Note: Descriptions are shown in the official language in which they were submitted.
CA 02495821 2005-02-16
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PROPORTIONAL CONTROL SYSTEM FOR A MOTOR
The present invention also provides a proportional control system for use in
an HVAC
unit within a ventilation system comprising a processing means prograrmned
with an
air exchange-defrost cycle. One or more sensing means are also positioned in
the
HVAC unit and operatively connected to the processing means and a damper
mechanism positioned in the HVAC unit wherein the sensing means and the
processing means determine the motor speed to be applied during the defrost
cycle.
FIELD OF THE INVENTION
The present invention pertains to the field of control systems and more
specifically to
a proportional control system for a defrost cycle within an HVAC unit for a
ventilation system.
BACKGROUND
The present invention generally relates to an apparatus for ventilation
systems which
have means for the transfer of sensible heat and/or water moisture between
exhaust air
(taken from inside a building) and exterior fresh air (drawn into the
building). Such an
apparatus may, for example, have means for the transfer of sensible heat
and/or water
moisture from warm exhaust air to cooler exterior fresh air, the systems using
warm
interior air as defrost air for defrosting the systems during cool weather.
Sensible heat and/or water moisture recovery ventilation systems are known
which
function to draw fresh exterior air into a building and to exhaust stale
interior air to
the outside. The systems are provided with appropriate ducting, channels and
the like
which define a fresh air path and an exhaust air path whereby interior air of
a building
may be exchanged with exterior ambient air; during ventilation the air in one
path is
not normally allowed to mix with the air in the other path.
A sensible heat and/or water moisture recovery ventilator device or apparatus,
which
may form part of a ventilation system, in addition to being provided with
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corresponding air paths may also be provided with one or more exchanger
elements or
cores, e.g. one or more rotary andlor stationary (i.e. non-rotary) exchanger
elements or
cores. Heat recovery ventilation devices may also have a housing or cabinet;
such
enclosures may for example be of sheet metal construction (e.g. the top,
bottom, side
walls and any door, etc. may be made from panels of sheet metal). The heat
exchanging core(s), as well as other elements of the device such as, for
example,
channels or ducts which define air paths, filtration means, insulation and if
desired
one or more fans for moving air through the fresh air and exhaust air paths
may be
disposed in the enclosure. Such ventilation devices may be disposed on the
outside of
or within a building such as a house, commercial building or the like;
appropriate
insulation may be provided around any duct work needed to connect the device
to the
fresh air source and the interior air of the building. A stationary heat
exchanger
elements) may, for example, take the form of the (air-to-air) heat exchanger
element
as shown in U.S. Pat. No. 5,002,118. Thus, the heat exchanger elements) may
have
the form of a rectangular paraellpiped and may define a pair of air paths
which are
disposed at right angles to each other; these exchanger elements) may be
disposed
such that the air paths are diagonally oriented so that they are self draining
(i.e. with
respect to any condensed or unfrozen water).
During the winter season, the outside air is not only cool but it is also
relatively dry.
Accordingly, if cool dry outside air is brought into a building and the warm
moist
interior air of the building is merely exhausted to the outside, the air in
the building
may as a consequence become uncomfortably dry. A relatively comfortable level
of
humidity may be maintained in a building by inter alia exploiting an above
mentioned
desiccant type thermal wheel for transfernng water from the stale outgoing air
to the
relatively dry fresh incoming air. During winter these types of heat
exchangers may
transfer up to 80% of the moisture contained in the exhaust air to the fresh
supply air.
Advantageously a rotary exchanger wheel may transfer both sensible and latent
heat
between fresh air and exhaust air; in this case the exhaust air stream as it
is cooled
may also be dried whereas the incoming fresh air may be warmed as well as
humidified. However, a problem with such heat recovery ventilation equipment
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having a desiccant type heat exchanger wheel, is the production of frost or
ice in the
air permeable heat exchange matrix of the thermal wheel.
During especially cold weather such as -10° F. or lower (e.g. -
25° C. or lower), prior
to expelling the relatively warm exhaust air, the equipment provides for the
transfer of
latent heat from the relatively warm moist exhaust air to the relatively cool
dry (fresh)
outside air by the use of a suitable desiccant type heat exchange wheel.
However, the
cooling of the relatively moist interior air by the cold exterior air can
result in the
formation of ice (crystals). An uncontrolled buildup of ice within the matrix
of a
rotary exchanger wheel can result in decreased heat transfer, and even
outright
blockage not only of the exhaust air path but the (cold) fresh air path as
well.
Accordingly a means of periodically defrosting such a system is advantageous
in order
to maintain the system's efficiency.
A defrost mechanism has been suggested wherein the fresh air intake is
periodically
blocked off by a damper and warm interior air is injected, via a separate
defrost air
conduit, into the fresh air inlet side of the fresh air path of the
ventilation apparatus.
However, during the defrost cycle, the stale inside air is still exhausted to
the outside
via the exhaust air path; this is disadvantageous since by blocking only the
fresh air
inlet and continuing to exhaust interior air to the outside, a negative air
pressure can
be built up in the interior of a building relative to the exterior atmosphere.
Such a
negative pressure may induce uncontrolled entry of air through any cracks and
cranies
in the structure of the building; the negative pressure may, in particular,
produce a
backdraft effect, for oil and gas type beating systems, whereby exterior air
may be
pulled into the chimney leading to the accumulation of gaseous combustion
products
in the building.
An alternate system has been suggested wherein both the fresh air inlet and
exhaust air
outlet are both blocked off such that warm interior air is circulated through
the fresh
air side of the heat exchanger element as well as through the exhaust air side
of the
heat exchanger element and is sent back into the building; see for example
U.S. Pat.
No. 5,193,610.
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Another problem with respect to ventilation systems comprising a heat
exchanger
element or core relates to the installation of an exchanger device in a
building such as
for example a house or other type of building. In order for the system to
operate
efficiently and effectively the outgoing exhaust air flow preferably at least
substantially equals the incoming fresh air flow; i.e. the exhaust and fresh
air flows
are preferably balanced so as to minimize or eliminate under-pressure or over-
pressure
in the house relative to the outside atmospheric pressure; a certain degree of
overpressure may, however, be tolerated.
Presently, such ventilation systems are balanced by means of balancing dampers
and
removeable flowmeters such as, for example, a pitot tube type flow measuring
device
comprising a manometer to measure pressure difference; these elements must
usually
be installed by the balancing technician at appropriate places in the duct
work
connected to the ventilation device.
Given the above, it would be advantageous to have a control system in order to
defrost
a ventilation system which does not require the use of motors at full speed
during the
defrost operation or the addition of a number of additional components to the
ventilation system. It would also be advantageous to have a ventilation system
with a
defrost system that is controlled by the outside temperature and the speed of
the
motors.
It would also be advantageous to have a defrostable ventilation apparatus
which is of
simple construction.
This background information is provided for the purpose of making known
information believed by the applicant to be of possible relevance to the
present
invention. No admission is necessarily intended, nor should be construed, that
any of
the preceding information constitutes prior art against the present invention.
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SUMMARY OF THE INVENTION
An object of the present invention is to provide a proportional control system
for use
in an HVAC unit within a ventilation system comprising a processing means
programmed with an air exchange - defrost cycle. One or more motor speed
sensing
means are also positioned in the HVAC unit and operatively connected to the
processing means and one or more temperature sensing means are positioned in
the
HVAC unit and operatively connected to the processing means wherein the
temperature and motor speed sensors determine the motor speed to be applied
during
the defrost cycle.
Another object of the present invention is to provide a proportional control
system for
use in an HVAC unit within a ventilation system comprising a processing means
programmed with an air exchange-defrost cycle. One or more sensing means are
also
positioned in the HVAC unit and operatively connected to the processing means
and a
damper mechanism positioned in the HVAC unit wherein the sensing means and the
processing means determine the motor speed to be applied during the defrost
cycle.
BRIEF DESCRIPTION OF THE FIGURES
Figure 1 is a side perspective of one embodiment of the present invention.
Figure 2 is a side perspective of a heat exchanger.
Figure 3 is a perspective, broken away enlarged and partially schematic view
of a
portion of the heat exchanger shown in Figure 2.
Figure 4 is a side perspective of one embodiment of the present invention.
Figure 5 is a flow chart showing the establishment of the high speed defrost
cycle.
Figure 6 is a side perspective of an HVAC unit with a mechanical damper used
in one
embodiment of the present invention.
Figure 7 is a side perspective of an HVAC unit with a mechanical damper used
in one
embodiment of the present invention.
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DETAILED DESCRIPTION OF THE INVENTION
Defiyiitio~s
The term "Sensing means" is used to define components capable of measuring
various
factors independent or dependent of a ventilation system. The sensing means
are
positioned in an area of the HVAC unit where exterior air enters the
ventilation
system. The sensing means measures one or more factors of the air and these
measurements are then sent to a processing means. The sensing means may also
encompass means to measure the motor speeds of impellers or fans commonly
found
in HVAC units. The motor speed may be measured through the voltage applied to
the
motor or through the motor revolutions.
The term "Processing mans" is used to defined an electronic circuit which
obtains
measurement readings from the sensing means operatively associated with a
ventilation system and subsequently evaluates the required power to be applied
to the
motors.
The term "Motors" is used to define a motor used to activate a blower or an
impeller
commonly found in a ventilation system. The motor is controlled by the
processing
means to evacuate stale air which is passed through a heat exchanger prior to
being
evacuated outside of a building.
The term "Contact Area" is used to defined an area where the presence of
undesired
materials is accumulated. The contact area is an area within a heat exchanger
of a
ventilation system. The undesired materials of the present invention is the
presence of
frost on a surface.
Unless defined otherwise, all technical and scientific terms used herein have
the same
meaning as commonly understood by one of ordinary skill in the art to which
this
invention belongs.
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The present invention provides a system that enables to control the speed of
motors in
relation to the measurement of factors independent of the motors. A processing
means, sensing means and motors are operatively associated to a ventilation
system.
The sensing means monitor atmospheric factors such as the air temperature and
the
HVAC unit motor speeds wherein such measurements are transmitted to the
processing means. The processing means through these measurements determines
the
appropriate motor speeds to potentially reduce the noise and wasted energy
emitted
from the use of the motors during the removal of frost accumulated on a
contact area.
The further variation of the motor speed may be determined through the sensing
means measurement.
Sensifag Meafas
In one embodiment of the present invention, the sensing means may be defined
as
components able to measure the air temperature, atmospheric pressure, relative
humidity or any other atmospheric factor known to a worked skilled in~ the
art. The
sensing means may also be define as components capable of measuring various
characteristics dependent of a ventilation system such as the air flow,
impeller or fan
motor speeds, the air pressure or the temperature of any components within a
~ ventilation system or any other characteristics of a ventilation system as
would be
known by a worker skilled in the relevant art. The components utilised to
measure
these characteristics may be defined as diodes, transistors, thermocouples,
thermistors,
semiconductors or any other appropriate measuring devices as would be known by
a
worker slcilled in the art.
Processing Mearas
In one embodiment of the present invention, the processing means may provide
sensor
excitation and signal conditioning circuits for each sensor system, a
digitizer, for
converting analog sensor signals to digital values, a microcontroller, having
non-
volatile program memory, volatile working memory, and persistent memory for
adaptive parameters. The processing means may also receive user input to
control the
operation and produce outputs including audible and visible alarms. The
processing
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means may be battery powered, and is preferably intrinsically safe, meaning
that, even
with a fault condition, it will not be capable of igniting a combustible gas
in the
environment. This intrinsic safety is achieved by the avoidance of energy
storage
elements configured to provide spark energy to ignite a flame, and through the
use of
flame arresters.
In another embodiment, the processing means may store a program in read only
memory (ROM). The processing means may operate by using temporary storage in
registers and random access memory (RAM). Sensor calibration data, as well as
environmental factors and data about the ventilation unit may be periodically
stored
and updated in electrically erasable programmable read only memory (EEPROM).
In one embodiment, the processing means has two states namely an active state
and a
defrost state. Both the active and defrost state are implemented by the
processing
means for a specific amount of time and at specific motor speeds respectively.
These
two states can be varied by the processing means dependent on the enviromnent
in
which the HVAC unit is installed. The active state can be prolonged or
diminished as
the defrost state can also be prolonged or diminished. The motor speeds can
also be
increased or diminished based on the environment in which the HVAC unit is
installed.
lVlOt03 S
In one embodiment, the motors are devices which provide the necessary
mechanical
power for the flow rate within a ventilation system such as an electrical
motor or any
other motor suitable for a ventilation system as would be known by a worker
spilled in
the relevant art.
Contact Area
In one embodiment of the present invention, the contact area may be defined as
the an
area within a heat exchanger located near the exhaust of a ventilation system.
The
materials used to manufacture heat exchangers may be composed of steel, metal,
plastic, or any other material as would be known by a worker skilled in the
art for the
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construction of heat exchangers. The contact area must also be of a rigidity
wherein
the accumulation of material such as frost will not shear or break the contact
area.
In one embodiment of the present invention, the material used to manufacture
the
contact area or the heat exchanger of the ventilation system may be material
with a
relatively high conductivity of electricity in order to allow the use of a
sensing means
that measures the conductivity of a material when frost is accumulated on the
contact
area.
In one embodiment and with reference to Figure 1, a ventilation system
encompasses
a proportional control system for a motor. The fresh air intake 10 with an
attached
impeller 20 pushes air through a heat exchanger 30. The heat exchanger 30 has
a
square shape and can be made of plastic. The heat exchanger 30 utilised in
this
embodiment will be further described below in greater detail. Once air passes
through
the heat exchanger 30, the air is then circulated within the ventilation
system through
the air exhaust 40. Stale air is removed from the ventilation system through
the stale
air intake 50 with an attached impeller 60. The stale air is then passed
through the heat
exchanger 30 and evacuated outside the building through the stale air exhaust
70.
In one embodiment and with reference to Figure 2, a commonly used heat
exchanger
for use in a ventilation system is shown. The heat exchanger 30 enables air to
pass
in the direction 80 or the direction 90. The outside air enters the heat
exchanger 30 in
the direction 80 and the stale air enters the heat exchanger 30 in the
direction 90.
25 With further reference to Figure 3, the heat exchanger structure comprises
a plurality
of plastic extrusions 100 with closely spaced parallel passageways 104
separated by
square extruded channel members 102 extending perpendicular to the direction
of the
passageways 104. Although only two of the extrusions 100 and a pair of channel
members are shown in Figure 3, for the sake of simplicity in the drawings, it
should
30 be understood that there are many extrusions and channel members in the
typical heat-
exchanger.
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With further reference to Figure 3, each extrusion 100 comprises a solid top
sheet 101
and a solid bottom sheet 103 with multiple vertical walls forming the
passageways
104. Thus, crossed air flow paths are funned by the passageways 104, on the
one
hand, and the spaces 106 between the channel members and the hollow interiors
of the
members 102. These crossed flow paths are isolated from one another by the
solid
sheets 101 and 103.
The exhaust air preferably flows through the larger passageways 106, as
indicated by
the arrow 107, and the outside air flows through the passageways 104. This
arrangement is preferred because the exhaust air may have entrained water
droplets
and condensation and ice may form in the exhaust air passageways so that the
larger
passageways will remain operative for heat transfer over a wider range of
operating
circumstances than if the smaller passages were used. Although condensation
also will
occur when hot, humid outside air is cooled in the heat exchanger, it is
believed that
the larger passageways will better suit the conduct of exhaust air.
The material of which the heat exchanger 30 is made preferably is polyethylene
or
polypropylene, or other plastic materials which also are impervious to
deterioration
under prolonged contact with water and flowing air.
Equivalent heat exchangers also can be used in the practice of the invention.
For
example, isolating heat exchangers made of various metals can be used, as well
as
heat pipes whose ends are isolated from one another with one end in the
outside air
flow and the other in the exhaust air flow. Hydronic heat exchangers with
liquid
working fluids also can be used.
The plastic heat exchanger described above is advantageous over the usual
metal heat
exchanger, even though the heat conductivity of the plastic is considerably
lower than
that of the metal. The plastic lasts a very long time without corroding and is
considerably less expensive than metal. Also, the plastic heat exchanger is
less
expensive to manufacture than metal heat exchangers. The added volume required
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the plastic heat exchanger to exchange the same amount of heat as a metal heat
exchanger is more than offset by the foregoing advantages.
The plastic heat exchanger is believed to be particularly advantageous when
used with
evaporative cooling because any scale which forms from the water spray can be
broken free relatively easily by flexing the heat exchanger
In one embodiment of the present invention and with reference to Figure 4,
specific
cycle times are pre-set for the ventilation system. The ventilation system
will be in the
active mode for 20 minutes and the defrost cycle will then be activated for 5
minutes.
The motor speeds of the stale air intake impeller 60 will be determined by the
outside
air temperature measured by the sensing means 120. The measurement by the
sensing
means will be sent to the processing means 130. The processing means 130 will
then
determine the speed of the stale air exhaust. For example, if the outside air
temperature is -5° Celsius, the speed of the stale air intake impeller
50 will be
activated at its lowest speed. The speed of the stale air intake impeller 50
will be
increased proportionally based on the outside air temperature wherein the
speed of the
stale air intake impeller 50 will be at its maximum when the outside air
temperature
reaches or is lower than -25° Celsius. The maximum impeller speed will
remain
active during the defrost cycle until the outside air temperature increases
higher then -
25° Celsius wherein the speed of the stale air intake impeller 50 will
be proportionally
diminished to a minimum speed only once the outside temperature reaches to -
5°
Celsius. For example, the speed of the stale air intake impeller will be at
mid range
when the sensing means measures an outside air temperature of -15°
Celsius. If the
outside air temperature reaches higher than -5° Celsius then the
defrost cycle will not
be initiated. The active cycle of the ventilation system will be activated
otherwise the
ventilation system operates for an active cycle of 20 minutes and then
activates a
defrost cycle for 5 minutes at variable motor speeds of the stale air intake.
The defrost
cycle will operate for 5 minutes during the first 24 hours of continuous
active cycles
and defrost cycles. If the continuous active~and defrost cycles persist for 24
hours, the
defrost cycle is then increased to 6 minutes for the following 24 hours. As
such, in
one embodiment of the present invention, the defrost cycle can vary within 48
hours
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of continuous active 20 minutes cycles each followed by 5 minutes defrost
cycles
wherein the defrost cycle is increased to 6 minutes after 24 hours of
continuous active
and defrost cycles.
With further reference to Figure 4, the contact area 140 is generally located
the area
where defrost will be generated. During the defrost cycle, frost will melt
creating
water which may be evacuated from the HVAC unit 150 through a drain 160.
In one embodiment of the present invention, prior to commencing the defrost
cycle,
the defrost high speed limits are determined by the processing means. These
high
speed defrost limits are when maximum power is applied to the motors for the
defrost
cycle, i.e. to the stale air impeller. Various parameters are measured and
considered
by the processing means in order to determine the high defrost speed limits.
The
processing means also has a table of speed indexes programmed within the
processing
means during the manufacturing process. The table of speed indexes may also be
changed by a trained technician after installation of the proportional
control. The table
of speed indexes has various speeds which are used to apply different speeds
to the
motors or impellers in an HVAC unit incorporating the proportional control
system of
the present invention. A worker skilled in the relevant art would be familiar
with the
use of speed indexes to apply power to a motor or an impeller.
In one embodiment of the present invention and with reference to Figure 5, the
processing means determines the defrost high speed limits. The first step 200
requires
that the speed of the fresh air impeller be measured. At step 210, if the
speed of the
fresh air impeller is greater or equal than to a pre-determined speed set
during
manufacturing of the proportional control system, then the defrost high limit
is equal
to the value X at step 220. The value X is a value within a table of speed
indexes as
described above wherein the values within the speed indexes can be modified.
Otherwise, the defrost lugh limit is the value Y at step 230 if the fan speed
of the fresh
air intake is less than the pre-determined speed. The value Y can also be
found in the
speed index table. The processing means completes the determination of the
high
speed defrost limit at step 240. The defrost low limit is always set at the
speed
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programmed during manufacturing for the continuous speed of the fresh air
intake
impeller during operation of the HVAC unit. As such, the defrost high limit
can be
two values. The use of different defrost high speed limits enables to better
control the
defrost cycle in different climates found around the world. In another
embodiment of
the present invention, the processing means may alternatively measure the
speed of
the fresh air impeller when the impeller is activated in the override mode in
order to
determine the high speed defrost limit. The speed of the motor in the overnde
mode
can also be found in the speed index table.
In another embodiment of the present invention, the defrost high limit can be
various
values since the processing means can be programmed to apply various defrost
high
limits based on the measurement of the fresh air impeller speed at various
stages of
use. A worker skilled in the relevant art would understand how to modify the
defrost
high limits based on various motor speed as measured for the fresh air intake
impeller.
Once the defrost high limits are established, the speed required to conduct
the defrost
operation is calculated through the use of a formula. The calculation of
defrost speed
is based on various factors such as the actual temperature, temperature at
which the
defrost cycle is commenced and a maximum temperature setting for maximum speed
for the defrost cycle. The equation is then used to calculate the defrost
speed. The
formula is as follows:
Defrost speed = INT(K Mult x (Defrost High Limit - Defrost Low Limit))
+Defrost
Low limit
For example, the following values can be applied to the equation parameters
stored in
the processing means:
Def Temp -5°C Temperature at which the defrost cycle is initiated
Max Temp - -20°C - Minimum temperature at which defrost is at
maximum
power
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Temp = Actual Temperature Value
K Mult = (Abs(Temp)) / (Abs(Max Temp))
Once the result is calculated, the defrost speed is applied to the stale air
intake
impeller in order to remove the defrost from the contact area.
In one embodiment of the present invention and with reference to Figure 6, a
ventilation system encompasses a proportional control system for a defrost
cycle to be
applied to a motor. The fresh air intake 10 pushes air through a heat
exchanger 30.
The air is pushed in the heat exchanger 30 through the use of an impeller not
shown.
The heat exchanger 30 has a square shape and can be made of plastic. Once air
passes
through the heat exchanger 30, the air is then circulated within the
ventilation system
through the air exhaust 40. Stale air is removed from the ventilation system
through
the stale air intake 50 with an attached impeller not shown. The stale air is
then passed
through the heat exchanger 30 and evacuated outside the building through the
stale air
exhaust 70. A damper mechanism 250 is also installed in the HVAC unit 5. The
use
of such a damper is required since under this embodiment, the defrost cycle
uses a
bypass system composed of a re-circulated air inlet 260. A certain time lag is
caused
when closing the mechanical damper. During this period cold air could be
introduced
at high speed without recovery directly into the dwelling. To prevent this
situation, a
mechanism was designed to compensate for the time lag caused by the activation
of
the mechanical damper. This mechanism uses the fresh air inlet temperature
sensor
(not shown) to detect if the mechanical damper 250 has closed or not. By
continuously sensing the probe, it is possible to determine if the damper 250
has
closed completely by sensing any rise in the air inlet temperature. Under this
embodiment, the defrost cycle starts by shutting down the fresh air intake
impeller and
activating the bypass damper 250. During this period the stale air impeller
(not
shown) at the stale air intake 50 is set to run at the calculated defrost
speed as
described above. The defrost cycle will operate in this fashion until the
processing
means senses a rise in the air inlet temperature. Once such a rise in
temperature as
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WO 2004/016457 PCT/CA2003/001221
occurred since the damper has been completely closed as shown in Figure 7, the
stale
air impeller is stopped and the fresh air intake impeller is activated at the
defrost
speed calculated. The damper 250 closes the fresh air inlet but still enables
the fresh
air impeller to vacuum air into the HVAC unit from the re-circulated air
inlet. A
worker skilled in the relevant art would be familiar with the various types of
dampers
that can be used to achieve this operation. The use of a damper 250 mechanism
also
enables a fail safe mechanism in case the damper mechanism fails.
In another embodiment of the present invention, an impeller could be installed
in the
re-circulated air inlet. As such, the damper could completely close the fresh
air
intake. The installation of an impeller in the re-circulated air inlet would
not require
the use of the fresh air intake impeller.
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
in the art are intended to be included within the scope of the following
claims.
