CA1117834A - Solar heater with integral heat trap glazing - Google Patents
Solar heater with integral heat trap glazingInfo
- Publication number
- CA1117834A CA1117834A CA000307619A CA307619A CA1117834A CA 1117834 A CA1117834 A CA 1117834A CA 000307619 A CA000307619 A CA 000307619A CA 307619 A CA307619 A CA 307619A CA 1117834 A CA1117834 A CA 1117834A
- Authority
- CA
- Canada
- Prior art keywords
- solar
- solar heater
- front wall
- heater according
- radiation
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F24—HEATING; RANGES; VENTILATING
- F24S—SOLAR HEAT COLLECTORS; SOLAR HEAT SYSTEMS
- F24S10/00—Solar heat collectors using working fluids
- F24S10/70—Solar heat collectors using working fluids the working fluids being conveyed through tubular absorbing conduits
- F24S10/75—Solar heat collectors using working fluids the working fluids being conveyed through tubular absorbing conduits with enlarged surfaces, e.g. with protrusions or corrugations
- F24S10/755—Solar heat collectors using working fluids the working fluids being conveyed through tubular absorbing conduits with enlarged surfaces, e.g. with protrusions or corrugations the conduits being otherwise bent, e.g. zig-zag
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F24—HEATING; RANGES; VENTILATING
- F24S—SOLAR HEAT COLLECTORS; SOLAR HEAT SYSTEMS
- F24S10/00—Solar heat collectors using working fluids
- F24S10/80—Solar heat collectors using working fluids comprising porous material or permeable masses directly contacting the working fluids
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F24—HEATING; RANGES; VENTILATING
- F24S—SOLAR HEAT COLLECTORS; SOLAR HEAT SYSTEMS
- F24S80/00—Details, accessories or component parts of solar heat collectors not provided for in groups F24S10/00-F24S70/00
- F24S80/50—Elements for transmitting incoming solar rays and preventing outgoing heat radiation; Transparent coverings
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F24—HEATING; RANGES; VENTILATING
- F24S—SOLAR HEAT COLLECTORS; SOLAR HEAT SYSTEMS
- F24S80/00—Details, accessories or component parts of solar heat collectors not provided for in groups F24S10/00-F24S70/00
- F24S80/50—Elements for transmitting incoming solar rays and preventing outgoing heat radiation; Transparent coverings
- F24S80/56—Elements for transmitting incoming solar rays and preventing outgoing heat radiation; Transparent coverings characterised by means for preventing heat loss
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E10/00—Energy generation through renewable energy sources
- Y02E10/40—Solar thermal energy, e.g. solar towers
- Y02E10/44—Heat exchange systems
Landscapes
- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Sustainable Energy (AREA)
- Life Sciences & Earth Sciences (AREA)
- Physics & Mathematics (AREA)
- Sustainable Development (AREA)
- Thermal Sciences (AREA)
- Combustion & Propulsion (AREA)
- Mechanical Engineering (AREA)
- General Engineering & Computer Science (AREA)
- Dispersion Chemistry (AREA)
- Laminated Bodies (AREA)
- Lining Or Joining Of Plastics Or The Like (AREA)
- Central Heating Systems (AREA)
- Photovoltaic Devices (AREA)
Abstract
SOLAR HEATER WITH INTEGRAL
HEAT TRAP GLAZING
Abstract A solar heater including a housing having a combined transparent front wall and heat trap, a radiation absorbent collector element positioned in the housing and arranged to accept incident solar radiation passing through the front wall, and means for passing a fluid medium to be heated through the housing in heat transfer relation-ship with the collector element. The combined front wall and heat trap are integrally formed in one piece from glass or a clear plastic composition which is opaque to infrared radiation emitted from the collector element.
S P E C I F I C A T I O N
HEAT TRAP GLAZING
Abstract A solar heater including a housing having a combined transparent front wall and heat trap, a radiation absorbent collector element positioned in the housing and arranged to accept incident solar radiation passing through the front wall, and means for passing a fluid medium to be heated through the housing in heat transfer relation-ship with the collector element. The combined front wall and heat trap are integrally formed in one piece from glass or a clear plastic composition which is opaque to infrared radiation emitted from the collector element.
S P E C I F I C A T I O N
Description
~7~3~
BACKGROUND OF THE INVENTION
I. Field of the Invention The present invention relates broadly to solar heaters which convert incident solar radiation into heat energy and transfer the absorbed heat ei~her to a gas such as air or a liquid such as water, the former being commonly referred to as a solar air heater and the latter being commonly referred to as a solar ~: water heater. More particularly, the present invention relates to solar heaters o either type which employ a heat trap between the absorber and the light-transmitting front wall.
II. Description of the Prior Art Various proposals have already been made in the prior art for employing a heat trap between the absorber and the front wall of a flat plate solar heater in order to reduce heat losses by natural con-vection and radiation. An example o~ the foregoing wherain a transparent honeycomb heat trap is used may be found in an article by Hollands entitled, "Honeycomb Devices in Flat Plate Solar Coll~ctors'9, Solar Energy, Vol. 9, pp. 159-169, Pergamon Press (1965).
One problem encountered with such proposals is that it may as a practical matter be necessary to provide space between the honeycomb heat trap and the front wall to allow for diferential thermal expansion o~ the solar heater elements. It has been found, however, that the presence of such a space can increase the heat loss by ~L~17~34 natural convection to the front wall. This lncreased heat loss results from the development of-natural convectLon currents be~ween adjacent cells of the honeycomb structure.
It has been observed in the results of recent work by Edwards, e~ al., in "End-Clearance Effects on Rectangular-Honeycomb Solar Collectors"
presented at the 1975 International Solar Energv Gongress and ~xposition, July 28 - August 1, 1975, UCLA, Los Angeles; also published in Solar Energy, Vol. 18, i~ pp. 253-257, Pergamon Press (1976), that this increasein heat loss may be reduced by providing a cpac~
between the honeycomb heat trap ~nd the fla~ plate . ~:
. - absorber rather than between the heat trap and the - front wall. The difficulty with this proposal, however, -~ is that the honeycomb must of necessity be made with relatlvely thin walls in order to act as an efficient heat erap and, consequently, the honeycomb is either ;~ too flexible to ~e self-~upporting if made of clear plastic or extremely fragile if ~ade of glass and, therefore, separate means for ~upporting ehe honeycomb struc~ure over lts e~tire area must be-provlded.
It has al o ~een proposed in the prior art to employ a honeycomb or other open cellular structure in contact with the front wall ~o act es a radiation trap and ~ir ~uffer in ~ transpiration solar air heater. Thus, in our cope~d~ng ~pplic~tion Canadiarl Serial No. 307,618 filed on even date herew~th and a~signed ~o the con~non ~signee hereo~" there i8 disclosed and claimed a 3~ transplration ~olar ~Ir heater wherein the cellular ~, radiation trap is held in at least firm mechanical contact with the front wall in order that it may sdditionally act as an air buffer layer. It has been demonstrated by experimental work, as reported in our co-pending Canadian application, that a significant improve-ment in thermal efficiency i~ attained when the radiatlon trap is held finmly in contact with or is actually bonded to the front wall. When the radiation trap, on the o~her hand, ~ only loosely held in place adjacent to the front wall, the problem arises that convection currents may pass through the heat trap and contact the front wall where heat losses may occur.
In the case of both the flat plate solar heater and the transpiration solar air heater described above, the heat trap may be supported in contact with the front wall by one or more rigid bars below the cellular or honeycomb heat trap or by the provision of adhesive joints between the heat trap and the front wall.
Although this type of support means effectively solves the problem of oonvective air flow throug~ the heat trsp, the drawback of support means of this type is that the bars or ~dhesive joints or other support elements lntroduce additional surfaces from which incident solar rays ~ay be re1ected or scattered in a direction away from the solar absorber and be lost.
SUMMARY_OF~ INVENTION
The present invention is directed to a novel ~nd improved solar heater which overcomes the above enumerated problems in either a flat plate solar hester . ~
_~_ B
~1~7B34 . "
or a transpiration solar air he-ater. The solar heater of the present invention includes a housing having a light-transmitting or transparent front wall and a radiation absorbent collector element arranged to accept incident solar radiation passing through the front wall.
The solar heater further includes a heat trap which is integrally formed in one piece with the front wall in accordance with the principles of the present invention.
The heat trap thus fo~med is significantly stronger than the unsupported cellular heat trap by itself and requires no further support to maintain it in position against the ront wall. The problems described above ~`
for both flat plate solar heaters and transpiration solar air heaters are thus solved without the intro-duction of support elements or adhesive bondq or joi~ts from which incident solar rays may be reflected away from the radiation absorbent element and be lost. In addition~ sînce there are no adhesive~bonds in the heat trap of the present invention, there are no problems with aging of the adhesive, i.e., dis oloratîon9 embrîttlement, cracking, etc.
For purposes of simplicîty, the combîned integrally formed heat trap and front wall shall be hereinafter reerred to as an "integral heat trap glazing"
throughout the following description.
The prîncipal object of the present invention is therefore to provide a solar heater having an integral heat trap glazing whîch îs self-supporting and which has a hîgher overall transmission of incîdent solar rays than heat traps supported adjacent to the front wall ~L7834 of prior art solar heaters.
Another object of the present invention is to provide a novel and improved integral heat trap glazing for use in solar heaters which is strong, durable, easy to handle and economical to manufacture.
A
DESCRIPTION OF THE DRAWING
The present invention will now be described ; in greater detail hereinafter with particular reerence to the accompanying drawing which shows the preferred ` 10 embodiments hereof and wherein:
Figure 1 is an elevational, schematic, cross-sectional view of a typical flat plate solar hea~er made in accordanc~ with the present invention;
- Figure 2 is a similar view showing a typical transpiration solar air heater also made in accordance with the present invention; and Figure 3 is a partially cut away perspective view of a preferred embodiment of the integral heat trap glazing of the present invention.
~` It will be understood that the principles of the present invention are applicable to both a flat plate solar heater and a transpiration solar air heater although the integral heat trap glazing performs some-what d~fferent functions in each type of solar heater.
For purposes of convenience,the principles of the present invention will be disclosed independently with respect to each type of solar heater in the following description.
83~
Referring now specifically to Figure 1 of the drawing, there is shown a flat plate sol~r heater embodying the present invention. The solar heater comprises a housing 10 including a flat radiation absorbent collector plate 12 spaced from a back wall 14.
A tubular coil 16 or other passage means for a fluid such as air or water is provided in the space below and in contact with the 1at plate absorber 12. Preferably, although not necessarily, the remaining space between the flat plate absorber 12 and the back wall 14 is filled with a suitable insulation as denoted by the reference numeral 18. The housing 10 may suitably be made of a rigid metal such as aluminum or steel or oth~r rigid material such as plastic or fiberglass.
The housing 10 further includes an integral heat trap glazing 20 which serves as the light transmit-ting front wall of the solar heater in accordance with the present invention. As shown, the integral heat trap glazing 20 is made in a single piece but has a flat upper surface 20a which faces outwardly from the solar heater and a lower surface 20b which faces inwardly and which i9 spaced a short distance above the flat absorber plate 12 to provide a small gap 22 of, for example, about S mm. or less. The lower surface 20b is formed by a multiplicity of cellular openings with walls which are substantially perpendicular to the upper surface 20a. The cellular openings which constitute the lower surface 20b may be in the form of a honeycomb or other cellular structure such as that formed by parallel fins. The integral heat trap glazing 20 may be made in ~ ~4~
7 ~ ~ ~
one piece by conventional forming ~r molding technlqués as shall be described hereinafter in greatPr detail.
Suitably, the glazing 20 may ~e made from glass or clear plast~c c~mp~sitions such ~s polyvinyl fluoride, polycarbonate, fluor~nated ethylene propylene, polymethyl methacrylate, aromat~c p~lysulfones~ polyethylene terephthalate, aromatic polyesters, polyvinylidene 1uorite, hexafluoropropylene, chlor~trifluoroethylene and tetraflu~rethyl~ne copolymers.
During operation of thç ~olar heater,incident solar rays pass l~hrough the integral heat trap glaz~ng 20 and are absorbed b~ the flat collector plate 12 and are co~verted to heat. This heat ~n turn ~s transferred by conduction and convection t~ a fluid ~uch as air or water which ls circulated through the co~l 16 in contact wi~h the collector plate 12.
In this ~mbodiment of the present ~nvention, the integral heat trap glazing 20 6erves the dual function of reducing the radiative heat loss from ~he 601ar heater and of ~uppressi~g the onset of ~atural c~nvection ~n ~he alr ~pace ~tween the,flat co~lector plate and the ~ront ~all. In order for ~be cellular lower ~urface 20b of the integral heat trap glazing 20 to effectively reduce heat loss by ra~iation, the c~11ular ~penlngs ~ust be of a sufficiently high a~pect ratio as described and cl~imed ~n detail in our Canadian Pstent 1,082,544, ~n ~he range of 2 to 10 for hone~comb cellular structures and 4 to 20 for ~ B
1~7834 finned cellular structures. hs shown ~n Figure 1, the walls of ehe cellular openings divide up the air space between the flat collector plate and the front wall and inhibit the development of natural convection currents.
At the s&me time, a small gap 22 is maintained between the lower surface 20b of the glazing 20 and the flat absorber plate 12 to allow for differential thermal expansion of the solar heater elements.
Figure 2 shows a transpiration solar air heater embodying the present invention. As shown, the transpira-tlon solar air heater comprises a housing 24 having a back wall 26, and an lnlet 28 in one ~ide wall and an outlet 30 in the opposite s~te wall which establish a flow path for a gas such as air to be heated as generally indicated by the arrows in the drawing. A porous, radiation absorbent collector plate 32 is mounted inside the housing 24 in spaced apart parallel relation to the back wall 26 and across the flow path established between the inlet 28 and the outlet 30. The porous collector plate 32 may be composed for example of a porous darkened or black fibrous mat, woven or stamped screens, or reticulated ~oæm. Although the porous collector plate 32 ~s shown ln spaced parallel relation to the back wall 26, it will be understood that ehe collector plate may be positioned in non-parallel relation to the back wall as disclosed and claimed in our copending application Serial NQ-307,618. If desired, a layer of insulation 34 may be placed adjacent to the back wall 26 and in spaced apart relation to the porous collec~or plate 32. Again, the housing 24 may be made o, arigid metal ~uch as aluminum ~; or steel or other rigid material such as plastic or fibergl~s~.
_g_ ~L~1783~
The housing 24 ~urther includes an integral - heat trap glazing 36 which also serves as the light-transmitting front wall of the transpiration solar air heater. The integral heat trap glazing 36 is of basically the same construction as that shown in Figure 1, including a flat upper surface 36a and a lower surface 36b which is formed by a multiplicity of cellular openings. In this instance, however, the assembly of the integral heat trap glazing 36 in the housing is such as to provide an enlarged space 38~
This space 38 provides a passage for the gas such as air to be heated betweeen the lower surface 36b of the heat trap glazing and porous collector plate 32.
The integral heat trap glazing may be abricated using the same conventional molding or forming techniques and the same glass or plastic compositions mentioned above.
The operation of the transpiration solar air heater is similar in that incident solar rays pass through the integral heat trap glazing 36 and are : absorbed by the porous collector plate 32 and converted to heat. However, in this instance, the gas or air to be heated enters the inlet 28 and follows the flow path between the inlet 28 and outlet 30. The gas or air passes or transpires through the entire porous collector plate 32 and is heated. The heated gas or air then exits via the space 40 below the collector plate 32 and through the outlet 30. It should be noted that in this embodiment, the integral heat trap glazing 36 serves the dual function of reducing the radiative heat 7~3 :
:
-~ loss from the solar heater and o providing an air buffer layer composed of baffles which prevent the forced convective flow of the gas or air to be heated adjacPnt to the front wall where heat losses may occur.
The geometry of the integral heat trap glazing 36 in this instance is basically the same as that described above ;that is, the aspect ratio may be in the same range of between about 2 and 10 for honeycomb cellular structures and 4 and 20 for finned cellular structures.
In the two embodiments of the present invention ~- illustrated schematically in Figures 1 and 2, the integral heat trap glazings 20 and 36 are shown with a lower surface composed of cells having relatively thick walls for purposes of illustration only. It will however be understood that in order to effectively function as a heat trap the walls must be made relatively thin, i.eO, in the range of between about 0.0002 and 0.0~
centimeters. The thickness of the remainin~ upper planar portion of the glazing may vary depending on the overall size of the glazing and also on the cell wall thickness - ~ selected. Obviously in those instances where the cell wall is very thin the upper planar portion of the glazing must carry a higher fraction of the total load te.g., its own weight, wind and snow loads, etc.) and therefore must be thicker. On the other hand~ where the cell walls are relatively thick,the upper planar portion can be made thinner than if the glazing were constructed without the lower cellular surface which constitutes the heat trap. Generally speaking, the thickness of the upper planar surface will vary between about 0.075 and 0.60 centimeters.
7~34 Figure 3 shows the preferred form of the integral heat trap glazing of the present invention. As shown, the integral heat trap glazing 42 is formed with an upper planar portion 42a having a substantially flat surface and a lower cellular portion 42b comprising cells which have a hexagonal cross section. The walls of the individual cells are integrally formed with the upper planar portion as at 44, providing a continuous distribution of the glazing and heat ~rap material with no internal surfaces, joints, or adhesive bonds from which incident solar rays might be scattered or reflected.
The integral heat trap gl~zing can be made by co~ventional forming or molding techniques well known in the art. For instance, the integral heat ~rap glazing can most advantageously be made by an expanded core process as disclosed and claimed in U.S. Patent No.
3,919,446 issued to W.H. Smarook on November 11, 1975, and assigned to the common assignee hereof~ Variations and improvements of this process and apparatus for carrying out the process are disclosed and claimed in the following patents: U.S. Pat. Nos. 3,765,810, 3,~19,379, 3,919,380 and 3,919,445. In the basic process, articles such as the integral heat trap glazing can be made by expanding the cross-section of a blank of thermoformable material in a manner whereby voids such as hexagonal cells are formed from one sur~ace of the ~ blank. The remaining unexpanded portion of the blank ; forms the upper planar portion of the integral heat - trap. Ordinarily, articles formed by this proc~ss include a perforated skin on the side opposite to the unexpanded 83~
planar por~ion which must be removed before the article is suitable for use as an integral heat trap glazing. The perforated skin, if not removed, would be oriented such that incident solar rays re1ected from it would be directed away from the solar absorber and be lost. The perforated skin may be removed by passing an electrically heated wire through the cell walls immediately adjacent to the skin or by use of a reverse-cutting,knife-edge band saw blade such as that used for the cutting of metallic honeycombs. For a better understanding of the process, reference should be made to the specifications of the aforementioned patents.
It will be further understood, ofcourse,that the integral heat trap glazing can be formed by other processes such as injection molding wherein thermoformable material is injected under pressure into a mold having the desired cellular coniguration.
It may be noted that the cellular portion of the integral heat trap glazing 42 has been shown in the drawing with cell walls perpendicular to the upper planar portion 42a. The present invention however is not so restricted and the cell walls may be disposed at angles other than perpendicular so long as any solar rays ~ reflected from the ~ell walls are not directed back toward - the upper planar portion during normal periods of opera-tion. Thus the term "substantially perpendicular to the upper planar portion", as used herein and in the appended claims is intended to include such other angles with reference to the orientation of cell walls. It has been determined that the cell walls may be dispos~d ~3L7~3~
, at ~ngles with respect to the perpendicular of up to about 22.5 degrees without incident solar rays being reflected away from the solar absorber when the normal period of operat~on is taken to be about three hours before and after solar noon. For a re detailed explanation of the c~ll wall angle and how it is derived, reference is made to our Canadian Patent No. 1,082,544.
From the foregoing, it will be readily seen that the present invention provides a solar heater in the lC fonm of either a flat plate heater or a transpiration . . air heater having an integral heat trap glazing which is self-supporting and which has a high ove~all trans-mission of incident solar rays. In addition, the present invention provites an integral heat trap glazing for use in solar heaters which has a high strength to weight ratio and which is durable, easy to handle, and economical to manufacture.
~14-,~
BACKGROUND OF THE INVENTION
I. Field of the Invention The present invention relates broadly to solar heaters which convert incident solar radiation into heat energy and transfer the absorbed heat ei~her to a gas such as air or a liquid such as water, the former being commonly referred to as a solar air heater and the latter being commonly referred to as a solar ~: water heater. More particularly, the present invention relates to solar heaters o either type which employ a heat trap between the absorber and the light-transmitting front wall.
II. Description of the Prior Art Various proposals have already been made in the prior art for employing a heat trap between the absorber and the front wall of a flat plate solar heater in order to reduce heat losses by natural con-vection and radiation. An example o~ the foregoing wherain a transparent honeycomb heat trap is used may be found in an article by Hollands entitled, "Honeycomb Devices in Flat Plate Solar Coll~ctors'9, Solar Energy, Vol. 9, pp. 159-169, Pergamon Press (1965).
One problem encountered with such proposals is that it may as a practical matter be necessary to provide space between the honeycomb heat trap and the front wall to allow for diferential thermal expansion o~ the solar heater elements. It has been found, however, that the presence of such a space can increase the heat loss by ~L~17~34 natural convection to the front wall. This lncreased heat loss results from the development of-natural convectLon currents be~ween adjacent cells of the honeycomb structure.
It has been observed in the results of recent work by Edwards, e~ al., in "End-Clearance Effects on Rectangular-Honeycomb Solar Collectors"
presented at the 1975 International Solar Energv Gongress and ~xposition, July 28 - August 1, 1975, UCLA, Los Angeles; also published in Solar Energy, Vol. 18, i~ pp. 253-257, Pergamon Press (1976), that this increasein heat loss may be reduced by providing a cpac~
between the honeycomb heat trap ~nd the fla~ plate . ~:
. - absorber rather than between the heat trap and the - front wall. The difficulty with this proposal, however, -~ is that the honeycomb must of necessity be made with relatlvely thin walls in order to act as an efficient heat erap and, consequently, the honeycomb is either ;~ too flexible to ~e self-~upporting if made of clear plastic or extremely fragile if ~ade of glass and, therefore, separate means for ~upporting ehe honeycomb struc~ure over lts e~tire area must be-provlded.
It has al o ~een proposed in the prior art to employ a honeycomb or other open cellular structure in contact with the front wall ~o act es a radiation trap and ~ir ~uffer in ~ transpiration solar air heater. Thus, in our cope~d~ng ~pplic~tion Canadiarl Serial No. 307,618 filed on even date herew~th and a~signed ~o the con~non ~signee hereo~" there i8 disclosed and claimed a 3~ transplration ~olar ~Ir heater wherein the cellular ~, radiation trap is held in at least firm mechanical contact with the front wall in order that it may sdditionally act as an air buffer layer. It has been demonstrated by experimental work, as reported in our co-pending Canadian application, that a significant improve-ment in thermal efficiency i~ attained when the radiatlon trap is held finmly in contact with or is actually bonded to the front wall. When the radiation trap, on the o~her hand, ~ only loosely held in place adjacent to the front wall, the problem arises that convection currents may pass through the heat trap and contact the front wall where heat losses may occur.
In the case of both the flat plate solar heater and the transpiration solar air heater described above, the heat trap may be supported in contact with the front wall by one or more rigid bars below the cellular or honeycomb heat trap or by the provision of adhesive joints between the heat trap and the front wall.
Although this type of support means effectively solves the problem of oonvective air flow throug~ the heat trsp, the drawback of support means of this type is that the bars or ~dhesive joints or other support elements lntroduce additional surfaces from which incident solar rays ~ay be re1ected or scattered in a direction away from the solar absorber and be lost.
SUMMARY_OF~ INVENTION
The present invention is directed to a novel ~nd improved solar heater which overcomes the above enumerated problems in either a flat plate solar hester . ~
_~_ B
~1~7B34 . "
or a transpiration solar air he-ater. The solar heater of the present invention includes a housing having a light-transmitting or transparent front wall and a radiation absorbent collector element arranged to accept incident solar radiation passing through the front wall.
The solar heater further includes a heat trap which is integrally formed in one piece with the front wall in accordance with the principles of the present invention.
The heat trap thus fo~med is significantly stronger than the unsupported cellular heat trap by itself and requires no further support to maintain it in position against the ront wall. The problems described above ~`
for both flat plate solar heaters and transpiration solar air heaters are thus solved without the intro-duction of support elements or adhesive bondq or joi~ts from which incident solar rays may be reflected away from the radiation absorbent element and be lost. In addition~ sînce there are no adhesive~bonds in the heat trap of the present invention, there are no problems with aging of the adhesive, i.e., dis oloratîon9 embrîttlement, cracking, etc.
For purposes of simplicîty, the combîned integrally formed heat trap and front wall shall be hereinafter reerred to as an "integral heat trap glazing"
throughout the following description.
The prîncipal object of the present invention is therefore to provide a solar heater having an integral heat trap glazing whîch îs self-supporting and which has a hîgher overall transmission of incîdent solar rays than heat traps supported adjacent to the front wall ~L7834 of prior art solar heaters.
Another object of the present invention is to provide a novel and improved integral heat trap glazing for use in solar heaters which is strong, durable, easy to handle and economical to manufacture.
A
DESCRIPTION OF THE DRAWING
The present invention will now be described ; in greater detail hereinafter with particular reerence to the accompanying drawing which shows the preferred ` 10 embodiments hereof and wherein:
Figure 1 is an elevational, schematic, cross-sectional view of a typical flat plate solar hea~er made in accordanc~ with the present invention;
- Figure 2 is a similar view showing a typical transpiration solar air heater also made in accordance with the present invention; and Figure 3 is a partially cut away perspective view of a preferred embodiment of the integral heat trap glazing of the present invention.
~` It will be understood that the principles of the present invention are applicable to both a flat plate solar heater and a transpiration solar air heater although the integral heat trap glazing performs some-what d~fferent functions in each type of solar heater.
For purposes of convenience,the principles of the present invention will be disclosed independently with respect to each type of solar heater in the following description.
83~
Referring now specifically to Figure 1 of the drawing, there is shown a flat plate sol~r heater embodying the present invention. The solar heater comprises a housing 10 including a flat radiation absorbent collector plate 12 spaced from a back wall 14.
A tubular coil 16 or other passage means for a fluid such as air or water is provided in the space below and in contact with the 1at plate absorber 12. Preferably, although not necessarily, the remaining space between the flat plate absorber 12 and the back wall 14 is filled with a suitable insulation as denoted by the reference numeral 18. The housing 10 may suitably be made of a rigid metal such as aluminum or steel or oth~r rigid material such as plastic or fiberglass.
The housing 10 further includes an integral heat trap glazing 20 which serves as the light transmit-ting front wall of the solar heater in accordance with the present invention. As shown, the integral heat trap glazing 20 is made in a single piece but has a flat upper surface 20a which faces outwardly from the solar heater and a lower surface 20b which faces inwardly and which i9 spaced a short distance above the flat absorber plate 12 to provide a small gap 22 of, for example, about S mm. or less. The lower surface 20b is formed by a multiplicity of cellular openings with walls which are substantially perpendicular to the upper surface 20a. The cellular openings which constitute the lower surface 20b may be in the form of a honeycomb or other cellular structure such as that formed by parallel fins. The integral heat trap glazing 20 may be made in ~ ~4~
7 ~ ~ ~
one piece by conventional forming ~r molding technlqués as shall be described hereinafter in greatPr detail.
Suitably, the glazing 20 may ~e made from glass or clear plast~c c~mp~sitions such ~s polyvinyl fluoride, polycarbonate, fluor~nated ethylene propylene, polymethyl methacrylate, aromat~c p~lysulfones~ polyethylene terephthalate, aromatic polyesters, polyvinylidene 1uorite, hexafluoropropylene, chlor~trifluoroethylene and tetraflu~rethyl~ne copolymers.
During operation of thç ~olar heater,incident solar rays pass l~hrough the integral heat trap glaz~ng 20 and are absorbed b~ the flat collector plate 12 and are co~verted to heat. This heat ~n turn ~s transferred by conduction and convection t~ a fluid ~uch as air or water which ls circulated through the co~l 16 in contact wi~h the collector plate 12.
In this ~mbodiment of the present ~nvention, the integral heat trap glazing 20 6erves the dual function of reducing the radiative heat loss from ~he 601ar heater and of ~uppressi~g the onset of ~atural c~nvection ~n ~he alr ~pace ~tween the,flat co~lector plate and the ~ront ~all. In order for ~be cellular lower ~urface 20b of the integral heat trap glazing 20 to effectively reduce heat loss by ra~iation, the c~11ular ~penlngs ~ust be of a sufficiently high a~pect ratio as described and cl~imed ~n detail in our Canadian Pstent 1,082,544, ~n ~he range of 2 to 10 for hone~comb cellular structures and 4 to 20 for ~ B
1~7834 finned cellular structures. hs shown ~n Figure 1, the walls of ehe cellular openings divide up the air space between the flat collector plate and the front wall and inhibit the development of natural convection currents.
At the s&me time, a small gap 22 is maintained between the lower surface 20b of the glazing 20 and the flat absorber plate 12 to allow for differential thermal expansion of the solar heater elements.
Figure 2 shows a transpiration solar air heater embodying the present invention. As shown, the transpira-tlon solar air heater comprises a housing 24 having a back wall 26, and an lnlet 28 in one ~ide wall and an outlet 30 in the opposite s~te wall which establish a flow path for a gas such as air to be heated as generally indicated by the arrows in the drawing. A porous, radiation absorbent collector plate 32 is mounted inside the housing 24 in spaced apart parallel relation to the back wall 26 and across the flow path established between the inlet 28 and the outlet 30. The porous collector plate 32 may be composed for example of a porous darkened or black fibrous mat, woven or stamped screens, or reticulated ~oæm. Although the porous collector plate 32 ~s shown ln spaced parallel relation to the back wall 26, it will be understood that ehe collector plate may be positioned in non-parallel relation to the back wall as disclosed and claimed in our copending application Serial NQ-307,618. If desired, a layer of insulation 34 may be placed adjacent to the back wall 26 and in spaced apart relation to the porous collec~or plate 32. Again, the housing 24 may be made o, arigid metal ~uch as aluminum ~; or steel or other rigid material such as plastic or fibergl~s~.
_g_ ~L~1783~
The housing 24 ~urther includes an integral - heat trap glazing 36 which also serves as the light-transmitting front wall of the transpiration solar air heater. The integral heat trap glazing 36 is of basically the same construction as that shown in Figure 1, including a flat upper surface 36a and a lower surface 36b which is formed by a multiplicity of cellular openings. In this instance, however, the assembly of the integral heat trap glazing 36 in the housing is such as to provide an enlarged space 38~
This space 38 provides a passage for the gas such as air to be heated betweeen the lower surface 36b of the heat trap glazing and porous collector plate 32.
The integral heat trap glazing may be abricated using the same conventional molding or forming techniques and the same glass or plastic compositions mentioned above.
The operation of the transpiration solar air heater is similar in that incident solar rays pass through the integral heat trap glazing 36 and are : absorbed by the porous collector plate 32 and converted to heat. However, in this instance, the gas or air to be heated enters the inlet 28 and follows the flow path between the inlet 28 and outlet 30. The gas or air passes or transpires through the entire porous collector plate 32 and is heated. The heated gas or air then exits via the space 40 below the collector plate 32 and through the outlet 30. It should be noted that in this embodiment, the integral heat trap glazing 36 serves the dual function of reducing the radiative heat 7~3 :
:
-~ loss from the solar heater and o providing an air buffer layer composed of baffles which prevent the forced convective flow of the gas or air to be heated adjacPnt to the front wall where heat losses may occur.
The geometry of the integral heat trap glazing 36 in this instance is basically the same as that described above ;that is, the aspect ratio may be in the same range of between about 2 and 10 for honeycomb cellular structures and 4 and 20 for finned cellular structures.
In the two embodiments of the present invention ~- illustrated schematically in Figures 1 and 2, the integral heat trap glazings 20 and 36 are shown with a lower surface composed of cells having relatively thick walls for purposes of illustration only. It will however be understood that in order to effectively function as a heat trap the walls must be made relatively thin, i.eO, in the range of between about 0.0002 and 0.0~
centimeters. The thickness of the remainin~ upper planar portion of the glazing may vary depending on the overall size of the glazing and also on the cell wall thickness - ~ selected. Obviously in those instances where the cell wall is very thin the upper planar portion of the glazing must carry a higher fraction of the total load te.g., its own weight, wind and snow loads, etc.) and therefore must be thicker. On the other hand~ where the cell walls are relatively thick,the upper planar portion can be made thinner than if the glazing were constructed without the lower cellular surface which constitutes the heat trap. Generally speaking, the thickness of the upper planar surface will vary between about 0.075 and 0.60 centimeters.
7~34 Figure 3 shows the preferred form of the integral heat trap glazing of the present invention. As shown, the integral heat trap glazing 42 is formed with an upper planar portion 42a having a substantially flat surface and a lower cellular portion 42b comprising cells which have a hexagonal cross section. The walls of the individual cells are integrally formed with the upper planar portion as at 44, providing a continuous distribution of the glazing and heat ~rap material with no internal surfaces, joints, or adhesive bonds from which incident solar rays might be scattered or reflected.
The integral heat trap gl~zing can be made by co~ventional forming or molding techniques well known in the art. For instance, the integral heat ~rap glazing can most advantageously be made by an expanded core process as disclosed and claimed in U.S. Patent No.
3,919,446 issued to W.H. Smarook on November 11, 1975, and assigned to the common assignee hereof~ Variations and improvements of this process and apparatus for carrying out the process are disclosed and claimed in the following patents: U.S. Pat. Nos. 3,765,810, 3,~19,379, 3,919,380 and 3,919,445. In the basic process, articles such as the integral heat trap glazing can be made by expanding the cross-section of a blank of thermoformable material in a manner whereby voids such as hexagonal cells are formed from one sur~ace of the ~ blank. The remaining unexpanded portion of the blank ; forms the upper planar portion of the integral heat - trap. Ordinarily, articles formed by this proc~ss include a perforated skin on the side opposite to the unexpanded 83~
planar por~ion which must be removed before the article is suitable for use as an integral heat trap glazing. The perforated skin, if not removed, would be oriented such that incident solar rays re1ected from it would be directed away from the solar absorber and be lost. The perforated skin may be removed by passing an electrically heated wire through the cell walls immediately adjacent to the skin or by use of a reverse-cutting,knife-edge band saw blade such as that used for the cutting of metallic honeycombs. For a better understanding of the process, reference should be made to the specifications of the aforementioned patents.
It will be further understood, ofcourse,that the integral heat trap glazing can be formed by other processes such as injection molding wherein thermoformable material is injected under pressure into a mold having the desired cellular coniguration.
It may be noted that the cellular portion of the integral heat trap glazing 42 has been shown in the drawing with cell walls perpendicular to the upper planar portion 42a. The present invention however is not so restricted and the cell walls may be disposed at angles other than perpendicular so long as any solar rays ~ reflected from the ~ell walls are not directed back toward - the upper planar portion during normal periods of opera-tion. Thus the term "substantially perpendicular to the upper planar portion", as used herein and in the appended claims is intended to include such other angles with reference to the orientation of cell walls. It has been determined that the cell walls may be dispos~d ~3L7~3~
, at ~ngles with respect to the perpendicular of up to about 22.5 degrees without incident solar rays being reflected away from the solar absorber when the normal period of operat~on is taken to be about three hours before and after solar noon. For a re detailed explanation of the c~ll wall angle and how it is derived, reference is made to our Canadian Patent No. 1,082,544.
From the foregoing, it will be readily seen that the present invention provides a solar heater in the lC fonm of either a flat plate heater or a transpiration . . air heater having an integral heat trap glazing which is self-supporting and which has a high ove~all trans-mission of incident solar rays. In addition, the present invention provites an integral heat trap glazing for use in solar heaters which has a high strength to weight ratio and which is durable, easy to handle, and economical to manufacture.
~14-,~
Claims (13)
1. In a solar air heater comprising, in combination:
a housing having a light-transmitting front wall for passing incident solar radiation and including an inlet and an outlet for establishing a flow path for a gaseous medium to be heated, a gas-permeable radiation absorbent collector element positioned across the flow path in said housing and arranged to accept incident solar radiation passing through said front wall and to transfer the absorbed heat to said gaseous medium passing along said flow path and through said collector element, and a radiation trap disposed in said housing adjacent to the surface of said front wall facing said collector element, said radiation trap comprising a cellular honeycomb structure containing a multiplicity of open cells in communication with said flow path and having cell walls which are substantially perpendi-cular to said front wall and which serve as baffle elements to inhibit the flow of said gaseous medium through said radiation trap in a direction substantially parallel to the plane of said front wall, said cellular structure being maintained in at least firm mechanical contact with said front wall and being composed of a light-transmitting material which is opaque to infrared radiation emitted from said collector element in a direction toward said front wall; the improvement of integrally forming said light-transmitting front wall and heat trap as a unitary member thereby eliminating interfacial surfaces, joints or adhesive bonds there-between which can act as scattering sites for incident light.
a housing having a light-transmitting front wall for passing incident solar radiation and including an inlet and an outlet for establishing a flow path for a gaseous medium to be heated, a gas-permeable radiation absorbent collector element positioned across the flow path in said housing and arranged to accept incident solar radiation passing through said front wall and to transfer the absorbed heat to said gaseous medium passing along said flow path and through said collector element, and a radiation trap disposed in said housing adjacent to the surface of said front wall facing said collector element, said radiation trap comprising a cellular honeycomb structure containing a multiplicity of open cells in communication with said flow path and having cell walls which are substantially perpendi-cular to said front wall and which serve as baffle elements to inhibit the flow of said gaseous medium through said radiation trap in a direction substantially parallel to the plane of said front wall, said cellular structure being maintained in at least firm mechanical contact with said front wall and being composed of a light-transmitting material which is opaque to infrared radiation emitted from said collector element in a direction toward said front wall; the improvement of integrally forming said light-transmitting front wall and heat trap as a unitary member thereby eliminating interfacial surfaces, joints or adhesive bonds there-between which can act as scattering sites for incident light.
2. A solar heater according to claim 1 wherein said transparent honeycomb is composed of a multiplicity of cells having a hexagonal cross-section.
3. A solar heater according to claim 1 wherein said transparent honeycomb is composed of a multiplicity of cells having a length to diameter ratio of between about 2 and 10.
4. A solar heater according to claim 1 wherein s id transparent honeycomb is composed of a multiplicity of cells having walls of a thickness within the range of from about 0.0002 to about 0.05 centimeters.
5. A solar heater according to claim 1 wherein said light-transmitting material is glass or a clear plastic composition selected from the group consisting of polyvinyl fluoride, polycarbonate, fluorinated ethylene propylene, polymethyl methacrylate, aromatic polysulfones, polyethylene terephthalate, aromatic polyesters, polyvinylidene fluoride, hexa-fluoropropylene, chlorotrifluoroethylene and tetrafluoroethylene copolymers.
6. A solar heater according to claim 1 wherein said means for passing a fluid medium to be heated comprises an enclosed passageway for circulating said fluid through said housing which is placed in at least close proximity to said radiation absorbent collector element.
7. A solar heater, according to claim 1 wherein said radiation absorbent collector element comprises a porous opaque mat made from a material selected from the group consisting of pressed fibers woven screen, stamped screen and reticulated foam.
8. A solar heater according to claim 1 wherein said radiation absorbent collector element is positioned in substantially parallel, spaced apart relation to said unitary member.
9. A solar heater according to claim 7 wherein said radiation absorbent collector element is positioned in non-parallel relation to said unitary member.
10. A solar heater according to claim 1 wherein said housing includes a bottom wall and opposite side walls and wherein said unitary member is mounted opposite to and spaced from said bottom wall.
11. A solar heater according to claim 1 wherein a layer of insulation is provided adjacent to said bottom wall.
12. A solar heater according to claim 1 wherein said housing is made of metal.
13. A solar heater according to claim 1 wherein said housing is made of a rigid insulating material.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US82410377A | 1977-08-12 | 1977-08-12 | |
| US824,103 | 1977-08-12 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1117834A true CA1117834A (en) | 1982-02-09 |
Family
ID=25240585
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000307619A Expired CA1117834A (en) | 1977-08-12 | 1978-07-18 | Solar heater with integral heat trap glazing |
Country Status (7)
| Country | Link |
|---|---|
| JP (1) | JPS5431640A (en) |
| CA (1) | CA1117834A (en) |
| DE (1) | DE2835372C2 (en) |
| ES (1) | ES472526A1 (en) |
| FR (1) | FR2400170B2 (en) |
| IT (1) | IT1105541B (en) |
| MX (1) | MX147282A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US10386095B2 (en) | 2014-11-25 | 2019-08-20 | Sabic Global Technologies B.V. | Solar collectors including acrylic based cover sheet and methods for making and using the same |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0079976B1 (en) * | 1981-11-20 | 1987-06-03 | Yazaki Corporation | Solar heat collector |
| DE3824759A1 (en) * | 1988-07-21 | 1990-01-25 | Fraunhofer Ges Forschung | SOLAR COLLECTOR FOR GENERATING HIGH TEMPERATURES |
| DE3908363A1 (en) * | 1989-03-15 | 1990-09-27 | Fraunhofer Ges Forschung | SOLAR COLLECTOR |
Family Cites Families (17)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3102532A (en) * | 1961-03-27 | 1963-09-03 | Res Prod Corp | Solar heat collector media |
| FR1601101A (en) * | 1968-04-02 | 1970-08-10 | ||
| BE793429A (en) * | 1971-12-29 | 1973-06-28 | Union Carbide Corp | THERMOPLASTIC MATERIALS FORMING APPARATUS |
| US3919380A (en) * | 1971-12-29 | 1975-11-11 | Union Carbide Corp | Process for expanding annealed thermoformable materials |
| US3919379A (en) * | 1971-12-29 | 1975-11-11 | Union Carbide Corp | Forming a multicell container from a blank of a thermoformable material |
| US3919445A (en) * | 1971-12-29 | 1975-11-11 | Union Carbide Corp | Process for forming expanded laminates and products |
| US3919446A (en) * | 1971-12-29 | 1975-11-11 | Union Carbide Corp | Process for expanding thermoformable materials and products |
| JPS499493A (en) * | 1972-05-26 | 1974-01-28 | ||
| JPS5241541B2 (en) * | 1973-09-12 | 1977-10-19 | ||
| US3875925A (en) * | 1974-01-08 | 1975-04-08 | John G Johnston | Solar heater |
| JPS50120036A (en) * | 1974-03-11 | 1975-09-19 | ||
| US4018211A (en) * | 1974-05-01 | 1977-04-19 | Aai Corporation | Solar energy collection and transfer arrangement and method, and method of assembly |
| DE2543687A1 (en) * | 1974-10-09 | 1976-04-22 | Laing | SOLAR ENERGY COLLECTORS AND DEVICES OPERATING WITH THESE |
| US4034736A (en) * | 1974-12-11 | 1977-07-12 | The University Of Delaware | Solar heating method and apparatus |
| US4019496A (en) * | 1975-04-07 | 1977-04-26 | Daystar Corporation | Collecting solar energy |
| JPS5241541U (en) * | 1975-09-19 | 1977-03-24 | ||
| DE2600598A1 (en) * | 1976-01-09 | 1977-07-14 | Paul Weuthen | Solar energy collector for liq. heating - has transparent upper and black lower walls separated by supports to form flow channels |
-
1978
- 1978-07-18 CA CA000307619A patent/CA1117834A/en not_active Expired
- 1978-07-31 MX MX174372A patent/MX147282A/en unknown
- 1978-08-11 FR FR7823799A patent/FR2400170B2/en not_active Expired
- 1978-08-11 JP JP9743278A patent/JPS5431640A/en active Granted
- 1978-08-11 ES ES472526A patent/ES472526A1/en not_active Expired
- 1978-08-11 IT IT50711/78A patent/IT1105541B/en active
- 1978-08-11 DE DE2835372A patent/DE2835372C2/en not_active Expired
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US10386095B2 (en) | 2014-11-25 | 2019-08-20 | Sabic Global Technologies B.V. | Solar collectors including acrylic based cover sheet and methods for making and using the same |
Also Published As
| Publication number | Publication date |
|---|---|
| FR2400170B2 (en) | 1985-06-21 |
| DE2835372A1 (en) | 1979-02-15 |
| JPS5636752B2 (en) | 1981-08-26 |
| JPS5431640A (en) | 1979-03-08 |
| FR2400170A2 (en) | 1979-03-09 |
| MX147282A (en) | 1982-11-05 |
| ES472526A1 (en) | 1979-04-01 |
| IT1105541B (en) | 1985-11-04 |
| DE2835372C2 (en) | 1984-12-13 |
| IT7850711A0 (en) | 1978-08-11 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US4334524A (en) | Solar heater with bondless honeycomb heat trap | |
| US4262657A (en) | Solar air heater | |
| US4019496A (en) | Collecting solar energy | |
| AU2002350429B2 (en) | Solar collector panel for heating ventilation air | |
| US5220462A (en) | Diode glazing with radiant energy trapping | |
| US4117829A (en) | Fur-like photothermal converter surface | |
| US4323053A (en) | Solar heater with integral heat trap glazing | |
| US4282856A (en) | Solar-energy collector | |
| US4224927A (en) | Solar collector for heating a fluid | |
| Buchberg et al. | Design considerations for solar collectors with cylindrical glass honeycombs | |
| CA1125125A (en) | Solar heater with bondless honeycomb heat trap | |
| US4130108A (en) | Solar collector for heating a fluid | |
| CA1117834A (en) | Solar heater with integral heat trap glazing | |
| CA2006971A1 (en) | Solar Window Air Heater | |
| US4304223A (en) | Fibrous absorber solar collector | |
| US4359042A (en) | Contoured insulation window for evacuated solar collector | |
| US4993403A (en) | Method and apparatus for trapping heat energy | |
| US4131109A (en) | Solar collector | |
| EP0076875B1 (en) | Solar energy collector | |
| FR2385053A1 (en) | Solar heating panel with large heat absorbent area - provided by blades through which the heat collecting fluid passes | |
| EP0270910B1 (en) | Substitute solar roof for replacing building roofs | |
| JPH09145166A (en) | Solar heat collecting device | |
| CH630716A5 (en) | Device for utilising the radiation energy of the sun | |
| CN110375440B (en) | Flat-plate solar air collector with top and periphery heat insulation | |
| GB2301178A (en) | Solar collector panel |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |