US3349998A

US3349998A - Ventilating apparatus

Info

Publication number: US3349998A
Application number: US548708A
Authority: US
Inventors: Leo M Stirling
Original assignee: Individual
Current assignee: Individual
Priority date: 1966-05-09
Filing date: 1966-05-09
Publication date: 1967-10-31
Anticipated expiration: 1984-10-31
Also published as: GB1131298A

Description

Oct. 31, 1967 v M. STIRLING 3,349,998

VENTILATING APPARATUS Filed May '9, 1966 INVENTOR Leo M. STIRLING A TTORNE Y 2 Sheets-Sheet 1 Oct. 31, 1967 1.. M. STIRLING 3,349,998

VENTILATI NG APPARATUS Filed May 9, 1966 2 Sheets-Sheet 2 INVENTOR Leo M. STIRLING A TTORNE Y United States Patent 3,349,998 I VENTILATING APPARATUS Leo M. Stirling, 7431 Kingsley Road, Apt. 405, Cote St. Luc, Montreal, Quebec, Canada Filed May 9, 1966, Ser. No. 548,708 23 Claims. ('Cl. 230-414) The present invention relates to ventilators, more particularly ventilators of the type having a single rotor rotatable by means of a motor and consisting of a centrifugal impeller component adapted to draw air upwardly and expel it radially outwardly and an axial flow impeller component mounted below the centrifugal component and radially outwardly of the centrifugal component inlet, for blowing air downwardly around the centrifugal component inlet. The invention is more particularly concerned with housing means for enclosing and supporting the motor and impeller for such ventilators.

The ventilators to which the present invention more particularly relates are particularly suited for mounting upon the roofs of buildings, a single impeller unit being rotated in one direction so as simultaneously to draw up and expel stale air and to take in and blow down fresh air. An early version of such a ventilator is described in US. Patent 2,790,596 (Apr. 30, 1957), and Canadian Patent 545,020, to the same inventor. This type of ventilator employed a single rotor having two concentric axial flow fan components, the components being arranged to direct air streams in opposite directions. An improved version of this unit, employing a combination centrifugal component and axial flow component, as described above, is set forth in US. Patent 3,199,773, also to the present inventor.

The use of a centrifugal impeller component allows the unit to operate at a higher static pressure. The fan unit may be further removed from the enclosure to be ventilated without loss of efliciency and noise level is reduced.

Due to the shape of the compound impeller and conventional housing, there is a likelihood that, at least under certain atmospheric wind conditions, part of the stale air stream will mix with the incoming fresh air stream. Thus, in the ventilator described in US. Patent 3,199,773, stale air is blown directly outwardly from the centrifugal impeller component and is only separated from the fresh air inlet by a dished horizontal flange. There is thus a likelihood of part of the stale air reentering at the fresh air inlet.

It is, therefore, one of the objects of the present invention to provide a housing for such a ventilator in which the likelihood of inadvertent recirculation of stale air is substantially eliminated.

It is another object to provide such a ventilator and housing therefor, which has a phasing and aerodynamic external shape. 7

In accordance with one aspect of the invention, there is provided housing means for a ventilator of the type having a single rotor rotatable by means of a motor and consisting of a centrifugal component adapted to draw air upwardly and expel it radially outwardly and an axial flow component mounted below the centrifugal component and radially outwardly of the centrifugal component inlet, for blowing air downwardly around the centrifugal component inlet, the said housing means comprising:

A generally cylindrical outer wall,

A generally annular peripheral outlet for stale air adjacent an upper end of said outer wall,

A generally annular peripheral inlet for fresh air adjacent a lower end of said outer wall,

Said inlet and outlet being spaced by a substantial part of the total height of the housing,

A sloping annular deflector abutting said outer wall intermediate said inlet and said outlet and extending radially inwardly and downwardly to the junction of said impeller components so as to divide the incoming air from the outgoing air and to define the outer boundary of an upward sloping path for said outgoing air,

Means for supporting the impeller motor and shaft,

Enclosure means surrounding said impeller motor and shaft with said impeller below the lower part of such enclosure,

Said enclosure extending inwardly from the upper end of said stale air outlet and being upwardly spaced from said deflector so as to define the inner boundary of said outgoing air path,

A pair of concentric cylindrical ducts arranged to guide stale air centrally upwardly to said centrifugal component inlet and to guide fresh air from beneath said defiector annularly downwardly between the ducts from said axial flow component, and

Means for retaining the parts of said housing together in an integral unit.

The invention also includes the combination of such a housing and a single rotor and motor as defined above. Modern ventilating and air conditioning systems have given rise to the need in certain circumstances, of recirculating warm exhaust air back into the building in order to conserve heat. In a preferred form, the present invention provides a particularly advantageous means of solving this recirculation problem in ventilators of the type described.

In accordance with a preferred feature of the invention, the housing means further comprise damper means in the said deflector, adapted upon opening to close at least partly the path of outgoing air from the centrifugal compressor and simultaneously to allow outgoing air from the centrifugal component to recirculate back through the fresh air outlet.

The damper mean preferably include a plurality of dampers arranged as portions of the said sloping floor, which portions are adapted to pivot away from the surface of the deflector about axes which are tangential to a circle concentric with the axis of the housing, to an upright fully open position. 7 I

Having thus generally described the invention, a preferred embodiment thereof is hereafter more particularly described and illustrated with reference to the accompanying drawings, in which: 7

FIGURE 1 is a vertical cross-section through a ventilator constructed in accordance with the present invention, the section being taken along the line 1-1 of FIGURE 3;

FIGURE 2 is a horizontal section along the line 2"2 of FIGURE 1;

FIGURE 3 is a horizontal section along the line 3-3 of FIGURE 1;

FIGURE 4 is a perspective view of the ventilator of FIGURE 1; and

FIGURE is a cross-section along the line 5-5 of FIGURE 2, showing a portion of the unit illustrating the damper control means.

The ventilating apparatus shown in the drawings comprises a housing 10 surrounding and supporting a single rotor or impeller 11 and an operating motor 12 therefor.

The housing 10' includes a first casing portion or inner wall 13 of generally upright cylindrical cross-section. Substantially closing the wall 13 at its lower end is a supporting floor or platform 14 upon which the motor 12 and the bearings 15 for the impeller are mounted. The mountings take the form of a pair of L brackets 16 to which is welded a transverse web 17. The motor 12 is bolted to the 3 central web 17 as are the thrust bearings for the impeller shaft 18.

The impeller 11 is slung beneath the platform 14 and consists of a centrifugal impeller component 11a and an axial flow impeller component 11b. The centrifugal component 11a consists of an inner hub 19 fastened to the shaft 18 by screws 20 and having an annular flange to which is bolted or riveted an upper base plate 21. The shaft 18 is provided with a pulley 18a connected to the motor by a belt 18b. Centrifugal impeller blades 22 are arranged between the upper base plate 21 and an annular lower base plate 23, the blades 22 being welded or riveted to the

base plates

21 and 23. Rigid with the lower base plate 23, for example, welded thereto, is a lower outer hub 24 which tapers inwardly from the outer periphery of base plate 23 and which terminates in a substantially cylindrical collar portion 25, which forms the inlet to the centrifugal impeller component.

The axial flow impeller component 11b consists of a plurality of axial flow impeller blades 26 joined at their roots by riveting or welding to the collar portion 25 for rotation therewith. The blades 26 are so arranged that in the normal direction of rotation of the centrifugal component 11a, they cause a downward draft of air in an annular path surrounding the inlet of the centrifugal impeller component as indicated by the arrows in FIG- URE 1. The axial flow blades 26 extend radially beyond the periphery of the centrifugal impeller 11a.

Surrounding the impeller 11 between the centrifugal and the axial flow components is an annular, frusto-conical deflector dividing floor 27. The inner rim of the deflector 27 is aligned with and substantially adjacent the upper termination of the tapering inlet hub 24 and extends upwardly and outwardly therefrom to an outer rim which is spaced radially outwardly from the periphery of the platform 14. The deflector 27 serves to divide the paths of the outgoing air from the centrifugal component and the ingoing air to the axial flow component. The inner rim of the deflector 27 terminates in an annular collar portion 28 of L-shaped cross-section, the horizontal flange of the collar extending inwardly and downwardly of the junction between the hub portion 24 and the annular base plate 23, so as substantially to prevent any mixing of the air streams.

The outer rim of the deflector 27 is provided with an upwardly directed flange 30 which is bolted to a second casing portion or outer wall 31 at a level intermediate the height of the wall 31.

The outer wall 31 extends upwardly to a level substantially above that of the upper impeller base plate 21 and extends downwardly to at least the approximate level of the axial flow fan blades 26. It can be seen that the upper and lower extremities of the outer wall 31 provide the minimum separation of the incoming and outgoing air. Thus, the incoming and outgoing air are separated by a distance which is a major proportion of the total height of the ventilating apparatus.

The motor supporting platform 14 is supported upon four symmetrically spaced columns 32 which are preferably steel tubes and which are welded to an annular inverted L-sectioned base 33. As shown, the platform 14 is bolted down upon bolts which form an extension of the upper ends of the columns 32. The columns 32 pass through the deflector 27 and collars 34 on the columns 32 provide support for the deflector 27 and the outer wall 31 which is attached thereto.

Extending upwardly and outwardly from the top of the inner wall 13 is a tapering, frusto-conical casing portion 35. The casing portion 35 may be integral with the inner wall 13 as shown or may be attached thereto, for example, by riveting or welding. The upper end of the portion 35 terminates in a cylindrical flange 36, to which is bolted the lower rim of a cap 37 which forms the top of the housing 10. The edge of the cap 37 is substantially flush with the outer wall 31 and upwardly spaced therefrom to define the outlet for the stale air leaving the centrifugal impeller component. The outlet is preferably covered as shown with a cylindrical screen 38 of expanded metal. Preferably, the rim of the cap 37 is outwardly turned slightly to prevent ingress of rain, and the upper edge of the outer wall 31 is inwardly turned for a similar purpose.

It will be apparent, therefore, that the platform 14, the inner wall 13, the casing portion 35, and the cap 37, provide an enclosure for the motor and bearings which is spaced inwardly and upwardly of the outer wall 31 and dividing floor 27 so as to form in this space an annular passage for the outgoing stale air, which passages slopes substantially continuously upwardly, so as to present as little resistance as possible to the outgoing air stream.

The inlet passage for the stale air leading to the centrifugal impeller inlet is provided by an inner cylindrical duct portion 39 which is of substantially the same diameter as the collar portion 25 to which it leads. The upper end of the duct portion 39 to slightly inwardly tapered to fit within the lower boundary of the collar portion 25, with which the duct portion 39 is substantially aligned. The inner duct portion 39 is mounted by means of vertical webs 40 to an outer duct portion 41, the upper end of which surrounds the axial flow blades 26 and terminates at a level just slightly above the blades 26. The outer duct,

41 provides between itself and the inner concentric duct 39 an annular flow passage for the incoming fresh air. The lower end of the duct 41 fits flush within the inner rim of the base 33 to which it is preferably welded.

Extending horizontally outwardly from the upper end of the outer duct portion 41 is a narrow annular floor 42. Downwardly tapering struts 43 are provided in circumferentially spaced positions around the outer duct 41 and assist in supporting the floor 42 which may in addition be welded to the columns 32 at its outer rim.

Ventilating pipes 44 are provided which extend across the space between the inner wall 13 and the outer wall 31 to allow cooling air to enter the motor enclosure for the purpose of cooling the motor and bearings. A space 45 is provided between the floor 14 and the impeller hub 19 to allow the cooling air to pass through to the centrifugal impeller component 11a by which it is expelled with the stale air.

An important additional feature is the provision of dampers 50 in the dividing floor or deflector 27. Four such dampers are provided in the embodiment shown, but more or fewer dampers may be provided as desired. The dampers form a part of the deflector 27 and are flush with apertures of substantially the same dimension which are cut in the deflector 27 to take the dampers. The dampers are rectangular in plan view as shown in FIGURE 2 and FIGURE 3 and are pivoted at 60 about axis 51 (shown in dotted lines in FIGURE 3) which are tangent to a circle concentric with the axis of the impeller and of a diameter between the inner and outer bounds of the narrow floor 42, that is, approximately the same diameter as that of the outer duct 41. The dampers may be pivoted to an upright position shown in dotted lines in FIGURE 1 in which they extend between the floor 42 and the platform 14, so as at least partly to shut off the escape of stale air as it leaves the centrifugal impeller component 11a and to divert the impeded air downwardly to the input side of the axial flow impellers 26.

Vertical L-section baflles are preferably provided at the sides of the dampers between the deflector 27 and the platform 14 and extending generally radially to restrict the exhaust air outlet to the width of the dampers 50 so as to prevent escape of air at the sides of the dampers 50 and when the latter are closed to recirculate substantially all the exhaust air through the fresh air outlet.

Abutments 61 on the radially outer edges of the dampers 50 abut the edge of the dividing floor 27 when the dampers are in the closed position. The edge of the dividing floor 42 is provided with an upwardly directed flange 62 to form an abutment for the edge of the dampers in the upright position. Stoppers 63 are provided to abut the inner edge of the floor 27 when the dampers are in the closed position.

It will be apparent that unless the baflles 100 are fitted, the dampers in the upright position do not entirely shut off the escape of stale air in that spaces are provided at the corners of the generally square enclosure defined by the upright dampers. However, without the baflles 100, at least 50% of the stale air may be recirculated through the fresh air outlet.

Means are preferably provided for operating the dampers thermostatically in accordance with the temperature of the building being ventilated. As shown, two damper motors 52 of conventional type (Type M828 sold by Minneapolis-Honeywell) are provided at diagonally spaced locations, so that each motor can operate two of the four dampers 50. Thus, a slotted upright flange 53 is provided on each damper and a forked arm 54 is arranged with a spigot 55 at the end of each limb adapted to slide within the slot of the flange 53. The forked arm 54 is centrally pivoted on a stationary arm 56 which extends. from the motor 52. An extension 57 of the forked lever 54 is pivotally attached to a movable arm 58 which is reciprocated by the motor 52 through a slot in the platform 14 so that the dampers 50 can be moved from a closed position in which they form a continuation of the dividing floor 27 and the upright position, as shown more particularly in FIG- URE 5.

The damper motors 52 are operated thermostatically by means well known in the art.

A short collar 47 is preferably provided extending upwardly from the deflector 27 below and within the inner wall 13 so as to prevent any rain entering the stale air outlet passage from running down into the impeller. Small apertures 48 are provided on the radially outer side of the collar 47 to cause accumulated rain to fall out through the fresh air inlet. The components of the housing are preferably made of aluminized pressed steel. The cap and outer wall 31 may conveniently be made of aluminum.

It will be apparent that many modifications may be made to the embodiments shown within the spirit and scope of the present invention. For example, the number of dampers is not critical, and the dampers are only needed in particular units to meet architects specifications. The shape of the compound impeller need not be exactly as shown, but may correspond in shape and construction with that shown in US. Patent 3,199,773, if desired. Furthermore, the motor need not be off-set and connected to the impeller shaft 18 by means of pulleys and belts as shown, but may be arranged to drive the impeller directly as also shown in US. Patent 3,199,773. While the dividing floor 27 and the tapering casing portion 35 have been shown frusto-conical, they may alternatively be bowlshaped, it being only necessary that a smooth upwardly sloping passage is provided for the outgoing stale air.

It will be apparent from a study of FIGURE 4 that the outward appearance of the ventilation apparatus presents a smoothly contoured exterior which is a substantial departure from the earlier apparatus of US. Patent 3,199,773. This smooth outer contour both presents a pleasant aesthetic appearance and also presents greatly less resistance to wind than the earlier apparatus. At the same time, the air inlet and air outlet are very greatly removed one from the other so that there is little or no risk of stale air from the outside of the unit re-entering at the inlet. Numerous further modifications may be made within the scope of the following claims.

I claim:

1. Housing means for a ventilator of the type having a single rotor rotatable by means of a motor and consisting of a centrifugal component adapted to draw air upwardly and expel it radially outwardly and an axial flow component mounted below the centrifugal component and radially outwardly of the centrifugal component inlet, for blowing air downwardly around the centrifugal component inlet, the said housing means comprising:

a generally cylindrical outer wall,

said inlet and outlet being spaced by .a substantial part of the total height of the housing,

means for supporting the impeller motor and shaft,

a pair of concentric cylindrical ducts arranged to guide stale air centrally upwardly to said centrifugal component inlet and to guide fresh air from beneath said deflector .annularly downwardly between the ducts from said axial flow component, and

means for retaining the parts of said housing together in an integral unit.

2. Housing means as claimed in claim 1 further comprising damper means in said deflector adapted upon opening to close at least partly the path of outgoing air from said centrifugal component and simultaneously to allow outgoing air from said centrifugal component to recirculate through the fresh air outlet.

3. Housing means as claimed in claim 2 wherein said damper means include a plurality of dampers arranged as portions of said deflector which portions are adapted to pivot about axes which are tangential to a circle concentric with the axis of the housing to an upright fully open position.

4. Housing means as claimed in claim 3 further including baflles extending vertically and generally radially at the sides of said dampers between said deflector and said enclosure means for preventing escape of exhaust air at the sides of the dampers when the latter are closed.

5. Housing means as claimed in claim 4 wherein said damper axes are each tangential to a circle of approximately the diameter of the outer of said concentric ducts. 6. Housing means as defined in claim 1 for a ventilator of the type having a single rotor rotatable by means of a motor and consisting of a centrifugal component adapted to draw air upwardly and expel it radially outwardly and an axial flow component mounted below the cen trifugal component and radially outwardly of the centrifugal component inlet, for blowing air downwardly around the centrifugal component inlet, the housing means comprising:

a substantially circular shaft and motor supporting platform adapted to support the motor above and the impeller beneath,

a peripheral wall upstanding from said platform,

a tapering wall extending upwardly and outwardly from the top of said peripheral wall,

a cap covering the tapering wall,

an outer wall of substantially circular cross-section spaced below the upper extremity of said tapering wall and of substantially the same diameter so as to leave therebetween a cylindrical outlet,

said outer wall extending at least to the general level of the axial flow impeller component,

inner and outer concentric cylindrical ducts extending downwardly from said impeller, said inner duct having substantially the same diameter as the centrifugal component inlet and being arranged to lead stale air upwardly thereto and said outer duct having substantially the same diameter as the outer extremity of said axial flow blade, and being arranged to lead fresh air entering beneath said outer wall downwardly through the annular space between said inner and outer ducts,

atapering annular floor sloping downwardly from an outer periphery abutting said outer wall intermediate its height to an inner periphery adjacent said impeller adjacent the junction of the two impeller components, said floor separating the path of incoming fresh air from the path of outgoing stale air and defining with said inner wall, outer wall and tapering wall, an upward and radially outward path for said stale air, and

means for retaining said walls, cap and ducts in a unitary construction.

7. Housing means as claimed in claim 6 further comprising damper means in said tapering fioor adapted upon opening to close at least partly the path of outgoing air from said centrifugal component and simultaneously to allow outgoing air from said centrifugal component to recirculate through the fresh air outlet.

8. Housing means as claimed in claim 7 wherein said damper means include a plurality of dampers arranged as portions of said tapering floor which portions are adapted to pivot about axes which are tangential to a circle concentric with the axis of the housing to an upright fully open position.

9. Housing means as claimed in claim 7 wherein there are baffles extending vertically and generally radially at the sides of said dampers between said tapering floor and said enclosure means for preventing escape of exhaust air at the sides of the dampers when the latter are closed.

10. Housing means as claimed in claim 9 wherein said damper axes are each substantially tangent to a circle of approximately the diameter of the outer of said concentric ducts.

11. Ventilating apparatus comprising a single rotor rotatable by means of a motor and consisting of a centrifugal component adapted to draw air upwardly and expel it radially outwardly and an axial flow component mounted below the centrifugal component and radially outwardly of the centrifugal component inlet, for blowing air downwardly around the centrifugal component inlet,

housing means, including a generally cylindrical outer wall,

means for supporting the impeller motor and shaft,

a pair of concentric cylindrical ducts arranged to guide stale air centrally upwardly to said centrifugal component inlet and to guide fresh air from beneath said sloping floor annularly downwardly between the ducts from said axial flow component, and

means for retaining the parts of said housing together in an integral unit.

12. Ventilating apparatus as claimed in claim 11 further comprising a plurality of dampers arranged as portions of said deflector which portions are adapted to pivot about axes which are tengential to a circle concentric with the axis of the housing to an upright fully open position, and baffles extending vertically and generally radially at the sides of said dampers between said deflector and said enclosure means for preventing escape of exhaust air at the sides of the dampers when the latter are closed.

13. Ventilating apparatus as claimed in claim 6 wherein said deflector is substantially frusto-conical.

14. Ventilating apparatus as defined in claim 9 and comprising:

a first casing portion of generally upright cylindrical cross-section,

a supporting platform substantially closing said first portion near the lower end thereof,

a shaft and bearing means for said shaft mounted upon said platform with said shaft protruding centrally through said platform,

a centrifugal impeller mounted upon said shaft below said platform with its inlet downmost,

said impeller having a plurality of circumferentially spaced blades mounted at their upper ends to a flat upper base plate and interconnected and covered at their lower ends by a downwardly tapering inlet said inlet casing terminating upwardly adjacent the radial extremities of the impeller blades in a frustoconical portion and terminating downwardly in a generally upright cylindrical collar portion,

a plurality of axial flow fan blades mounted at their roots to said collar portion extending radially beyond the periphery of said centrifugal impeller, and arranged to blow air downwardly,

a floor portion of annular configuration having an inner rim surrounding and aligned with said upper termination of said inlet hub and extending upwardly and outwardly therefrom to an outer rim which is spaced radially outwardly from the periphery of said platform,

a second casing portion of generally upright cylindrical cross-section connected at an intermediate height to and surrounding said outer rim of said floor portion,

said second casing portion extending upwardly to a level substantially above said upper impeller base plate and extending downwardly to at least the approximate level of said axial flow blades,

a tapered annular casing portion having a lower inner rim connected to the upper end of said first casing p0rt1on and extending upwardly and outwardly to an upper outer rim of substantially the diameter of said second casing portion and spaced upwardly of the upper extremity of said second casing portion,

a domed cap portion enclosing the upper rim of said tapered annular casing portion and defining a motor chamber above said first supporting floor,

a motor in said motor chamber operatively connected to said shaft,

an annular peripheral stale air outlet defined between the upper extremities of said second casing portion and said tapered annular casing portion,

a stale air inlet duct portion of upright cylindrical configuration and diameter substantially the same as that of said impeller collar portion and having an upper rim generally aligned therewith so as to guide air upwardly to said centrifugal impeller inlet,

a fresh air outlet duct portion concentrically spaced outside said stale air inlet duct portion and of lesser diameter than said second casing portion, having an upper mm at a level a little above said axial fiow blades and defining between its upper extremity and the lower extremity of said second casing portion a fresh air inlet,

said fresh air outlet duct portion being arranged to conduct fresh air from said fresh air inlet downwardly within an annular passage between said concentric duct portions, and

means for connecting said casing portions, platform,

floor portion, duct portions and cap together in a rigid housing unit.

15. Ventilating apparatus as claimed in claim 14 further comprising a plurality of circumferentially arranged dampers each arranged as part of said tapering fioor portion and adapted to pivot about an axis tangent to a circle concentric with said impeller axis to an upright open position in which it extends across the stale air outlet path between said platform and the upper extremity of said fresh air outlet duct portion thereby impeding the outlet of stale air and allowing at least part of the latter to be recirculated through the said axial flow impeller blades.

16. Ventilating apparatus as claimed in claim 15 wherein said damper pivot axes are centrally situated in each damper and are tangent to a circle of substantially the same diameter as said fresh air outlet duct.

17. Ventilating apparatus as claimed in claim 16 further including bafiles extending vertically and generally radially at the sides of said dampers between said deflector and said enclosure means for preventing escape of exhaust air at the sides of the dampers when the latter are closed.

18. Ventilating apparatus as claimed in claim 17 wherein the dampers are controlled by one or more actuators supported upon said platform and having linkages extending through apertures in said platform.

19. Ventilating apparatus as claimed in claim 11 wherein said fresh air outlet duct is secured to a base plate and said platform is mounted directly to said base plate by means of a plurality of upright columns extending through said tapering floor.

20. Ventilating apparatus as claimed in claim 11 wherein vent pipes are provided extending from the outside of the housing into said motor enclosure for cooling purposes, additional apertures being provided in said platform adjacent the impeller bearing for exhausting the cooling 7 all.

References Cited UNITED STATES PATENTS 1/ 1957 Solzman 98 43 8/1965 Wasson et a1. 230117 LAURENCE V. EFNER, Primary Examiner.

Claims

1. HOUSING MEANS FOR A VENTILATOR OF THE TYPE HAVING A SINGLE ROTOR ROTATABLY BY MEANS OF A MOTOR AND CONSISTING OF A CENTRIFUGAL COMPONENT ADAPTED TO DRAW AIR UPWARDLY AND EXPEL IT RADIALLY OUTWARDLY AND AN AXIAL FLOW COMPONENT MOUNTED BELOW THE CENTRIFUGAL COMPONENT AND RADIALLY OUTWARDLY OF THE CENTRIFUGAL COMPONENT INLET, FOR BLOWING AIR DOWNWARDLY AROUND THE CENTRIFUGAL COMPONENT INLET, THE SAID HOUSING MEANS COMPRISING: A GENERALLY CYLINDRICAL OUTER WALL, A GENERALLY ANNULAR PERIPHERAL OUTLET FOR STALE AIR ADJACENT AN UPPER END OF SAID OUTER WALL, A GENERALLY ANNULAR PERIPHERAL INLET FOR FRESH AIR ADJACENT A LOWER END OF SAID OUTER WALL, SAID INLET AND OUTLET BEING SPACED BY A SUBSTANTIAL PART OF THE TOTAL HEIGHT OF THE HOUSING, A SLOPING ANNULAR DEFLECTOR ABUTTING SAID OUTER WALL INTERMEDIATE SAID INLET AND SAID OUTLET AND EXTENDING RADIALLY INWARDLY AND DOWNWARDLY TO THE JUNCTION OF SAID IMPELLER COMPONENTS SO AS TO PROVIDE THE INCOMING AIR FROM THE OUTGOING AIR AND TO DEFINE THE OUTER BOUNDARY OF AN UPWARD SLOPING PATH FOR SAID OUTGOING AIR, MEANS FOR SUPPORTING THE IMPELLER MOTOR AND SHAFT, ENCLOSURE MEANS SURROUNDING SAID IMPELLER MOTOR AND SHAFT WITH SAID IMPELLER BELOW THE LOWER PART OF SUCH ENCLOSURE, SAID ENCLOSURE EXTENDING INWARDLY FROM THE UPPER END OF SAID STALE AIR OUTLET AND BEING UPWARDLY SPACED FROM SAID DEFLECTOR SO AS TO DEFINE THE INNER BOUNDARY OF SAID OUTGONG AIR PATH, A PAIR OF CONCENTRIC CYLINDRIAL DUCTS ARRANGED TO GUIDE STALE AIR CENTRALLY UPWARDLY TO SAID CENTRIFUGAL COMPONENT INLET AND TO GUIDE FRESH AIR FROM BENEATH SAID DEFLECTOR ANNULARLY DOWNWARDLY BETWEEN THE DUCTS FROM SAID AXIAL FLOW COMPONENT, AND MEANS FOR RETAINING THE PARTS OF SAID HOUSING TOGETHER IN AN INTEGRAL UNIT.