U.S. patent application number 12/178211 was filed with the patent office on 2010-01-07 for perforated transparent glazing for heat recovery and solar air heating.
Invention is credited to Christian Vachon.
Application Number | 20100000520 12/178211 |
Document ID | / |
Family ID | 40299589 |
Filed Date | 2010-01-07 |
United States Patent
Application |
20100000520 |
Kind Code |
A1 |
Vachon; Christian |
January 7, 2010 |
PERFORATED TRANSPARENT GLAZING FOR HEAT RECOVERY AND SOLAR AIR
HEATING
Abstract
A heat collector comprises a transparent glazing exposed to the
ambient. The transparent glazing is spaced from a back surface to
define a plenum therewith. A plurality of perforations is defined
through the transparent glazing for allowing outside air to flow
through the transparent glazing into the plenum and substantially
maintain the transparent glazing at the ambient temperature,
thereby providing for higher thermal efficiency.
Inventors: |
Vachon; Christian; (Magog,
CA) |
Correspondence
Address: |
OGILVY RENAULT LLP
1, Place Ville Marie, SUITE 2500
MONTREAL
QC
H3B 1R1
CA
|
Family ID: |
40299589 |
Appl. No.: |
12/178211 |
Filed: |
July 23, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60952057 |
Jul 26, 2007 |
|
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Current U.S.
Class: |
126/675 |
Current CPC
Class: |
F24S 80/56 20180501;
Y02B 30/90 20130101; F24S 10/503 20180501; F24S 90/00 20180501;
Y02A 30/00 20180101; F24F 2005/0064 20130101; F24S 80/58 20180501;
Y02E 10/44 20130101; F24F 5/0075 20130101 |
Class at
Publication: |
126/675 |
International
Class: |
F24J 2/22 20060101
F24J002/22 |
Claims
1. A heat collector comprising a transparent glazing exposed to the
ambient, the transparent glazing being spaced from a back surface
to define a plenum therewith, a plurality of perforations defined
through the transparent glazing for allowing outside air to flow
through the transparent glazing into the plenum, the perforations
being distributed over a surface area of the transparent glazing,
the plenum having an outlet, and air moving means to draw heated
air from said plenum via said outlet.
2. The heat collector defined in claim 1, wherein the back surface
includes a solar radiation absorbing panel.
3. The heat collector defined in claim 2, wherein said solar
radiation absorbing panel overlies a layer of insulation
material.
4. The heat collector defined in claim 2, wherein said solar
radiation absorbing panel is curved.
5. The heat collector defined in claim 1, wherein the back surface
comprises at least one photovoltaic panel.
6. The heat collector defined in claim 1, wherein the back surface
is of a light color.
7. The heat collector defined in claim 2, wherein the solar
radiation absorbing panel is corrugated.
8. The heat collector defined in claim 1, wherein the back surface
has an elongated pipe-like configuration with the perforated
glazing running longitudinally along one side thereof.
9. The heat collector defined in claim 1, wherein the plenum is at
least partly delimited by a building wall.
10. The heat collector defined in claim 1, wherein the back surface
includes a transparent membrane forming part of a building envelope
of a greenhouse.
11. The heat collector defined in claim 1, wherein the back surface
is at least partly defined by a ground surface.
12. A device for heating air comprising a perforated transparent
surface allowing solar radiations to pass therethrough, a solar
radiation absorption surface located behind said perforated
transparent surface for absorbing the solar radiations, and a gap
of air defined between said perforated transparent surface and said
radiation absorption surface, the air flowing in the gap absorbing
heat from the radiation absorption surface while fresh ambient air
flowing through the perforations of the perforated transparent
surface provides for a minimal temperature delta through the
transparent surface.
13. The device defined in claim 12, wherein air moving means are
provided for maintaining said gap under negative pressure.
14. The device defined in claim 13, wherein the perforated
transparent surface is mounted to a building surface, the gap of
air being defined between the perforated transparent surface and
the building surface.
15. The device defined in claim 14, wherein the building surface is
a transparent membrane extending over a greenhouse skeleton
structure.
16. The device defined in claim 14, wherein the building surface
forms part of the solar radiation absorption surface and is of a
light color.
17. The device defined in claim 12, wherein the solar radiation
absorption surface comprises a collector panel mounted to a
building surface, the perforated transparent surface separating the
collector panel from the ambient.
Description
TECHNICAL FIELD
[0001] The present application generally relates to a device suited
for pre-heating fresh outside air by means of free energy, such as
solar energy and/or heat recovery.
BACKGROUND ART
[0002] Design of traditional glazed solar air heaters generally
comprises a glass, polycarbonate or Lexan.RTM. transparent cover
placed in front of a dark solar absorber. The front transparent
cover is provided for minimizing heat losses from the top of the
collector. Fresh outside air is traditionally admitted at on end of
the collector between the front transparent cover and the solar
absorber. The air passes through the collector along fins and
absorbs heat from the solar absorber as it travels therealong. Warm
or hot air is discharged at the opposite extremity of the
collector. As air progresses inside the collector, its temperature
rises above ambient. The higher the temperature in the collector
is, the higher the heat loss towards the ambient becomes. Heat loss
happens through the bottom, the edges and the top (where the
glazing is) of the collector. Typically the edges and the bottom
are insulated, so that heat loss mostly occurs through the top,
that is by convection between the absorber and the glazing and then
by conduction through the glazing. When the glazing becomes very
warm, the collectors become less efficient.
[0003] Various unglazed solar air heaters have also been designed
over the years. Current transpired collector designs are such that
the solar absorbing surface is located outside facing the sun,
unprotected by means of a glazing. The perforated absorber is
coupled to a fan which creates a negative pressure between the
building (or the bottom of the collector) and the absorber. When
the fan is in operation, the air is drawn through the absorber. The
air passing through the perforations in the outer opaque absorber
breaks the naturally occurring warm film of air on the outside
facing side (the boundary layer) of the absorber. This method
provides acceptable performances when the flow of air per unit area
exceeds 6 cfm per square foot of collector. However, for unitary
flow rates below 5 cfm per square foot, the amount of cool air
leaching the perforated plate is insufficient to prevent the
collector plate from heating up, thereby negatively affecting the
overall thermal efficiency of the system. Efficiencies at the rate
of 2 cfm per square foot drop to 30% or even less.
SUMMARY
[0004] It is therefore an aim to address the above mentioned
issues.
[0005] Therefore, in accordance with a general aspect of the
present application, there is provided a heat collector comprising
a transparent glazing exposed to the ambient, the transparent
glazing being spaced from a back surface to define a plenum
therewith, a plurality of perforations defined through the
transparent glazing for. allowing outside air to flow through the
transparent glazing into the plenum, the perforations being
distributed over a surface area of the transparent glazing, the
plenum having an outlet, and air moving means to draw heated air
from said plenum via said outlet.
[0006] In accordance with a further general aspect, the back
surface includes a solar radiation absorbing panel.
[0007] In accordance with another general aspect, there is provided
a device for heating air, the device comprising a perforated
transparent surface allowing solar radiations to pass therethrough,
a solar radiation absorbing surface located behind the perforated
transparent surface for absorbing the solar radiations, and a gap
of air defined between the perforated transparent surface and the
radiation absorbing surface, the air flowing in the gap absorbing
heat from the radiation absorbing surface while fresh ambient air
flowing through the perforations of the perforated transparent
surface providing for a minimal temperature delta through the
transparent surface.
[0008] In accordance with still another general aspect, there is
provided a transparent and perforated surface exposed to the
ambient. The perforated transparent surface is spaced from a back
surface so as to define an air gap or plenum therebetween. Fresh
outside air is drawn into the plenum through the perforated
transparent surface. The back surface can, for instance, be
provided in the form of a bottom of a solar collector, a building
wall or roof, an outer surface of a greenhouse, a photovoltaic
panel, the ground or any non-porous surface. Between the perforated
transparent surface and the back surface, the gap of air is
maintained under negative pressure due to mechanical or natural
means. An outlet is provided for allowing the air flowing through
the plenum to be drawn into a duct or a channel, for use as
make-up, ventilation, process or combustion air to a device which
consumes or needs thermal energy.
[0009] The air in the plenum is heated either by incident solar
radiation on the surface of the back panel, which acts as a solar
absorber, and/or by heat escaping from the back surface. The device
can therefore act as a solar air heater and/or as a heat recovery
unit. When used as a solar air heater, the back surface can be of a
dark color, so that incident solar radiation passing through the
perforated transparent surface is absorbed by the back surface in
the form of heat and not reflected back to outer space. However, if
the back surface, for any aesthetic reason or other, must be of
light color, the solar thermal efficiency remains higher than other
conventional unglazed collector design. This is particularly true
when the device is used as a heat recovery device, since the back
surface can be of any color with no influence on efficiency (it can
even be transparent like in the case of a greenhouse), but the
lower the thermal resistance (insulation) of the back surface, the
greater the heat recovery rate. The device can be simultaneously
used for both functions of solar heating and heat recovery.
[0010] If necessary, the preheated air leaving the device can have
an auxiliary heating device located downstream (e.g. a gas-fired
system) to bring its temperature to a given set point.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a schematic side view of a solar collector
including a perforated transparent surface in accordance with an
embodiment of the present invention;
[0012] FIG. 2 is a schematic side view of another embodiment of a
solar collector having a perforated transparent glazing;
[0013] FIGS. 3 and 4 are schematic side views of ground-mount
configurations of solar collectors having perforated transparent
glazing in accordance with further embodiments of the present
invention;
[0014] FIG. 5 is a schematic side view of a wall mounted solar
collector having a perforated transparent glazing;
[0015] FIG. 6 is a schematic side view of a roof mounted solar
collector having a perforated transparent glazing;
[0016] FIG. 7 is a schematic view illustrating a perforated
transparent glazing surrounding a greenhouse shell for pre-heating
cold outside air before being drawn into the greenhouse by a
ventilation system; and
[0017] FIG. 8 is a graphic comparing the efficiency of perforated
glazing collectors vs. unglazed perforated collectors as a function
of the quantity of air flowing therethrough.
[0018] The term "glazing" is herein intended to broadly refer to
any transparent surface allowing the light to pass
therethrough.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0019] FIG. 1 shows a solar air heater 10 provided in the form of
an elongated conduit-like enclosure mounted on a base and including
a sun facing perforated transparent glazing 12 exposed to the
ambient and placed in front of a back panel having an arcuate solar
radiation absorber plate 14 applied over an insulation layer 15.
The back panel is generally provided in the form of a half-pipe
wall covered with the perforated transparent glazing 12. The
absorber plate 14 can be of a dark color to maximize solar gain.
The perforated glazing 12 can be provided in the form of a
perforated polycarbonate or transparent UV-resistant plate. Other
transparent polymers could be used as well. The glazing 12 can be
rigid or flexible. The perforations can be distributed over the
entire surface of the glazing or over only a selected surface area
thereof. The density of perforations can be uniform or variable
over the glazing surface.
[0020] The perforated glazing 12 and the solar radiation absorber
plate 14 define a plenum 16 therebetween. A fan or other suitable
air moving means 17 is operatively connected to an outlet 18
provided at one end of the back panel to draw fresh outside air
through the perforated glazing 12 into the plenum 16 before being
directed to a ventilation system, such as a building ventilation
system. The solar radiations passing through the perforated
transparent glazing 12 are absorbed by the absorber plate 14. The
air in the plenum 16 picks up the heat absorbed by the absorber
plate 14 before being drawn out of the plenum 16. As air travels
longitudinally along the plenum 16 between the absorber plate 14
and the perforated glazing 12, additional fresh outside air is
drawn through the perforated glazing 12. In this way, the glazing
12 remains at a temperature substantially equal to the ambient
temperature. Accordingly, the temperature differential between the
incoming air and the ambient is equal to zero or close to zero, so
that thermal efficiency remains at the highest possible value. Heat
losses through the glazing cover are thus kept to a minimum.
[0021] FIG. 2 shows a second embodiment in which like reference
characters refer to like components. The solar air heater 10a shown
in FIG. 2 essentially differs from the solar air heater 10 shown in
FIG. 1 in that the solar air heater 10a has a planar configuration
characterized by spaced-apart parallel transparent glazing and back
panel. The back panel is provided in the form of a flat absorber
plate 14a applied over a planar layer of insulation material 15a.
The absorber plate 14a could be corrugated. Sidewalls or supports
19a are provided along the perimeter of the back panel and the
perforated transparent glazing 12a in order to create a uniform air
gap 16a therebetween. The perforated glazing 12a and the back panel
are preferably co-extensive. The back panel 14a can be provided in
the form of photovoltaic (PV) panels to provide the double function
of air heating and cooling the PV panels, which produce more
electricity when their surface is kept at cool temperatures. As
shown in FIGS. 1 and 2, the perforated transparent glazing 12a is
preferably supported at an inclination equal to the latitude of a
given location, and facing the equator, depending on use. However,
it is understood that the transparent glazing could be oriented and
inclined otherwise. For instance, FIG. 4 shows a horizontally
oriented perforated transparent glazing, whereas FIG. 5 shows a
vertically oriented glazing.
[0022] As shown in FIGS. 3 and 4, the solar air heater can be
mounted directly on the ground, the ground surface forming the back
panel of the device. In the embodiment of FIG. 3, wherein like
reference characters refer to like components, the plenum 16b is
formed by the perforated transparent glazing 12b, a building wall
20b and the ground G. The fresh outside air drawn in the plenum 16b
is heated by the solar radiations absorbed by the ground G as well
as by the heat escaping from the building through wall 20b. The
fresh outside air flowing through the perforations defined in the
transparent glazing 12b maintains the temperature delta across the
glazing close to zero, thereby ensuring high thermal efficiency.
The heated air is drawn out from the plenum 16b and circulated in
the building B via the building ventilation system (not shown). As
shown in FIG. 4, where like reference characters again refer to
like components, the solar air heater can also be provided in the
form of an enclosure having a perimeter wall 19c, a closed bottom
end formed by the ground, and a top end covered by the perforated
transparent glazing 12c. An outlet 18c connected to suitable air
moving means is provided for withdrawing the heated air from the
enclosure.
[0023] As shown in FIGS. 5 and 6, the perforated transparent
glazing 12d and 12e can be mounted in opposed facing relationship
to a building wall 20d or the roof 22e of a building. In the
embodiment of FIG. 5, the plenum 16d is formed between the outside
surface of the building wall 20d and the adjacent vertically
oriented perforated transparent glazing 12d. In the embodiment of
FIG. 6, the plenum 16e is formed by the outside surface of the
building roof 22e and the perforated transparent glazing 12e. In
both embodiments, the heat escaping from the building envelope
through the wall 20d or the roof 22e is recovered to heat the air
in the plenum 16d and 16e. The roof 22e and the building wall 20d
both act as solar radiation absorbers to further heat the ambient
air drawn in the plenums 16d and 16e. The solar radiations pass
through the perforated transparent glazing and are absorbed by the
underlying building wall or roof surfaces and the air in the plenum
absorbs the heat from the building wall or roof. As opposed to
conventional solar walls or solar roofs wherein solar radiation are
directly absorbed by dark panels covering the wall or roof of the
buildings, the transparent glazing does not negatively alter the
appearance (i.e. change the color of the building wall or roof) of
the building. Unlike the prior art, the performance of the system
is not influence or restricted by the color of perforated. panels
installed on the building wall or roof. The perforated glazing 12d
and 12e are transparent and thus they do not change the color of
the building wall or roof. No compromise has to be done for
aesthetic purposes.
[0024] FIG. 7 shows a further potential application of the present
invention. More particularly, FIG. 7 illustrates a greenhouse B'
having a skeleton framework covered with a transparent skin 12f or
membrane, as well know in the art. A perforated transparent glazing
12f is mounted to the greenhouse wall and roof to define a
double-walled structure including an air gap 16f defined between
the perforated transparent glazing 12f and the inner transparent
skin 25. In this embodiment, the perforated transparent glazing 12f
acts as a second insulation layer for the greenhouse B'. The heat
escaping from the greenhouse through the inner skin 25 is recovered
in the air gap 16f. A fan or the like can be provided for drawing
heated air from the air gap back into the greenhouse B'. The
perforated transparent glazing 12f maintains the required
transparency required for plant growth.
[0025] As can be appreciated from the above embodiments, the device
can be used in several applications including: [0026] Solar thermal
air heaters [0027] Solar fresh air preheater mounted on building
walls or roofs [0028] Hybrid solar air/water heating systems [0029]
Preheating of air-to-air and air-to water heat pumps [0030]
Transparent energy recovery device for greenhouses [0031] Cooling
of photovoltaic panels [0032] Residential, low-cost solar
preheater
[0033] Also various apparatus can be provided downstream of the
device for further processing the air. For instance, the device
could be coupled to the following units: [0034] Gas-fired make-up
air unit [0035] Air-based heat pump (air-to-air or air-to-water)
[0036] Swimming pool heat pump [0037] Combustion chamber [0038]
Heat recovery unit
[0039] The above described transpired or perforated glazing offers
numerous benefits. The incoming air is admitted throughout the
glazing surface, either on a large proportion of its surface or
over the entire surface. Accordingly, the glazing surface remains
cold so that collector top heat loss is substantially prevented.
Furthermore, the air temperature inside the collector remains
relatively cold, lowering heat losses through the bottom and the
edges. The proposed perforated transparent glazing design provides
solar efficiencies at least as good as that provided by the
perforated plate design at high flow rates. For lower flow rates,
however, the solar efficiency remains high and by far exceeds that
of opaque perforated collectors, and even exceeds that of glazed
collectors, for less than half the cost. That can be readily
appreciated from FIG. 8. More particularly, it can be seen that for
flow rate between 2 and 6 cfm per square foot of perforated
surface, the efficiency of a perforated glazing with a black
backing surface is greatly superior to that a conventional black
perforated sheet metal solar collector. The difference in
performance is even more noticeable for light or white color solar
collectors. The perforated glazing with a white color backing
surface is up to 100% more efficient than a white perforated sheet
metal collector. It can also be appreciated that the difference in
performance between conventional unglazed perforated collectors and
the above described perforated glazed designs is even more
significant at low flow rates of, for instance, 3 or 4 cfm per
square foot.
[0040] It will be apparent to one skilled in the art that
modifications may be made to the illustrated embodiments without
departing from the spirit and scope of the invention as hereinafter
defined in the claims.
* * * * *