Patent Publication Number: US-8978639-B2

Title: Secondary room air heat exchanger and method of heating secondary room air

Description:
BACKGROUND 
     Gas, electric, and wood burning fireplaces provide warmth and/or the visual appeal of a fire within a room. Thermally efficient fireplaces save fuel cost and environmental impact. While various improvements in fireplace efficiency have been achieved, further improvements remain to be realized. 
     SUMMARY 
     Some aspects relate to a fireplace system including a fireplace and a secondary heat exchanger. The fireplace includes a housing, a combustion chamber, a combustion assembly, an exhaust duct, and a fresh air intake duct, The housing has a front, a back, a first side, and a. second side. The combustion chamber is disposed within the housing, the combustion chamber and the housing combining to define a primary heat exchanger about the combustion chamber, the primary heat exchanger having an inlet for receiving primary room air from a room in which the fireplace is installed and an outlet for delivering air that has passed through the primary heat exchanger back into the room in which the fireplace is installed. The combustion assembly includes a burner configured for burning combustible gas in the combustion chamber. The exhaust duct carries exhaust air generated by combustion of the combustible gas in the combustion chamber out of the combustion chamber and away from the fireplace. The fresh air intake duct for carries fresh air from outside of the fireplace to the combustion assembly. The secondary heat exchanger includes an exhaust air conduit, a secondary room air conduit, an intake air conduit, and a coupling duct. The exhaust air conduit receives the exhaust air from the exhaust duct of the fireplace. The secondary room air conduit receives secondary room air. The intake air conduit passes fresh intake air into the fresh air intake duct of the fireplace, the secondary heat exchanger being configured to transfer heat from the exhaust air passing through the exhaust air conduit into the secondary room air passing through the secondary room air conduit and the fresh intake air passing through the fresh intake air conduit. The coupling duct passes secondary room air from the secondary heat exchanger into the primary heat exchanger. 
     Other aspects relate to a method of heating a room in a structure with a fireplace. The method includes feeding combustible gas to a burner of a combustion assembly of the fireplace to create heat and flames with hot exhaust air passing out of a combustion chamber of the fireplace through an exhaust duct and into an exhaust air conduit of a secondary heat exchanger and out of the structure. Fresh intake air is passed from outside the structure into an intake air conduit of the secondary heat exchanger through an intake duct of the fireplace and to the combustion assembly. Primary room air is passed from the room in the structure through a primary heat exchanger in the fireplace to transfer heat from the combustion chamber to the primary room air. Secondary room is passed through the secondary heat exchanger and from the secondary heat exchanger into the primary heat exchanger, the secondary heat exchanger transferring heat from the exhaust air into the fresh intake air and the secondary room air. 
     While various aspects of embodiments are disclosed, stilt other embodiments of the present invention are disclosed and should be apparent to those skilled in the art from the following detailed description, which shows and describes illustrative embodiments of the invention. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not restrictive. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic vim of a fireplace system for heating a room in a structure, according to some embodiments. 
         FIG. 2  is an isometric view of the system of  FIG. 1 , according to some embodiments, 
         FIG. 3  is an isometric view of a secondary heat exchanger of the system of  FIG. 1 , according to some embodiments. 
         FIG. 4  is an isometric view of the secondary heat exchanger of the system of  FIG. 1  in an unassembled state, according to some embodiments. 
         FIG. 5  is a side view of the secondary heat exchanger of  FIG. 3  and  FIG. 6  is a sectional view of the secondary heat exchanger along line  6 - 6  of  FIG. 5 , according to some embodiments. 
         FIG. 7  is an isometric view of another fireplace system for heating a room in a structure, according to some embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     Various embodiments relate to fireplace systems including a secondary heat exchanger for improved fireplace efficiency. More specifically, some embodiments relate to direct vent gas fireplaces having a top (“vertical direct vent”) or rear exhaust/inlet duct (“horizontal direct vent”) coupled to a secondary heat exchanger, Examples of suitable fireplaces for the system include those sold by Heat-N-Glo Fireplace Products, Inc. of Lakeville, Minn., such as the product identified by Model Number 600DVT. Generally, the fireplace is provided with a primary heat exchanger which accepts primary room air that passes under a combustion chamber of the fireplace, around the back of the combustion chamber, and over the top of the combustion chamber back into the room to provide an efficient convection and radiant heating system. 
     In some embodiments, the fireplace does not require inside air (i.e., air inside the structure which the fireplace is being used to heat) for combustion, but instead utilizes air passing into the combustion chamber from the exhaust/inlet duct. In some embodiments, the secondary heat exchanger coupled to the exhaust/inlet duct is positioned in a fireplace chase in which a fireplace is installed and driven off a blower housed within the fireplace to draw additional heat off combustion exhaust exiting the fireplace through the exhaust/inlet duct. 
     Various additional or alternate features and advantages to the foregoing should be apparent with reference to the text and drawings. Although described with reference to direct vent fireplaces, the system optionally includes any of a variety of prefabricated gas fireplaces, such as universal vent, B-vent, horizontal/vertical-vent, dual direct vent, or others. 
       FIG. 1  is a side, schematic view of a horizontal direct vent configured fireplace system  10  for heating a room R in a structure S, according to some embodiments. The system  10  includes a fireplace  12  with a primary heat exchanger  14  and a secondary heat exchanger  16  connected to the fireplace  12 . The fireplace  12  is installed in a framed in chase C, or secondary room, within the structure S and vents exhaust gases to the environment E outside of the structure S. As understood by those of skill in the art, gas fireplaces are often installed in a chase structure that is designed to hold the fireplace with sufficient clearance to be safe and meet local code standards. The fireplace chase is optionally described as a small, secondary room adjacent to the primary room that a fireplace is heating. The fireplace  12  also includes a combined exhaust outlet and combustion air ink: formed by a coaxial duct  18  including an exhaust duct  20  and a fresh air intake duct  22  disposed coaxially about the exhaust duct  20 . During operation of the fireplace  12 , fresh air entering through the intake duct  22  is preheated by hot exhaust gases passing out of the fireplace through the exhaust duct  20 . The fireplace  12  includes a housing  24 , a combustion chamber  26 , a blower  28 , and a combustion assembly  30 . 
     In some embodiments, the housing  24  forms an outer shell of the fireplace  12  and combines with the combustion chamber  26  to define at least a portion of the primary heat exchanger  14 , the housing  24  forming an outer wall of the primary heat exchanger  14 , according to some embodiments. The housing  24  includes a front  32 , a back  34 , atop  36 , a bottom  38 , a first side (not shown) and a second side (not shown). 
     The combustion chamber  26  includes a front  50 , a back  52 , a top  54 , a bottom  56 , a first side  58  ( FIG. 2 ), a second side  60  ( FIG. 2 ), and a support panel  62 . Preferably, the front  50  is transparent to allow viewing of components (e.g., a simulated log set) and flames disposed within the combustion chamber  26 . 
       FIG. 2  is an isometric view showing the secondary heat exchanger  16  mounted to the housing,  24 , according to some embodiments, with the sides  58 ,  60  and back  52  of the housing  24  removed for illustration purposes. As shown in  FIG. 2 , the blower  28  includes a quiet, tow speed motor  70 , a first fan assembly  72 , and a second fan assembly  74 , each of the first and second fan assemblies  72 ,  74  being connected to the motor  70 . The first fan assembly  72  includes an inlet  76  and an outlet  78  and the second fan assembly  74  includes an inlet  80  and an outlet  82 . The first fan assembly  72  helps provide a negative pressure for drawing primary room air through the primary heat exchanger  14  and the second fan assembly  74  helps provide a negative pressure for drawing secondary room air through the secondary heat exchanger  16 . In some embodiments, the blower  28  is connected to a controller (not shown) and is operated according to a desired blower timing or based upon addition or alternative input, such as a thermistor that allows the controller to activate the blower  28  once a certain temperature is achieved in the combustion chamber  26 , primary heat exchanger  14 , and/or secondary heat exchanger  16 . 
     As shown in  FIG. 1 , the combustion assembly  30  includes a burner  90 , a gas line  92 , a gas valve  94 , and a log set  96 . The burner  90  is positioned in the combustion chamber  26  (e.g., above or below the support panel  62 ) to combust gas and thereby generate heat and flames. The burner  90  is coupled by the gas line  92  to a source of combustible gas (not shown). The gas valve  94  is positioned in-line with the gas line  92  and is configured to be opened and closed to regulate or modulate the flow of combustible gas to the burner  90 . The log set  96  is optionally positioned above the burner  90 , being supported by the support panel  62  and including one on more simulated logs that are formed, for example, of ceramic fibers and a binder. 
     In some embodiments, the primary heat exchanger  14  defines a primary room air inlet  100  in the front  32  toward the bottom  38  of the housing  24  as well as a primary room air outlet  102  in the front  32  toward the top  36  of the housing  24 . The primary heat exchanger  14  includes a. bottom plenum  104 , a rear plenum  106 , and a top plenum  108  between the housing  24  and the combustion chamber  26 . In some embodiments, the blower  28  and/or convective air flow move (primary room air from a room being heated and in which the fireplace  12  is installed into the primary room air inlet  100 , through the lower, rear, and top plenums  104 ,  106 ,  108 , respectively, and out of the primary room air outlet  102  back into the room being heated. 
     As shown, the combustion chamber  26  is disposed within the housing  24  with the combustion assembly  30  positioned to generate heat and flames in the combustion chamber. The coaxial duct  18  is secured to the housing  24  with the exhaust duct  20  in fluid communication with the combustion chamber  26  to receive combustion byproducts, also described as exhaust air, and the fresh air intake duct  22  configured to deliver intake air from outside the structure in which the fireplace  12  is installed through afresh air plenum  110  to the combustion assembly  30  for generating heat and flames with the burner  90 . 
       FIG. 3  is an isometric view of the secondary heat exchanger  16  in an assembled state and  FIG. 4  is a view of the secondary heat exchanger  16  in a disassembled state.  FIG. 5  is a side view of the secondary heat exchanger  16  and  FIG. 6  is a sectional view of the secondary heat exchanger  16  along line  6 - 6  of  FIG. 5 . As shown, the secondary heat exchanger  16  includes an exhaust air conduit  120 , a secondary room air conduit  122 , an intake air conduit  124 , a guard  126 , and one or more coupling ducts  128  ( FIG. 2 ). 
     In some embodiments, the exhaust air conduit  120  is formed as a substantially rectangular box with an inlet duct  130 , an outlet duct  132 , first and second end caps  134 ,  136  ( FIG. 6 ), a first side  138 , a second side  140 , a top  142 , and a bottom  144 . As shown, the exhaust air conduit  120  defines an exhaust air plenum that is closed to the environment (e.g., the interior of the structure in which the fireplace  12  is installed) and configured such that exhaust air is able to pass into the inlet duct  130 , around the outsides of the secondary room air conduit  122  and the inside of the intake air conduit  124 , and out of the outlet duct  132 . As shown in  FIG. 6 , the exhaust air conduit  120  provides an exhaust air pathway EA through the secondary heat exchanger  16 , the exhaust air pathway EA entering the inlet duct  130 , passing about portions of the secondary room air conduit  122  within the rectangular box, and then passing out of the outlet duct  132 . 
     In some embodiments, the secondary room air conduit  122  includes a plurality of tubes  150  ( FIG. 6 ) maintained by the end caps  134 ,  136 , an inlet cover  152 , and an outlet cover  154 . As shown in  FIG. 4 , the inlet and outlet covers  152 ,  154  are each formed as a part of L-shaped pieces  156 ,  158  to facilitate assembly of the secondary heat exchanger  16 . The inlet cover  152  optionally includes a screen or grate and the outlet cover optionally includes an adapter for connection to ductwork. As shown in  FIG. 6 , the secondary room air conduit  122  ( FIG. 3 ) provides a secondary room air pathway SRM through the secondary heat exchanger  16 , the secondary room air pathway SRM entering through the inlet cover  152 , passing through the plurality of tubes  150 , and out of the outlet cover  154 . 
     As shown in one or more of  FIGS. 3-6 , the intake air conduit  124  includes an inlet duct adapter  170 , and outlet duct adapter  172 , and first and second outer walls  174 ,  176  that define opposed plenums with the first and second sides  138 ,  140  of the exhaust air conduit  120 . In turn, the inlet and outlet duct adapters  170 ,  172  define opposed plenums with the top and bottom  142 ,  144  of the exhaust air conduit  120 . As shown in  FIG. 6 , the intake air conduit  124  ( FIG. 3 ) provides an intake air pathway IA through the secondary heat exchanger  16 , the intake air pathway entering through the inlet duct adapter  170 , passing around the exhaust air conduit  120  (through the plenums created between the sides  138 ,  140  ( FIG. 4 ) and top and bottom  142 ,  144  ( FIG. 4 ) of the exhaust air conduit  120  and the intake air conduit  124 ), and out the outlet duct adapter  172 . 
     From the foregoing, it should be understood that both the intake air conduit  124  and the secondary room air conduit  122  draw heat off the exhaust air conduit  120 , with the intake air pathway IA being generally in counterflow with the exhaust air pathway EA and the secondary room air pathway SRM generally being in crossflow with the exhaust air pathway EA, according to some embodiments. As shown in  FIGS. 1 and 2 , the secondary heat exchanger  16  is mounted to the fireplace  12  with the coaxial duct  18  of the fireplace  12  connected to an outlet duct adapter  172  ( FIG. 6 ) of the intake air conduit  124  ( FIG. 3 ) and the inlet duct  130  ( FIG. 6 ) of the exhaust air conduit  120  ( FIG. 3 ). The coupling duct  128  is secured to the second fan assembly  74  of the blower  28 . 
     During operation of the system  10 , combustible gas is fed to the burner  90  to create heat and flames with hot exhaust air passing out of the combustion chamber  26  through the exhaust duct  20  into the exhaust air conduit  120  of the secondary heat exchanger  16  and out of the structure S. Combustion is fed by fresh intake air from outside the structure S, with the fresh intake air passing into the intake air conduit  124  of the secondary heat exchanger  16  through the intake duct  22 , and to the combustion assembly  30 . As the exhaust air and fresh intake air pass into the secondary heat exchanger  16 , as well as the exhaust and intake ducts  20 ,  22 , is shed from the exhaust air and transferred to the fresh intake air prior to combustion in the combustion chamber  26 . The blower  28  of the fireplace  12  operates to help draw primary room air into the primary heat exchanger  14  so that heat from the combustion chamber  26  is transferred to the primary room air before it is released back into the room R. The blower  28  also draws secondary room air from the chase C into the secondary heat exchanger  16 , which is preheated by the exhaust air passing through the secondary heat exchanger  16 . The secondary room air is injected by the blower into the primary heat exchanger  14  which mixes with the primary room air and is ultimately delivered into the room R being heated. 
       FIG. 7  is an isometric view of a vertical direct vent configured fireplace system  10 A including a secondary heat exchanger  16 A mounted to a housing  24 A of the system  10 A, according to some embodiments. As shown in  FIG. 7 , the rear venting feature is capped, where the sides and back of the housing  24 A are removed for illustration purposes. Various features of the systems  10 ,  10 A are substantially similar and, thus, are referenced cumulatively to features of the system  10 , where, in the drawing and text, similar features of the system  10 A are accorded similar reference numbers to that of the system  10  followed by an “A.” 
     Various modifications and additions can be made to the exemplary embodiments discussed without departing from the scope of the present invention. For example, while the embodiments described above refer to particular features, the scope of this invention also includes embodiments having different combinations of features and embodiments that do not include all of the above described features.