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Description  |
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BACKGROUND OF THE INVENTION
1. Summary of the Invention
The present invention relates to solar heat collectors, and in particular
relates to a very simple unit with efficient heat transfer
characteristics.
2. Description of the Prior Art
Many different systems have been designed for use in connection with solar
heat collectors. The art contains examples of single tubes, aligned in
fixed beds to evaporate water and produce steam, conical collectors with
central fluid transfer systems, spherical units, and many other different
styles of units. All of these fixed type of units suffer from the
disadvantage of being immobile, and thus being incapable of compensating
for the daily motion of the sun from horizon to horizon. In order to
overcome this type of problem, various complex units have been designed.
An exemplary unit is that disclosed in U.S. Pat. No. 3,884,217 of Wartes
which utilizes plural prismatic, independently adjustable reflectors which
pivot to collect the sun's rays, and reflect them to a second reflective
surface which then directs them to the actual heat transfer section. The
whole collector is also pivoted to aid the compensating for the sun's
daily motion. The unit is thus quite complex and expensive and requires
considerable mechanical manipulation in order to function properly.
The complexity of this type of system is overcome, for example, by the
system disclosed by Futch in U.S. Pat. No. 4,086,911. This system merely
uses numerous tubes positioned in a truncated cone designed to absorb
heat. Such a simple system, however, is quite inefficient as it cannot be
moved in order to increase the amount of energy absorbed to the level of
complex systems.
Additionally, various other attempts at producing functional solar heating
systems are disclosed in U.S. Pat. Nos. 4,109,640 of Smith; 4,119,085 of
Knowles et al, and 4,138,061 of Besack. All of these lack efficiency or
are quite complex.
U.S. Pat. No. 4,015,584 of Haberman discloses another apparatus for solar
heat collecting. The apparatus utilizes a plurality of vertical tubes, and
the structural requirements for window mounting result in a relatively
complex unit of limited size and heating capacity. Thus, it is of
relatively limited utility as compared to a fixed position,
high-surface-area unit. On the other hand, Wilson, in U.S. Pat. No.
3,954,097, discloses a simpler unit, in that a vertical tube is used to
both provide fluid flow and support a parabolic surface. However, in order
to provide the fluid flow, a complex, expensive structure is necessary.
Further, a significant relatively flat, external cross-sectional surface
area is disclosed, which would present dangers when roof-mounted as
suggested, due to possible wind damage.
It is therefore an object of the present invention to develop a simple
solar heat collector which is more efficient that the "flat plate" type of
units that are normally placed on rooftops, and also close to the
efficiency of the units which are movable in two planes (azimuth and
elevation) without requiring the complex structure needed for such motion.
It is a further object of the present invention to provide maximum surface
area, with minimum use of space during orientation or rotation of the
unit. Also an object is to provide such a unit that has the ability to
withstand winds of relatively high speed and that is rotatable during such
high wind velocities, without great increase in structural weight.
SUMMARY OF THE INVENTION
To the above ends, a solar heat collector has been designed which is
mechanically much simpler that the two-plane adjustable collectors.
Further, it heats air nearly as well as such collectors, and is more
efficient than flat plate collectors. These and other improvements are
effected by the production of a solar collector in which a vertically
oriented, elongated tube or pipe is used as a mast, or main mounting
portion, for the solar collector. The tube or pipe is provided with an air
or other fluid inlet at the top, preferably to the side at the top, with
mounting means for the remainder of the unit being placed at the very top
of the collector tube or mast. The mast has an outlet at the bottom for
fluid exit. A parabolic reflective surface is mounted in a relatively
cylindrical shell which is transparent in the region facing the concave
side of the parabolic reflector. Those two pieces, the reflector and
shell, are provided as a unit and mounted to the mast in a rotatable
manner, such that the axis of the mast is identical to the focal axis of
the parabolic reflective surface and, preferably, the same as the axis of
the surrounding cylindrical shield. At the bottom of this structure, a
manifold is provided surrounding the mast. Air or other fluid inlet means
is connected to the manifold and the manifold communicates directly with
the internal portion of the chamber produced by the shell and the
parabolic reflector. It should be noted that the radius of the manifold,
as far as the fluid supply portion thereof is concerned, should be equal
to or less than the radius of the cylindrical shell so that the manifold
is in continual supply contact with the chamber. Preferably, mounted
externally around the manifold are an electrical motor and drive means,
such as a ring gear, mounted on the underside of the container. The drive
structure is utilized to rotate the parabolic reflector and keep it
pointing directly towards the sun. One example of the equipment useful in
performing the function of a heliostat or sun tracker, which controls the
rotation, is disclosed in U.S. Pat. No. 4,027,651 to Roland W. Robbins,
Jr. but other devices, known in the art, may be used.
As a result of the design of the present invention, a solar collector with
significantly higher energy absorption than the planar fixed-position type
of collector is provided. Additionally, the absorption characteristics of
the collector of the present invention are very nearly equivalent to those
of the complex units which are adjustable both in elevation and azimuth.
As a matter of fact, the present unit is usually equivalent to the complex
units at all times except when the sun is at its maximum height, and at
this time there is only a slight efficiency decrease as compared to the
more complex units.
BRIEF DESCRIPTION OF THE DRAWINGS
A better understanding of the present invention may be had by considering
the following detailed description, taken in conjunction with the
accompanying drawings in which:
FIG. 1 shows a side view of a solar collector of the present invention;
FIG. 2 is a section taken along lines 2-2 of FIG. 1;
FIG. 3 is an isometric view, in schematic form of one preferred embodiment;
FIG. 4 is a sectional view taken along lines 4-4 of FIG. 1;
FIG. 5 is a schematic top view of another embodiment;
FIG. 6 is a partial schematic view of a third embodiment; and
FIG. 7 is a graphical representation comparing the efficiency of various
collectors.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In FIG. 1, the single plane solar collector of the present invention,
generally indicated by number 10, is supported on the ground 12 or other
similar surface by base 14. In is understood that the unit could be
roof-mounted, and plural brackets could be provided for support. The
positioning of the collector of the present invention, of course, would be
dictated by the availability of sunlight, which depends on such factors as
geographical location, adjacent buildings, trees, etc.
In any event, in the embodiment shown the fluid to be heated, which is
preferably air but may be other gaseous material if desired, enters pipe
16 and is discharged through mast 18 and pipe 20, after being heated in
the solar collector 10. In the embodiment shown, manifold 22 is connected
to pipe 16, but it is to be understood that pipe 16 could be located
inside mast 18, which is hollow, and feed manifold 22 from the inside, or
directly feed chamber 26. In the preferred embodiment, a blower 21 is
provided downstream of pipe 20 to pull the air through the solar collector
of the present invention, and to direct the heated air to utilization
equipment. Exemplary uses include the heating of a bed of rock or other
material with a high specific heat for storage, direct heating of room
air, or heating of water for domestic use.
The air entering pipe 16 and manifold 22 is vented into chamber 26 through
ventholes 24 shown in FIG. 1. The air then travels upward through chamber
26 of the solar collector, being heated during the whole of its passage by
direct exposure to the sunlight, enters mast 18 at aperture 28 and is
drawn downward through the mast and heated further. The focal axis of
parabolic reflector surface 32 is the center of the mast (as better shown
in FIG. 2) and, thus, significant heating occurs during the downward
travel of the air. Further, by this arrangement, colder air enters the
lower portion of the solar collector of the present invention, is heated,
and rises to the upper portion, at least somewhat by its own accord. This
arrangement in the present design minimizes fan load requirements. As
better shown in FIG. 2, transparent surface 34 cooperates with parabolic
reflector surface 32, and along with lower surface 30 and upper surface 36
of the collector, these provide a chamber which is sealed from external
atmospheric involvement.
Furthermore, mast 18 is provided with cap 38 which cooperates with upper
cover 36 to position mast 18 so that its axis is also the focal axis of
the parabolic reflective surface. In its preferred form, in this portion
of the structure of the present invention, shaft 38 is centered in
indentation 40 in cover 36 and would be held in place, for example, by a
bearing or bushing to ease the rotation of the unit of the present
invention.
Rotation is effected by motor 46 mounted conveniently adjacent manifold 22,
and provided with gear drive 42 which drives gear 44 on the bottom of the
unit of the present invention. The rotation of the unit about the mast 18
can be effected by the driving of the motor 46 responsive to the signals
of a heliostat or sun tracker 47 to maintain the parabolic reflector
facing the sun at all times. Other drive means could be utilized, but this
drive means allows rotation of the collector of the present invention
without great space requirements, produces accurate rotation, and does not
require provision of flexible couplings since the drive gear can be sealed
against manifold 22, and be an integral portion of collector 10.
FIG. 2, the section taken on along lines 2--2 of FIG. 1, shows transparent
surface 34, parabolic reflective surface 32, and mast 18 in section. Mast
18, in this area, would preferably be painted black for maximum energy
absorption, and would be directly impinged by sunlight as indicated by
arrows 54. Air is provided through inlets 24 which communicate directly
with manifold 22. In addition, the area between the rear of parabolic
reflector 32 and the exterior 50 of the collector is preferably insulated
with, for instance, a lightweight foamed plastic 52, such as polyurethane.
It should be noted that rear surface 50 may be of the same material as
transparent surface 34 or different, and it is not necessary that this
rear surface be transparent.
In FIG. 3, an additional embodiment of the present invention is shown in a
schematic drawing. Mast 58 is provided with collector 60, in an
alternative form which is more fully described in FIG. 5. Collector 60 may
take the same circular shape as defined in FIGS. 1 and 2; however, in this
embodiment a flat reflector plate 62 is provided extending horizontally
outward from the base of the assembly. This plate 62 reflects sunlight
into the parabolic reflector, thus providing an additional capture area
without altering the single axis rotational feature of the unit. As
indicated by arrows 64, the sunlight is directed to the axis of collector
60, and thus the energy available for absorption by the fluid in the solar
collector of the present invention is significantly increased.
FIG. 4 is a further detailed drawing taken along the lines 4--4 of FIG. 1
showing in section, rear surface 50, insulation 52, mast 18, parabolic
reflective surface 32 and transparent surface 34, as in FIGS. 1 and 2.
However, in this figure, mounting shaft 38 is more clearly shown. Shaft 38
is mounted, as described hereinabove, to provide the appropriate stability
and seal for the solar collector of the present invention.
In FIG. 5, an alternative embodiment with a different external shape is
depicted. In this embodiment, transparent surface 70 is of an appropriate
curvature to decrease wind friction and force upon the collector, and is
sealed and secured to parabolic reflective surface 72 by means of the
seals 74. The schematic view in FIG. 5 is essentially a section taken
along the same location at line 2-2 in FIG. 1 and thus shows mast 76 in
its central location having an axis which is the same as the focal axis of
the parabolic reflector 72. Fluid inlet apertures 78 provide for fluid
flow into the chamber in the solar collector of this embodiment.
In FIG. 6, another embodiment of the present invention is shown
schematically. In this figure, mast 80 and parabolic solar collector 82
are generally shown, along with fluid inlet 84 and manifold 86. These
portions function in the same manner as previously described. However, in
this embodiment, an additional fluid inlet and outlet system is added to
the unit. In this system the fluid would normally be water, for use in
household hot water heating, and the water would be provided at inlet 88,
and traverse spirally up the inside of mast 80 through tubing 90 to the
area near the top of the unit. At this point, unit 90 would be coupled
with vertical straight tubing section 92 and the water would be drawn
downward to and through outlet 94. The preferred direction of flow is
upward through the long spiral section and downward through the shorter
section so that heat absorption and thus efficiency could be maximized. In
this form, mast 80 could be clear or the spiral tubing could be in
intimate contact with the mast, such as by welding the two together, in
order to increase absorption. It would further be preferable that vertical
line 92 be heat absorptive, or black, in order to further maximize heat
and energy absorption.
In FIG. 7, a comparison, on a relative basis, of the energy absorption
characteristics of various types of solar collectors is made. Arc 94
represents an approximation of the angle of deflection of the sun from the
horizon during a given day, and thus energy availability. The center of
the arc being approximately at noon, when the sun reaches its highest
point and the angle of deflection at dawn and at dusk being minimal. Curve
96 shows the relative absorption of energy by a fixed plate solar
collector, the unit being positioned for maximum absorption, and absorbing
the maximum amount of energy at the time when the sun is highest in its
arc. Curve 98 shows the energy absorption of a double plane adjustable
solar collector wherein there is relatively constant adjustment, both as
to azimuth and elevation, to compensate for the changing position of the
sun. Using this equipment, once the sun has reached a reasonable angle
from the horizon, and the level of energy available from the sun has
become significant, the level of absorption by this complex type of unit
is maximized, and stays relatively constant until the sun starts to set.
Curve 100 shows the capacity for energy absorption by the unit of the
present invention in comparison with the other curves. The single planar
adjustment used in the present invention causes the absorption rate to
rise as rapidly as it does with a double adjustable unit, and follow the
same pattern. However, there is a slight decrease in absorption when the
sun is providing its maximum energy. Thus, a very efficient, simple unit
is provided. It should be noted that all of the curves indicated by 96, 98
and 100 are normalized to per-unit area, and thus are comparisons of
relative unit output.
Although there have been described above specific arrangements of a single
plane, parabolic collector in accordance with the invention, for the
purpose of illustrating the manner in which the invention may be used to
advantage. It will be appreciated that the invention is not limited
thereto. For example, while the invention has been disclosed in the
context of association with air heating, the principles of the invention
are equally applicable to the heating of other gaseous material. Further,
a particular arrangement for the inlet and exit of the air is provided,
but the invention would be easily applied to the manifolding of the
entrance air into a central tube, inside the mast at the manifold to
provide the air to the bottom of the collector container. Accordingly, any
and all modifications, variations or equivalent arrangements, including
those noted above, which may occur to those skilled in the art, should be
considered to be within the scope of the invention as defined in the
appended claims.
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