US3405922A

US3405922A - Door heater

Info

Publication number: US3405922A
Application number: US594870A
Authority: US
Inventors: Marvin K Rohrs
Original assignee: Aero Flow Dynamics Inc
Current assignee: Aero Flow Dynamics Inc
Priority date: 1966-11-16
Filing date: 1966-11-16
Publication date: 1968-10-15
Anticipated expiration: 1985-10-15

Description

Oct. 15, 1968 Filed Nov. 16, 1966 M. K. ROHRS 3,405,922

DOOR HEAT ER I5 Sheets-Sheet 1 M. K. ROHRS Oct. 15, 1968 DOOR HEAT ER 6 Sheets-Sheet 2 Filed NOV. 16. 1966 wmww M. K. ROHRS DOOR HEATER Oct. 15, 1968 5 Sheets-Sheet 5 Filed NOV. 16. 1966 United States Patent O 3,405,922 D0011 HEATER Bier-Vin K. Rohrs, Fanwood, Nl, assignor to Aero-Flow Dynamics, Inc., (L. 3. Wing Mfg. Co. Division) Linden, NJ, a corporation of New York Filed Nov. 16, 1966, Ser. No. 594,379 14 Claims. (Cl. 26319) ABSTRACT OF THE DISCLOSURE Overhead door heater unit having separately subassembled burner section, horizontal duct section, blower section, controls section, and downwardly projecting air discharge section. Burner section includes line type, raw gas burner mounted at air inlet side of profile plate; airflow sensitive sail switch within separate opening of profile plate; and temperature high limit switch on profile plate above burner. Duct section is unobstructed. Blower section includes pair of laterally spaced apart blowers; temperature distribution 'baffie between blowers; air flow baflies at downstream side of blower inlets; and Snorkels for cooling blower bearings. Discharge section includes vertical front plate particularly located with respect to blower outlets; back plate at 52 angle; 122 expansion plates at sides; thermostat for controlling a temperature modulating control valve; and automatic reset high temperature limit switch adjacent blower outlets. Controls section includes said temperature modulating control valve in gas line section; solenoid actuated gas shut-off valve; and manual gas shut-off valve. Other features per specification.

This invention generally relates to space heaters for heating environmental air in factories, warehouses, commercial establishments and the like. Particularly, the invention relates to so-called door heaters of the gas-fired type.

Door heaters are those which are mounted overhead adjacent to outside doorways or the like, especially doorways which are normally or frequently opened, for the purpose of blowing heated air downwardly to shield the interior of the building from any inrush of cold air, and to heat any cold air which does enter through the open doorway. Such heaters incorporate steam coils, gas flame, or sometimes electrical heating elements for heating the air which a contained blower draws therethrough and discharges in the downward direction to form the air shield at the doorway. The incoming air to the heater may be drawn either from the outside of the building, as through an air duct connecting the air-inlet side of the heater to the exterior atmosphere, or from within the building in the vicinity of the heater, the latter arrangement necessarily including the introduction of some fresh air since the heater is adjacent an open doorway.

It is apparent that, to be effective, a door heater must emit a stream of uniformly heated air in a generally planar pattern of such height and width as to reach the floor and extend the width of the doorway, and in such volume and direction, and with such force as to nullify and effectively block the admission into the building of cold, outside air which will normally tend to enter through the doorway due to established diiferences between interior and exterior temperature and pressure conditions, wind conditions and the like. Prior door heaters have not always been adequate in these respects. Moreover, and of course, doorways are not all the same size, or even of standard sizes in height and width, and the particular environmental conditions under which the heater must operate vary widely as between given locations of intended installation. Prior heaters of a standard size and design are 3,405,922 Patented Get. 15, 1968 more often suitable within only a limited range of application with respect to doorway size and operating conditions and, therefore, manufacturing costs are usually abnormally high by reason of the need for frequent departures from the standard to adapt the heater for a particular installation, or equivalent increased costs to the customer are involved by the need for installing two standard heaters where only one properly designed heater would do.

The present invention provides a door heater which is suitable for use under a wide range of conditions of operation, such as higher or lower or narrower or wider doorway dimensions, anticipated large or small temperature variations, and other 'variable factors, without the need for special adaptation of the unit to suit the given conditions. Thus, true rnass production techniques may be employed in its manufacture, thereby reducing the unit costs, and ultimate costs to the customer are reduced, especially in particular circumstances where the one unit adequately serves where normally two or more of the previously known types of heaters would have been installed.

In the gas-fired door heater to be described, these result sare afforded by the overall arrangement of the heater, its inclusion of multiple spaced apart blowers and certain air baffling and air directioning elements, and other features, all of which provide improved air flow efiiciency through and out of the heater, very uniform temperature distribution throughout the emitted stream of heated air, and a particular angular disposition of the emerging air stream. These characteristics measurably improve the suitability of the heater for use over a wide range of doorway sizes and other prevailing conditions.

In raw gas-fired door heaters, an additional problem is presented in that insufficient air through the heater, as might be caused by blower failure, can cause incomplete combustion and resulting toxic fumes to be emitted. The heater of the present invention incorporates features which automatically prevent or discontinue emission of gas under such circumstances. One such feature is the inclusion of a sail switch for sensing the necessary flow of air. Although sail switches for the purpose are known, the particular mounting and arrangement of it in accordance with the invention provides more definite assurance of its effective operation. Another such feature is the inclusion of an additional so-called high-limit temperature switch which, in the heater to be described, is actuated upon direct impingement of flame. While such switches have been used in gas-fired heaters of the type, the particular location and setting of the switch is such that it will not be actuated unless air flow through the heater is discontinued. Such avoids spurious shutdown, while also assuring that shutdown will occur under stated conditions.

Briefly and generally describing the invention in its preferred embodiment, within its elongated housing enclosure the heater includes a burner section, a duct and blower section, and a controls section, these sections being in tandem alignment with each other. A fourth basic section of the heater is its discharge section which is adjacent to the blower output, and projects below the underside of the main housing.

The burner section includes a single burner of the elongated, raw gas type, and a profile plate in surounding relation therewith to control and increase the velocity of the air flow through and around the burner. The aforementioned sail switch is mounted within a slot of the profile plate which provides a separate airstream for its actuation, and which removes it from the influence of excessively high temperatures. The high-limit temperature switch is mounted on the air-inlet side of the profile plate directly above the burner. The burner is electrically ignited by a conventional igniter, and includes a conventional flame sensing device, both of which are actuated in proper sequence by controls mounted in the controls section.

The duct and blower section includes a straight duct portion, extending from the profile plate of the burner section, for unrestricted flow of heated air to a pair of blowers. The blowers are aligned in spaced apart relation in the transverse direction of the heater, and discharge the initially horizontal air flow in downward direction. A temperature distribution bailie spans the spacing between the blowers, the bafiie facing and altering the horizontal flow of air to the blowers from the burner. This temperature distribution bafile effects a more even temperature distribution within the air stream at the outlet of the discharge section, as will be later described in greater detail. Additionally vertically disposed baflles are situated and extend in transverse direction within the spacing between each of the respective blowers and the respectively adjacent side walls of the housing, and a third vertical bafile is similarly situated within the spacing between the blowers, these baffles being in alignment with each other and located immediately rearward of the blower inlet openings, as will be seen. They extend the full height of the housing, and serve not only to deflect the flowing air into all four of the blower inlet openings, but also serve to insulate the controls section from the influence of the heated air flow.

The control section mounts appropriate controller apparatus for initiating, terminating and controlling the flow of raw gas to the burner, and for automatically modulating the gas fiow to effect constant temperature of the heated air in accordance with any predetermined temperature setting. Temperature setting control is effected by a control knob which is exposed at the underside of the heater housing, the control knob being adapted to be engaged by a separate and specially formed cup-like adjustment device so that the adjustment may be remotely effected as is necessary by reason of the high elevation of the heater when mounted overhead at a doorway.

The discharge section includes a vertical front plate and an angularly disposed back plate which project below the underside of the main housing and between which the discharging heated air will flow. The back plate is disposed at an angle of 52 with respect to the horizontal, facing towards the air inlet end of the heater. At each of the respective ends of the discharge section (i.e., at the respective sides of the heater unit), the discharge opening is terminated by an expansion plate which is disposed at an angle of 122 with respect to horizontal as measured from the plane of the discharge opening of the adjacent blower. In additon, within the path of the discharging air from each blower there are mounted two longitudinally extending vanes for pivotal adjustment in transverse direction.

These and other objects, features and advantages of the invention will be more apparent from the following detailed description of a preferred embodiment thereof, when taken together with the accompanying drawings in which:

FIGURE 1A is a diagrammatic, sectional side elevation showing, to a reduced scale, of a typical gas-fired door heater installation at the doorway of a loading platform or the like in a factory building;

FIGURE 1 is a top plan view of a gas-fired door heater in accordance with the invention, its top panel being omitted for clarity;

FIGURE 2 is a sectional side elevation of the door heater, the view being taken at lines 22 of FIGURE 1 and certain elements being omitted for clarity;

FIGURE 3 is a somewhat enlarged end view of the airinlet end of the door heater, the view being partially in cross-section as seen from line 3-3 in FIGURE 1 and certain elements having been omitted for clarity; and

FIGURE 4 is a sectional end view, to the scale of FIGURE 3, of the opposite end of the door heater, the

4 view being taken at lines 4-4 in FIGURE 1 and partially broken away to show certain details;

FIGURE 4A is an enlarged section side elevation showing a means for adjusting the temperature of the discharging air.

Referring first to FIGURE 1A, a gas-fircd door heater 10 in accordance with the invention is mounted overhead at the interior side of an outside doorway 11 of a factory building or the like, the floor of which is indicated by reference numeral 12. The doorway 11 may have a conventional type overhead sliding door 13, which is shown in its up or open position adjacent a ceiling 14. Where the doorway 11 is at a truck loading platform 15 or the like, the door 13 may remain open for relatively long periods of time during which, especially in cold weather, large quantities of cool air tend to enter the building. The door heater it) is intended to blow heated air H in downward and outward direction from its discharge opening 10a as shown, in the form of a curtain of warm air extending across the doorway opening, to eliminate drafts and the reduction or disruption of established room temperatures as would otherwise occur within the building by reason of the doorway being open. A single unit 10 in its preferred embodiment has nominal main body dimensions 55 /2" wide x 64" long x 19 /2" high, and has been successfully tested on doorways as large as 17 high and 14' 4" wide. Even under extreme temperature, pressure and wind conditions, the preferred embodiment will, on a conservative rating basis, efiiciently service a doorway up to 12 high and 10 wide. Further, by simply increasing the rating of its motor and blowers, it will service doorways as high as 22., or doorways adjacent to which there exists unusual wind condition, or unusually high negative pressure conditions within the building. Of course, two or more door heater units 10 may be mounted sideby-side, spaced or not, to service very wide doorways as, for example, those greater than 14' 16 wide.

FIGURE 1A shows that the gas-fired door heater 10 is suspended from a pair of laterally extending angle iron supports 15, the integrally formed

hanger elements

17 or 17a (alternatively) of the unit 10 (FIGURES 1, 3 and 4) being bolted thereto. Its air inlet end 10b is spaced horizontally away from the doorway 11 as shown to facilitate entry of outside or make-up air C, and its top is preferably spaced vertically away from the ceiling 13 to facilitate the passage of recirculated air R from the room interior to the inlet end 10b as shown. Alternatively, and although not illustrated, an inlet air duct may be installed connecting the inlet end 10b directly to outside air, as though an opening formed in the outside wall 14a of the building. A gas service pipeline 18 delivers raw gas fuel to the heater 10 and, although not illustrated, it will be understood that an electric service line for the operation of the contained blower motors, solenoid switches, etc. also leads to the heater unit 10.

Referring now to FIGURES 1 and 2, the door heater 10 in the longitudinal direction within its enclosed housing 19 includes four basic sections: a burner section which is generally indicated by reference numeral 20; a duct and blower section generally indicated by numeral 21; a controls section indicated by numeral 22; and a discharge section 23 (FIGURE 2) at the underside of the housing 19. Air to be heated flows through the heater 10 in the direction of the arrows, the air entering through a grillwork (FIGURE 3) at its inlet end 10b and flowing first horizontally through the burner section 20 and the duct and blower section 21, and then downwardly through the discharge section 23 to discharge at the discharge opening 10a.

The draft through the heater is forced by a transversely spaced apart pair of centrifugal blowers, respectively identified by reference numerals 24a and 24b, which discharge in the downward direction into the discharge section 23 as shown. In the preferred embodiment, each blower is rated at 1 HR, and both have a 1% diameter common shaft which is rotated at 1010 r.-p.m. by a 2 HF, 1750 r.p..m., S-phase, open dripproof type motor 26 via a belt and pulley arrangement 27. Alternatively, for servicing larger doorways or doorways at which special conditions prevail as previously mentioned, a 3 HP. motor may be used, and the blowers rotated at appropriately higher speed. The shaft 25 is journaled between a pair of bearings 28a, 28b these being mounted in conventional manner centrally of the outwardly facing air inlet openings 29a, 29b of the respective blowers 24a, 2417 as shown. Each blower 24a, 24b has a second axial air inlet opening, respectively 30a, 30b, at its side which faces inwardly of the unit 10. Thus, the air flow through the duct and blower section 21 enters the two blowers via-a total of four blower inlet openings, as will be understood. The driven pulley 31 of the belt and pulley arrangement 27 is attached to an outwardly projecting end 25a of the shaft 25 adjacent the blower 24b as seen in FIGURE 1, the drive pulley 32 being attached to the motor shaft 33. It should be here noted that, in addition to being centrally spaced 10" from each other, each blower 24a, 24b is spaced in transverse direction a distance of about 7" from that sidewall of the housing 19 which is adjacent to it. Moreover, the duct area of the duct and blower section 21, forward of the blowers 24a, 241;, does not have baffling or other air directioning elements therein. Apart from contributing to lower manufacturing costs, this unrestricted duct area, and the transverse spacing apart of the blowers from themselves and from the housing sidewalls, as shown, smoothes the air flow and contributes to the air flow efficiency of the systern.

A pair of snorkel pipes 55a, 55b (FIGURES 1 and 2) are respectively disposed immediately above each of the blower bearings 28a, 28b, each being attached to the side of its associated blower, as by strap connections 56a, 56b, and each extending through the topwall of the housing 19 as seen in FIGURE 2. Thus, the blowers 24a, 24b draw a small, continuously flowing quantity of outside air across their respective bearings 28a, 28b for aircooling the same during operation.

The downwardly facing air outlet openings of the blowers 24a, 24b are adjacent to, and discharge air through the respective housing air openings 1% of the same size and shape formed at the underside of the housing 19, as will be better understood from FIGURES 2 and 4.

Referring to FIGURES 1 and 2, a temperature distribution bafiie 34, having height of 3 on either side of the elevational plane of the shaft 25', spans across the 10" spacing between the 15" wide blowers 24a, 24b at the forward ends of their housing enclosures, i.e., the ends which face towards the burner section 20. In the preferred embodiment, the temperature distribution baffle 34 is creased transversely midway of its height as seen in FIGURE 2, to provide a vertical upper air deflector portion 340, and rearwardly inclined lower air deflector portion 34b, which generally follow the curvature of the blower housings, as will be apparent. The temperature distribution baffie 34 provides evenness of temperature distribution throughout the heated air as it discharges through the discharge section 23. This will be more fully understood after considering the general arrangement of the heater 10, as will now be described.

Raw gas fuel enters the heater 10 from the exterior gas surface line 18, the line 18 being coupled by a coupling 18:: to a gas supply conduit 35 which is mounted within the heater housing 19. The conduit 35 conducts the gas to an elongated, line-type raw gas burner 43 within the burner section 20. The conduit 35 and burner 43 are mounted by support brackets 36-39. As it enters the conduit 35, the gas flows first through a normally closed, solenoid actuated shut-01f valve 40, thence Emerging from the manifold 43a via appropriate gas orifices t-herealong (not shown), the gas is mixed with combustion air derived from the incoming air to be heated, the combustion air entering the burner 43 via its combustion air apertures 43b. The front face 430 of the burner is completely open, and is situated centrally of a 14 /2" x 28% profile plate opening, generally indicated by reference numeral 44 (FIGURE 3), which is provided by a transversely disposed profile plate adjacent, but a short distance behind the plane of the front face of the burner, as shown. The profile plate is actually formed by a framing including a pair of transversely extending and centrally spaced apart

plates

45, 46 having

respective flange portions

45a, 45!) which face inwardly in the direction of air flow, the

plates

45, 46 being attached at the respective opposite sides of the unit as by spot welding between respective top and bottom transversely extending angle iron frame pieces 47, 48 which also serve to constrict the opening 44 at its top and bottom. Burner 43 is 24" long X 6 /2" high at its front.

Thus, with respect to the function of the temperature distribution bafile 34 and referring first to FIGURE 2, air to be heated is drawn into the duct portion of the burner section 21 through the grillwork by action of blowers 24a, 24b. As indicated by the arrows, the air flows through the profile plate opening 4 around and through the burner 43, to emerge in stratums of heated air which in the vertical direction may be described as: a hot stratum H extending towards the blowers from the burner 43 at the center of the opening 44, and relatively cooler air stratums H extending adjacent and respectively above and below the central hot stratum. Similar air temperature stratification occurs in the transverse direction, as will be understood from FIGURE 1. That is, air flowing through the profile plate opening 44 at the respective sides of the burner 43, rather than through the burner, is heated to a lesser extent and emerges into the duct section 21 in two respective air stratums H adjacent the hot centrally disposed air stratums H emanating from the burner itself. Of course, the stratum H is actually continuous, in surrounding relation to the hotter stratum H The bafiie 34 tends to block the otherwise direct flow of the hot central stratum H into the ceutermost blower inlets 30a, 30b, and to divert the hot stratum to the top, bottom and sides of the duct area where it mixes with the cooler stratums of air to promote uniform temperature throughout all of the air flowing into the blower inlet openings 29a, 29b, 30a and 30b. The temperature distribution bafl le 34 is sized and arranged to provide optimum temperature distribution With in the total air flow at H as it emerges through the heater discharge opening 19a.

Referring to FIGURE 2, it will be noted that the height of the housings of blowers 24a, 24b is such as to contact the top plate of housing 19 so as to avoid air-flow over and beyond the blower tops. Vertically disposed and transversely aligned

air flow bafiies

49, 50 and 51 (FIG- URE 1) respectively disposed at either side and attached between the blowers 24a, 24b immediately adjacent the rearward sides of their inlet openings 2%, 29b, 30a and 30b, as shown, assist air flow efficiency by mechanically turning the air into the blower inlet. The

bafiles

49, 50 and 51 extend the full height of the unit 10 (see FIG- URE 2) and thereby also separate the controls section 22 from the duct and blower section 21, and protect the electrical and gas control apparatus within the former from the heat within the latter. As seen in FIGURES 1 and 2, the air flow bafiie 49 has a narrow vertical opening 52 for passage of the belt of the pulley system 27 therethrough.

As shown in FIGURE 2, the discharge section 23 includes a vertically disposed front plate 23a and a fixed back plate 231:, the latter being disposed at an angle 0 equal to 52 with respect to the horizontal, so that the downwardly emerging air from blowers 24a, 24b is deflected in angular direction generally towards the inlet end 10b of the unit, as indicated by the arrow. In addition, and referring to FIGURE 4, the discharge section 23 includes fixed expansion plates 230 at the respective opposite sides thereof, each plate 230 being disposed at a downward and outwardly flaring angle equal to 122 with respect to the horizontal, as shown. In addition to permitting diverting of the emerging high velocity air towards the respective sides of the unit, the expansion plates 230 permit expansion of the heated air and contribute to the efliciency of its discharge from the blowers, the particular angular disposition of the plates having been found to be optimum for the purpose. Diverting of the discharge air to the respective sides is controlled by the setting of the respective independently positionable vanes 23d, two of which are mounted in alignment with the discharge from each blower 24a, 24b as shown in FIGURE 4. Each adjustable vane 23d is mounted for pivotal movement in transverse direction as indicated by the arrows, about pivot points 23e, to any desired position. The expansion plates 23c and vanes 23d adapt the heater 10 to serve a wide range of doorway widths, up to about 14' 6". Further, it will be noted that, as shown in FIGURE 2, each vane 23d in the longitudinal direction has length substantially equal to the length, about 8 /2", of the discharge opening of its associated blowers 24a or 24b, whereas the vertical front plane 23a of the discharge section is located about 1 /2" forward (ie., towards inlet end 10b) of the forward, curved end of the blower discharge opening. At its upper extremity, where its front and back plates 23a, 23b are joined to the underside of the housing 19, the width of the discharge section 23 (i.e., in the longitudinal direction as seen in FIGURE 2) is therefore approximately 10". The depth of the discharge section, as measured below the underside of the housing 19, is 4 /2". Considering the width and depth of the discharge section 23, the positioning relative to the blower outlet of its front plate 23a, and the 52 angular disposition of its back plate 23b, the resutling angle of air discharge in the forward direction has been found to :be most effective in causing the heater 10 to be suitable for use at any of a variety of doorway heights.

At 1010 rpm. each blower 24a, 24b delivers 2800 c.f.m. The same blowers can be rotated faster, by changing the size of the pulleys of the pulley system 27, to deliver 3250 c.f.m. per blower, if desired.

The burner 43 has a turn down ratio of :1, its rating being from 150,000 B.t.u./hr. to 750,000 B.t.u./l1r. Although not shown in detail, it is ignited by a conventional spark ignition system whose transformer 60 is mounted on profile plate 46, as indicated in FIGURES 2 and 3. An electrical connection box 61 is mounted therebelow for making wiring connections (not shown). Referring to FIGURE 1, and as only partially indicated in FIGURES 2 and 3, a small 7 0D.) gas line 62 delivers a fixed, continuously flowing supply of gas to the burner manifold 43a from a takeoff location on the main gas conduit 35 between the manual shutoff valve 51 and the temperature modulation control valve 42. Thus, when the manual valve 41 is open and the solenoid valve 40 has been electrically opened, an initial small supply of gas flows to the burner 43 for ignition by the conventional spark ignition system. Subsequent to ignition, the gas line 62 continues to furnish a small, unmodulated, fixed input of gas to the burner, as aforesaid. However, the gas line 62 might also include conventional flow control means (not shown) so that the line 62 would then function simply as a pilot gas line, gas flow therethrough being terminated after burner ignition.

Although not illustrated, there is also mounted within the flame shield 43d of the burner a flame sensing rod which is a part of a conventional lectronic flame safeguard device, whose actuating apparatus 63 is mounted on the control panel 64 within the controls section 22 of the unit, as shown in FIGURE 4. The flame sensing apparatus 63 is for the conventional purpose of sensing and monitoring the appearance of flame within the burner 43.

Also mounted on the control panel 64 is a magnetic starter 65 for actuating the blower motor 26. The control panel 64 also mounted a terminal board 66 and a fuse block 67 for necessary wiring connections. 4

Referring again to FIGURE 3, safeguard against blower failure is provided by a sail switch 63 and a manual-reset high limit switch 69, only a portionof theelectric wiring 70 to the latter being illustrated. These safeguard switches 68, 69 are electrically connected in series with the solenoid actuated gas inlet valve 40 so that, in the event of failure of the blowers 24a, 241; the valve 40 will automatically close, thereby cutting off all flow of gas'to the heater unit 10. This prevents emitting of toxic fumes from the heater, as might occur upon blower failure due to an insufliciency of draft air as is necessary for complete combustion of the raw gas fuel. Specifically, during normal operation when the valve 40 is in opened condition as is maintained electrically by power to its incorporated solenoid, and while the blowers 24a, 24b are normally rotating so that a constant draft of air is passing through the unit, the normally open sail switch 68 is held in closed (i.e. circuit-completing) condition by the deflecting force of drafted air on its sail element 68a as the air passes through the opening 72 (FIGURE 3) within which the sail 63a is mounted. The normally closed temperatureactuated, manual reset high-limit switch 69 adjacent the burner 43 is also in closed condition. Should the blower motor 26 fail, or the blowers 24a, 24b otherwise cease to rotate (as by a loosened connection to their shaft 25, etc.), the force of air will diminish through the sail switch opening 72, whereupon the sail 68a will no longer be deflected and the sail switch 68 will open so that the series circuit will be opened. The valve 40 should then close by deactivation of its solenoid.

If for any reason the valve 40 fails to shutso that the feed of raw gas continues, the gas flames or heat emating from burner 43 will then tend to rise vertically in the absence of draft air, which normally forces the heat and flames in horizontal direction. The vertically rising heat will heat-up and expand the bi-metallic high limit switch 69 thereabove, the switch being set to trigger at 300 'F. Triggering of the switch 69 will also break the circuit necessary for continued operation of valve 40, whereupon the valve 40 should close.

The location of the sail switch opening 72 within the profile plate element 46, and therefore spaced away from the profile plate opening 44 and burner 43, assures a steady, rather than turbulated flow of air past the sail element 68a responsive to the draft of blowers 24a, 24b which draws air directly through the opening 72. Elimination of turbulence or similar buifeting of the sail element 68a eliminates any tendency for intermittent on- .olf operation of the sail switch 68. In addition, the location away from the burner 43 retains the switch 68 in relatively cool condition to further assure its proper opera tion.

The location of the bi-metallic, high limit switch 69 above the burner 43 and at the air-inlet side of the profile plate element 47 assures that it will remain relatively cool, and therefore will not actuate,"while th heater unit is operating normally. At the same time, it' is located such that it will promptly actuate upon impingement of heat or flame rising from the burner 43 in the event of blower failure, as previously explained. Its setting is appropriate for the purpose. 7

The temperature of the heated air is regulated by adjustmentof the rotatable knob 42a (FIGURES 2 and 4) of the modulating controlvalve 42. The knob 42a is exposed and accessible through a housing opening 19 11 at the underside of the unit as shown, and its adjustment in either clockwise or counterclockwise direction adjusts the setting of the valve 42 to provide a greater or lesser average flow of gas to the burner 43. The valve 42, itself, automatically further adjusts the gas flow in accordance with its sensing of the actual temperature of the discharging air to maintain a constant temperature air discharge. The valve 42 is of a conventional self-contained, non-electrical, thermostatic type which is actuated by the hydraulic pressure of a fluid which expands or contracts in accordance with the temperature which a sensing instrument 90 of the apparatus detects. The sensing instrument 90 is, of course, mounted within the air discharge section 23, as indicated in FIGURE 2.

An automatic reset type high limit switch 71 (FIGURE 2) is mounted within the discharge passage of at least one of the blowers 24a, 24b to monitor air-discharge temperature therein for the purpose of safeguarding against failure in the operation of the modulating control valve 42. The switch 71 is electrically connected in series within the series circuit which contains the blower-failure safeguard switches 68, 69 and the solenoid actuated gas inlet valve 40. The switch 71 is normally closed, thereby completing the electric circuit as is necessary to continue the feed of gas. Should the modulating control valve 42 fail to function and remain in its open condition in which a high rate of gas flows to the burner 43, the high limit switch 71, which is of any conventional type for the purpose, will sense the abnormally high temperature of the discharge air emanating from the blowers, and will automatically open to cause a shutting of the main gas valve 40. Upon cooling, the switch 71 automatically closes.

FIGURE 4A illustrates the engagement of a special, cup-like adjustment device 75 with the valve knob 42a for turning the latter, to avoid the use of a step-ladder or the like as would otherwise be necessary to manually turn the knob 42a, considering that the unit is mounted from 8 to 17' overhead. The cylindrical cup-shaped adjustment device 75, which is attached at the end of a pole 76 as by nails 76a, is open at its outer end for receiving the knob 42a in surrounding relation as shown. It includes an oppositely disposed pair of detents 75a for engaging a corresponding pair of peripherally disposed grooves 42b formed in the knob 42a adjacent its underside, as shown. The device 75 is easily inserted into and withdrawn from the housing aperture 19a when adjustment is to be made. Of course, an appropriate temperature scale, or other knob setting indication, is marked on the housing 19 adjacent the opening 19a, and on the knob 42a itself.

The general arrangement of the heater 10 is such that it may be conveniently manufactured in component subassemblies. That is, the burner 43 is part of a burner subassembly comprising the pair of angle iron frame elements 47, 48 having the oppositely disposed

profile plate elements

45, 46 attached (as by welding) therebetween, the burner 43 being mounted thereon by the

attachment brackets

38, 39, as will be understood from FIGURE 3. The switches 68, 69, the transformer 60, and electrical connections box 61 form a part of this subassembly. Referring to FIGURES 1 and 2, a blower subassembly is formed by the pair of transversely exmending angle iron elements 57, 80, which are connected by a longitudinally extending pair of triangular shaped and vertically disposed side plates 81 at the respective sides of the unit, thus forming a frame on which both of the blowers 24a, 241) are mounted together with their

baffle plates

34, 50, 51 and 52, and snorkel pipes 55a, 55b. In addition, this blower mounting framework includes a third transversely extending angle iron element 82 (FIGURES 2 and 4), to which the control panel 64 will be attached. The blower subassembly also includes the motor 26 and its associated adjustable mounting apparatus 83, and the belt and pulley arrangement 27. The gas pipe hanger straps 36 and 37 also form a part of the blower subassembly. The discharge section 23 is a separate subassembly comprising its front plate 23a, its back plate 23b, expansion plates 23c, and respective outer side plates (unnumbered, but seen in FIGURE 4), the vanes 23d being pivotally mounted between the plates 23a, 23b as seen in FIGURE 2. Although not illustrated in detail, the horizontal duct or housing 19 is formed by a pair of longitudinally extending, L-shaped duct portions attached in opposite, abutting relation along their horizontal lower leg portions, thus forming the bottom and side walls of the duct, and a pair of removable top panels which extend between the upwardly projecting side wall portions. As seen in FIGURE 3, the side walls are bent longitudinally, midway of their height, as are the respectively cofacing pair of triangular shaped vertical elements 81 of the blower subassembly (see FIGURE 2, for example). The two blower-air outlet openings 1% at the underside of the housing 19 are respectively formed in the abutting bottom wall portions of the 'housing, the connection between the L-shaped duct portions being midway of the width of the unit. As previously mentioned, a framed grill-work is attached at the inlet end 10b of the housing 19 and, as will be understood from FIGURE 2, a removable panel 10d, is attached across the housing at its opposite end. The burner and blower subassemblies are attached to one of the L-sha-ped halves of the housing 19, after which the other longitudinally extending L-shaped half of the housing is attached, thus initially forming a U-shaped enclosure around these subassemblies. The piping 35, 62, valves 40-42, and appropriate electrical wiring are mounted and connected therein, whereupon the top panel plates,

hangers

17 or 17a, grill-work ltlc, end closure panel 10d, and discharge section 23 are attached.

Thus has been described a gas-fired door heater which achieves all of the objects of the invention.

What is claimed is:

1. An air heater for mounting overhead at a doorway or the like, comprising horizontal duct means being open at a forward end thereof to provide an air inlet, transversely disposed profile plate means within said duct means near its said air inlet and defining a centrally disposed profile plate opening smaller than the transverse area of said duct means, air heater means adjacent said profile plate means for heating air passing through said profile plate opening, a pair of centrifugal blowers for inducing a flow of air from said duct means air inlet through said profile plate opening and having respective blower housings mounted within said duct means at a location spaced longitudinally a distance away from said profile plate means and said air heater means whereby said heating by said air heater means is completed before the air reaches said blower housings, said blowers being aligned with and spaced apart from each other in the transverse direction of :said duct means and each blower being spaced away from the sidewall of said duct means to which it is adjacent, each said blower housing having an axial air inlet opening at each side thereof and a downwardly facing air outlet opening, means defining an underside opening of said duct means immediately adjacent and communicating with each of said air outlet openings of the blower housings, respectively, and means defining an air discharge section projecting below said duct means, said air discharge section being in surrounding relation with respect to both said underside openings thereof and having means for merging the air emanating from said air outlet openings of the blower housings into a single stream of substantially downward flowing air extending substantially the Width of said duct means between its said sidewalls.

2. An air heater according 'to claim 1 which further comprises an air-temperature distribution bafiie spanning between said spaced apart blower housings at the end thereof which faces said profile plate means, said airtemperature distribution bafile having portions respectively extending above and below the horizontal axial plane of said blowers to partially block and deflect that portion of said flowing air as would otherwise flow directly to those of said blower inlet openings which are disposed between said blowers.

3. An air heater according to claim 2 wherein the overall height of said air-temperature distribution battle is substantially equal to one-third /3) the height of said horizontal duct means, said bafile portions being substantially equal in height.

4. An air heater according to claim 2 which further comprises vertically disposed air baffle means extending transversely of said duct means within the respective spacings between said blowers and between each said blower and the respectively adjacent sidewall of said duct means, said air baffle means being disposed substantially immediately adjacent said axial air inlet openings of said blowers at the side thereof which is farthest from said forward end of the duct means.

5. An air heater according to claim 4 wherein each said blower housing, and said air baffle means, has height which is substantially equal to the height of said duct means.

6. An air heater according to claim 5 wherein the interior of said duct means between said profile plate means and said air-temperature distribution baffie is substantially unobstructed with respect to said flow of air from said profile plate opening to said air inlet openings of the blowers.

7. An air heater according to claim 1 wherein said air discharge section projecting below said duct means comprises a vertically projecting and transversely extending front plate substantially adjacent that side of each said duct means underside opening which is nearest said forward end of the duct means, and a transversely extending back plate immediately adjacent that side of each said underside opening which is farthest from said forward end of the duct means, said back plate being disposed at an angle substantially equal to fifty-two degrees (52) with respect to the horizontal in direction towards said forward end of :the duct means.

8. An air heater according to claim 7 wherein the downwardly projecting height of said discharge section is substantially equal to one-half /2) the width, as measured in the longitudinal direction of said duct means, of said underside openings of the duct means, said underside openings'having equal width, and said front plate of the discharge section is spaced away from each said underside opening, in direction towards said forward end of the duct means, a distance substantially equal to one third /a) of said height of the discharge section.

9. An air heater according to claim 8 wherein said discharge section funther comprises a pair of air-expansion plates disposed between said front and back plates thereof, said expansion plates being respectively disposed substantially adjacent the respective outermost ends, in the transverse direction of said duct means, of said underside openings of the duct means, each said expansion plate projecting downwardly from the underside of said duct means at an angle substantially equal to one hundred twenty-two degrees (122) with respect to the horizontal in direction towards that sidewall of said duct means to which the respective expansion plate is adjacent.

10. An air heater according to claim 9 wherein said discharge section further includes a pair of longitudinally extending and transversely spaced apart vanes mounted for adjustable pivotal movement within the downwardly projected area of each of said underside openings of the duct means.

11. An air heater according to claim 1 wherein said 12. L a blowers have a common shaft of rotation, said shaft being journaled between a pair of bearings, each bearing of the pair being mounted substantially within one of said axial air inlet openings of one of said blower housings, and which further comprises a snorkel pipe communicating with the exterior of said duct means and having an open end immediately adjacent each of said bearings for aircooling the latter responsive to activation of said blowers. 12. An air heater according to claim 1 wherein said air heater means comprises a line-type raw gas burner mounted centrally of said profile plate opening whereby a portion of said air flowing .through said profile plate opening enters said burner to furnish comb ustion air therein and the remaining portion flows around said burner, gas conduit means for feeding raw gas fuel to said burner, said gas conduit means having an, electrically actuated gas shut-off valve therein, and means responsive to substantial absence of said flow of air for inducing automatic closing of said shut-off valve, said flow responsive means comprising means defining a second opening through said profile plate means at a location spaced away from the first said profile plate opening whereby a small additional flow of air passes through said second opening from said duct means air inlet responsive to activation of said blowers, and a sail switch having a sail element mounted substantially within said second opening, said sail switch being electrically connected to said shutoff valve.

13. An air heater according to claim 12 wherein said flow responsive means further comprises a high-heat responsive switch mounted above said burner on that side of said profile plate means which faces towards said forward end of the duct means, said switch being electrically connected to said sail switch and said shut-off vlave.

14. An air heater according to claim 1 wherein said air heater means comprises a line-type raw gas burner mounted centrally of said profile plate opening whereby a portion of said air flowing through said profile plate opening enters said burner to furnish combustion air therein and the remaining portion flows around said burner, gas conduit means for feeding raw gas fuel to said burner, said gas conduit means having an electrically actuated gas shut-off valve therein, and means responsive to substantial absence of said flow of air for inducing automatic closing of said shut-off valve, said gas conduit means further having a modulating flow control valve therein at a location between said shut-off valve and said burner, a thermostat adjacent at least one of said blower outlet openings and connected to said fiow control valve for modulation of the latter responsive to the temperature at said location of the thermostat, and a rotatable knob on said flow control valve for adjusting the temperature responsive range thereof, said knob being exposed at the underside of said duct means.

References Cited UNITED STATES PATENTS Re 25,626 7/ 1964 Yeo et al. 263-19 2,171,275 8/1939 Morrison 26319 2,604,313 7/1952 Grantham 26333 3,086,441 4/1963 London 9836 3,112,686 12/ 1963 Peterson 9836 3,210,059 10/1965 Nesbitt et a1 263-19 FREDERICK L. MATTESON, 111., Primary Examiner.

E. G. FAVORS, Assistant Examiner.