Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02690655 2010-01-22
SOLAR UV TRANSMISSIVE DEVICE FOR STERILIZING
AND/OR HEATING AIR
TECHNICAL FIELD
The present application generally relates to a device and a method
suited for sterilizing and/or heating air by means of free energy, such as
solar energy.
For instance, the device can be used for heating and sterilizing the air of a
building.
BACKGROUND ART
The sterilizing effect of UV rays
Ultraviolet rays (UV rays) are known to have a purifying effect on
water as well as on air.
In closed systems, the re-circulated building air accumulates
pathogeneous organisms that may generate diseases. Among the various types of
UV
rays, the UV-C rays are known to inhibit the growth and the reproducing of
germs,
viruses, allergies and bacteria's that circulate in warm or cold air ducts
systems.
Over the years various UV rays generators have been developed in an
attempt to process and purify air in a given environment. While it is known
that solar
radiation contains UV rays that have a sterilizing effect, there is, according
to
applicant's knowledge, no device currently on the market which makes active
use of
the benefits or solar energy to sterilize the air. There is a need to take
advantage of
solar radiation in the duct systems to further increase the effectiveness of
existing UV
ray systems.
Solar collectors and UV rays
Design of traditional glazed solar air heaters generally comprises a
glass or 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 one end of the collector
between the solar
absorber and the insulated bottom of the collector. The air passes through the
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collector along fins and absorbs heat from under 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.
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.
The air circulating under or behind the absorbers never "sees" sunlight
and therefore the sterilizing properties of the sun are not being put to
advantage.
Furthermore, traditional glass used as top glazing is not transparent to the
sun's UV
rays, thererefore the heated air never gets the sterilizing benefits of the
sun's UV rays.
In view of the foregoing, there is a need for a relatively low
maintenance and simple solar energy based device that can be used to sterilize
and/or
heat air.
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SUMMARY
It is therefore an aim to address the above mentioned issues.
According to one general aspect of the present application, there is
provided a solar heat collector which also provides for air sterilization by
allowing
the incoming UV rays to irradiate the air passing behind or under a UV
transmissive
surface.
In accordance with another general aspect of the present application,
there is provided a heat collector and air sterilization device comprising a
UV
transmissive glazing exposed to the ambient, the UV transmissive glazing
allowing at
least a portion of the UV rays of the sunlight to pass therethrough, the UV
transmissive glazing being spaced from a back surface to define a plenum
therewith,
a plurality of perforations defined through the UV transmissive glazing for
allowing
outside air to flow through the transparent glazing into the plenum, the
perforations
being distributed over a surface area of the UV transmissive glazing, the
plenum
having at least one outlet through which air contained in the plenum can be
removed
after having been warmed up and at least partly sterilized by the UV rays of
the
sunlight. The back surface can be provided in the form of a solar radiation
absorbing
panel or the like.
In accordance with another general aspect, there is provided a device
for heating and sterilizing air comprising a perforated UV transmissive
surface
allowing at least part of the solar radiations, including UV rays, to pass
therethrough,
a solar radiation absorption surface located behind said perforated UV
transmissive
surface for absorbing the solar radiations, and a plenum defined between said
perforated UV transmissive surface and said radiation absorption surface, the
air
flowing in the plenum absorbing heat from the radiation absorption surface
while
being exposed to UV rays, thereby providing for the combined heating and
sterilization of the air in the plenum by solar energy. The perforations in
the UV
transmissive surface provides for a reduced temperature delta through the UV
transmissive surface, thereby ensuring a better heat transfer efficiency.
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In accordance with still another general aspect, there is provided an
outdoor transparent and perforated surface exposed to the ambient. The
perforated
transparent surface is permeable to UV rays and 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, a ground surface 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 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. As the air travels along the plenum it
is
being purified under the action of the UV rays passing through the perforated
transparent surface.
The air in the plenum can be 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 and/or as a sterilization 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 substantially 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 all three functions of solar heating, heat recovery and UV
sterilization.
It is understood that in warmer climates, the back panel or surface may
event be of white color, of reflective surface or even transparent if no solar
heat gain
is necessary.
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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.
If necessary, the at least partially sterilized air leaving the device can
be further processed by an auxiliary air sterilizing device (e.g. a UV-C
generator
system or chemical based purifying system) located downstream of the outlet of
the
outdoor plenum to further purify the air to a given set point.
In accordance with a still further general aspect, there is provided an
outdoor system for sterilizing the air of a building, the outdoor system
comprising:
- at least one air sterilization device mounted outside of the building; the
device comprising a plenum having a UV transmissive surface exposed to
sun rays, the UV transmissive surface allowing at least part of the UV rays
of the sun to pass therethrough in order to sterilize the air in the plenum,
- the plenum having at least one inlet feed with air from the building; and
- at least one outlet feeding the building with sterilized air from the
plenum.
The system for sterilizing the air of a building may further comprise:
at least one auxiliary sterilization device that can be disposed downstream of
the air
sterilization device in order to further sterilize the air before the same be
returned
back into the building. The auxiliary sterilization device could for instance
take the
form of a UV ray generator, a chemical sterilization device or a photocatalyst
device.
A controller could be provided for selectively actuating the auxiliary
sterilizing device. For instance, the controller could be programmed or
otherwise
configured to actuate the auxiliary sterilization device for producing
additional UV
rays during the night or by covered weather. Suitable sensors could be
connected t o
the controller to provide feedback on the quality of the air and the intensity
of the sun
rays.
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According to an embodiment, the system for sterilizing the air of a
building can comprise at least two auxiliary sterilization devices mounted in
parallel
or in series.
In accordance with a still general aspect, the system can also be used
to pre-heat the air before returning the same into the building. This can be
accomplished by providing a solar radiation panel behind the UV transmissive
cover
of the plenum. Also, if an income of fresh outside air is desired, the UV
transmissive
cover can be perforated to allow fresh outside air to flow into the plenum and
mix
with the recirculation air of the building.
The air sterilization device of the system can take the form of an
outdoor conduit connected to the ventilation system of the building. In this
example,
at least a portion of the conduit would be transparent to UV rays to allow the
air
flowing through the conduit to be exposed to the UV rays of the sun while
flowing
through the conduit.
The roof mounted conduit may comprise a plurality of duct sections
adapted to be connected end to end in fluid flow communication to form a fluid
passage for allowing air to flow therethrough. At least some of the plurality
of duct
sections could be provided with a ballast receiving portion, and a ballast
material
could be placed on said ballast receiving portion for anchoring the duct
sections to a
flat roof under the weight of the ballast material. The duct sections and the
ballast
material would have a combined weight selected to render the duct sections
substantially immovable to side winds on the flat roof of the building.
According to a still further general aspect of the application, there is
provided a method for heating and sterilizing air, the method comprises
directing air
to be processed into a plenum having a UV transparent surface, exposing air
through
said UV transparent surface to UV rays of the sun, absorbing at least a
portion of the
sun rays passing through said UV transparent surface onto a solar radiation
absorbing
surface located behind said UV transparent surface, and heating the air in the
plenum
with the solar radiation absorbed by said solar radiation absorbing surface.
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According to a still further general aspect, there is provided a process
for building a heat and sterilization device according to anyone of claims 1
to 16
comprising the step of assembling the different constituting elements of the
device.
The assembly can be done through the used of any suitable methods including
welding, fitting, bolting and/or screwing.
According to a still further general aspect, the system for sterilizing
the air of a building can be used for disinfecting buildings such as hospital,
school,
grocery stores, office towers, medical practices, waiting rooms etc. This can
contribute to substantially reduce the amount of disinfecting compounds such
as
biocides, fungicides, bactericides and antibiotics injected in the air
circulating in such
buildings.
According to a still further general aspect, there is provided a process
for heating and at least partially disinfecting a contaminated air source,
which process
comprises circulating the contaminated air at least one time through at least
one
sterilization device as generally defined hereinabove.
The term "glazing" is herein intended to broadly refer to any
transparent surface allowing the light to pass therethrough.
The terms "UV transparent" and "UV transmissive" are herein
intended to refer to a surface which allows sunlight to pass through without
substantially blocking the UV rays.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. I is a schematic side view of a solar collector including a
perforated transparent surface in accordance with an embodiment of the present
invention;
Fig. 2 is a schematic side view of another embodiment of a solar
collector having a perforated transparent glazing;
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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;
Fig. 5 is a schematic side view of a wall mounted solar collector
having a perforated transparent glazing;
Fig. 6 is a schematic side view of a roof mounted solar collector
having a perforated transparent glazing;
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;
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;
Fig 9 is a schematic view of a system for heating and sterilizing the air
of a building, according to one embodiment of the present invention, mounted
on the
building surface;
Fig. 10 is a schematic view of a system for heating and sterilizing the
air of a building, according to an embodiment of the invention, comprising an
air
collector mounted separately from the building; and
Fig. 11 is a graphic illustrating the UV transmitance of Sl-UV
Ultraviolet Grade Fused Silica manufactured by the company ESco Products as a
function of the Wavelength of the light.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
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
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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. As will be seen hereinafter, the glazing 12
can be
selected so as to be transparent or permeable to UV rays in order to also
provide for
UV rays sterilization of the air flowing through the conduit-like enclosure.
This is
advantageous in that it allows to simultaneously pre-heat and at least partly
sterilized
the air using solar energy. 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.
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
can
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.
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
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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.
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.
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
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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.
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 25f 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.
As mentioned hereinbefore, the sun facing glazing 12 of the various
embodiments of the heat collector illustrated in Figs. 1 to 7 can
advantageously be
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made of a UV transmissive material to take benefit of the purifying or
sterilization
properties of the UV rays on the air. The exposition of the air to the UV rays
of the
sun in the plenum allows sterilizing the air while the same is being heated up
in the
plenum.
The UV transmissive glazing is preferably made of a material selected
from the group consisting of: polycarbonates and fused silicae. The UV
transmissive
glazing could, for instance, be made of fused silicate offered by the company
ESco
Products.
Particularly recommended for use as the sun facing glazing 12 of the
above described embodiments of the solar air heater are S1-UV Ultraviolet
Grade
Fused Silica, Grades A and B of the ESco Products company. As shown in Fig.
11,
such materials have an optimum transmission range (more than 90% UV
transmissive) for wavelength comprised between 180 nm - 2.0 m and are thus
excellent UV transmitters.
Such pure fused silica materials offer good transmittance down into
the deep UV. They provide great homogeneity making them ideal for applications
demanding superior wavefront performance. As fused silica materials, they show
no
fluorescence or discoloration when exposed to radiation shorter than 290 rim.
S1-
UVA has slightly better homogeneity and fewer and smaller bubbles than S 1-
UVB.
Other materials that are permeable to UV rays of the C-type, and
having a UV transmittance rate that is higher than 80%, and preferably higher
than
85%, more preferably higher than 90% are contemplated as well.
Fig. 9 illustrates one possible embodiment of a combined solar air
heater and air sterilization device 29. The air heater and sterilization
device 29
comprises an outdoor UV transmissive panel 12' mounted on a sun facing wall
20' of
a building and defining therewith a plenum 16'. As illustrated, the UV
transmissive
panel 12' can be perforated to allow fresh outside air to flow into the plenum
16'.
The building wall 20' can be made of a dark color to absorb solar energy. An
outlet is
provided at the upper end portion of the plenum 16' for allowing heated and UV
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sterilized air to be drawn from the plenum 16' into a ventilation conduit 35'
of the
building by operation of a fan 32. An auxiliary UV generator 33 can be
disposed
between the plenum outlet and the building ventilation conduit 35 to provide
additional air purification before the air be directed into the building
ventilation
system. The auxiliary UV generator 33 is operated by a controller 30 which is
in turn
operatively connected to a light intensity sensor 31 and first and second air
quality
sensor 37, 36. The sensor 31 is disposed to measure the intensity of the
incident sun
rays on the UV transparent panel 12'. The first and second air quality sensors
37 and
36 are respectively disposed at the exit of the plenum 16' and at the exit of
the
auxiliary UV generator 33 for measuring the quality of the air being fed to
the
building ventilation system. In operation, the controller 30 receives signals
from the
solar radiation sensor 31 and from the first air quality sensor 37, positioned
upstream
to the ventilator 32. If the quality of the air flowing out of the UV exposed
plenum is
not as good as desired, a signal is sent from the controller 30 to the UV
generator 33
for producing the amount of artificial UV rays necessary for reaching the
desired
purity value. The sensor 36 measures the purity of the air feeding the
building 35 and
provides feedback to the controller to determine whether a control command
should
be send to the auxiliary UV generator to produce more or less UV rays. The
controller can also be connected to the fan 32 to adjust the residence time or
UV
exposure time of the air in the plenum as a function of the intensity of the
sunlight.
The residence time of the air in the plenum behind the UV
transmissive glazing 12 can be lower or equal to about 5 minutes and
preferably no
longer than about 1 minute. However, the air must be exposed to the sun UV
rays for
a sufficient period of time in order for the sterilization process to occur.
The
residence or UV exposed time will vary depending on the intensity of the sun
rays
and the mass flow of air in the plenum 16'.
According to one example, the auxiliary UV generator 33 is:
a) deactivated when the intensity of the solar exposition on the site as
detected
by sensor 31 is greater than or equal to about 600 W/m2 and permanently
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activated when the intensity of the solar exposition is lower than about 300
W/m2, and
b) deactivated when the total exposure time (residence time) to UV rays of the
air within the plenum 16' is greater than abut 60 seconds and permanently
activated when the exposure time is less than about 30 seconds.
It is understood that the auxiliary UV generator could take the form of
any other suitable air purifying system. For instance, a chemical
sterilization device
or a photocatalyst device could be used in place of the UV ray generator 33.
Also
more than one auxiliary air sterilizing devices could be disposed between the
UV
exposed plenum 16' and the conduit 35.
Fig. 10 shows another embodiment wherein the UV exposed plenum
16" is integrated in an air recirculation system of a building in order to
purify the
ventilation air using solar energy before the air be returned back into the
building.
More particularly, the UV exposed plenum 16" can be provided in the form of a
UV
transmissive conduit that could be mounted on the roof of the building or on
any
other suitable outdoor surface separate from the building. The conduit is
provided at
one end thereof with an inlet 40 for receiving contaminated air from the
building. The
conduit has an outlet 42 at the opposed end thereof for returning purified air
into the
ventilation system of the building. The wall of the conduit is at least partly
made of a
UV transmissive material for allowing the air to be purified by the UV rays of
the sun
as the air flows from inlet 40 to outlet 42. The wall of the conduit does not
have to be
perforated if no fresh air admission is needed. As disclosed in connection of
the
embodiment of Fig. 9, the system can comprise a controller 30, a fan 32, a
light
intensity sensor 31, an auxiliary UV generator 33, and a pair of air quality
sensors 36,
37. The duplicate description of these components is herein omitted for
brevity. In
this example, the system is mainly used to purify/sterilize the air and not
necessarily
to heat the air using solar energy. Accordingly, this embodiment could be
provided
without any solar radiation absorber.
The integration of such a passive UV air sterilization device in the
ventilation system of a building:
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- reduces or eliminates the use of chemical agents such as bioci, germicide,
viricide
or antibiotic in building ventilation systems;
- reduces or eliminates recourses to artificial UV sources to treat the air;
and
- contributes to reduce building electrical consumption.
Furthermore, as can be appreciated from the above embodiments, the
device can be used in several applications including:
= Solar thermal air heaters
= Solar fresh air preheater mounted on building walls or roofs
= Hybrid solar air/water heating systems
= Preheating of air-to-air and air-to water heat pumps
= Transparent energy recovery device for greenhouses
= Cooling of photovoltaic panels
= Residential, low-cost solar preheater
= Sterilization systems for schools, hospital, senior houses...
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:
= Gas-fired make-up air unit
= Air-based heat pump (air-to-air or air-to-water)
= Swimming pool heat pump
= Combustion chamber
= Heat recovery unit
= UV producing systems as well as other suitable air sterilizing systems
The above described UV transmissive 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
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CA 02690655 2010-01-22
heat losses through the bottom and the edges, or, if in a specific design with
high
residence time of the solar-heated air within the collector, the edges and
bottom may
be appropriately insulated. 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. This high efficiency at low
flow rates is a
major advantage for air sterilizing applications where relatively long
residence times
are or may be needed. High efficiencies at low flow rates 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 with 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.
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.
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