Note: Descriptions are shown in the official language in which they were submitted.
CA 02626472 2010-05-31
HEAT EXCHANGE CHAMBER FOR EXTRACTING EARTH
ENERGY TO HEAT AND COOL HOUSES WITHOUT USE OF
HEAT PUMPS
The earth is a storage device for the sun's energy. Every year the sun
supplies about
500 times more energy than we use and the earth absorbs this solar energy and
retains
it. This invention is based on the principle that, at below frost level, the
ground
maintains a constant temperature of 50 F to 70 F all year round depending on
the
geographic location. In Canada the ground temperature is constant at 50 F to
61 F.
Ancient Iranians dug long tunnels from outside into their desert palaces to
supply
cool air and this was effective because of the heat exchange between the earth
and the
air as it passes through. Recent practitioners of this idea bury tens of feet
of pipes in
the ground in an arrangement called the earth tube system. This invention is a
scaled
down version of this idea and based on the concept of routing air through a
network
of pipes that are installed in a concrete or PVC box filled with water and
buried
below frost level and is operated in a combination of an open and a closed
loop. This
box is the heat exchange chamber. Air is drawn into the pipes from the loop
using the
standard furnace blower inside the house and distributed in the regular duct
assembly.
A heat exchange takes place between the air and the surrounding water mass and
the
air enters the house at a temperature of between 68 F to 76 F in Canada, this
is an
ideal indoor temperature.
This is a low-tech method of maintaining comfortable indoor conditions and its
effectiveness is dependent on the delivery fan strength, the soil type, the
temperature
differential between the air in the pipes and the water mass and also the
total area of
contact with the water mass. The temperature of the water is kept constant by
the heat
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exchange with the surrounding soil mass thus ensuring that air drawn into the
house
is constant temperature all day. The absence of heat pump in this technology
and the
elimination hundreds of feet of small pipe and the attendant antifreeze fluids
or
refrigerants that are the hallmark of other similar technologies makes this
invention
very affordable because it eliminates the high upfront costs associated with
their
installation. Operational and maintenance costs are low because furnace
blowers use
less than a third of the electricity needed by the compressor based heat pumps
and
because of fewer moving parts and no antifreeze fluids or refrigerants to
manage. An
average furnace blower uses 700 watts/hour of electricity while an average
central
A/C consumes 3500 watts/hour. These facts make this technology very affordable
and suitable for use in developing countries. It also aids preservation of the
environment. This technology is for residential and commercial use and can be
installed in new constructions or as a retrofit in older houses. The national
standard
for the design and installation of earth energy systems in Canada is CAN/CSA-
C448.
The system is designed to cool houses during summer, removing need for air
conditioning units, and maintain ideal interior conditions during mild winter
but
serve to preheat the house during normal and severe winter when electric
heaters
could be used intermittently to achieve ideal conditions. It works by
transferring the
heat from the ground, it does not create heat or concentrate heat, therefore
it is very
cheap to operate. The heating load of the supplementary heater, if needed, is
reduced
significantly.
THE PRIOR ART
The first majors efforts at inventions that use earth energy to heat and cool
homes
was in the 1970's after the oil crises. Current earth energy systems comprise
mainly
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of the geo-exchange ground source heat pump technology and to lesser extent
the
earth tube technology. There are several variations of the ground source heat
pump
systems but the main limitation is the high upfront installation costs and the
need for
significant amount of electricity to operate its compressor based heat pumps.
It is also
difficult to install as a retrofit due to the required yard space and
accessibility
problems of the heavy machinery needed for the installation. The high demand
for
electricity means it is not environmentally friendly. The earth tube
technology, on
which this invention is based, is more enviro-friendly and less expensive but
has
several limitations in its present form. Principal among these limitations is
the
inability to maintain constant temperature indoor after a short period of
operation. As
the thermal exchange occurs between the air in the tubes and the surrounding
soil the
temperature in both mediums begin to stabilize towards the incoming air. This
requires the system to be shut down intermittently to enable the soil to
`recharge', the
efficiency of the system is thereby reduced by this shut down. Achieving
constant
temperature requires burying hundreds of feet of tubes taking up large spaces,
this is
neither practical nor economical.
The second limitation is the health problems that could occur as a result of
condensation occurring in the tubes and with time leading to growth of mould
and
fungi. This occurs mostly when the system is operated as a closed loop. A
closed loop
is when indoor air is re-circulated in the earth tubes in order to increase
the efficiency
of the system. This air quality issue has been addressed in different ways
including
sloping the pipes at 2 to 3 degrees into the house and pumping the condensed
water
with a condensate pump while others have used air filters with the blower
fans. PVC
pipes have been found to be better for mildew control than cement pipes which
retain
moisture and encourages fungi growth.
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Most of the current earth tube systems do not deliver heating or cooling with
the
efficiency of the geothermal ground source heat pump systems. The lower the
speed
of the delivery fan the more ideal the temperature of air but lower fan speeds
will not
send the required air to upper floors of houses and this draw back tends to
restrict the
use of earth tubes to houses with one floor.
The above mentioned limitations of the earth tube heating and cooling
technology
has been addressed by this invention in the following manner. Since the total
area of
contact of tubes with the heat exchange media is of paramount importance, this
design consists of six layers of 4-inch diameter PVC schedule 40 pipes, each
layer
totalling 60 feet long, constructed as shown in fig.1 and enclosed in a 7ft x
12ft x 7ft
concrete or plastic box. This totals 360 feet and eliminates the need to dig
up a large
space. To maintain constant temperature this box is filled water because water
has
good thermal mass and retains the earth energy long enough to prevent positive
or
negative heat gain before it is `recharged' by heat conduction by the
surrounding soil.
The water also enables a very efficient contact with the pipes which ensures
effective
heat transfer to the air by conduction and convection. This box is surrounded
by at
least 10 feet thick of clay soil to ensure this continuous `recharge'. An
average house
needs between 30,000-40,000Btu/hr of cooling and this invention meets this
criteria
as proven below:
Circumference of 4-inch diameter = nd =3.14x0.33 = 1.04ft (aprox. = 1 ft)
Area of each layer of pipe = 1 ft x 60ft = 60sq.ft.
Total area of pipes in box = 6 layers x 60sq.ft. = 360sq.ft.(i.e. surface
area, A)
The engineering formula for the surface area (A) of heat exchange is: A =
Q=UxAT
Where :
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Q = rate of transfer
U = coefficient of heat transfer
AT = mean temperature difference
This implies that : Q = AxUxAT
Referencing Overall Heat Transfer coefficient Tables, the heat transfer
coefficient, U,
for the fluid exchange surface of water to air for PVC schedule 40 pipe is
taken to be
= 4Btu/sgft.hr. F
If for example we have an incoming temperature of 90 F during summer and the
ground temperature of 55 F, our anticipated rate of heat transfer will be thus
:
Mean temperature difference, AT = 90 - 55 = 35 F
Rate of transfer, Q =A xUxAT = 360 x 4 x 35 = 50,400Btu/hr of cooling
The system will cool at this rate for a few hours and begin to reduce as the
heat
exchange continues and then stabilize at about 37,000Btu/hr as the water
begins to
absorb energy from the surrounding soil by conduction. An indoor temperature
of
about 72 F will be maintained. Same conditions will be achieved during winter
if, for
example, the incoming temperature is 20 F because the temperature difference
is still
35 F and the ground condition is constant. In winter situations the buildings'
exterior
envelope will need to be very efficient in order to able to retain this
comfort
temperature zone.
To eliminate the possibility of health problems arising from fungi growth due
to
condensation in the pipes, the outlet pipe to each layer is sloped towards the
house
and all layers are connected to a tightly sealed enclosure fitted with self
priming
sump pump that removes the accumulated water. Condensation can also be
prevented
by operating the system as a combined loop during the day by leaving the fresh
air
inlet open to allow dry air pass through the pipes. HEPA filters can also be
installed
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at the point of air distribution inside the house. Grille and insect screen is
also
installed at the fresh air inlet to prevent insects and rodents from entering
the pipes
and dying inside. The use of schedule 40 PVC pipes ensures strength, dryness
and
smoothness of the air passage route as mildew hardly develops in these
conditions.
The average blower fan speed used with conventional home heating is adequate
for
the system to supply an immediate upper floor. The operation of the blower fan
is
controlled by a standard thermostat.
LIST OR DRAWINGS
Fig. 1 shows a cross section of the heat exchange chamber and how it is
connected to
the house. The heat exchange chamber, which is item No.7 in the drawing,
contains
the six layers of pipe network and is filled with water after installation.
The unit is
produced elsewhere and brought to site for installation after excavation. The
inlet and
outlet air pipes and drainage units are then connected to it.
Fig. 2 shows the view from top of the heat exchange chamber before the top
cover is
installed. Heavy duty plastic clips are used to keep the pipes in the required
position.
Fig. 3 shows the six air inlet pipes, one for each layer in the chamber, and
the method
of securing them in place at above grade level. The cross section of this
construction
is shown as item No. F in Fig. 1.
Fig. 4 shows detail of the connection of the heating and cooling pipes into
the house
and the method of feeding the air to the furnace blower. This whole
construction is
completely sealed and made airtight and watertight in order to achieve full
suction.
Fig. 5 shows the connection joint of the return air pipe from the house and
the fresh
air pipe from outside. This is what makes this system operate as a combined
loop.
Fig. 6 shows the coupling between the outlet pipes from the heat exchange
chamber
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and the pipes that take the air into the house. The chamber is produced in a
workshop
and brought into the ground after excavation. The air inlet and outlet pipe
network
are installed at site.
Fig. 7 shows the detail of the air outlet pipes connection to the sump pump to
take
away the water from condensation. All six air outlet pipes are linked to this
pump.
Fig. 8 shows the coupling of the air inlet pipes to the pipes in the chamber.
All six
inlet pipes are connected the same way.
DETAILED DESCRIPTION
The heat exchange chamber is the medium by which the act of cooling and
heating,
or preheating, a house is achieved. This is the invention and it consists of
the
reinforced concrete or PVC box which is item No.7 in Fig. 1, the six layers of
schedule 40 PVC pipe network which is items Nos.1,2,3,4,5,6 in Fig. 1. The
first
layer of this pipe network is shown as item No.l in Fig. 2 constructed in the
manner
shown at the top of the box and the rest of the layers are constructed in same
manner.
The sixth layer is at the bottom of the slab. These layers are attached to the
box using
heavy duty plastic clips, item No. 15 Fig.2, and if a PVC box is used there
should be
half inch perforations one feet apart at the sides of the box. 90 PVC
couplings, item
No. M Fig.l and Fig.8, are used to connect the air inlet pipes, item No.8 Fig.
1, to the
layers - one inlet pipe to each layer. The inlet pipes for the lower layers
are extended
to above the top of the box, item No. 14 Fig.2, before the top cover is
sealed. The
dimensions of the box are: length, item No. A Fig. I and Fig.8, is 12 feet;
width, item
No. N Fig.2, is 7 feet; height, item No. B Fig. 1, is 7 feet. The box if
filled with water,
item No. R Fig. 1, after installation into the ground. The dept of the
chamber, item No.
C Fig. 1, from the natural grade, item No. 11 Fig. 1, should be 5 feet or
more. All
other pipes are connected to the chamber in a manner consistent with
established
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good plumbing practices in order to effect inflow and outflow of air through
the heat
exchange chamber and into the house and these connections are not part of the
invention.
Air is let into the heat exchange chamber from outside and the return air
pipes by the
suction effect created when the furnace blower is turned on. The return air
pipes, item
No. 9 Fig. 1, are six in number and connected to each fresh air inlet pipes,
item No. 8
Fig.1 also six in number. The air is sucked into the house after the heat
exchange via
outlet pipes connected to the chamber using straight couplings as shown by
item No.
Gy Fig.1 and Fig.6 and are six in number, one for each layer in the chamber.
These air
outlet pipes are sloped as shown towards the house and are connected to a self
priming sump pump enclosure, items No. 12 and 13 Fig. 1, to remove any water
resulting from condensation in the tube. The connection is done using T -
couplings as
shown in item No. L Fig.1 and the pipes are routed into the house to a 2ft by
2ft
airtight and watertight enclosure, item No. H fig.1 and fig.4, which is
connected to
the furnace blower via a duct, item No. 0 Fig.1 and Fig.4. Sealants, item No.
S
Fig.4,are used inside and outside the building wall, item No. K Fig. 1 and
Fig.4. Y -Y
is the cross section detail. Item No. J Fig.1 is the inside air feeder pipe to
the return
air pipe and item No. 4 Fig.4 is the connection of layer number 4 from the
chamber.
The six fresh air inlet pipes should be a minimum of 3 feet above grade level,
item
No. D Fig. 1, and secured using a concrete slab, item No. F Fig. 1, as shown
by items
No. 16,17,18 Fig.3 which are 7ft, 1.5ft, and 0.5ft respectively. Items No.8
and 19
Fig.3 are the air inlet pipes and the concrete slab cross section
respectively. X-X is
the cross section detail. The shown arrows in any drawing indicate the
direction of
air movement.
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OPERATION
The heat exchange chamber is installed in the ground with the top at a level
not less
than 5 feet below grade in manner shown in Fig. 1. An excavation is first
undertaken,
the installation follows and a backfill is done. It functions when the furnace
blower
inside the house is turned on. The term cooling and heating is used with
reference to
the air temperature outside the house. Because the air sucked into the house
from the
heat exchange chamber is at constant 68 F - 76 F, if the air outside is hotter
than this
range of temperature inside it is termed cooling and if far colder it is
termed heating.
The air that comes into the chamber undergoes a heat gain or loss, depending
on
outside conditions, from the pipes by conduction and convection and is sucked
into
the house at a constant temperature year round. The temperature of the water
is kept
constant by heat conduction from the surrounding 10 feet or more of clay soil.
The
best condition is when the ground water table high. The furnace blower is
activated
by regular house thermostat and that triggers the movement of air into the
house. This
air movement towards the house pulls along any condensed water in the pipes
and
into the sump pump thus ensuring a healthy atmosphere. An air filter can also
be
installed at the furnace. A shutter is installed at the outside fresh air
inlet so that this
inlet can be occasionally closed during severe winter and the system operated
as a
closed loop. A grille and screen is also installed at this point to keep out
insects and
rodents.
It is important that the chamber be installed at a slight slope as indicated
in the
drawing Fig.1 and that all connections be air and water tight. It also
important that
the top elevation of the chamber be no less than 5 feet below grade.
The heat exchange chamber is intended for use in residential and commercial
houses.
