Note: Descriptions are shown in the official language in which they were submitted.
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Solar collectors are used to convert the sun's rays
into heat energy, usually transferring this heat to a liquid
or gas which may be transported to a point of use.
One type of conventional collector includes a flat
plate to which is attached a metallic tubular coil. The flat
plate is adapted to collect the sun's rays, convert these rays
to heat energy and conduct this heat energy to the tubular coil.
A fluid, either a gas or liquid, is circulated through the coil.
The fluid is heated in the process. The heated fluid is then
transported to some other location where heat energy is ex- ~;
tracted normally for the ultimate purpose of heating a building
structure or water, or cooling a building by means of absorp
tion refrigeration.
In one form of collector, the flat plate has been
fabricated of aluminum. Aluminum has the drawback of being
subject to electrolysis with resultant corrosion. Unless
careful precautions are taken, aluminum structure may deteri-
orate rapidly. .
In another form, the flat plate and tubular coil are
fabricated of copper which has been considered the best materialfor solar collectors. Copper provides almost twice the conduc-
tivity of aluminum. However, the cost of copper is extremely
high. The total area reguired in many cases may result in t~e
cost of the solar collector being prohibitive. --
Copper collectors usually consist of a hairpin or
s~rpentine (or other) flat copper tubing attached to a copper `~
plate. The coil may be mechanically held against the plate by
means of a clamp~ More often, the coil is soft soldered to the
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plate by means of a lead-tin solder. In either case, the
method of attaching the coil to the plate is considered to be
a bottleneck in the transfer of heat from the plate to the
coil. A mechanical joint does not p~ovidè the best heat trans-
fer connection. Additionally, corrosion, which generally occurs
after a period of use, results in the mechanical joint being
even less effective. The "soft solder" connection also often
used is a bottleneck because the conductivity of lead-tin
solder is only one-eighth that o~ copper and "soft solder"
is also susceptible to corrosion.
Steel has not been extensively used in the past or
solar collector flat plates or tubular coils because of the
generally low heat conductivity properties of steel. In accor-
dance with the present invention, a flat steel plate and steel
tubular coil are used. The steel coil is hydrogen copper brazed
to the flat steel plate. This process results in a fillet o~ -
each side of the tube and a flat pool of copper between the
fillets joining the steel tube and steel plate. me result
is that heat is conducted from the steel plate to the steel
tube at approximately ten times the rate that it would be in
an all copper collector where the conduction between plate and
tube is made through lead-tin solder or a mechanical connection. ~-
While it is true that copper is a much better conductor than
steel, the relatively low cost of steel permits heavier gages
of steel to be used thereby offsetting some of this advantage.
The steel tubes may also be placed closer together thereby
further reducing the advantage of the superior heat conduc~
tivity enjoyed by copper. By this means, the performance
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diffexence between a collector employing copper and a collector
employing steel as the collecting device is practically eli-
minated.
A further advantage of the present invention is that
hydrogen copper brazing is a more economical way to attach a
coil to a plate than is soft soldering. Copper plates and
tubing could not be hydrogen copper brazed because in this
process, the structure is passed through a hydrogen atmos-
phere control furnace at approximately 2100 Fahrenheit. At
this temperature, copper melts which in the nature of things
is desired in connection with brazing steel parts togethar but
would be impossible for use in connection with brazing copper
parts togsthex. Hydrogen brazing is also desirable because it
is a clean process minimizing the necessity to clean the finished
parts. ;;-
In essence, the hydrogen copper brazed steel col- ~;
lector can approach the efficiency of a copper collector and
possibly in some cases exceed such efficiency. However, the ~;
hydrogen copper brazed steel collector is only a fraction of
the cost of a copper tubing and copper plate collector.
The solar collector comprises a housing in which a
steel plate is mounted to absorb sun rays and convert such
rays to heat energy. Steel tubing is secured ko the plate or -
conduction of heat energy from the plate to the tubing. ~he
tubing is adapted for the flow of fluid therethrough to transfer
heat energy from the solar collector to a point of use. A
copper bond is brazed between the tubing and the plate, forming
both a mechanical bond and a heat conducting medium. A
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transparent plate is provided on the housing to permit sun
rays to impinge upon the steel plate.
In the drawing, Fig. l is a top plan view of one
embodiment of the solar collector of the present invention;
Fig. 2 is a sectional view taken substantially along
the line 2--2 of Fig. l ~ooking in the direction of the arrows;
Fig. 3 is a sectional view taken substantially along
the line 3--3 of Fig. l looking in the direction of the arrows;
and
Fig. 4 i9 a top plan view illustrating connection of
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three of the solar collectors of Fig. 1 together to form a
unitary solar collector of greater capacity than a single
collector unit.
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Fig. 5 illustrates another embodiment.
The solar collector lO includes an elongated housing ~
comprising side walls 12, 14, end walls 16, 18 and bottom wall ;
20. These housing elements are preferably fabricated of tr~ted
wood which resists deterioration when exposed to the weather.
The housing is secured together by means of metallic end cor-
ners 22, 24, 26, 28. Screws may be used as fastening devices.
A flat steel plate 30 is provided within the housing
spaced from the bottom wall 20. Heat insulating material 32 is
provided in the space between the bottom wall 20 and plate 30. :
This heat insulation prevents loss of heat from the plate 30
through the bottom of the housing. A steel tubular coil 34 is
attached to the plate 30 by means of hydrogen-copper brazing.
The runs of the coil 34 are closely spaced together to maximize
heat transfer between the plate 30 and the coil. The ends 36,
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38 of the coil are bent upwa~dly slightly to permit connection
to a hose for the circulation of fluid, either a liquid or a
gas, through the coil. Openings 40, 42 are provided in side
walls 12, 14 for insertlon of hoses into the housing for con-
nection to the coil 34.
Referring to Fig. 3, it will be noted that the
copper fillets ~4, 46 are brazed on either side of tube section
48 forming part of the coil 34. These fillets extend for the
entire le~gth of the coil. The fillats provide a mechanical
connection between the coil and the plate. Additionally, the
fillets provide a heat conductor between the plate 30 and coil
34. It will be noted that the fillets are relatively thick,
not only providing the structure necessary to bond the coil to
plate 30 but also additional material to improve heat con~
ductivity between the plate and coil. What is termed a
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"selective surface" 50 is also provided on the surface of
plate 30 when the coil 34 is hydrogen brazed thereto. A
selective surface is a surface provided on a collector plate
to improve the energy collecting ability of the plate. In - ~;
the present instance, this selective surface is also provided
over the coil so that the coil itself may directly absorb sun
energyO
A method for both hydrogen-copper brazing the coil
34 to the plate 30 and also providing selective surface 50 on
the plate 30 and an additional selective surface 52 on the coil
34 is disclosed in United States Patent ~o. 3,432,910. In t~is
method, a copper-containing ~razing material is first provided -~
at the joint of the coil and plate as a relatively thick layer.
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The entire exterior surface of both the plate and coil is then
coated with a copper-containing material in ~inely dividecl form
in a liquid carrier. The assembly is then dried to form a thin
layer of the brazing material in finely divided form over the
entire surface. The asse~bly is then subjected to heat in a
brazing furnace preferably having a reducing atmosphere. The
heating is continued for a time su~ficient to braze the joint
and braze the relatively thin layer to form a continuous coating
over the entire exterior surface of the assembly~ The surface
o the assembly is pre~erably ~irst prepared by roughening or
by uniformly oxidizing before application of the thin layer of
brazing material. This step improves the adhesion of the layer.
The copperized surface thus provided over the plate
and coil result~ in several advantages. First, this surface ~
provides an improved selective surface to prevent re1ection ~;
and to trap the sun's rays causing them to be converted to heat
energy on the collector plate surface. Secondly, the copperized
surface improves the heat conductivity of the plate. ~inally,
the copperized surface protects the steel coil and plate from
corrosion.
Othex selective surfaces may be used. Such other
selective surfaces rnay be applied by a plating process or may
be painted on. For example, a coat of paint may first be
applied to protect the steel against corrosion, a second coat
may be provided to improve the heat conductivity and a final
coat may be provided to prevent reflection and trap the sun's
rays, causing them to convert to heat energy on the collector -
sur~ace.
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A transparent cover plate 54 is secured to the top
of the housing. The plate 54 may be, for e~ample, clear glass
or plastic. Preferably, either the glass or plastic is treated
so as to tend to pass light rays into the collector while re-
sisting passage of reflected rays back through in the opposite
direction. For example, shee~ glazing material such as PVF
film type 400~G20TR, sold by the DuPont Company under the
trademark "Tedlar" may be adhered to the outer surface of
plate 54~
lQ A single layer o~ l'Tedlar" film is satisfactory for
applications where liquid is to laa~e the collector at low
temperatures, such as for use with a solar assisted heat pump.
However, where higher liquid temperatures are required, double
glazing is usually necessary. Preferably the two layers of
"Tedlar" should be separated by a minimum of 1/2", although
little would be gained by separating the layers by over 3/4"~
Individual collectors 10 are readily joined together
in series as shown in Fig. 4 by means of hoses 56, and clamps
58, 60 to form a battery of collectors. If a large number of
collectors 10 are to be connected together in a bank, it is
preferable that they be connected in parallel to reduce the
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pressure drop.
Fig. S illustrates another embodLment which employs
a different type of coil arrangement. The collector plate 64
is the same as previously described and is adapted to be
mounted in a housing as described.
Instead of a serpentine coil as in Fig. 1, the coil
comprises a plurality of spaced apart ~ubes 66 which are
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connected at each end to a pair of manifolds ~8, 70. Fluid ispumped into one of the manifolds, passes through the tubes 66
and is extracted via the other manifold.
The tubes 66 are brazed to plate 64 as previously
described and the surface of plate 64 and tubes 66 may be
copperized in the manner previously descrlbed.
