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Accordingly, the following is claimed as the invention:
1. A solar energy collector apparatus comprising
a double-wall tubular solar collector member wherein said walls include an
annular space therebetween sealed at subatmospheric pressure, said member
being closed at one end and open at the other end and including an energy
absorbing surface on the inner wall thereof, said outer wall being
transparent and said inner wall defining a chamber extending between said
ends,
a cup element defining a mouth opening receiving the open end of said solar
collector member, and including means providing a annular liquid seal
between said cup and tubular solar collector member,
an elongated hollow vent tube extending into said cup element and said
chamber, said tube having an axial passageway that is open at its one end
within said chamber,
a fluid connection means connected into said cup element remote from said
vent tube, said means including a fluid flow restriction means for fluid
flow into said chamber at a rate substantially less than the fluid flow
rate permitted by said vent tube passageway out of said chamber,
fluid conduit means connected to said fluid connection means outside said
cup element for supplying fluid therethrough, and
separate fluid conduit means connected to said vent tube outside said cup
element.
2. The apparatus of claim 1 in which there are plural cup elements
connected together by an elongated rigid reinforcing member, the mouth of
each of said cup elements facing a common direction with their central
axes parallel, a plurality of said solar collector members, one of said
collector members being sealingly connected about its open end with the
mouth of each of said cup elements, the said vent tubes in each of said
cup elements being connected externally of each cup element to a first
pipe, and the said restricted fluid connection means to each of the cup
elements being connected externally thereof to a second pipe, said cup
elements, vent tubes, restricted fluid connection, first and second pipes
providing a manifold for circulation of liquid internally of said solar
collector members in parallel circuit.
3. The apparatus of claim 2 in which the manifold includes a low density
foamed polymer insulation surrounding said elongated reinforcing member,
the exterior of said cup elements, said fluid connection means thereto,
the connection of said vent tubes depending outside said cup elements and
said first and second pipes.
4. The apparatus of claim 3 wherein the manifold also includes a shell
layer of plastic over the exterior of said low density foamed polymer
insulation.
5. The apparatus included in claim 1 or claim 2 wherein said restricted
fluid connection means comprises an aperture through a side of said cup
element, a conduit connected to the cup element at said aperture, and an
orifice insert element in said aperture, said orifice insert element
including an axial restricted passageway for liquid flow to said cup
element.
6. The apparatus of clam 5 in which the orifice insert element is
detachably supported in said aperture by an annular, yieldable gasket
member.
7. The apparatus included in claim 1 or claim 2 wherein said elongated vent
tube extends axially of the solar collector chamber and includes therein a
straight portion and a bent portion terminating at said end opening within
said chamber.
8. The apparatus of claim 2 in which each said cup element includes an
annular pipe fitting attached thereto opposite its said mouth and opening
at one end interiorly of said cup element, the other end thereof depending
outside said cup elementf and connected to said first pipe of the
manifold, the vent tube of said cup element comprising a length of glass
tubing open at its ends and seated in said pipe fitting.
9. The apparatus of claim 8 in which said elongated reinforcing member
nestingly engages said pipe fittings at substantially equally spaced
intervals along said reinforcing member in the manifold.
10. The apparatus of claim 8 in which said end of the glass tubing is
seated in said pipe fitting by an annular gasket.
11. In a solar energy collector apparatus including a double-wall,
evacuated, glass tubular collector closed at one end and open at the
opposite end defining a chamber open at said opposite end, a cup-like
manifold receptacle sealingly connected to the open end of the tubular
collector and closing said opposite end of the chamber, the improvement
therein comprising:
an axially extending hollow vent tube providing a first passageway to said
chamber adjacent said closed end of the tubular collector and extending to
the exterior of said receptacle, and
an orifice in said receptacle providing a second passageway to the chamber,
said first passageway being substantially larger in cross-sectional
dimension than said second passageway, the latter restricting flow of
liquid into said chamber at a rate less than a full flow of liquid
permitted in the first passageway, whereby the first passageway upon
overflow of liquid in said chamber also provides an air vent for the
chamber during flow of liquid into the chamber through said second
passageway.
12. A drainable solar energy collector apparatus
having plural tubular solar energy collectors each defining an open end and
an elongated liquid manifold for interconnecting said tubular collectors
in parallel liquid flow, said manifold comprising:
a plurality of cups receiving said collectors at their open end, said cups
each including:
an annular side wall defining a mouth opening at one end for receiving the
open end of said tubular solar energy collector and
an end wall opposite said mouth, the mouth opening of the cups facing a
common direction and the axes of the cups being substantially parallel to
one another,
an axially extending, elongated tube means supported by said cup end wall
and depending outwardly therefrom,
a restricted-flow aperture in the cup wall spaced from said tube means,
said aperture being substantially smaller in section than the internal
section of said elongated tube means,
a first conduit,
a means connecting each of the restricted flow apertures of said cups to
said first conduit,
a second conduit separate from said first conduit and
means connecting each said elongated tube means at the outwardly depending
end to said second conduit,
said first and second conduits communicating with each other through said
tubular solar collector for liquid flow therebetween through parallel
interconnection of said restricted flow apertures and said tube means of
said plural cups.
13. The apparatus of claim 12 wherein the axially extending, elongated tube
means comprises a pipe fitting fastened to the cup end wall at an aperture
therein and depending outside the cup, said pipe fitting being connected
at its outer depending end to the second conduit, and a length of glass
tubing open at its opposite ends, one end being connected to said pipe
fitting.
14. The apparatus of claim 13 which includes an elongated straight, rigid
member disposed lengthwise of the liquid manifold and aligning all of the
cups along the manifold at the end walls thereof.
15. The apparatus of claim 14 in which said glass tubing is connected to
the pipe fitting by an encircling resilient gasket.
16. The apparatus of claim 15 in which the pipe fittings depending from the
end wall of the cups nestingly engage said elongated member at intervals
defining substantially equal spacings of the cups along said member,
thereby locating the position of the cups in the manifold.
17. The apparatus of claim 16 in which the manifold includes a low density,
cellular polymeric insulation layer exteriorly around the annular side
wall and end wall of the cups, said elongated member, the depending pipe
fittings, and first and second lengthwise conduits.
18. The apparatus of claim 17 which includes a shell layer of non-cellular
plastic overlyingd and substantially encasing the cellular insulation of
the manifold.
19. The apparatus of claim 12 wherein said elongated tube means comprises a
length of tubing which includes an axial straight portion supported by the
cup end wall and a terminal bend portion.
20. The apparatus of claim 17 which includes a third conduit lengthwise in
the manifold and included in the said insulation, said conduit being
suitable to house electric control wires or the like.
21. The apparatus of claim 18 in which said shell layer of a non-cellular
plastic is fiber glass reinforced.
22. The appartus of claim 1 in which the said cup element includes an
annular pipe fitting attached thereto opposite said mouth of the cup and
opening at one end interiorly of said cup element, the other end said pipe
fitting extending outside said cup element and connected to said separate
fluid conduit means.
23. The apparatus of claim 22 wherein the vent tube includes a length of
glass tubing open at both its ends, one end thereof being seated in said
pipe fitting.
24. The apparatus of claim 1 in which the ratio of inside dimension of the
cross section of the vent tube passageway to the inside dimension of the
cross section of the fluid flow restriction in the fluid connection means
is substantially greater than 1.
25. The apparatus of claim 24 in which said ratio is at least 2.5.
26. The apparatus of claim 25 in which said ratio is greater than 5.0.
27. A drainable solar energy collector apparatus comprising a plurality of
tubular solar energy collectors having an open end, and
an elongated liquid manifold for interconnecting said tubular collectors in
parallel liquid flow, said manifold comprising:
a plurality of cups receiving said collectors at their open end, said cups
each including:
an annular side wall defining a mouth opening at one end for receiving said
tubular solar energy collector, and
an end wall opposite said mouth, the mouth opening of the cups facing a
common direction and the axes of the cups being substantially parallel to
one another,
a restricted-flow aperture in the cup wall,
an axially extending, elongated vent tube means extending through the wall
of said cup into the tubular collector and depending outwardly from said
cup,
the ratio of the inside cross-dimension of said vent tube to the inside
cross-dimension of said aperture being substantially greater than 1.0,
a first conduit,
a means connecting each of the restricted flow apertures of said cups in
parallel to said first conduit,
a second conduit separate from said first conduit, and
means connecting each said vent tube means to said second conduit,
said first and second conduits communicating with each other throughd said
tubular collector.
28. The apparatus of claim 27 in which the said means by which said vent
tube means are each connected to said second conduit are for parallel
flow.
29. The apparatus of claim 27 wherein said ratio is at least 2.5.
30. The apparatus of claim 27 wherein said ratio is greater than 5.0. |
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Claims |
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Description |
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The present invention relates to the collection of solar radiant energy and
transforming that energy to heat in a liquid, such as water; and more
particularly to an evacuated tubular collector device used in a circuit
whereby the collector is efficiently and safely operable by drainability
in the circuit.
BACKGROUND OF THE INVENTION
Advanced, efficient solar collectors of the type disclosed in U.S. Pat.
Nos. 3,952,724; 4,043,318; 4,018,215; and 4,033,327 are currently in use.
The collectors are comprised of glass concentric tubes, one within the
other, and sealed together to provide an annular space between them that
is evacuated to a hard vacuum i.e. 10.sup.-4 Torr. The outer "cover tube"
is transparent and the inner "absorber tube" is selectively coated over
the surface that is in the vacuum space. These tubes are inserted in
liquid tight connections in a manifold and placed along opposite sides of
the manifold which cross-connects the tubes to each other and serially
connects the tubes along the manifold such that liquid, e.g. water, is
pumped into each of the absorber tubes to fill them and pumped through the
tubes in series to extract and collect the heat of the solar radiation
absorbed by the absorber tubes.
The collectors also are equipped with various reflectors, as is set out in
U.S. Pat. No. 4,002,160, such that diffuse as well as direct sunlight
reach the absorber tubes of the device.
It is most significant to utilize water as the heat extraction medium for
many uses and for many reasons; which include the economy and availability
of water, its desirable thermal coefficients as a heat extraction medium,
and its non-toxic properties. On the other hand, water freezes at
relatively undesirable high temperature in field service and during
inactive periods in cold climates, such as in the northern regions of the
United States in winter, requiring precautions against freeze up in the
system. Heretofore, mixes of anti-freeze compounds in the water have been
used as one way to combat this problem, however, such measures introduce
toxic properties to the heat extraction media.
Also, in the prior systems wherein water is used with or without
anti-freeze compounds in mixtures, the collector system must be operated
continuously to extract the heat of the solar energy collected so as to
prevent excessive operating temperature buildup on the tubes. Accordingly,
as an example of domestic hot water demand or heating and cooling demands
or the combination thereof in a solar operated installation there are
periods, such as in spring or fall seasons, when excess solar energy is
being absorbed by the collector of the system over the needs or demand for
thermal energy thereby.
The excess collection requires "dumping" some of the energy, that is, the
excess must be diverted to special air handlers or cooling towers
resulting in nonproductive energy cost and equipment expenditure of a
system.
SUMMARY OF THE INVENTION
The present invention provides a drainable collector apparatus for use in a
system which will permit a variety of methods of operation in extraction
of the heat from absorbed solar radiation; and will provide complete
drainability of the liquid upon command or upon power failure; and pure
water can be used in the system without danger or freeze up by virtue of
the ability to fully drain the collectors; i.e. the absorber tubes. The
drainable collector comprises an elongated manifold which feeds a number
of the evacuated collector tubes connected on the higher elevation side of
the manifold such that the manifold is at the lower elevation of an array
of the tubes. The liquid is fed into each tube from the manifold through
an orifice designed to restrict the flow rate into each tube and the tubes
are all connected in parallel on the manifold. The restricted orifice
supplies a pressure drop across it at the entrance of liquid to the tube
and this is substantially greater than the pressure drop along the length
of the manifold connecting the several tubes together, plus any difference
in elevation of the outlet of the collector tubes along the manifold, i.e.
the manifold should be pitched upwardly from its drain end to the far end.
The collector tube includes a small diameter longitudinal pipe which
extends from the manifold to near the tip end of its absorber tube. The
longitudinal pipe has sufficient diameter such that during filling each
tube any liquid as may tend to overflow into the pipe will not fill it and
thereby always vent the air in the absorber tube.
The basic element in the collector is the restricting orifice located at
the base of the collector tube and in the manifold. The combined
parameters of the size of restriction provided by the orifice in the base
of the tube and the size of the vent pipe allows the collectors to operate
without siphoning.
The present invention further provides a tubular collector in which the
tubes may be filled in parallel under control and with sufficient pressure
drop in the orifice between the main flow in the manifold and inside the
absorber tube to enable variations in the elevation of fill of the
absorber tubes by reason of some variation in length of the vent pipes
resulting in a variation in the elevation of placement of the open tip end
within the absorber tube chamber. This feature also avoids siphoning and
differential boil of liquid in some tubes of the array and overflow in
others. Siphoning may occur at a time when the vent pipe is plugged, such
as with an overflow of water sufficient to fill the pipe and retain a slug
of water. The invention includes the discovery that a relationship between
diameter (I.D.) of the vent pipe and diameter of the restricting orifice
should be maintained so as to prevent filling at a rate to overflow the
vent pipe full or to obtain the slug-of-water condition. This is best
stated as a finite ratio of vent pipe I.D. to I.D. of orifice of a number
substantially greater than 1, viz, a ratio of approximately 2.5 or
greater; and preferably a ratio above 5.0. The use of the restriction
orifice in the liquid system controls liquid flow rate as to gpm such that
the vent pipe does not completely fill at any time the pump is on.
However, as a theoretical matter, the pumping may be precisely controlled
in rate, as a substitute; and therefore, the restricting orifice in the
feed of liquid into each of the collector tubes provides the practical
control to achieve this and the pumping rate, i.e. the pump itself, need
not be so precisely controlled but merely set to a predetermined gpm rate.
The invention also provides a structural arrangement for convenience of
manufacture, fabrication, installation and ease of maintenance of the
collector array; and, further the array of collectors may be made up of
several modular units of collectors in a row, such as by connecting the
feed and vent header pipes in the modular manifold sections in an
end-to-end fashion. The collector tubes are seated at their open ends in a
fabricated cup or receptable that is predrilled to receive soldered
fittings for the vent pipe connecting it to the vent pipe along the
manifold, and to receive an insert machined prior to assembly to provide
the precise restricting orifice in the liquid connection between the
liquid feed pipe in the manifold and the inside chamber of the absorber
tube. The structure of manifold, tubes and mounting fixtures are
fabricated into a modular unit, and the modular units are connected one to
another to make the total collector of the installation. Thus, the unit
needs only a minimum of assembly in the field.
Other advantages and features of the invention will become apparent from
the following description and the accompanying drawings which are
illustrative of a preferred embodiment and the contemplated best mode of
the invention herein claimed.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of the drainable, evacuated tubular solar
collector of my invention in operating position on the pitched roof of a
building;
FIG. 2 is a sectional view taken along line 2--2 on FIG. 1;
FIG. 3 is a fragmentary view of the connection between two modules or
sections of the collector shown on FIG. 1;
FIG. 4 is a side elevational view of the receptacles for evacuated
collector tubes and the connection of each with a liquid feed pipe and an
air vent pipe along the manifold, as employed on FIG. 1, minus the
manifold insulation and other structural parts supporting the manifold;
FIG. 5 is a sectional view taken along line 5--5 on FIG. 4;
FIG. 6 is a schematic diagram for the drainable solar collector, shown on
FIG. 1, connected for use in a system for producing solar heated water;
FIG. 7 is a schematic electrical control diagram for the operation of the
system shown on FIG. 6; and
FIG. 8 is a fragmentary sectional view of the upper portion of a solar
tube, similar to a portion of the sectional view of FIG. 2, showing a
second embodiment of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FIGS. 1-5, the drainable solar collector is illustrated in an
operating installation on the roof 10 of a building. The roof has some
pitch from the upper ridge 11 to the eaves 12. In the illustrated example
on FIG. 1, the pitch of about 20.degree. (the angle A) above horizontal is
used. (The collector's pitch angle A is variable from very near 0.degree.
to near 80.degree.. ) The solar collector is preferably installed on a
southern exposure (northern hemisphere) of the building such that the axis
of manifold 13 lies in the east/west direction and the axes of the
parallel array of plural solar collector tubes 14 (but one of which is
shown in FIG. 1 for simplicity of illustration) are in the North/South
direction. Accordingly, the sun during a "solar day" moves from right to
left in FIG. 1 across tubes 14. The tubes 14 are assembled in a modular
unit, or units (two of which are indicated on FIG. 1) which comprise the
manifold 13, the upper bracket channel 15, tube end caps 16 and the tie
rods 17 threaded at their ends and bolted at one end in the manifold (as
will be presently described) and bolted at the other end to the channel
bracket 15. The modular unit also includes some form of backside
reflector, which is in the form illustrated a planar diffuse reflector
surface 18, such as disclosed in U.S. Pat. No. 4,002,160, or may
incorporate shaped reflectors as is disclosed in U.S. Pat. No. 4,091,796,
or in U.S. Pat. No. 4,002,499.
As shown on FIG. 2, the solar collector tube 14 is comprised of a double
wall glass hollow test-tube shaped element having a transparent glass
outer wall 19 and radially spaced inner wall 20. Tube 14 is preferably on
the order of 2-1/2 inch O.D. and 4-7 foot length. The outer surface of
inner wall 20 is coated with a wave length selective coating and the outer
wall 19 is sealed by annular fusion with the inner wall 20 near or at the
open end 21 of the double wall glass tube. The enclosed annular space 24
between walls 19 and 20 surrounding the tube is evacuated to a hard vacuum
on the order of 10.sup.-4 Torr and tipped-off in conventional fashion at a
tubulation on the closed end 22 of the tube. Inside wall 20 defines an
interior chamber 23 open at the one end. The tube 14 as constructed is
described more completely in the patent to Pei, U.S. Pat. No. 4,043,318,
mentioned hereinabove. This comprises an advanced, glass, evacuated
tubular solar collector element that is highly efficient in converting
solar radiation into thermal energy at the tube interface on wall 20. The
energy conversion from solar to thermal is accomplished by the coating on
wall 20, and in the use of selective coatings, this conversion is
relatively, highly efficient (on the order of 70% efficiency).
The solar tube 14 is connected onto a manifold 13 by a ring gasket or
grommet 25 in the flange of annular receptacle or cup 26 of the manifold.
There are a plurality of the cups 26 spaced along one side of manifold 13
and each cup opening is facing the same direction. The center axes of cups
26 are substantially parallel. In a preferred construction, cup 26 and a
pipe fitting 27 is assembled in the cup bottom by brazing, soldering or
the like. The pipe fitting 27 has a lower reduced end pipe 28 that depends
in an axial direction from the cup 26. For simplicity of construction, the
pipe fitting 27 is placed off center of the bottom of cup 26 on what will
eventually be the high elevation side thereof when assembled for operation
(see FIG. 2). Along tapered sidewall 29 of the cup and opposite the pipe
fitting 27 is a second aperture adjacent bottom end of cup 26 into which a
stub-pipe 30 is firmly fastened. The axis of the stub-pipe 30 is located
at the low elevation side of the cup in the manifold when assembled for
operation (see FIG. 2).
In the assembly of the manifold parts, a steel or structural angle member
31 includes arcuate, spaced-apart notches (not shown) on its upper flange
32 which receive the depending pipe fitting 27 and nest them in place. The
bottom end of cups 26 butt on the top of flange 32. This places the cups
in their proper attitude for operation, as will become more apparent
hereinafter, and the manifold is further fabricated by placing two larger
diameter header pipes in place and attaching the connections to the cups,
as follows. The end 28 of pipe fitting 27 is securely fastened (e.g. by
brazing or soldering) at a preformed opening in air header pipe 33. Pipe
33 extends the length of manifold 13. Preferably, the air header pipe 33
is metal, i.e. copper or brass, which provides a suitable material match
with cup 26 and pipe fitting 27. The holes for connecting the ends 28 of
the series of fittings of the cups are formed along the length of pipe 33.
In a similar manner, the second pipe, which is water header pipe 34 made
of a similar material, has the spaced predrilled holes to receive the
outer open end of stub-pipe 30, which are likewise securely fastened, i.e.
brazed or soldered, onto the pipe 34 thereby connecting each of them into
pipe 34.
The manifold insulation 35 is molded around the metal structure, just
described, to form the manifold as shown on FIGS. 1 and 2. Additionally,
the manifold includes a lengthwise conduit 36 which will receive electric
control wires 37 as needed to connect the control sensors and the like.
This is added in the manifold structure so that electrical components used
with any of the tubes 14 of a collector module or a series of modules may
be conveniently located and installed in the system. The manifold
insulation 35 is preferably a cellular, light-weight material, such as
foamed polyurethane of about 3 lb. per cu. ft. density. The mold in
forming the insulation 35 matches with the tops of cups 26 to define
annular ports each defined by a continuous side 38 (FIG. 2) and end 39.
These ports open along one side of the manifold which will face the high
elevation of manifold 13 when the solar tubes 14 are assembled. Foam
(rubber or synthetic) inserts prefabricated as cylindrical sleeves 40 are
placed in the ports of the manifold and fit adjacent the mouth flange of
cups 26. Cylinder sleeves 40 will be compressed by the glass wall 19 of
each tube 14 as it is placed in a cup 26 in assembled position. The sleeve
40 being of the compressible material mentioned assures a liquid tight
seal of each tube 14 in manifold 13 keeping out rain, moisture or the
like. The sleeve further insulates against heat loss or heat transmission
at the solar tube's connection in the manifold. The exterior of the
insulation 35 is covered with a formed shell 41, which is preferably
molded from a fiber glass reinforced, resin sheet as two complementary
half segments 42 and 43. The edge 44 of top segment 42 is offset outwardly
to overlap with the adjacent edge 45 of lower segment 43. In a similar way
the other edge 46 of the bottom segment 43 is outwardly offset and
overlaps on the edge 47 of the top segment. The overlaps at 44, 45 and at
46, 47 are fastened together, such as by rivets, to finish the manifold.
As shown on FIG. 1, the opposite ends of the shell for the manifold modular
sections include parallel arcuate tabs 48. Prefabricated, half section
inserts 49 (in dotted outline on FIG. 1) are placed at the ends of the
modules and similar inserts (not shown) are secured in place between
modules connected to one another in end-to-end fashion. Intermodular
connection of the pipes 33 and 34 is shown on FIG. 3.
As may be seen on FIG. 2, the manifold 13 of a module is attached by
nut-bolt fasteners 50 extending through the overlap layers 47, 46 of
manifold shell 41, through a stringer member 41 and the roof 10 fastening
it in place. It is important that the manifold be pitched down from its
end toward the pipe connections for the piping circuits 34 and 33 of the
system. Utilizing a pitch angle of about 2.degree. from horizontal will
fully drain the collector. At the upper end of the module the bracket
channel 15 is fastened by cap screw 52 into an upper stringer member 53
attached to roof 10 by nut-bolt fasteners 54. The reflector, such as a
white panel 18, is attached for support by the stringer members 51 and 53.
Tubes 14 are held seated in cups 26 by an end cap device which includes
truncated inner cup 55 made of plastic engaging its closed end and an
outer plastic truncated cup 16. The outer cup extends through a splined
aperture 57 formed in the vertical web of the channel bracket 15 (see FIG.
1). The edge of cup 16 at its large open end has radially extending spaced
bosses 56 which match in size and location with the spline cut-outs of the
aperture 57 in the bracket 15 so that outer cup 16 and inner cup 55 may be
assembled from the side of bracket 15 opposite the manifold. In assembly,
the tube 14 is inserted through an aperture 57 and the open end 21 is
seated in manifold cup 26 inside gasket 25. The inner cup 55 is placed
over the protruding closed end 22 of the tube 14 and outer cup 16
concentrically placed over cup 55 such that the outwardly flanged bosses
56 thereof (FIG. 2) pass through the spline cut-outs of aperture 57 (FIG.
1). After bosses 56 are through aperture 57, the outer cup 16 is twisted
(rotated) to lock bosses 56 along the manifold side of bracket 15. Tension
is applied to axially load tube 14 in the manifold cup 26 by tightening
the center screw 59 in the threads of the journal aperture 58 at the
closed end of cup 16 against the closed end of inner cup 55. This loading
by tightening screw 59 holds the tube 14 in the manifold cup 26. The end
bolted tie rods 17 spaced along the module fasten the bracket 15 and the
angle member 32 in the manifold together mechanically to prevent the
manifold's buckling; in other words, the manifold 13 is tied rigidly to
the bracket channel 15 by the series of rods 17. The rods 17 are disposed
along the bracket and manifold, respectively, at spaced intervals located
between certain of the tubes 14.
The solar collectors being in place, as described, the one header pipe 33
is connected to a pipe 60 (FIG. 1) of the solar tank system by a hydraulic
clamp-style coupling 62; and the other header pipe 34 is similarly
connected to a pipe 61 of the solar tank system of the same style of
coupling 63. The successive modules mounted in a line along the roof are
connected (FIG. 3) together by a hydraulic coupling 62a connecting the
lengths of header pipe 33 to each other and a hydraulic coupling 63a
connecting the lengths of header pipe 34 to each other. The far ends of
the last module in the installation have the pipes 33 and 34,
respectively, capped and sealed so as to close the end of that pipe.
The important aspect of the invention will now be described in reference to
FIGS. 2, 4 and 5. As a key part of the assembly of the tubular collector
and manifold in the closed system of the drainable collector of this
invention, the pipe fitting 27 in each cup 26 receives an air vent tube
64. Preferably, tube 64 is glass, such as laboratory or chemical tubing.
The vent tubes 64 are desirably of equal length and extend such that their
open upper end 65 is near the top of the chamber 23 within the tube 14.
This is shown in one form on FIG. 2 utilizing a straight length of glass
tubing. The lower end 66 of tube 64 is seated in an annular gasket 67 held
in the large section of pipe fitting 27.
Another key part of this assembly for each tube is the orifice insert 68
placed in the innermost end of the stubpipe 30 in the water line and held
by a tube-like gasket 69. The insert 68 has a precise size of axially
extending passageway 70 bored through it to connect water in pipes 34, 30
to the chamber 23 inside solar tube 14. The insert 68 may take other forms
such as by threading it in pipe 30 or swagging it therein, etc.; however,
it is desirable to remove inserts 68 from time to time for operational
reasons or for maintenance. Therefore, it is desirable to provide a
readily removable insert in pipe 30.
OPERATION OF THE COLLECTOR
An installation of the collector is schematically illustrated on FIG. 6 in
use in a hot water system. The header pipe 33 is shown in an alternative
hook-up of collector modules wherein pipe line 60 is T-connected to the
header 33 at an intermediate point between modules. In similar fashion,
the water header pipe 34 is T-connected to the pipe line 61. In such
installation, the manifolds on either side of the T-connections is sloped
slightly toward their drain end into the pipes 60, 61. Pipe 60 extends
into the top level of solar water tank 71, preferably into the head space
of that tank. The pipe 61 extends to a junction point 72 from which one
leg of pipe 61a is connected to a solenoid-operated valve 73. At the
opposite side of this valve the pipe extends into the top portion of tank
71. Beyond pipe junction 72, pipe line 61 is connected in series to a
one-way check valve 74, a flow regulating valve 75, flow-rate meter 76,
water pressure gauge 77 and the outlet side of a centrifugal motor driven
pump 78. Pipe 61 is connected at the inlet side of pump 78 into the bottom
strata of the solar water tank 71. The circuit of the system just
described is a closed system and includes a pressure relief valve 80 on
the tank 71 and a vacuum breaker vent 81 in a pipe 82 that is connected in
the line 60 near the collectors and extends into the air space (headspace)
in tank 71. Also, relief valve 83 is attached onto the fill pipe 34 and
relief valve 83a is attached onto vent pipe 33. The relief valves 80, 83
and 83a are set at suitable pressures for normal operation of the system;
e.g. valve 80 releases at 25 psi, valve 83 releases at 28 psi and valve
83a releases at 30 psi. In the invention, it is preferable to set relief
valve 83 to release at pressure below the setting of relief valve 83a.
Should the fill line 61 become blocked to tank, liquid will release at
valve 83 when gas pressure in the tubes 14 become excessive and close
again when the pressure in the tubes return to neutral. Should both lines
61 and 60 become blocked to tank 71 and relief valve 83 malfunction,
relief valve 83a will release excessive gas pressure in the tubes 14 and
close again when the pressure in the tubes return to neutral. Should both
lines 61 and 60 become blocked to tank and relief valve 83 malfunction,
relief valve 83a will release excessive gas pressure in the tubes 14 and
close again when pressure in the tubes return to neutral. Any time the gas
pressure in the system, including pressure in the headspace of tank 71,
becomes excessive, relief valve 80 will release to a neutral pressure. The
relief valves provide a triple safety factor in the event of malfunction
in venting or draining in the system.
In the illustrated hot water system of FIG. 6, a conventional hot water
tank 90 with electric resistance or gas fired heater as standby energy is
connected near the bottom to the inlet of pump 91. The pump outlet is
connected to a heat exchanger coil 92 inside solar tank 71 and it is
connected to the top of tank 90. The hot water is withdrawn from tank 90
through pipe 94 connected to conventional mixing valve 104 which may be
thermostatically operated. Also, cold water supply line 102 is T-connected
to the pump circuit 91-93 to supply make-up water to the tank 90 and
T-connected by pipe 103 to the mixing valve 104.
Referring to FIG. 7, the schematic electrical control diagram for the unit
of FIG. 6 includes 24 volt D.C. electric power source 84 connected in a
series circuit 85 including a thermostatic snap-action switch 86 located
near the base of solar water tank 71 sensing water temperature. Switch 86
responds to temperature of the water in the lower strata of solar water
tank 71 to close at temperatures below a preset level, say 180.degree. F.
This regulates the maximum level of energy in solar tank 71. Switch 87 is
a solar cell or light-operated switch that will close upon sensing
daylight and open at sunset. This switch responds to the solar day. An
example of such switch is commercially available at Lumitrol switch Model
T-15, NO. Also in circuit 85 is a first thermostatic switch 88, such as is
used in controlling electric ranges (stoves), with variable end set points
to close the switch between a range of temperatures. An example is a
General Electric Model No. WB 21.times.178 temperature limit switch with a
48 inch temperature probe (89 on FIG. 7) and extra packing gland. The
switch 88 is set so that the circuit will close upon sensing temperatures
at its probe element 89 below the range 240.degree. F-290.degree. F. This
switch is normally open above the set temperature limits. Each collector
array of the installation should include a switch 88 sensing temperature
conditions (by 89) in one of the tubes 14 at all times. However, as
further safety measure a redundant switch 88' which is the same as switch
88 is preferably installed in separate tube 14 in each array of modules
and in series with the first such switch 88. Should the first (switch 88)
fail to open in a high temperature condition occurring in the tubes
outside the temperature limits selected, this second switch 88' will add
assurance that the circuit 85 will be opened. The second switch 88' has
its probe element 89' in a separate tube 14 of the module, as is
illustrated. The circuit 85 also includes a starter solenoid (shown
closed) for the pump motor M driving water pump 78. Motor M of the pump
includes its starter control in the 110 v. a.c. power line circuit for
power to run the motor and drive the pump. A circuit 85a in parallel with
the starter solenoid for electric motor M includes the contacts of the
solenoid of solenoid-operated 73. Valve 73 is normally-open and is closed
when circuit 85a is energized so that, in closed position, valve 73 is set
for blocking pipe line 61a (FIG. 6).
Circuits 85 and 85a are each energized when the series of switches 86, 87,
88 and 88' are closed. This establishes a pumping circuit for flow of
solar water from solar tank 71 (FIG. 6), through pump 78 and into the
water header pipe 34 of the collectors. (See solid arrows along pipe 61 on
FIG. 6). Pump flow and output is regulated in line 61 by the flow valve 75
and flow meter 76 to the desired gpm, as will be mentioned hereinafter.
Referring again to FIGS. 2, 4, and 5, the pump will fill the water header
pipe 34 when (a) daylight exists, (b) water in the solar tank is below the
preset upper limit, e.g. 180.degree. F., and (c) the inside of tubes 14
are at a temperature within the temperature range limits set for the
temperature limit switch(s) 88. The pumping rate in gpm is preferably set
for a selected size (dia.) of passageway 70 in the orifice insert and I.D.
of vent tube 64. During pumping there is a pressure drop across the
passage 70 from pipe 34 to the interior of cup 26-chamber 23 of each solar
tube in the system. Water will fill the solar tubes 14 in parallel flow
until the water level in the collector tube chamber 23 allows water to
spill over the open end 65 of the vent pipe 64, but most importantly the
pumping rate will be less than a flow of water through passageway 70 and
overflow into vent tube 64 that is needed to completely fill the vent
tube. Accordingly, there remains an open air vent passage through tube 64
to the header pipe 33 and back to the solar tank 71. Additionally, the
flow, or overflow as the case may be, of water from tube 64 will be to
header pipe 33, which is designed to be of sufficient size (diameter) to
maintain a flow of both water and air to the solar tank. It is important
that the pipe 33 will never fill with water to block the air flow to the
tank; otherwise, an undesirable siphoning condition will occur.
The method of operation of the collector described is a "full continuous
flow" mode of operation in which the pump operates continuously throughout
the solar day subject to conditions which maintain the series switches of
the control circuit closed. The continuous flow operation utilizes a
principle of thermal stratification of the water in the solar tube chamber
such that the uppermost (hottest) water in the solar tube chamber is drawn
off and returned to the solar tank.
When the solar tank water contains thermal energy converted from absorbed
solar radiation, and the system wishes to utilize that energy, the water
(or media) to be heated thereby is pumped from the lower strata of a
conventional domestic hot water tank 90 and circulated by pump 91 through
heat exchange coils 92 in the solar water tank, then back to the top of
water tank 90 via the discharge pipe 93. Hot water as needed is withdrawn
by the water line 94 for domestic hot water or like utilization.
Again considering the foregoing full continuous flow method of the
invention, if during solar day operation a condition arises to cause one
of the switches in the series circuit 85 to open (FIG. 7), two things will
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