Note: Descriptions are shown in the official language in which they were submitted.
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VARIABLE EFFECTIVENESS HEAT RECOVERY VENTILATOR
=
Description
Technical Field
[0001]The present disclosure relates to heat recovery ventilators.
Background
(0002] Heat recovery ventilators are utilized in ventilation units to exchange
thermal
energy between outgoing air exhausted from a conditioned space and incoming
fresh
air supplied to the conditioned space. By exchanging thermal energy, more
efficient
heating or cooling can be achieved compared to the same energy input to an
electric
heater or an air conditioner of the ventilation unit in which thermal energy
is not
exchanged.
[0003] Prior art heat recovery ventilators may have a single heat exchanger
through
which incoming and exhaust airflows both pass without mixing with one another.
As the
two airflows pass through the heat exchanger, the warmer air flow transfers a
portion of
its heat to the cooler airflow by conduction through the heat exchanger. In
this way heat
is `recovered' from the warmer airflow, hence the name `heat recovery
ventilator'.
[0004]In prior art heat recovery ventilators, thermal energy exchanged through
.a
thermally conductive barrier separating the incoming and outgoing airflows.
The
amount of thermal energy exchanged is based on the temperature difference
between
the incoming and outgoing airflows. When the warmer outgoing airflow is cooled
below
its dew point, i.e., the temperature at which water vapour in the outgoing
airflow
condenses, moisture will condense out of the outgoing airflow and collect on
the
thermally conductive barrier. If the temperature of the thermally conductive
barrier is
below 0 C, the moisture will form a layer of ice that can eventually block the
flow of the
outgoing airflow.
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[0005] When the outgoing airflow is blocked due to ice build-up, prior art
heat recovery
ventilators may enter a 'defrost mode' in which the flow of incoming fresh air
is stopped
so that the warm outgoing air can blow against the built-up ice to cause
thawing. Thus,
during the defrost mode, incoming fresh air is not supplied to, and outgoing
air is not
removed from the conditioned space. In climates having extremely cold
temperatures,
the amount of time that the heat recovery ventilator spends in defrost mode
may be
such that the air quality of the conditioned space is negatively impacted.
[0006] Prior art that prevents condensation before it occurs in space
conditioners may
rely on varying the ratio of incoming to outgoing airflow rates or the input
of additional
energy to raise temperatures inside the device. Both approaches work reliably
and
economically when the temperature difference between the conditioned and
unconditioned spaces is relatively close. However, as conditioned and
unconditioned
temperatures diverge, prior art devices that prevent condensation may develop
limitations to reliably providing adequate ventilation to a conditioned space
similar to
those encountered by designs employing a 'defrost mode', or become undesirably
expensive to build and operate.
[0007] Improvements to heat recovery ventilators are desired.
Summary
[0008]One aspect of the invention provides a heat recovery ventilator for
transferring
thermal energy from an outgoing airflow to an incoming airflow, the heat
recovery
ventilator includes an outgoing duct having an outgoing fan for moving the
outgoing
airflow from a conditioned space through the outflow duct, an incoming duct
having an
incoming fan for moving the incoming airflow through the incoming duct into
the
conditioned space, a heat exchange pump within a closed-loop heat exchange
duct for
circulating a heat exchange fluid within the closed-loop heat exchange duct,
the closed-
loop heat exchange duct comprising a first portion in thermal communication
with the
outgoing duct and a second portion in thermal communication with the incoming
duct, a
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sensor located in the outgoing duct downstream from a location within the
outgoing duct
that is in thermal communication with the first portion of the closed-loop
heat exchange
duct, wherein the sensor measures a temperature of the outgoing airflow at the
location,
and a controller operatively coupled to the sensor and the heat exchange pump
and
programmed to cause the heat exchange pump to circulate the heat exchange
fluid
within the closed-loop heat exchange duct at an initial rate of circulation,
receive a
signal from the sensor associated with at least the temperature of the
outgoing airflow,
determine, based on the signal, that the temperature of the outgoing airflow
is at or
below a threshold temperature, and in response to determining that the
temperature is
below the threshold temperature, cause the pump to circulate heat exchange
fluid at a
reduced rate of circulation which is lower than the initial rate of
circulation to reduce the
thermal energy that is transferred from an outgoing airflow to an incoming
airflow.
[0009]According to another aspect, the threshold temperature is determined
based on
an error limit of the sensor.
[0010] Acco rd n g to another aspect, the reduced rate of circulation is a
predetermined
percentage of the initial rate of circulation.
[0011]According to another aspect, the threshold temperature is zero degrees
Celsius.
[0012] Acco rd i n g to another aspect, causing the pump to circulate heat
exchange fluid
at a reduced rate of circulation includes turning off the heat exchange pump.
[0013] According to another aspect, the sensor measures a relative humidity of
the
outgoing airflow.
[0014] According to another aspect, the threshold temperature is determined
based on a
dew point determined from the relative humidity.
[0015] Acco rd n g to another aspect, the heat exchange fluid is air.
[001 6]According to another aspect, the heat exchange pump is an impeller.
[0017] Acco rd i n g to another aspect, the initial rate of circulation is a
rate of circulation at
which a mass flow rate of heat exchange fluid multiplied by a heat capacity of
the heat
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exchange fluid equals the lesser of an airflow mass flow rate multiplied by an
airflow
heat capacity for the outgoing airflow or the incoming airflow.
[0018]According to another aspect, the threshold temperature comprises a first
threshold temperature and a second threshold temperature lower than the first
threshold
temperature, and the controller is programmed to, in response to determining
that the
temperature is at or below the first threshold temperature, cause the pump to
circulate
heat exchange fluid at a first reduced rate of circulation, and in response to
determining
that the temperature is at or below the second threshold temperature, cause
the pump
to circulate heat exchange fluid at a second reduced rate of circulation that
is lower than
the first rate of circulation.
[0019]According to another aspect, the first threshold temperature is
determined based
on an error limit of the sensor, and the first reduced rate of circulation is
a percentage of
the initial rate.
[0020]According to another aspect, the second threshold temperature is zero
degrees
Celsius, and the second reduced rate of circulation is provided by turning the
heat
exchange pump off.
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Drawings
[0021] The following figures set forth embodiments in which like reference
numerals
denote like parts. Embodiments are illustrated by way of example and not by
way of
limitation in the accompanying figures.
[0022] FIG. 1 is a schematic representation of a heat recovery ventilator
according to an
embodiment;
[0023] FIG. 2 is a schematic representation of a heat recovery ventilator
according to
another embodiment;
[0024] FIG. 3 is a flow chart illustrating a method for controlling a heat
recovery
ventilator according to an embodiment;
[0025] FIG. 4 is a flow chart illustrating a method for controlling a heat
recovery
ventilator according to another embodiment;
[0026] FIG. 5 is a flow chart illustrating a method for controlling a heat
recovery
ventilator according to another embodiment;
[0027] FIG. 6 is an isometric view of a heat recovery ventilator according to
an
embodiment;
[0028] FIGS. 7a is the same view of the heat recovery ventilator shown in FIG.
6 with
portions of the housing cut away;
[0029] FIG. 7b is an isometric view of a backside of the heat recovery
ventilator shown
in FIG. 6 with portions of the housing cut away;
[0030] FIG. 8 is a front view of the heat recovery ventilator according to the
embodiment
shown in FIG. 6 with the front wall of the housing removed; and
[0031] FIG. 9 is a schematic isometric view depicting the airflow through the
heat
recovery ventilator according to the embodiment shown in FIGS. 6 with the
housing
removed.
Detailed Description
[0032] The following describes a heat recovery ventilator in which heat is
exchanged
between an outgoing airflow flowing through an outgoing duct and an incoming
airflow
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through an incoming duct via a heat exchange fluid flowing through a closed-
loop heat
exchange duct. The rate of circulation of the heat exchange fluid is
adjustable to vary
the amount of thermal energy transferred between the incoming airflow and the
outgoing airflow. A controller is utilized to control the rate of circulation
of the heat
exchange fluid based on the temperature of the outgoing airflow to inhibit
condensate in
the outgoing duct from freezing without interrupting the ventilation of the
conditioned
space. The disclosed heat recovery ventilator may be utilized to ventilate
conditioned
spaces located in environments in which the incoming air is below 0 C for
extended
periods of time, such as in arctic or sub-arctic climates, for example
Northern Canada.
[0033] For simplicity and clarity of illustration, reference numerals may be
repeated
among the figures to indicate corresponding or analogous elements. Numerous
details
are set forth to provide an understanding of the examples described herein.
The
examples may be practiced without these details. In other instances, well-
known
methods, procedures, and components are not described in detail to avoid
obscuring
the examples described. The description is not to be considered as limited to
the scope
of the examples described herein.
[0034] Referring to FIG. 1, a heat recovery ventilator 100 includes an
outgoing duct 102,
an incoming duct 108, and a closed-loop heat exchange duct 114. The outgoing
duct
102 and incoming duct 108 are separate to keep an outgoing airflow,
represented by
the arrow 104, flowing through the outgoing duct 102 from intermingling with
an
incoming airflow, represented by the arrow 110, flowing through the incoming
duct 108.
Thermal energy is exchanged between the outgoing airflow 104 and the incoming
airflow 110 by a heat exchange fluid, represented by the arrow 115, that flows
through
the closed-loop heat exchange duct 114.
[0035] The outgoing airflow 104 is air from inside a conditioned space 130,
such as the
inside of a room or a building, for example. The outgoing airflow 104 flows
through the
outgoing duct 102 to be vented outside of the conditioned space 130, such as
the
environment outside a building housing the conditioned space, for example. The
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incoming airflow 110 is air from outside the conditioned space that flows
through the
incoming duct 108 into the conditioned space 130. The outgoing airflow 104
removes
air from within the conditioned space and the incoming airflow 110 replaces
the
removed air with fresh air.
[0036] The outgoing airflow 104 is forced through the outgoing duct 102 by an
outgoing
fan 106 and the incoming airflow 110 is forced through the incoming duct 108
by an
incoming fan 112. The outgoing fan 106 and incoming fan 112 may include, for
example, an impeller or other suitable mechanism for forcing air through the
respective
outgoing duct 102 and incoming duct 108. The outgoing fan 106 and incoming fan
112
may be electrically powered, for example.
[0037] The closed-loop heat exchange duct 114 includes a first portion 116, in
which the
heat exchange fluid 115 is in thermal contact with the outgoing airflow 104,
and a
second portion 118, in which the heat exchange fluid is in thermal contact
with the
incoming airflow 110. The first portion 116 and the second portion 118 of the
closed-
loop heat exchange duct 114 may be, for example, heat exchange cores, or any
other
suitable structures for providing thermal contact between the heat exchange
fluid 115
and the outgoing airflow 104 and the incoming airflow 110. Heat exchange cores
include at least two channels separated by a thermally conductive wall such
that two
fluid streams flowing through a respective channel can exchange thermal energy
without the two streams intermingling. Heat exchange cores are discussed in
more
detail below with reference to FIGS. 7a and 7b.
[0038] The closed-loop heat exchange duct 114 includes a pump 120 that
circulates the
heat exchange fluid 115 through the closed-loop heat exchange duct 114. The
pump
120 is a variable speed pump to enable adjustment of a rate of circulation of
the heat
exchange fluid 115. In an embodiment, the heat exchange fluid 115 may be a
gas,
such as air, for example. In this embodiment, the pump 120 may be a fan having
an
impeller or other suitable mechanism for circulating the air through the
closed-loop heat
exchange duct 114. In another embodiment, the heat exchange fluid is a liquid
such as,
for example, water or a water-glycol mix. In this embodiment, the pump 120 may
be
any mechanism suitable for circulating the liquid through the closed-loop heat
exchange
duct 114.
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[0039] In conditions in which the temperature of the incoming airflow 110 is
less than
zero degrees Celsius, such as in the winter in colder climates, or in arctic
environments,
the rate of circulation of the heat exchange fluid 115 may be varied to reduce
the
amount of thermal energy transferred from the outgoing airflow 104 to the
incoming
airflow 110 such that the temperature of the outgoing airflow 104 is not
reduced to the
point that condensate in the outgoing duct 102 freezes, forming ice.
[0040] In operation, the pump 120 is turned on to circulate the heat exchange
fluid 115
through the closed-loop heat exchange duct 114. A portion of the heat exchange
fluid
115 in the first portion 116 absorbs thermal energy from the outgoing airflow
104,
heating the heat exchange fluid 115 in the first portion 116 and cooling the
outgoing
airflow 104 such that the outgoing airflow 104 downstream of the first portion
116 is
cooler than the outgoing airflow 104 upstream of the first portion 116. The
heated heat
exchange fluid 115 exiting the first portion 116 flows through the closed-loop
heat
exchange duct 114 into the second portion 118 where thermal energy is
transferred
from the heat exchange fluid 115 in the second portion 118 to the incoming
airflow 110,
cooling the heat exchange fluid 115 in the second portion 118 and heating the
incoming
airflow 110 such that the incoming airflow 110 downstream of the second
portion 118 is
warmer than the incoming airflow 110 upstream of the second portion 118.
[0041] In FIG. 1, the heat exchange fluid 115 is shown circulating through the
closed-
loop heat exchange duct 114 in a counterclockwise direction, however the heat
exchange fluid 115 could also flow in a clockwise direction.
[0042]A controller 122 is also operatively coupled to a sensor 124 within the
outgoing
duct 102. The sensor 124 measures the temperature of the outgoing airflow 104
prior
to exiting the outgoing duct 102. The sensor 124 may be coupled to a wall
within the
outgoing duct 102 downstream from the first portion 116 of the closed-loop
heat
exchange duct 114. Locating the sensor 124 immediately downstream of the first
portion 116 is desired so that the sensor 124 measures the temperature of the
outgoing
airflow 104 immediately after passing over the first portion 116. The
temperature of the
cooled outgoing airflow 104 immediately downstream of the first portion 116
provides
the best indication of whether the condensate in the outgoing duct 102 is at
risk of
freezing.
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[0043]In some embodiments, the sensor 124 may also measure the relative
humidity of
the outgoing airflow 104 in addition to measuring temperature. A single sensor
124 may
be utilized to measure both the temperature and humidity, or the sensor 124
may
comprise separate temperature and humidity sensors. For example, the sensor
124
may be a Relative Humidity/Temperature Transmitter manufactured by Omega TM
under
model number HX94A. Relative humidity measurements may be utilized to
determine,
for example by the controller, a dew point of the outgoing airflow 104, which
provides a
better indication of the temperature at which water vapour in the outgoing
airflow 104
will condensate. In this embodiment, a determination that ice is likely to
form may be
made when the temperature of the outgoing airflow 104 is below the lesser of 0
C and
the dew point of the outgoing airflow 104.
[0044]The amount of thermal energy transferred from the outgoing airflow 102
to the
heat exchange fluid 115 and from the heat exchange fluid 115 to the incoming
airflow
110 depends on the mass flow rates and the thermal heat capacities of the
outgoing
airflow 104, the incoming airflow 110 and the heat exchange fluid 115, and on
the
temperature differences between the outgoing airflow 104 and the heat exchange
fluid
115 in the first portion 116 and between the incoming airflow 110 and the heat
exchange fluid 115 in the second portion 118. Assuming that the temperature
differences between the airflows 104, 110 and the heat exchange fluid, and the
mass
flow rates of the airflows 104, 110 are substantially constant, varying the
rate of
circulation of the heat exchange fluid 115 through the closed-loop heat
exchange duct
114 varies the mass flow rate of the heat exchange fluid 115 which, in turn,
varies the
amount of thermal energy transferred from the outgoing airflow 104 to the
incoming
airflow 110 via the heat exchange fluid 115.
[0045] The controller 122 is operatively coupled to the pump 120 to vary the
rate of
circulation of the heat exchange fluid 115 through the closed-loop heat
exchange duct
114 by, for example, varying the voltage supplied to the pump 120. The
controller 122
may include, for example, a microprocessor 125 that executes computer-
executable
code stored in a memory 127 to determine whether to reduce the rate of
circulation of
the heat exchange fluid 115 to inhibit ice formation in the outgoing duct 102
based on
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the temperature, and relative humidity in some embodiments, measured by the
sensor
124. The microprocessor 125 may be, for example, an Arduino TM
microcontroller.
[0046] Referring to FIG. 2, in an alternative embodiment of a heat recovery
ventilator
145, a first sensor 140 is located in the outgoing duct 102 upstream from the
first portion
116. A second sensor 142 is located in the incoming duct 108 upstream from the
second portion 118. In this embodiment, rather than measuring the temperature
of the
cooled outgoing airflow 104 downstream of the first portion 116 directly, the
theoretical
temperature value of the cooled outgoing airflow 104 is calculated, for
example by a
controller 123, based on the temperature of the outgoing airflow 104 upstream
of the
first portion 116, measured by the first sensor 140, and the temperature of
the incoming
airflow 110, measured by the second sensor 142.
[0047] The controller 123 controls the pump 120 to vary the rate of
circulation of the
heat exchange fluid 115 based on the calculated temperature value. The
controller 123
may include a microprocessor 125 that executes computer-executable code stored
in a
memory 129 to calculated the temperature of the cooled outgoing airflow 104
based on
the temperature measurements of the first sensor 140 and the second sensor 412
and
to determine whether to reduce the rate of circulation of the heat exchange
fluid 115
based on the calculated temperature.
[0048] Referring now to the flow chart of FIG. 3, a method for controlling
heat recovery
ventilator 100 is shown. The method may be carried out by software executed,
for
example, by a processor of the controller 122. Coding of software for carrying
out such
a method is within the scope of a person of ordinary skill in the art given
the present
disclosure. The method may contain additional or fewer processes than shown
and/or
described, and may be performed in a different order. Computer-readable code
executable by a processor of the controller 122 to perform the method may be
stored in
a computer-readable medium, such as a non-transitory computer-readable medium.
[0049] The rate of circulation of the heat exchange fluid 115 is set to an
initial rate at
202. The initial rate of circulation may be a predetermined rate that, for
example,
exchanges the greatest amount of thermal energy between the outgoing airflow
102 and
the incoming airflow 110. The initial rate of circulation for the heat
exchange fluid 115
that provides the greatest amount of thermal heat exchange may be determined
by
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determining a rate of circulation for which the product of the mass flow rate
times the
thermal heat capacity of the heat exchange fluid 115 is equal to the lesser of
the
products of the mass flow times the thermal heat capacity for the outgoing
airflow 104
and the incoming airflow 110. When the heat exchange fluid 115 utilized is
air, which
has approximately the same thermal heat capacity as the outgoing and incoming
airflows 104, 110, the greatest exchange of thermal energy occurs when the
rate of
circulation in which the mass flow of the heat exchange fluid 115 is equal to
the lesser
of the mass flows of the outgoing airflow 104 and the incoming airflow 110.
(0050] At 204, the temperature of the outgoing airflow 104 downstream of the
first
portion 116 is measured. The temperature may be determined by the sensor 124
or
may be determined by the controller 122 based on a signal received from the
sensor
124. Measuring the temperature may include the controller 122 signaling for
the sensor
124 to take a measurement. As discussed above, rather than directly measuring
the
temperature of the outgoing airflow 104 downstream of first portion 116, the
temperature determined at 204 may be a theoretical value calculated from
temperature
measurements by a first sensor of the temperature of the outgoing air 104
entering the
outgoing duct 102 and by a second sensor of the temperature of the incoming
airflow
110 entering the incoming airflow side.
[0051]At 206, a determination whether the temperature meets a first threshold
is made.
Determining that the first threshold is met may include determining that the
measured
temperature is less than or equal to the first threshold. The first threshold
may be set
at, for example, 0 C because 0 C is the temperature at which freezing may
begin to
occur. In other embodiments, the first threshold may be set to be within the
sensor's
124 error limit of 0 C. For example, if the sensor's 124 error limit is 3 C,
then the first
threshold may be set at 3 C.
(0052] When the determination at 206 is NO, the method returns to step 204 and
further
measurements of the temperature are made as described above. In this way, the
temperature of the outgoing airflow 104 and, in some embodiments the incoming
airflow
110, is monitored overtime.
(0053] When the determination at 206 is YES, the method continues to 208 and
the rate
of circulation is set to a reduced rate that is lower than the initial rate.
Setting the rate of
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circulation of the heat exchange fluid 115 to a reduced rate reduces the
amount of
thermal energy transferred from the outgoing airflow 104 to the heat exchange
fluid 115
to inhibit the formation of ice in the outgoing duct 102. The reduced rate may
be, for
example, a rate that optimizes the amount of thermal energy exchanged between
the
outgoing airflow 104 and incoming airflow 110 while inhibiting ice formation
within the
outgoing duct 102. In an embodiment the reduced rate may be, for example, a
predetermined percentage of the initial rate. In another embodiment, the
reduced rate
may be effectively zero, which is provided by turning off the power to the
pump 120. A
reduced rate of effectively zero will provide effectively no exchange of
thermal energy
between the outgoing airflow 104 and the incoming airflow 110 and may be
utilized
when the temperature of the outgoing airflow 104 is such that ice formation in
the
outgoing duct 102 is imminent or has already begun.
[0054]After the rate of circulation is set to the reduced rate at 208, the
method
continues to 210 in which the temperature of the outgoing airflow 104 is
measured
again. Step 210 is carried out similarly to step 204 and, therefore, is not
further
described to avoid repetition.
[0055]At 212, a determination is made whether the measurement at 210 meets a
second threshold. Determining that the second threshold is met may include
determining that the measurement is greater than or equal to the second
threshold. In
some embodiments the second threshold may be the same as the first threshold.
In
other embodiments, the second threshold may be higher than the first
threshold.
[0056] When the determination at 212 is YES, the method continues to 202 and
the rate
of circulation is set to the initial rate of circulation. By setting the rate
of circulation to
the initial rate of circulation when the temperature of the outgoing airflow
meets a
second threshold increases the rate of circulation and, thus, the amount of
thermal
energy exchanged between the outgoing airflow 104 and the incoming airflow 110
in
order to increase the energy efficiency of the heat recovery ventilator 100
when the risk
of ice formation in the outgoing duct 102 is reduced.
[0057] When the determination at 212 is NO, the method returns to 210 and a
further
temperature measurement is made. In this way, the outgoing airflow 104 and, in
some
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embodiments the incoming airflow 110, is monitored after the rate of
circulation is set to
the reduced rate of circulation.
[0058] Referring to FIG. 4, a flow chart illustrating an alternative method of
controlling
the heat recovery ventilator 100 is shown. In the method shown in FIG. 4,
steps 302-
312 are similar to steps 202-212, respectively, shown in FIG. 3 and described
above
and, therefore, will not be further described to avoid repetition.
[0059] However, when the measurement does not meet a second threshold, i.e.,
"NO"
at 312, the method continues to 314 and a determination whether the
temperature
meets a third threshold is made. The third threshold may be less than the
first threshold
at 308. Determining that the temperature meets the third threshold may include
determining that the temperature is less than or equal to the third threshold.
[0060] When the determination 314 is YES, the method continues to 316 in which
the
rate of circulation is set to a second reduced rate of circulation. The second
rate of
circulation may be less than the first rate of circulation. In an embodiment,
the first
threshold may be 3 C, the reduced rate may be half of the initial rate, the
second
threshold may be 0 C, and the second reduced rate may be effectively zero.
[0061]After the rate of circulation is set to the second reduced rate, the
method returns
to 310 in which the temperature is further measured.
[0062] By providing two thresholds having an associated reduced rate of
circulation of
the heat exchange fluid, the heat recovery ventilator 100 may address the
situation in
which the temperature of the outgoing airflow 104 continues to drop after the
rate of
circulation is set to the reduced rate.
[0063] In other embodiments, any number of thresholds having associated
reduced
rates of circulation may be included. Increasing number of thresholds, each
threshold
having an associated rate of circulation of the heat exchange fluid 115,
provides a heat
recover ventilator 100 with increased energy efficiency by better optimizing
the amount
of thermal energy exchanged between the outgoing airflow 104 and the incoming
airflow
110 while inhibiting the formation of ice within the outgoing duct 102.
[0064] Referring to FIG. 5, a flow chart illustrating a method of controlling
the heat
recovery ventilator 100 in which the sensor 124 measures both temperature and
relative
humidity is shown. In the method shown in FIG. 5, steps 350, 356-362 are
similar to
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steps 202, 206-212, respectively, shown in FIG. 3 and described above and,
therefore,
will not be further described to avoid repetition.
[0065]At 352, both the temperature and relative humidity of the outgoing
airflow 104 are
measured. The temperature and relative humidity may be determined by the
sensor
124 or may be determined by the controller 122 based on signals received from
the
sensor 124. Measuring the temperature and relative humidity may include the
controller
122 signaling for the sensor 124 to take a measurement.
[0066]At 354, first and second thresholds are determined based on the measured
relative humidity. As discussed above, the relative humidity and temperature
of the
outgoing airflow 104 determines the dew point at which water vapour
condensates out
of the outgoing airflow 104. In an embodiment, the first threshold may be set
to the
lesser of the dew point and 0 C. The second threshold may be determined to be
the
same as the first threshold. In other embodiments, the second threshold may be
higher
than the first threshold.
[0067]When the relative humidity of outgoing airflow 104 is very low, the dew
point may
be less than 0 C. By setting the first threshold to a dew point that is below
0 C, the heat
recovery ventilator 100 exchanges more thermal energy while inhibiting ice
formation
and, thus is better optimized, than if the first threshold were set to 0 C.
(0068] Referring now to FIGS. 6, 7a, and 7b, an example heat recovery
ventilator 400
utilizing a heat exchange fluid 115 is shown. The heat recovery ventilator 400
is usable
with controller 122 to vary a rate of circulation of a heat exchange fluid
115. The heat
recovery ventilator 400 utilizes air as the heat exchange fluid 115 and
utilizes a pair of
heat exchange cores 432, 436 that generally correspond to the first portion
116 and
second portion 118 of the closed-loop heat exchange duct 114 discussed with
reference
to FIG. 1.
[0069]The heat recovery ventilator 400 includes a housing having an inside
wall 404
that is positioned closest the conditioned space when the heat recovery
ventilator 400 is
installed, an outside wall 406 that is positioned away from the conditioned
space,
sidewalls 408, 410, a top wall 412, and a bottom wall 414. The inside wall 404
includes
two openings 416, 418 and the outside wall 406 includes two openings 420, 422.
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[0070] Within the housing 402, a dividing wall 424 separates the housing 402
into an
outgoing airflow side 428 and an incoming airflow side 430.
[0071] Outgoing side dividers 440, 441, 442, 443 extending from the dividing
wall 424
into the outgoing airflow side 428 separate the outgoing airflow side 428 into
four
quadrants 470, 471, 472, and 473. Quadrant 470 includes an outgoing impeller
446
coupled to an outgoing airflow inlet 444 that extends from the opening 416 in
the
outside wall 404 to the outgoing side divider 442. The outgoing impeller 446
functionally corresponds to the outgoing fan 106 in FIG. 1.
[0072] The outgoing airflow side 428 includes an outgoing heat exchange core
432.
The outgoing heat exchange core 432 includes two sets of channels 434 and 435.
The
channels 434 facilitate air flowing between quadrant 470 and quadrant 472, and
the
channels 435 facilitate air flowing between quadrant 471 and quadrant 473.
[0073] An outgoing duct 480 functionally corresponding to the outgoing duct
104 of FIG.
1 is formed by the outgoing airflow inlet 444, quadrant 470, channels 434 of
the heat
exchange core 432, and quadrant 472.
[0074] Incoming side dividers 445, 447, 449, and 451 extend from the dividing
wall 424
into the incoming airflow side 430 to separate the incoming airflow side 430
into four
quadrants 474, 475, 476, and 477. Quadrant 477 of the incoming airflow side
430
includes an incoming impeller 450 coupled to an incoming airflow inlet 448
extends from
the opening 420. The incoming impeller 450 functionally corresponds to the
incoming
fan 112 in FIG. 1.
[0075] The incoming airflow side 430 includes an incoming heat exchange core
436.
The incoming heat exchange core 436 includes two sets of channels 438 and 439.
The
channels 438 facilitate air flowing between quadrant 475 and quadrant 477, and
the
channels 439 facilitate air flowing between quadrant 474 and quadrant 476.
[0076] An incoming duct 482 functionally corresponding to the incoming duct
108 in FIG.
1 is formed by the incoming airflow inlet 448, quadrant 477, channels 438 of
the
incoming heat exchange core 436, and the quadrant 477.
[0077]Although the outgoing heat exchange core 432 and the incoming heat
exchange
core 436 shown in FIGS. 7a and 7b include four channels each (two channels in
each of
the two sets of channels), in other embodiments the outgoing heat exchange
core 432
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CA 02877249 2016-08-29
and the incoming heat exchange core 436 may include more or less than four
channels.
Increasing a number of channels in a heat exchange core increases the surface
area
over which the two airflows are in thermal contact, increasing the efficiency
of the
exchange of thermal energy between the airflows. An example of a heat exchange
core
type usable as the outgoing heat exchange core 432 and the incoming heat
exchange
core 436 is the 167999 series heat exchange cores manufactured by AIR-ERV
TechonologyTM.
[0078] Quadrant 476 of the incoming airflow side 430 includes a heat exchange
impeller
454 coupled to a heat exchange conduit 452 that extends from the dividing wall
424 to
the sidewall 410. The heat exchange impeller 454 is a variable speed impeller
and
functionally corresponds to the pump 120 in FIG. 1. The heat exchange impeller
454
may be a DB175-XX55 series variable speed centrifugal fan manufactured by
McLean TM, which has a variable speed between 0 and 2875 RPM associated with
input
power voltages between OV and 12V, for example.
[0079] A closed-loop heat exchange duct 484 functionally corresponding to the
closed-
loop heat exchange core 114 in FIG. 1 is formed by the heat exchange conduit
452 and
the quadrants 471, 477, 474 and 476.
[0080] Referring now to FIG. 8, the quadrant 472 that forms part of the
outgoing duct
480 includes a trough 456 disposed over an inside surface of the bottom wall
414. The
trough 456 collects condensate that forms when the air in the outgoing duct
480 is
cooled in the outgoing heat exchange core 432. The condensate that is
collected in
trough 456 flows out of the housing 402 through a drain 458 in the bottom wall
414.
[0081] The quadrant 472 also includes a sensor 624 functionally corresponding
to the
sensor 124 in FIG. 1. The sensor 624 is a HX94A temperature and humidity
sensor
manufactured by Omega TM. The sensor 624 extends into the quadrant 472 from an
upper portion of the outgoing side divider 443. The sensor 624 includes a
casing 625
that thermally separates the sensor 624 from the outgoing side divider 443 to
reduce
effect of the temperature of the outgoing side divider 443 on the measured
temperature.
The sensor 624 is positioned near the outgoing heat exchange core 432 to
measure the
temperature of the air in the outgoing duct 480 exiting the outgoing heat
exchange core
432.
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CA 02877249 2016-08-29
[0082]The sensor 624 is operatively coupled to a controller, such as
controller 122, that
is located outside of the housing 402 of the heat recover ventilator 400 in
the present
example. The controller 122 is also operatively coupled to the heat exchange
impeller
454, the outgoing impeller 446, and the incoming impeller 450. The controller
122 is
connected to the sensor 624, the heat exchange impeller 454, the outgoing
impeller
446, and the incoming impeller 450 by, for examples, wires 628 that pass into
the
housing 402. In some embodiments, the controller 122 may be wirelessly
connected to
the sensor 624, the heat exchange impeller 454, the outgoing impeller 446, and
the
incoming impeller 450. Power supplies are connected to the outgoing impeller
464 and
the incoming impeller 446 by wires that also pass into the housing 402.
[0083] The controller 122 also includes a power supply (not shown) to supply a
variable
input power voltage to the heat exchange impeller 454 to vary a rate of
circulation of an
airflow through the heat exchange duct 484 based on the temperature
measurements
from the sensor 624, as described above.
[0084] Referring now to FIG. 9, the passage of airflows through the outgoing
duct 480,
the incoming duct 482, and the closed-loop heat exchange duct 484 will be
described.
[0085] The outgoing impeller 446 generates an outgoing airflow 804
functionally
corresponding to the outgoing airflow 104 in FIG. 1. The outgoing impeller 446
draws
air from the conditioned space (not shown) through the opening 416 and into
the
outgoing airflow inlet 444. From the outgoing airflow inlet 444, the outgoing
impeller
446 forces the air into the quadrant 470, through the channels 434 of the
outgoing heat
exchange core 432 into the quadrant 472 and out through opening 422 into the
external
environment (not shown).
[0086] The opening 416 may be open directly to the conditioned space or may be
connected to the conditioned space by a duct (not shown). The opening 422 may
be
open directly to the external environment of the conditioned space or may be
connected
to the external environment by a duct (not shown).
[0087] In the heat recovery ventilator 400, the outgoing airflow 804 exits the
outgoing
duct 480 at a lower portion of the housing 402 such that any condensate that
is
generated from the cooling of the outgoing airflow 804 in the outgoing heat
exchange
core 432 is collected by the trough 456 and exits the housing 402 through the
drain 458.
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CA 02877249 2016-08-29
[0088]The incoming impeller 450 generates an incoming airflow 810 functionally
corresponding to the incoming airflow 110 in FIG. 1. The incoming impeller 450
draws
air from the external environment through the opening 420 and into the
incoming airflow
inlet 448. From the incoming airflow inlet 448, the incoming impeller 450
forces the air
into the quadrant 477, through the channels 438 of the incoming heat exchange
core
436 into the quadrant 475, and out of the incoming duct 482 through opening
418 into
the conditioned space.
[0089]The opening 420 may be open to the external environment directly or may
be
connected to the external environment through a duct (not shown). The opening
418
may be open to the conditioned space directly or may be connected to the
conditioned
space by a duct (not shown).
(0090] The heat exchange impeller 454 generates a heat exchange airflow 815
functionally corresponding to the heat exchange fluid 115 in FIG. 1. The heat
exchange
impeller 454 draws air from the quadrant 473 through the opening 423 and into
the heat
exchange conduit 452. From the heat exchange conduit 452, the heat exchange
impeller 454 forces the air into the quadrant 476, through the channels 439 of
the
incoming heat exchange core 436 into the quadrant 474, through the opening 425
into
the quadrant 471, through the channels 435 of the outgoing heat exchange core
back
into the quadrant 473 where the air is drawn through the opening 423 to repeat
the
cycle. .
[0091]As the heat exchange airflow 815 passes through the outgoing heat
exchange
core 432, thermal energy from the outgoing airflow 804 is absorbed, heating
the heat
exchange airflow 815 and cooling the outgoing airflow 804. The heated heat
exchange
fluid 815 then passes through the incoming heat exchange core 436 where
thermal
energy is absorbed by the incoming airflow 810, cooling the heat exchange
airflow 815
and heating the incoming airflow 810 prior to the incoming airflow flowing
into the
conditioned space.
(0092] The present disclosure describes a heat recovery ventilator in which
the rate of
circulation of a heat exchange fluid may be adjusted to adjust the amount of
thermal
energy transferred between an incoming airflow and an outgoing airflow.
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[0093] Utilizing a heat exchange fluid circulating between an outgoing airflow
and an
incoming airflow, as well as a controller facilitates heat recovery during
uninterrupted
ventilation of a conditioned space that inhibits the outgoing airflow from
being cooled to
the point that ice forms in an outgoing duct.
[0094] In very cold conditions, the disclosed heat recovery ventilator is able
to adjust the
amount of thermal energy exchanged between the outgoing and incoming airflows
to
inhibit ice formation, without having to enter a 'defrost mode' in which
incoming airflow is
stopped in order to thaw formed ice within an outgoing duct, such as in prior
art heat
recovery ventilators. During a defrost mode, no fresh air is introduced. The
colder the
incoming air, such as in very cold climates, the less ventilation of the
conditioned space
occurs because a greater amount of time is spent in defrost mode, which may
seriously
affect the air quality and occupant health within the conditioned space.
[0095] The disclosed heat recovery ventilator adjusts the effectiveness of the
heat
exchange between the incoming and outgoing airflows in response to the
temperature
of the outgoing airflow to better optimize the amount of thermal energy
transferred while
inhibiting ice formation, facilitating uninterrupted ventilation of the
conditioned space.
[0096] In the disclosed heat recovery ventilator, the temperature of the
outgoing airflow
may be measured immediately after exiting an outgoing heat exchange core in
order to
better determine when ice formation in the outgoing duct is likely and, thus,
when to
reduce the rate of circulation of the heat exchange fluid.
[0097] The amount of heat exchanged between the outgoing and incoming airflows
may
be better optimized by utilizing a dew point of the outgoing airflow,
determined from the
measured relative humidity of the outgoing airflow, to determine when ice
formation in
the outgoing duct is likely and, thus, when to reduce the rate of circulation
of the heat
exchange fluid.
[0098] In the preceding description, for purposes of explanation, numerous
details are
set forth in order to provide a thorough understanding of the embodiments.
However, it
will be apparent to one skilled in the art that these specific details are not
required. In
other instances, well-known electrical structures and circuits are shown in
block diagram
form in order not to obscure the understanding. For example, specific details
are not
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provided as to whether the embodiments described herein are implemented as a
software routine, hardware circuit, firmware, or a combination thereof.
[0099] The above-described embodiments are intended to be examples only.
Alterations, modifications and variations can be effected to the particular
embodiments
by those of skill in the art. The scope of the claims should not be limited by
the
particular embodiments set forth herein, but should be construed in a manner
consistent
with the specification as a whole.
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