Patent Publication Number: US-7222591-B1

Title: Ducted secondary air fuel-fired water heater LDO detection

Description:
BACKGROUND OF THE INVENTION 
   The present invention generally relates to fuel-fired heating apparatus and, in a representatively illustrated embodiment thereof, more particularly provides a fuel-fired water heater having incorporated therein a burner clogging detection and shutdown system. 
   Fuel-fired water heaters typically operate in locations (such as, for example, attics, closets, basements, sheds, etc.) which are not regularly cleaned, and have ambient air containing particulate matter such as lint, dirt and/or oil (commonly referred to as “LDO”). It is this contaminant-laden air which is delivered to the water heater as combustion air for its burner system. The airborne particulate matter in such combustion air can, over time, clog the water heater&#39;s burner and undesirably increase its production of carbon monoxide. 
   In view of this it would be desirable to provide a fuel-fired water heater with a burner clogging detection system which could monitor the degree of burner clogging caused by airborne particulate matter ingested by the burner and prevent further burner combustion in response to the detection of a predetermined level of burner clogging. It is to this goal that the present invention is primarily directed. 
   SUMMARY OF THE INVENTION 
   In carrying out principles of the present invention, in accordance with a preferred embodiment thereof, a specially designed fuel-fired heating apparatus, representatively a gas-fired water heater, is provided. The water heater comprises a tank for storing water to be heated, and a combustion chamber in thermal communication with the tank. A fuel burner, representatively a radiant burner, is operative to create hot combustion products within the combustion chamber, the fuel burner being progressively cloggable by particulate matter (such as lint, dirt and/or oil) entrained in primary combustion air being delivered thereto during firing of the burner. 
   A first air supply structure is provided for supplying primary combustion air to the fuel burner from outside of the combustion chamber without exposing the supplied primary combustion air to the is interior of the combustion chamber on its way to the fuel burner. Additionally, a second air supply structure is provided for receiving secondary combustion air from outside the combustion chamber and discharging the received secondary combustion air into the interior of the combustion chamber, at a discharge velocity, for flow therethrough to the fuel burner, the second air supply structure being progressively cloggable at a greater rate than the fuel burner, by particulate matter entrained in the received secondary combustion air in a manner progressively reducing the discharge velocity of the secondary combustion air. 
   According to a key aspect of the present invention, a system is provided for monitoring the secondary combustion air discharge velocity within the combustion chamber and responsively terminating operation of the fuel burner when the discharge velocity decreases to a predetermined magnitude indicative of a predetermined degree of clogging of the second air supply structure. Preferably, such system includes a temperature sensor, representatively a thermal release device (TRD), disposed within the interior of the combustion chamber and positioned to be impinged by secondary combustion air being discharged into the combustion chamber from the second air supply structure. The system is operative to monitor the temperature of the temperature sensor (thus also indirectly monitoring the secondary combustion air discharge velocity) and responsively terminate the operation of the fuel burner when the temperature reaches a predetermined magnitude indicative of a predetermined reduction in the cooling of the temperature sensor caused by a reduction in the secondary combustion air discharge velocity. 
   Preferably, the fuel burner is disposed within the combustion chamber, and the first air supply structure includes a primary combustion air supply duct extending through the combustion chamber, from a location exterior thereto, and operatively connected to the fuel burner. 
   The second air supply structure preferably includes a cloggable perforate structure disposed on an outer wall of the combustion chamber, and further includes a duct disposed in said combustion chamber and having an open inlet end connected to the cloggable perforate structure, and an open outlet end through which secondary combustion air may be discharged into the combustion chamber at the aforementioned discharge velocity. 
   According to an aspect of the invention, the open outlet end of the secondary combustion air supply duct has a smaller cross-sectional area than its open inlet end, whereby the secondary combustion air discharge velocity is greater than the velocity of the secondary combustion air across the cloggable perforate structure disposed on the outer wall of the combustion chamber. 
   In an illustrated preferred embodiment thereof, the fuel-fired water heater further comprises a fuel supply system including a fuel supply pipe connected to the fuel burner and having a fuel valve connected therein. The temperature sensor is operative to output a control signal indicative of the temperature of the temperature sensor increasing to a predetermined elevated temperature and being useable to terminate burner combustion by, for example, shutting off further combustion air or fuel flow to the system. 
   Preferably, the radiant burner has a cloggable flame-holding metal mesh wall section, and the cloggable perforate structure disposed on an outer wall of the combustion chamber is a metal mesh structure of a finer mesh size than the cloggable flame-holding metal mesh wall section of the radiant burner. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic cross-sectional view through a lower end portion of a representative fuel-fired hot water heater incorporating therein a specially designed burner clogging detection and shutdown system embodying principles of the present invention; 
       FIG. 2  is an enlarged scale bottom end elevational view of the water heater taken along line  2 — 2  of  FIG. 1 ; and 
       FIG. 3  is an enlarged scale interior elevational view of the water heater taken along line  3 — 3  of  FIG. 1 . 
   

   DETAILED DESCRIPTION 
   schematically illustrated in  FIG. 1  in cross-sectional form is a lower end portion of a fuel-fired heating appliance, representatively a natural draft gas-fired water heater  10 , embodying principles of the present invention. While the heating appliance is representatively a water heater, it could alternatively be a different type of fuel-fired heating appliance, such as, for example, a fuel-fired boiler or air heating furnace without departing from principles of the present invention. 
   Water heater  10  is shown resting on a horizontal support surface such as floor  12 , on elevating support legs  13 , and includes a cylindrical, vertically extending insulated metal tank  14  in which a quantity of pressurized heated water  16  is stored for on-demand delivery in the usual manner to plumbing fixtures (not shown) such as sinks, showers, dishwashers and the like. The bottom wall of the tank  14  defines the top wall  18  of a combustion chamber  20  that underlies the tank  14 . Extending upwardly from the wall  18 , through the water  16 , is a flue pipe  22  communicating with the interior of the combustion chamber  20 . Combustion chamber  20  has a bottom wall  23 . 
   A main gas burner  24 , representatively a radiant burner, is disposed within the interior of the combustion chamber  20 . Other types of fuel burners could alternatively be utilized without departing from principles of the present invention. Firing of the burner  24  creates hot combustion products  26  that pass upwardly through the flue pipe  22  and transfer combustion heat to the stored water  16 . 
   Radiant burner  24  has a horizontally elongated hollow body  28  with a top perforate flame-holding wall section  30  which is illustratively of a metal wire mesh construction. The interior of the burner body  28  is supplied with primary combustion air  32 , via a conduit  34 , from outside the combustion chamber  20 . The primary combustion air  32  delivered to the burner body  28  is mixed with fuel supplied through a fuel supply pipe  36  having a normally closed gas valve  38  installed therein and being held open in a suitable conventional manner during fuel supply to the burner  24 . The fuel and primary combustion air  32  are suitably ignited to form a burner flame  40  on the mesh flame-holding wall section  30  of the burner  24 , and thereby create the hot combustion products  26  upwardly traversing the flue  22 . 
   During firing of the burner  24 , secondary combustion air  42  from outside the combustion chamber  20  is drawn into the combustion chamber  20  through a cloggable perforate structure in the form of a metal mesh section  44  of the bottom combustion chamber wall  23 . Mesh  44  is of a finer mesh size than the coarser burner mesh  30 , and is thus more rapidly clogged by particulate matter (such as lint, dirt and/or oil) entrained in the incoming secondary combustion air  42  compared to the rate of clogging of the burner mesh  30  by particulate matter entrained in the incoming primary combustion air  32 . 
   As used herein, the term “primary combustion air” means air which passes through the burner  24  and is combusted with fuel to form the burner flame  40 , and the term “secondary combustion air” means air that is externally delivered to the burner  24  to support combustion of the already-formed burner flame  40 . 
   The mesh section  44  forms a portion of a unique clogging detection system  46  shown in  FIGS. 1–3 , embodying principles of the present invention and operative to shut down the water heater  10  prior to a predetermined degree of clogging of the burner flame holding mesh  30 . In addition to the mesh  44 , the clogging detection system  46  preferably includes an air delivery duct  48 , and a temperature sensor  50  disposed within the combustion chamber  20 . 
   Representatively, the temperature sensor  50  may be a suitable thermal release device (TRD), or any other one of a variety of other conventional temperature sensing devices, such as a thermocouple, without departing from principles of the present invention. 
   Duct  48  has an open inlet end  52  coupled to the mesh section  44 , and is preferably of a tapered configuration providing the duct with a substantially smaller area open outlet end  54 . During firing of the water heater  10 , the secondary combustion air  42  from outside the combustion chamber  20  is drawn upwardly through the mesh section  44 , through the interior of the duct  48 , and is outwardly discharged through the duct outlet end  54  at a substantially increased velocity relative to its inlet velocity through the mesh  44 . Secondary combustion air  42  exiting the duct  48  impinges upon and cools the temperature sensor  50 . 
   As the secondary combustion air inlet mesh  44  begins to clog with particulate matter entering the duct  48  with the incoming secondary combustion air  42 , the flow rate and discharge velocity of the secondary combustion air  42  are decreased, thereby reducing its cooling of the temperature sensor  50 . When the mesh  44  is substantially completely clogged (at a point in time well before the substantially coarser burner mesh  30  is unacceptably clogged) the temperature of the temperature sensor  50  increases to a predetermined trigger temperature which responsively causes the temperature sensor  50  to output to a controller  56  a shutoff signal  58 . In response, the controller  56  outputs a shutoff signal  60  used to terminate burner combustion. 
   The signal  60  may be used, in a known conventional manner, to terminate further combustion air flow into the combustion chamber  20 , or (as schematically depicted in  FIG. 1 ) be transmitted to the gas valve  38  causing it to return to its normally closed position and shut off further gas flow to the burner  24 . In this manner, the clogging detection system  46  functions (via its monitoring of the temperature of the temperature sensor  50 ) as a shutdown system for indirectly monitoring the discharge velocity of the secondary combustion air  42  exiting the duct  48  and responsively terminating operation of the fuel burner  24  when such secondary combustion air discharge velocity decreases to a predetermined magnitude. 
   While it is preferable that the outlet  54  of the duct  48  be smaller than its inlet  52 , to thereby increase the velocity of the secondary combustion air  42  that is discharged from the duct  48  and impinges upon the temperature sensor  50 , the outlet  54  could alternatively be essentially the same size as the inlet  52 —particularly when the water heater  10  is a forced draft water heater utilizing a draft inducer fan (not shown) to increase the draft through the flue  22 . With a sufficient draft through the water heater during firing thereof, in some instances the duct  48  could conceivably be eliminated altogether. 
   The foregoing detailed description is to be clearly understood as being given by way of illustration and example only, the spirit and scope of the present invention being limited solely by the appended claims.