Note: Descriptions are shown in the official language in which they were submitted.
CA 02509571 2005-06-09
PRESSURE SENSITIVE BYPASS DEFROST SYSTEM
1
FIELD OF THE INVENTION
This invention relates to air exchange ventilators for admitting fresh air
into an
enclosure while exhausting stale air. More particularly, this invention
relates to a defrost
arrangement for air exchange ventilators which include a heat exchanger to
extract heat
6 from the stale air and transfer it to the incoming fresh air, and which
introduces warm air
in both channels of the heat exchanger to accelerate defrost, continue some
ventilation of
stale warm air, and recirculate a portion of the stale air flow at mild
temperatures as
opposed to the lower temperatures of incoming fresh air.
11 BACKGROUND
Highly energy efficient buildings are generally designed to avoid uncontrolled
intake and out-take of air. As some air exchange is necessary to remove stale
air and
replace it with fresh air, it is desirable in winter to first remove heat and
or energy from
16 the stale air and replace it with fresh air, and it is preferable to first
remove heat and or
energy from the stale air being exhausted to avoid losing this heat. A
heat/energy
recovery ventilator is therefore used for this purpose.
A heat recovery ventilator includes a heat exchanger with two discrete air
21 passageways; one for stale air exhaust, and the other for fresh air supply.
As the exhaust
air passes out of the enclosure or building through the heat exchanger, it
gives up its heat
to the fresh supply air entering the enclosure through the heat exchanger.
Accordingly,
the heat is recovered in the ventilator during the ventilation process and
hence the name,
"heat recovery" ventilator. Note: The heat exchangers performance is dependant
on the
26 difference in temperature and energy recovery unit works because of a
difference in
enthalpy between the two airstreams.
Problems ensue with heat recovery ventilators in situations where the fresh
air
supply is near or below freezing temperatures. During colder seasons, as the
stale air
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CA 02509571 2005-06-09
1 generally contains moisture, once it passes up heat the moisture will freeze
in the stale air
exhaust passageway or on components in the heat recovery ventilator.
Eventually, ice-
build up will block the passageway, preventing or inhibiting the exhausting of
stale air,
or cross contamination due to flap leakage may occur; Balanced ventilation
suggests that
both incoming and outgoing flows are equal and that pressure drops created
within the
6 heat exchanger are higher on the fresh air channel because of its fluted
passageway, thus
preventing the flap from opening.
Different mechanisms have been proposed in order to defrost the ventilator,
for
example, as disclosed in Canadian Patent No. 2,059,195 and Canadian Patent No.
11 2,140,232. According to the latter, two actuators and respective valves or
flaps are used
to close the exhaust outlet and fresh supply air inlet. Stale air is thereby
redirected to
return back through the fresh supply air passageway to defrost the stale
exhaust air
passageway. This is carried out periodically, typically before the passageways
totally
freeze up. A drawback to this arrangement is the cost and complexity
associated with
16 utilizing two actuators each controlling separate valves or flaps.
The former patent suggests that instead of having two actuators, it is
possible to
prevent the cold supply infiltration inlet by diverting stale air exhaust back
through the
fresh supply air passages in the heat exchanger. While this does eliminate a
valve or flap
21 and an actuator, it does present its own problems. As the actuator and
flaps are disposed
adjacent the cold supply there is a possibility of their freezing, thereby
rendering them
inoperable. Furthermore, while the fresh air supply is closed stale air is
recirculated.
Other problems inherent with conventional heat recovery ventilators is that,
while
26 such ventilators in a continuous operational mode, with both fans
operating, to circulate
air through the heat exchanger provides a balanced ventilation, during defrost
mode,
however, the fresh air intake motor shuts off to allow the stale air to warm
up the heat
exchanger, and such a shut off system can contribute to the depressurization
within the
dwelling. What is required is a heat recovery ventilator defrost system which
introduces
31 warm air in both channels of the heat exchanger to limit the
depressurization and increase
the efficiency of a defrost system.
2
CA 02509571 2005-06-09
1 SUMMARY OF THE INVENTION
An object of the present invention is to provide an improved heat recovery
ventilator defrost system utilizing a bypass section which supplies warm air
in both
channels of the heat exchanger to accelerate defrost, continue some
ventilation of stale
6 cold air, and recirculate a portion of the warm stale air flow to limit the
depressurization
effect, so as to maintain the heating capacity of the heat exchanger.
According to another object of the present invention, there is provided an
improved heat recovery ventilator defrost system which utilizes a non-
motorized bypass
11 section for supplying warm air to both channels of the heat exchanger.
A still further object of the present invention is to provide an improved heat
recovery ventilator defrost system which uses two independent air flows for
defrosting of
the heat exchanger.
16
A still further object of the present invention involves providing a means for
protection against system failures. A malfunction that would have both motors
operate
continuously in wintertime would eventually produce frost build up in the
stale air
passageway of the heat recovery element, thus increasing the pressure drop
that would in
21 turn open the bypass section to let the warm stale air flow in the fresh
air passageway to
reheat the heat exchanger.
According to one aspect of the present invention, there is provided a heat
3
CA 02509571 2005-06-09
1 recovery ventilator comprising a heat exchanger having discrete inlet and
exhaust
passageways extending therethrough for providing heat transfer and flow
between
respective fluids flowing along said inlet and said exhaust passageways, said
inlet
passageway providing fluid communication between an inlet plenum and a supply
plenum, said exhaust passageway providing fluid communication between an
exhaust
6 plenum and an exhaust discharge plenum; and a bypass section positioned
between said
inlet plenum and said exhaust plenum, the bypass section being movable between
a
venting configuration, in which the bypass section is in a closed position for
allowing
fluid communication between the exhaust plenum and the exhaust discharge
plenum, and
a defrost configuration, in which the bypass section is in an open position
and permits
11 fluid communication between said inlet plenum and said exhaust plenum, in
addition to
allowing fluid communication between the exhaust plenum and the exhaust
discharge
plenum.
According to another aspect of the present invention, there is provided a heat
16 recovery ventilator comprising a heat exchanger having discrete inlet and
exhaust
passageways extending therethrough for providing heat transfer and flow
between
respective fluids flowing along said inlet and said exhaust passageways, said
inlet
passageway providing fluid communication between an inlet plenum having an
inlet port
for admitting supply air into said inlet plenum and a supply plenum having a
supply port
21 for discharging supply air, said exhaust passageway providing fluid
communication
between an exhaust plenum having an exhaust inlet port and an exhaust
discharge
plenum, said exhaust discharge plenum having an exhaust port for discharging
exhaust
4
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1 air from said exhaust discharge plenum; and a bypass section positioned
between said
inlet plenum and said exhaust plenum, the bypass section being movable between
a
venting configuration, in which the bypass section is in a closed position for
allowing
fluid communication between the exhaust plenum and the exhaust discharge
plenum, and
a defrost configuration, in which the bypass section is in an open position
and permits
6 fluid communication between said inlet plenum and said exhaust plenum, in
addition to
allowing fluid communication between the exhaust plenum and the exhaust
discharge
plenum.
Yet another aspect of the present invention provides for a heat recovery
ventilator
11 comprising a heat exchanger having discrete inlet and exhaust passageways
extending
therethrough for providing heat transfer and flow between respective fluids
flowing along
said inlet and said exhaust passageways, said inlet passageway providing fluid
communication between an inlet plenum having an inlet port for admitting
supply air into
said inlet plenum and a supply plenum having a supply port for discharging
supply air,
16 said exhaust passageway providing fluid communication between an exhaust
plenum
having an exhaust inlet port and an exhaust discharge plenum, said exhaust
discharge
plenum having an exhaust port for discharging exhaust air from said exhaust
discharge
plenum; a supply fan mounted within the inlet plenum for augmenting fluid flow
along
said inlet passageway; an exhaust fan mounted within one of the exhaust plenum
and the
21 exhaust discharge plenum for augmenting fluid flow along the exhaust
passageway; and a
bypass section positioned between said inlet plenum and said exhaust plenum,
the bypass
section being movable between a venting configuration, in which the supply fan
is turned
CA 02509571 2005-06-09
1 on and the bypass section assumes a closed position for allowing fluid
communication
between the exhaust plenum and the exhaust discharge plenum, and a defrost
configuration, in which the supply fan is turned off and the bypass section
assumes an
open position and permits fluid communication between said inlet plenum and
said
exhaust plenum, in addition to allowing fluid communication between the
exhaust
6 plenum and the exhaust discharge plenum.
The advantage of the present invention is that it provides an improved heat
recovery ventilator defrost system utilizing a bypass section which supplies
warm air in
both channels of the heat exchanger to accelerate defrost, continue some
ventilation of
11 stale cold air, and recirculate a portion of the warm stale air flow to
limit the
depressurization effect, so as to maintain the heating capacity of the heat
exchanger.
Yet another advantage of the present invention is that it provides an improved
heat recovery ventilator defrost system which utilizes a non-motorized bypass
section for
16 supplying warm air to both channels of the heat exchanger.
A still further advantage of the present invention is that it provides an
improved
heat recovery ventilator defrost system which uses two independent air flows
for
defrosting of the heat exchanger.
21
A still further advantage of the present invention is that it provides a means
for
protection against system failures. A malfunction that would have both motors
operate
6
CA 02509571 2005-06-09
1 continuously in wintertime would eventually produce frost build up in the
stale air
passageway of the heat recovery element, thus increasing the pressure drop
that would in
turn open the bypass section to let the warm stale air flow in the fresh air
passageway to
reheat the heat exchanger.
6 BRIEF DESCRIPTION OF THE FIGURES
Figure 1 is a side perspective view, which illustrates the intake of fresh air
and exhaust of
stale air in a conventional air exchange ventilation system;
Figure 2 is a side perspective view of one embodiment of the present
invention, which
11 illustrates the intake of fresh air and exhaust of stale air, and which
illustrates the airflow
of two independent air flows for defrosting of the heat exchanger; and
Figure 3 is a diagram of an interior of a heat recovery ventilator according
to the present
invention in a ventilation mode;
16
Figure 4 is a side view which illustrates the intake of fresh air and exhaust
of stale air in a
conventional air exchange ventilation system;
Figure 5 is a side view which further illustrates the embodiment shown in
Figure 3, and
21 which shows an interior of a heat recovery ventilator according to the
present invention in
a ventilation mode;
Figure 6 is a side view which further illustrates the embodiment shown in
Figure 3, and
which shows an interior of a heat recovery ventilator according to the present
invention in
26 a ventilation mode; and
7
CA 02509571 2005-06-09
1 Figure 7 is a side view which further illustrates the embodiment shown in
Figure 3, and
which shows an interior of a heat recovery ventilator according to the present
invention in
a ventilation mode.
DESCRIPTION OF THE PREFERRED EMBODIMENT
6 The present invention provides a defrost arrangement for air exchange
ventilators
which includes a heat exchanger to extract heat from the stale air and
transfer it to the
incoming fresh air, and which introduces warm air in both channels of the heat
exchanger
to accelerate defrost, continue some ventilation of stale warm air, and
recirculate a
portion of the stale air flow at mild temperatures as opposed to the lower
temperatures of
11 incoming fresh air. In conventional systems, during the defrost mode the
fresh air motor
shuts off, and warm stale air is used to defrost the heat exchanger. This air
is then totally
expelled outdoors which can contributes to the depressurization within the
dwelling or
building. With reference to Figures 1 and 4, incoming fresh air is admitted
into the air
exchange system at (2) to flow through an inlet passageway (4), which is then
passed
16 through the heat exchanger (6), to flow (8) into an enclosure. Exhaust air
to be
discharged from the enclosure flows at (10) through the heat exchanger (6) to
an outlet
passageway (12) and out of the enclosure at (14).
In the present invention, the heat recovery ventilator utilizes a non-
motorized
21 bypass section (flap) to introduce warm air to both channels of the heat
exchanger, so as
to accelerate defrost, continue some ventilation of stale warm air, and
recirculate a
portion of the stale air flow, so as to warm incoming cold fresh air. In the
present
invention, because the stale air is under a positive pressure, the air being
bypassed is
8
CA 02509571 2005-06-09
1 being sucked back into the dwelling, thus reducing the net stale air
exhausted to the
outdoors. Thus, the present invention provides a highly effective defrost
arrangement for
air exchange ventilators which operates to provide extreme weather
performance, and
withstand extreme cold. During normal ventilation, the static pressure created
by air
moving through the fresh air passages in the heat exchanger creates more of a
pressure
6 drop than the strait air passages on the stale air side. Thus, this
differential pressure is
used to close off the bypass section (flap).
In one embodiment of the present invention and with reference to Figure 2, a
heat
recovery ventilator 1 utilizes a non-motorized bypass section (flap) 42 to
introduce warm
11 air to both channels of the heat exchanger or heat exchanger 6 during
defrost, in one air
flow marked as S to warm one channel of the heat exchanger 6, and another
independent
air flow 7, which flows through the bypass section (flap) 42 to warm the other
channel of
the heat exchanger 6.
16 During defrost, and with further reference to Figures 3, 5, 6 and 7, at the
heat
exchanger of the heat recovery ventilator 1 is a heat exchanger 6 having an
inlet
passageway illustrated by arrow 20 and an exhaust passageway illustrated by
arrow 36.
To augment air flow along the inlet passageway 20 and exhaust passageway 36,
an
exhaust fan 54 may be mounted within an exhaust plenum 34, and a supply fan 60
may
21 be mounted in an inlet plenum 24. Of course, providing such fans within the
heat
recovery ventilator 1 is desirable in order to make the heat recovery
ventilator 1 a "stand
9
CA 02509571 2005-06-09
1 alone" unit. Preferably, these fans should be of similar capacity and may be
arranged, if
required, to share a common motor (not shown).
A housing (not shown) defines an exterior of the heat recovery ventilator 1,
and it
will be appreciated that the actual unit will have a front cover, which is not
shown in the
6 Figures so as to show its interior. The inlet passageway 20 and outlet
passageway 36
allow heat transfer between respective fluids flowing therealong without
allowing co-
mingling of the fluids. As is common with air to air heat exchangers, the heat
exchanger
6 may comprise a plurality of individual passageways therein (not shown),
which allows
fluids flowing in the inlet passageway 20 and exhaust passageway 36 and
through the
11 heat exchanger 6 a greater surface area with which to enhance heat
transfer. The inlet
passageway provides fluid communication between the inlet plenum 24 and supply
plenum 26. The outlet passageway provides fluid communication between the
exhaust
plenum 34 and discharge plenum 40. The inlet plenum 24 has an intake port 30
for
admitting fresh supply air (outside air) 28 into the inlet plenum 24.
16
The supply plenum 26 has a supply port 31 for discharging air 29, which has
passed through the heat exchanger 6 from the heat recovery ventilator 1 into
an enclosure
or dwelling. The discharge plenum 40 has an exhaust port 33 for discharging
exhaust air
37 from the discharge plenum 40. The exhaust plenum 34 has an exhaust inlet
port 35 for
21 admitting warm air 38 from an enclosure or dwelling into the exhaust plenum
34. It will,
however, be understood that external fans (not shown) might also be connected
to the
exhaust inlet port 35 and the intake port 30 to assist in augmenting air flow
along the
CA 02509571 2005-06-09
1 inlet passageway 20 and outlet passageway 36.
A non-motorized bypass section (flap) 42 separates the inlet plenum 24 and the
exhaust plenum 34, and, when the bypass section (flap) 42 is opened, provides
fluid flow
and communication therebetween, in a discharge mode. As noted previously, the
heat
6 recovery ventilator utilizes a non-motorized, passive bypass section (flap)
42 to introduce
warm air to both channels of the heat exchanger 6, so as to accelerate
defrost, continue
some ventilation of stale warm air, and recirculate a portion of the stale air
flow, so as to
warm incoming cold fresh air. In the present invention, because the air is
under a
negative pressure, the air being bypassed is being sucked back into the
dwelling, thus
11 reducing the net stale air exhausted to the outdoors. With further
reference to Figure 3,
when heat recovery ventilator 1 is in its ventilation mode, warm moist air
from a
dwelling is replaced with fresh outside air, while, at the same time,
recovering the heat
from the warm moist air to be expelled and transferring it to the incoming
fresh outside
air, while at the same time accelerating defrosting of the heat exchanger 6.
Of course, the
16 transfer of heat to the incoming fresh air will cause condensation on the
heat exchanger,
which will accumulate, thus requiring defrosting of the heat exchanger 6.
As noted above, the air being exhausted (by way of the exhaust fan) through
the
exhaust plenum 34 is under a negative pressure, so the stale air will still be
sucked out,
21 and fresh air drawn in, even when the fresh air supply fan is not on (such
as during
defrost mode). In the embodiment of the present invention shown in Figure 3,
warm
exhaust air 38 to be expelled enters the exhaust inlet port 35 and into the
exhaust plenum
34. Because the air being exhausted (by way of the exhaust fan) through the
exhaust
plenum 34 is under a negative pressure, the stale air will still be sucked out
through
26 exhaust passageway 36 into discharge plenum 40 (along flow path 77 in
Figure 3 and
11
CA 02509571 2005-06-09
1 which is also indicated as flow path "B" in Figure 5), but also through the
passive non-
motorized bypass section (flap) 3 (which move to allow the air flow
therethrough under
the negative pressure) into inlet plenum 24 (along flow path 79 in Figure 3
and which is
also indicated as flow path "A" in Figure 5). Further, because fresh air
continues to be
drawn into inlet plenum 24, due to the negative pressure, the warm stale air
which has
6 passed through the bypass section (flap) 42 into inlet plenum 24 is then
drawn through
the heat exchanger 6 along the inlet passageway 20 into supply plenum 26, and
out
through supply port 31 into the enclosure or dwelling. With reference to
Figures 3,5,6
and 7, it can be seen that two independent air flows are introduced in both
channels of the
heat exchanger 6, so as to accelerate defrost, continue some ventilation of
stale warm air,
11 and recirculate a portion of the stale air flow at mild temperatures as
opposed to the
lower temperatures of incoming fresh air. During normal ventilation (that
being, when
the fresh air supply motor is engaged after the defrost mode), the static
pressure then
created by air moving through the fresh air passages in the heat exchanger
creates more
of a pressure drop than the strait air passages on the stale air side. Thus,
this differential
16 pressure is used to then close off the bypass section (flap).
The invention being thus described, it will be obvious that the same may be
varied in many ways. Such variations are not to be regarded as a departure
from the spirit
and scope of the invention, and all such modifications as would be obvious to
one skilled
21 in the art are intended to be included within the scope of the following
claims.
12
