HVAC furnace

A heating, ventilation, and/or air conditioning (HVAC) furnace has a flat burner comprising an upstream side and a downstream side, the flat burner being configured to receive an air-fuel mixture therethrough, a first flow path located adjacent the flat burner and downstream relative to the flat burner, the first flow path configured to receive fluid exiting the flat burner, and a plurality of second flow paths located downstream relative to the first flow path, the plurality of second flow paths being configured to receive fluid from the first flow path.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not applicable.

REFERENCE TO A MICROFICHE APPENDIX

Not applicable.

BACKGROUND

Heating, ventilation, and/or air conditioning (HVAC) furnaces are widely used in commercial and residential environments for heating and otherwise conditioning interior spaces. Gas-fired furnaces are known to generate and emit oxides of nitrogen (NOX). NOX is a term used herein to describe the various oxides of nitrogen, in particular NO, N2O and NO2. NOX emissions from gas-fired furnaces are typically attributable to less than optimal air-fuel mixtures and combustion temperatures.

SUMMARY

In some embodiments, a heating, ventilation, and/or air conditioning (HVAC) furnace is provided. The HVAC furnace may comprise a flat burner comprising an upstream side and a downstream side, the flat burner being configured to receive an air-fuel mixture therethrough, a first flow path located adjacent the flat burner and downstream relative to the flat burner, the first flow path configured to receive fluid exiting the flat burner, and a plurality of second flow paths located downstream relative to the first flow path, the plurality of second flow paths being configured to receive fluid from the first flow path.

In other embodiments, a method of operating a furnace is provided. The method may comprise providing a flat burner comprising an upstream side and a downstream side, mixing air and fuel upstream of the flat burner to provide an air-fuel mixture to the upstream side of the flat burner, and pulling the air-fuel mixture through the flat burner.

In yet other embodiments, a furnace may be provided that may comprise a mixture distributing box, a post-combustion chamber coupled to the mixture distributing box, wherein the coupling of the mixture distributing box and the post-combustion chamber substantially envelope a cavity, a flat burner disposed within the cavity, an upstream heat exchanger comprising a plurality of parallel heat exchanger flow paths configured to receive fluid from the cavity, and an inducer blower in fluid communication with the upstream heat exchanger, the inducer blower being configured to pull fluid through the flat burner and the upstream heat exchanger.

DETAILED DESCRIPTION

Lowering NOXemissions attributable to a furnace may be accomplished by lowering the burn temperature of an air-fuel mixture in the burners of a gas-fired furnace. It may be desirable to lower the NOXproduction to below 14 nano-grams per joule (ng/J) of energy used. It may also be desirable to lower the NOXproduction to below 14 ng/J in an economical and space efficient manner. Accordingly, a furnace with a so-called flat burner for efficiently lowering the burn temperature of an air-fuel mixture is provided. The furnace may comprise one or more flat burners substantially similar to the flat burners sold by Worgas of Formigine, Italy, although other flat burners may be used. The flat burner may be inserted between a mixing box and a post-combustion chamber of a furnace so an air-fuel mixture is provided to a first side of the flat burner. Because mixing of the air and the fuel primarily occurs upstream relative to the flat burner, the flat burner may be referred to as a premix flat burner. A second side of the flat burner may face a heat exchanger configured to receive fluid that flows from the flat burner.

Referring toFIGS. 1 and 2, an oblique exploded view and an orthogonal side view of a furnace100are shown, respectively. The furnace100may comprise a partition panel110, a mixture distributing box122, a flat burner125, a post-combustion chamber126, at least one first or upstream heat exchanger130, a manifold132, a second or downstream heat exchanger134, and a heat exchanger exhaust chamber140.

The mixture distributing box122may be mounted to the partition panel110so that an inlet123of distributing box122may direct an air-fuel mixture toward flat burner125. The mixture distributing box122may promote even distribution of the air-fuel mixture across a cross-sectional area of an air-fuel mixture flow path and/or may promote even distribution of the air-fuel mixture across an upstream side of the flat burner125, as will be discussed further herein. The flat burner125may be thin and/or compact and may occupy little space within the furnace100, especially in the upstream/downstream directions of primary air-fuel mixture flow, thereby providing a space efficient furnace100. The mixing of the air and fuel prior to entering the distributing box122may be aided by a mixing device such as a premixer152(seeFIG. 2) to promote homogenous mixing of the air and fuel prior to entering the mixture distributing box122. Alternatively, fuel may be introduced directly into the mixture distributing box122by a gas supply valve. The gas supply valve may be controlled electrically, pneumatically, or in any other suitable manner to obtain a beneficial air to fuel ratio for increased efficiency and lower NOXemissions. The gas supply valve may be configured for either staged operation or modulation type operation. For example, staged operation may have two flow rate and/or capacity settings, where modulation type operation may be incrementally adjustable over a large range of flow rates, for example from 40% to 100% output capacity of the furnace100.

In some embodiments, the flat burner125may extend across substantially an entire cross-sectional area of the air-fuel mixture flow path. The air-fuel mixture may flow from the mixture distributing box122through the flat burner125and into the post-combustion chamber126. The flat burner125may be permeable, such as to allow the air-fuel mixture to travel through the flat burner125without a substantial pressure drop across the flat burner125. For example, the flat burner125may comprise a great number of small perforations over a substantial portion of the upstream and downstream sides of the flat burner125. Alternatively, a substantial portion of the upstream and downstream sides of the flat burner125may comprise one or more layers of woven material configured to allow the air-fuel mixture to flow therethrough. Still further, in other alternative embodiments, the flat burner125may comprise a combination of both perforations and woven material.

The flat burner125may be received within a cavity formed by the coupling of the mixture distributing box122and the post-combustion chamber126. In some embodiments, a flange129of the flat burner125may be sandwiched between the mixture distributing box122and the post-combustion chamber126so that substantially all of the air-fuel mixture may pass through the flat burner125prior to exiting the above-described cavity. When the flat burner125is received within the above-described cavity the upstream side of the flat burner125may face the mixture distributing box122and an opposing downstream side of the flat burner125may face the post-combustion chamber126. Post-combustion chamber126may be configured to output the combusted air-fuel mixture into multiple parallel flow paths, as will be discussed further herein.

The one or more upstream heat exchangers130may be configured to receive an at least partially combusted air-fuel mixture downstream of the flat burner125and each upstream heat exchanger130may form a separate flow path downstream relative to the flat burner125. The downstream heat exchanger134may be configured to receive the at least partially combusted air-fuel mixture from the upstream heat exchangers130. Heat exchanger134may comprise a fin-tube type heat exchanger and/or plate-fin type heat exchanger, either of which may comprise one or more tubes136. In other embodiments, the heat exchanger may comprise a so-called clamshell heat exchanger.

In some embodiments, the at least partially combusted air-fuel mixture may be transferred from the one or more upstream heat exchangers130to downstream heat exchanger134through the manifold132. While furnace100is described above as comprising one flat burner125, alternative furnace embodiments may comprise more than one flat burner125. In some cases, additional flat burners125may be utilized to increase an overall heating capacity. In some embodiments, several flat burners125may be aligned in parallel, so that multiple parallel air-fuel mixture flow paths may be formed. Further, while furnace100is disclosed as comprising at least one upstream heat exchanger130and a downstream heat exchanger134, alternative furnace embodiments may comprise only one upstream heat exchanger no downstream heat exchanger134, and/or multiple downstream heat exchangers134.

An igniter154(seeFIG. 2) may be mounted partially within the post-combustion chamber126proximal to the downstream side of the flat burner125to ignite the air-fuel mixture a short distance downstream from the downstream side of the flat burner125. The air-fuel mixture may be moved in an induced draft manner by pulling the air-fuel mixture through the furnace100and/or in a forced draft manner by pushing the air-fuel mixture through the furnace100. The induced draft may be produced by attaching a blower and/or fan downstream, such as inducer blower150(seeFIG. 2) relative to the heat exchanger exhaust chamber140and pulling the air-fuel mixture out of the system by creating a lower pressure at the exhaust of the heat exchanger exhaust chamber140as compared to the pressure upstream of the flat burner125. Inducing flow in the above-described manner may protect against leaking the at least partially combusted air-fuel mixture and related products of combustion to the surrounding environment by ensuring the at least partially combusted air-fuel mixture is maintained at a pressure lower than the air pressure surrounding the furnace100. With such an induced flow, any leak along the flow path of the air-fuel mixture may result in pulling environmental air into the flow path rather than expelling the at least partially combusted air-fuel mixture and related products of combustion to the environment. In alternative embodiments, the air-fuel mixture may be forced along the air-fuel mixture flow path by placing a blower or fan upstream relative to the flat burner125and creating higher pressure upstream of the flat burner125relative to a lower pressure at the exhaust of the heat exchanger exhaust chamber140. In some embodiments, a control system may control the inducer blower150to an appropriate speed to achieve desired fluid flow rates for a desired firing rate through the flat burner125. Increasing the speed of the inducer blower150may introduce more air to the air-fuel mixture, thereby changing the characteristics of the combustion achieved by the flat burner125. In some embodiments, a so-called zero governor regulator and/or zero governor gas valve may be additionally utilized to provide a desired fuel to air ratio in spite of the varying effects of an induced draft and/or other pressure variations that may fluctuate and/or otherwise tend to cause dispensing or more or less fuel in response to the pressure variations and/or negative pressures relative to atmospheric pressure.

Substantially enclosing the flat burner125within a cavity formed by the connecting of the mixture distributing box122and the post-combustion chamber126and substantially combusting the air-fuel mixture near the flat burner125may reduce the surface temperatures of the post-combustion chamber126and upstream heat exchangers130as compared to embodiments utilizing other types of burners. While the downstream side of the flat burner125is disclosed as facing the post-combustion chamber126while the upstream side of the flat burner125faces the mixture distributing box122, in alternative embodiments, the flat burner125may be positioned differently and/or the flow of the air-fuel mixture may be passed through the flat burner125in a different manner. The post-combustion chamber126is connected to the upstream heat exchangers130so that the at least partially combusted air-fuel mixture enters directly into the upstream heat exchangers130, as will be discussed further herein. The post-combustion chamber126may seal the air-fuel mixture flow path from secondary dilution air as well as position the flat burner125in a manner conducive for transferring the at least partially combusted air-fuel mixture to the upstream heat exchangers130. While the upstream heat exchangers130are disclosed as comprising a plurality of tubes, in alternative embodiments, the upstream heat exchangers may comprise clamshell heat exchangers, drum heat exchangers, shell and tube type heat exchangers, and/or any other suitable type of heat exchanger.

Referring now toFIG. 2, the furnace100is shown as comprising the inducer blower150, the air-fuel premixer152, the igniter154, and the flame sensor156. Premixer152may comprise a Venturi style air-fuel mixer or any other suitable style of air-fuel mixers. The igniter154may comprise a pilot light, a spark igniter, a piezoelectric device, and/or a hot surface igniter. The igniter154may be controlled by a control system and/or may be manually ignited. The flame sensor156may comprise a thermocouple, a flame rectification device, and/or any other suitable safety device.

Referring now toFIG. 3, an oblique view of mixture distributing box122is shown. The mixture distributing box122may comprise an inlet123and a deflector124. Deflector124may be connected to and received within mixture distributing box122. The shape and positioning of deflector124within mixture distributing box122with respect to inlet123may be configured to promote even distribution of the air-fuel mixture entering mixture distributing box122over a cross-sectional area of the flow path of the air-fuel mixture and/or to promote even distribution of the air-fuel mixture over an upstream side of the flat burner125disposed downstream of the deflector124. The above-described increased even distributions of the air-fuel mixture may promote a more homogenous temperature distribution within the post-combustion chamber126and/or the upstream heat exchangers130. While deflector124is shown as comprising a rectangular plate with an upstream side facing inlet123, in alternative embodiments, a deflector may comprise any another shape and/or device configured to disturb fluid flow entering mixture distributing box122.

Referring now toFIG. 4, an oblique view of post-combustion chamber126is shown. In this embodiment, igniter154and flame sensor156are disposed within an inlet127of post-combustion chamber126. Post-combustion chamber126may further comprise a plurality of outlets128that may be configured to directly couple to the upstream heat exchangers130. Flat burner125may be disposed upstream of post-combustion chamber126, an inputted air-fuel mixture may be ignited by igniter154, and the at least partially combusted air-fuel mixture may pass through a substantially undivided space of the post-combustion chamber126prior to passing into a plurality of separate flow paths via outlets128.

Referring toFIG. 5, a schematic view of an embodiment of a flat burner combustion system300is shown. In this embodiment, system300may comprise a fluid flow path305that extends from an air-fuel premixer310through a chamber320and into one or more heat exchanger tubes340. Chamber320may comprise a flat burner330that extends over substantially an entire cross-sectional area of the chamber320. Flat burner330may generally denote a fluid-permeable boundary between an upstream chamber volume322and a downstream chamber volume324. As an air-fuel mixture flows along flow path305, the air-fuel mixture may exit premixer310and enter upstream chamber volume322before contacting flat burner330. As shown inFIG. 5, the entirety of flow path305may extend through flat burner330before entering downstream chamber volume324. Thus, substantially all fluid flowing along flow path305may flow through flat burner330to enter downstream chamber volume324. As the fluid flowing along flow path305flows through flat burner330and enters downstream chamber volume324, it may be ignited by an ignition source to cause at least partial combustion of and/or rapid heating of the fluid. The fluid within downstream chamber volume324may thereafter enter one or more heat exchanger tubes340. Heat exchanger tubes340may each comprise an exterior surface in contact with a second fluid flow configured to receive heat from the fluid flowing along flow path305.

Referring now toFIG. 6, a block diagram depicting a method400of operating a furnace is shown. The method may begin at block410by mixing a fuel and air together. An air-fuel mixer and/or so-called premixer may be utilized to accomplish the mixing of the fuel in the air. The fuel may comprise natural gas available from a gas valve attached to a mixture distributing box or to an air-fuel premixer upstream of the mixture distributing box. Alternatively, the fuel may comprise propane and/or any other suitable fuel. The air may be introduced to the mixture distributing box or to the air-fuel mixer by a so-called forced draft or a so-called induced draft.

The method400may continue at block420where the air-fuel mixture is distributed so that it may be more evenly distributed across an upstream side of a flat burner. The mixing process may be aided by a deflector located within the mixture distributing box that may have the effect of deflecting or disturbing the flow of the air-fuel mixture. For example, the deflector may be placed in front of the outlet of the air-fuel mixing box, altering the flow of the air and fuel within the air-fuel mixing box and thereby causing the air-fuel mixture to be more evenly distributed across a cross-sectional area of the air-fuel mixture flow path.

The method400may continue at block430where the air-fuel mixture may be moved through a flat burner. The flat burner may comprise a thin and elongated body with an upstream side and a downstream side. The upstream side and downstream side of the flat burner may be permeable to allow the air-fuel mixture to pass through the flat burner. For example, the flat burner may comprise a great number of small perforations and/or a woven material over a substantial portion of the upstream and downstream sides of the flat burner. Further, the flat burner may be contained within a cavity comprising internal space of a mixture distribution box and internal space of a post-combustion chamber so that the air-fuel mixture leaving the air-fuel mixture distribution box passes through the upstream and downstream sides of the flat burner.

The method400may continue at block440, where the air-fuel mixture may be ignited. The downstream side of the flat burner may face the post-combustion chamber. An igniter may be mounted in the post-combustion chamber near the downstream side of the flat burner. The igniter may comprise a pilot light, a piezoelectric spark, or a hot surface igniter. As the air-fuel mixture passes through the flat burner, the igniter may ignite and cause at least partial combustion of the air-fuel mixture to begin near the downstream side of the flat burner.

The method400may continue at block450by venting the at least partially combusted air-fuel mixture through a heat exchanger. Combustion may occur at least partially near the downstream side of the flat burner so that heat is generated and forced downstream of the flat burner and into the post-combustion chamber. In this embodiment, the combustion may occur generally at or near the downstream side of the flat burner. In alternative embodiments, combustion may occur both at the upstream and downstream sides of the flat burner as well as within an interior of the flat burner. The post-combustion chamber may be configured to divide the single flow path associated with the flat burner into multiple parallel flow paths. One or more of the multiple parallel flow paths may comprise a heat exchanger. The heat exchangers may be tubular in design with an upstream end connected to the post-combustion chamber and a downstream end connected to either a heat exchanger exhaust chamber or to a manifold. An upstream end of a downstream heat exchanger may be connected to the manifold and a downstream end of the downstream heat exchanger may be connected to a heat exchanger exhaust chamber. A heat exchanger exhaust chamber may be disposed downstream from the heat exchanger(s) and may be configured to recombine the plurality of flow paths within the heat exchanger(s) into a single flow space. The at least partially combusted air-fuel mixture may comprise NOX. The level of NOXin the at least partially combusted air-fuel mixture may be lowered by varying the combustion temperature of the air-fuel mixture and/or the ratio of air to fuel within the mixture.

The method400may continue at block460by conditioning air outside of the heat exchanger. As the hot at least partially combusted air-fuel mixture travels through either the heat exchanger(s) toward the heat exchanger exhaust chamber, the heat exchanger(s) may be heated. Air that is exterior to the heat exchanger(s) may be moved into contact with the heat exchanger(s). As the air moves across the heat exchanger(s), heat may be transferred from the heat exchanger(s) to the air passing by the heat exchanger(s).

The method400may conclude at block470by venting the conditioned air into an air conditioned space, for example, an office space or living area of a home. The heated air may be used to warm the space in order to increase comfort levels for occupants and/or to maintain the contents of the space at a pre-determined temperature.

Referring now toFIG. 7, a furnace500is shown. Furnace500comprises a circulation air blower502that receives incoming airflow504and passes incoming airflow504into contact with downstream heat exchanger134and upstream heat exchanger130to transfer heat from the heat exchangers134,130to the air. Exiting airflow506may be distributed to an area that is to be conditioned with the heated air. A partition panel110may isolate the air-fuel mixture that may be at least partially combusted from the incoming and exiting airflows504,506. Due to a thin and elongate flat burner that may be disposed between the mixture distributing box122and post-combustion chamber126, a size of the furnace500may be reduced relative to other furnaces that do not comprise a premix flat burner configured for use with an inducer draft.