Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02592819 2007-06-28
DE-MISTING SYSTEM FOR MULTI-PANE GLAZING
BACKGROUND OF THE INVENTION
This invention is directed to a system for removing moisture and water vapour
from
the interior cavity or cavities of multi-pane glazing units, and includes
provisions to maintain
such de-misted cavities in an ongoing, substantially de-misted condition,
including application of
the system to new window units.
2. Multi-pane glazing units usually consist of an inner and an outer pane,
generally
of glass, having a hermetic seal about the periphery, and frequently
containing rare gases such as
argon, to minimize thermal transfer through the unit. Owing to imperfections
of such peripheral
seals, and for other possible causes, moisture penetrates into the interior
cavity of the glazing
unit, to form a mist over its inner surfaces, and mar its appearance. Also,
such moisture
contamination has been found to reduce the insulative R value of the unit by
as much as 80%.
One prior system that attempts to deal with the problem involves accessing the
interior cavity,
spraying a de-moisturizing agent within the cavity, and sealing the access
aperture by way of a
simple flap valve that is intended to permit ready egress of gases from the
unit cavity, while
preventing the ingress of outside air to the cavity. This prior system is
ineffective, both in its
initial de-misting, and in the effectiveness of the flap valve provision.
BRIEF SUMIVIARY OF THE INVENTION
In accordance with the present invention there is provided a system,
applicable to pre-
existing and new glazing units, having an apparatus for pumping dry air at a
controlled
flow rate into and through a selected window cavity, to dry-out and purge that
cavity of
any moisture present, and to fill it with de-moisturized air, followed by the
application of
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sealing means to control access to the cavity and to substantially re-seal the
window
cavity.
In a preferred embodiment, the air is pre-dried, and may be heated to optinuze
the rate of
moisture removal; and the sealing means consists of a plug of controlled
permeability,
permitting the up-take and outward transfer of moisture from the cavity, while
resisting
any reversed moisture transfer into the cavity. This plug may include a water-
attracting
hydrophilic portion that is positioned within the window cavity, and a
hydrophobic end
portion that encloses the cavity aperture, to resist the ingress of moisture
to the cavity.
The hydrophilic portion of the plug may be blended with particles of dessicant
material, such as silica jel, to enhance water up-take. Thus, the plug valves
may be
comprised of porous polymers that may or may not contain dessicants.
The 'plug valves' can consist of plastic porous resins (e.g.. Polymers). The
alternatives
of ceramics, and fibers that transfer moisture through capillary action and
forces of
adhesion, cohesion, and surface tension are contemplated. Material selection
is based
upon providing an effective performance, where porosity, costs, aesthetics and
enviromental consideration come into play. Both metal and plastic materials
may be
sintered to provide predetermined degrees of porosity, in order to control the
rate of
pressure change within the window cavity in response to wind gusts operating
against the
outer window face; and to achieve acceptable levels of air flow/moisture
transfer by way
of wicking, capillary action, venting/aeration and moisture evaporation from
the cavity.
The control valves can be comprised of a range of plastic and other materials,
including:
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polycarbonate (PC) material ; polypropylene, (PP); polyethylene, (PE);
ceramics,
powdered metals, many of the well known polyolefins and materials that can be
polymerized.
These material are sintered; making the material porous in nature, thus
allowing
a) equilization of pressure, and
b) passage of air/moisture via wicking, capillary action, venting/aeration and
evaporation
from the cavity of the glass unit.
In comparing the structural strength of existing non-vented windows with new
windows
vented in accordance with the present invention, the outer sheet of the vented
new
window may be made of greater thickness, for improved gust resistance. Also,
the
subject plug valves may have predetermined low air transfer rates, to promote
wind-gust
load transfer from the outer window sheet to the inner window sheet.
In purging the window cavity, the air displacement apparatus receives air from
a
compressor, passes the compressed air through a dryer, to reduce the amount of
moisture that may be present, filters the air, and reduces the pressure to a
predetermined
lower range of pressures.
The air may be heated to a predetermined temperature, in accordance with the
ambient
conditions, and the characteristics of the window. Safe operating temperatures
lie in the
range of 20 to 40 degrees Celsius, and temperature and air flow rate selection
are
predicated upon window size and the thickness of the glass.
Larger window size and the use of thinner glass both adversely affect the
permissible
value of selected air temperature and the rate of air admission.
The dried, filtered, pressure-controlled air , preferably in a heated
condition for
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enhanced drying rates, passes to an air gun equipped with a nozzle hose, for
passage as a
purging medium within the cavity of a multi-pane glazing unit.
In the case of existing, non-vented windows that require venting, ventilation
access holes
are drilled at the bottom and the top of the subject glazing unit, preferably
in mutual
diagonal relation, so that the purging medium can flow diagonally upwardly
through the
unit cavity, vapourizing and entra.ining moisture that is present, and
removing it from the
cavity.
On completion of a purging operation the ventilation access holes are each
plugged with
a sealing plug, as described above.
The access holes may be drilled from the interior of the window, or from the
exterior,
and may traverse the window, or be limited to penetration of the window
cavity.
In applying the earlier teachings of the subject parent case to the venting of
new-
construction windows, a single venting cavity may be provided in an upper
comer,
usually in the window outer sheet.
The venting cavity is preferably plugged with a plug of predetermined low
permeability,
so that under high wind gust conditions there is a gradual change in the
internal pressure
within the window unit, so as to preserve the strength characteristics of the
unit.
Thus, in addition to serving as a vapour vent, this plugged cavity can also
provides the
function of controlled pressure equalization, such that changes in atmospheric
pressure
are adjusted to, with associated stress reduction in the glass sheets, and
more particularly,
in the peripheral boundary seals.
The strength of window units may be enhanced by the adoption of a thicker
outer
window sheet, to promote the gust resistance integrity of the unit.
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The present invention thus provides a multi-pane glazing unit having at least
two
glazing panels in mutually spaced substantially parallel relation; a
peripheral seal in
substantial sealing relation about the periphery of the panels; to form an
enclosed cavity
therewith; at least one access aperture connecting the cavity to atmosphere;
and plug
means removably inserted in the access aperture, to provide access to said the
cavity.
The access aperture may extend through a glazing panel, or through the
peripheral seal
of the glazing unit, so as to establish communication between the panel cavity
and the
plenum space surrounding the glazing unit.
The glazing unit may have two such access apertures positioned in
substantially
diagonally opposed relation in the unit, or in mutually spaced relation
adjacent the top
and the bottom of the unit.
One glazing panel may be of greater thickness than the other glazing panel, to
resist
wind gusts.
The plug means is preferably of predetermined permeability to provide
atmospheric
access to the cavity.
The plug means is preferably of sintered material selected from the group
consisting of
polycarbonate; polypropylene, polyethylene, ceramics, powdered metals, and
polymerizable polymer, being preferably of predetermined permeability.
The sintered plug material is of predetermined particle size to provide its
predetermined
permeability.
The permeable plug means may include a cylindrical hydrophilic inner portion
for
insertion within the cavity of the unit, and a hydrophobic outer portion to
substantially
seal the cavity against ready moisture transfer inwardly therethrough.
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The plug means may be of high porosity plastic, to enable the transfer of
water therethrough.
The hydrophobic plug portion may include a dessicant material in blended
relation with
a high porosity plastic.
The invention thus provides a method of controlling pressure and humidity
conditions
within the cavity of a multi-pane glazing unit, comprising the steps: forming
at least one
atmospheric access aperture to the glazing pane cavity, to connect the cavity
with
atmosphere, and plugging the access aperture with a plug of predetermined
permeativity,
made of material selected from the group consisting of polycarbonate,
polypropylene,
polyethylene, ceramics, powdered metals, and polymerized polyolefin material,
to
facilitate the egress of water vapour from the cavity, and to substantially
maintain
atmospheric pressure within the cavity.
Two such access apertures to the cavity may be formed, in mutually spaced
relation to
facilitate the passage of a moisture-entraining gas through the cavity.
The compressed gas may be dried prior to passing it into the cavity; also, it
may be
heated and compressed prior to passing the gas into the cavity, to enhance the
uptake of
moisture by the gas within the cavity.
The glazing unit may have one of its panes of greater thickness than the other
glazing
pane, to better withstand wind forces acting on the glazing unit.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
Certain embodiments of the invention are described by way of illustration,
without
limitation thereto other than as set forth in the accompanying claims,
reference being
made to the accompanying drawings, wherein:
Figure 1 is a schematic general view of a glazing unit having ventilation
access holes;
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Figure 2 is a side elevation of an embodiment of a vapour-purging apparatus in
accordance with the present invention;
Figures 3 and 4 are sectioned side views of two embodiments of window cavity
sealing
plugs in accordance with the present invention;
Figure 5 is a general view from the outside of a new window unit incorporating
the
present invention, applied through the glazing unit;
Figure 5A is a scrap view, with application through the peripheral seal;
Figure 6 is a view similar to Figure 5 of a further embodiment of a new window
unit; and,
Figure 6A is a scrap view showing a second plug applied through the peripheral
seal.
DETAILED DESCRIPTION OF THE INVENTION
It will be understood by those skilled in the art that the above disclosure is
directed
primarily to specific embodiments of the present invention, and that the
subject invention
is susceptible of reduction to practice in other embodiments that fall within
the scope of
the appended claims.
Referring to Figure 1, a glazing unit 10 comprising a thermopane (T.M.) window
has an
inner glazing sheet 12 and an outer glazing sheet 14, the periphery of which
sheets are
sealed in spaced relation by an initially hermetic peripheral seal 15.
The unit 10, as is well known, is installed with supporting hardware (not
shown), as
part of a wall of a building.
For purposes of the present invention the unit 10 is presumed to have suffered
failure of
the hermetic seal 15, with consequent inward leakage of moisture into the unit
inner
cavity 16, which results in misting of one or both of the inner glazing
surfaces of unit 10.
Access to the cavity 16, as a preliminary step of the present process is
attained by the
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drilling of access bores 18, 20, respectively located at the bottom and top of
the window
unit 10. Typically, the bores 18, 20 are in the order of three to four
millimeters
diameter (i.e. about 0.12 to 0.16 inches diameter).
Turning to Figure 2, the air displacement apparatus 22 has a tubular support
stand 26
supported on a base member 27. The support stand 26 has a transversely
extending hose
rack 28 on which service hoses 30 are stored and transported.
A cylindrical air dryer 36 is mounted vertically on the stand 26, having an
air inlet 38
and air outlet 40. The dryer 36 is charged with silica gel dessicant 37,
through which air
travels upwardly. A lower drain valve 43 permits downward drainage of
accumulated
water from the dryer 36. The air outlet 40 connects to an air filter 42, the
outlet of which
connects with a pressure regulating valve 44, a flow valve 46 and an air
heater 48, all
connected in series relation. The heater 48 has a heat shield thereabout.
The outlet of the heater 48 connects with a manifold 50, having a number of
quick-
disconnect couplers 54, to which small diameter air hoses 30 (of which only
one is
illustrated) are connected. Each air hose 30 serves a respective air gun 60,
having a
control lever 63. The gun 60 is fitted with a small diameter outlet hose 64
that is sized to
fit the access bore 18 in the glazing sheet 12.
Turning to Figures 3 and 4, the window unit of Figure 3 is drilled from the
inside,
having only the inner sheet 12 drilled; while the unit 10 of Figure 4 is
drilled from the
outside, having the outer sheet 14 and the inner sheet 12 both drilled.
The sealing plugs 66 have a cylindrical body portion 68 consisting of a high
porosity
plastic compound of hydrophilic polyurethane, possibly blended with a
dessicant, and an
outer end portion 70 of high porosity hydrophobic polyurethane.
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Other plug embodiments may be selected from the above-recited group of
materials.
The outer end portion 70 may have an adhesive surface coating 72 at its
interface with the
glazing sheet 12.
The sealing plugs 66 are sized diametrically to provide a tight push fit with
the access
bores 18, 20.
In use, to treat a defective glazing unit 10 that has evidenced water vapour
fogging of
its inner surface or surfaces or droplet formation, access bores 18, 20 are
drilled near the
bottom and top corners of the glazing unit, through the edge seal or through
the edges of
the accessible glazing sheet such as inner glazing sheet 12 of unit 10. The
glazing
sheets may be of glass or plastic.
An air displacement apparatus 22 is coupled at air inlet 38 by hose to a
compressed air
supply (not shown), operating at standard supply pressure in the range 100 to
125 psi.
The admitted air flows through the air dryer 36, passes through the air filter
42 to the
pressure regulator 44 and flow valve 46, where the pressure is dropped to a
value of 5-10
psi (gauge).
In the heater 48 the temperature of the air may be raised a desired amount, to
promote
drying rates. This temperature selection may be influenced by the length of
the air hoses
58 and the ambient temperature to which the window outer glazing sheet 14 is
subject, so
as to avoid thermal shock to the unit 10, with consequent damage.
The several outlet couplers 54 of the manifold 50 permits the apparatus to
service a
corresponding number of adjacent windows simultaneously.
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In the case of new installations, such as illustrated in Figures 5, 5A, 5B and
Figure 6, the
outer glazing sheet 82 of a glazing unit 80 is illustrated as having greater
thickness than
the inner glazing sheet 84, for the reasons given above.
It will be appreciated that the drawings are purely illustrative, showing only
the glazing
units with their plugged apertures, and are not to scale.
In Figure 5, the provision of upper and lower plugged apertures 86 and 88
enables the unit
to be purged with dry air or other gases, at the time of installation. Figures
5A and 5B show
alternative manners of use, locating the plug through the peripheral seal of
the unit.
The apertures 86 and 88 are illustrated as being diagonally positioned in
Figure 5, for
optimum scouring effect by the purge gas. Figure 5A shows the location of
aperture 86 in
the upper portion of the peripheral seal of the unit. Figure 5B shows an
aperture 88
located in a lower corner of the peripheral seal of the unit.
In Figure 6, there is shown a single plugged aperture 86, such that the cavity
16 is
maintained substantially at atmospheric pressure, while the humidity level is
maintained at a
low level by the action of the plugged aperture 86. By selection of a low
permeability
formulation for the plug, the rate of change of pressure in cavity 16 may be
such as to act in
the manner of a shock absorber, when wind gusts are encountered.
The location of the plug or plugs in the top run of the peripheral seal may
communicate
with, and ventilate to the crown space located above the glazing unit.
