Ventilator scroll arrangement

A rooftop ventilator includes a fan arranged for rotation about a generally vertical axis. The fan is on a rooftop curb through which air is drawn by the fan from the building interior. A housing extends over the fan and the fan terminates above and spaced from a curb to define a discharge opening for air drawn through the curb. A scroll arrangement is located above the curb and arranged around the periphery of the fan to receive air discharged by the fan and direct it toward the discharge opening. The scroll arrangement is made up of a plurality of scroll elements equally spaced around the periphery of the fan. Each of the scroll elements includes a first elongated element having one end generally adjacent the fan periphery and extending away from the fan periphery; a second elongated element, connected to the first elements to provide a generally continuous extension from the fan periphery. Each of the first and second scroll elements are linear. The scroll arrangement also provides the support for the basic structural parts of the ventilator.

BACKGROUND OF THE INVENTION 
This invention relates to air diffusers wherein an air impeller, such as a 
fan, discharges air through a housing, airflow control apparatus, or the 
like associated with the fan. The discharge can be either into a confined 
space such as a room or into the atmosphere. 
This invention will be discussed in connection with a building rooftop 
ventilator which uses a centrifugal fan to draw air from a building 
interior and discharges that air into the ambient atmosphere. It is to be 
appreciated, that the invention is not necessarily limited to that type of 
application. 
Generally, such rooftop units are mounted on a curb which is attached to 
the roof and communicates with the building air delivery system. 
Specifically, the unit exhausts air from the building to the atmosphere. 
The centrifugal fan used as the air impeller and its associated drive 
elements are covered by a shroud, or other type of housing, for protection 
against the weather. An air discharge opening is provided in the 
protective housing. Exhaust air from the building travels through the 
interior of protective housing and out the discharge opening to the 
atmosphere. 
In the past, such building air exhaust systems have been, for the most 
part, what may be referred to as a bulk transfer of air. That is, they 
have merely provided a forced withdrawal of air from the building interior 
and a more or less random discharge through the protective structure with 
little, if any, thought being given to aerodynamic properties. The 
problems and/or shortcomings of such prior systems have been relatively 
ineffective and inefficient transfer of air from the building interior to 
the atmosphere, and noise generation. Ineffective and inefficient air 
transfer impacts in a negative manner on the building air exhaust system. 
This, in turn, can impact negatively on the overall building air delivery 
system. It can also create a noise problem, of particular concern where 
the building is in a heavily populated urban area; although even in an 
isolated building noise can be a problem with respect to the building 
occupants and any operations carried on in the building. 
It has been noted in such prior systems that part of the kinetic energy 
imparted to the exhaust air by the air impeller, and which could best be 
utilized in enhancing exhaust airflow, has been lost due to the random 
uncontrolled airflow within the rooftop unit. 
SUMMARY OF THE INVENTION 
Among the general objects of this invention, is to provide an efficient air 
discharge system. A more specific object in that regard is to provide an 
air discharge system wherein for a given size fan motor an increased 
volume of air can be discharged or, for a given volume of air, a smaller 
horsepower rated motor can be used. 
Also among the general objects of this invention, is to provide an air 
exhaust system which reduces the amount of generated noise. 
Of course, these Performance and noise comparisons are in reference to 
prior air exhaust systems. 
Another object of this invention is to simplify the exhaust system 
structure while achieving the above-mentioned objectives. 
A further general object of this invention is to make effective use of the 
kinetic energy imparted to the exhaust air by the exhaust fan. 
In ventilators of the type to which this invention relates an air impeller, 
e.g., a centrifugal fan, draws air from the building interior as part of 
the overall air delivery system. That air is discharged from the periphery 
of the centrifugal fan, the fan imparting sufficient velocity to the air 
for it to pass through the interior of the ventilator housing and out to 
the atmosphere. For the achievement of the above objects, this invention, 
in a broad sense, contemplates controlling the flow of air from the 
centrifugal fan to discharge to the atmosphere. 
More specifically, air leaving the tips of the centrifugal fan blades has, 
with reference to the axis of rotation of the fan, both a radial and a 
tangential component. From the standpoint of effective and efficient air 
discharge it has been observed that, whereas the tangential component 
provides a desirable airflow influence, the radial component can be a 
negative component. The radial component tends to cause turbulence at the 
air exit point from the fan blades and increases back pressure, 
particularly where the fan is enclosed in a shroud or other protective 
housing. The increased back pressure retards airflow and ultimate 
discharge to the atmosphere and places a larger load on the fan motor. The 
turbulence and back pressure also contribute to increased noise 
generation. 
This invention proposes to confine the air leaving the fan and to influence 
that flow and the expansion of that air in a manner which reduces the 
radial components and produces a corresponding increase in the tangential 
component. This reduces turbulence at the blade tips and within the 
shroud, and lowers the pressure around the periphery of the fan, and 
thereby results in more effective air discharge with increased efficiency 
in fan motor operation and reduced noise. That is, a smaller motor can be 
used to move the same volume of air or a given size motor will move a 
larger volume of air. 
More specifically and in the preferred embodiment, a scroll assembly is 
provided between the centrifugal fan and the discharge opening, or 
openings, defined in and at the shroud. The scroll is made up of a 
plurality of elements which extend generally from the fan periphery toward 
the shroud discharge opening. Those elements all have the same general 
configuration. Each element has a first generally linear segment which is 
located adjacent the fan blade tips where it receives air being discharged 
from the fan. The first linear segment projects, relative to the 
circumference and a radius of the fan, at least at a tangent or at an 
angle beyond the tangent. Each also includes a second generally linear 
segment which extends from a location remote from the fan periphery toward 
the first linear segment and at an angle to the first linear segment. The 
first and second linear segments are joined to form a continuous member 
extending from adjacent the fan blade periphery toward the discharge 
opening in the shroud. Preferably, the two segments are formed in one 
piece and meet at an obtuse angle, approximately 140.degree.. The 
plurality of elements of the scroll are equally spaced around the 
periphery of the fan capturing and directing all of the air being 
discharged from the fan. The second linear segment of one element forms a 
discharge opening with the first linear segment of the next adjacent 
element and through which air passes to the shroud discharge opening. 
With this scroll configuration, as mentioned generally above, the otherwise 
radial component of the air leaving the fan is redirected in a more 
tangential direction thereby imparting an increased tangential influence 
to the air being discharged. By utilizing linear segments in the scroll 
elements, larger discharge openings are defined. Both the increased 
tangential influence and the large discharge openings reduce turbulence 
with a resultant decrease in back pressure to give the above-mentioned 
desirable results. In essence, the scroll, configured as described above, 
recaptures some of the kinetic energy which would otherwise have been lost 
in the undesirable radial component and converts it into usable kinetic 
energy in a tangential sense. 
This invention also proposes, in its preferred form, to utilize the scroll 
to simplify the exhaust system by having the scroll provide the basic 
support for the stationary elements of the system. 
Other objects and advantages will be pointed out in, or be apparent from, 
the specification and claims, as will obvious modifications of the 
embodiment shown in the drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The rooftop ventilator embodying this invention, and referring to FIG. 1, 
consists of the general components, a rooftop curb 10, an outer housing 
12, a drive mechanism 14 connected to a centrifugal fan 16 and scroll 
assembly 18. The curb 10 is connected to the rooftop of a building (not 
shown) and is attached thereto in a conventional manner (also not shown). 
The outer housing 12 is made up of two primary sections, a motor and 
mechanical component cover 20 and a shroud 22. The shroud 22 extends over 
a portion of the axial length of the scroll 18 and terminates in spaced 
relation from the scroll, and the curb, and thereby defines an generally 
annular discharge opening 24 extending around the periphery of the shroud 
assembly 18. 
In operation, a centrifugal fan draws air from the building interior up 
through the curb 10. That air is then discharged radially from the 
centrifugal fan through the shroud 18 and is expelled to the atmosphere 
through the discharge opening 24. The path of airflow is illustrated by 
the arrows in FIG. 1. 
Specific reference will now be made to FIG. 3 for a more detailed 
structural description of the unit components and their arrangement. 
The curb 10 includes a conventional venturi section 26 through which air is 
drawn. The scroll assembly 18 rests on the upper surface of curb 10 and is 
made up of four identically configured elements 28, 30, 32, and 34. 
The centrifugal fan 16 fits within the scroll assembly and over the curb 
venturi 26. 
A mounting plate 36 fits over the top of the centrifugal fan 16 and is 
attached to the individual elements 28-34 of the scroll assembly in a 
manner to be discussed more specifically hereinafter. A stubshaft 38 of 
the centrifugal fan extends through a central opening 40 in the mounting 
plate and is attached to a power shaft 42 which is part of a motor drive 
and mount assembly 44 attached to the upper side of mounting plate 36. 
More specifically, the motor mount of assembly 44 consists of two angle 
brackets 46 and 48, which are attached by screws (not shown) extending 
into openings 50 in mounting plate 36. Angle brackets 46 and 48 are in 
turn attached to a motor mount 52 which supports a drive motor 54 shown 
only in FIG. 1. Drive shaft 42 attaches to stubshaft 38 and through a 
transmission arrangement 56 illustrated schematically in FIG. 1, the motor 
54 (shown only in FIG. 1) that, when energized, rotates centrifugal fan 
16. 
The shroud 22 has a generally horizontal shoulder portion 58 which 
terminates in a circular opening 60. A skirt 62 extends downwardly from 
the shoulder portion 58 and is the portion of the shroud which overlaps a 
part of the vertical extension of the scroll assembly 18. The motor 44 and 
drive and mount assembly 54 project upwardly through opening 60 and are 
enclosed in the upper housing portion 20. 
With this arrangement, all of the components are operationally and 
structurally interconnected to provide a compact operating unit. The drive 
elements and the fan are protected from the weather by the housing parts 
20 and shroud 22. 
To prevent entry of birds and large insects, screening 64, 66, 68, and 70 
is provided between adjacent scroll elements 28, 30, 32, and 34, 
respectively. The screening elements, for convenience, have only been 
illustrated in FIG. 1. 
Turning now to FIG. 2, the configuration of the elements making up the 
scroll will be described as will be the operation and advantages resulting 
therefrom. 
Each of the scroll elements 28, 30, 32, and 34 have an identical 
configuration and, therefore, only one, 28, will be described in detail. 
Similar structural elements will be identified in a relative manner for 
the other scroll elements, that is, designations a, b, and c will be used 
for scroll elements 30, 32, and 34, respectively. 
Scroll element 28 includes a first linear segment 74. The linear segment 74 
extends from a location adjacent the periphery 72 of the centrifugal fan. 
A second linear segment 76 projects from an area remote from the periphery 
of the fan 72 back toward the first segment 74. That remote area is in the 
vicinity of the discharge opening 24 so that the scroll elements terminate 
adjacent that discharge opening. Segments 74 and 76 are suitably joined. 
In the preferred embodiment, the two segments are a one-piece structure 
meeting at a sharp angle 78. 
Linear segment 74 is arranged relative to the circumference and a radius of 
the centrifugal fan 16 such that it projects at least at a tangent. More 
specifically, as illustrated, segment 74 is arranged as a tangent to the 
periphery of the centrifugal fan 16. It will be appreciated that the 
periphery of the centrifugal fan 16 also defines the path of rotation of 
the fan blade tips. The tangential relationship can be varied but it 
should not be less than a tangent and should either be at an angle which 
establishes a tangent or beyond. This provides for efficient and effective 
receipt, by the scroll element 28, of the air being discharged from the 
centrifugal fan and transmission of that air outwardly from the 
centrifugal fan toward the shroud discharge openings 24. 
The scroll elements are equally spaced around the periphery of the 
centrifugal fan. This provides four equally spaced discharge openings 80, 
82, 84, and 86. It will be noted that the discharge openings are provided 
between the segments 76, 76a, 76b, and 76c, and the segments 74a, 74b, 
74c, and 74, respectively. By having linear extensions at the terminal 
ends of both of the segments 74 through 74c and 76 through 76c, the size 
of the discharge openings formed are large and therefore effectively 
accommodate the airflow through and out of the scroll assembly. 
As was noted generally above, as the air is expelled from the centrifugal 
fan 16, it has both a radial and a tangential component as it leaves the 
fan blade tips and relative to the fan circumference on the periphery 72. 
Linear segments 74, 74a, 74b, and 74c interrupt the flow of the radial 
component of that air discharge and smoothly and effectively redirect it 
in a tangential manner. By doing so, the overall tangential component of 
the air being discharged from the centrifugal fan is increased, thereby 
more effectively moving more air away from the impeller and through the 
unit. The relatively larger discharge openings 80, 82, 84 and 86 
accommodate this volume of air, the combination of the linear segments 74, 
74a, 74b, 74c and the large discharge opening defined in the shroud 
thereby cooperating in this effective air discharge. More specifically, 
the radial and tangential components of the air being discharged from the 
centrifugal fan represents kinetic energy; but the kinetic energy of the 
radial component, unless controlled, will be lost in turbulence and 
resultant back pressure. With the arrangement of this invention, that 
otherwise lost kinetic energy is recaptured and redirected in an effective 
manner to contribute to an enhanced discharge through the rooftop unit. 
For operational purposes, and for structural purposes as will be defined 
hereinafter, linear segment 76 and 74 meet at an angle 78. Preferably, 
that angle is approximately 140.degree.. The joining of the linear 
segments 74 and 76 at an angle has two advantages, one as described above 
in the enhanced airflow properties. The other is that it simplifies the 
fabricating procedures. The scroll elements 28, 30, 32, and 34 can then be 
made as a one-piece structure, preferably sheet metal. The sheet metal can 
be effectively and simply formed in a break press to provide the angle 78. 
This is a relatively simple fabricating procedure. 
By utilizing the above linear constructions, it is also possible to provide 
the scroll elements 28, 30, 32 and 34 with flanges 90, 92, 94, 96, 98, 
100, 102, 104. Similar flanges can be provided on the lower ends of the 
scroll elements, but are not shown. These flanges can be produced in a 
simple bending operation and then provide a means of attachment of the 
scroll element to the curb and also to mounting plate 36. The flanges are 
connected to that mounting plate through use of a plurality of machine 
screws 106, only one of which is illustrated in FIG. 1a. The scroll 
assembly then provides the basic structural support, or the basic 
structural connection, for all of the elements of the rooftop unit to the 
curb, achieving a simplification in the overall structure of the 
ventilator unit. 
A rooftop unit with the scroll arrangement of this invention improves the 
overall air exhaust performance of the rooftop unit. That is, for a given 
volume of air a smaller fan motor can be utilized, or for a given size 
motor a larger volume of air will be exhausted. The chart of FIG. 4 
illustrates this improved performance. FIG. 4 charts the performance 
"Capacity" vs. static pressure inches of water for two different motors, 
one, with the scroll and one without the scroll. The unit without the 
scroll utilized a fan motor which measured a maximum brake horsepower of 
0.43 whereas the unit with the scroll utilized a fan motor which measured 
a maximum brake horsepower of 0.39. As can be seen from the chart, with 
the scroll and the smaller motor, the overall performance of the unit was 
shifted up and to the right thereby illustrating an overall improvement in 
the unit operation. The performance charted in FIG. 4 is typical of 
various fan or impeller sizes. 
Although this invention has been illustrated and described in connection 
with a particular embodiment thereof, it will be apparent to those skilled 
in the art that various changes and modifications may be made therein 
without departing from the spirit of the invention or from the scope of 
the appended claims.