Optical Frost Detector With Gas Blow Off

CROSS REFERENCE TO RELATED APPLICATIONS

[1] This application claims the benefit of the priority date of provisional patent application serial number 61/070,317, filed March 21, 2008, which application is hereby incorporated by reference in its entirety.

FIELD OF THE INVENTION

[2] 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

[3] 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.

[4] 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.

[5] 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'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.

[6] 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

[7] 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.

[8] 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.

[9] 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.

[10] 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.

[11] 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.

[12] 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: -40F to +40F 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).

BRIEF DESCRIPTION OF THE HGURES:

[13] 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.

[14] Figure 1 show a representative or example refrigeration system including a frost detection device built in accord with the invention.

[15] Figure 2 show a perspective view of a frost detector embodiment built in accord with the invention.

[16] Figure 3 shows a side view of the frost detector embodiment of Figure 2.

[17] Figure 4 show a perspective view of the frost detector of figure 2 installed on an evaporator coil.

[18] Figure 5 shows a generic example optical sensor.

[19] Figure 6 shows an example frost detector system built in accord with the invention.

[20] Figure 7 shows an alternate example frost detector system.

DETAILED DESCRIPTION

[21] 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.

[22] 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.

[23] 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.

[24] 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.

[25] 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.

[26] 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.

[27] 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.

[28] Turning now to the figures, Figure 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.

[29] In more detail, Figure 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.

[30] Figure 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.

[31] Figure 3 shows a side view of the frost detector 102 of Figure 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.

[32] Electrical communication wire 324 carries signals from the temperature sensor to the controller (Seen in Figures. 1, 6 and 7), and electrical communication wire 326 carries signals from optics held in optics housing 316 to the controller.

[33] The frost detector 102 is preferably configured to attach to one or a few fins 202 on an evaporator. Figure 4 shows the example frost detector of Figure 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.

[34] 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.

[35] 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.

[36] Figure 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.

[37] 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.

[38] 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 Figure 6, however wireless communications may also be used between some components.

[39] 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.

[40] 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.

[41] 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.

[42] 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.

[43] 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

[44] 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.

[45] 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.

[46] 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.