Note: Descriptions are shown in the official language in which they were submitted.
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10 ~iIGIi EFF~CI~TCY CEILING FAN
REFERENCE TO RIELATED APPLICATION
This is a continuation-in-part of Application Serial
No.lO/194,699 filed July 11, 2002.
TECHNICAL FIBLD
This invention relates generally to ceiling fans, and
specifically to electrically powered ceiling fans and
their efficiencies.
HACKGROtIND OF THE ITTVIIf~N
Ceiling fans powered by electric motors have been used
for years in circulating air. They typically have a motor
z5 within a housing mounted to a downrod that rotates a set of
fan blades about the axis of the downrod. Their blades
have traditionally been flat and oriented at an incline or
pitch to present an angle of attack to the air mass in
which they rotate. This causes air to be driven
downwardly.
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When a fan blade that extends generally radially from
its axis of rotation is rotated, its tip end travels in a
far longer path of travel than does its root end for any
given time. Thus its tip end travels much faster'than its
root end. To balance the load of wind resistance along the
blades, and the air flow generated by their movement, fan
blades have been designed with an angle of attack that
diminishes towards the tip. This design feature is also
conventional in the~design of other rotating blades such as
marine propellers and aircraft propellers.
In 1997 a study was conducted at the Florida Solar
Energy Center on the efficiencies of several commercially
available ceiling fans. This testing was reported in U.S.
Patent No. 6,039,541. It was found by the patentees that
energy efficiency, i.e. air flow (CFM) per power
consumption (watts), was increased with a fan blade design
that had a twist in degrees at its root end that tapered
uniformly down to a smaller twist or angle of attack at its
tip end. For example, this applied to a 20-inch long blade
(with tapered chord) that had a 26.7° twist at its root and
a 6.9° twist at its tip.
Another long persistent problem associated with
ceiling fans has been that of air flow distribution. Most
ceiling fans have had their blades rotate in a horizontal
a5 plane, even though oriented at an angle of attack. This
has served to force air downwardly which ;does
advantageously provide for air flow in the space beneath
the fan. However air flow in the surrounding space has
been poor since it does not flow directly from the fan.
Where the fan blades have been on a dihedral this problem
has been reduced. However this has only been accomplished
at the expense of a substantial diminution of air flow
directly beneath the fan.
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S~~F THB ~~ION
It has now been found that a decrease in angle of
attack or twist that is of a uniform rate is not the most
efficient for ceiling:fans. The tip of a 2-foot blade or
propeller travels the circumferences of a circle or 2n(2~
in one revolution. Thus its midpoint one foot out travels
2rt(1) or half that distance in one revolution. This linear
relation is valid for an aircraft propeller as its orbital
path of travel is generally in a plane perpendicular to its
flight path. A ceiling fan however rotates in an orbital
path that is parallel to and located below an air flow
restriction, namely the ceiling itself. Thus its blades do
not uniformly attack an air mass as does an aircraft. This'
is because "replacement" air is more readily available at
the tips of ceiling fan blades than inboard of their tips.
Air adjacent their axis of rotation must travel from
ambience through the restricted space between the planes of
the ceiling and fan blades in reaching their root ends.
With this understanding in mind, ceiling fan
efficiency has now been found to be enhanced by forming'
their blades with an angle of attack that increases non
uniformly from their root ends to their tip ends. More
specifically, it has been found that the rate of change in
angle of attack or pitch should be greater nearer the blade
tip than nearer its root. This apparentlylserves to force
replacement air inwardly over the fan blades beneath the
ceiling restriction so that more air is more readily
available nearer the root ends of the blades. But whether
or not this theory is correct the result in improved
efficiency has been proven. By having the change in angle
of attack at a greater rate at their tip than at their
roots, fan efficiency has been found to be substantially
enhanced.
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BRIEF DESCRIPTION OF THE DRANINO
Fig. 1 is a side view of a ceiling fan that embodies
the invention in its preferred form.
Fig. 2 is a diagrammatical view of a fan blade of Fig.
1 shown hypothetically in a planar form for illustrative
purposes.
Fig. 3 is a diagrammatical view of the fan blade of
Fig. 2 illustrating degrees of blade twist at different
locations along the blade.
Fig. 4 is a diagram of air flow test parameters.
Fig. 5 is a side view of one of the blades of the fan
shown in Fig. 1.
Fig. 6 is a top view of one of the blades of the fan
shown in Fig. 1.
Fig. 7 is an end-on view of one of the blades of the
fan shown in Fig. 1.
Fig. 8 is a perspective view of a ceiling fan that
embodies the invention in another preferred embodiment.
Fig. 9 is a diagrammatical view of a fan blade of Fig.
8 shown hypothetically in a planar form for illustrative
purposes.
Fig. 10 is a series of diagrammatical view of the fan
blade of Fig. 8 illustrating degrees of blade twist at
different locations along the blade.
DETAILED DF~.SCRIPTION
The fan blade technology disclosed in U. S. Patent No.
30- 6,039,541 followed the assumption that all air flow into
the fan blades is from a direction that is perpendicular to
the plane of rotation for the blades. In addition, it
assumed that the airflow is of a constant velocity from the
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root end to the tip end of the blades as used in aircraft
propeller theory. Using this assumption the blades were
designed with a constant twist rate from root end to tip
end.
Twisting of the blade is done in an attempt to
optimize the relative angle of attack of the airf 1 ow
direction relative to the blade surface. This is done to
ensure that the blade is operating at its optimum angle of
attack from root end to tip end. This angle changes to
accommodate the fact that the tip of the blade moves faster
than the root end of the blade diameter. This increase in
velocity changes the direction of the relative wind over
the blade.
Again, this assumption has now been found to be
invalid for ceiling fans. Ceiling fans are air re
circulating devices that do not move through air as an
aircraft propeller does. Air does not move in the same
vector or even velocity over their blades from root end to
tip end.
Fig. 1 illustrates a ceiling fan that is of~
conventional construction with the exception of the shape
of its blades. The fan is seen to be mounted beneath a
ceiling by a downrod that extends from the ceiling to a
housing for an electric motor and switch box. Here the fan
is also seen to have a light kit at its bottom. Power is
provided to the motor that drives the blades by electrical
conductors that extend through the downrod to a source of
municipal power.
The fan blades are seen to be twisted rather than flat
and to have a graduated dihedral. Air flow to and from the
fan blades is shown by the multiple lines with arrowheads.
From these it can be visually appreciated how the fan
blades do not encounter an air mass as does an airplane
propeller. Rather, the restricted space above the blades
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alters the vectors of air flow into the fan contrary to
that of an aircraft.
Each fan blade is tapered with regardvto its width or
chord as shown diagrammatically in Fig. 2. Each tapers
from base or root end to tip end so as to be narrower at
its tip. In addition, each preferably has a dihedral as
shown in Fig. 1 although that is not necessary to embody
the advantages of the invention. The dihedral is provided
for a wider distribution of divergence of air in the space
beneath the fan.
With continued reference to Figs. 2 and 3 it is seen
that the blade is demarked to have three sections although
the blade is, of course, of unitary construction. Here the
24-inch long blade has three sections of equal lengths,
i.e.-8 inches each. All sections are twisted as is evident
in Fig. 1. However the rate of twist from.root to tip is
nonuniform. The twist or angle of attack deceases from
root end down to 10° at the tip end. Thia decrease;
however, which is also apparent in Fig. 1, is at three
different rates. In the first 8-inch section adjacent the
root end the change in twist rate is 0.4° per inch. For
the mid section it is 0.7° per inch. For the third section
adjacent the tip it is at a change rate of 1.0° per inch.
Of course there is a small transition between each section
of negligible significance. Thus in Fig. 3 there is an 8°
difference in angle of attack from one end of the outboard
section to its other (1° per inch x 8 inches). For the mid
section there is about 6°difference and for the inboard
section about 3°.
Figs. 5-7 show one of the blades 10 of the fan of Fig.
1 in greater detail. The blade is seen to have its root
end 11 mounted to the fan motor rotor hub 12 with its tip
end 13 located distally of the hub. The hub rotates about
the axis of the downrod from the ceiling as shown in Fig.
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1 which is substantially vertical. As most clearly noted
by the blade centerline l5, the blade has a 0° dihedral at
its root end 11 and a 10° dihedral dt at its tip 13. The
fan blade here is continuously arched or curved from end to
end so that its dihedral is continuously changing from end
to end. As shown by the air flow distribution broken lines
in Fig. 1 this serves to distribute air both directly under
the fan as well as in the ambient air space that surrounds
this space. Conversely, fans of the prior art have mostly
directed the air downwardly beneath the fan with air flow
in the surrounding space being indirect and weak. Though
those fans that have had their blades inclined at a fixed
dihedral throughout their length have solved this problem,.
such has been at the expense of diminished air flow
directly under the fan.
The blade dihedral may increase continuously from end
to end. However, it may be constant near its root end
and/or near its tip with its arched or curved portion being
along its remainder. Indeed, the most efficient design,
referred to as the gull design, has a 0° dihedral from its
root end to half way to its tip, and then a continuously
increasing dihedral~to its tip where it reaches a dihedral
of 10°. In the preferred embodiment shown the blade root
end has a 0° dihedral and its tip a 10° dihedral. However,
its root end dihedral may be less than or more than 0° and
its tip less than or more than 10°. Fan size, power,
height and application are all factors that may be
considered in selecting specific dihedrals.
The fan was tested at the Hunter Fan Company
laboratory which is certified by the environmental
Protection Agency, for Energy Star Compliance testing. The
fan was tested in accordance with the Energy Star testing
requirements except that air velocity sensors were also
installed over the top and close to the fan blades. This
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allowed for the measurement of air velocity adjacent to the
fan blade. During the testing it was determined that the
velocity of the air is different at various places on the
fan blades from root end to tip end. Test parameters are
shown in Fig. 4. The actual test results appear in Table
1.
T 8
Sensor Avg. Air Rotor ResultantResultantDeg/inch
Vel. V Vel FPS Vel Angle
FPM FPS
0 283 4.? 22.7 . ~ 23.2 11.7 ,
1 303 5.1 24.4 24.9 1 f.7 0.07
,
2 320 5.3 26.2 26.7 11.5 0.16
3 325 5.4 27.9 28.4 11.0 0.54
4 320 5.3 29.7 30.1 10.2 0.79
5 313 5.2 31.4 31.8 9.4 0.76
6 308 5.1 33.1 33.5 8.8 0.63
7 305 5.1 34.9 35.3 8.3 0.51
8 290 4.8 36.6 ~ 37.0 7.5 0.77
9 275 4.6 38.4 38.7 ~ 6.8 0.71
10 262 4.4 40.1 40.4 . 6.2 0.60
11 235 3.9 41.9 42.0 5.3 0.87
12 174 2.9 43.6 43.7 3.8 1.54
13 132 2.2 45.4 45.5 2.8 1.03
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Comparative test results appear in Table 2 where blade
1 was the new one just described with a 10° ffixed dihedral,
blade 2 was a Hampton Hay Gossomer Wind/Windward blade of
the design taught by Patent No. 6,039,541, and blade 3 was
a flat blade with a 15° fixed angle of attack. The
tabulated improvement was in energy efficiency as
previously defined.
TABLE 2
Blade Motor . With Improve- Improve-Without Improve-Improve-
Cylinder ment ment cylindermeat meet
Over Over Over Outside
4
Hampton Standard Hampton ft
Bay Bay
1 172x18A 12,878 21% 29% 37,327 24% 27%
M
2 188x15 10,639 NA 6% 30,034 NA' NA
3 172x18A 10,018 -6/ NA 28,000 -7% -7%
M
With reference next to Figs. 8-10, there is shown a
ceiling fan having blades incorporating the present
invention in another preferred form. Here, it is seen that
the blade is demarked to have six sections although the
blade is, of course, of unitary construction. Here the 24-
inch long blade has six sections of various lengths. The
first section adjacent the root is approximately 3 inches;
the second section is approximately 5 inches, the third
section is approximately 2 inches, the fourth section is
approximately 7 inches the fifth section is approximately
7 inches and the sixth section is approximately 1 inch.
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All sections except for the first section are twisted as is
evident in Figs. 8-10. However the rate of twist is
nonuniform. The twist or angle of attack deceases from
inboard portion of the third section to the tip end. This '
decrease, however, which is also apparent in.Fig. 1, is at
two different rates. In the third section the change in
twist rate is approximately 0.5° per inch. For the fourth,
fifth and sixth sections it is approximately 0.7° per inch.
Of course there is a small transition between the sections
of negligible significance. Thus, in Fig. 10 the third
section commences at a 24° angle of attack and ends at a
23° angle of attack, thus there is an 1° difference in
angle of attack from one end of the third section to its
other (1° per inch x 2 inches). The fourth section
commences at a 23° angle of attach and ends at a 18° angle
of attack, thus there is an 5° difference in angle of
attack from one end of the fourth section to its other (5°
per inch x 7 inches). The fifth section commences at a 18°
angle of attach and ends at a 14° angle of attack, thus
there is an 4° difference in angle of attack from one end
of the fifth section to its other (4° per inch x 6 inches).
It should be understood that the second embodiment is
similar in principle to the first embodiment shown in Fig.
1 except for the fact that the blade root commences
horizontally then dips down before commencing~the blade's
normal angle of attack. This difference stems from the
blade being mounted generally perpendicular to the motor
axis at the actual root rather than the blade initially
being set at an angled to the motor axis, i.e., the blade
initially having an angle of attack. However, it should be
understood that in the second embodiment the "root" may
simply be thought of as being positioned outboard from the
actual "root" or actual inboard end of the blade. Thus, as
used herein the term "root" may also be considered the
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position along the fan adjacent the fan axis wherein the
angle of attack to produce the desired air flow commences,
which in this embodiment is the inboard portion of the
third section.
It thus is seen that a ceiling fan now is provided
of substantially higher energy efficiency than those of the
prior art and with enhanced flow distribution. The fan may
of course be used in other locations such as a table top.
Although it has been shown and described in its preferred
form, it should be understood that other modifications,
additions or deletions may be made thereto without
departure from the spirit and scope of the invention as set
forth in the following claims.
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