Patent Publication Number: US-2009235679-A1

Title: Optical frost detector with gas blow off

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of the priority date of provisional patent application Ser. No. 61/070,317, filed Mar. 21, 2008, which application is hereby incorporated by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The invention includes apparatus and method for operating any system where changes in light absorption can be used to detect frost formation. More particularly, the present invention relates to a system and method for controlling frost formation on the evaporator of a device operating in a refrigeration cycle. 
     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. Frost accumulation reduces the effectiveness and efficiency of cooling. 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 and temperature sensors 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. Optical frost sensors have been tried because such sensors can detect early frost formation better than some other prior art methods. However, a frequent problem with such devices is that water or dust and debris may accumulate on the optical frost sensors degrading their performance. 
     What is needed is a refrigeration control system including an optical frost sensor to allow refrigeration or freezer systems to operate at any ambient air temperature and limit frost build up, while providing an effective and reliable means to defrost them without degrading the product within, and a reliable and inexpensive means for removing any residual material such as water and debris from the frost sensor that might otherwise degrade performance. 
     SUMMARY OF INVENTION 
     The present invention relates to systems, methods, and components used 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 a frost sensor or detector that monitors changes in the absorption of electromagnetic radiation energy wavelengths to detect frost formation. When frost is detected, a signal is sent to a controller which activates a defrost cycle. Systems built in accord with 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. Water and debris or other material may accumulate on the frost detector during the defrost cycle, and may degrade performance if not removed. Embodiments of the invention further include apparatus for delivering gas at volumes and velocities sufficient to remove material including residual water and debris that may have collected on the frost detector. 
     In one embodiment the frost detector is used to initiate refrigeration defrost cycles on demand, which means the defrost cycle is initiated only as required or desired. The frost detector signals the defrost cycle to begin, however, any means may be used to signal the end of the defrost cycle including but not limited to optical frost sensor or detector readings, temperature readings, refrigeration gas pressure readings, and timers. Some embodiments of the invention may include both an optical means for detecting frost, and a thermal or temperature sensing device on the same sensor body. In some embodiments having both a frost detector and a temperature sensor, the defrost cycle end is signaled by a temperature sensing element of the embodiment. In alternate embodiments the temperature sensor may be located elsewhere in the refrigeration system. Some embodiments of the invention are intended to easily retrofit a variety of refrigeration units. 
     In some embodiments the frost detector includes a pre-focused optical target. This target is preferably configured to approximate the frosting condition on the leading edges of frost collecting evaporator surfaces. 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. The frost detector is preferably placed in the flow of air that passes through the evaporator. 
     In some embodiments, the frost sensor 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 frost sensor. Some alternate embodiments may include a heating element to heat or assist in defrosting the frost detector. In some embodiments the frost detector of designed to fit at a selected location on a single evaporator coil. 
     In some embodiments, the frost detector is capable of detecting changes in energy absorption on the target to detect frost formation. Supporting electronics control a contrast set point. The contrast set point may be pre-set or adjustable. When the contrast point is achieved, a signal, compatible with most industry refrigeration controllers is sent by the frost detector to a controller, which will initiate a defrosting cycle in any system where operational change may be controlled using an embodiment of the invention. Virtually any known controller may be useable. Embodiments of the invention permit 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. 
     Advantages of the invention may include allowing refrigeration or freezer systems using embodiments of the invention to operate at any practical ambient air temperature while limiting frost build up and providing an effective reliable means to defrost the evaporator without degrading the product stored in the refrigeration or freezer system. In some embodiments features of the sensor 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, (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), and (6) reduced ambient air temperature rise (further protecting the refrigerated or frozen product). 
    
    
     
       DETAILED DESCRIPTION OF THE INVENTION 
       BRIEF DESCRIPTION OF THE FIGURES 
       Figures are provided solely as examples 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. 
         FIG. 1  show a representative or example refrigeration system including a frost detection device built in accord with the invention. 
         FIG. 2  show a perspective view of a frost detector embodiment built in accord with the invention. 
         FIG. 3  shows a side view of the frost detector embodiment of  FIG. 2 . 
         FIG. 4  show a perspective view of the frost detector of  FIG. 2  installed on an evaporator coil. 
         FIG. 5  shows a generic example optical sensor. 
         FIG. 6  shows an example frost detector system built in accord with the invention. 
         FIG. 7  shows an alternate example frost detector system. 
     
    
    
     DISCUSSION 
     The present invention relates to apparatus and methods 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 of electromagnetic radiation energy wavelengths to detect frost formation. Embodiments of the invention further include apparatus for delivering gas at a volume and velocity sufficient to removing residual water and debris from the frost sensor that might degrade performance. The gas used may be any acceptable gas including air. When frost is detected, a signal is sent to a controller which activates a defrost cycle. Systems built in accord with 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. 
     As used herein, frost shall mean the growth of ice crystals generated by collecting water molecules on any material. Ice shall mean any frost crystals which have melted and refrozen. 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 a controller, such as timing circuit in a microprocessor used as a controller. 
     As used herein, a “refrigeration system” refers to apparatus for reducing temperature using the well-known thermodynamic cycle of gas compression used, for example, in many commercial refrigerators. The term refrigeration system may also refer to apparatus for reducing temperature using the peltier effect. 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 refrigeration system, 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 one or more integral timers. 
     As used herein, “ambient air temperature” refers to the temperature of atmospheric air external to or in the environs wherein the evaporator system is located. 
     The terms “defrosting” or “deicing” are used in this application to mean the removal of crystallized water from the evaporator coils or possibly also other parts of a refrigeration system. 
     Turning now to the figures,  FIG. 1  shows an example refrigeration system in which a frost detector and frost detector system built in accord with the invention may be used. However, frost detectors and frost detector systems 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, and embodiments of the invention can be used by itself or in association with other known devices for initiating or halting defrosting cycles. 
     In more detail,  FIG. 1  shows a typical refrigeration system  100  except that the refrigeration system  100  shown includes both hot gas bypass  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 defrost system is required. In the embodiment described, an optical frost detector  102  will preferably mount to a fin  104  of a refrigeration evaporator  106 . The frost detector is preferably placed in the flow of air passing through the evaporator. However, in other embodiments, the frost detector  102  may be mounted in many alternative locations. In some embodiments, more than one frost detector  102  may be used. As frost begins to form on the fins and on an optical target (visible in later figures) on the optical frost detector  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 a 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 based on a signal from a temperature sensor, but in other embodiments may also or alternatively be ended by a signal from a frost detector, a refrigeration gas pressure sensor, or a timer. 
       FIG. 2  shows an example embodiment of the optical frost detector  102 . In this example embodiment, the body  300  includes a clip  304  for gripping an evaporator fin, an optional temperature sensor holder  302  for holding a temperature sensor, and an optics housing  316  for holding parts of the optics used to detect frost formation. This example embodiment shows an optional window  320  which allows electromagnetic radiation to pas through, but protects the lenses of the optics from contact with water, frost or debris. Many acceptable materials can be used for the window  320 , however the window  320  is preferably fabricated from a material or coated with a coating that inhibits the formation of frost, or tends to shed water. The lenses are focused at or near the surface of the target  318  where the growth of frost will be detected. An optional backstop  322  supports the target  318 . A gas conduit  306  may be coupled to a source of pressurized gas. The conduit includes slots  308  and  310 . Slot  308  allows gas delivered through conduit  206  to blow onto the window  320  to clear water and debris, while slot  310  allows gas delivered through conduit  206  to blow onto the target  318  to clear water and debris. Slots  314  are optional and may be included if it is desirable to prevent water or debris accumulation on other areas of the body  300  near the target. Optional side duct  312 , which includes at least one slot  324 , may be included if it is desirable to prevent water or debris accumulation on other areas of the body  300  away from the target. In general, the location and shape of the slots is determined by the area that must be cleared by the flow of gas, and therefore other variations may be used. 
       FIG. 3  shows a side view of the frost detector  102  of  FIG. 1 , mounted on a fin  202  of an evaporator. In this embodiment, a tube  328  can be seen coupled to the conduit  306  to deliver pressurized air to conduit  306 . The flow of air or gas may be constant or intermittent and of varying strength over time. An optional thermal element  328  is seen mounted to the body  300  by attachment to the thermal sensor holding  302 . However, in alternate embodiments there may be no thermal element, or the thermal element may be located elsewhere in the refrigeration system. 
     Electrical communication wire  324  carries signals from the temperature sensor to the controller (Seen in  FIGS. 1 ,  6  and  7 ), and electrical communication wire  326  carries signals from optics held in optics housing  316  to the controller. 
     The frost detector  102  is preferably configured to attach to one or a few fins  202  on an evaporator.  FIG. 4  shows the example frost detector of  FIG. 3  attached to a fin  202  of an evaporator. However, in alternate embodiments, the frost detector  102  may be coupled to the evaporator at other locations. Virtually any acceptable means for attaching the body  300  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  300  is preferably fabricated from a single piece of thermally conductive material, but may be formed from separate pieces joined together. Acceptable materials for making the body  300  include but are not limited to copper, copper beryllium alloys, and various plastics. The body  300  may include a coating selected to enhance the shedding of condensed water from the surface of the body  300 . The thickness, shape, contours and angles of the frost detector body  300  are preferably selected for operational functionality and reliability. 
     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. 
       FIG. 5  shows an example embodiment of a typical optical sensor  500 . The optical sensor  500  includes a light emitting element  502  comprising a light emitting diode for transmitting light energy (preferably infrared, but other wavelengths including but not limited to visible wavelengths may be useable), and a receiving element  504  comprising a transistor. The transmit element  502  and the receiving element  504  are preferably pre-focused 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 . The target  506  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 to detect frost formation will become apparent to those skilled in the art based on the disclosures herein; all such approaches are within the scope of this invention. 
     Embodiments of the invention also include a system for controlling frost formation on the evaporator of a device operating in a refrigeration cycle by initiating defrost cycles when frost is optically detected. Referring to  FIG. 6 , an example system  600  built in accord with the invention includes a frost detector  602  attached to an evaporator  604 . The frost detector is in communication with a controller  606  via wires  612 . The frost detector is also in gas communication through pipe  608  with a valve  610 . The valve  610  is in communication with a controller  606  via wires  616 . The valve is also in gas communication through pipe  614  with a pressure container  618 . Pressure container  618  optionally includes a pressure sensor in communication with the controller  606  via wires  620 . In some embodiments the pressure container is in gas communication with a pump  622  via pipe  624 . Power cord  626  connects to a power source, not shown. Wires  624  allow the controller  606  to communicate with the pump  622 . The system described here is provided as an example. Many other configurations may be useable. For example the system  600  could use a large pressure container that is replaced when the pressure gets too low for operation, rather than using the pump  622  to refill the pressure container  618 . Also, in some embodiments the system  600  may connect the pump  622  directly to the frost detector  602 , without using a pressure container  618  or valve  610 . The various parts of the system  600  may be located generally as desired in, on, or around the refrigeration device on which the frost detector is installed. Wire based communications are shown between the various components in the example embodiment seen in  FIG. 6 , however wireless communications may also be used between some components. 
     Alternate embodiments of the system for controlling frost formation may also include more than one frost detector at various points on the evaporator.  FIG. 7  shows an alternate embodiment in which the example system  700  includes more than one optical detector  602 . This alternate embodiment also shows an optional temperature sensor  628  located on the evaporator  604  some distance from the frost detectors  602 . In still other embodiments, temperature sensors may be located at other places in the refrigeration system. The temperature sensor  628  is in communication with the controller via communication wire  630 . The system  700  may optionally include a timer  632  in communication with the controller  606  via communication line  634 . 
     The mounting position of the frost detector is preferably selected for operational functionality and reliability. The frost detector 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. In many embodiments it will be preferable to position the frost detector on the portion of the evaporator likely to frost first, and preferably in the flow of air passing through the evaporator. 
     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, and 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 this is where the invention described herein is of the greatest utility. 
     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. Then signaling the controller to halt the defrost cycle. As seen in the table below, the signal to halt can be a signal from the frost detector, a temperature sensor, refrigeration gas pressure sensor, and a timer. When a refrigeration system begins a hot bypass gas cycle, the refrigeration gas pressure may rise sufficiently high to damage components of the system, such as the compressor. It may therefore be desirable to monitor the refrigeration gas pressure and halt the defrost cycle when such pressure rises above a safety threshold. 
     
       
         
           
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Signal source causing activation of 
                 Signal source causing  
               
               
                 defrost cycle 
                 de-activation of defrost cycle 
               
               
                   
               
             
            
               
                 Optical Frost detector 
                 Optical Frost detector 
               
               
                 Optical Frost detector 
                 Temperature sensor 
               
               
                 Optical Frost detector 
                 Refrigeration gas pressure detector 
               
               
                 Optical Frost detector 
                 Timer 
               
               
                   
               
            
           
         
       
     
     When a selected level of frost is detected, 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. 
     At some point during or after the defrost cycle, the system will allow pressurized gas or air to blow any residual water or debris of the frost detector. The characteristics of this air stream will generally be chosen for effectively removing water and debris in the environment in which the frost detector is used by configuring the release of a selected volume of air at a selected velocity for a selected period of time, and if more than one pulse is used, at selected intervals. 
     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.