US3186697A

US3186697A - Gas-fired heater

Info

Publication number: US3186697A
Application number: US423896A
Authority: US
Inventors: Edward J Haedike; Steve W Zavodny
Original assignee: Mid Continent Metal Products Co
Current assignee: MIDCO-INTERNATIONAL Inc
Priority date: 1964-12-23
Filing date: 1964-12-23
Publication date: 1965-06-01
Anticipated expiration: 1982-06-01

Description

June l, 1965 E, J. HAI-:BIKE ETAL 3,186,697

Y GAS-FIRED HEATER Original Filed July 23, 1962 2 Sheets-Sheet 1 Izzi/167250725' June l, 1965 E, J. HAI-:BIKE ETAL GAS-FIRED HEATER Original Filed July 23. 1962 2 Sheets-Sheet 2 Hm of@ No WO www@ M o omo mwl vlllll.. ..w @.lwl .o M j M1 l uw@ um@ M. N nl MQW@ H @nl v u H M United States Patent O 19 Claims. (Cl. 263-19) This Iapplication is iiled as a continuation of pending application Serial No. 211,523 tiled July 23, 1962, now abandoned.

This invention relates to gas-tired heaters and moreE particularly is concerned with a gas-tired burner.

The invention iinds important application in make-up.

air heaters which are now commonly employed to alleviate heating problems caused by excessive ventilation. Whenever a condition exists where the air within 4a building lmust be continuously replaced, for health or comfort reasons, the additional heating load may overtax the heating system. Conditions such as these are frequently found in paint spray shops, foundries, chemical plants, welding shops, large restaurant-s, bowling alleys, etc. The make-up air heater is used to temper the incoming `air, raising it to room temperature and thus relieving the building heating plant of the extra load. l

The make-up air heater is always gas-tired because products of combustion are mixed directly into the stream and no smoke or odors are permissible. Gas Iburns clean so it is the only acceptable fuel; any traces of fumes `are of no consequence since the products of combustion are diluted to such an extent that they are undetectable. No build-up of contaminants is possible because the make-up air is never recirculated; once it is heated, it enters the building where it may receive additional heat from the regular heating equipment, and subsequently it is discharged by the exhaust system.

The most important characteristic required of the burner is that it have a long turn down range. In the case of mild outdoor temperatures the makeJup air may need to be raised but |a few degrees, whereas in severe winter conditions the rise may need to approach 100 degrees. The accepted industry standard is a range of 20 to l. With the ordinary gas burner, capable of but 4 or 5 to 1 turn down, it is apparent that the make-up air burner must be of some .specialized form to meet the requirements.

Many attempts have :been made by workers in this to solve this problem with contemporary line burners equipped with expensive facilities for zoning the burner into 4 or 5 sections. Another approach utilizes special powered mixing equipment for accurate control of the critical low tire performance through premixing of the air and gas. This, too, is unduly expensive.

Accordingly, the principal objects of the invention are to provide: a low cost .burner having a long turn down range; a burner having a low iire zone contained within itself on raw gas with no air supply other than the circulating air stream in which the lburner is disposed; a burner that has an air port .arrangement providing odor free and CO free combustion (by way of example, less than ten parts CO per million at the discharge at 100F.

temperature rise is considered good); and a burner having facilities to prevent :llame impingement on cold .surfaces particularly to laid CO prevention at low capacities.

Another object of the invention is to provide a .burner with simpliiied facilities operable at low fire conditions for controlling air admittance to achieve partial premix in 'the burner and improve the low iire performance.

The partial premix provided at low iire makes low iire more even and stable, allows for a lower setting, and

fieldV 3,185,697 Patented June l, 1965 lCe provides greater resistance to uneven air flow disturbances. Moreover, the low re lighting is improved and generation of CO is inhibited.

Other objects and vadvantages will become apparent dur-ing the course of the following description.

In the accompanying drawings forming a part of this speciication and in which like numerals are employed to designate like parts throughout the same:

FIG. l is a diagrammatic side elevational view illustrating the burner of this invention mounted in an air duct;

FIG. 2 is a View showing the duct in cross-section Vand illustrating the burner and its connection t-o a gas supply and control system;

FIG. 3 is atop view of a burner assembly with portions thereof .broken away and sectioned to facilitate the disclosure;

FIG. 4 is a transverse cross-sectional view through the burner and is taken' on the line 4 4 of FIG. 3;

FIG. 5 is a detailed sectional view of an automatic air admittance valve useful in conjunction with the burner of this invention.

Referring no w to the drawings, for purposes of illustrative disclosure the burner 10 of this invention is shown embodied in a heater arrangement for preheating incoming fresh air to raise it to room temperature. Make-up air heaters are used for this purpose in buildings that require extensive ventilation. The burner of this invention may also be utilized in oven heaters and in numerous other heating applications.

In FIG. l, a make-up air heater arrangement is shown as including an -air duct D leading inwardly from a Wall opening of an exterior building wall W. A blower B iS mounted in the duct D and is operable to draw a stream" of fresh air fordischarge into the building. The .burner 10 of this invention is disposed crosswi'se in the duct on" fthe suction side of the circulating blower B. A prole plate P is provided within the duct at the burner to enhancethe air ow 4rate in the immediate vicinity of the burner. While the burner preferably is on the suction side of the blower B, as illustrated herein, it may, Where desired, be located in an air duct on the discharge side of the blower.

As is best illustrated in FIGS. 2 and 3, the burner unit is comprised of an assembly of standardized

burner sections

11, 12, and 13 bolted together end-to-end to form a complete unit of the proper size and shape. The burner sections may be provided in a range of lengths and in various shapes such as Ls, trees, and crosses to satisfy the various different mounting arrangements that are encountered in practice. In this disclosure, burner section 11 is a pilot section and is shown with a pilot gas feed line llP and with a suitable spark rod assembly 11S and iiame rod assembly 11F.

The burner sections illustrated herein are 12 inches in length and each comprises a cast iron burner manifold 14 and ported bai-hes 15 fixed lengthwise along the manifold and dening a combustion zone 16 that diverges outwardly from the manifold and is of generally V-shape in transverse cross-section. The baffles 15 are preferably of stainless steel but any other heat;` resistant material is suitable. The manifolds of the standard burner sections 12 and 13 are open end-to-end whereas in the pilot section 11 an internal wall 11W isolates pilot gas from the main In FIG. 2, the main gas supply line is shown as including a manual shut otf valve 17, an automatic shut oit valve 18 and an automatic tempertaure control Yvalve'19.

The general operation of the heater arrangement shown in FIGS. l and 2 is now described. When fresh make-up air `is necessary in the building, the circulating blower B is started either manually or automtaically. If

the tempertaure of the discharge air from the blowers is below the selected comfort range a control system (not shown) is energized automatically to ignite the pilot section of the burner. When the pilot flame is detected by the ame rod assembly llF (FIG. 4) the automatic shut olf valve 18 (FIG. 2) is opened to admit gas to the main sections of the burner and thereby ignite the entire burner. The automatic temperature control valve 19 meters the gas supply as required to maintain the desired discharge temperature.

The actual combustion zone varies with the gas supply rate. Combustion occurs only when the proper mixture of air and gas is achieved. `The combustion air is derived from the air stream in which the burner is located and the steel baies 15 Von the present fburner are provided-:with a progressive arrangement of ports to create -an air supply into the combustion zone that increases progressively with distance from the manifold.

Thus, if the outdoor-air becomes colder, more gas is supplied to the burner until at high lire the required proper air-gas mixture is achieved only at the outer reaches of the 'combustionzone If the outdoor air becomes warmer, the automatic temperature control valve 19 reduces the gas supply and the dame recedes to a new location within the combustion zone of lesser air supply.

The principal advantage of the burner of this invention is the fact that it develops a long turn down range without need for expensive zoning controls or special air mixing equipment. The critical aspect in achieving a long turn down range is the low re performance and it has in the past been diliicult to achieve the desired stability at low re in the presence of the strong air currents in the duct in which the burner is located.

The burner arrangement 'of this invention provides careful control of the combustion air at the low tire area which is indicated generally at 20 in FIG. 4. Uncontrolled air entry to the low tire area would impair the stability of the low fire flame and must'be avoided. In the preferred burner arrangement illustrated herein the burner manifold 14 is provided with integral external mounting ledges 21 that are lengthwise coextensive and that are `spaced apart slightly to define a slot that extends the length of the manifold and constitutes the low re area of the combustion zone.

In the burner disclosed for purposes of illustration gas ports 22 are spaced at 1 inch intervals along the manifold to discharge gas directly into the low fire zone and air ports 23 are provided on 1 inch intervals through each ledge to supply combustion air from the circulating air` stream into the base of the slot that forms the low lire zone. In the preferred arrangement each gas port is centered between a pair of air ports, The stainless steel baffles have bottom anges 15F mating with the ledge faces and aixed directly thereto by means of an elongated clamping bar 24 and bolts 25. The joint between the ledges and the anges of the stainless steel batles is diicult to seal against air leakage and one advantage of the present arrangement is that this joint is located above the critical low re region so that any leakage that should occur there will not impair the stability of ther low fire performance.

As is best seen in FIGS. 3 and 4, each of the stainless steel ballles is provided with lengthwise spaced holes dening rows of air ports with the holes 26 that are adjacent to the low fire area being smaller as they function v principally to supply combustion air for intermediate fire and with the holes 27 of the outermost rows being somewhat larger as they functionto supply combustion air for high fire. Between each adjacent set of rows for the 'intermediate iire area are located elongated deector strips Z8 fixed on the innerface of each baie plate 15( These strips redirect the air entering the intermediateports 26 and prevent ame impingement on cold surfaces of the burner unit. This feature aids in CO prevention at low llame.

As described thus far, the burner unit functions effectively even when handling raw gas directly. It offers a long turn down range on the order of 20 to l under these conditions. The low re performance of the burner is improved to the order of more than 30 to 1 by the addition of small quantities of air as a partial premix during low lire conditions. An extremely simple arrangement for providing partial premix is illustrated in FIG. 2 wherein the gas supply line 30 to the burner is shown with a T coupler 31 to accommodate a branch line 32 for' admitting air to the burner under low tire conditions. In this branch line, a conventional adjustable air metering valve 33 and an automatic air admittance Valve 34 are provided. The

source of air for `this branchv line may be taken directly from the room or preferably the air line 35 may loop around to the air duct and face directly into the air stream flowing therethrough.

The air admittance valve 34 comprises a divided casing 35 having an air inlet chamber 36, an air outlet chamber 37 and a vent chamber 38 that is open to ambient atmospheric pressure. A exible diaphragm 39 divides the outlet chamber 37 from the vent chamber 38. Air ow from the inlet chamber to the outlet chamber is regulated by a valve head 40 that cooperates with a soft valve seat 41, the valve head 40 being carried on a stem 42 rigidly connected to a Weight 43 that is mounted on the exible diaphragm 39.50 that movement of the diaphragm controls opening and closing of the admittance valve.

Assuming that the circulating blower B is running, the pilot is burning, and the burner is ready for ignition, the functioning of the air admittance Valve 34 may now be described with reference to FIG. 2. Under these condi- 1 tions, the burner manifold and the pipe 30 feeding it are subjected to negtaive pressure because this entire region of the duct, being on the suction side of the blower, is subjected to a static negative pressure and because air flow through the duct and passing across the burner develops additional suction. This negative pressure acts on the upper face of the diaphragm 39 in the air admittance valve 34 causing the diaphragm to rise and unseat the valve lead 40 to allow entry of air to the burner as determined by the settting of the air metering valve 33.

Assuming the main gas valve 19 opens to its low re position, so little gas is admitted to the manifold that the pressure condition there remains negative. Thus, air and gas are premixed in the burner manifold to a proportion selected by the air metering valve 33. As the temperature control valve 19 opens further on demand for more heat the negative pressure in the burner is reduced and ultimately will reach zero and then become positive and approach the full line pressure for maximum ow in the gas line.

Under conditions of positive pressure the diaphragm 39 of the air admittance valve moves downwardly to close the valve head 40 on its seat 41. The weight 43 on the diaphragm insures its early closure as desired; however, when the seat first closes there is little seating force since the system may still be under negative pressure. At this time leakage, if any, would be into the burner. On a rise in pressure the increased force acting on the diaphragm tightens the valve.

This air premix system is also operable when connected to a burner tiring on the positive pressure side of the blower because the negative pressure generated by air ow across the burner will overcome the positive duct pressures that are typical of such applications. Other arrangements may be employed for controlling admittance of air to the burner manifold at low fire conditions; for example, a differential pressure switch may be connected to the burner manifold and may be arranged to operate ansehe?" that the claims should be construed as broadly as prior art will permit.

What is claimed is:

1. In a gas burning direct tired makeup air type heating apparatus that includes a high turndown gas burner and means for ilowing a low pressure air stream forwardly past the burner at a substantially constant velocity, the improvement comprising means having a ilow ratio range on the order of 20 to l when variable amounts of raw gas fuel are admitted to said burner while constant air stream velocity is maintained by said air owing means, and said burner comprising an elongated burner manifold adapted to be disposed in said air stream crosswise thereof and connected in receiving relation to said supply means, said manifold having an external lengthwise wall portion along a downstream region thereof and provided with a number of gas ports spaced apart lengthwise therealong for issuing gas supplied from said supply means in a downstream direction from the manifold, elongated external wall structure disposed lengthwise along said manifold and providing opposed elongated wall portions leading generally downstream from said manifold in closely spaced flanking relation to said gas ports to shield said gas ports from regions of said air stream that are externally thereadjacent, with said opposed wall portions defining cooperatively with said manifold wall portion a transversely narrow low lire zone extending externally along said gas ports, said external wall structure having elongated baille wall portions leading generally downstream from said opposed wall portions and progressively diverging in a downstream direction to terminate in a transversly wide burner mouth, said baille wall portions being provided with a multiplicity of broadly distributed spaced openings many times greater than said number of gas ports, said baille wall portions projecting downstream from said opposed wall portions to deiine an intermediate fire zone merged with and leading generally downstream from said low lire zone to extend part way along said baflle wall portions and also to define a high lire combustion zone merged with and leading generally downstream from said intermediate lire zone and extending through the burner mouth, at least one of said opposed wall portions having ports opening therethrough at locations adjacent said gas ports and in said low lire zone for directing air from said stream into said low re zone for supporting continuous combustion within said low lire zone of gas issuing from said gas ports when said supply means is at the lower limit of its ow range, said burner while disposed in said air stream and supplied with raw gas over a 2O to 1 ow range being capable of presenting a stable flame characterized by producing less than 100 parts per million of CO in the heated air and being substantially soot free and odorless.

2. Apparatus in accordance with claim 1 and wherein said baille wall openings at the intermediate iire zone are substantially aligned in a direction along the length of said manifold and are smaller than the openings which are adjacent the high lire zone, and wherein said baille wall portions have elongated ydeilector strips adjacent and extending alongside the aligned baille wall openings of the intermediate re zone and exposed directly thereto.

3. Apparatus in accordance with claim 1 and wherein said manifold and said opposed elongated wall portions are integral parts of a one piece casting.

4. Apparatus in accordance with claim 1 and including an automatic air admittance valve having an inlet connected to a source of air and an outlet connected to supply air into said burner manifold, said valve having means exposed through said outlet to respond to pressure conditions within said manifold and automatically control said valve to admit air to said burner only during the existence of negative pressure conditions in said burner manifold.

' 5. in a gas burning direct fired makeup air type heating apparatus that includes a high turn-down gas burner and means for flowing a low pressure air stream forwardly past the burner at a substantially constant velocity, the improvement comprising means having a ilow ratio range on the order of 20 to l to supply variable amounts of raw gas fuel to said burner while constant air stream velocity is maintained by said air flowing means, and said yburner comprising a burner manifold adapted to be disposed in said air stream and connected to receive raw gas from said supply means, said manifold having an external wall portion at a downstream region thereof and provided with a gas port for issuing raw gas supplied from said supply means in a downstream direction from the manifold, external wall structure disposed on said mani-V fold and providing opposed wall portions leading generally downstream from said manifold in closely spaced ilanking relation to said gas port to shield said gas port from regions of said air stream that are externally thereadjacent, said burner including means cooperable with said opposed wall portions and with said manifold wall portion to Vdefine a transversely limited area externally at said gas port within which gas from said port must undergo continuous combustion at low fire, said external wall structure having baille wall portions leading generally downstream from said opposed wall portions and progressively diverging in a downstream direction to terminate in a transversely wide burner mouth, said baille wall portions being provided with a multiplicity of broadly distributed spaced openings, said b-airle wall portions'projecting downstream from said opposed wall portions to denne an intermediate fire zone merged with and leading generally downstream from said low tire zone to extend part way along said baille wall portions and also to deline a high fire combustion zone merged with and leading generally downstream from -said intermediate lire zone and extending through the burner mouth, at least one of said opposed wall portions having a port opening therethrough at a location adjacent said gas port and in said low fire zone for directing air from said stream into said low lire zone yfor supporting continuous combustion within said low fire zone of raw gas issuing from said gas port when said supply means is at the lower limit of its ow range, said burner While disposed in said air stream and supplied with raw gas over a 20 to 1 ow range being capable of presenting a stable llame characterized by producing less than parts per million of CO in the heated -air and being substantially soot'free and odorless.

6. Apparatus in laccordance with claim 5 and wherein said manifold and said opposed wall portions are integral parts of a one piece casting.

7. Apparatus in accordance with claim 5 and including an automatic air admittance valve having an inlet connected to a source of air and an outlet connected to supply air into said burner manifold, said valve having means exposed through said outlet to respond to pressure conditions within said manifold and automatically control said valve to admit -air to said burner only during the existence of negative pressure conditions in said burner manifold. 8. ln a gas burning direct tired makeup air type heating apparatus that includes a high turn-down gas burner and means for ilowing a low pressure air stream forwardly past the burner at a substantially constant velocity, the improvement comprising means having a flow ratio range on the order of l5 to l to supply variable amounts of raw gas fuel to said burner while substantially constant air stream velocity is maintained by said air iiowing means, and said burner being of a nozzle mixing type and comprising an elongated burner manifold adapted to be disposed in said air stream crosswise thereof and connected in receiving relation to said supply means, said manifold having an external lengthwise wall portion along a downstream region thereof and providing a lengthwise distributed gas port means for issuing gas supplied from said supply means in a downstream direction from the manifold, elongated external wall structure disposed lengthwise along said manifold and providing opposed elongated wall portions leading generally` downstream from said manifold in closely spaced ilanking relation to said gas port means to shield said gas port means from regions of said air stream that are externally thereadjacent, with said opposed wall portions defining cooperatively with said manifold wall portion a transversely narrow low iire zone extending externally Aalong the lengthwise wall portion of said manifold, said external wall structure having elongated baille Wall portions leading generally downstream from said opposed wall portions and progressively diverging in a downstream direction to terminate in a transversely wide burner mouth, means including a multiplicity of broadly distributed spaced openings in said baille wall portions to diver-t a portion of the air stream into the space between the baffle wall portions, said baille wall portions projecting downstream from said opposed wall portions to define an intermediate tire zone merged with and leading generally downstream from said low tire zone to extend part way along said baille wall portions and also to define a high re combustion zone merged with and leading generally downstream from said intermediate lire zone and extending through the burner mouth, at least one of said opposed wall portions having ports opening therethrough at locations adjacent regions of said low lire zone to which gas is delivered by llow through said gas port means for directing air from said stream into the last-named regions of said low lire zone to enable support of continuous combustion within said low fire zone of raw gas issuing from said gas ports when said supply means is at the lower limit of its ilow range, with the area at said burner mouth being at least iive times the area of said low lire zone at said port location-s, said burner while disposed in said air stream and supplied with raw gas over a l to 1 flow range being capable of presenting a stable flame characterized by producing less than l0() parts per million of CO in the heated air and being substantially soot free and odorless.

9. Apparatus in accordance with claim 8 and wherein said baille wall openings at the intermediate tire zone are substantially alignedin a direction along the length of said mani-fold and are smaller than the Iopenings which are adjacent the high lire zone, and wherein said baille wall portions have elongated deilector strips adjacent and extending alongside the aligned baffle wall openings of the intermediate fire zone and exposed directly thereto.

1t?. Apparatus in accordance with claim S and wherein said manifold and said opposed elongated wall portions are integral parts of a one-piece casting.

11. Apparatus in accordance with claim 8 and including an automatic air admittance valve having an inlet connected to a source of air and an outlet connected to supply air into said burner manifold, said valve having means exposed through said outlet to respond to pressure conditions within said manifold and automatically control said valve to admit air to said burner only during the existence of negative pressure condition-s in said burner manifold. y

12. In a gas burning direct iired makeup air type heating apparatus that includes a high turn-down gas burner and means for flowing a low pressureV air stream forwardly past the burner at a substantially constant velocity, the improvement comprising means having a ilow ratio range on the order of to l when variable amounts of raw gas fuel are admitted to said burner while substantially constant air stream velocity is maintained by said air flowing means, and said burner comprising an elongated burner manifold adapted to be disposed in said air stream crosswise thereof. and connected in receiving relation-to said supply means, said manifold having an external lengthwise wall portion along a downstream region thereof and providing a lengthwise distributed gas port means for issuing gas supplied from said supply means in a downstream direction from the manifold, elongated external wall structure disposed lengthwise along said manifold and providing opposed elongated'wall portions leading generally downstream from said manifold in closely spaced flanking relation to said portmeans to shield said gas port means from regions of said air stream that are externally thereadjacent, with said opposed wall portions defining cooperatively with said manifold wall portion a transversely narrow low lire zone extending externally along the lengthwise wall portion of said manifold, said external wall structure having elongated baffle wall portions leading generally downstream from said opposed wall portions and progressively diverging in a downstream direction to terminate in a transversely Wide burner mouth, said baille wall portions being provided with a multiplicity of broadly distributed spaced openings, said baille wall portions projecting downstream from said opposed wall portions to define an intermediate lire zone merged with and leading generally downstream from said low lire zone to extend part `way along said baille wall portions and also to define a high lire combustion zone merged with and leading generally downstream from said intermediate fire zone and extending through the burner mouth, atleast one offsaid opposed wall portions having ports opening therethrough at locations immediately adjacent regions of said low lire zone to which gas is delivered by ilow through said gas port means for directing air from said stream into the last named regions of said low fire zone for supporting continuous combustion within said low tire zone of gas issuing from said gas ports when said supply means is at the lower limit of its flow range,.said burner while disposed in said air stream and supplied with raw gas over a 2O to l ow range being capable of presenting a stable llame characterized by producing less than parts per million of CO in the heated air and being substantially soot free and odorless.

13. Apparatus in accordance with claim 12 and including an automatic air admittance valve having an inlet conected to a source of air and an outlet connected t0 supply air into said `burner manifold, said valve having means exposed through said outlet to respond to pressure conditions within said manifoldand automatically con-V trol said valve to admit air to said burner only during the existence of negative pressure conditions in said burner manifold.

14. Apparatus in accordance with claim 8 and wherein said baille Wall openings at the intermediate zone are smaller than the openings which are adjacent the high fire zone, there being a row of said smaller wall openings distributed along each baille wall to define the beginning of the intermediate lire zone, with the number of openings in said rows being greater than the number of said ports and with the size of the openings in said rows corresponding to the size of the air ports.

15. Apparatus in accordance with claim 14 and including an automatic air admittance valve having an inlet connected to a source of air and an outlet connected to supply air into said burner manifold, said valve having means exposed through said outlet to respond to pressure conditions within said manifold and automatically control said valve to admit air to said burner only during the existence of negative pressure conditions in said burner manifold. l

16. In a gas burning direct tired makeup air type heating apparatus that includes a high turn-down gas burner and means for flowing a low pressure air stream forwardly past the burner at a substantially constant velocity while the burner is operating within its high-low gas` burning range, the improvement wherein the gas burner is of the nozzle mixing type and comprises an elongated gas manifold having a downstream wall provided with spaced gas ports therein,V an elongated chamber downstream of said downstream wall and defined by said downstream Wall and by spaced walls joined to the manifold and extending downstream to a point where, in at least one of said spaced Walls, a series of air ports provide communication between said air stream and said chamber, outwardly ared walls downstream'of said chamber having openings therein permitting air to flow from said air stream into the space between said ared walls to provide a combustion zone for said burner, the distance between the ilared wall at their downstream extremity being at least ve times as great as the distance between said spaced walls at the outer extremity of the chamber, and means including said gas ports and said air ports for causing the burner to have a turn-down range of at least to l when the gas in the manifold is a raw gas, said burner while disposed in said air stream and supplied with raw gas throughout said 15 to 1 turn-down range being capable of presenting a stable flame characterized by producing less than 100 parts per million of CO in the heated air and being substantially soot free and odorless.

17. In a gas burning direct iired makeup air type heating apparatus that includes a high turn-down gas burner and means for flowing a low pressure air stream forwardly past the burner at a substantially constant velocity while the burner is operating within its high-low gas burning range, the improvement wherein the gas burner is of the nozzle mixing type and comprises an elongated gas manifold having a downstream wall provided with spaced gas ports therein, an elongated chamber downstream of said downstream wall and defined by said downstream wall and by spaced walls joined to the manifold and extending downstream to a point where, in at least one of said spaced walls, a series of air ports provide communication between said air stream and said chamber, outwardly ared walls downstream of said chamber having openings therein permitting air to flow from said air stream into the space between said flared walls to provide a combustion zone for said burner, the distance between the ared walls at their downstream extremity being at least ten times as great as the distance between said spaced walls at the outer extremity of the chamber, and means including said gas ports and said air ports for causing the burner to have a turndown range of at least 2O to l when the gas in the manifold is a raw gas, said burner while disposed in said air stream and supplied with raw gas throughout said to l turndown range being capable of presenting a stable ame characterized by producing less than 100 parts per million of CO in the heated air and being substantially soot free and odorless.

18. In a gas burning direct fired makeup air type heating apparatus that includes a high turn-down gas burner and means for owing a low pressure air stream forwardly past the burner at a substantially constant velocity, the improvement comprising means having a ow ratio range on the order of 20 to l to supply variableamounts of raw gas fuel for said burner while constant air stream velocity is maintained by said air owing means, and said burner being of aV nozzle mixing type and comprising a burner manifold adapted to be disposed in said air stream and connected in receiving relation to said supply means, said manifold having an external wall portion at a downstream region thereof and provided with gas port means for issuing gas supplied from said supply means in a downstream direction from the manifold, external wall structure disposed on said manifold and providing opposed wall portions leading generally downstream from said manifold in closely spaced anking relation to said gas port means to shield said gas port means from regions of said air stream that are externally thereadjacent, said burner including means cooperable with said opposed wall portions and with said manifold wall portion to define a transversely limited area externally at said gas port means within which gas from said gas port means must undergo continuous complete combustion at low tire, said external wall structure having baille wall portions leading generally downstream from said opposed wall portions and progressively diverging in a downstream direction to terminate in a transversely wide burner mouth, means including a multiplicity of broadly distributed spaced openings in said baille wall portions to divert a portion of said air stream into the space between said bathe wall portions, said bathe wall portions projecting downstream from said opposed wall portions to define an intermediate iire zone within which gas from said gas port means must undergo continuous complete combustion at intermediate tire, said intermediate lire zone being merged with and leading generally downstream from said low tire zone to extend part way along said baille wall portions and also to dene a high tire combustion zone within which gas from said gas port means must undergo continuous complete combustion at high re, said high fire zone being merged with and leading generally downstream from said intermediate iire zone and extending through the burner mouth, at least one of said opposed wall portions having air port means opening therethrough at a location within the transversely restricted area of low iire for admitting air from said stream to said restricted area for continuously supporting substantially complete combustion when said supply means is at the lower limit of its flow range and is delivering raw gas, the distance between said baiie wall portions across said mouth being at least ten times as great as the distance between the said opposed walls at the location of said air port means, said burner, when disposed in said air stream, being capable of continuously supporting complete combustion of raw gas when supplied to the burner at any rate within said 20 to 1 flow range, and being further capable of presenting a stable flame characterized by producing less than parts per million of CO in the heated air and being substantially soot-free and odorless.

19. In a gas burning direct red makeup air type heating apparatus that includes a high turn-down gas burner and means for owing a low pressure air stream forwardly past the burner at a substantially constant velocity, the improvement comprising means having a How ratio range on the order of 15 to 1 to supply variable amounts of raw gas fuel for said burner while constant air stream velocity is maintained by said air flowing means, and said burner being of a nozzle mixing type and comprising a burner manifold adapted to be disposed in said air stream and connected in receiving relation to said supply means, said manifold having an external wall portion at a downstream region thereof and provided with gas port means for issuing gas supplied from said supply means in a downstream direction from the manifold, external wall structure disposed on said manifold and providing opposed wall portions leading generally downstream from said manifold in closely spaced flanking relation to said gas port means to shield said gas port means from regions of said air stream that are externally thereadjacent, said burner including means cooperable with said opposed wall portions and with said manifold wall portion to define a transversely limited area externally at said gas port means within which gas from said gas port means must undergo continuous complete combustion at low tire, said external wall structure having baffle wall portions leading generally downstream from said opposed wall portions and progressively diverging in a downstream direction to terminate in a transversely wide burner mouth, means including a multiplicity of broadly distributed spaced openings in said bae wall portions to divert a portion of said air stream into the space between said bafe wall portions, said baffle wall portions projecting downstream from said opposed wall portions to dene anv intermediate re zone within which gas from said gas port means must undergo continuous complete combustion at intermediate tire, said intermediate fire zone being merged with and leading generally downstream from said low fire zone to extend part way along said bafde wall portions and also to define a high tire combustion zone within which gas from said gas port means must undergo continuous complete combustion at high lire, said high tire zone being merged with and leading generally downstream from said intermediate re zone and extending through the burner mouth, at leastY one of said opposed wall portions having air port means opening therethrough at a llocation within the' transversely restricted area of low re for admitting air from said stream to said restricted area for continuously supporting substantially complete combustion Ywhen said supply means is at the lower limit of its'ow range and is delivering raw gas, the distance between said baille -wall portions across said mouth being at least 5 times as great as the distance between the said opposed walls at the location of said air port means, said burner, `when disposed in said air stream, being capable of continuously supporting complete combustion of raw gas when supplied to the burner at any rate within said 15 to 1 flow range, and being further capable of presenting a stable flame characterized by producing less than 100 parts per million of CO in the heated air and being substantially soot-free and odorless.

ReferencesCited by the Examiner UNITED STATES PATENTS 3/36 Russell 263-19 11/37 Ames 263-19 4/45 Miller 11S-115 6/50 McMahan 263-19 5/52 Way et al.

9/58 Freeman 263-19 12/60 Woltfrodt 263-19 7/ 62 Skerkoske et al. 263-19 8/62 Yeo et al. 263-19 FOREIGN PATENTS 12/52 Canada. 12/ 31 Great Britain.

CHARLES SUKALO, Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,186,697 l'June 1, 1965 Edward J. Haedike et al.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 8, line 3, after "said", first occurrence, insert gas line 36, for "conected" read connected column 9, line S, for "wall" read walls signed and $66166 this 19th day of octobr 196s.

SEAL) A nest:

ERNEST w. SWIDER EDWARD J. BRENNER Attesting Officer Commissioner of Patents

Claims

17. IN A GAS BURNING DIRECT FIRED MAKEUP AIR TYPE HEATING APPARATUS THAT INCLUDES A HIGH TURN-DOWN GAS BURNER AND MEANS FOR FLOWING A LOW PRESSURE AIR STREAM FORWARDLY PAST THE BURNER AT A SUBSTANTIALLY CONSTANT VELOCITY WHILE THE BURNER IS OPERATING WITHIN ITS HIGH-LOW GAS BURNING RANGE, THE IMPROVEMENT WHEREIN ITS HIGH-LOW GAS IS OF THE NOZZLE MIXING TYPE AND COMPRISES AN ELONGATED GAS MANIFOLD HAVING A DOWNSTREAM WALL PROVIDED WITH SPACED GAS PORTS THEREIN, AN ELONGATED CHAMBER DOWNSTREAM OF SAID DOWNSTREAM WALL AND DEFINING BY SAID DOWNSTREAM WALL AND BY SPACED WALLS JOINED TO THE MANIFOLD AND EXTENDING DOWNSTREAM TO A POINT WHERE, IN AT LEAST ONE OF SAID SPACED WALLS, A SERIES OF AIR PORTS PROVIDED COMMUNICATION BETWEEN SAID AIR STREAM AND SAID CHAMBER OUTWARDLY FLARED WALLS DOWNSTREAM OF SAID CHAMBER HAVING OPENINGS THEREIN PERMITTING AIR TO FLOW FROM SAID AIR STREAM INTO THE SPACE BETWEEN SAID FLARED WALLS TO PROVIDE A COMBUSTION ZONE FOR SAID BURNER, THE DISTANCE BETWEEN THE FLARED WALLS AT THEIR DOWNSTREAM EXTREMITY BEING AT LEAST TEN TIMES AS GREAT AS THE DISTANCE BETWEEN SAID SPACED WALLS AT THE OTHER EXTREMITY OF THE CHAMBER, AND MEANS INCLUDING SAID GAS PORTS AND SAID AIR PORTS FOR CAUSING THE BURNER TO HAVE A TURNDOWN RANGE OF AT LEAST 20 TO 1 WHEN THE GAS IN THE MANIFOLD IS A RAW GAS, SAID BURNER WHILE DISPOSED IN SAID AIR STREAM AND SUPPLIED WITH RAW GAS THROUGHOUT SAID 20 TO 1 TURNDOWN RANGE BEING CAPABLE OF PRESENTING A STABLE FLAME CHARACTERIZED BY PRODUCING LESS THAN 100 PARTS PER MILLION OF CO IN THE HEATED AIR AND BEING SUBSTANTIALLY SOOT FREE AND ODORLESS.