U.S. patent application number 10/525582 was filed with the patent office on 2006-07-13 for proportional control system for a motor.
Invention is credited to Bertrand Poirier.
Application Number | 20060151165 10/525582 |
Document ID | / |
Family ID | 31722364 |
Filed Date | 2006-07-13 |
United States Patent
Application |
20060151165 |
Kind Code |
A1 |
Poirier; Bertrand |
July 13, 2006 |
Proportional control system for a motor
Abstract
The present invention provides 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.
Inventors: |
Poirier; Bertrand; (New
Brunswick, CA) |
Correspondence
Address: |
KATTEN MUCHIN ROSENMAN LLP
575 MADISON AVENUE
NEW YORK
NY
10022-2585
US
|
Family ID: |
31722364 |
Appl. No.: |
10/525582 |
Filed: |
August 18, 2003 |
PCT Filed: |
August 18, 2003 |
PCT NO: |
PCT/CA03/01221 |
371 Date: |
November 1, 2005 |
Current U.S.
Class: |
165/247 ;
165/59 |
Current CPC
Class: |
F24F 2012/007 20130101;
F24F 12/006 20130101; Y02B 30/56 20130101; F24F 11/77 20180101;
Y02B 30/70 20130101; F24F 2110/12 20180101; F24F 11/41
20180101 |
Class at
Publication: |
165/247 ;
165/059 |
International
Class: |
F24F 11/04 20060101
F24F011/04; F24F 11/06 20060101 F24F011/06; F24F 7/00 20060101
F24F007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 16, 2002 |
CA |
2399160 |
Claims
1. A proportional control system for use in an HVAC unit within a
ventilation system comprising: a) a processing means programmed
with an air exchange-defrost cycle; b) one or more motor speed
sensing means positioned in the HVAC unit and operatively connected
to the processing means; and c) one or more temperature sensing
means 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.
2. The proportional control system of claim 1 wherein a first
temperature sensing means is positioned the fresh air inlet intake
of the HVAC unit.
3. The proportional control system of claim 1 wherein a first speed
sensing means is positioned on the fresh air intake impeller.
4. The proportional control system of claim 1 wherein a second
sensing means is positioned in the stale air intake of the HVAC
unit.
5. The proportional control system of claim 1 wherein a damper
mechanism is installed in the air inlet intake of an HVAC unit.
6. A proportional control system for use in an HVAC unit within a
ventilation system comprising: a) a processing means programmed
with an air exchange-defrost cycle; b) one or more sensing means
positioned in the HVAC unit and operatively connected to the
processing means; and c) a damper mechanism positioned in the HVAC
unit; wherein the temperature sensing means determine the motor
speed to be applied during the defrost cycle.
7. The proportional control system of claim 6 wherein a first
temperature sensing means is positioned in the air inlet intake of
the HVAC unit.
8. The proportional control system of claim 6 wherein a motor speed
sensor is incorporated within the processing means.
9. The proportional control system of claim 6 wherein a damper
mechanism is installed in the air inlet intake of an HVAC unit.
Description
[0001] The present invention also provides 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.
FIELD OF THE INVENTION
[0002] 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
[0003] 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.
[0004] 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.
[0005] 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 corresponding air paths may also
be provided with one or more exchanger elements or cores, e.g. one
or more rotary and/or 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
element(s) 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 element(s) 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 element(s) 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).
[0006] 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 transferring 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 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.
[0007] During especially cold weather such as -10.degree. F. or
lower (e.g. -25.degree. 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.
[0008] 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.
[0009] 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.
[0010] 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.
[0011] 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.
[0012] 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.
[0013] It would also be advantageous to have a defrostable
ventilation apparatus which is of simple construction.
[0014] 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.
SUMMARY OF THE INVENTION
[0015] 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.
[0016] 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
[0017] FIG. 1 is a side perspective of one embodiment of the
present invention.
[0018] FIG. 2 is a side perspective of a heat exchanger.
[0019] FIG. 3 is a perspective, broken away enlarged and partially
schematic view of a portion of the heat exchanger shown in FIG.
2.
[0020] FIG. 4 is a side perspective of one embodiment of the
present invention.
[0021] FIG. 5 is a flow chart showing the establishment of the high
speed defrost cycle.
[0022] FIG. 6 is a side perspective of an HVAC unit with a
mechanical damper used in one embodiment of the present
invention.
[0023] FIG. 7 is a side perspective of an HVAC unit with a
mechanical damper used in one embodiment of the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
Definitions
[0024] 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.
[0025] The term "Processing means" 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.
[0026] 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.
[0027] 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.
[0028] 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.
[0029] 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.
[0030] 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.
[0031] The further variation of the motor speed may be determined
through the sensing means measurement.
Sensing Means
[0032] 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
skilled in the art.
Processing Means
[0033] 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 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.
[0034] 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).
[0035] 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 environment 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.
Motors
[0036] 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 skilled in the
relevant art.
Contact Area
[0037] 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 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.
[0038] 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.
[0039] In one embodiment and with reference to FIG. 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.
[0040] In one embodiment and with reference to FIG. 2, a commonly
used heat exchanger 30 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.
[0041] With further reference to FIG. 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 FIG. 3,
for the sake of simplicity in the drawings, it should be understood
that there are many extrusions and channel members in the typical
heat-exchanger.
[0042] With further reference to FIG. 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 formed 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.
[0043] 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.
[0044] 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.
[0045] 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.
[0046] 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 for the plastic heat
exchanger to exchange the same amount of heat as a metal heat
exchanger is more than offset by the foregoing advantages.
[0047] 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 FIG. 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.degree.
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.degree. Celsius. The maximum impeller speed
will remain active during the defrost cycle until the outside air
temperature increases higher then -25.degree. 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.degree. 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.degree. Celsius. If the
outside air temperature reaches higher than -5.degree. 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 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.
[0048] With further reference to FIG. 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.
[0049] 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.
[0050] In one embodiment of the present invention and with
reference to FIG. 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 high 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 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 override mode can also be found in the speed index table.
[0051] 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.
[0052] 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.sub.--Mult.times.(Defrost High
Limit-Defrost Low Limit))+Defrost Low limit
[0053] For example, the following values can be applied to the
equation parameters stored in the processing means:
Def_Temp=-5.degree. C. Temperature at which the defrost cycle is
initiated
Max_Temp=-20.degree. C.--Minimum temperature at which defrost is at
maximum power
Temp=Actual Temperature Value
K_Mult=(Abs(Temp))/(Abs(Max_Temp))
[0054] 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.
[0055] In one embodiment of the present invention and with
reference to FIG. 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 occurred since the damper has been
completely closed as shown in FIG. 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.
[0056] 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.
[0057] 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.
* * * * *