U.S. patent application number 11/724129 was filed with the patent office on 2008-09-18 for retrofittable air conditioner to refrigeration conversion unit.
Invention is credited to Ronald Ravi Khosla, Timothy John Weber.
Application Number | 20080223052 11/724129 |
Document ID | / |
Family ID | 39761282 |
Filed Date | 2008-09-18 |
United States Patent
Application |
20080223052 |
Kind Code |
A1 |
Khosla; Ronald Ravi ; et
al. |
September 18, 2008 |
Retrofittable air conditioner to refrigeration conversion unit
Abstract
A conversion unit for an air conditioning system to cause it to
act like the cooling unit of a refrigeration system comprises a
frost detector, a heater and a control unit which operate together
to force the range of operation of the air conditioning unit into
the range of operation of a refrigeration unit. The conversion unit
is particularly useful for providing low cost cooling systems for
farmers in third world countries for keeping their produce fresh
and safe, not to mention its use by all farmers around the world
and by florists or others in need or desire of an economical
refrigeration alternative.
Inventors: |
Khosla; Ronald Ravi;
(US) ; Weber; Timothy John; (US) |
Correspondence
Address: |
Lawrence D. Cutter
11 Deer Path Drive
New Paltz
NY
12561-2813
US
|
Family ID: |
39761282 |
Appl. No.: |
11/724129 |
Filed: |
March 14, 2007 |
Current U.S.
Class: |
62/150 ; 62/172;
62/275 |
Current CPC
Class: |
F25D 29/00 20130101;
F25D 2400/02 20130101; F25B 2700/11 20130101 |
Class at
Publication: |
62/150 ; 62/172;
62/275 |
International
Class: |
F28B 9/00 20060101
F28B009/00; F25D 21/00 20060101 F25D021/00; F25D 21/06 20060101
F25D021/06 |
Claims
1. A device to adapt an air conditioning unit to a lower
temperature of operation, said device comprising: a sensor for
detecting the presence of frost on fins of said air-conditioning
unit; a heater for disposition adjacent to a temperature sensor for
said air conditioning unit; and a control unit, for activating said
heater upon the condition that said sensor provides an indication
that frost is not present on said fins.
2. The device of claim 1 in which said control unit includes a
display for displaying temperature.
3. The device of claim 2 in which said display is selected from the
group consisting of an LCD display and an LED display.
4. The device of claim 1 in which said control unit includes a
means for setting desired temperature.
5. The device of claim 1 in which said control unit includes a
means for setting a threshold for frost detection on said fins.
6. The combination of the device of claim 1 together with said air
conditioning unit.
7. The combination of claim 6 further including a thermally
insulated enclosure.
8. The combination of claim 7 in which said air conditioning unit
is disposed through a wall in said enclosure.
9. The device of claim 1 in which said frost sensor is a
temperature indicating probe.
10. A device to adapt an air conditioning unit to a lower
temperature of operation, said device comprising: a sensor for
detecting the presence of frost on fins of said air conditioning
unit; a first heater for disposition adjacent to a temperature
sensor for said air conditioning unit; a second heater disposed
internal to said device for controlling condensation therein; and a
control unit, for activating said first heater upon the condition
that said sensor provides an indication that frost is not present
on said fins.
11. The device of claim 10 in which power is supplied at distinct
times to said first heater and said second heater.
12. A method for operating an existing air conditioning unit having
fins across which air is directed to cool it, so as to achieve a
lower temperature of operation for said air conditioning unit, said
method comprising the steps of: applying heat to a temperature
sensor in said air conditioning unit; sensing the presence of frost
on said fins in said air conditioning unit; and controllably
adjusting the heat applied to said temperature sensor to produce
continued operation without producing significant frost build up on
said fins.
13. The method of claim 12 in which said steps are carried out by
an adapter coupled to said air conditioning unit and connected
thereto for supplying power to said adapter.
14. A method for converting an existing air conditioner into a unit
capable of operating as the core of a refrigeration system, said
method comprising the steps of: thermally connecting a heater in an
adapter to a temperature sensor of said air conditioner; disposing
a frost sensor from said adapter adjacent to fins in said air
conditioner; and electrically connecting said adapter to said air
conditioner to supply said adapter with power for its
operation.
15. The method of claim 14 in which said adapter includes a
controller for controlling said heater so as to reduce frost build
up on said fins.
Description
TECHNICAL FIELD
[0001] The present invention is generally directed to the
conversion of conventional air conditioning system units so as to
operate more capably as part of a complete refrigeration system.
Thus, as compared to conventional air conditioning units, the
present invention permits the economical construction of insulated
volumes which are now capable of being cooled to near freezing
levels. More particularly, the present invention is directed to a
separate unit, which is configured with a conventional
air-conditioning unit in order to convert it to the core of a
refrigeration system, as opposed to its function as a mere air
conditioner.
BACKGROUND OF THE INVENTION
[0002] It is well known that air conditioning units are relatively
inexpensive. They can often be purchased for amounts even as low as
$30. In contrast, refrigeration systems that are employed in
commercial settings tend to be expensive and have relatively high
power demands and installation requirements. Accordingly, it is
seen that there is a need for a mechanism, which is capable of
converting an inexpensive air-conditioning unit so that it operates
as the core of a refrigeration system.
[0003] It is further noted that there is a significant need for
inexpensive refrigeration systems. In particular, farmers would
very much like to have an inexpensive method for keeping their
produce and crops at reduced temperatures were for storage and for
longer shelf life. Additionally individuals such as florists,
restaurants, and grocery stores would also benefit from having
inexpensive refrigeration systems. Furthermore, as desirable as
these systems are in the United States, they are immeasurably more
desirable in other parts of the world where refrigeration is at a
premium but which is nonetheless a necessity because of the
elevated temperatures of the climates in these regions.
[0004] In addition to the fact that refrigeration systems are
expensive, it is also the case that such systems are very demanding
in terms of their electrical power requirements. It is therefore
seen that there is also a need for cooling systems that do not
require anything more than the standard AC outlet.
[0005] One of the problems with using a conventional
air-conditioning unit as part of a refrigeration system is that
such units are designed with specific controlling features in mind,
which limit their operations, cycle duration and their cooling
capabilities. For example, the control units for a conventional
window air conditioner are set so that the units turn off at a
relatively high sensed temperature. Nonetheless, for purposes of
using a conventional air-conditioning unit as the core of a
refrigeration system, these air conditioners, with their
conventional control units are set up so that it is always far from
the case that humidity is allowed to condense on the fins of the
unit in the form of ice. In short, in their normal mode of
operation, conventional air-conditioning systems are designed to
cut out at a relatively high temperature. It is therefore seen that
in their off-the-shelf state, these units are not capable of
operating as refrigeration units. The adapter units of the present
invention provide a retrofit mechanism which extends the range of
operation for a conventional air conditioning unit. This is found
to be particularly advantageous in relatively small and inexpensive
window units.
SUMMARY OF THE INVENTION
[0006] Accordingly, in order to solve these problems, there is
provided a simple retrofittable conversion unit, which includes a
frost detector, a control unit and a heater, which is used to
"fool" the temperature sensor in a conventional air conditioner.
The present invention comprises a device to adapt an
air-conditioning unit to a lower temperature of operation. The
device comprises a sensor for detecting the presence of frost on
the fins of the air conditioning unit and a heater for disposition
adjacent to a temperature sensor for the air conditioning unit. A
control unit deactivates the heater upon the condition that the
sensor provides an indication that there is frost on the fins.
There is also provided a method of installation of the present
device so that it easily works with a conventional, off-the-shelf
A/C unit.
[0007] In accordance with another embodiment of the present
invention, there is provided a corresponding method for operating
an existing air conditioning unit having fins across which air is
directed to cool it, so as to achieve a lower temperature of
operation. This method includes the following steps: applying heat
to a temperature sensor present in the air conditioning unit;
sensing the presence of frost on the fins the air conditioning
unit; and controllably adjusting heat applied to the temperature
sensor to produce continued operation without producing significant
frost build up on the fins.
[0008] In accordance with yet another embodiment of the present
invention, there is provided a method for the conversion of an
existing air conditioning unit into a unit capable of operating as
the core of a refrigeration system which operates at near freezing
temperatures. In this method a heater in an adapter is thermally
connected to the temperature sensor of the air conditioner. A frost
sensor in the adapter unit is disposed adjacent to the fins of the
air conditioner. The adapter is electrically connected to the air
conditioner to supply the adapter with power. These steps may be
performed in any convenient order.
[0009] Accordingly, it is an object of the present invention to
bring the advantages of refrigeration to areas of the country and
the world where it is most needed and least affordable.
[0010] It is also an object of the present invention to provide a
retrofit mechanism which extends the range of operation of
conventional A/C units.
[0011] It is a still further object of the present invention to
provide a method for easy installation of the present device.
[0012] It is yet another object of the present invention to provide
an effective and economical refrigeration system.
[0013] It is also an object of the present invention to provide an
economical device and system for the improved preservation of
produce together with all of the health and food safety benefits
that that entails.
[0014] Lastly, but not limited hereto, it is an object of the
present invention to provide an add-on device for controlling A/C
units so as to make them usable in conjunction with easily
implementable insulated or insulatable volumes which can be kept at
near freezing temperatures.
[0015] Additional features and advantages are realized through the
techniques of the present invention. Other embodiments and aspects
of the invention are described in detail herein and are considered
a part of the claimed invention.
[0016] The recitation herein of a list of desirable objects which
are met by various embodiments of the present invention is not
meant to imply or suggest that any or all of these objects are
present as essential features, either individually or collectively,
in the most general embodiment of the present invention or in any
of its more specific embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] The subject matter which is regarded as the invention is
particularly pointed out and distinctly claimed in the concluding
portion of the specification. The invention, however, both as to
organization and method of practice, together with the further
objects and advantages thereof, may best be understood by reference
to the following description taken in connection with the
accompanying drawings in which:
[0018] FIG. 1 is a front view of a conventional room or window
air-conditioning unit, illustrating the typical controls provided
with such a unit;
[0019] FIG. 2 is a block diagram view of a conventional room or
window air-conditioning system;
[0020] FIG. 3 is a block diagram of the retrofit apparatus of the
present invention used to modify the conventional operation of room
or window air-conditioning units in order to provide a
refrigeration function;
[0021] FIG. 4 is a front view of a human interface panel that is
employable with the present invention;
[0022] FIG. 5 is a block diagram illustrating the control circuit
and the overall structure of the present invention; and
[0023] FIG. 6 is a diagram illustrating the adapter of the present
invention being employed with a surrounding insulated structure
through whose back wall a conventional air conditioning unit is
disposed.
DETAILED DESCRIPTION
[0024] FIG. 1 illustrates a conventional room or window
air-conditioning unit 100. The front of such units typically
include vent openings 102, through which cooled air is supplied to
a room. Such units also typically include vent openings 104,
through which room air may be exhausted. In particular fans or
other air moving devices are operated in reverse mode under control
of switch 107. Switch 107 is typically provided with the control
function of supplying air to the room or removing air from the room
in an exhaust mode. Such a mode of operation is conveniently
provided so that the fan provided with unit 100 is capable of
supplying cooler evening air from the outside through vents 102
while at the same time, exhausting warmer interior air through
exhaust vent 104. Switch 107 controls this function. Additionally
there is also provided temperature control switch 106, which allows
a user to choose a temperature below which the unit ceases its
cooling function. Once a desired temperature is reached, the units
compressor function is shut down. However, the units fan may
continue operation for a predetermined time following the
determination that he desired room temperature has been reached.
Conventional unit 100 also includes control switch 105, which
selects the mode of operation. In one mode of operation, a user may
select to operate only the fan and not the units compressor or
cooling function. This may be desirable for example, in situations
in which a simple exchange of room air with outside air is desired.
Mode control switch 105 also typically provides to other modes of
operation: hi cool and low cool. The hi cool mode of operation is
one in which greater electrical current is supplied to either or
both of the fan motor and or compressor motor to select either the
degree and or speed of cooling.
[0025] Since the structure and operation of the present invention
is based upon a modification of the conventional system employed in
off-the-shelf room and window air conditioners, it is appropriate
to consider the usual refrigeration cycle and the controls that are
normally imposed thereon. Accordingly, the structural block diagram
shown in FIG. 2 is provided in order to enhance one's understanding
of the parameters and controls involved. In particular, it is seen
that motor 200 drives compressor 202, which compresses a
refrigerant. This refrigerant flows through conduit 203 to
expansion valve 204. In expanding through this valve, the
compressed refrigerant is cooled in accordance with well known
thermodynamic principles. The cooled fluid is passed through
conduit 205 to condenser 206. Condenser 206 includes fins across
which fan 208 blows air which is cooled via its thermal contact
with the fins of condenser 206. In condenser 206 refrigerant is
warmed by the passage of air across its fins and the fins are
cooled by being in thermal contact with the refrigerant which has
been cooled by its passage through expansion valve 204. Thus warmed
coolant is returned via conduit 207 to compressor 202 at which
point the cycle repeats.
[0026] Motor control 210 controls the operation of compressor motor
200, and fan motor 201. Under control of selector switch 107 fan
208 may be operated in reverse to provide an exhaust function. More
particularly, motor control 210 responds to signals input from
temperature sensor 209. Motor control 210 also receives input
signals from switches 105, 106 and 107 shown in FIG. 1.
[0027] The present invention provides a retrofit apparatus, which
is used to better control the conventional refrigeration cycle
illustrated in FIG. 2. Since the normal temperature range of
operation for a room or window air conditioner is not so low as to
cause ice build up on the fins of condenser 206, there is no need
in such units to provide for frost or ice detection. Since these
units have not been contemplated for use as the central core of a
refrigeration system, as opposed to a simple room air cooling
system, frost or ice detection has not been seen as either a
desired or necessary function. However, if one wished to use such
units in any refrigeration function where the temperature range is
significantly lower, frost or ice accumulation is a problem.
Accordingly, one of the elements provided in the retrofit apparatus
of the present invention is frost or ice sensor 400 as shown in
FIG. 3. This is preferably implemented as temperature sensor,
however, any convenient means for detecting frost may also be
employed including electrical conduction and/or optical
sensors.
[0028] Additionally, as noted above, conventional room or window
air conditioners are not designed to function below certain
temperatures. Such units are designed essentially for cooling a
room not for turning it into a refrigeration structure.
Accordingly, the retrofit apparatus of the present invention also
includes heater 500, which is disposed in close proximity to
temperature sensor 209. Control 300 operates to activate heater 500
so as to effectively fool temperature sensor 209. However, it is
noted that by choosing to operate at lower temperatures, frost or
ice detector 400 is employed, whereas before no such sensor was
needed or desired.
[0029] Accordingly, it is seen that the present invention provides
a retrofit apparatus having three complements. Heater 500 is
employed to essentially force the air conditioning unit to operate
so as to produce lower temperature air. Frost or ice sensor 400 is
employed to ensure continued operations at the lower desired
temperature, which is more in the range of a refrigeration system
than in the range of a room cooling system. Control unit 300
separately receives a user supplied indication of desired
temperature. Using heater 500 and sensor 400 control unit 300
operates to control the conventional room or window
air-conditioning unit in the manner described above. In preferred
embodiments of the present invention, heater 500, sensor 400 and
control unit 300 are provided in a single package, which is easily
connected into and coupled with a conventional room or window
air-conditioning unit to provide a refrigeration function.
[0030] FIG. 5 is a block diagram illustrating the various
components of the adapter of the present invention. In particular
microcontroller 300 is implementable as PIC Microchip
microcontroller Model No. 16F916, though many low-end
microcontroller chips would also be just as satisfactory. This chip
contains code burnt into an EEPROM for implementing the control
algorithm and user interface functions described above. There is
included also included internal heater 510 included on the main
circuit board to prevent short-circuits due to condensation.
Internal heater 510 is controlled by controller 300. As described
above, there is also provided external heater 500 connected via
wires 450. This heater is disposed as described elsewhere herein.
The heater itself is located on an external cable that plugs into
the main circuit board. Heater 500 is also controlled with
controller 300. Also provided is power on indicator 426 which is
lit when DC power is connected. Two temperature sensors 330 and
335, measuring the room temperature and the temperature of the air
conditioner's fins respectively. These sensors are mounted on
external cables that plug into the main circuit board. Controller
300 communicates with them using a serial protocol to read the two
temperatures at appropriate times. Three input buttons, 410, 415
and 420 are accessible from the front panel and are used to change
the parameters of the cooling algorithm, as well as for diagnostic
purposes. Their functions are also described in greater detail
elsewhere herein. Display 405 is made up of two modules, DIS1 and
DIS2. The display is provided in the present implementation solely
as a matter of convenience. The relevant aspect of the display is
that there are a sufficient number of digits to display the
temperature or any optional diagnostic settings. Controller 300
uses these digits to display running status, to provide feedback
while the user sets algorithm parameters, and to support diagnostic
tests. There are also preferably two status indicator lights (470
and 480 in FIGS. 4 and 5). Indicator 470, which is controlled by
controller 300, is lit when the control algorithm determines that
the air conditioner should be turned on. Indicator 480, which is
also controlled by controller 300, is lit by when the control
algorithm determines that current is required in heater 500 in
order to heat it to a level that will trigger the air conditioner
to turn on.
[0031] Attention is now directed to a method by which the present
invention is added to an existing air conditioning unit. The first
step in this process is the construction of an insulated volume.
Materials useful in this process include Styrofoam and SprayFoam
which can be applied to seal any cracks or gaps in the structure.
At this stage, one should also consider adding extra insulation. If
there are windows present in the structure, they should be sealed
with Styrofoam or any other useful or available insulative
material.
[0032] If it does not already exist, a conventional
air-conditioning unit is disposed through an opening in the
structure wall. The edges of the opening are sealed as well. The
next step is the removal of the front portion of the
air-conditioning unit. This front portion is typically plastic.
It's removal also typically exposes air filters present in the
unit. These air filters are also preferably removed. It is
recommended that this front portion not be reinstalled. This
exposes the fins of the air conditioning unit which produces both
an advantage and a disadvantage. The disadvantage is that the fins
can be bumped and bent. The advantage is that the fins can easily
be cleaned and be bent back into shape as needed.
[0033] The next step in the installation procedure is the location
and the freeing of the thermocouple sensor that normally comes with
the air conditioning unit. Note that this freeing operation is not
an electrical disconnection, but rather a moving of the
thermocouple away from the fins of the air conditioning unit.
Typically the thermocouple is disposed on a long and flexible wire,
which is easily bent away from the fins. If there are any plastic
ties or other structures holding the thermocouple in place, these
are preferably removed as well so as to have the thermocouple swing
free of the fins.
[0034] The next step in the installation process is the mounting of
the device of the present invention on a wall of the structure near
the air conditioning unit. Here on this device is referred to
herein as the CoolBot, The CoolBot may be provided with any
convenient wall fastening means, including screws, adhesives,
Velcro or even hung on nails. The CoolBot is hung on the wall in a
position sufficiently close to the air conditioning unit that wires
extending from the CoolBot are capable of being connected to
appropriate points on the air conditioning unit.
[0035] The next step in the installation process is the mating of
the thermocouple with the warming element of the CoolBot. This
coupling is designed to ensure close thermal contact between the
two elements. In particular, it is possible to join these two
elements by placing them next to one another and wrapping them with
aluminum foil. Even a single layer of the aluminum foil is
adequate; however, multiple layers provide a more secure
coupling.
[0036] The next step in the installation process is the connection
of the CoolBot's frost sensor to the fins of the air conditioning
unit. Looking at the fins in a typical air-conditioning unit, one
sees that there are copper pipes carrying the units refrigerant.
The frost sensor is disposed, just below one of the lower copper
pipes, which is typically several inches above the bottom of the
air conditioning unit. The frost sensor is inserted between two of
the fins. One may rely upon a friction fit to hold a frost sensor
in place or more preferably, one may bend some of the adjacent the
fins together to more ably hold the frost sensor in position. This
is easily done with one's fingernails or with a screwdriver
[0037] For air-conditioning units, which are Energy Star compliant,
there is an additional step that is also performed as part of the
installation procedure. In particular, the frost sensor that
normally accompanies such units is moved. Note, however, that this
sensor is not removed only repositioned away from the fins so that
it does not interfere with the operation of the CoolBot. The
CoolBot is also provided with an ambient room temperature sensor.
This sensor should be allowed to hang freely in the cooled
volume.
[0038] The present invention thus renders it very easy to retrofit
a conventional room or window air-conditioning unit so as to
operate as the core of a refrigeration system. The only other thing
that needs to be provided is some form of insulated airtight
structure. Wood and Styrofoam structures, which are readily
available in rural and third world areas readily suffice for
carrying out this function.
[0039] Attention is now directed to a view of the front panel of
CoolBot device 400. In particular, the front panel includes LED (or
other technology) display 405 which is used to not only display the
current temperature, but is also used to set desirable temperatures
to be achieved at the air conditioner fins. It is noted that any
convenient display device may be employed and the display is not
limited to LED devices; LCD displays are employable; however, it is
noted that in many refrigeration environments lighting may be so
low that LED displays are a significantly preferred choice.
Likewise, LED displays are preferred in situations where
condensation may be a factor. Front panel 400 includes the three
buttons labeled room, frost, and delay (having reference numerals
410, 415, and 420, respectively). Pressing the "ROOM" Button lets
one pick the desired room temperature. In current preferred
embodiments, the lowest selectable temperature is 32.degree. F.
Every time you push the ROOM button, the temperature goes up one
degree; when it reaches a maximum temperature, it then starts over
again at 32.degree. F. Pressing the "FROST" button allows one to
change the frost detection settings. The CoolBot device is provided
with a default temperature setting for this value, but if ice forms
on the fins, pressing the FROST button so that it goes up one or
two degrees typically stops this from happening. If the room isn't
getting cold and ice is never forming, then the frost temperature
is set too high. Pressing the FROST button until it cycles back to
the starting point should solve this problem. If no frost is ever
forming then either: (1) one has a new Energy Star compliant unit
and didn't move its frost sensor; (2) the room is extremely leaky
and uninsulated; or (3) the room is too big for the given air
conditioning unit. The solution to these last two problems is
sealing the room better, adding a second A/C unit or using a single
larger unit.
[0040] Pressing the DELAY button changes the Delay Mode. This
button controls the delay between the time that both sensors'
temperatures are above their respective thresholds and when the air
conditioner is triggered to operate. The default is ten seconds.
Increasing the delay allows the room to get warmer before
triggering the air conditioner. This is sometimes useful for air
conditioners that have an enforced minimum on-time due to internal
control circuitry, so that they run for their minimum on-time
without frost forming before they may be turned off.
[0041] The CoolBot unit shown in FIG. 4 also includes several wires
or devices, which need to be connected to the air-conditioning
unit. In particular, lead 425 is connected to a DC power source.
While a conventional battery could be employed to power the
electronic components in control unit 400, the demands of heating
element 500 which is placed in thermal contact with thermocouple
209 means that it is significantly more preferred to connect unit
400 to a separate DC power supply. In preferred embodiments of the
present invention, the DC power supply is from a converter, which
is coupled into the alternating current power supply for the
air-conditioning unit. It may also be powered separately. Also
shown in FIG. 4 is lead 435 which is connected to frost sensor 400.
Likewise, lead 430 is connected to heater 500. These items are
considered in the discussion above with respect to FIG. 3.
[0042] FIG. 6 illustrates a typical installation of the adapter
described above in its natural environment. This drawing is not to
scale, so that all of the features and aspects may better be
presented. In particular, conventional but modified air conditioner
100 is disposed through a back wall of insulated structure 600. Air
conditioner 100 is depicted as if it had its front cover removed.
Adapter device 400 is shown connected to air conditioner 100 in
three ways: (1) via DC electrical connection 425; (2) via frost
sensor 335 (not visible) connected via wire 435; and (3) via heater
500 connected to temperature sensor 209 via connection 450. FIG. 6
also illustrates the presence of alternating current power outlet
620 into which a power cord from air conditioner 100 is inserted
(not shown for reasons of improving clarity of the view). Also
shown in FIG. 6 is room temperature sensor 330 connected to unit
400 via connecting cable (wire) 430.
[0043] Attention is now directed to a description of specific
control methods employed in the operation of the CoolBot device.
For purposes of efficiency, it is desirable to turn the air
conditioner unit on and off with as little lag time as possible,
that is, with the shortest possible delay between when the
algorithm says "A/C off" and when the A/C stops emitting cold air.
Turn-on delay is primarily limited by how fast the sensor heater
warms up; turn-off delay is limited by how fast it cools down. To
be more precise, turn-on delay is the time it takes for the heater
to go from its "turned off" temperature past the air conditioner's
threshold temperature, and turn-off delay is the time it takes for
the heater to go from its "steady state on" temperature past the
air conditioner's threshold in the other direction. The turn-on
delay is smallest when the "turned off" temperature is high (but
below under the air conditioner's threshold temperature) and when
the current put through the external heater 500 is largest. The
turn-off delay is smallest when the "steady state on" temperature
is low (but greater than the air conditioner threshold temperature)
and when the room temperature is much cooler than that temperature.
Accordingly, desirable performance levels are achieved if the
current supplied to heater 500 is just sufficient to keep the
temperature just above the air conditioner's threshold temperature
while it's "on" and to supply slightly less current while it's
"off."
[0044] One way to accomplish this control is through the use of a
PID (position, integral, differential) control. This allows for
precise control of the heater's temperature, but it also requires
an additional sensor for feedback, which adds an expense, both for
parts and for assembly. However, in certain cases where precise
control over a long period of time is desirable for reasons of
efficiency, this expense is tolerable.
[0045] The following items further describe a control algorithm and
method for using the CoolBot device: [0046] When turning on the
heater, keep it completely on (full current flow) for an initial
length of time, approximately one minute; however, this value may
be increased or decreased depending on the current room
temperature. [0047] Use a relatively low resistance for heater 500,
so that it "sees" a relatively high current and gets hot fast.
[0048] After the initial turn-on period, use Pulse Width Modulation
(PWM) to reduce the average current through the heater, and thus
the heat dissipated. This stabilizes the heater temperature, rather
than driving it as hot as it can possibly go. Thus, when the heater
is turned on, its lower temperature results in faster turn-off
[0049] In short, PID control is an option but there is a trade-off
between cost and performance. Using PWM to reduce steady-state
temperature makes for faster turn-off and customizing the PWM
period (100% initially, decreasing later) makes for faster
turn-on.
[0050] The use of PWM as a form of control is also relevant to a
cooperative control method for supplying power to internal heater
510 and external heater 500. Internal heater 510 is used to reduce
condensation on the circuit board. Its use is also beneficial in
that it contributes to the elimination of a manufacturing step in
which a conformal coating is applied to the circuit board and its
components to ameliorate problems associated with condensation
and/or other environmental contaminants. However, it is noted that,
if internal heater 510 runs constantly, peak current load goes over
one ampere in the current design. A DC power supply capable of
producing more than one ampere often costs significantly more than
one designed for less than one ampere. Accordingly, control in the
CoolBot device turns internal heater 510 off whenever external
heater 500 is on. Since only one heater is on at any given time,
the peak load is not the combined load but the maximum. It's much
easier to keep this under one ampere and to thus employ a less
expensive power supply.
[0051] While the invention has been described in detail herein in
accordance with certain preferred embodiments thereof, many
modifications and changes therein may be effected by those skilled
in the art. Accordingly, it is intended by the appended claims to
cover all such modifications and changes as fall within the true
spirit and scope of the invention.
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