Abstract:
A gas appliance, flue assembly, or vent adapter including an adjustable flow regulator which regulates the proportions and volume of dilution air and combustion products into the vent is disclosed. The flow regulator can be adjusted to allow a given appliance to exhaust vent gases through a range of different venting systems constructed from a wide range of materials. The appliance installer may adjust the appliance vent gases for a particular pre-existing or installed vent. The flow regulator also provides flow resistance which helps prevent backdrafting and the free escape of dilution air (which may be heated room air in some instances) through the vent to the outside atmosphere.

Description:
This invention relates to venting systems for gas-burning appliances. More specifically, the present invention relates to a device that adjusts the dilution air flow and combustion product flow from an appliance to adapt the appliance vent gas composition for venting systems built from a variety of materials. 
     CROSS-REFERENCE TO RELATED APPLICATIONS 
     Not Applicable. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable. 
     BACKGROUND OF THE INVENTION 
     Conventional gas heating appliances such as furnaces, boilers, and water heaters provide the consumer with safe, economical space and water heating, while requiring little maintenance during a long lifespan. These appliances typically use single wall galvanized vent connectors and either a masonry chimney or Type B vent pipe to vent the flue gases created during operation. The American National Standards Institute (ANSI) categorizes gas appliances based on the pressure produced in a special test vent and the difference between the actual temperature and dew point temperature of the flue gas. 
     A category I appliance is one which has a vent expected to operate under negative static vent pressure with a minimum of condensation. A category I furnace or boiler has an Annual Fuel Utilization Efficiency (AFUE) range of 78% minimum to approximately 83%. Moisture does not condense from the flue gas in category I appliances because the actual flue gas temperature is generally more than 140° F. above its dew point temperature. Traditional draft hood equipped appliances are category I appliances. However, many mid-efficiency, fan-assisted appliances are category I appliances as well. Such appliances can be made category I appliances by adjusting the flue gas temperature to be in the same range as the traditional category I appliance, and by designing the vent system to maintain a negative pressure even in the presence of the fan. Venting systems for category I appliances typically include Type B vents, lined masonry chimneys, and single wall metal vents. 
     Category II appliances also operate with negative vent pressure. However, the vent gas temperature is generally less than 140° E above its dew point temperature. The condensation occurring in these appliances requires the designer to use a corrosion resistant vent to exhaust the flue gases. There are few, if any, category II appliances on the market. 
     Category III appliances operate with a positive vent pressure and with a vent gas temperature generally at least 140° F, above its dew point temperature. Their AFUE ranges from approximately 78% to 83%. Because the pressure in the vent exceeds that of the surrounding atmosphere, these appliances require an airtight vent to prevent leakage of flue gases before they reach the outside venting location. An example of a category III appliance would be a mid-efficiency furnace that is vented horizontally through the wall. Venting systems for category III appliances typically include high temperature plastic and single wall stainless steel metal vents. 
     Category IV appliances include furnaces, boilers, and other devices that operate with a positive vent pressure and with a vent gas temperature less than 140° F above its dew point temperature. They generally have AFUE values above 83%. Because the pressure in the vent exceeds that of the surrounding atmosphere and because condensation occurs in the vent, these appliances require an airtight, corrosion-resistant vent that is equipped for condensate disposal. Category IV appliances are usually high-efficiency, condensing devices. Venting systems for category IV appliances typically include high temperature plastic, polyvinyl chloride (“PVC”), or chlorinated polyvinyl chloride (“CPVC”) vents. 
     ANSI Z21.47-1993 provides the current category certification requirements for gas furnaces. These requirements define and use the concept of Steady State Thermal Efficiency (SSTE) in making a category determination. SSTE measures the appliance&#39;s operating efficiency by dividing the total gas energy input to the appliance into the amount of energy gainfully used by the appliance (essentially one minus the amount of energy expelled up the flue (wasted energy)) while the appliance is operating in a steady state. AFUE, on the other hand, is an overall assessment of an appliance&#39;s annual operating efficiency. ANSI Z21.47-1993 uses flue gas temperature and the flue gas carbon dioxide content to distinguish between category I and non-category I appliances based on a SSTE of 83%. The flue gas temperature of an appliance with a given SSTE varies with the amount of excess air used for combustion and the amount of dilution air added prior to the vent. These amounts, in turn, determine the percentage of carbon dioxide in the flue (7-9% for most appliances). The ANSI specification indicates, for example, that an appliance having between 7-9% carbon dioxide in the flue gas qualifies as a category I appliance when the flue gas is approximately 140° F, or more above its dew point temperature. 
     Assigning an appliance to a specific category is important because the category determines the type, size, material, and installation requirements of the venting system for that specific appliance. For example, a category I appliance may use traditional venting materials such as Type B vent pipe or a masonry chimney, while a category IV furnace requires a vent system built from corrosion resistant materials, and category III and IV appliances require airtight vent systems. 
     The flue gas of natural draft appliances, such as furnaces and water heaters, contains a large amount of water vapor. As the industry has moved to high efficiency appliances, and subsequently to lower flue gas temperatures, condensation of water and corrosive substances from the flue gas onto exhaust conduit surfaces has become a major design issue. Most new appliances are connected to an old vent, often using a single wall vent connector. In many cases, the vent is a masonry chimney. However, in today&#39;s building codes, the use of single wall metal vent connector is severely limited, and most masonry chimneys require relining before the new appliance may be installed. Converting to a Type B connector from a single will connector may cost the building owner up to 60.00, while relining a chimney to protect against condensation can cost from around 200 to 800. For another example, problems with category III appliances using high temperature plastic vents have prompted some jurisdictions and some appliance manufacturers to prohibit the use of high temperature plastics. Alternative stainless steel vent systems cost roughly twice as much as high temperature plastic systems, in the 100 to 300 range. In short, the existing vent may be completely inadequate for the new appliance and may either prevent the building owner from installing gas appliances or require the building owner to undergo an expensive and time consuming vent system replacement. 
     In an attempt to avoid these costs, several manufacturers have designed appliances with draft hoods that entrain dilution air into the vent. Entraining dilution air into the vent reduces the amount of condensation formed during operation and therefore reduces the number of installations which would require chimney relining. Unfortunately, this process also allows heated room air to escape in an uncontrolled fashion, both while the appliance is operating and while the appliance is idle. The escaping heat increases the heat load on the building and therefore increases the energy cost associated with controlling the building temperature. In addition, the typical draft hood equipped appliance is susceptible to backdrafting, which is especially troublesome in the multi-story housing market. 
     BRIEF SUMMARY OF THE INVENTION 
     Accordingly, one object of the present invention is to decrease the installed cost of a modern gas appliance. 
     Another object of the present invention is to decrease the overall energy consumption of a building. 
     Still another object of the present invention is to increase the installation venting options available to the gas appliance installer. 
     Yet another object of the present invention is to reduce backdrafting and increase the safety of the appliance vent system. 
     One or more of the preceding objects, or one or more other objects which will become plain upon consideration of the present specification, are satisfied in whole or in part by the invention described in this specification. 
     One aspect of the invention is a gas-burning appliance adapted for varying the proportions of combustion products to dilution air in its vent gas. The appliance can be a furnace, a water heater, a boiler, or some other gas appliance which is externally vented and normally used within a building or other structure. 
     A combustion chamber is provided for burning gas and producing combustion products. A flue gas outlet is included for passing flue gas to a mixing chamber. A dilution air inlet is used for passing dilution air into the mixing chamber. The appliance has at least one valve element defining at least a first dilution air aperture and at least a first combustion product aperture. 
     In one embodiment of the invention, the valve element is a flat plate and the apertures are pairs of holes in the plate. The different apertures can also be formed in other ways, as by the cooperation of two relatively movable elements (analogous to the rotating covers of some spice or parmesan cheese dispensers). 
     The valve element may be fixed, or the valve element may be movable between one or more positions. In the first position of a moveable valve element, the first dilution air aperture is placed between the dilution air inlet and the flue gas mixing chamber, and the first combustion product aperture is placed between the combustion chamber and the flue gas mixing chamber. The first dilution air and first combustion product aperture pair are respectively adapted to provide a first ratio of dilution air to combustion products passing into the flue gas mixing chamber when the valve element is in its first position. 
     In the second position of a movable valve element, the second dilution air aperture is positioned between the dilution air inlet and the flue gas mixing chamber, and the first combustion product aperture is positioned between the combustion chamber and the flue gas mixing chamber. The second dilution air and second combustion product aperture pair are respectively adapted to provide a second ratio of dilution air to combustion products passing into the flue gas mixing chamber when the movable valve element is in its second position. 
     The first and second ratios of dilution air to combustion products passing into the flue gas mixing chamber are different, due to the different size hole ratios or other adaptations of the dilution air aperture and combustion product aperture. This allows the combustion-products-to-dilution-air ratio to be selected to match the appliance to the venting system it will be attached to. This allows modern, high-efficiency gas appliances to be connected to traditional venting systems without causing vent corrosion, and without producing an inappropriately high or low pressure of combustion products in the vent. 
     In the configuration in which the valve element is fixed, the first dilution air aperture is placed between the dilution air inlet and the flue gas mixing chamber. The first combustion product aperture is placed between the combustion chamber and the flue gas mixing chamber. The valve element is secured in this position to continuously provide a first ratio of dilution air to combustion products in the flue gas mixing chamber. 
     Another aspect of the invention is an adapter for varying the proportions of combustion products to dilution air in the vent gas of a fuel-burning appliance. The adapter has a dilution air inlet: a combustion product inlet: a flue gas mixing chamber, and at least one fixed or movable valve element. The valve element defines at least a first dilution air aperture and at least a first combustion product aperture, and has at least a first position and hole ratio as described before. The adapter can be part of the appliance, part of the venting arrangement, or a separate, add-on installation for attachment between an appliance and a venting arrangement. 
     Yet another embodiment of the invention is a flue assembly adapted for varying the proportions of combustion products to dilution air passing through it The assembly comprises a dilution air inlet: a combustion product inlet: a flue gas mixing chamber, and at least one fixed or movable valve element as previously defined. Again, the assembly provides one or more ratios of dilution air to combustion products passing into the vent. This flue assembly can be installed in a building to adapt the building to receive a variety of gas appliances having different categories. 
     One significant advantage of the invention is its simplicity, as the flows of dilution air and combustion air can be coordinated by operating a single valve element. The valve element or adjacent structure can be marked to indicate the proper positions of the valve element for different categories of appliances (if it is installed as part of the vent system) or different vent types (if it is incorporated in the appliance), or both. This multiple-function valve element makes selection of the proper valve element position much less subject to miscalculations and errors, such as confusion about which of two separate valve elements controls the dilution air and which controls the combustion products. A fixed valve element would not require any adjustment in the field to obtain the correct ratio of dilution air to combustion products. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic view illustrating one embodiment of the present invention. 
     FIG. 2 shows a cross-section of a movable valve aperture plate taken along line  2 — 2  in FIG. 1, and having three pairs of apertures for category I, III, and IV appliances. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     While the invention will be described in connection with one or more preferred embodiments, it will be understood that the invention is not limited to those embodiments. On the contrary, the invention includes all alternatives, modifications, and equivalents as may be included within the spirit and scope of the appended claims. 
     FIG. 1 shows a gas burning appliance, for example a gas furnace, generally indicated by reference numeral  10 . The appliance  10  burns natural gas, propane, or some other combustible gas in the combustion chamber  12  The resulting combustion product gases flow through the heat exchanger  14 , the flue product passage  16 , and the combustion flue inlet  18  into the flue gas mixing chamber  20 . The combustion flue inlet  18  is shown in FIG. 1 as one end of the flue product passage  16 . The appliance  10  also draws dilution air into the dilution air inlet opening  22  from outside the furnace  10 , preferably from outside the building being heated. The dilution air then passes through a dilution air inlet  24 , and into the mixing chamber  20 . The combustion gases and dilution air both flow through the orifice plate  26 , which is the valve element in this embodiment, then they mix in the flue gas mixing chamber  20  to form vent gases (combustion products mixed with dilution air). The blower  28  helps draw flue gas and dilution air through the mixing chamber  20  during on-cycles and helps exhaust the vent gases through the vent  29  to the outside atmosphere. The position of blower  28  downstream of the dilution air and combustion product inlet serves to restrict off-cycle air flows through the dilution air inlet and through the combustion flue inlet. The vent  29  may be constructed from any of the materials appropriate for a category I, II, III, or IV appliance. The blower  28  may be an integral part of the appliance, but is not so limited and may also be part of the vent system. 
     The orifice plate  26  includes first and second major faces and  31  perforated by pairs of dilution air apertures and combustion product apertures that may be rotated and secured the dilution air opening  24  and the combustion flue inlet  18 . 
     FIG. 2 shows an orifice plate  26  with three pairs of apertures: Category I apertures  32  and  34 , and category III apertures  40  and  42 , category IV apertures  36  and  38 . Each “aperture” as defined here may include more than one opening within the scope of the present invention. The selected aperture  32 ,  36 , or  42  passes combusting gas from the combustion flue inlet  18 . The selected aperture  34 ,  38  or  40  passes dilution air from the dilution air inlet  24 . The orifice plate  26  may contain as many or as few aperture pairs as the size of the manufacturer&#39;s orifice plate, the combustion flue opening, and the dilution air opening allow. The selected aperture pair  32 - 34 .  36 - 38 , or  40 - 42  controls the ratio of dilution air and combustion product gases in the flue gas mixing chamber  20  so the resulting vent gas may pass through the selected or existing vent  29  without damaging the vent  29  materials or causing undesired condensation. In FIG. 2, the aperture pair  32 - 34  have been selected by registering them with the dilution air inlet  24  and the combustion flue inlet  18 . 
     Each diametrically opposed aperture pair  32 - 34 .  36 - 38 .  40 - 42  may restrict the dilution air and flue gas flows by different amounts and in different ratios to configure the appliance for a different type of vent  29  material. During installation of the appliance  10 , the installer rotates the orifice plate  26  to its proper position based on the construction of the vent  29 . The proper position is indicated by the category legends I, III, and IV, one of which is aligned with an external reference mark  44 . The proper position places the particular pair of holes  32 - 34 ,  36 - 38 ,  40 - 42  which match the vent gas mixture for the construction of vent  29  over the dilution air inlet  24  and the combustion flue inlet  18 . 
     The openings in the orifice plate  26  (and the blower  28 , if present) generate flow resistance that makes the appliance  10  less susceptible to backdrafting than a typical draft hood equipped appliance. The flow resistance also restricts the flow of dilution air during the appliance  10  off-cycle, which helps to prevent heated air from escaping freely through the vent  29 . Thus, less energy is required to maintain room temperature. 
     Each appliance  10  manufacturer may use different diameters or shapes for the dilution air inlet  24  and the combustion flue inlet  18 . The orifice plate  26  itself and its hole pairs  32 - 34 ,  36 - 38  and  40 - 42  are not restricted to a round shape, but need only control the ratio of dilution air to flue gas entering the post-orifice mixing chamber region  20 . The manufacturer uses Table 1 to determine the proper size for the orifice plate  26  hole pairs,  32 - 34 .  36 - 38 , and  40 - 42 , that will appropriately adjust the dilution air/flue gas mixture for their desired appliance category. The orifice plate  26  is preferably constructed from a non-corrosive stainless steel. 
     Natural gas produces about 1,000 Btus of heat energy per cubic foot of gas burned. About 14 cubic feet of air are needed per cubic foot of natural gas for acceptable combustion and a gas appliance with no dilution air needs to exhaust about 15 cubic feet of combustion products per 1.000 Btu. A gas furnace that operates at 100,000 Btus per hour needs to exhaust about 1,500 cubic feet of combustion products per hour or about 22 standard cubic feet per minute (scfm). Dilution air, as used in Table 1, is measured as a percentage of flue products. A table value of 100 percent dilution air, for example, means approximately 15 cubic feet of dilution air per 1000 Btu of gas burned, for a total of 30 cubic feet of vent gases per 1,000 Btu. In other words, a hole pair in the orifice plate  26  must be sized to allow equal amounts of dilution air and combustion gas to mix in the flue gas mixing chamber  20 . A gas furnace that operates at 100,000 Btu per hour, which needs 100 percent dilution air, needs to exhaust approximately 44 scfm of vent gases. As shown in Table 1, the percentage of dilution air required differs depending on whether the appliance uses outdoor (42° F.) dilution air, or indoor (60° F.) dilution air. 
     As an example, assume that a manufacturer anticipates that its indoor dilution air. SSTE  81  appliance will be installed in locations that may have one of three venting systems: PVC, CPVC, or high-temperature plastic. In this situation, rather than design and manufacturing three separate appliances that meet the vent gas requirements for each possible venting system, the manufacturer may design and manufacture one appliance with an orifice plate  26  having three aperture pairs  32  and  34 - 36  and  38 , and  42 . Table 1 indicates, for example, that the orifice plate  26  should include a hole pair  36  and  38  that mixes approximately 300% dilution air to combustion products for a PVC system, a hole pair  32  and  34  that mixes approximately 110% dilution air to combustion products for a CPVC system, and a hole pair  40  and  42  that mixes approximately 150% dilution air to combustion products for a high-temperature plastic vent system. The suggested mixing percentages in Table 1 are targeted at meeting the flue gas criteria (also shown in Table 1). For example, keeping the flue gas temperature under 140° F, in a PVC vent system. Furthermore, the installer need not know beforehand which venting system the installation site uses, because the installer can rotate the orifice plate  26  during installation to adjust the flue gas output of the appliance  10  for the venting system used in the building. 
     The orifice plate  26  is not limited to any particular number of apertures or sets of apertures, nor to any particular aperture shape or number of apertures. The manufacturer, for example, may choose to use a large plate with enough area for many aperture pairs, or a small plate with enough area for fewer aperture pairs. The apertures need only be sized and positioned correctly to adjust the mixture of combustion product gases and dilution air according to Table 1. The SSTE ranges and the flue gas criteria shown in Table 1are not all inclusive. The invention may be used with additional SSTE ratings or additional criteria not indicated in the table simply by determining the criteria of interest and adjusting the orifice plate  26  aperture pairs such as  32 - 34 ,  36 - 38  or  40 - 42  to meet those criteria. 
     
       
         
               
             
               
               
               
               
             
               
             
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
             
             
               
                 Approximate Vent Ditution Air Requiremsnts for Gas Appliances 
               
               
                   
               
             
          
           
               
                 Venting System: 
                 Plastic PVC 
                 Plastic 
                 High Temperature 
               
               
                   
                 Vent System 
                 CPVC Vent 
                 Plastic Vent 
               
               
                   
                   
                 System 
                 System 
               
               
                 Flue gas 
                 Flue Gas 
                 Flue Gas 
                 Vent Dries 
               
               
                 Criteria: 
                 Temperature 
                 Temperature 
                 Completety 
               
               
                   
                 Less Than 
                 Less Than 
               
               
                   
                 140° F. 
                 210° F. 
               
               
                 Outdoor (42° F.) 
               
               
                 Dilution Air 
               
               
                 SSTE 80 
                 350% 
                 130% 
                 200% 
               
               
                 SSTE 81 
                 300% 
                 110% 
                 — 
               
               
                 SSTE 82 
                 250% 
                 80% 
                 — 
               
               
                 SSTE 83 
                 200% 
                 60% 
                 — 
               
               
                 Indoor (60° F.) 
               
               
                 Dilution Air 
               
               
                 SSTE 80 
                 350% 
                 130% 
                 100% 
               
               
                 SSTE 81 
                 300% 
                 110% 
                 150% 
               
               
                 SSTE 82 
                 250% 
                 80% 
                 300% 
               
               
                 SSTE 83 
                 200% 
                 60% 
                 — 
               
               
                 SSTE 85 
                 100% 
                 10% 
                 — 
               
               
                 SSTE 87 
                 30% 
                 0% 
                 — 
               
               
                   
               
             
          
           
               
                 Approximate Vent Dilution Air Requirements for Gas Appliance 
               
               
                   
               
             
          
           
               
                 Venting 
                 High Temperature 
                 Type B 
                 Interior 
                 Exterior 
               
               
                 System: 
                 Plastic 
                 Vent 
                 Masonry 
                 Masonry 
               
               
                   
                 Vent System 
                 System 
                 Chimney 
                 Chimney 
               
               
                 Flue gas 
                 All Interior 
                 Maintain 
                 Maintain 
                 Maintain 
               
               
                 Criteria: 
                 Portions of 
                 Negative 
                 Negative 
                 Negative 
               
               
                   
                 the Vent 
                 Pressure: 
                 Pressure: 
                 Pressure: 
               
               
                   
                 Dry by the 
                 Avoid 
                 Avoid 
                 Avoid 
               
               
                   
                 End of the 
                 Excessive 
                 Excessive 
                 Excessive 
               
               
                   
                 Burner On- 
                 Conden- 
                 Conden- 
                 Conden- 
               
               
                   
                 cycle 
                 sation 
                 sation 
                 sation 
               
               
                 Outdoor (42° F.) 
               
               
                 Dilution Air 
               
               
                 SSTE 80 
                 100% 
                 0% 
                 — 
                 — 
               
               
                 SSTE 81 
                 200% 
                 0% 
                 — 
                 — 
               
               
                 SSTE 82 
                 — 
                 0% 
                 — 
                 — 
               
               
                 SSTE 83 
                 — 
                 0% 
                 — 
                 — 
               
               
                 Indoor (60° F.) 
               
               
                 Dilution Air 
               
               
                 SSTE 80 
                 50% 
                 0% 
                 50% 
                 — 
               
               
                 SSTE 81 
                 100% 
                 0% 
                 — 
                 — 
               
               
                 SSTE 82 
                 150% 
                 0% 
                 — 
                 — 
               
               
                 SSTE 83 
                 200% 
                 0% 
                 — 
                 — 
               
               
                 SSTE 85 
                 — 
                 — 
                 — 
                 — 
               
               
                 SSTE 87 
                 — 
                 — 
                 — 
                 — 
               
               
                   
               
               
                 *Dilution air required to cool flue gases to a safe temperature is determined by the requirements for the warmest expected day (60° F.); condensation is based on a typical day (42° F.).