Solar collector

A solar collector having a blow-molded frame and an integral absorber plate. The frame is larger in thickness than is the thickness of the absorber plate portion. The absorber plate portion of the blow-molded part has a channel system molded therein for conveying a liquid therethrough. The blow-molded part has rigidifying sections therein to enhance the stability of the solar collector.

FIELD OF THE INVENTION 
The invention relates to a solar collector for collecting the radiant heat 
energy of the sun and for transmitting this heat to a liquid heat carrier, 
in particular water, comprising a pipeline system, which has at least one 
supply port and one discharge port, for conducting the heat carrier 
therethrough and preferably a glazing for example of glass, which permits 
heat radiation to pass therethrough and the pipeline system is part of a 
platelike blow-molded absorber plate made of plastic, in which adjacent 
pipes are separated from one another by thermoplastically welded mash 
seams. 
BACKGROUND OF THE INVENTION 
Usage of solar collectors is becoming more and more widespread in view of 
the energy problems which are slowly becoming known. Solar collectors are 
particularly suited for the house technique for heating up of water to be 
used and for heating up of water for warm-water heating systems. However, 
the thermal yield, in relationship to the unit area of a solar collector, 
is not very great, in particular in regions in which there is not much 
sunshine. However, particularly in these moderate and colder regions much 
heat energy is used up. In order to replace an amount of the energy 
consumption, which amount is worth mentioning, with solar energy, solar 
collectors must have relatively large surface areas, for example several 
square meters for a one-family house. The building costs of heat-producing 
systems with solar collectors are considerable. Even though operating 
expenses are hardly created, the profitableness of such systems is still 
low because of the high capital investment. For a better profitableness, 
it is important to manufacture solar collectors as inexpensively as 
possible. 
Various forms of solar collectors are known, for example those which have a 
dark-colored pipeline system, through which a liquid is moved. The liquid 
is heated up by the radiant heat energy of the sun and a reflection is 
substantially avoided by the dark coloring. The mentioned glazing prevents 
the heat which is absorbed by the collector from being radiated back. 
A pipeline system can be manufactured particularly inexpensively with the 
aid of a blow molded absorber plate. The manufacture of a pipeline system 
from a blow-molded part is known from German OS No. 24 44 706 for a 
flat-heating element and can in principle also be utilized in a solar 
collector. 
To achieve a further reduction in price during the manufacture of solar 
collectors, the basic purpose of the invention is to design a solar 
collector, in which the pipeline system is formed by a blow-molded 
absorber plate so that aside from the blow-molded absorber plate, the 
glazing and possibly heat-insulation material, no further parts are needed 
for the actual solar collector. 
This purpose is attained according to the invention in such a manner that a 
hollow frame which is made of one piece with the blow-molded absorber 
plate is formed on the edge of the plate-shaped blow-molded absorber 
plate, which frame has a closed cross section. 
Such a collector is extremely inexpensive, because the support 
construction, in which the pipeline system is arranged, consists of one 
piece with this pipeline system and is manufactured during the same 
operation. It is only still possible to mount on the blow-molded absorber 
plate a glazing and possibly on the back side thereof heat insulation 
material. Further operations are not needed. Because of the inexpensive 
manufacturing possibility, it is possible to provide also large surface 
areas at an affordable price. With the aid of the invention because of a 
strong reduction of the building costs, the feasability of heat-producing 
systems utilizing solar collectors is improved considerably. The hollow 
frame which is formed on the edge of the blow-molded absorber plate has a 
sufficient stability to hold a relatively large collector surface, for 
example a collector surface of approximately 1 m.sup.2, reliably in its 
mold. 
Grooves are preferably provided in the frame. As a result, the glazing 
plate and/or an insulation layer can be mounted and held comfortably in 
their correct position, without requiring special aligning operations. The 
glazing which is permeable for the heat radiation is spaced as a rule a 
certain distance from the pipes of the pipeline system to define an air 
space therebetween, for which reason a fluted mortise has a suitable 
position relative to the pipes. The insulation layer, however, can rest 
directly on the pipes or it may have also a certain spacing therefrom. 
Fluted mortises are not absolutely necessary, because a glazing or an 
insulation layer, for example could rest on the upper side or the bottom 
side of the frame. 
The arrangement of support projections has the advantage that the solar 
collector has as a whole a greater rigidity. Also this prevents 
large-surface glazings from sagging in the midsection. The arrangement of 
the support projections will be chosen in accordance with the respective 
size, form and remaining structure of the collector. The collector may 
have any desired basic forms. In most cases one will choose a basic 
rectangular form. However, the invention is not limited to this. To adjust 
to special surface relationships, it is also possible for other forms to 
be advantageous. 
Fastening holes are mounted preferably on the corners of the frame. 
However, this is also not absolutely necessary. It would also be possible 
to hold a collector for example also with clamps or other fastening 
elements, which do not extend through the blow-molded absorber plate, but 
only grip around same. 
The pipeline system may be designed differently. For example a zigzag 
channel 7 is preferable. 
A particularly preferable manufacture of a solar collector can be achieved, 
as stated above, by the blow-molding process. The communication between 
the cavities during the manufacturing process has the advantage that blown 
air needs to be supplied at only one single point. However, it is also 
easily possible to provide several supply points. The cavities then do not 
need to communicate with one another, if to every connected cavity an air 
supply is connected. 
The form of the frame results in a particularly good rigid structure 
crosswise of the frame plane. Since solar collectors are generally 
arranged lying inclined to the vertical, for example on a roof surface, 
rigidity in this direction is particularly advantageous. Also a thin frame 
takes up little surface so that the surface which is utilized for the 
production of heat is not reduced too much by the frame. 
The inventive solar collector has also the advantage that it is 
particularly lightweight. This again has an effect on the entire building 
costs of a heat-producing system because the solar collector applies only 
a small load to a support structure, for example the roof construction of 
a house, and this roof construction can be constructed correspondingly 
with a smaller load factor. 
As a material, plastics of any kind which can be worked in the blow-molding 
process can be used if they are sufficiently resistant to the 
deteriorating effects of the sun's radiation. Black-colored polypropylene 
is well suited.

DETAILED DESCRIPTION 
As can be seen from FIG. 2, the solar collector consists of a blow-molded 
absorber plate which is identified as a whole by the reference numeral 1, 
a glazing 2 and an insulation layer 3. The collector has as a whole a flat 
rectangular shape (see FIG. 1). In the present relationship of width and 
length to thickness, one can speak of a platelike part. 
The blow-molded absorber plate 1 forms simultaneously a pipe system which 
is identified as a whole by the reference numeral 4 and which is 
constructed in one piece with a plate portion 5 and a hollow frame portion 
which as a whole is identified by the reference numeral 6. 
The pipe system has a long zigzag channel 4a extending back and forth 
across the width of the collector along the length thereof. Long sections 
of the channel 4a extend parallel to the short side of the rectangular 
collector, while short channel sections, which connect the long sections, 
extend parallel to the long sides thereof. An end section 4'a of the 
channel 4a is connected to a collecting pipe 8 through connections 7 
extending perpendicular to the section 4'a and pipe 8. The entire solar 
collector is symmetrical with respect to the dash-dotted line 9 extending 
midway along the length and parallel to the short sides so that a 
collecting pipe which corresponds with the collecting pipe 8 is provided 
also at the other end of the collector. 
The collecting pipe 8 terminates at its two ends in openings 10 in the 
plate 5. Sockets 11 extend from said openings 10 and terminate in the 
cavity of the frame 6. The formation of these sockets will be discussed 
with reference to the description of the manufacturing process. 
Three support projections 12 and 13 are provided in the longitudinal center 
of the solar collector, which center is defined by the dash-dotted line 9. 
As can be seen from FIG. 2, the support projection 12 extends to the 
underside 2a of the glazing 2, while the support projections 13 extend to 
the inner surface 3a of the insulation layer 3. In order to make room for 
the support projections 12 and 13, two adjacent sections of the channel 4a 
are arranged in the center of the collector at a slightly greater distance 
than in the remaining area of the collector. 
The cross section of the frame can be taken from FIG. 2. The height or 
thickness h of the frame is greater than its width b. This results in a 
good rigid structure, particularly transversely to the general plane of 
the solar collector. Fluted mortises 14 and 15 exist along the inside of 
the frame. The fluted mortise has a contact surface 14a for the edge zone 
of the underside 2a of the glazing 2 and a peripheral surface 14b, which 
centers the glazing 2 on its edge 2b. The glazing can be secured to the 
frame for example by gluing or cover strips. 
The fluted mortise 15 has suitable surfaces 15a and 15b, which has in 
cooperation with the insulation plate 3 the same purposes as the 
corresponding surfaces 14a and 14b of the fluted mortise 14. 
Starting out from the center plane of the collector, which plane is 
indicated by the dash-dotted line 16 (FIG. 2), the sections 17a, 17b and 
the surfaces 14b and 15b converge outwardly in order to comfortably permit 
the opening of the blow-molded absorber plate. 
A lug 18 is provided on each corner of the frame and has a fastening hole 
19 therein for receiving a fastening element, for example a screw. The lug 
18 has no cavity and is manufactured of two layers of material which are 
pressed onto one another and are connected by mash welding, just as in the 
case with the plate 5. The lugs 18 lie in the same plane as the plate 5. 
The blow-molded absorber plate is manufactured as follows: 
When the mold is open, a tube of plastic is extruded into the mold, as this 
is common in a blow-mold process, which tube is made preferably of a 
black-colored polypropylene. After the extrusion of the tube, the mold is 
closed when the tube is still in a plastic state, by squeezing the tube 
off at the top and bottom. The joint line of the mold which is not 
illustrated in the drawings is in the plane which is indicated by the 
dash-dotted line 16. 
After the mold is closed, pressurized air is introduced, for example at a 
point in the outer frame 6. Due to the pressurized air, the still flexible 
and formable and weldable skin of the extruded tube is pressed against the 
walls of the mold. Where there are no cavities in the mold, two material 
layers, for example the material layers 5a and 5b, are welded together. 
Where cavities exist, a welding does not take place, namely the mold 
cavities are lined by the material of the extruded tube. While two 
material layers are welded together where there are no cavities, only one 
material layer exists where cavities exist. 
In the illustrated exemplary embodiment, all cavities communicate with one 
another during the manufacture thereof. During the blowing operation, the 
collecting pipes 8 are connected to the cavity 6a of the frame 6 through 
pipe sections 20 which are illustrated by dash-dotted lines. Therefore, 
one single connection point for the blown air is sufficient. After the 
plastic has remained for a certain period of time in the mold, it becomes 
cooled and rigid enough so that the absorber plate is inherently stable 
and can be removed from the mold. Windows 10 are now punched out at every 
corner and the dash-dotted pipe sections 20 are cut out. Only the already 
described sockets 11 remain. As a result, the cavity of the pipe system 4 
is separated from the cavity 6a of the frame so that a connection to the 
pipe system is now possible. The ports 21 which are shown in FIG. 1 are 
the supply ports. Discharge ports 21A are provided at the lower end. 
After the blow-molded absorber plate is finished so far, the insulation 
plate 3 and the glazing plate 2 can be installed. They can be easily 
installed because they are centered in the mortises 14 and 15. The support 
projection 12 extends upwardly so far above the plate 5 that its end 
surface 12a rests on the inside surface 2a of the glazing 2. The 
projections 13 have such a height that their end surfaces 13a rest on the 
inside surface 3a of the insulation plate 3. 
Hoses or solid pipes are connected to the supply ports 21 and the discharge 
ports 21A prior to a mounting of the glazing, said pipes being guided 
through the frame. As a result, outer pipe connections are formed, with 
which the solar collector can be connected into a pipeline system. It is 
also possible to directly create the connection to an adjacent collector 
through a piece of hose or a section of a pipe. 
Although a particular preferred embodiment of the invention has been 
disclosed in detail for illustrative purposes, it will be recognized that 
variations or modifications of the disclosed apparatus, including the 
rearrangement of parts, lie within the scope of the present invention.