US20080223052A1 - Retrofittable air conditioner to refrigeration conversion unit - Google Patents

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.

Description

TECHNICAL FIELD
• 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
• 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.
• 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.
• 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.
• 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
• 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.
• 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.
• 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.
• 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.
• 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.
• It is a still further object of the present invention to provide a method for easy installation of the present device.
• It is yet another object of the present invention to provide an effective and economical refrigeration system.
• 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.
• 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.
• 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.
• 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
• 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:
• FIG. 1 is a front view of a conventional room or window air-conditioning unit, illustrating the typical controls provided with such a unit;
• FIG. 2 is a block diagram view of a conventional room or window air-conditioning system;
• 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;
• FIG. 4 is a front view of a human interface panel that is employable with the present invention;
• FIG. 5 is a block diagram illustrating the control circuit and the overall structure of the present invention; and
• 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
• FIG. 1 illustrates a conventional room or window air-conditioning unit100. The front of such units typically includevent openings102, through which cooled air is supplied to a room. Such units also typically includevent openings104, through which room air may be exhausted. In particular fans or other air moving devices are operated in reverse mode under control ofswitch107.Switch107 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 withunit100 is capable of supplying cooler evening air from the outside throughvents102 while at the same time, exhausting warmer interior air throughexhaust vent104. Switch107 controls this function. Additionally there is also providedtemperature control switch106, 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 unit100 also includescontrol switch105, 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 switch105 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.
• 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 inFIG. 2 is provided in order to enhance one's understanding of the parameters and controls involved. In particular, it is seen thatmotor200 drivescompressor202, which compresses a refrigerant. This refrigerant flows throughconduit203 toexpansion valve204. In expanding through this valve, the compressed refrigerant is cooled in accordance with well known thermodynamic principles. The cooled fluid is passed throughconduit205 tocondenser206.Condenser206 includes fins across whichfan208 blows air which is cooled via its thermal contact with the fins ofcondenser206. Incondenser206 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 throughexpansion valve204. Thus warmed coolant is returned viaconduit207 tocompressor202 at which point the cycle repeats.
• Motor control210 controls the operation ofcompressor motor200, andfan motor201. Under control ofselector switch107fan208 may be operated in reverse to provide an exhaust function. More particularly,motor control210 responds to signals input fromtemperature sensor209.Motor control210 also receives input signals fromswitches105,106 and107 shown inFIG. 1.
• The present invention provides a retrofit apparatus, which is used to better control the conventional refrigeration cycle illustrated inFIG. 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 ofcondenser206, 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 orice sensor400 as shown inFIG. 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.
• 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 includesheater500, which is disposed in close proximity totemperature sensor209.Control300 operates to activateheater500 so as to effectively fooltemperature sensor209. However, it is noted that by choosing to operate at lower temperatures, frost orice detector400 is employed, whereas before no such sensor was needed or desired.
• Accordingly, it is seen that the present invention provides a retrofit apparatus having three complements.Heater500 is employed to essentially force the air conditioning unit to operate so as to produce lower temperature air. Frost orice sensor400 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 unit300 separately receives a user supplied indication of desired temperature. Usingheater500 andsensor400control unit300 operates to control the conventional room or window air-conditioning unit in the manner described above. In preferred embodiments of the present invention,heater500,sensor400 andcontrol unit300 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.
• FIG. 5 is a block diagram illustrating the various components of the adapter of the present invention. Inparticular microcontroller300 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 includedinternal heater510 included on the main circuit board to prevent short-circuits due to condensation.Internal heater510 is controlled bycontroller300. As described above, there is also providedexternal heater500 connected viawires450. This heater is disposed as described elsewhere herein. The heater itself is located on an external cable that plugs into the main circuit board.Heater500 is also controlled withcontroller300. Also provided is power onindicator426 which is lit when DC power is connected. Twotemperature sensors330 and335, 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.Controller300 communicates with them using a serial protocol to read the two temperatures at appropriate times. Three input buttons,410,415 and420 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.Display405 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.Controller300 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 and480 inFIGS. 4 and 5).Indicator470, which is controlled bycontroller300, is lit when the control algorithm determines that the air conditioner should be turned on.Indicator480, which is also controlled bycontroller300, is lit by when the control algorithm determines that current is required inheater500 in order to heat it to a level that will trigger the air conditioner to turn on.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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
• 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.
• 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.
• Attention is now directed to a view of the front panel ofCoolBot device400. In particular, the front panel includes LED (or other technology)display405 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 panel400 includes the three buttons labeled room, frost, and delay (havingreference numerals410,415, and420, respectively). Pressing the “ROOM” Button lets one pick the desired room temperature. In current preferred embodiments, the lowest selectable temperature is 32° 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° 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.
• 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.
• The CoolBot unit shown inFIG. 4 also includes several wires or devices, which need to be connected to the air-conditioning unit. In particular, lead425 is connected to a DC power source. While a conventional battery could be employed to power the electronic components incontrol unit400, the demands ofheating element500 which is placed in thermal contact withthermocouple209 means that it is significantly more preferred to connectunit400 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 inFIG. 4 is lead435 which is connected to frostsensor400. Likewise, lead430 is connected toheater500. These items are considered in the discussion above with respect toFIG. 3.
• 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 modifiedair conditioner100 is disposed through a back wall ofinsulated structure600.Air conditioner100 is depicted as if it had its front cover removed.Adapter device400 is shown connected toair conditioner100 in three ways: (1) via DCelectrical connection425; (2) via frost sensor335 (not visible) connected viawire435; and (3) viaheater500 connected totemperature sensor209 viaconnection450.FIG. 6 also illustrates the presence of alternatingcurrent power outlet620 into which a power cord fromair conditioner100 is inserted (not shown for reasons of improving clarity of the view). Also shown inFIG. 6 isroom temperature sensor330 connected tounit400 via connecting cable (wire)430.
• 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 theexternal heater500 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 toheater500 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.”
• 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.
• The following items further describe a control algorithm and method for using the CoolBot device:
• • 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.
  • Use a relatively low resistance forheater500, so that it “sees” a relatively high current and gets hot fast.
  • 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
• 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.
• The use of PWM as a form of control is also relevant to a cooperative control method for supplying power tointernal heater510 andexternal heater500.Internal heater510 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, ifinternal heater510 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 turnsinternal heater510 off wheneverexternal heater500 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.
• 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.

Claims (15)

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 ofclaim 1 in which said control unit includes a display for displaying temperature.

3. The device ofclaim 2 in which said display is selected from the group consisting of an LCD display and an LED display.

4. The device ofclaim 1 in which said control unit includes a means for setting desired temperature.

5. The device ofclaim 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 ofclaim 1 together with said air conditioning unit.

7. The combination ofclaim 6 further including a thermally insulated enclosure.

8. The combination ofclaim 7 in which said air conditioning unit is disposed through a wall in said enclosure.

9. The device ofclaim 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 ofclaim 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 ofclaim 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 ofclaim 14 in which said adapter includes a controller for controlling said heater so as to reduce frost build up on said fins.

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