High-Efficiency Gas-Fired Forced-Draft Condensing Hot Water Boiler

Abstract

A high-efficiency hot-water boiler for a heating system of a building is provided. The boiler includes a boiler enclosure that contains a furnace area compartment within an insulated sealed casing, a first watertube compartment within a sealed casing, a second watertube compartment within a sealed casing, and an air-to-air preheat exchanger within a sealed casing. A plurality of separate, closely-spaced watertubes extends within each of the compartments and provides paths for working fluid to flow through the compartments for purposes of transferring heat to the working fluid. A burner is located within the furnace area compartment for combusting an air/gas mixture. The casings include openings for directing the passage of the products of combustion to make a first pass through the furnace area compartment, a second pass through the first watertube compartment and a third pass through the second watertube compartment and then through the air-to-air preheat exchanger to preheat fresh combustion air before being exhausted from the enclosure via the flue. An air/gas mixer and a burner ignition system are also disclosed.

1 . A high-efficiency boiler for a heating system of a building, comprising:
 a boiler enclosure containing a furnace area compartment within an insulated sealed casing, a first watertube compartment within a sealed casing, a second watertube compartment within a sealed casing, and an air-to-air preheat exchanger within a sealed casing;   a plurality of separate, closely-spaced watertubes extending within each of said furnace area, first watertube and second watertube compartments for providing paths for working fluid to flow through said compartments for transfer of heat to the working fluid;   a burner located within said furnace area compartment for combusting an air/gas mixture; and   openings for passage of products of combustion between said furnace area compartment and said first watertube compartment, said first watertube compartment and said second watertube compartment, and said second watertube compartment and said air-to-air preheat exchanger;   said openings positioned to enable the products of combustion to make a first pass through the furnace area compartment, a second pass through the first watertube compartment and a third pass through the second watertube compartment and then through said air-to-air preheat exchanger to preheat fresh combustion air before being exhausted from the enclosure via a flue.   
     
     
         2 . A high-efficiency boiler according to  claim 1 , further comprising an air blower located within said enclosure adjacent said air-to-air preheat exchanger at an end of said boiler enclosure for directing fresh combustion air into said air-to-air preheat exchanger. 
     
     
         3 . A high-efficiency boiler according to  claim 2 , further comprising:
 a fresh combustion air inlet formed in a wall of said enclosure adjacent an opposite end of said boiler such that, when said blower draws fresh combustion air into said enclosure via said fresh combustion air inlet, the fresh combustion air must travel substantially a full length of said enclosure to reach said blower and said air-to-air preheat exchanger;   wherein the fresh combustion air is initially preheated in said enclosure due to heat radiating from said casings and is further preheated by heat exchange with the products of combustion as the fresh combustion air passes through said air-to-air preheat exchanger.   
     
     
         4 . A high-efficiency boiler according to  claim 3 , further comprising:
 a burner box located within said enclosure adjacent said opposite end of said enclosure on a wall of said furnace area compartment;   a duct providing passage of the preheated fresh combustion air from said air-to-air preheat exchanger to said burner box; and   a mixer located within said burner for mixing the preheated fresh combustion air from said burner box with a supply of natural gas or propane and for uniformly distributing the mixture within said burner.   
     
     
         5 . A high-efficiency boiler according to  claim 4 , further comprising:
 a base header extending substantially horizontal within said enclosure along a base of said enclosure directly underneath said compartments, said base header having a return inlet adjacent said end of said enclosure for receiving a return working fluid; and   an upper header extending substantially horizontal within said enclosure along a top of said enclosure directly over said compartments, said upper header having a supply outlet adjacent said opposite end of said enclosure for providing a supply of heated working fluid;   each of said watertubes in said compartments having opposite ends with one of said ends connected to said base header and an opposite end connected to said upper header;   wherein the working fluid is returned to the boiler via the base header at a return temperature, flows through said watertubes where the working fluid is heated, flows into said upper header from said watertubes, and then out of the boiler at a supply temperature.   
     
     
         6 . A high-efficiency boiler according to  claim 5 , wherein the boiler is a condensing boiler and has a drain, and wherein said drain collects and discharges from said enclosure condensation that forms on exterior surfaces of said watertubes. 
     
     
         7 . A high-efficiency boiler according to  claim 6 , wherein said return temperature is about 160° F., said supply temperature is about 180° F. and a thermal efficiency of the boiler is at least 90%. 
     
     
         8 . A high-efficiency boiler according to  claim 6 , wherein each of said watertubes has an intermediate section between its opposite ends, wherein said intermediate section has an undulating shape that extends substantially across a full width of said furnace area, first watertube, or second watertube compartment. 
     
     
         9 . A high-efficiency boiler according to  claim 8 , wherein said opposite ends of said watertubes include a reduced diameter throat section and an outwardly-extending circumferential flange having an outer diameter no greater than an outer diameter of said intermediate section so that said watertubes can be closely spaced within said compartments. 
     
     
         10 . A high-efficiency boiler according to  claim 9 , wherein said opposite ends of said watertubes are integral formed ends and do not include separately-manufactured fitments welded thereto. 
     
     
         11 . A high-efficiency boiler according to  claim 8 , wherein said burner includes a metal fiber burner head that extends between undulations of said intermediate sections of said watertubes in said furnace area compartment. 
     
     
         12 . A high-efficiency boiler according to  claim 11 , wherein only two different shapes of watertubes are contained within said enclosure, wherein said watertubes are made of stainless steel, and wherein each watertube is individually replaceable. 
     
     
         13 . A high-efficiency boiler according to  claim 12 , wherein said enclosure has removable access panels and is of modular construction, and wherein the boiler has a heating capacity of 3,000 MBH to 2,000 MBH. 
     
     
         14 . A high-efficiency boiler according to  claim 1 , wherein said burner is a metal fiber burner and has a two-stage ignition system in which an ignition flame is ignited to ignite a main gas pilot flame and the main gas pilot flame is ignited to, in turn, ignite said burner. 
     
     
         15 . A high-efficiency boiler according to  claim 14 , wherein said two-stage ignition system includes an electrically-operated pilot ignition gas valve for providing gas to an ignition tube for creating the ignition flame with a spark igniter, and wherein said two-stage ignition system further includes a separate electrically-operated main pilot gas valve for separately providing gas to a main pilot gas divider that exists on only a small portion of said metal fiber burner. 
     
     
         16 . A high-efficiency boiler according to  claim 15 , wherein, during a first trial period for igniting said burner, the ignition flame fueled by said electrically-operated pilot ignition gas valve ignites the main gas pilot flame at said main pilot gas divider which is fueled by said separate electrically-operated main pilot gas valve, and wherein, after the main gas pilot flame is ignited, said system automatically de-energizes said electrically-operated pilot ignition gas valve to extinguish the ignition flame. 
     
     
         17 . A high-efficiency boiler according to  claim 16 , wherein, during a second main burner trial period, gas is introduced into said burner via a main gas burner supply line and said burner is ignited by the main gas pilot flame, and wherein, after the burner is ignited, said system automatically de-energizes said electrically-operated main pilot gas valve to extinguish the main gas pilot flame. 
     
     
         18 . A high-efficiency boiler according to  claim 1 , wherein said burner has a air/gas mixer, wherein said mixer has a central hub and hollow spokes extending radially therefrom, and wherein said central hub is adapted to direct a supply of gas into said hollow spokes. 
     
     
         19 . A high-efficiency boiler according to  claim 18 , wherein said mixer has channels between said spokes through which a supply of combustion air flows through said mixer, and wherein said spokes have outlets in the sides thereof to discharge the gas into the flow of combustion air such that the gas is discharged in a direction substantially perpendicular to the flow of combustion air. 
     
     
         20 . A high-efficiency hot-water boiler according to  claim 19 , wherein said mixer has additional spokes with apertures through which the combustion air flows to generate additional turbulence. 
     
     
         21 . A burner for a high-efficiency hot-water boiler, comprising:
 a hollow, cylindrical, elongate metal fiber burner head having a distal end and a proximal end; and   an air/gas mixer located adjacent a proximal end of said burner head for uniformly distributing an air/gas fuel mixture within said burner head, said mixer having a central hub and hollow spokes extending radially therefrom, said central hub receiving a supply of gas and directing it into said hollow spokes.   
     
     
         22 . A burner according to  claim 21 , wherein said mixer defines channels between said spokes for receiving a supply of combustion air that flows transversely through said mixer into said burner head, and wherein said spokes have gas outlets in the sides thereof that discharge gas into the flow of combustion air such that the gas is discharged in a direction substantially perpendicular to the flow of combustion air. 
     
     
         23 . A burner according to  claim 22 , wherein said mixer has additional spokes with apertures through which the combustion air flows to generate additional turbulence. 
     
     
         24 . A method of igniting a metal fiber burner head of a high-efficiency boiler, comprising:
 igniting an ignition flame by energizing an electrically-operated pilot ignition gas valve to provide gas to an ignition tube and by igniting an air/gas fuel mixture in the ignition tube by energizing a spark igniter;   simultaneously with said ignition flame igniting step, energizing a separate electrically-operated main pilot gas valve for separately providing gas to a main pilot gas divider that is located on a small portion of the metal fiber burner head;   after said ignition flame igniting step, igniting a main gas pilot flame with the ignition flame by igniting a air/gas fuel mixture at the main pilot gas divider;   after said step of igniting the main gas pilot flame, de-energizing the electrically-operated pilot ignition gas valve to extinguish the ignition flame;   after said step of igniting the main gas pilot flame, uniformly distributing an air/gas fuel mixture to the burner head and igniting the burner head with the main gas pilot flame; and   after said igniting said burner head, de-energizing the electrically-operated main pilot gas valve to extinguish the main gas pilot flame.