Note: Descriptions are shown in the official language in which they were submitted.
CA 02713831 2010-08-27
THERMAL STORAGE SYSTEM FOR USE IN CONNECTION WITH
A THERMALLY CONDUCTIVE WALL STRUCTURE
FIELD OF THE INVENTION
The present invention relates to thermal storage systems adapted to store
energy in
the ground, absorb the stored energy from the ground and transfer the stored
energy
into a thermally conductive wall structure.
BACKGROUND OF THE INVENTION
Heating and cooling buildings consumes a large amount of energy. This is
particularly
the case in climates where there is a great disparity between maximum summer
and
minimum winter temperatures, as in much of North America, where it is
necessary
that buildings are cooled in the summer and heated in the winter.
Buildings are cooled and heated by a variety of means, including air
conditioning
units, electric heaters, wood stoves, forced air gas furnaces, and hot water
or steam
radiators. It is generally the case that a constant indoor temperature is
desired
depending on the external temperature. For example, room temperature (a
temperature at which humans are generally accustomed for indoor living) is
typically
between 64-74 F (approximately 18-23.5 C), however local climate conditions
may
acclimatise people to higher or lower temperatures.
To minimize heat transfer between a building and its surrounding environment,
various construction techniques have been developed which minimize the amount
of
energy required to maintain constant indoor temperatures. Examples of such
techniques include designing and using building materials and insulation with
high
values of thermal resistance (also known as R-values), and employing air-flow
heat
exchangers which minimize the amount of heat lost to the external environment
in the
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winter and reduce the amount of heat gained from the external environment in
the
summer.
Another way to improve the energy efficiency of a building is to make use of
available
geo-thermal energy. As is well known, the ground temperature below the frost
line in
much of North America is a relatively stable 55-56 F on average (approximately
13 C)
throughout much of North America, ranging from around 41 F (5 C) in northern
climates to about 71 F (21.6 C) in southern climates.
Ground-source heat pumps are one well known type of technology which take
advantage of this physical phenomenon. Heat pumps typically have a series of
heat
exchanging coils buried in the ground below the frost line. In warm summer
months,
water can be cooled to the ground temperature when circulating through these
coils.
This cooled water can then be circulated in radiators located inside the
building to
cool the interior space, among other applications. In a similar way, a
building can be
heated in the winter by warming the water in the heat exchanging coils.
However, there has been a lack of construction technology specifically
designed to
take advantage of the fact that the ground surrounding and underlying a
building can
be used as a heat sink in the summer and a heat source in the winter.
Furthermore, there has also been a lack of construction technology adapted to
store
abundant heat energy in the summer for use as a heat source in the winter
months.
Therefore, there is a need for building structures and techniques which reduce
energy
consumption by using the ground for heat storage in the summer such that the
ground can be as a source of heat in the winter.
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BRIEF DESCRIPTION OF THE INVENTION
The present invention provides a thermal storage system for storing heat in
the
ground beneath a building such that the stored heat can be transferred to a
thermally
conductive ground engaging footing. Therefore, in at least one embodiment, the
thermally conductive ground engaging footing can form the below grade
foundation of
a vertical wall structure that is contemplated to absorb the stored heat from
the
ground through the footing into the interior structure of the wall. This
arrangement can
reduce the heating costs of a building by raising the internal temperature of
the
vertical wall structure in the winter.
In at least one embodiment, the thermal storage system of the present
invention can
be used to cool the ground beneath a building by conducting heat from the
vertical
wall structure through a thermally conductive ground engaging footing into the
ground. This arrangement can reduce the cooling costs of a building by
lowering the
internal temperature of the vertical wall structure in the summer.
In at least one embodiment of the present invention, there is provided a
thermal
storage system which includes a longitudinally extending ground engaging
footing,
the footing extending horizontally through the ground below the frost level
and having
an upper surface and a lower surface, pumping means configured to circulate a
working fluid, a heat exchanger, the heat exchanger configured to transfer
heat
between the working fluid and the outside environment, the heat exchanger
fluidly
communicating with the pumping means, at least one supply outlet, the at least
one
supply outlet fluidly communicating with the heat exchanger, at least one
length of
pipe, the at least one length of pipe fluidly communicating with the supply
input, the at
least one length of pipe thermally communicating with the ground under the
longitudinally extending ground engaging footing, at least one return inlet,
the at least
one return inlet fluidly communicating with the at least one pipe such as the
pumping
means circulates the working fluid through the heat exchanger to the at least
one
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length of pipe by way of the supply outlet, the working fluid experiencing
heat transfer
with the at least one length of pipe, the at least one length of pipe
experiencing heat
transfer with the ground, the working fluid returning to the pumping means by
way of
the return inlet.
In at least one embodiment of the present invention, there is provided a
method of
storing heat in the ground beneath a building which includes the steps of
burying at
least one length of pipe in the ground below the frost level, the at least one
length of
pipe configured to receive a working fluid from a heat exchanger, the at least
one pipe
thermally communicating with the ground below the frost level, forming a
longitudinally extending footing in the ground above the at least one length
of pipe,
supporting a vertical wall on the footing, the vertical wall extending
upwardly from the
footing to a selected height above grade, sheathing the vertical wall in
insulation,
lacing the interior of the vertical wall and the footing with thermally
communicating
heat conducting members, at least some of the heat conducting members
extending
outwardly from the footing into the ground a selected distance to facilitate
heat
transfer between the ground and the vertical wall.
BRIEF DESCRIPTION OF THE DRAWINGS
Preferred embodiments of the present invention will now be described in
greater
detail and will be better understood when read in conjunction with the
following
drawings in which:
FIGURE 1 is a side elevational transversely cross-sectional view of one
embodiment
of a conductive wall structure for use in connection with the present
invention;
FIGURE 2 is a side elevational transversely cross-sectional view of another
embodiment of a conductive wall structure for use in connection with the
present
invention;
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FIGURE 3 is a side elevational view showing one embodiment of the above ground
connection of conductive elements within a wall for use in connection with the
present
invention;
FIGURE 4 is a side elevational transversely cross-sectional view of one
embodiment
of a conductive wall structure for use in connection with the present
invention;
FIGURE 5 is a side elevational transversely cross-sectional view of one
embodiment
of a conductive wall structure for use in connection with the present
invention;
FIGURE 6 is a plan view of one embodiment of the thermal storage system of the
present invention; and
FIGURE 7 is a cross sectional view one embodiment of the thermal storage
system of
the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
As is well known, the temperature inside the ground below the frost line is a
relatively
stable 55-56 F on average (approximately 13 C) throughout much of North
America,
ranging from around 41 OF (5 C) in northern climates to about 71 OF (21.6 C)
in
southern climates. This temperature is above the normal ambient atmospheric
temperature during northern winters and below normal ambient atmospheric
temperatures during the summer in most places. This delta temperature has
therefore
been previously used to effect a heat transfer that warms in the winter and
cools in
the summer. The heat transfer however has typically been accomplished using
conventional heat exchangers that transfer heat from one fluid to another by
means of
direct thermal coupling or airflow.
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The present invention seeks to store energy in the ground beneath a building
and use
this stored heat to heat a wall structure through direct thermal conduction.
Alternatively, the present invention can be used to cool the ground beneath a
building
such that a wall structure can be cooled through direct thermal conduction
with the
cooled ground beneath the building.
With reference to Figure 1, an exemplary wall structure 10 adapted to use heat
energy stored in the ground in the manner described below generally comprises
a
ground engaging concrete footing 15, a vertical wall 25 and an envelope of
insulation
40 that completely sheaths wall 25 except for the wall's lowermost surface 26
where it
connects with footing 15. Any openings in the wall for windows, doors and the
like will
similarly and preferably be lined with insulation.
The ground 2 itself is the heat source for the present wall structure during
the heating
season so footing 15 is the primary thermal interface between the ground and
wall 25
where the ground's energy is picked up.
Footing 15 will advantageously be positioned at least three feet below the
local frost
level, this level being the depth to which the ground will normally freeze in
the coldest
part of the winter, and is a poured concrete slab having a preselected
transverse
width of preferably at least 24 inches. Smaller widths are possible but
testing shows
that better results are obtained at 24 inches or greater. The footing's height
will
preferably be at least 8 inches but again this is variable. As will be
appreciated, local
building codes and engineering requirements will dictate the footing's minimum
structural and dimensional requirements but the present invention may require
that
those minimums be exceeded.
The concrete for the footing will be gravel type having a minimum thermal
conductivity
of 2.0 W/mK. As will be known in the art, some concretes are not thermally
conductive and the use of these for the footing is preferably avoided. Avoided
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concretes include lightweight, pumice powder, cellulose, isolation or slag
concretes,
all of which have significantly lower thermal conductivity. Applicant has
found that the
conductivity in the footing is increased using gravel having a 19 millimetre
average
particle size.
To increase heat transfer from the ground to the footing, the interface 5
between the
two may optionally be laced with galvanized steel dowels 50. These can be laid
in a
cross-hatched pattern or linearly in the longitudinal direction of the footing
on 16 inch
centers, although other spacings are contemplated as well. Other patterns and
configurations are possible, the idea simply being to facilitate heat transfer
from the
ground to the footing by means of these conductive elements. More effective
means
of promoting heat transfer from the ground to the footing are described below.
Within the footing itself, there will normally be reinforcing bar (rebar) in
any event for
strengthening the slab as necessary to meet local code and engineering
requirements. Advantageously, the rebar will include a plurality of
longitudinally
extending continuous runs of steel 15M(#5) rebar 55. This rebar is normally
located
below the footing's horizontal center line as shown most clearly in Figure 1.
The
typical placement of the rebar will be approximately 2 inches above the bottom
of the
footing. The rebar can be placed above or at the center line but for
structural reasons,
this is considered undesirable. Each run of rebar 55 will extend continuously
and
preferably without gaps or breaks from one end of the footing to the other and
for a 24
inch wide footing, there will preferably be at least three of such runs.
A continuous and longitudinally extending strip 57 of heat conducting material
is
positioned on the footing's upper surface 29 in the position shown most
clearly in
Figure 1 offset relative to vertical wall's 25 center line. As seen in Figure
1, the strip is
located on top of the footing adjacent the wall's interior surface 24. In one
embodiment constructed by the applicant, strip 57 is a two inch wide 24 gauge
piece
of galvanized steel anchored in place by spaced apart galvanized steel dowels
58
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that pass downwardly through the footing, through the soil-footing interface 5
and
then into the soil itself to a predetermined depth, preferably a minimum of 4
inches.
The next element in the ground source pickup is a series of vertically
oriented,
longitudinally spaced apart dowels 52 that extend from a point in the footing
close to
but preferably not in contact with the ground/soil interface 5, vertically
upwardly
through the remainder of the footing and into the lower reaches of wall 25 as
shown
most clearly in Figure 1. These dowels are preferably located along the wall's
center
line and contact the edge 56 of conductive strip 57 where the dowels emerge
from the
footing for thermally conductive contact with the strip. The dowels can be
welded,
wired to or simply biased against strip 57 for heat transfer therebetween. In
one
embodiment constructed by the applicant, dowels 52 are 1OM(#4) steel rebar,
are
horizontally spaced apart at minimum 16 inch centers and each extends into
wall
section 25 by approximately 16 inches. This length of penetration can vary,
but 16
inches has been found to provide good results.
In the alternative to using the two sets of dowels 52 and 58, dowels 58 can be
eliminated if dowels 52 are downwardly elongated to penetrate through the
footing
and into the ground to a predetermined depth, preferably at least 4 inches as
shown
in Figure 2. The dowels would then need to be corrosion protected, and the use
of
galvanized steel would be preferred in this application.
The next element of the wall system is to provide a conductive path for the
heat
absorbed from the ground into wall 25 itself.
With reference to Figure 1 again, this can be accomplished in a number of ways
with
one particularly preferred configuration being shown in the drawing. This
configuration
is essentially a grid or grids of conductive elements located inside wall 25.
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The conductive elements of the grid are center line vertical conductors 80,
horizontal
center line conductors 85, off center vertical conductors 90, off center
horizontal
conductors 95 and horizontal continuity links 100.
Starting from the bottom of wall 25, off center conductors 90 extend upwardly
from
strip 57 to a point in wall 25 a selected vertical distance above grade. The
lower end
of each conductor is biased, welded or otherwise connected to strip 57 so the
two are
thermally connected for heat transfer purposes. Conductors 90 are located off
center
of the wall more towards its interior surface 24 to better isolate the
conductors from
the wall's cold outer surface 26 and any moisture that might penetrate the
wall from
the ground. Off center horizontal conductors 95 are tied or otherwise
connected to
vertical conductors by means of metal wire, clips or other means known in the
art, the
only requirement being that all intersections between the conductors be
thermally
conductive. As seen in Figure 1, conductors 95 can be located on alternating
sides of
vertical conductors 90 or the horizontal conductors can be located on both
sides of
the vertical conductors as shown in Figure 3.
Above grade, vertical conductors 80 can be positioned along the wall's
vertical center
line with the horizontal conductors 85 connected thereto in the same manner
described above with respect to conductors 90 and 95.
A thermally conductive continuity link 100 connects lower conductors 90/95 to
upper
conductors 80/85. The link can be made up of short sections of the same
conductors
used for conductors 80, 85, 90 and 95 that thermally connect the upper and
lower
conductor grids together for heat transfer therebetween.
The conductors in wall 25 can be lengths of 10M(#4) steel reinforcing bar
connected
together in a preferably minimum 16 inch on center grid in both the horizontal
and
vertical directions. As will be appreciated, the conductors can perform double
duty as
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reinforcing for the wall itself in accordance with local building code
requirements and
engineering specifications.
As will be seen in Figure 1, the conductive grids extend from the bottom of
wall 25 to
near its top where the wall includes a sill plate 160 which will normally be a
piece of
dimensional lumber for the connection of joists, rafters, trusses or other
structural
elements to the wall. To prevent heat loss, a thermal break (not shown) can be
provided at the interface of sill plate 160 and the trusses etc. This can be
achieved by
using a rigid non-thermally conductive material such as polycarbonate
insulation
between the trusses etc. and the sill plate.
Unlike footing 15, wall 25 is preferably poured from low thermal conductivity
concrete
to minimize heat transfer from its warm side to its cold side. Again the
concrete can
be gravel concrete but using gravel having a 12 millimetre average diameter is
preferred.
As mentioned above, the wall from footing 15 all the way to its top should be
monolithically sheathed in insulation 40 so that there are no significant
breaks, gaps
or openings in the coverage. The insulation can be a foam type such as
expanded
polystyrene readily available from most building supply stores and which is
manufactured in sheets. The foam insulation can be connected to the wall by
means
of adhesives, staples or any other means known in the art that are not
thermally
conductive. Whichever means are chosen should obviously minimize thermal
conduction from the wall/insulation interface to the insulation's outer
surface. For
good results, the insulation on the wall's vertical surfaces should be minimum
R9, and
R25 along the wall's upper edge 27.
Any openings in wall 25 for doors, windows or other features should preferably
be
lined with slabs of foam or other equivalently insulative materials to prevent
thermal
loss around the opening edges. Equivalent materials can include for example
the use
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of low expansion insulating foams injected into the peripheral gaps between
the
window/door and the wall openings to secure the windows/doors in place. The
use of
metal fasteners between the windows/doors and the concrete of wall 25 is
preferably
avoided to minimize thermal conduction.
Advantageously, the upper surface 29 of footing 15 on the side of interior
wall surface
24 is also insulated for example by a piece of foam 31 (preferably minimum R8)
to
insulate the footing from the building's floor slab.
Wall 25 will itself extend from the building's footings 15 up_to its eaves. It
is preferable
that wall 25 has minimal openings and penetrations as it is important to
maintain as
monolithic a construction as possible to maintain the integrity of the wall's
thermal
conductivity.
In operation, it has been found that a wall structure as described above
conserves
heat within the building and significantly reduces heat transfer from the
inside to the
outside in winter and from the outside to the inside in the cooling season. As
will be
appreciated, during the cooling season, the wall acts in reverse to its
operation as
described above in relation to the heating season and will conduct heat from
above
grade to the ground below grade.
With reference to Figure 4, another embodiment of the present invention is
illustrated
wherein vertical conductor 90 is aligned with dowel 58. Therefore, dowel 58 is
in
thermal communication with conductive strip 57. Dowels 58 project through
concrete
footing 15 and through the soil-footing interface 5 into ground 2 as described
above
with reference to Figures 1 and 2. This construction eliminates the need for
dowels
52.
With reference to Figure 5, another embodiment of the present invention is
illustrated
wherein vertical conductors 80 extend vertically through wall 25, such that
vertical
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conductors 90 are not required. Typically, each vertical conductor 80 will be
located
along the centre line of wall 25 towards inner wall surface 24 in the location
of
conductors 90 in Figures 1 and 4. In this embodiment, vertical conductor 80 is
aligned
with dowel 52. Therefore, dowel 52 is in thermal communication with conductive
strip
57 and dowel 52 projects through concrete footing 15 and through the soil-
footing
interface 5 into ground 2 as described above in connection with Figures 1 and
2. This
embodiment eliminates the need for two sets of dowels 52 and 58. Structurally
however, this embodiment may not comply with local building codes that require
below grade rebar to be located towards the wall's inner (tension) side due to
the
pressure of the earth on the wall's outer side. As well, in this embodiment,
as in the
others described above, the conductors in wall 25 can be thermally connected
directly
or indirectly to the dowels that extend into or through the footing which can
eliminate
the need for conductive strip 57 in some instances.
Thermal Storage System
The present invention also relates to a thermal storage system 200 that will
now be
described with reference to Figures 6 and 7, in which like elements have been
identified using like numerals. Storage system 200 is designed to operate in
tandem
with thermally conductive wall structure 10, embodiments of which have been
described above. The thermal storage system 200 increases the efficiency of
wall
structure 10 by providing a heat sink which can store heat during the warm
summer
months for use as an additional heat source in the cooler winter months.
Referring now to Figure 6, a preferred embodiment thermal storage system 200
is
illustrated wherein a working fluid is pumped through underground piping 202
for heat
transfer purposes by means of a pumping means such as pump 220. Pump 220 can
be any suitable pump for the purpose such as, for example, a progressive
cavity,
positive displacement, reciprocal or centrifugal pump. Pump 220 will typically
be
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electrically powered, however it is also contemplated that the pump could be
powered
by an internal combustion engine or any other suitable prime mover.
The working fluid can be water, glycol, a mixture of glycol and water, or any
other fluid
that has suitable environmental and heat transfer properties for use in the
present
invention.
In the embodiment shown in Figures 6 and 7, which is configured and
dimensioned
for climatic conditions prevailing in Western Canada, underground piping 202
consists
of two concentric loops of pipe or conduit 204 and 206 buried beneath a
building's
floor slab 300. The horizontal spacing between the conduits is about 12 inches
but
this spacing can be increased or decreased. Measured from the mid point
between
the two conduits, they are inset approximately 30" on all sides from the inner
edge of
footing 15 as it follows the floor plan of the building, as can be seen most
clearly in
Figure 6. As will be discussed below, this distance will vary depending on a
number of
factors including climatic conditions. As well, the layout of underground
piping 202
can take a different shape such as an ellipse, square or circle and could be
larger or
smaller relative to the perimeter of the floor plan of the building depending
on
climactic conditions. Furthermore, underground piping 202 could take a variety
of
shapes other than simple loops such as crisscrossed patterns or concentric
spiral
loops underneath building slab 300.
It is also contemplated that a single loop of piping could be buried beneath
slab 300,
and furthermore three or more loops of piping could also be employed in the
present
invention.
In one embodiment contemplated by the applicant, underground piping 202 is
typically buried approximately 32" beneath the lower surface 301 of slab 300,
however underground piping 202 could be located deeper or shallower depending
on
climactic conditions, and soil thermal conductivity.
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Underground piping 202 can be constructed of schedule 40 stainless steel
tubing,
however pipes of different thickness and constructed of different materials
are also
contemplated. For example, climactic conditions permitting, underground piping
could
be constructed of plastic or other metals, such as titanium, galvanized steel,
cast iron
or aluminum.
Conduit 204 has an inlet end 208 and an outlet end 209. Similarly, conduit 206
has
an inlet end 210 and an outlet end 211. These ends are connected to a manifold
215
for the supply and return of working fluid from pump 220. Specifically,
working fluid is
pumped from pump 220 and enters conduits 204 and 206 through their inlet ends
208
and 210 respectively via manifold 215. After circulating through conduits 204
and
206, the working fluid leaves the conduits through their outlet ends 209 and
211,
respectively, into manifold 215 where the return flows are combined for flow
back to
pump 220. In embodiments with more or less than two loops, there will be a
corresponding number of supply inlets and outlets and an appropriately
modified
manifold.
In at least one embodiment, the working fluid is pumped through a heat
exchanger
230 where the fluid can be either cooled or heated depending on the exterior
ambient
temperature and the availability of solar radiation. Heat exchanger can simply
be a
series of radiation absorbent plastic or metal pipes located on the roof of
the building,
or it could be a more sophisticated model including those which could recover
waste
heat emitted from the building and or sources from within the building. Heat
exchanger 230 can be a solar collector or any other type of exchanger that is
suitable
for the use in connection with the present invention. Heat exchanger 230 can
be an
open loop or closed loop configuration.
The heat exchanger can be located either upstream or downstream from pump 220,
such that it can receive either depressurized return working fluid before it
is
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pressurized by pump 220 or it can receive pressurized working fluid after it
has been
pressurized by pump 220 depending on the thermodynamic requirements of the
application.
Therefore, in one embodiment of the present invention, the working fluid is
pressurized by pump 220 and supplied to heat exchanger 230 so that in the warm
summer months, the heat exchanger transfers heat from the environment into the
working fluid. Warmed working fluid is then circulated to underground piping
202 in
the manner described above, causing the temperature of the soil in a heating
zone
255 surrounding the piping within a radius 260 to rise as the warmed working
fluid
continuously circulates.
As will be seen, the radius 260 of heating zone 255 is selected so that from
the mid
point between pipes 204 and 206, the zone ideally reaches but does not
significantly
overlap footings 15 so that there is minimal heat transfer to the thermal
walls during
the cooling season. Obviously, it is not possible to precisely control the
size of
heating zone 255 due to fluctuations in solar radiation, soil type and
density, the
presence of ground water and other factors, but for any given geographic area,
historical temperature and climatic records and soil measurements can be used
to
calculate the placement of pipes 204 and 206 with reasonable accuracy. In the
example shown in Figure 7, which is based on conditions prevailing in western
Canada, radius 260 will be approximately 44 inches or 1.1 metres.
In other words, in western Canada, there are, on average, enough days having
an
above ground temperature in excess of ground temperature to heat a zone having
a
radius 260 of approximately 44" inches. In geographic areas having more warm
days, this radius will be greater and conversely, in colder climates having
fewer warm
days, the radius will be smaller.
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If preferred, temperature sensors can be strategically placed to read soil
temperatures and to transmit signals based on the temperatures to actuators to
discontinue the circulation of working fluid if and when zone 255 begins to
encroach
on footings 15.
To contain the heat beneath the building during the heating season, it is
preferred that
slab 300, rather than being a typical reinforced poured concrete floor, is
instead an
insulating layer. To this end, slab 300 can be constructed in a number of ways
that
will be apparent to those skilled in the art. In a preferred embodiment, slab
300
consists of a layer of gravel eg 40 millimeter) compacted to a thickness equal
to the
thickness of footing 15, which in the example given above, is 8 inches, topped
by a 4
inch thick covering 270 of expanded polystyrene foam insulation. Additional 2
inch
thick strips 275 of EPS insulation can be embedded in the gravel directly
above
conduits 204 and 206, the width of the strips being selected to intersect the
radius
260 of heating zone 255 at points 261 and 262. As will also be seen in Figure
7, top
dead center of radius 260 will intersect with the upper surface 271 of EPS
layer 270.
In this way the present invention provides a means for storing heat under
building
slab 300. Once the weather turns cooler in the fall and winter, this stored
heat, which
will migrate towards the cooler ground around footings 15, can be used to heat
wall
structures 10, offering a reduction in energy input for heating and associated
reduction in energy costs during the winter months.
It is contemplated that at certain times of the year the system may not be as
thermodynamically effective, as the temperature difference between the soil
under the
building and the ambient environmental temperature may be negligible.
Therefore, in
at least one embodiment, valve 214 is provided so that circulation of the
working fluid
can be slowed or halted when climactic conditions dictate or when system
maintenance is necessary. The valve can include an outlet for example to
replenish,
drain or replace the working fluid. A user can monitor the system and when it
is
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determined that the climactic conditions are not ideal for running the thermal
storage
system 200 in connection with the wall structure 10, the valve can be closed
off.
Furthermore, two valves can be provided, one upstream and one downstream of
pump 220, so that the pump can be effectively "locked out" for maintenance or
replacement.
In another embodiment, the present invention can be configured such that
working
fluid is glycol or a glycol-water mix that does not freeze in winter
temperatures. In this
embodiment, the system can be operated towards the end of the winter months to
cool the soil beneath the building by circulating the working fluid to heat
exchanger
230 when ambient environmental temperatures are colder than the soil
temperature
beneath the building. In this way, when working fluid passes through heat
exchanger
230, heat will be transferred from the working fluid and dissipated by heat
exchanger
230 so that the temperature of working fluid will decrease and the soil
surrounding
underground piping 202 will be cooled. In this arrangement, the cool ground
can be
used to cool wall structure 10 and reduce energy input for cooling and
associated
energy costs in the summer months.
Example
By way of example, the thermal storage system of the present invention was
tested
using the following input parameters:
Variable Value Unit Comments
soil thermal conductivity 1.5 W/mK This value is fixed and estimated for dry
soil
pipe thermal conductivity 0.51 This value is fixed and known for pipe selected
W/m=K
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inside pipe temperature 80 This value is fixed and known
oC
desired ground temperature 23 This value is chosen as a set point
oC
inside pipe radius 0.013 m This value will depend on pipe selection
outside pipe radius 0.019 m This value will depend on pipe selection and is
selectable and variable
distance from pipe to 1.119 m This value is chosen by installing engineer and
footing will depend on application
maximum volumetric 2500000 This value is fixed and estimated for dry soil
specific heat of soil
J/m3=K
minimum volumetric 2000000 This value is fixed and estimated for dry soil
specific heat of soil
J/m3=K
specific heat of working 3558.8 This value is known for this working fluid
fluid (50-50 water/glycol
mix) J/kg = K
density of working fluid (50- 1041 kg/m3 This value is known for this working
fluid
50 water/glycol mix)
conductive heat transfer Calculate W/m This value is calculated based on
system
temperature loss / meter of Calculate C/m This value is calculated based on
system
pipe
mass flow rate Calculate kg/sec This value is calculated based on system
desired soil length 37 m This will depend on building
desired length of 74 m This is based on a system with two loops
underground piping
Based on the above input parameters, the skilled person in the art can now
calculate
the conductive heat transfer, the temperature loss from the input of the
working fluid
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CA 02713831 2010-08-27
to the return of the working fluid, and the necessary mass flow rate for the
system,
using heat transfer and thermodynamic calculations known in the art, for
proper
configuration of the system, including the depth the conduits 202 are buried
below the
lower surface 301 of slab 300, and the horizontal spacing or inset of the
conduits from
the inner edge of footing 15.
Thermal storage system 200 can be retrofitted to an existing structure by
trenching
around its periphery for installation of conduits 204/206, or as the case
might be, and
an insulating barrier over the conduits to perform the function of slab 300
and EPS
layer 270.
The above-described embodiments of the present invention are meant to be
illustrative of preferred embodiments of the present invention and are not
intended to
limit the scope of the present invention. Various modifications, which would
be readily
apparent to one skilled in the art, are intended to be within the scope of the
present
invention. The only limitations to the scope of the present invention are set
out in the
following appended claims.
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