U.S. patent application number 10/837934 was filed with the patent office on 2005-01-06 for high efficiency ceiling fan.
Invention is credited to Bird, Gregory M., Srass, Hadi, Stauffer, Michael J..
Application Number | 20050002791 10/837934 |
Document ID | / |
Family ID | 36567569 |
Filed Date | 2005-01-06 |
United States Patent
Application |
20050002791 |
Kind Code |
A1 |
Bird, Gregory M. ; et
al. |
January 6, 2005 |
High efficiency ceiling fan
Abstract
Ceiling fan energy consumption efficiency is enhanced with fan
blades that have an angle attack that decreases from root end to
tip end at higher rates of decrease nearer their tip ends than at
their root ends.
Inventors: |
Bird, Gregory M.;
(Colliersville, TN) ; Stauffer, Michael J.;
(Memphis, TN) ; Srass, Hadi; (Arlington,
TN) |
Correspondence
Address: |
Dorian B. Kennedy
Baker Donelson Bearman Caldwell & Berkowitz
Suite 900
Five Concourse Parkway
Atlanta
GA
30328
US
|
Family ID: |
36567569 |
Appl. No.: |
10/837934 |
Filed: |
May 3, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10837934 |
May 3, 2004 |
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10194699 |
Jul 11, 2002 |
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6733241 |
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Current U.S.
Class: |
416/210R |
Current CPC
Class: |
F04D 25/088 20130101;
Y02T 70/50 20130101; F04D 29/384 20130101 |
Class at
Publication: |
416/210.00R |
International
Class: |
B63H 001/20 |
Claims
1. A high efficiency ceiling fan having a plurality of fan blades
mounted for rotation about a fan axis of blade rotation and with
the blades having a greater angle of attack at a location adjacent
said fan axis than distally said fan axis with the rate of change
in angle of attack therebetween being non-uniform, the blade angle
of attack decreasing continuously from adjacent said fan axis to
distally said fan axis, and therein the blade angle of attack
decreases at a plurality of incrementally different rates from
adjacent said fan axis to distal said fan axis.
2. The high efficiency ceiling fan of claim 1 wherein the blade
angle of attack decreases in two different incrementally fixed
rates.
3. The high efficiency ceiling fan of claim 2 wherein the blade
angle of attack decreases approximately 0.5 degrees per inch
adjacent said fan axis to approximately 0.7 degrees per inch
distally said fan axis.
4. A high efficiency ceiling fan having a plurality of fan blades
mounted for rotation about a fan axis of blade rotation and with
the blades being twisted at a plurality of fixed rates of decrease
as they extend from a position adjacent the fan axis at a twist
rate that decreases non-uniformly from a position adjacent the
motor to the blade tip end.
5. The high efficiency ceiling fan of claim 4 wherein the blade
angle of attack decreases in two different incrementally fixed
rates.
6. The high efficiency ceiling fan of claim 5 wherein the blade
angle of attack decreases approximately 0.5 degrees per inch
adjacent said fan axis to approximately 0.7 degrees per inch
distally said fan axis.
Description
REFERENCE TO RELATED APPLICATION
[0001] This is a continuation-in-part of application Ser.
No.10/194,699 filed Jul. 11, 2002.
TECHNICAL FIELD
[0002] This invention relates generally to ceiling fans, and
specifically to electrically powered ceiling fans and their
efficiencies.
BACKGROUND OF THE INVENTION
[0003] Ceiling fans powered by electric motors have been used for
years in circulating air. They typically have a motor 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.
[0004] 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.
[0005] 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. Pat. 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.degree. twist at its root and a
6.9.degree. twist at its tip.
[0006] 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 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.
SUMMARY OF THE INVENTION
[0007] 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 2.pi.(2) in one revolution. Thus its
midpoint one foot out travels 2.pi.(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.
[0008] 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 apparently serves 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.
BRIEF DESCRIPTION OF THE DRAWING
[0009] FIG. 1 is a side view of a ceiling fan that embodies the
invention in its preferred form.
[0010] FIG. 2 is a diagrammatical view of a fan blade of FIG. 1
shown hypothetically in a planar form for illustrative
purposes.
[0011] FIG. 3 is a diagrammatical view of the fan blade of FIG. 2
illustrating degrees of blade twist at different locations along
the blade.
[0012] FIG. 4 is a diagram of air flow test parameters.
[0013] FIG. 5 is a side view of one of the blades of the fan shown
in FIG. 1.
[0014] FIG. 6 is a top view of one of the blades of the fan shown
in FIG. 1.
[0015] FIG. 7 is an end-on view of one of the blades of the fan
shown in FIG. 1.
[0016] FIG. 8 is a perspective view of a ceiling fan that embodies
the invention in another preferred embodiment.
[0017] FIG. 9 is a diagrammatical view of a fan blade of FIG. 8
shown hypothetically in a planar form for illustrative
purposes.
[0018] 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 DESCRIPTION
[0019] The fan blade technology disclosed in U.S. Pat. No.
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 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.
[0020] Twisting of the blade is done in an attempt to optimize the
relative angle of attack of the airflow 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.
[0021] 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.
[0022] 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.
[0023] 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 alters the vectors of air flow into the fan
contrary to that of an aircraft.
[0024] Each fan blade is tapered with regard to 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.
[0025] 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.degree. at the tip end. This 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.degree. per inch. For the mid section it is
0.7.degree. per inch. For the third section adjacent the tip it is
at a change rate of 1.0.degree. per inch. Of course there is a
small transition between each section of negligible significance.
Thus in FIG. 3 there is an 8.degree. difference in angle of attack
from one end of the outboard section to its other (1.degree. per
inch.times.8 inches). For the mid section there is about 6.degree.
difference and for the inboard section about 3.degree..
[0026] 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. 1 which is substantially vertical. As most
clearly noted by the blade centerline 15, the blade has a 0.degree.
dihedral at its root end 11 and a 10.degree. dihedral d.sup.t 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.
[0027] 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.degree. 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.degree.. In the preferred embodiment shown
the blade root end has a 0.degree. dihedral and its tip a
10.degree. dihedral. However, its root end dihedral may be less
than or more than 0.degree. and its tip less than or more than
10.degree.. Fan size, power, height and application are all factors
that may be considered in selecting specific dihedrals.
[0028] 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 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.
1TABLE 1 Avg. Vel. Air V Rotor Resultant Resultant Deg/ Sensor FPM
FPS Vel FPS Vel Angle inch 0 283 4.7 22.7 23.2 11.7 1 303 5.1 24.4
24.9 11.7 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
[0029] Comparative test results appear in Table 2 where blade 1 was
the new one just described with a 10.degree. fixed dihedral, blade
2 was a Hampton Bay Gossomer Wind/Windward blade of the design
taught by U.S. Pat. No. 6,039,541, and blade 3 was a flat blade
with a 15.degree. fixed angle of attack. The tabulated improvement,
was in energy efficiency as previously defined.
2TABLE 2 Improvement Improvement Over Improvement Over With Hampton
Over Without Hampton Improvement Blade Motor Cylinder Bay Standard
cylinder Bay Outside 4 ft 1 172 .times. 18 AM 12,878 21% 29% 37,327
24% 27% 2 188 .times. 15 10,639 NA 6% 30,034 NA NA 3 172 .times. 18
AM 10,018 -6% NA 28,000 -7% -7%
[0030] 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. 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.degree. per inch. For
the fourth, fifth and sixth sections it is approximately
0.7.degree. 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.degree. angle of attack and ends at a
23.degree. angle of attack, thus there is an 1.degree. difference
in angle of attack from one end of the third section to its other
(1.degree. per inch.times.2 inches). The fourth section commences
at a 23.degree. angle of attach and ends at a 18.degree. angle of
attack, thus there is an 5.degree. difference in angle of attack
from one end of the fourth section to its other (5.degree. per
inch.times.7 inches). The fifth section commences at a 18.degree.
angle of attach and ends at a 14.degree. angle of attack, thus
there is an 4.degree. difference in angle of attack from one end of
the fifth section to its other (4.degree. per inch.times.6
inches)
[0031] 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 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.
[0032] 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.
* * * * *