US3101038A

US3101038A - Air and light distributor unit

Info

Publication number: US3101038A
Application number: US831282A
Authority: US
Inventors: Lee A Archer
Original assignee: Pyle National Co
Current assignee: Pyle National Co
Priority date: 1959-08-03
Filing date: 1959-08-03
Publication date: 1963-08-20
Anticipated expiration: 1980-08-20

Description

0, 1963 L. A. ARCHER 3,101,038

AIR AND LIGHT DISTRIBUTOR UNIT Filed Aug. 3, 1959 4 Sheets-Sheet 1 LU/l I g l k\\\\\\\\\\\\\ INVENTOR ATTORNEYS 0, 1963 L. A. ARCHER 3,101,038

AIR AND LIGHT DISTRIBUTOR UNIT Filed Aug. 3, 1959 4 Sheets-Sheet 2 n. 1 Y I 1 a k \RM 1: i {a TM -v s I X I 13 1.- Q 1 A? l w a 1 1: s 1 11 1 1 1 [51 1x 5 l\ 1*. 1 U 1 5 K 1 a 1 m H INVENTOR [5'] Q U Zeeddrafier ATTORNEYS 1963 L. A. ARCHER AIR AND LIGHT DISTRIBUTOR UNIT 4 Sheets-Sheet 3 Filed Aug. 5, 1959 INVENTOR Lee 4. flrafier ATTORNEYS Aug. 20, 1963 L. A. ARCHER 3,101,038

AIR AND LIGHT DISTRIBUTOR UNIT I Filed Aug. 3, 1959 4 Sheets-Sheet 4 4 4 INVENTOR Lee a drain ORNEYJ United States Patent 3,101,038 AIR AND LIGHT DESTRBUTOR UNIT Lee A. Archer, Wheaten, llll., assignor to The Pyle- National Company, Chicago, 111., a corporation of New Jerse y Filed Aug. 3, 1959, Ser. No. 831,282

8 Claims. (Cl. 984fl) This invention relates to improvements in ventilating and illuminating apparatus and more particularly relates to such an apparatus particularly adapted to air condition and illuminate rooms and the like.

A principal object of the invention is to provide an improved form of air and light distributor unit of the class described so constructed as to provide a comfortable condition of air diffusion in the living portion of the room with no down drafts.

Another object of the invention is to provide an improved air and light distributor unit recessed within a false ceiling of the room, together with an improved form of air diffusing and bathing means directing the air straight down into the room and so constructed as to avoid the joining together of the air streams where two devices may be mounted end-to-end in the ceiling of the room.

A still further object of the invention is to provide a combined air and light distributor unit of a type adapted to be recessed within a false ceiling substantially flush with the false ceiling, in which the air is introduced from -a plenum chamber of the unit outside of the source of light for the unit, and in which the plenum chamber is so arranged as to convert part of the velocity head of the air entering the chamber into static head and to redirect the endwise velocity components of the air in an ineificient manner, effecting the direction of air turbulently from the unit straight down into the room.

A still further object of the invention is to provide a light and ventilating unit adapted to be recessed within a false ceiling and be substantially flush with the ceiling having a trofler light housing having elongated fluorescent tubes therein with a ventilating duct leading into the trofler light housing above the fluorescent tubes into a plenum-chamber, so arranged as to partially change the velocity head of the air into static head and to direct the air from the plenum chamber in uniform quantities per unit length with uniform velocity head without horizontal velocity components, to dissipate this vertical velocity head by turbulence and direct the air from the plenum chamber in spaced relation with respect to the fluorescent tubes in a straight down direction at a low velocity head.

These and other objects of the invention will appear from time to time as the following specification proceeds and with reference to the accompanying drawings wherein:

FIGURE 1 is a fragmentary perspective View of an air and light distributor unit constructed in accordance with the invention, showing a series of air and light distributor units recessed within a false ceiling, with a main air distributor duct supplying the units, and with part of the false ceiling broken away and shown in section;

FIGURE 2 is a diagrammatic transverse sectional view illustrating the passage of air through the air and light distributor unit;

FIGURE 3 is a longitudinal sectional view taken through the air and light distributor unit;

FIGURE 4 is an enlarged transverse sectional view taken substantially along line IV-IV of FIGURE 3, and illustrates wherein the light difl'usion means may include either a glass lens or a louvered panel;

FIGURE 5 is a bottom plan view of a cover section for the plenum chamber for the unit, showing the deflector vanes extending along opposite ends thereof;

FIGURE 6 is a bottom plan view of the air damper valve and housing, showing the deflector vane and baflle 3,101,038 Patented Aug. 2t), 1963 arrangement extending along opposite sides of the damper valve and preventing the high static and velocity heads in this region from causing a disproportionate quantity or velocity of flow from this area of the plenum.

FIGURE 7 is a fragmentary perspective view of one of the light traps for carrying a glass lens, and accommodating the air to pass straight down along the outer sides of the lens, looking at the light trap from the inside thereof.

In the embodiment of the invention illustrated in the dnawings, I have shown in FIGURE 1 a ceiling 10 having an air supply duct 11 extending therealong and depending therefrom. I have also shown a false ceiling 12 spaced beneath the ceiling 1i and shown as extending along the bottom of the air duct 11 and having a plurality of air and light distributor units 13 recessed therein substantially flush with said false ceiling and supplied with air through flexible conduits 14 leading from said supply duct and suitably connected with the air and light distributor units 13.

The false ceiling 12 is diagrammatically shown in FIG- URE 2 as having openings 15 therein for receiving the air and light distributor units 13 and accommodating the mounting of the units substantially flush with the false ceiling.

As shown in FIGURES 3 and 4, each air and light distributor unit 13 comprises a troffer light housing 16 having side walls 17 extending upwardly and inwardly from opposite sides thereof and end walls 19 connecting said side walls together. The side and

end walls

17 and 19 are flanged at the lower ends thereof as indicated by reference character 2% to engage the undersurface of the false ceiling 12 around the opening 15 and are constructed to accommodate a lens 21 or a louvered bottom plate 22 to be mounted substantially flush with the ceiling (FIG- URE 4).

The side walls 17 of the troffer light housing extend upwardly and curve inwardly from shouldered portions 23 of said housing and terminate into vertical wall portions 24, turned inwardly at their upper end portions, and forming a top cover for the troiter light housing, having a central opening 25 therein intermediate the ends thereof, through which extends a generally cylindrical collar or damper valve housing 27. The collar 27 has a butterfly type of damper valve 29 suitably mounted therein and including a pair of damper blades so pivoted on a common pivot pin 31. The damper blades 30' are biased toward an open position into engagement with a stop 32 on the upperend of an adjustment screw 33, by a torsion spring 35 encircling the hinge pin 31. The adjustment screw 33 is threaded within a cross member 37 extending across the collar 27 and suitably secured to the wall thereof at its opposite ends. The adjustment screw 33 is slotted at its lower end to receive a screw driver or the like to turn said adjustment screw and raise or lower the stop 32 with respect to the pivot pin 31 to vary the open positions of the damper blades 30 with respect to the valve housing 27 and the flow of air into a plenum chamber 40 extending for a substantial portion the length of the trofler light housing. I

The lower margins of the plenum chamber 40 are defined by a flat deflector plate or balfle 41 terminating along its sides in spaced relation with respect to the side walls thereof, adjacent the upper ends of the inwardly turned wall portions 17, to provide air passageways 43 for the passage of air along the inner sides of said wall portions and suitably coated to form reflectors 44 for the trofter light housing.

A reflector plate 45 reflecting light emanating from laterally spaced elongated fluorescent tubes 47, supported beneath said reflector plate, is suitably secured to and extends along the bottom of the flat baflle 4-1 and beyond p of the plenum chamber.

oneness the ends thereof. The reflector plate 45 has downwardly inclined bafiies 49 extending from the length thereof and generally parallel to lines drawn tangent to the surfaces of the fluorescent tubes 47, and spaced radially therefrom. The bafiles 4% terminate into bafi'les 5d of an inverted V-shape in cross section, the end portions of which are generally parallel to the baffles 4-9 and serve to aid in deflecting the air along the wall portions 44 to prevent the air from contacting the fluorescent tubes 4'7.

The fluorescent tubes 47 are carried at their opposite ends in the usual mounting brackets 51 located at opposite ends of the trolier light housing 16. The mounting brackets 51 may carry the usual sockets and conductors (not shown) connected with the usual electric circuitry to effect energization of the fluorescent tubes 47, in a manner well known to those sltilled in the art and forms no part of the present invention and is not herein shown or described further.

Referring now in particular to the plenum chamber th, and the cooperation of the collar or valve chamber 27 with the flat deflector plate ll, for partially changing the verse center thereof and in direct alignment with the valve chamber 27 are tabs or baflles 53 (FIGURES 3, 4 and 6). The tabs or baflles 53 extend in front of and along op positely inclined deflector vanes 54 inclined in opposite directions from the transverse center line toward the ends of the plenum chamber. The tabs 53 each have a generally vertically extending front face 55 and side wfll" d5 diverging outwardly in the planes of the oppositely inclined center deflector vanes 54- and have cars 57 at the upper inner corners thereof. The cars 57 of the tabs 53 are adapted to be welded or otherwise secured to side walls 53 depending from a top cover portion 59 for the plenum chamber 48* (FIGURES 3, 4 and 6).

The tabs or bafiles 53 extend over the greater part of the inner edges of vanes 54 and serve to deflect the velocity head and restrict the static head of the air bouncing from the baflle plate ll along the p-lenumchamber 4d, and to thereby prevent a disproportionate quantity or velocity of flow from the region of the passageways 43.

The vanes 54, as shown in FIGURE 3, have tabs 61 extending from the outer sides thereof, adapted to be welded or otherwise secured to the side Walls 58 of the cover portion 59 for the plenum chamber 4d. As shown in the bottom plan view in FIGURE 4, four vanes 54 are mounted on each side of the cover portion 5% of the for receiving and supporting the lens 21.

plenum chamber 4i two being located on each side of the transverse center of the plenum chamber. The vanes on oneside of the transverse center of the plenum chamber are inclined outwardly with respect to the transverse center of the deflector plate 41 toward one end of the plenum chamber. The vanes 54 on the opposite side of the transverse center of the plenum chamber and deflector plate 41 are inclined outwardly with respect to the transverse center of the plenum chamber toward the opposite end Spaced outwardly of the vanes 54 are vanes-63 extending parallel to the vanes dd and extending along the plenum chamber above the discharge passageways 43 for substantially the length thereof. The

first vanes 63 are shown as being mounted on the cover portion 59 and are like the vanes 5'4 except that they extend closer to the center of the plenum chamber than the vanes 54. The remaining vanes 63 are mounted on side walls 62 of cover portions 64 for the plenum chamber 4d. The vanes 54- and oS form in eifect inemcient turbine blades along which the air flows and goes out. The outthe lower surface of the flanges 2d going air leaving the spaces between the

vanes

54 and 63 impinges against the outgoing air which was deflected by

vanes

54 and 63 resulting in a combined turbulent air stream emerging through the discharge passageways 43 in a straight down direction without endwise velocity components. This combined air stream flows along the reflectors M outside of the fluorescent tubes 4'7 at a low velocity with an optimum cooling effect on the fluorescent tubes.

Referring now to FIGURES 3, 4 and 7, and the mounting of the lens 21 along the bottom of the troifer light housing, accommodating the downward direction of the air and shielding the light of the fluorescent tubes 47, light traps es extend along each side of the trofler light housing is beneath the shouldered portion 23 thereof.

Each light trap 65 has a glass channel 66 opening toward the longitudinal center of the trolf'er light housing Each light trap 65 also hasa horizontal wall portion 67 spaced upraardly from the channel 65 by a plurality of spaced spac rs 63, forming a central air slot 79 in the space therebetween (HGURE 7) and longitudinally spaced air slots 71 on opposite sides of said central air slot. The slots 71 have vanes '73 therein and extending beneath the horizontal wall portions 67 andinclined in opposite directions from the central air slot7d to catch the air flowing through the air slots '71 and to reverse the endwise velocity components, resulting from impingement of the air ilow along reflectors 4:3 with the lens 21, so that when the airemerging from slots 75 impinges against the air from slots 71 the longitudinal velocity components are canceled in the same manner as they were at the discharge passageways 43.

7t; leading vertically therethrough along the inner legs of upwardly and downwardly facing angle members 7'7 and 79 respectively. As shown in FIGURE 4, the upwardly facing angle member 77 defines the outer margins of the vertical air slots 75, and the horizontal leg of the angle member '77 extends horizontally over the air slots 75' to shield said air slots from light and to dene t the air into said air slots. The horizontal legs or the angle members 7% extend outwardly toward a stepped wall portion 8 of the trofler light housing 16 to further shield the frame from light, and have spaced hinges Ell suitably secured to the upper sides thereof, and forming a means for securing the light traps and the glass 21 to the troffer light housing; As herein shown, the hinges 81 each have a vertically extending leg 33 having a hooked uper end portion 84 adapted to extend through an apertured portion 85 in the shoulder 23 and also has an opposite leg 86, abutting the outside of a vertical leg 87 0f the angled member 79. The glass lens and the light traps supporting said glass lenses, therefore, may be readily secured to the troffer light housing 16 in depending relation with respect to the shouldered portions 23 thereof With the lower surfaces thereof substantially flush with of said trotfer light frame.

The light trap 65 in addition to forming a support lmeans'for the glass lens 21 and shielding the air discharge passageways-along opposite ends of the glass lens from glaringlight, also cooperates with the inclined vanes fldand -63 to reduce the endwise components of air and to direct the air straight downwardly of the trolfer light housing at a low velocity, and to thereby avoid drafts that would occur by the accumulation of air at opposite ends of the trolfer light frame, particularly where a series of trotfer light frames are supported in endwise relation with respect to each other, as diagrammatically shown in FIGURE 1. I

In the modification of the invention shown hand half of FTGURE 4, t

louvered grill 22 has been substituted for the glass lens El. In this form of the in the right I invention, a plate 89 extends along the bottom edges of the trofler light frame inwardly and outwardly of the margins thereof and forms a slidable support for the louvered grill Z2 accommodating sliding of the grill into position along the inwardly extending portion of the plate 87-9 and under retaining strips 90, extending inwardly of spacer strips 91 extending along inner wall portions 93 of the troifer light housing. The space between the plate 89 and the retainer plate 90 forms a channel to slidably receive a reduced :end portion 95 of the louvered grill 22, to retain said louvered grill in position and accommodate insertion and removal of the louvered grill from the trotfer light housing 16, in an obvious manner.

In this form of the invention the air passes directly downwardly through the louvers of the louvered grill at a low velocity with no drafts.

it may be seen from the foregoing that the trolfer light housing of the invention provides a simplified form of air and light distributor unit, in which the air is maintained away from the region of the fluorescent tubes, and thereby avoids the impairment of the efllciency of the tubes caused by undue cooling of the tubes.

it may still further be seen that the flat deflector 41, the baffles or tabs 55, and the

oppositely facing vanes

54 and 63 inclined in opposite directions from the transverse center of the troifer light housing all contribute to convert part of the velocity head of the air entering the valve chamber 27 to static head and that this static head serves to deflect the air with its velocity head into the vanes which cause the remaining velocity heads to oppose each other in such a manner that their power is dissipated in turbulence and also to eliminate the endwise velocity components of the air in a straight down direction along the inner walls 44 of the troiier light housing, for direction through the light traps 65 or the louvered grill 22 straight downwardly at a low velocity with no drafts.

It should further be understood that for the air control attained by the present invention to be done by conventional means, either a plenum chamber would be required which would have to be of sufficient size to convert all of the entering velocity head into a static head, and uniform flow and direction would then be achieved by the use of a high friction drop static pressure baffle, resulting in a plenum chamber of such size as to be impractical; or an additional supply of static pressure from the duct system would be required which would have to be of sufficient magnitude to allow the air flow to be redirected and proportioned due to its friction drop through foraminous material. With the second method, the total pressure drop would be considerably higher and the sound generated by throttling this pressure would be objectionable in normal installations.

It should further be understood that the light and distributor unit of the invention avoids the accumulation of relatively large volumes of air at the ends of the unit which would be a cause of drafts where two units are connected together in endwise relation with respect to each other, and that by directing the air straight downwardly, in addition to eliminating drafts also avoids dirt smudges on the ceiling or the adjacent walls, which has heretofore been objectionable with ceiling ventilating units, as Well as providing amore uniform distribution of the air without detracting from the efficiency of lighting.

While I have herein shown and described one form in which my invention may be embodied, it should be understood that various variations and modifications of the invention may be attained without departing from the spirit and scope of the novel concepts of the invention as de fined by the claims appended hereto.

I claim as my invention:

1. In combination with a ceiling of a space to be illuminated and ventilated, a false ceiling spaced below said ceiling, an air and light distributor unit in said false coiling comprising a troifer light housing having upwardly and inwardly extending inner side wall portions forming a light trough above the level of said false ceiling, a reflector extending along said housing along the upper margins of said inner wall portions and having edge portions spaced inwardly from said inner wall portions to form downwardly opening air passageways, elongated fluorescent tubes extending along said housing beneath said reflector, a plenum chamber above said reflector, an air inlet leading into said plenum chamber from the top thereof at substantially the transverse center of said plenum chamber, a plurality of vertically extending vanes extending across said air passageways, the vanes on opposite sides of the transverse center of said plenum chamber being inclined in opposite directions towards the opposite ends of said plenum chamber and reducing the endwise velocity components of the air and directing the air for discharge downwardly through said air passageways in a generally straight downwardly direction, and parallel batfles extending vertically along the inner sides of the central vanes of said oppositely inclined vanes and deflecting the stream of air entering said plenum chamber and restricting the stream of air bouncing from the bottom of said plenum chamber, to prevent the conversion of the static head of air into a velocity head.

2. In combination with a ceiling of a space to be illuminated and ventilated, a false ceiling spaced below said ceiling, an air and light distributor unit in said false ceiling comprising a troffer light housing having upwardly extending inner wall portions forming a light trough above the level of said false ceiling, a reflector extending along said housing adjacent the upper margins of said wall portions and having edge portions spaced inwardly from said wall portions to form downwardly opening air passageways, elongated fluorescent tubes extending along said housing beneath said reflector, a plenum chamber extending along said housing above said reflector, an inlet into said plenum chamber from the top thereof adjacent the transverse center thereof, a flat battle extending along the top of said reflector and facing said air inlet, vertically extending vanes spaced along opposite sides of said plenum chamber and extending across said air passageways, said vanes on opposite sides of the transverse center of said plenum chamber being inclined in opposite directions and effecting the impingement of the air coming into the spaces between said vanes with the air going out from the spaces between said vanes, and thereby reducing the endwise velocity components of the air and effecting the discharge of the air downwardly through said air passageways enenally straight downward directions, and downwardly and outwardly inclined baflle-s eX- tending along opposite edges of said reflector in outwardly spaced relation with respect to said fluorescent tubes for deflecting the downwardly passing air from said fluorescent tubes.

3. An air and light distributor unit adapted for mounting in a false ceiling comprising a trotfer light housing having upwardly extending inner wall portions forming a light trough above the level of the false ceiling, a reflector extending along said housing along the upper margins of said wall portions and having edge portions spaced inwardly from said wall portions to form downwardly opening air passageways extending for substantially the length of said housing, elongated fluorescent tubes mounted in said housing beneath said reflector, a plenum chamber above said reflector and extend-ing along said housing for substantially the length thereof, an air duct leading into said plenum chamber from the top thereof intermediate the ends thereof, means converting part of the stream of air entering said plenum chamber into a static pressure head and reducing the endwise velocity components of air along said plenum chamber comprising a flat baffle plate facing said air inlet, vertically disposed deflector vanes extending across said air passageways, said vanes on opposite sides of the transverse center of said plenum chamber being inclined in the direction of flow of air towards the ends of said plenum chamber and effecting the impingement of the air coming into the spaces between said vanes with the outgoing air leaving the spaces between said vanes, to thereby reduce the endwise velocity components of air passing through said outlet passageways and direct the air through said outlet passageways in generally straight downward directions, and baffle means extending vertically along the inner sides of the central deflecting vanes at opposite sides of said flat bafiie and deflecting the stream of air entering said plenum chamber and restricting the static head of air bouncing from said flat baflie, to thereby prevent the conversion of the static head of air into a velocity head and assure the discharge of air downwardly along said side walls in a generally straight down direction.

' 4. In a ceiling no draft air and light distributor unit, a

troirer light housing having upwardly and inwardly extending wall portions forming a light trough and having vertical Wall portions forming an upward continuation of said inwardly extending wall portions and forming a plenum chamber, a reflector extending along the upper margins of said upwardly and inwardly extending inner wall portions, elongated fluorescent tubes in said light trough beneath said reflector, an air inlet into said plenum chamber from the top thereof and intermediate the ends thereof, opposite sides of said reflector being spaced in- Wardly of said inner wall portions, the spaces between opposite sides of said reflector and said inner wall portions forming air passageways leading from said plenum chamber along said inner wall portions, spaced substantial distances outwardly of said fluorescent tubes, and means for reducing the endwise components of air in said plenum chamber and discharging the air through said passageways in a straight down direction comprising a plurality of vertically extending inclined vanes extending across said air passageways and inclined oppositely from the transverse center of said plenum chamber in an upward direction toward the ends of said plenum chamber, a flat baifle extending along said reflector in alignment with the inlet, and positioned to cause the air entering said plenum chamber through the inlet to bounce and to thereby convert part of the air stream into a static head of air, and baffles extending vertically along the center of the vanes and deflecting the air stream and restricting the stream of air bouncing off of said flat baflies to pre- 53. vent a disproportionate quantity and velocity of flow of air from the region \of said passageways.

5. In an air-light trofler, an elongated trotler housing forming a lighting trough for fluorescent lighting tubes, means forming a correspondingly elongated plenum chamber at the upper portion of the troffer, an inlet for said plenum chamber comprising a relatively small opening intermediate the ends of said plenum chamber and receiving air cfrom a source at increased pressure and directing the air into the plenum chamber in the form of a stream having longitudinal endwise velocity components and downward transverse components, said plenum chamber having an elongated outlet formed on each side thereof extending for a substantial length of said troiier housing and disposed to provide an air passageway along the side of the lighting trough and communicating with the lower portion of the troffer, and inclined deflector vanes inclined in opposite directions on opposite longitudinal sides of said inlet toward the respective ends of the trotfer housing and being disposed in alignment with each said elongated outlet to intercept portions of the stream of air to reduce endwise velocity components and promoting uniform diffusion of air through said outlets.

6. In an air-light troifer as defined in claim 5, said deflector vanes having tabs extending from the outer sides thereof for securing said vanes to an adjoining Wall of said plenum chamber.

7. In an air-light troffer as defined in claim 5, said inlet having a collar comprising an adjustable valve, whereby the flow of supply or return air throughthe troffer may be adjustably controlled. a

8. In an air-light t-roiter as defined in claim 5, a flat baffle plate in said plenum chamber directly beneath said inlet for engagement by incoming air, thereby to convert part of the velocity head to static pressure.

References Cited in the file of this patent UNITED STATES PATENTS Kurth et al Nov. 15, 1960

Claims

1. IN COMBINATION WITH A CEILING OF A SPACE TO BE ILLUMINATED AND VENTILATED, A FALSE CEILING SPACED BELOW SAID CEILING, AN AIR AND LIGHT DISTRIBUTOR UNIT IN SAID FALSE CEILING COMPRISING A TROFFER LIGHT HOUSING HAVING UPWARDLY AND INWARDLY EXTENDING INNER SIDE WALL PORTIONS FORMING A LIGHT TROUGH ABOVE THE LEVEL OF SAID FALSE CEILING, A REFLECTOR EXTENDING ALONG SAID HOUSING ALONG THE UPPER MARGINS OF SAID INNER WALL PORTIONS AND HAVING EDGE PORTIONS SPACED INWARDLY FROM SAID INNER WALL PORTIONS TO FORM DOWNWARDLY OPENING AIR PASSAGEWAYS, ELONGATED FLUORESCENT TUBES EXTENDING ALONG SAID HOUSING BENEATH SAID REFLECTOR, A PLENUM CHAMBER ABOVE SAID REFLECTOR, AN AIR INLET LEADING INTO SAID PLENUM CHAMBER FROM THE TOP THEREOF AT SUBSTANTIALLY THE TRANSVERSE CENTER OF SAID PLENUM CHAMBER, A PLURALITY OF VERTICALLY EXTENDING VANES EXTENDING ACROSS SAID AIR PASSAGEWAYS, THE VANES ON OPPOSITE SIDES OF THE TRANSVERSE CENTER OF SAID PLENUM CHAMBER BEING INCLINED IN OPPOSITE DIRECTIONS TOWARDS THE OPPOSITE ENDS OF SAID PLENUM CHAMBER AND REDUCING THE ENDWISE VELOCITY COMPONENTS OF THE AIR AND DIRECTING THE AIR FOR DISCHARGE DOWNWARDLY THROUGH SAID AIR PASSAGEWAYS IN A GENERALLY STRAIGHT DOWNWARDLY DIRECTION, AND PARALLEL BAFFLES EXTENDING VERTICALLY ALONG THE INNER SIDES OF THE CENTRAL VANES OF SAID OPPOSITELY INCLINED VANES AND DEFLECTING THE STREAM OF AIR ENTERING SAID PLENUM CHAMBER AND RESTRICTING THE STREAM OF AIR BOUNCING FROM THE BOTTOM OF SAID PLENUM CHAMBER, TO PREVENT THE CONVERSION OF THE STATIC HEAD OF AIR INTO A VELOCITY HEAD.