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Description  |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a solar heat collector.
2. Description of the Prior Art
Numerous devices have been proposed for utilizing solar energy as a source
of heat, particularly for domestic home heating needs. Commercialization
of such devices, however, has been inhibited because of the typically high
initial capital costs of the solar heating systems presently available.
For example, a solar thermal collector is typically constructed of
expensive materials which will sustain working pressures of 125 psi at
temperatures above 190.degree. F. since the temperatures within such
collectors can be quite high, indeed even above 300.degree. F., as the
heating load requirement of the collector system decreases. In other
words, collectors have been designed to withstand temperatures and
pressures under no flow or stagnant conditions; and such designed
collectors require expensive coatings and materials of construction. Thus,
there remains a need for a solar heat collector which is not only simple
in construction but lower in cost, thereby overcoming some of the
drawbacks of the solar heat collectors of the prior art.
SUMMARY OF THE INVENTION
Briefly stated, this invention features a mechanism within a flat plate
solar collector for modulating the temperature therein by reflecting
incident solar radiation with a solar reflective surface and as a function
of the temperature within the flat plate collector. The mechanism
comprises a movable solar reflective surface which is positioned so as to
permit at least partial and preferably complete exposure of a solar energy
absorbing surface within the collector when the temperature within the
flat plate collector is at a predetermined low level and it is positioned,
preferably automatically, so as to at least partially and preferably
completely reflect incident solar radiation when the temperature within
the flat plate collector is above a predetermined high temperature level.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of a flat plate solar heat collector unit
constructed in accordance with the teachings of the present invention and
having portions removed for the purposes of clarity.
FIG. 2 is a cross-sectional view of the solar heat collector unit taken
along line 2--2 of FIG. 1.
FIG. 3 is a fragmentary cross-sectional view taken along line 3--3 of FIG.
1.
FIG. 4 is an isometric view of a flat plate collector of this invention
including the glass cover, particularly showing the movable solar
reflector in accordance with one embodiment of the present invention.
FIG. 5 is a fragmentary cross-sectional view taken along line 5--5 of FIG.
4.
FIG. 6 is a cross-sectional view of a flat plate solar collector having a
movable solar reflector surface for a flat plate collector in accordance
with an alternate embodiment of the present invention.
FIG. 7 is a schematic diagram showing a movable solar reflector having
baffles disposed therein to define a fluid flow path in a fluid plenum.
DESCRIPTION OF THE INVENTION
Referring now to the drawings and particularly with reference to FIGS. 1, 2
and 3, the flat plate solar heat collector 10 of this invention includes a
generally rectangular frame 12 having upwardly extending side walls 14 and
end walls 15. Any material can be used in fabricating the rectangular
frame; however, it is particularly preferred in the practice of the
present invention that the rectangular frame be formed from a lightweight
thermally insulating inexpensive material. For example, the frame 12 can
be formed from a glass fiber reinforced polyurethane foam having the
requisite structural strength and thermal insulating characteristics.
Other materials can also be employed.
The solar heat collector 10 includes a cover plate 16 thereby defining a
chamber between the cover plate 16 and the base of frame 12. The cover
plate is made of any material which is generally transparent to solar
radiation. Typically, cover plate 16 is made of glass or clear plastic.
A movable solar energy reflecting surface 18 is located within the chamber
of flat plate collector 10. In the embodiment shown in FIGS. 1, 2 and 3,
the reflective surface covers one-half of an endless belt. The other half
of the endless belt is coated with a solar energy absorbing material. The
solar energy absorbing surface of the endless belt is shown generally as
reference numeral 19. As can be seen in FIGS. 1 through 4, when the
reflecting surface 18 is facing upwardly in the direction of the incident
solar radiation, then the absorbing surface 19 is facing downwardly.
Any material which is capable of reflecting solar radiation may be used as
the reflecting surface material. For example, silver paint and other types
of metallic coatings may be applied on the endless belt. In contrast
thereto, the absorbing surface generally will be painted black or will
contain a dark absorbing coating that has a high solar absorptivity. It is
desirable that this coating also have a low emissivity. Such coating
materials are well known in the art as selective absorber coatings.
Typically, the endless belt will be made of a material which will readily
transfer or conduct heat to the fluid surrounding it. For example, the
belt can be a thin metallic member of aluminum, steel or the like.
The endless belt with its reflecting and absorbing surface is mounted over
a pair of rollers such as rollers 20, for example, having drive means such
as gears 21 with raised gear teeth for engaging openings 22 in the
marginal edges of the endless belt. The absorbing and reflecting surfaces
as they are positioned over the rollers 20 define a channel or plenum 17
between the surfaces for the passage of a heat transfer fluid such as air
or water.
Fluid inlet 23 is located in one end 15 of flat plate collector 10 which
communicates with the plenum 17. At the opposite end of the flat plate
collector 10 there is an outlet 24 communicating with the fluid plenum
defined by the reflecting and absorbing surfaces.
Manifold means (not shown) mounted in communication with inlet 23 and
outlet 24 can be provided to connect a plurality of solar collectors 10 in
parallel relationship. Alternatively, a manifold or other suitable device
(not shown) can be provided to communicate with inlet 23 and outlet 24 and
to permit the serial connection of a plurality of collectors 10.
Optionally and preferably, fan or pump means (not shown) are provided for
circulating the heat transfer fluid through the inlet of the solar
collector and outwardly to a source or point of use of such heated fluid.
Rollers 20 are journaled in the end walls 15 of solar collector 10 and
extend outwardly to be operatively connected to drive means such as gear
wheel 26 which can be optionally chain-driven by a motor (not shown).
Also, optionally and preferably located within the solar collector 10 is a
thermal detector (not shown) such as a thermocouple probe for sensing the
temperature of the fluid in the collector. Alternatively, a temperature
sensor can be located on the surface of the collector 10, the temperature
of which can be related to the fluid temperature in the collector.
In operation, when the temperature of the solar energy collector 10, or
optionally and preferably the temperature of the fluid in the collector,
falls below a predetermined selected temperature, say, for example,
75.degree. F., the reflecting surface 18 is moved such that it faces
downwardly in the solar collector and the absorbing surface 19 faces
upwardly. This change of position can be done manually; however, it is
preferred that the position of the reflecting surface 18 be changed
automatically in response to an appropriate signal from the thermal
detector located within collector 10 and operably connected to an
automatic means for switching on a drive mechanism for the movable solar
reflecting surface, thereby moving the reflecting surface 18 so as to face
downwardly and the absorbing surface 19 to face upwardly. Thus, with the
absorbing surface 19 facing upwardly to receive incident solar radiation,
the fluid within the solar collector will be heated. Natural convection
will cause the fluid to circulate through the collector 10 to a point of
use external the collector 10. Preferably, however, at a predetermined
higher temperature detected, for example, by a thermocouple probe, the
heated fluid will be circulated by pump or fan means.
At any point in time when there is a lack of demand for heated fluid and
the circulating means are turned off, the temperature will begin to
increase within the solar collector 10 to even higher temperatures. At a
predetermined elevated temperature, say at a temperature above about
220.degree. F., as detected with the thermocouple, the reflecting surface
18 is moved into position so as to reflect the incident solar radiation,
thereby decreasing the stagnant fluid temperature within the solar
collector. Again, repositioning of the reflecting surface can be automated
so as to operate in response to thermal conditions existing within the
collector.
As will be readily appreciated, the positioning of the reflecting surface
can be varied between a partial to full reflecting and a partial to full
absorbing surface, thereby offering the ability to more accurately control
or modulate the temperature within the solar collector. However, for most
purposes, it is adequate that upon reaching a predetermined elevated
temperature and a predetermined lower temperature, the movable surface can
be positioned between full reflecting and full absorbing condition.
As can be seen in FIG. 3, it is particularly desirable to provide grooves
or rabbet cuts 28 in end walls 15 of the solar thermal collector to
accommodate the marginal edges of the endless belt with its absorbing and
reflecting surfaces and to provide a fluid seal for the fluid in fluid
plenum 17.
In the alternate embodiment shown in FIG. 6, the solar absorbing surface 27
is permanently fixed within the solar collector; however, the solar
reflecting surface is mounted over rollers and has tape means for winding
the reflector so as to substantially cover the absorbing surface at points
in time when the temperature in the solar collector exceeds a
predetermined maximum temperature. The heat transfer fluid, such as air,
is circulated over the solar absorbing surface 27. Alternatively, surface
27 can be applied to a heat transfer plate through which a heat transfer
fluid such as water is circulated.
For greater heat transfer efficiency and especially when air is the working
fluid, baffles can be located within the fluid plenum 17. As is seen in
FIG. 7, baffles 30 are mounted on end plates 31 thereby defining a
tortuous path through which the fluid must flow in route from the inlet to
outlet of the collector. The end plates can be mounted on end walls 15 of
frame 12, for example. The inlet 23 and outlet 24 of frame 12, then, of
course, are sized and positioned to correspond with the inlet 33 and
outlet 34 of the fluid plenum.
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