Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
25~
1 The present invention ~elat2s gener~lly to the
field of solar energ~ utilization apparatus and, more
particularly~ to a solar collector lncluding means for
preventing cover plate ~luid condensation, a sel~-jigging
5 method of ~abricating a solar collector heat trap ~ro~n
flexible plastic roll material~ and an automatic ~reeze
~rate~ion s~stem for use ln such solar energy collectors.
Owing to the energy crisis, a great deal oF research
~o activity is presently being conducted throughout the ~rorld with
respect to solar collectors for heating fluids ~or appl;cations
in the fields of water heating, space heating, air conditioning~
etc., to thereby reduce the quantities of sonventional fuels
consumed. While numerous solar collectors may be found in the
15 prior art, there is a continuing effort to produce collectors
which have very high thermal efFiciencies and yet ~Ihich are
relatively inexpensive to fabricate. The use of inexpensive
materials, and the employment o~ labor saving techniques is o~
paramount importance in facllitating the widespread use of the
20 collectors) and hence, in reducing the quantities oF conventional
fuel consumed.
In accordance with a preferred embodiment of the invention,
a first heat insulating layer having high tempera~ure resistance '
25 characteristics and a second heat insulating layer of plastic
foam material is positioned beneath the planar heat absorbing
~
.,
5 ~
member of a solar collec~or, ~Ihich in turn is positioned beneath
a heat trap having walls of polyethylene terephthalate ~or in
hibiting the production of convection currents within the cells
and radiation losses. A cover glass or window of soda lime glass
is employed to retard heat loss and to prevent ultraviolet
radiation from discoloring the polyethylene tereph~halate walls
of the heat traps, The first heat insulating layer prevents
the polyurethane foam from assuming a temperature level which
causes the release of toxic flu-ids which may form condensation
on the inside of the window to thereby reduce thermal efficiencies.
The heat trap support means are made of materials having low
heat conductivity, thereby to inhibit heat loss due to con-
ductivity. The use o-f polyester film for ~or~ing the wa71s o,
the heat trap in combination with the above-mentioned first and
second insulating layers, together with heat trap support means
o~ low heat conductivity, results in extre~ely high efficiencies.
Furthermore, these materials have been carefully selected to
maintain costs at a minimum, thereby to increase the market which
2Q in turn results in lower consumption rates of conventional fuels.
ln accordance with a preferred method oF the present in-
Yention, a method of fabricating wall por~ions of the cells of
a solar energy heat trap is carried out by winding a unitary
;~rip of flexible wall material, preferably polyethylene
25 terephthalate, about rows of dowels positioned a-t opposite
âi des of the frame of the solar collector. A roll of the
,^lexible wall material is passed back and forth between oper-
ators stallding at opposite sides of the collector frame, and
~ 2~ ~
1 the wall material is wrapped about one D, tne dowels associ~t2d
with one side of the frame and is passed back to ~he other
operator who wraps the wall material abou~ another dowel asso-
ciated with the oppos;te side of the frame. Just after the
5 wrapping s~ep, the operator inserts the do~lel into a receptor
channel positioned along the side of the frame, and therea,ter
passes the roll to the other operator, and as a result, elongated
heat trap cells are produced by zigzagging the ~aterial across
the collector about the dowels Optionally, an adjustable com-
10 pression member is positioned across the collector to push thedowel receptor channels away from each other to maintain tension
in the flexible wall material after a given section o, the heat
trap has been fabricated~ khereby to prevent wall sagsing and
the resulting loss in transmittance of the solar energy ihrougr,
15 the heat trap.
Another aspect of the present in~ention is dir~cted
towards a problem which is encoun~ered in cold weather climates.
Specifically, in thoEeareas wherein outside temperatures may
drop near or below the ~reezing point of water, some ~orm o~
20 protec~ion must be provided to prevent water ~rom freezing up
within the collector or within the plumbing leading to and
~rom the collector as its expansion by ~reezing can obviously
cause very severe damage to the entire system.
One solution to this proble~ which has been susgested
2~
in the prior art is to add anti-free~e to the water in the C31-
lector. Anti-~reeze, however, is not only expensive in and of
~0
- 4 -
. .
æs~
1 itself, but it is also poisonous and, accor~ingly, ~hen used,
necessitates the addition of costly safety equipment to ensure
that Ihe anti-freeze/water solution will not enter into the main
~Yater supply of the home of other building. For example, it is
usually necessary to isolate the anti-freeze/water m;xture from
the ma;n water supply by maintaining it in a closed loop system,
and to then ùse the heated anti-~reeze/water mixture to heat the
main water s~pply through appropriate heat exchange means. This
will not only raise the cost of the system9 but ~Jill also lo~ler
0 its efficiency. Furthermore, notwithstanding the isolation of
the anti-freeze/~later mixture, there is always some danger that
a certain amount of leakage into the main water supply could
occur. For this reason, some states have forbidden its use in
solar energy systems.
Yet a further disadvantage of such systems is the
fact tllat, although the anti-freeze/water mixture will not
freeze, it can drop to quite a low temperature during the ni~ht.
Accordingly~ when the sun comes up in the morning and begins
hea~ing the water, substantial time is needed rO heat the cold~
fluid to a usable temperature, and this also results in a sig-
nificant loss in efficiency.
In accordance with the present invention, a solar
energy collector system that avoids many of the inadequacies
inherent ln the prior art is provided. Specifically~ in accord~
ance w,th the present invention, a system is provided that aYoids
the need for anti-Freeze and, hence, of the closed loop ~ater
system, heat exchangers, and other desirable safety eguipment
- 30
5 -
~ ~ 6 ~ ~ ~
1 necessitated thereby. Instead, with the present invention, only
a single water circulating system is required with water circu-
lating from the collector directly into a water heater ~or
storage or utilization.
In order to prevent the water from free~ing up in the
collector when the temperature drops near or below the ~reezing
point, an automated freeze protection system is provided. Speci~
fically, a temperature sensor is supported, preferably within
the collector, and when the temperature ~ithin the collector
approaches the freezing point of water, the sensor will auto-
matically actuate appropriate valYe means to rapidly drain the
water from the collector. This normally will occur only at
night or on very cloudy days when there is no available sunlight,
so that there is essentially no loss in operating e~ficiency
as compared with more conventional systems. ~Ihen the te~pera-
ture in the collector thereafter rises to a predetermined level,
the sensor means will a~ain automatically actuate the valve
mèans to ref;ll the collector with fresh water and the system
20 will be back in operation.
Thus, the present invention proYides a ~ully automated
system that will permit effeGtive solar energy collection, while
at the same time, avoid the need for anti~freeze and ihe expens~
and risks introduced thereby.
%~
A further advantage obtained is that the water used
to refill the collector can be ordinary ho-use water which is
usually at a temperature of about 50F. Thus, the water will
be relatively warm to start with and, accordingly, can more
rapidly be heated up by the sun to utilization temperatures
than a fluid that may have been subjected to sub-freezing
temperatures for several hours. Yet other features and
advantages of the invention will be set out hereinafter in
conjunction with the detailed descrip-tion of the drawings~
Other objects, features, and advantages of the
present invention will become apparent upon the perusal of
the following Detailed Description taken in conjunction with
the drawings in which:
FIG. 1 discloses a portion of a solar collector
assembly;
FIG. 2 illustrates a plan view of the collector
fabricated in accordance with the teachings of the present
invention;
FIG. 3 discloses a side sectional view of the
collector of the present invention; and
FIG. 4 illustrates, in schematic form, the freeze
control system according to a presently most preferred
embodiment of the invention.
In FIG. 1, a cover plate or window 1 i5 positioned
above heat trap 2 which is formed of wall members 3 which make
up the cells of the heat trap. Absorber 4 is positioned beneath
the heat trap, and typically includes pipes 6 containing fluid
which is pumped through the absorber and is heated by solar
radiation which passes through the heat trap. The widths of
the heat traps are typically 3/8" to inhibit radiative losses
and the formation of convection currents to maintain the air
in stagnant condition9 thereby to reduce thermal loss.
In FIG, 2, a first side 7 of the collector frame includes
a first receptor means or channel 8 (shown more clearly in
FIG. 3), and a second side of the collector means 9 includes a
second receptor means or channel ll for receiving and support-
ing the heat trap wall support members. In heat traps fabricated
in accordance with the teachings of the invention, the flexible
wal1 material forming the wal1s of the cell are wrapped about
rows of wall support members, which in the particular embodi-
ment illustrated consist of wooden dowels. A first row of
15wooden dowels l2 on one side of tne collector and a second row
of wooden dowels l3 on the other side of the collector support
the wall members 10 which make up the cells of the heat trap.
These cells are built up by positioning one operator at one
side of the collector frame and a second operator at the
opposite side of the collector frame. A roll oF plas~ic sheet
material, pre~erably pol~ethylene terephthalate, marketed under
the trademark "~IYLAR," having a thickness of approximately .OOl"
and a width of ~roximately ~" is passed back and forth across
25 the heat trap by the operators. As each operator receives the
roll of plastic, she wraps the plastic about a dowel held in her
hand to produce a 180 turn and just after this wrapping step,
tilts the dowel SQ that it may be inserted within the dowel
~ 8
. . .
1~3962SB
1 receptor channel. She thereafter straight2ns ~he dowel so -that
it is vertical.ly oriented within the channel and so that it
cannot be pulled out oF the channel by the creation of tension
in the plastic sheet material. She -then inserts a spacer do~/el
in a similar manner to provide proper spacing~ In other ~ords,
every other dowel in each row oF dowels functions as a spacer
and does not support tape. The process is repeated as the
plastic roll material is zigzagged back and forth across the
col1ector. Upon the completion o~ a section of a heat trap,
0 optionally, a square locking dowel may be inserted into the
receptor channel and tension is induced within the plastic ro~l
material preferably by means of a compression member 14, ~Jhich
is positioned between the wall support member receptors or
channels, as illustrated in FIG. 2. Other tape locking means
15 may, o~ course~ be employed. Compression is induced by the
relative rotation o~ threaded member 16 with respect to associa~ed
threaded members which could comprise nu~s t7 and 18. ~he
result of the above-described ~abrication method is that a
highly efficient heat trap is rapidly and inexpensively fabri
cated, the trap having walls which do not droop (to provide
maximum solar transmission3 owing to the tension which may be
easily induced within the plastic sheet material, the material
being readily available and relatively inexpensive. ObviOuâly,
other wall support members may be employed rather than elongated
~ 5 ~
1 cylindrical members such as dowels, and o~her receptor means may
be utilized other than the above-described channels. ~owever,
the above-described arrangement is greatly preferred since the
elongated wall support members are automatically aligned in
proper position without receptor holes, ror example, or o~her
individual mounting means. The me-thod has the advantage of
being self-jigging. It is preferable that the dowels actually
contact one another. The elimination of individual receptor
means for each wall support member reduces manuFacturing costs,
wnîch is of prime importance with regard to the mass ~arketir.
of solar collectors.
The use of commercial grade polyurethane foam for insula~ing
the lower portions of the solar collector is greatly preferred
to reduce manufacturing costs. One drawback of this material
t5 is that it releases toxic fluids when the foam exceeds pre-
determined temperature levels to produce a safety hazard. Con-
densation of the -fluid upon the underside of the window will
also reduce solar energy transmission through the window.
This problem has been overcome by the in~entor by adding a layer
of heat insulating material o~er the polyure~hane -foam layer and
under the heat absorber. Such layer insulates the polyurethane
foam which generally maintains the temperature of the foam belo~
the predetermined temperature which causes the release of toxic
fluids. The preferred material for the first layer is fiber-
glass which is employed along with polyurethane on the collectors
sold in the marketplace. The preferred thickness di~ensions are
approximately 1" for the first layer and approximately 3" for
the second layer.
_ 10 --
~ 6~ ~
1 In FIG. 3, the ~irst layer of insulating material 21 is
shown positioned beneath heat absorber 22 ~,Ihich contains a
fluid passage 23. The second insulating layer 24 is positioned
~eneath first insulating layer 21 to insulate the absorber to
prevent heat ~low through the lower portions of the solar
collector This ~oam material is also positioned along the
sides of the collector as is shown in FIG. 3 at 26. One of the
above-mentioned dowels 27 is shown positioned within channel
portions 28 and 29, to be maintained in position as shown. A
wall portion of the above-mentioned so~ar cells 31 mad2 o,
plastic roll material, is illustrated in position, wrapped
about dowel 27.
It has been found that the use of a very thin flexible
polyethylene terephthalate in roll form readily lends itself
to the rapid production of the cells in accordance with the
above~mentioned fabrication technique. Additional7y~ through
experimentation, it has been found that this particular plastic
material has exceptionally hi~h solar transmittance and reflec-
20 tance characteristics. However, one of tne disadvantages OTthis material is that it discolors upon being exposed to sun-
light which could result in reduoed solar transmittance upon
aging. Expressions o~ disbelief of the practicality of using
this material have been voiced to the manufacturer of the dis-
25 closed collector. In order to eliminate this drawback, ~ window
,
- 1~
1 oF soda lime 91ass 32 has been employed in order to filter oilt
ultraviolet radiation which is believed to be tne principal a3~nt
in causing~such discoloration. A-fter a six month e~posure to
the sun o~ thè collector fabricated in accordance with the above-
mentioned techniques~ it has been observed that no discolora~ionhas been produced.
Thermal efficiencies ranging between 51% and 66% have
actually been obtained in rooftop mounted collectors fabricated
in accordance with the present invention, and thus~ it should
1~ be apparent tha~ the teachings set forth a~ove result in highly
marketable, efficient, and inexpensive units. Efficiencies
above 80% are believed obtainable by these collectors.
An additional feature of the ahove-described solar collector
is the use of non-metallic components in the interior portion,
~5 of the collector in order to reduce heat loss through c.onduct,on;
for example, the dowels are preferably made cf wood Tne ~em~er
20 sho~Yn in FIG. 3 ~Yas made of masonite.
The term polyethylene terephthalate used herein is intended
20 to cover other materials having the following characteristics:
The capability of withstanding temperatures or
300F without significant deformation.
Minimum tensile strength to withstand a one
pound force pulling on a 4" wide tape of a thick-
ness of ,001" ~50 pounds per square inch).
The material should be optically clear.
- 12 -
58
1 Figure 4 illustrates~ in schematic form, the auto~
matic freeze protection system according to a presently pre
~erred embodiment of the invention. Reference number 110
identifes the solar collector which is mounted outside the
5 house or other buLlding to receive the heating rays of the
sun. Its specLfic construction is not important to the
present invention and any one of a number of collector ~esigns
~ay be employed. One suitable collector, however, is described
in detail with regard to Figures 1 to 3 of the drawings.
The s~stem, as illustrated in Figure 4, further
includes a plumbing system for carrying water to and ~rom
the collector as required. Specifically, the system includes
a cold water inpu-t line 111 for carrying water from a source,
not shown~but conveniently from an ordina~y city ~ater line~
into the solar collec-tor to be heated; and a hot water output
line 112 for carrying heated wa~er out of ~he collector to
a hot water tan~ 113 for storage and utilization through pipe
114 as i.s understood in the art. In ordinary operation, hot
water ~rom the collector will be trans~erred to the tank 113
through line 112 from lines 123 and/or 122 as needed and be
replaced by fresh water from line 111 and lines 122 and 123
in a conventional manner whic'n need not be discussed in detail
herein.
Because anti freeze or other harmful or potentially
harmful materials are not used in the present invention, the
heated water in the collector can be directly util;zed in any
desired manner as discussed above.
..
2~i~
Because anti-Freeze or the like is not used, however,
and because the collector and some of the plumbing is located
outside in a potentially cold weather area (as indicated in
FigureL~),it is necessary that the water be prevented from
5 freezing up as ~his will cause severe problems. Thusg the
present invention provides an automatic freeze control system
'or this purpose. Specifically~ the present invent-ion provides
a sensor means 116mounted within the collector to continuously
monitor the temperature therein. Sensor 116 is ~lectrically
coupl ed through el ectrical coupl ing 115 to a doubl e 3-way sol enoid
valve operatorll7 which, in turn, actuates valves 118 and 119 in
the input and output linesll~ andll2 oF the collector.
Whenever the temperature within the col l ector approaches
a precietermined level near the free~ing point oF water, e.g.,
around 38-4G~F, sensorll6 will autamatically actuate opera~orll7
to move valves 118 and119 to the position to drain the collector
through drain pipel21 via linesl22,123 andl20. Once drained,
the collector and plumbing is, of course, in no dan~er of being
damaged by freezing temperatures.
In order to ensure that the water will drain rapidly
and smoothly ~rom the collector, an insulated air relief valve
~4(e.g., a ball valve), is provided and is mounted at the
highest point of the system to allow air to enter into the water
l i nes to hel p dra i nage .
- 14 -
z~
l As long as the temperature in the collector remains
below a safe level, the collector will remain drained and inopera-
tive. When, howeverS the temperature rises to a certain pre-
determined safe level, e.g., 40-50F, sensor 116~ill again auto-
5 mat;cally actuate operatorll7 ~o return valves 118and 119 to their
operating position wherein the collector will be refilled with
water through lines1~ 112 and/or123 for normal operation. Air
relie~ valve 124 is also positioned to allow air lo escape fro~
the collector during refilling -to avo;d the ~ormation of air
pockets in the system.
Thus, the system provided will rapidly and automa~ically
drain the collector wheneYer the temperature therein drops to a
first predetermined danger level, and will thereafter auto~ati-
cally refil7 the collector for operation when ~he temperature
15thereafter rises to a second predetermined safe level.
The sensor 116 itself may take 2 Yariety of for~s. In
the present embodimentl it comprises a bimetallic disc sold by
Te~as` Instruments~ Inc. under the tradename "Klixon". When the
temperature drops to the -First predetermined level, ~he disc will
snap away ~rom a contact to open the circu;t to the operator
117and cause ~he valves to switch and drain the collector.
When the temperature thereafter rises to the second predetermined
level, the disc will automatically snap back to close the switch
and return the valves to their operating posi-tion. In other
words, the sys~em is designed such that the circu;t between the
sensor and the valve operator is closed and the solenoid valves
are actuated dur;ng normal operating conditions~ while the cir-
- 15
~6~
l cuit will be open during periods when the collector is drained
and not operatir,g. This is an important feature because should
a power failure occur, the valves will automatically drain the
collector to ensure against the accidental freezing o~ ~later
5 within the collector during such periods.
The sensor is pre~erably positioned in the co7lector
near the bottom thereof and close to the water lines whete the
coldest temperatures will be encountered.
In summary, the present ;nvention provides a highly
lO efficient solar energy system designed for use in cold weather
climates. The system provided avoids the need ~or anti-freeze
or other materials to prevent water freeze-up, and, in doing so,
also eliminates ~he need for a closed loop water system in the
collector as suggested in the prior art9 together with heat
exchangers to transfer heat from the collector water io the
house water~ as well as other safety equipment often necessitated
by the use o~ anti-free~e. Because heat exchangers are not
needed, greater efficiency is obtainable at reduced expense.
2~ I~!hile what has been described is a presently most
preferred embodiment, it should be recognized that the inven-
tion may ta~e many other forms. For example, the system could
also be provided ~lith appropriate by-pass lines to by-pass the
valves 118and ll9. These lines can be manually lnserted into
25 -the fluid circuit during the cummer months when there is no
danger af freezing. This will permit the solenoid valves to
~ 16 -
.
$ ~
be shut off for energy conservation. Also, it should be under-
stood that many other types of valves and sensors could be used
w;th the invention if so desired. Finally, it should be empha-
sized that the invention can be used in a wide variety of appli-
5 cations in addition to domestic hot water systems. For eY~ample,it could conveniently be employed in pool heating, space hea ing
and other-app1ications.
1~
26
