Abstract:
The present invention relates to a device and method for operating a fully automatic, “on demand” refrigeration defrost cycle and controlling the frost build-up on the evaporative surfaces of both medium temperature (above freezing), and low temperature (below freezing) refrigeration devices or on any system or device requiring control by optical contrast.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   The present invention claims the priority of the following provisional patent applications, Ser. No. 60/534,940 filed Jan. 7, 2004 entitled “Device and Method for Operating a Refrigeration Deicing Cycle”, Ser. No. 60/546,420 filed Feb. 19, 2004 entitled “Optical/Thermal Clip and Sensor”, Ser. No. 60/580,744 filed Jun. 18, 2004 entitled Optical/Thermal Mounting Clip and Sensor, each of which is hereby incorporated by reference in their entirety. Patent application Ser. No. 10/603,578 entitled Device and Method for Operating a Refrigeration Cycle Without Evaporator Icing” is also hereby incorporated by reference in its entirety. 

   FIELD OF THE INVENTION 
   The present invention relates to a device and method for controlling frost formation on the evaporator of a device operating in a refrigeration cycle. More particularly, the invention includes a method of operating any system where changes in light absorption can be used to detect frost formation. 
   BACKGROUND OF THE INVENTION 
   The refrigeration cycle has numerous uses including refrigeration and freezing, air conditioning, and removing water from moist air to dehumidify air or to produce water. 
   During operation refrigeration evaporator coils of a refrigeration system tend to collect frost. As the frost grows, the airflow through the evaporator is reduced which reduces the effectiveness and efficiency of the refrigeration. For example, when evaporators on refrigerator storage systems freeze the interior air temperature of the system rises, possibly degrading or spoiling the product within. As the evaporator continues to collect water vapor the frost becomes hard ice, which can take hours to defrost. Such systems must be deiced, either manually or automatically, preferably before sufficient frost or ice has formed to cause a reduction in performance. 
   Present systems are generally defrosted by means of timers which turn the system off and/or use electrical heaters or hot gas to defrost the evaporator coils. Typical refrigeration systems have no means to “know” if they need to be defrosted or if defrosting is complete. Furthermore, many of the defrost systems currently available require a significant amount of power to complete, and the commercial refrigeration industry is responsible for the consumption of a large part of the world&#39;s power budget. 
   What is needed is a means to allow refrigeration or freezer systems to operate at any ambient air temperature, limit frost build up, while providing an effective, reliable means to defrost them without degrading the product within. The system described herein will accomplish these requirements. 
   SUMMARY OF INVENTION 
   The present invention relates to a device and method for controlling frost formation on the evaporator of a device operating in a refrigeration cycle by initiating defrost cycles when frost is optically detected. In preferred embodiments the invention uses changes in the absorption electromagnetic radiation energy wavelengths to detect frost formation. When frost is detected, a signal is sent to a controller which activates a defrost cycle. The invention may be used in virtually any refrigeration system using virtually any defrost method, including but not limited to hot or medium gas bypass, ambient air defrost, and electric element defrost. 
   Another aspect of the invention includes an optical/thermal device that can be installed on an evaporator coil of a refrigeration system. In this embodiment the device includes both an optical means for detecting frost, and a thermal or temperature sensing device. In one embodiment the optical/thermal device described herein is used to initiate and/or end refrigeration defrost cycles on demand, which means the defrost cycle is initiated only as required or desired. The sensor signals the defrost cycle to begin, however, any means may be used to signal the end of the defrost cycle. In the preferred embodiment, the defrost cycle end is signaled by the temperature sensing element of the optical/thermal device. In alternate embodiments the defrost termination sensor may be located elsewhere in the refrigeration system. 
   The present invention may be used for other applications as well where detection of changes in light absorption is a requirement. The invention also includes a device intended to easily retrofit a variety of refrigeration units. In other embodiments, the optical/thermal sensor may be used in conjunction with other sensors or timers to control the defrost cycle. 
   In one embodiment, the housing which houses the optical sensor, includes a prefocused optical target. This target is preferably configured approximate the frosting condition on the leading edges of frost collecting evaporator surfaces. 
   Advantages of the invention may include allowing refrigeration or freezer systems to operate at any ambient air temperature, limit frost build up while providing an effective reliable means to defrost them without degrading the product within. In some embodiments features of the invention may further include: (1) Operational range: −40 F to +40 F and return in 10 minutes. (2) Monitoring frost and ice growth in real time. (3) The ability to defrost itself and shed water droplets that may otherwise affect operation. The target may be positioned and shaped to allow frost or ice growth, but be protected by shape or external means from retaining condensed water droplets. (4) easy installation on any evaporator without bolts, nuts or screws. (5) Fast “on demand” de-ice or defrost cycle (because excess frost is inhibited from building). (6) Reduced ambient air temperature rise (further protecting the refrigerated or frozen product). 
   In some embodiments, the frost controlling device has the ability to defrost itself by means of thermal dynamics. Specifically, the device has the ability to harvest heat generated by the defrost cycle. For example, as the evaporator fins warm during defrosting, heat is transferred to the optical/thermal device. In optical/thermal embodiments of the invention the defrosting signal may be activated when the thermal element detects that the device has reached a preset temperature. 
   In some embodiments portions of the device are fabricated form, materials having good thermal transfer properties. In some embodiments the device may be fabricated from materials including but not limited to copper or beryllium copper, or other materials such as plastics. In some applications the frost detecting device of the invention is designed to fit at a selected location on a single evaporator coil. 
   In one embodiment the optical/thermal device is designed to enclose optics operating in any selected wavelength or spectrum (including but not limited to infrared and visible light spectrums) and transmit its signal over conventional wire, wireless transmission, or fiber optic cable, preferably via interface electronics, to a standard refrigeration controller. 
   The optical/thermal device can be used in virtually any known refrigeration system. As previously mentioned, the optical/thermal device is preferably designed to allow frost to grow on the frost detection target at a rate similar to the rate on which frost is forming on the evaporator coils. The ability to adjust the frost set point may be added as an option. 
   In preferred embodiments, the optics are capable of detecting changes in energy absorption on the target to detect frost formation. Supporting electronics control the contrast set point. When the contrast point is achieved, a signal, compatible with most industry refrigeration controllers is sent by the optical electronics to a refrigeration controller, which will initiate a defrosting cycle in any refrigeration system or any system where operational change may be controlled using the device of the invention. This device has the ability to initiate defrosting on demand with most existing refrigeration controllers which have their own ability to end defrost, by time or temperature. Virtually any known controller may be useable in the invention. 
   The invention includes a device that permits the operation of a refrigeration cycle while at temperatures above freezing 32 degrees F. avoiding evaporator icing, or below 32 degrees F., in systems intended to generate frost formation, including but not limited to air conditioners, dehumidifiers, water makers, and both commercial and consumer refrigerators and freezers. 

   
     DETAILED DESCRIPTION OF THE INVENTION 
     BRIEF DESCRIPTION OF THE FIGURES 
     Figures are provided solely to aid the reader in understanding the invention. They are not intended and are not to be construed as limiting the scope of this invention in any manner whatsoever. 
       FIG. 1  show a representative or example refrigeration system including a frost detection device built in accord with the invention. 
       FIG. 2  show a frost detector embodiment built in accord with the invention. 
       FIG. 3  shows the frost detector embodiment of  FIG. 2  in stalled on an evaporator coil. 
       FIG. 4  shows an example drip tube. 
       FIG. 5  shows an example optical sensor. 
   

   DEFINITIONS 
   As used herein, frost shall mean the growth of ice crystals generated by collecting water molecules on any material whose temperature is below 32 degrees F. Ice shall mean any frost crystals which have melted and allowed to re-refreeze. Ice is generally, but not always clear. 
   A timer as used herein shall mean any known apparatus or method for timing events including but not limited to a timing circuit integral with the controller, such as timing circuit in a microprocessor used as the controller. 
   As used herein, a “refrigeration system” refers to apparatus using the of well-known thermodynamic cycle of gas compression to a hot, high pressure gas, condensation of the hot, high pressure gas to a warm, high pressure gas with concomitant release of heat energy to the external surroundings, metering of the warm, high pressure gas through a device permitting expansion of the liquid to afford a cool, low pressure liquid, evaporation of the cool, low pressure liquid to a cool, low pressure gas with concomitant absorption of heat energy from the external surroundings and re-compression of the cool, low pressure gas to begin the cycle again. In one sense, the refrigeration cycle is considered to be a cooling means. However, if air in contact with the outside of the evaporator contains water vapor and the temperature of the cool liquid in the evaporator is below the dew point of the air, then water will condense on the outside of the evaporator resulting in its removal from the air. Thus, the refrigeration cycle may be considered a water-removal means as well as a cooling means. With regard to the terms “hot,” “warm” and “cool,” when referring to the refrigerant liquid/gas used in the device herein, it is to be recognized that these terms are being used strictly in their comparative sense, that is, “hot” is a higher temperature than “warm,” which is a higher temperature than “cool.” It is unnecessary to the understanding or operation of the device and method of this invention to speak in terms of absolute temperatures or temperature ranges, except where expressly set forth, because these will depend on ambient air temperature, the refrigerant used, the degree of pressurization of the refrigerant in the compressor, the amount of heat that must be removed from the hot, high pressure gas in the condenser to obtain a liquid, etc. and each of these is readily determinable by those skilled in the art using standard thermodynamic principles. The term refrigeration system comprehends the use of the system to include any known purpose including but not limited to refrigerating, freezing, dehumidifying, and water condensing. 
   As used herein, a “thermal sensor” or a “temperature sensor” refers to a device that is capable of measuring temperature at a specific location and includes, without limitation, a thermometer, a thermocouple, a thermistor and the like. 
   As used herein, a “controller” refers to a device that is capable of causing an event based on a received signal. For example, a controller upon receiving the appropriate signal from one or more of a timer, a temperature sensing means, or an ice detecting means, is capable of causing the hot gas bypass to open or close and thereby permit or prohibit the mixing of hot gas and cool liquid initiating any system required event. A controller may comprise mechanical, electrical or optical components of combinations thereof. In a presently preferred embodiment of this invention, a controller comprises a microprocessor. In some embodiments, the controller may incorporate the signal source. For example the controller could be a microprocessor with a integral timers. The controller may also initiate defrosts using electric heaters. 
   As used herein, “ambient air temperature” is meant the temperature of atmospheric air external to or in the environs wherein the evaporator system is located. 
   Discussion 
   The present invention relates to a device and method for controlling frost formation on the evaporator of a device operating in a refrigeration cycle by initiating defrost cycles when frost is optically detected. In preferred embodiments the invention uses changes in the absorption electromagnetic radiation energy wavelengths to detect frost formation. The terms “defrosting” or “deicing” are used in this application to mean the removal of crystallized water form the evaporator coils or possibly also other parts of the refrigeration system. 
     FIG. 1  shows an example refrigeration system in which an optical frost sensing device built in accord with the invention may be used. However, optical frost sensing devices built in accord with the invention can be configured for use in virtually any kind of refrigeration system using virtually any known means for defrosting the evaporator coils. The optical device can be used by itself or in association with other known devices for initiating or halting defrosting cycles. 
     FIG. 1  shows a typical refrigeration system  100  except that the refrigeration system  100  shown includes both hot gas by pass  112  and electrical heating element  114  for defrosting. Normally a refrigeration system will only include one or the other, and both are shown here merely to indicate that the devices of the invention may be used with many kinds of defrost systems, and not that both hot gas bypass  112  or electrical heaters  114  or any other particular system is required. In the preferred embodiment described, the optical frost sensor  102  will preferably mount to a single fin  104  of a refrigeration evaporator  106 . As frost begins to form on the fins and optical target (visible in later figures) on the optical frost sensor  102 , an optional optical interface unit  108  detects a change in energy absorption at the target. When a predetermined set point is reached the optical interface unit  108  unit will send a compatible signal to the refrigeration controller  110  to initiate a defrost cycle, which in the example could be either hot gas by pass or electric defrost. The controller will typically handle all other defrost control functions. In preferred embodiments defrost is terminated by temperature, but may also be ended optically or by timer. 
     FIG. 2  shows an example embodiment of the optical frost sensor  200 . The embodiment discussed includes an optional thermal element (identified below). However, in alternate embodiments there may be no thermal element, or the thermal element may be located elsewhere in the refrigeration system. 
   Referring still to  FIG. 2 , a optical frost sensor  200  is shown attached to a fin  202  of an evaporator. In this embodiment, the optical frost sensor  200  has a body  204  that includes a body clip portion  206 , an optical housing  208  and a thermal housing  210 . Communication lines  212  are coupled to a controller (seen in  FIG. 1 ). 
   The optical frost sensor  200  is preferably configured to attach to one or a few fins  202  on an evaporator. However, in alternate embodiments, virtually any acceptable means for attaching the optical frost sensor  200  to the evaporator may be used including but not limited to soldering, adhesives (preferably thermally conductive adhesives), and other known means for coupling parts to an evaporator. 
   The body  206  is preferably fabricated from a single piece of thermally conductive material, but may be formed form separate pieces joined together. Acceptable materials for making the body  204  include but are not limited to copper, copper beryllium alloys, and various plastics. The body  204  may include a coating selected to enhance the shedding or condensed water form the surface of the body  204 . 
   In the embodiment shown the optical housing  208  for housing the optical sensor and the thermal housing  210  for housing the temperature sensor are cylindrical, but could be any shape desired in alternate embodiments. 
   Optical sensors are well known and typically include a light emitting source such as a light emitting diode, and an energy receiving apparatus such as a photo transistor. Many kinds of acceptable optical sensors are available commercially. The temperature sensor may be any kind of temperature sensor available on the market compatible with typical refrigeration controllers. In the embodiment shown in  FIG. 2 , the temperature sensor is a thermister. 
   The optical sensor is preferably pre focused on the target  216 . The target  216  is preferably configured to approximate the frost generating conditions experienced by the evaporator. Optional optical support electronics may be included in the optical sensor to provide an electrical optical interface for communication with the controller. In other embodiments the electrical optical interface may be in the controller, or the controller may receive signals directly from the optical sensor. 
   In some alternate embodiments, rather than detecting changes in light absorption caused by frost formation, it is possible that an optical sensor could be configured to detect minute changes in the distance between the optical device and the target as frost begins to build up. Other ways to use optics or “seeing” electronics will become apparent to those skilled in the art based on the disclosures herein; all such approaches are within the scope of this invention. 
     FIG. 3  shows a perspective view of the frost detector  200  of  FIG. 2  attached to a fin  202  of an evaporator. 
   In some embodiments, It may be desirable to prepare a drip tube or sleeve  400  to cover the body  204  of the frost detector.  FIG. 4  shows an example sleeve  400 . In this embodiment the sleeve  400  is preferably fabricated from a material that is hydrophobic, which may prevent significant frost formation on portions of the frost detector  200  and may enhance the shedding or condensed water droplets. The target  216  is protected by the sleeve  400 , from condensate, but not from “seeing” ingested air and therefore will experience frost formation. In the embodiment shown, the sleeve  400  includes a dimple  402  which interacts with a feature on the body of the optical frost sensor to hold the sleeve  400  in position. The sleeve  400  may also include an air flow slot  404  intended to allow the target  216  to experience air flow approximating the air flow experienced by the evaporator fins, while preventing a condensate or water droplet to interfere with the system operation. 
     FIG. 5  shows an example embodiment of the optical sensor  500 . The sensor preferably fits within a 0.25 inch diameter cylinder and includes a light emitting element  502  comprising a light emitting diode for transmitting light energy (preferably infrared, but other wavelengths including visible wavelengths may be useable), and a receiving element  504  comprising a transistor. The transmit element  502  and the receiving element  504  are preferably prefocused on the target  506  during manufacturing of the optical frost sensor. The relative angle between the transmit element  502  and the receiving element  504  depends on the distance to the target  506 . 
   In addition to advantages discussed elsewhere, further advantages of the invention may include operating virtually frost free systems while reducing energy costs due to significantly shortened defrosting cycles, reduced product loss due to significantly reduced ambient air change, reduced compressor wear because compressors are never turned off except if a system reaches temperature or capacity. 
   Some embodiments of the optical frost sensor of the invention are designed to be easily retrofitable into existing functional units to capitalize on reduced energy costs and product loss. While the frost detectors described of the invention may operate at any temperature, the invention is particularly useful at low ambient temperatures; i.e., temperatures below about 55° F. and even at temperatures at or below freezing (below 32° F.). Minor frosting or icing can be necessary to insure optimum system performance. It is at the lower ambient air temperatures that frosting or icing is particularly problematic and is where the invention described herein is of the greatest utility. 
   A device of this invention may also comprise one or more frost sensors at various points on the exterior surface of the evaporator as an added icing deterrent during extreme temperature or prolonged continuous operation conditions. 
   When frost is detected at pre-set levels, the optical interface electronic transmits a signal to the controller which initiates a defrost cycle. As previously stated, any desired means for defrosting may be used. 
   The mounting position, thickness, shape, contours and angles of the optical frost sensor are preferably selected for operational functionality and reliability. The optical frost sensor is preferably mounted to assure optimum thermal conductivity and optical targeting, and in some embodiments, the means for mounting the optical frost sensor is not only to attach to the evaporator, but also to provide a thermal path to the target and the optional temperature sensor. Those skilled in the art will position the bracket on the portion of the evaporator likely to frost first. 
   Methods of the invention include mounting an optical frost detector built in accord with the invention on an evaporator. Monitoring frost formation, and signaling a controller to activate a defrost cycle when the frost has grown to equal or exceed a predetermined level. The signaling the controller to halt the defrost cycle. As seen in the table below, in alternate embodiments, the signal to halt can be a signal from the optical sensor, a temperature sensor, and a timer. 
   
     
       
             
             
           
         
             
                 
             
             
               Signal source causing activation 
               Signal source causing de-activation 
             
             
               of defrost cycle 
               of defrost cycle 
             
             
                 
             
           
           
             
               Optical Frost detection 
               Optical Frost detection 
             
             
               Optical Frost detection 
               Temperature 
             
             
               Optical Frost detection 
               Time 
             
             
                 
             
           
        
       
     
   
   It will be appreciated that the present invention provides a device and method for controlling frosting or providing “on demand” defrosting of the surface of an evaporator during operation of a refrigeration cycle. Although certain embodiments and examples have been used to describe the present invention, it will be apparent to those skilled in the art based on the disclosures herein that changes in the embodiments and examples shown may be made without departing from the scope of this invention. Other embodiments are within the following claims.