Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
32314
VENTILATING HEAT RECOVERY SYSTEM
FIELD OF T~E INVENTION
The present invention relates to ventilating
heat recovery systems and more particularly to venti-
lating systems constructed to exchange heat between
stale air being exhausted from a building and fresh air
being blown into the building, either to warm or cool
the incoming fresh air.
BACKGROUND
With the increasing costs of building heating
and cooling, it has become more and more common to make
buildings as air tight as possible. This brings with
it the significant problem of lack of ventilation and
the consequent build-up of stale air in a building.
One solution to this latter problem is the use of a
ventilating system drawing fresh air in from the out-
side of the building and exhausting stale air to the
outside While transferring the heat content of the warm
air to the cold air. This saves heat in cold condi-
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tions and reduces incoming heat in hot ambientconditions.
The present invention is concerned with a
novel form of ventilating heat recovery system for this
purpose.
SUMMA~Y
According to the present invention the:re is
provided a ventilating heat recovery system including
an air-to-air heat exchanger comprising:
a plurality of substantially rectangular,
flat plates spaced one above the other in a vertical
stack, the plates defining therebetween alternating
first and second flat duct sections;
first arcuate duct sections extending along
opposite first and second sides of the stack and join-
ing the first flat duct sections in sequence to provide
a first duct for carrying stale air, each first arcuate
duct section extending along the full length of the
associated side of the stack;
second arcuate duct sections extending along
opposite third and fourth sides of the stack and join-
ing the second flat duct sections in se~uence to pro-
vide a second duct in heat exchange relationship with
the first duct for carrying fresh air, each second
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arcuate duct extending along the full length of the
associated side of the stack;
each of the first flat duct sections having
an open cross section, substantially unobstructed in
the direction between the first and second sides of the
stack;
each of the second flat duct sections having
an open cross section, substantially unobstructed
between the third and fourth sides of the stack;
a flow-directing curved wall within each
arcuate duct section;
flow straighteners in each flat duct section
aligned with an end of the flow-directing curved wall
in an adjacent arcuate duct section and extending
partially along and in spaced substantially parallel
relationship with the associated flat duct section;
and
end plates joining the edges of adjacent ends
of the flat, stacked plates between the arcuate duct
sections.
The ventilating heat recovery system of the
present inventi.on is compact and can be easily
installed. It is operated in a combined counter-fl.ow
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and cross flow mode to ensure the most efficient heat
transfer consistent with minimal condensation problems.
Therefore the unit may be installed outside as well as
inside the building.
BRIEF DESCRIPTION OF THE ~RAWINGS
In the accompanying drawings, which illus-
trate exemplary embodiments of the present invention:
Figure 1 is a perspective view o~ a flat,
square multi-pass heat exchanger for use in a ventilat-
ing heat xecovery system;
Figure 2 is a cross-section along line 2-2 of
Figure 1;
Figure 3 is a cross-section along line 3-3 of
Figure 1;
Figure 4 is a cross-section of a duct
return;
Figure 5 is a cross-section of another
embodiment of duct return;
Figure 6 is a pictorial representation of a
ventilating heat recovery system;
Figure 7 is a perspective view of a heat
exchange unit of the system of Figure 6.
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_FT~ILED DESCRIPTION
Referring to the accompanying drawings,
Figure 1 illustrates a compact, square heat exchanger
10 With a sinous stale air duct 12 With plural flat,
s~uare sections 1~ spaced one above the other and
connected in sequence by arcuate duct sections 16. l'he
stale air inlet 18 is an open end of the duct 12 at the
top of the recovery system, while the stale air outlet
20 is an open end of the duct at the bottom, and on the
opposite side. The fresh air duct 22 is arranged
perpendicular to the stale air duct and consists of
flat sections 24 interposed between the flat sections
14 of the fresh air duct 12. The flat sections 24 are
connected in sequence by arcuate duct sections 26. The
~resh air inlet 28 is located at the bottom, along one
side perpendicular to the stale air inlet 18 and outlet
20, and the outlet 3a for fresh air is along the
opposite side at the top.
The heat exchanger is constructed of a stack
of square plates 32, the arcuate duct sections or
returns 16 and 26 and end plates 34 forming the sides
of the flat sections of the two ducts.
As illustrated in Figures 2, 3 and 4, the
arcuate duct sections 16 and 26 fit into the ends of
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the associated flat duct sections. They are removable
to allow cleaning of the inside of the heat exchanger.
The arcuate duct sections are not circular in
profile but are flattened so that the flow cross
section remains relatively constant throughout the
length of the duct section. At the centre of the
section, the flow cross-section at B (Figure 4) is no
more than ten percent greater than the flow cross-
section at A, the inlet and outlet.
Each of the arcuate duct sections is also
equipped with a flow divider 36. This is a curved
plate extending from the inlet to the outlet to define
two separate flow zones in the arcuate duct section.
The function of this device is to prevent the air flow
from concentrating at the outside curved wall due to
the effects of inertia as the air flows around the flow
reversing return. At the outlet of the arcuate
section, the flow divider lines up with a flow
straightening vane 3~ extending part way along the
following flat duct section. This flow straightener
confines the air flowing on the inner side of the flow
divider to flow along the adjacent plate 3~. In the
absence of this confining straightener, a low pressure
zone would tend to form along the inlet edge of the
~3~
plate, limiting heat transfer through the plate and
thus reducing the efficiency of the heat exchange as a
whole.
With larger sized heat exchangers, two or
more flow dividers may be used in the arcuate duct
sections as illustrated in Figure 5. Additional flow
straighteners could then be used in the flat duct
sections to limit the flow disturbing effects of the
flow reversal.
Figure 6 illustrates a ventilating heat
recovery system for a building incorporating a heat
exchanger as described in the foregoing. The building
illustrated is an industrial building containing
processing or shop e~uipment 42. A duct 44 is provided
for collecting fumes and stale air from the shop area.
This air is drawn through a filter box 46 by a fan 48.
The fan delivers the stale air to a stale air outlet
duct that passes through the roof of the building into
an insulated duct section 52 discharging in turn into a
heat exchanger contained within a housing 54 on the
roof of the building. A stale air exhaust 56 leads
from the opposite side of the housing for discharge to
ambient air.
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Beside the housing 54 is a fresh air inlet
58. This includes a filter 60 through which fresh air
is drawn by a fan 62 and a fresh air supply duct 64
through which the fresh air is fed into the housing 54.
An insulated fresh air inlet 66 from the housing
through the roof of the building leads to an internal
fresh air inlet duct 68 terminating in a fresh air
distributor 70.
The construction of the housing is illustrat-
ed most particulariy in Figure 7. The housing is
enclosed by a series of panels 72 that are secured in
place with screws 74 so that they can readily be
removed for servicing purposes. The panels are of a
sandwich construction with internal insulation 76. The
heat exchanger 10 is enclosed by the housing, with the
space around the heat exchanger ventilated. Also,
vents 78 through the roof connect to the heat exchanger
ducts near the top. These serve to exhaust fumes that
may collect at the top of the unit when the fans are
stopped. The housing 54 is supported on four adjust-
able legs 80.
Figure 7 also illustrates a bypass 82 which
is a flat, rectangular duct on top of the heat
exchanger. The bypass receives stale air from the
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stale air outlet duct 52 and bypasses that air through
the housing 54 to the next heat exchanger unit in a
case where more than one unit is employed. The units
then opera~e in parallel. Where a single unit is in
use, the bypass 82 is blanked off.
In use of the unit for heat recovery
purposes, the warm, stale air is ejected under pressure
into the top of the heat exchanger, while cold, ~resh
air is injected into the bottom. As the warm air is
cooled, it descends through the heat exchanger, while
the warming fresh air rises.
Both sides of the heat exchanger are fed
under pressure by the fans rather than having the fans
draw air through the exchanger. This limits the effect
of any leakage in the unit by minimizing any cross
leakage and produces an over pressure inside the unit
so that infiltration is eliminated. This also ensures
that there is constant air contact with the plates
between the ducts.
By injecting the fresh air at the bottom, to
exhaust at the top and injecting the warm, stale air at
the top to exhaust at the bottom, a combined counter
and cross flow effect is produce which provides a
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gradual temperature change of the two air flows to
minimize condensation and resultant corrosion.
While specific embodiments of the invention
have been described in the foregoing, it is to be
understood that the invention is not limited to those
embodiments alone. The scope of the present invention
is to be ascertained by reference to the accompanying
claims.
