 , where the created hot combustion gases are doubled back on the flame F to provide an efficient burning of the oil before re-directing the path of the combustion gases back toward the rear wall  22  to pass into and through the circular array of the exhaust tubes  25  opened to the burner chamber  20  through the rear wall  25  thereof 
     The heated combustion gases passing interiorly through the exhaust tubes  25  transfer heat through the walls of the exhaust tubes  25  to the ambient air being blown through the heat exchanger  30  through which the exhaust tubes  25  pass before connecting with the header  27 . The combustion gases are then collected in the header  27  and discharged from the furnace  10  through the discharge opening  28 . The combustion gases created from the ignition and combustion of the oil from the burner assembly  15  heats the structure of the burner chamber  20 , the back wall  22 , the exhaust tubes  25 , and the header  27 . Accordingly, heat can be absorbed from all of these devices. In addition, the annular nature of the header  27  and exhaust tube arrangement spreads the combustion gases around better to eliminate cold spots that cause premature wear within the exhaust system. 
     First, ambient air, whether from the immediate environment or a remote location, is blown into the heat exchanger  30  by a blower  32 . The unheated air from the blower  32  is blown against and around the header  27  and, primarily, through the circular opening  29  passing through the header  27 , gaining some heat transfer from the header  27 . The air passing through the circular opening  29  is directed against the back wall  22  of the burner chamber  20  where some additional heat can be transferred to the ambient air. Primarily, however, most of the heat transferred to the ambient air blown into the heat exchanger  30  by the blower  32  is absorbed from the exhaust tubes  25  and, eventually, from the outer periphery  20   a  of the burner chamber  20 . 
     After deflecting off of the rear side of the back wall  22  of the burner chamber  20 , the ambient air is circulated around and outwardly through the array of exhaust tubes  25  and then through an annular opening  39  in the generally vertical divider wall  38  extending around the back wall of the burner chamber  20 . The ambient air is then directed around the outer periphery  20   a  of the burner chamber  20  in a generally laminar flow path by the horizontal baffles  40  to absorb some additional heat from the burner chamber  20  before being discharged from the cabinet shell  12  through the utilized heated air discharge opening  35 - 37  near the front of the cabinet shell  12 . 
     The above-described structure provides a multi-oil furnace that has a minimized height and width dimension in favor of an extended length dimension, as the heat exchanger is positioned primarily rearwardly of the burner chamber instead of primarily surrounding the burner chamber as is taught in U.S. Pat. No. 5,531,212. The circular opening  29  in the rear header  27  enables the ambient air to be directed through the header  27  to collect heat therefrom before being passed into the heat exchanger area  30  where the spaced exhaust pipes  25  are arranged in a circular array. The proven burner assembly  15  and burner chamber  20  construction can be maintained and incorporated into the new furnace design without sacrificing dimensional requirements of some installations. The heat exchanger  30  will provide an efficient air-to-air transfer of heat from the combustion gases. Service and cleaning efficiencies of the prior multi-oil furnace taught in the aforementioned U.S. Pat. No. 5,531,212, can also be retained due to the pivoted burner assembly  15  and the pivoted front door  13 , and due to the positioning of the discharge opening  28  at the bottom of the header  27  to facilitate the cleaning of ash and other debris therefrom in an easy and convenient manner. 
     Referring now to FIGS. 9 and 10, the mounting of the thermostatic control switches can best be seen. The control switch  42  for initiating the operation of the blower  32  to blow ambient air through the heat exchanger  30  is mounted on the forward end of the burner chamber  20  for access through an access panel  45  on top of the cabinet shell  12 . Typically, the fan control switch  42  is mounted directly on the outer periphery  20   a  of the burner chamber  20  such that the interaction between the switch and the burner chamber is a linear contact due to the planar switch meeting a circular burner chamber  20 . 
     According to the principles of the instant invention, the fan control switch  42  is mounted on a mounting plate  43  which is preferably welded to the top surface of the burner chamber  20 . The mounting plate  43  through its welded connection to the burner chamber  20  is substantially at the same temperature as the outer periphery  20   a  of the burner chamber  20 . Thus, the mounting of the fan control switch  42  directly on the mounting plate  43  provides a generally planar contact for the fan control switch  42  to enhance the sensing performance of the switch. 
     In operation, the fan control switch  42  initiates the operation of the blower  32  whenever the temperature of the burner chamber  20  reaches a predetermined level so that the air being blown through the heat exchanger  30  by the blower  32  will extract heat from the heat exchanger  30  and blow warmed air from the discharge opening  35 - 37 . Next to the fan control switch  42 , also accessible through the access panel  45 , are the high temperature limit switch  47  and the reset switch  48 . If the temperature within the cabinet shell  12  exceeds a predetermined temperature, the high limit switch  47  will stop operation of the burner  15 . The reset switch  48  is operable to re-start operation of the burner  15  whenever the temperature within the cabinet shell  12  has cooled sufficiently to permit safe operation of the furnace  10 . 
     The mounting of the fan control switch  42  on the mounting plate  43  permits a more accurate sensing of the temperature of the burner chamber  20  due to the planar contact between the switch  42  and the plate  43 . Proper operation of the fan control switch  42  will initiate operation of the blower to extract heat from the heat exchanger  30 , thus cooling the temperature within the cabinet shell  12  before exceeding the maximum allowable temperature set by the high temperature limit switch  47 . 
     It will be understood that changes in the details, materials, steps and arrangements of parts which have been described and illustrated to explain the nature of the invention will occur to and may be made by those skilled in the art upon a reading of this disclosure within the principles and scope of the invention. The foregoing description illustrates the preferred embodiment of the invention; however, concepts, as based upon the description, may be employed in other embodiments without departing from the scope of the invention.