US 3101662 A
Description (OCR text may contain errors)
Aug. 27, 1963 1 1 ALLDRITT 3,101,662
RooF VENTILATOR Filed Sept. 5, 1959 l 3 Sheets-Shea?I 1 LAWRENCE L. ALLDRITT A TTORNE Y United States Patent() 3,101,662 ROF VENTELATR Lawrence L. Alldritt, 59 NW.-14th St., Miami 32, Fla.
Filed Sept. 3, 1959, Ser. No. 837,906 S Claims. (Ci. 935-43) vair moves parallel to the yaxis of rotation of the fan;
while in the latter air, moves radially Ioutwardly of the axis of rotation of the fan.
Each of these -two types has certain advantages fand disadvantages. Axial flow fans, such as the usual propeller-type fans, have the advantage that they are relatively quiet in operation, but have the disadvantage that they cannot operate effectively against 'a substantial static head of pressure. Centrifugal fan-s have the advantage that they can operate against a substantial head of pressure, and in fact operate'with greatest efficiency against pressure; but ,they have the disadvantage of noisy operation.
Both axial ow and centrifugal fans have been known for many years. More recentlya type of roof ventilator has come into use, which is characterized by a casing open at its top and bottom and adapted to be mounted on a roof over an opening therein, the casing being protected `at its top by a rounded, downwardly concave hood or dome spaced above `and laterally outwardly from the upper edge of the casing on all sides thereof, so that .the hood and casing have the appearance of the cap` and ystem of ia mushroom. Fan means associated with the hood or casing :cause the air to iiow up through the casing and downwardly outwardly 4on all sides of the casing between the hood and the casing.
These later hooded or domed roof ventilators have been both of the axial ilow and yof the centrifugal type.
The axial dow type has been characterized for example by the use of a propeller fan wheel Within the casing, as in U.S. Patent No. 2,571,513, October 16, 195i. 'The centrifugal type of domed roof ventilator is represented for example by a power driven rotating dome provided with vanes on the interior thereof, as in U.S. Patent No. 2,824,502, February 25, 1958.
The adaptation of both axial .and centrifugal fans for use in domed roof ventilators has imposed 'addi-tional disadvantages in connection with the operation of each type of fan. For example, the axial flow fan, when provided with a hood, not only remains incapable of drawing against an appreciable static head, las before, but isl further rendered unsatisfactory by the fact that :air is delivered axially against the dome and must be diverted so as almost to double back upon itself in its direction of movement, with consequent loss of efficiency. Indeed, the eiciency of an 4axial flow domed roof venti lator decreases the closer the dome is moved toward the fan wheel, so that the fan mushs out, that is, suffers a sharp decrease in `air delivery accompanied by a sharp rise in noise level. ln the case of centrifugal domed roof ventilators, yalthough the noise is reduced from that of a squirrel cage rotor, there is `an `added safety yproblem raised by the exposed, rapidly rotating dome, so that this type of ventilator may not be suitable for installation on schools and the like.
Accordingly, it is an object of the present invention to .provide domed roof ventilators having the advantages ICC 2 both `of 'axial flow types and of centrifugal types, without the disadvantages of either type.
it is another object of the present invention to providedorned roof ventilators having a number of desirable characteristics of centrifugal fans but operating .at `greatly reduced noise levels.
Still another object of the present inventioniis the provision of domed roof ventilators having the advantages of centrifugal fans but having a stationary dome.
A further object yof the present invention is the pro- Vision of domed roof ventilators having theadvantages of axial llow type fans but yadapted to work against substantial heads of pressure. v 1
A still further object of the present invention is the provision of domed roof ventilators having the advantages of axial ow fans but at the Sametime operating at increased efficiency by virtue of 'the presence'of the dome. l
Finally, it is an object of the present invention to 'provide a roof ventilator that is relatively inexpensive to manufacture, easy to install, opera-te and repaineiiicient in operation, and rugged and durable in use.
Broadly stated, the present invention comprises ythe :discovery that a domed roof ventilator having la propellertype fan wheel can be made to take on all the `advantages but none of the disadvantages of la centrifugal type fan by shaping, proportioning land disposing the blades relative to the axis -of rotation, the upper edge ofthe `casing Iand the dome ias -will be set forth hereinafter in "greater detail.
Other objects, features and advantages ofthe present invention will become apparent .from a consideration of ,the following description, taken in connection with the accompanying drawings, in lwhich:
FIGURE 1 is 4a side cross-sectional view of a roof ventilator according to the present invention;
FIGURE 2 is la plan View `of la roof ventilator according to the present invention but with the dome'v removed;
FlGURE 3 is an enlarged elevational view lof =a fan wheel according to the present invention, viewed perpendicular -to the axis lof rotation of the fan Wheel, the fan wheel being in that rotated position in which that vertical plane is viewed edgewise which includes theaxis of rotation :of the fan wheel 'and bisects themounting bracket of the blade shown on the near side;
FIGURE 4 is ta view similar fto FIGURE 3 but showing the fan Wheel in a further rotated position and with one blade shown in section along the line `4-4- of FIGURE 3;
FIGURE 5 is a' plan 'View of the Afan wheel of the present invention; y t
FIGURE `6 is ian oblique viewyof tthefan wheel of the present invention, with one blade viewed broadside, that is, perpendicular to fthe plane of the blade at lthe section line 4 4 of FIGURE 3; and
FIGURE 7 is a `cross-sectional View o-f aa propeller fan blade according to the present invention, taken ton the line 7 7 of FIGURE 6.- v v `Referring now to the drawings in greater detail, there is shown a roof ventilator indicated general-ly tatl -1 and comprising la round casing 3 mounted with its axis vertical on a roof S over yan opening 7 therein. Casing 3 is provided with the usual hashing at its lower end whereby it is adapted to the rectangular cont-our of opening 7. Casing 3 may be in the form of 1a truncated conical sheet, as shown, or in' the form of `a cylindrical sheet, or otherwise rounded; and the term round is intended to comprehend :all of these shapes. Casing 3, terminates at its upper end in an upper edge 9 which is circular.
An electric motor 11 is mounted coaxially and concentrically in casing 3 @by means of a bracket 13 having attachment to the side walls of casing 3 forming a cradle Patented Aug. 27, 1963 for the motor. Motor 11 is of course provided with electrical wires (not shown) for lappropriate connection to a source of electric power. Motor l11 has a rotatable drive shaft 15 extending upwardly therefrom coaxially concentrically with casing 3 and motor 11. It will be understood that instead of mounting motor I1.1 coaxially, it can be mounted to one side of the easing and belt-connected to :a fan shaft `coaxial with the casing.
Mou-nted concentrically and coaxially above casing 3, and spaced therefrom, is a rounded, downwardly `concave hood 17 supported on support brackets 19 which in turn are mounted on the outer upper surfaces of casing 3 and terminate in upper ends which extend through holes in hood 17 and :are provided with removable fasteners 21 detachably to secure hood 17 in place on brackets 19. In this way, hood 17 is mounted ixedly yon casing 3 and is spaced above land laterally outwardly from the upper edge 9 of `casing 3 on all sides thereof.
A rotatable fan wheel 23 of the propeller type has a central hub 25 by which it is mounted coaxially for rotation on the upper end of drive shaft 15 lof motor 11. Hub 25 has a plurality :of brackets 27 extending generally radially outward therefrom and spaced peripherally thereabout, each bracket being pierced with a plurality lof holes for the reception vof rivets 29 by which a propeller fan blade 31 is secured xedly on the upper side of each bracket 2.7.
Blades 31thus rotate about the common axis 33 of casing 3, drive shaft 15, hood 17, fan wheel 23 and hub 25, and are inclined forwardly downwardly, in their direction of movement while exhausting lair, at la relatively jsteep -average pitch.
A major distinguishing feature of the disposition of blades 31, however, is that in addition to their pitch rela- .tive to their direction of movement, they `are -given a second pitch radially of their axis of rotation. Specifically, in addition to being inclined forwardly downwardly in 4their direction of rotation in the usual manner of fan blades, they are inclined radially outwardly downwardly with regard to their axis of rotation. Brackets 2'7 are roughly bisymmetr-ic; and this second pitch will be more particularly appreciated when it is recognized that the vertical plane' which includes the `axis of rotation of the -fan wheel and which substantially bisects brackets 27, intersects the upper surface of blade 31 in an imaginary line 35 which forms `a negative acute angle with the horizontal land is'inclined downwardly outwardly from line 33. Thus, in FIGURE 3, line 35 coincides with section line 4--4, so that FIGURE 3 is a view edgewise of the plane which intersects the upper surface of blade 31 in line 35. Stated another way, the upper surface of blade 31 `adjacent line 35 can never be viewed edgewise in a yhorizontal plane but only obliquely.
Line 35, although imaginary, is `a very important reference point for further description of the blade. This l-ine may bje considered to divide blades 31 arbitrarily into an upper portion 37 and -a lower portion 39. Another important feature of the present invention resides in the tfact that upper portion 37 is upwardly concave "and lower portion 39 is downwardly concave. This concavityyhowevenris a two dimensional curve rather than the usual three dimensional `curve of fan blades. Specifically, the upper surface of upper portion 37 is comprised of an infinite number of straight lines parallel to each other and parallel -to Iimaginary line 35. The same is true of the upper surface of lower portion 39. Moreover, 'in the illustrated embodiment, imaginary line 35 marks in effect the ex point of the cross-sectional contour of blade 31, that is, the line of `camber reversal between upper and lower portions 37 and 39. This is to say that the upper surface of blade 31 is essentially uniplanar `at least for small distances on either side of i-maginary line 35. BelowV line 35, therefore, the upper sur- 'face of blade 31 is downwardly concave `and above line 35 it is upwardly concave; but at line 35 the curves meet and reverse. Although line 35 iand the line of camber reversal are shown in the illustrated embodiment tas being one and the same straight line, it will of course be understood that small variations from this relationship can be tolerated without departing `from the |ambit of the -invention. Thus, the two lines need not be precisely coincident nor precisely parallel nor precisely straight in order to achieve the essential operative characteristics of the present invention.
It should also be noted that, yas shown in FIGURE 7, blade 35 has an edgewise profile which `at no point is of greater width than the thickness ofthe material of blade 31. Also, it should be noted that although the pitch of blade 31 in its direction of movement is steep at all places, it is at a minimum iadjacent imaginary line 35 and at -a maximum on both sides of line 35. l
Indeed, the pitch progressively increases from line 35 :to the portions of the blade on either side thereof which are farthest from line 3S. Thus, portion 41, which is the portion of blade 31 farthest from line 35, is the blade portion of greatest pitch vabove line 35; while portion 43, which is that part of lower portion 39` farthest from line 35, is the blade portion of maximum pitch on the other side of line 35. It should also be noted that portion 41 is spaced radially outward from `axis 33 la substantially greater distance than is portion 43. Also, portions 41 and 43 are spaced apart from each other a distance consider- `ably greater than the length of line 35. Also, it should be noted that the 'greatest arc subtended by blade 31 is more than 360 divided by the number of blades 31, so that an upper portion of each blade overlies a lower portion of each succeeding blade. Furthermore, it Ishould be noted that the area of the upper surface of portion 37 is considerably greater than the area of the upper surface of portion 39.
Finally, it `should be noted that the outer edge of blade 31 is a fairly smooth curve, as indicated at 45. But continuing upwardly rabout this curve, it will be noted that the smooth continuity of the curve is broken at portion 41 'and the fan blade is of substantially less area than if the smooth curve 45 lwere continued beyon-d portion 41. ln effect, the blade is `cut away las at 47, the edge of 47 being convexly rounded `but still recessed relative to ya continu-ation of curve 45.
The shape and orientation of blades 31 have been discussed; and further important features of the invention reside in the orientation and disposition of the blades relative to the casing and hood. Thus, another important features of the invention is that line 35 is above upper edge 9 of the casing. Although line 35 extends radially downwardly outward, it never crosses'or extends within that circular line which marks upper edge 9. Also, it should be note-d that blades 31 extend a substantial distance radially outwardly beyond upper edge 9, the point of farthest outward extension of blades 31 being located on upper portion 37 thereof. Moreover, a portion only of lower portion 39 of blade 31 extends down into casing' 3 below upper edge 9. At the other or lupper end of blade 31, it should be noted that portion 41 is that part of the blade which most closely approaches the underside of hood 17. From that point of closest approach, the outer edge of blade 31 and the underside of hood 17 progressively diverge from each other.
It will thus be observed that although the lower portions of blades 31 serve to some extent as an axial iiow fan, the major portion of the blades is given over to operation as a centrifugal fan. Thus, the. major portion of the blades coacts' with hood 17 in much the same manner `as a squirrel cage rotor coacts with its surrounding scroll. From a visual inspection of the device, it is diicult to recognize that the upper portions of the blades are in effect serving as a centrifugal fan in cooperation with the hood; but it will `be realiz-'ed that this is true when it is seen how the above-described features are directed toward securing this operation. Specifically, portion 43 and the lower end of lower portion 39 in effect dig down into the casing to serve eiiiciently to induce axial ow; but from then on, the flow of the air becomes increasingly centrifugal in character by the interaction f the specially formed and oriented blade and the hood. The positioning of imaginary line 35 above upper edge 9 assures that the upper portion of the blade will coact with the hood as a scroll rather than with the casing as in an axial flow device. The negative radial outward pitch of the blades, evidenced by the negative inclination of line 35, is `an extremely important feature, assurling as it does that a radially outward impulse be imparted to the air in the manner of a centrifugal fan. The upward concavity of upper portion 37 of the blades along an infinite number of straight lines parallel to line 35 imparts a radially downwardv and outward component of thrust to the air which further turns the air outward and downward in cooperation with the curvature of the hood.
The diiferent radial distances of portions 43 and 4l, the former being closer to the axis of rotation than the latter, assures that as the air passes from the former to the latter, it is given a further radial outward impulse; and the portion cut away as at 47 assures that the upper tip comprising portion 41 will be radially outwardly positioned for this purpose. The overhang of portion 37 radially outward beyond upper edge 9 also coacts with the differential radial spacing of portions di and 43 further to achieve the same result. Also, the progressively increasing pitch upward from line 35 to portion 41, in combination with the radially outward negative pitch, assures that the outward impulse on the air increases as it moves up along blade 31, so that a minimum of air is thrown against hood 17. Indeed, air is travelling substantially parallel to the under surface of the hood when it reaches that height. 'Ihe great length of blade 31 between portions 41 and 43, relative to the length of line 35, also assures that blade 3l will reach suiiiciently far down into casing 3 to perform its axial function, but at the same time will reach up suiiiciently close to hood 17 to cause hood 17 to coact therewith in the manner of a scroll. from closest portion 41 downwardly outwardly about curve 45 corresponds functionally to the divergence between a squirrel cage rotor and its scroll from the cutoi point about the rotor to the discharge.
Precise dimensions cannot be given for the present invention, as these will vary depending on a number of factors such as casing size, hood diameter, fan wheel diameter and speed, and static pressure head. By way of example, however, it might be noted that for a well-supplied airspace without ductwork, a ventilator with a 30- inch casing upper diameter, a 351/2-inch fan wheel diameter, a 54-inch inside diameter of the dome at the bottom thereof, an angle for line 35 of -l2 from the horizontal, a speed of 1180 rpm., and a least distance between fan blades and dome of 11/2 inch, are typical of the invention. It is not true that the very least possible spacing between portions 41 and the hood is necessarily the best spacing. The best spacing must be determined with due regard to the other variables listed above. In general, however, the faster the fan speed the lower and closer to the blades should be the hood.
The centrifugal nature of the operation of ventilators according to the present invention is demonstrable by a simple experiment in which the hood is removed and the eiciency of lthe unit is computed with the unit acting solely as an axial flow fan. The hood is then held several feet Iabove the unit, so that the hood furnishes an obstruction to axial iiow but does not yet coact with the blades to induce centrifugal ow. The efliciency is again computed and it is noted that this eiiciency Iis lower than the first efliciency. Finally, 4the hood is lowered into operative position, with portions dll closely adjacent the under side of the hood and the llower edge of the hood at least as low as upper edge 9 of casing 3. A sharp rise Indeed, the divergence of the hood and blade in eicien'cy is noted, to a level above the eiciency with the hood removed entirely. In the rst step, air was moving axially only. In the second step, t-he fan was loaded with an impediment in theair stream'. But in the third step, the fan blades and the hood were coactin-g to induce centrifugal iiow at high efficiency. Hence, in contrast to previous fixed dome roof ventilators, in which the hood bodily deilects the air and reduces the efficiency of the d-evice, the present invention is characterized in that the hood and the blades coact together to induce centrifugal ow at greater efficiency than if the hood were removed. Another characteristic yof the present invention which demonstrates its centrifugal nat-ure is the absence of overloading when the air supply is shut olf. Shutting off the air supply of an axial iiow fan overloadsthe motor and soon burns it out; but shutting off the rair supply of the present invention actually unloads the mot-or, as is characteristic of most centrifugal fans. Furthermore, adding a dome to an axial flow fan raises the noise level; but adding the dome vto the present lfan actually reduces the noise level in the same manner as adding a scroll to a squirrel cage fan rotor.
From a consideration of the foregoing, it will be obvious that all the initially reci-ted objects ofthe present invention have been achieved.
It is lto be understood that the appended claims are to be accorded a range of equivalents commensurate in scope with the advance made over the prior art.
What is claimed is:
l. In a power driven roof ventilator including a round casing open at its top and bottom and adapted to be mounted with its axis vertical on'a roof over an opening therein and terminating upwardly in an upper edge, a rounded, downwardly concavely curved hood fixedly mounted coaxially above the casing and extending laterally outward beyond said upper edge of the casing on all sides of the casing, a fan wheel mounted for rotation beneath the hood coaxially of the casing and including a plurality of outwardly extending propeller fan blades, and power means for rota-ting the fan wheel about said axis; the improvement comprising the fan blades having an upper portion having an upwardly concave upper surface made up of an infinite number of parallel straight lines one of which passes through the axis of rotation of the fan wheel and is inclined downwardly outwardly at an acute angle to the :horizontal :and is disposed above said upper edge, at least a portion of the blade extending below said upper edge.
2. Apparatus as claimed in claim l, said upper portion extending a substantial distance laterally outwardly beyond said upper edge.
3. Apparatus as claimed in claim l, the hood and the blades approaching each other most closely yat the portion of said upper portion farthest from said one line.
4. In a power driven roof ventilator including a round casing open at its top and bottom adapted to be mounted with its axis vertical on a roof over an opening therein and terminating upwardly in an upper edge, a rounded, downwardly concavely curved hood iixedly mounted coaxially above the casing and extending laterally outward beyond said upper edge of the casing on all sides of the casing, a -fan wheel mounted for rotation beneath the bood coaxially of the casing and including a central hub having a plurality of fan blade mounting brackets extending outwardly therefrom and a propeller fan blade mounted on and extending outwardly from each said bracket, and power means for rot-ating the fan wheel about said axis; the improvement comprising the fan blades being reverse cambered and having a downwardly concave lower portion and an upwardly concave upper portion and being inclined downwardly outwardly such that a plane which includes said axis and which substantially bisects a said bracket intersects the upper surface of the associated blade in -a downwardly outwardly inclined line that is 7 disposed -above said upper edge, at least a lportion o-f the blade extending below said upper edge. 5. Apparatus as fel-aimed in claim 4, the portionof the blade closest to the hood being the portion yof the blade of greatest pitch.
6. In a power driven roof ventilator including =a round easing open at its ltop and bottom and adapted to be mounted with its axis vertical on a roof over an opening therein and terminating upwardly in -an upper edge, a Irounded, downwardly concavely curved hood ixedly mounted coaxially above the casing and extending laterally outward beyond said upper edge of the casing on all sides of the easing, a fan wheel mounted for rotation beneath the hood coaxially of the casing and including a plurality of outwardly extending propeller fan blades, and power means for rot-ating the fan wheel about said axis; the improvement comprising the .fan blades being reverse cambered and havin-g ya downwardly concave lower portion and 'an upwardly `concave upper portion and having upper surfaces at Ileast partly made up of an infinite number of straight lines, one of said `lines passing through the yaxis of rotation and being inclined downwardly at an acute angle, said line being disposed above said upper edge, at
least a portion of the blade extending below said upper edge. v
7. Apparatus as claimed in claim 6, the blade on the upper side of said line extending a substantial distance laterally outwardly beyond said upper edge.
8. Apparatus as claimed in claim 6, said straight lines above said one `line being parallel to each other and to said `one line.
References Cited in the le of this patent UNITED STATES PATENTS 578,360 Phil-lips Mar. 9, 1897 1,508,086 Crawford Sept. 9, 1924 1,953,4'17 Lindberg Apr. 3, 1934 2,082,955 Hagen June 8, 1937 2,516,184 Christie July 25, 1950 2,571,513 Ammerman Oct. 16, 1951 2,581,873 Morrison Jan. 8, 1952 FOREIGN PATENTS 1,047,583 V'France Dec. 15, 1953 819,012 Great Bri-tain Aug. 26, 1959