Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF INVENTION:
. . . _
Field of Invention
The present invention relates to a method and
apparatus for impregnating one side of a porous board,
such as a gypsum board, with a precise amount of compat-
ible phase change material. The invention also relates to
a gypsum board having a single surface impregnated,
substantially uniformly, with a compatible accurate amount
of phase change material to increase the thermal capacity
of the board.
Description of Prior Art
It is desirable to increase the thermal inertia
of the envelope of buildings, rooms and other spaces to
facilitate temperature control and to allow utilization of
short duration energy sources on a longer period. For
instance, during the heating season, thermal inertia
stores excess solar heat reducing overheating and restores
the heat at night reducing the heating demand. Therefore,
an increase of the thermal inertia facilitates energy
conservation. During the cooling season low cost
electricity or natural cooling can be used at night to
store cooling using the high thermal inertia and reducing
the cooling demand of the following cooling period. Also
thermal inertia reduces inside temperature variations
improving comfort for the occupants.
Thermal inertia can be increased by increasing
the in~ide mass of spaces using, for instance, heavy
masonry walls. Another method is to incorporate to
construction materials or components products that melt
and solidify at or near the space comfort zone. Those
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products store a great deal of energy within a slight
temperature variation during the phase change without
using a large volume of these products and add only little
weight to the spaces. Those products are commonly called
Phase Change Materials (PCM).
Thermal inertia in spaces can be increased by
incorporating a PCM to the materials used to cover the
inside surface of walls and ceilings (gypsum wallboard,
ceiling tiles, etc.). There are major advantages to this
including a large surface area for heat transfer between
the PCM and the inside air, a close contact between the
storage medium and the air to cool ox heat, a uniform air
temperature because air is surrounded by the storage
medium, storage is added without utilization of useful
volume, and there is no additional cost for storage medium
installation during construction. The storage medium is
invisible to users and does not require any control device
(passive temperature regulation).
A board, such as a gypsum wallboard, containing
a PCM is described in U.S. Patent 4,797,160 by Salyer.
The PCM choice includes alkyl hydrocarbons having 14 or
more carbon atoms and having a transition temperature
between OC and 80C depending on the utilization
envisaged. For occupants comfort, the typical transition
temperature is around 18C to 24C. There is actually no
such product available commercially in part because there
is no proven method to incorporate the PCM in a way to
obtain an acceptable product.
Five different methods are known and which have
been tried to incorporate PCM into gypsum wall boards.
These are:
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(i) simultaneous incorporation of macro-capsules of
PCM linked together and arranged in a grid and of the
gypsum paste between the two finishing papers;
(ii) incorporation of macro-capsules of PCM using
grooves made on the backside of dry gypsum wallboards;
(iii) incorporation of small PCM impregnated pellets
during the incorporation of the gypsum paste between the
finishing papers;
(iv) direct mixing of the PCM with the paste; and
(v) dipping of dry wallboards into melted PCM.
It has been observed that incorporation of
capsules or pellets may reduce interval binding strength
of the boards.
The PCM can be directly mixed with the gypsum
paste at concentrations up to 20 percent by weight
according to U.S. Patent 4,797,160. A critical step in
gypsum wallboard fabrication is the high drying rate of
boards to force premixed starch to migrate to the
gypsum-papex interface; the starch assures a good adhesion
of the paper on the gypsum core. It is expected that over
a certain (undetermined) amount of organic PCM in the
paste, starch migration rate will be reduced and that
adhesion problems will affect the quality of the product.
Finally, PCM can also be incorporated into
gypsum wallboards by dipping dry boards into a melted and
heated PCM for a certain amount of time. This method is
simple but has some drawbacks. Impregnation rate of PCM
into gypsum wallboards depends on the temperature of the
board, the tempexature of the PCM, the porosity of the
board, the relative diffusivity of the PCM into gypsum and
on the duration of the operation. In a dipping process it
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is difficult to control all those parameters to obtain a
precise amount of PCM impregnation. Another important
drawback of this method is that all the volume of the
wallboard is impregnated including the face exposed of the
board. This changes the appearance of the product and may
case problems such as paint peeling, odors, and
inflammability could occur.
SUMMARY OF INVENTION:
It is a feature of the present invention to
provide a method and an apparatus which substantially
overcomes all of the above-mentioned disadvantages of the
prior art.
Another feature of the present invention is to
provide a novel gypsum board which has a single surface
thereof impregnated substantially uniformly with a
compatible accurate amount of phase change material (PCM)
to increase the thermal capacity of the board.
Another feature of the present invention is to
provide a method and an apparatus that allows absorption
of a precise amount of PCM to porous boards and that
permits a control of the fraction of volume impregnated.
The method of the pxesent invention consists in
absorbing through one side of the board with the desired
amount of PCM. Usually the side through which the absorp-
tion is performed is the back surface of the board when
installed. Several methods can be used to absorb PCM
through one side of the board, the process can be conti-
nuous, semi-continuous or in batch.
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In a few aspects of the method of the invention
the PCM is sprayed uniformly at a lower rate than the
absorption rate of the PCM into the board. For a small
scale production in batch, the boards are maintained
horizontally , a liquid tight border is applied and the
desired amount of PCM is added to as to cover the surface.
Typical absorption time is 60 seconds.
The board impregnated using this invention is
quite different from the board impregnated by dipping.
The amount of PCM absorbed is known precisely; the PCM is
not uniformly distributed in the volume but concentrated
in the desired part of the volume, one suxface of the
board is not affected by the process and looks as the
regular product avoiding problems related to adhesion,
odors and inflammability. It is expected that absorption
through one side is the simplest process that can provide
such a product.
According to a still further broad aspect of the
present invention there is provided a method of impregnat-
ing one side of a porous board with a precise amount of
compatible PCM. The method comprises applying a predeter-
mined amount of the PCM at a predetermined rate to the
said surface so that a predetermined amount of the PCM is
impregnated. This application rate is lower than the
absorption rate of the PCM. At least the said one side of
the board is at a temperature above the melting point of
the PCM during the impregnation.
According to a further broad aspect of the
present invention, there is provided an apparatus for
impxegnating one side of a porous board with a precise
amount of compatible PCM. The apparatus comprises means
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to support the board with the one side facing up. Appli-
cation means is further provlded for applying a predeter-
mined amount of PCM to the said one side in a substan-
tially uniform manner. At least the one side of the board
is at a temperature above the melting point of the PCM.
According to a still further broad aspect of the
present invention there is provided a gypsum board having
a single surface thereof impxegnated substantially
uniformly with a compatible accurate amount of PCM to
increase the thermal capacity of the board.
BRIEF DESCRIPTION OF DRAWINGS:
A preferred embodiment of the present invention
will now be described with reference to the examples
thereof as illustrated in the accompanying drawings in
which:
FIGURE 1 is a fragmented perspective view
showing a method of impregnating one side of the porous
board with a compatible phase change material (PCM);
FIGIRUE 2 is a simplified side view showing a
modification of the application means of the apparatus of
Fig. l; and
FIGURE 3 is a simplified perspective view
showing another method of impregnating a porous board with
a compatible PCM.
DESCRIPTION OF PREFERRED EMBODIMENTS:
In accordance with the present invention a phase
change material (PCM) is absorbed thxough one face of a
porous board to increase the thermal capacity of the
board. An expected application of this invention could be
the impregnation of a paraffin mix into gypsum wallboards
to increase the inside thermal mass of buildings.
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The process is applicable to several porous
materials including cement, ceiling tiles and gypsum
wallboards. In case of gypsum wallboards, the board could
be a standard board or a board with fiberglass (the fiber-
glass is added to increase internal bond strength). Lab
tests have shown that fiberglass acts as a barrier for the
PCM, concentrating the PCM on the side of impregnation.
If an increase of the board internal thermal conductivity
is necessary, the board could contain metallic fibers. If
an amount of PCM larger than what the board can retain is
needed, the board could contain a wetting agent. If
inflammability of the board does not meet standards for
the application, a fire retardant could be added to the
PCM or to the board during making. The paper on the
absorption face could be the one used at the present time
or a more porous paper or a perforated paper or a thinner
paper or another type of porous film to increase the rate
of absorption.
As a general rule, during the absorption
operation, the temperature of the board has to be above
the melting temperature of the PCM but under the maximum
temperature that the board or PCM can reach without any
deterioration or degradation of properties. In the case
of a paraffin absorption into gypsum wallboards, the
maximum temperature is about 95C; over this temperature
there is a risk of deterioration of the interface gypsum-
paper. Laboratory tests have also shown that the rate of
paraffin absorption into gypsum wallboards increases when
the board temperature is increased. Another possibility
is to increase the temperature only on the absorption face
to concentrate the PCM in this part of the volume. This
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could be made by radiant heating, by a quick cooling of
the other side or using a hot PCM on a colder board. The
temperature of the PCM has to be above its melting point
and in many cases its viscosity is reduced while heated;
this improves the rate of absorption.
If not micro-encapsulated, the PCM must be
compatible with the material of the board. The PCM must
not represent any risk for health and has to be chemically
and physically stable over a long period. The necessary
amount of PCM must be retainable by the board material and
a wetting agent could be added, if necessary. A list of
organic PCM with possible additives is given in U.S.
Patent 4,797,160 by Salyer.
This suggests that, in an actual manufacturing
process as presently practiced, the PCM absorption could
be performed immediately after the boards exit or are
removed from the drying oven (their temperature being at
that moment about 90C).
When the PCM absorption operation is completed,
the face of the board, through which the PCM has been
absorbed, could remain as is or could be covered with a
protective coating or material. The surface could be
covered with a paint or a varnish or a paper to prevent
losses of PCM by evaporation and by capillarity with other
materials in direct contact with the board. In the case
of ceiling tiles and gypsum wallboards impregnated using
the back surface, covering of the surface by an aluminum
film could prevent heat loss or gain by radiation from
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inside the wall or ceiling, could prevent losses of the
PCM, could prevent bacteriological deterioration of the
PCM and could reduce the inflammability of the impregnated
board.
One example of the method is the spray process
as illustrated in Figure 1, and it is adapted to a mass
production for continuous operation. The board 1 is
disposed on a moving conveyor belt 2 with the surface to
be impregnated on top. The board enters a spray chamber 3
inside of which a uniform amount of liquid PCM 4 strikes
the surface. The rate of liquid sprayed is less than the
rate of absorption into the board to avoid liquid accumu-
lation OR the surface. The amount of PCM impregnated into
the board depends on the belt speed or on the spray
chamber length. For instance, consider a spray chamber 15
m long and a spray rate of 1 L/m2.min; to absorb 1.25 L/m2
into boards the belt speed has to be 0.2 m/s.
Another similar pxocess is shown in Figure 2
wherein the sprayers are replaced by successive porous
rolls 5 continuously fed with liquid PCM 6.
The flooding process shown in Figure 3 is better
adapted to a small scale production. The board 1 is
disposed at level and has its surface to be impregnated on
top. A grid 7 is placed on the surface to create separate
small surfaces to flood with the desired amount of liquid
PCM 8 released by jet nozzles of spouts 9.
Another possibility is to cover the surface to
be impregnated with solid PCM or partially melted PCM when
the board is hot or on cold board heated after. If the
rate of melting is lower than the rate of absorption, no
liquid accumulation will occur on the surface.
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It is within the ambit of the present invention
to cover any obvious modifications of the examples illus-
trated herein provided such modifications fall within the
scope of the appended claims.
