MXPA99008474A - Condensation control system for heated insulating glass units - Google Patents

Abstract

A glass heating system (26) includes a low emissivity sheet of coated glass (34) and an optical sensor (28) mounted on the surface of the glass (34) for optically detecting condensation on the glass (36). The low emissivity glass (36) is economical to produce and provides superior thermal properties. The low emissivity glass (36) has improved thermal characteristics for use in insulating glass doors for freezers and refrigerators. The optical sensor (28) is positioned between the sheets of glass (34, 36) in the insulating glass unit (26) for detection of moisture on the outer surface. When condensation is detected, the controller (30) transmits power through theconductive coating on the unexposed surface of the glass (36) to heat the glass and eliminate the condensation. In a two paned insulating glass door (34, 36), the control circuit (30) can be conveniently mounted in the frame of the door (32).

Description

CONDENSATION CONTROL SYSTEM FOR UNITS INSULATED GLASS INSULATORS BACKGROUND OF THE INVENTION Field of Invention The present invention relates to a condensation control system for heated glass and heated insulating glass units and, more particularly, to a low emissivity glass sheet, with a resistive coating, which is connected to an energy source. An optical moisture sensor is placed between the two glass sheets to detect moisture on the outer surface of the glass, caused by condensation. When used in an insulating glass unit for freezer doors and commercial reflectors, the sensor controls the selective heating of the glass, to prevent condensation from forming on the doors.

Summary of the Related Technique. The insulating glass units, used in glass doors for freezers and commercial refrigerators, are of a construction of double glass sheets or triple glass sheets. The insulating glass units generally include a conductive coating on one of the glass surfaces, to electrically heat the glass. The heating of the glass keeps the doors free of frost and condensation, so that customers can see the products inside the freezer or refrigerator. Clear glass doors improve sales and prevent frost and condensation from damaging products for sale and cooling equipment. Because the temperature of the surface of a glass door is reduced below the room temperature by the cooled interior, moisture tends to condense on the surface of the glass, when the temperature of the glass falls below the dew point of the air in the store. The object of glass heating is to keep the temperature of the glass above the dew point temperature of the hottest ambient air. By heating the glass above the dew point, the formation of condensation and frost on the glass of the door is prevented.

In a door consisting of a two-leaf insulating glass unit, the unexposed surface of one or both of the glass sheets is coated with a conductive material. This conductive coating is connected to an alternating current power supply by two busbars or other electrical connectors, mounted on the opposite edges of the glass. As the current passes through the coating, the surface of the glass is heated to provide a surface free of condensation. The coating on an insulating glass unit door is normally applied to the unexposed surface of the most front glass sheet. This more frontal glass sheet, although exposed to ambient air, can be kept free of frost and condensation. In a humid environment, when the door is opened, the innermost glass sheet is also exposed to ambient air and condensation can form on the exposed surface of the innermost door. Consequently, the unexposed surface of the innermost glass sheet can also be coated to heat the innermost glass sheet.

The current can be transferred through the coating on the glass in a continuous base. In order to minimize the increase in cost caused by the heat that migrates to the freezer or refrigerator cabinet, the doors are generally constructed of triple-glazed units for the freezers and double-pane glass units for the chillers of refrigeration. The units are typically operated with low heat dissipation. The control of the energy dissipated by the door of the freezer or refrigerator is of great importance. If the energy is too low, condensation and frost will form on the glass. If the power dissipation is too high, additional costs will be incurred. The additional energy required to heat the door is a nominal cost, but the operating costs on the cooling system to keep the freezer or refrigerator at the desired temperature can be significant. In general, the goal is to keep the units free of frost and condensation, with a low energy dissipation density.

The heated glass can also be used in other applications to prevent condensation, such as in vending machines, bathroom mirrors, or skylight lights. Such units may also include a control system for selectively transmitting current through the coated surface of the glass, when condensation is detected. Glass sheets suitable for heating applications are provided with a transparent, conductive coating on a surface. Typical conductive, transparent coatings include tin oxide, indium oxide and zinc oxide. The coating on the glass sheet has a resistance, which is typically measured in "ohms per square", which is the strength of a square piece of glass. The strength of the sheet, in ohms per square, is a term well known in the art and is used in accordance with such meaning. For a square piece of coated glass, which has a known resistance of the sheet, the resistance between the opposite sides of the square piece of coated glass remains constant for any size of the square. This resistance can be measured using a 4-point probe ohmmeter or other similar measuring device. The coated glass used in the aforementioned applications is often rectangular in shape. The resistance between the opposite side of the rectangular part of the coated glass varies depending on the dimensions of the glass. However, once the strength of the sheet, in ohms per square, of a specific type of coated glass sheet is known, the resistance between the opposite sides of any rectangular piece of glass can be calculated, based on the Actual dimensions of the rectangular glass sheet, by the following equation: RG = (d / w) Rs where RG is the resistance of the rectangular piece of the coated glass, as measured between the opposite sides on which the busbars are mounted, d is the distance between the two sides with the busbars, w is the length of the two sides on which the busbars, and Rs is the surface resistance, in ohms per square, of a square piece of coated glass. The ratio of d / w is often referred to as an aspect ratio. Assuming the coating is applied in a uniform thickness, the resistance will be uniform through the coated glass. The strength of the coated glass can also be changed by varying the thickness of the coating applied on the glass. For a coated glass directly connected to a power supply, the dissipation of energy can be controlled by varying the resistance of the coated glass. A common size for a freezer door is 183 by 61 centimeters. For such a freezer door, with a coating that has a resistance of 100 ohms per square, the resistance of the freezer door would be 300 ohms, measured between the sides of 61 cm. , and of 33.33 ohms, measured between the sides of 183 cm. When the current is continuously applied to the coating on the door of the glass freezer, the preferred density of energy dissipation for a Freezer door in a humid environment typically varies from 4 to 10 watts per 929 cm2 (square foot). The density of energy dissipation is reduced for less humid applications, such that the preferred range, in general, is from 1 to 10 watts per 929 cm2. Energy dissipation densities above 10 watts per 929 cm2 will not generally place undue thermal stress on the coated glass, but will result in inefficient operation of the general cooling system. For a freezer door of 61 x 183 cm, with a power dissipation of 6 watts per 929 cm2, to heat the door, the total energy dissipation for the door is 72 watts. The energy dissipated by the door can be controlled by adjusting the voltage, current and / or resistance in the system used to heat the door (power = VI 0 V2 / R = I2RG). For a 61 x 183 cm door, with busbars directly connected to a 115 volt power, with a dissipation density of 6 watts per 929 cm2, and a power dissipation of 72 watts, the resistance of the coating on the door of glass needs to be 183.7 ohms. The coating in ohms by 929 cm2 to achieve The desired resistance depends on which side of the busbar is placed. If the busbars are placed along the short sides, the required 929 cm2 ohms should be 61.2. If the busbars are placed on the long sides of the door, the ohms per 929 cm2 of the cover should be 551. The required coating varies depending on the size of the door and the placement of the busbars. In the production of freezer and refrigerator doors, for direct connection to a power supply, it has not generally been possible to specify a simple coating for the glass produced for the doors. Differences in the size of the glass door, power dissipation requirements, line voltages, and mounting configurations, require a number of different coatings with different resistances in ohms per 929 cm2. Due to the fact that the required doors vary in the resistances of the leaves, most of the glass for the doors is covered in a production process customary off line, in order to supply the requirement of correspondence of the resistance. In an off-line production operation, the tin oxide conductive coating has traditionally been applied to glass using a batch process of pyrolytic spraying, in a reheat oven. The blade resistance is selected to provide adequate energy dissipation for the door size and line voltage. The pyrolytic process is very suitable to supply the relatively high sheet resistance required for direct connection to a power line. However, such a process has a number of problems. Coating the glass with tin oxide in an off-line process results in high costs, poor uniformity, interference colors that degrade the appearance of the coated glass, and over-spraying to the opposite surface. On the other hand, the glass coated with tin oxide in a high volume, the online production operation provides lower cost and an easily available product, which has improved properties of clarity and uniformity and thermal transfer. Glass producers with high volume production lines for low-emissivity glass often use a coating process consisting of atmospheric chemical value deposit (ACVD) to produce architectural window glass. Such glass has low hemispheric emissions, which improve the insulating properties of glass. A glass of low emissivity (also named low E glass) can also be manufactured by spraying off-line batches and vacuum coating off-line. Low-emissivity pyrolytic glass produced in the off-line process often includes one or two layers that suppress color to suppress the unwanted color of the sprayed tin oxide. In a pyrolytic process of online production, the coating is applied while manufacturing the glass. The coating equipment is located in the tin bath in the floating glass process, where the glass is formed so that the residual heat of the glass is used to facilitate the chemical reaction for the coating process.

In units of multi-sheet insulating glass, such as in the doors of a freezer, the glass of the insulating glass unit must be heated to remove condensation, but still have good insulating properties, to minimize heat transfer to the freezer cabinet. The goal is to provide a coating on the glass, with a low semispherical emissivity and with a high insulating value (R value). An uncoated glass has a hemispherical emissivity of 0.84, and a freezer door should typically have units of triple sheets of glass, in order to minimize heat transfer in the freezer cabinet. Depending on the thickness, glass coated in the off-line process will typically have a hemispherical emissivity between 0.4 and 0.8, while a low-emissivity coated glass can achieve an improved emissivity in the range of 0.05 to 0.45. Emissivity is a measure of both the absorption and the reflectance of light at given wavelengths. It is usually represented by the formula: Emissivity = 1 -reflectance of the coating. The term of emissivity used to refer to the emissivity values measured in the infrared range by ASTM standards. Emissivity was measured using radiometric measurements and reported as hemispheric emissivity and normal emissivity. A triple glass sheet insulating glass door, constructed of uncoated glass, will have an R-value of 2.94 insulation. A door with triple sheet glass, with a coated glass having a hemispherical emissivity of approximately 0.45, will have an improved R value of 3.70. Using a low emissivity glass of 0.15, the thermal performance will be improved, so that the double-glass unit, of lower cost, can be provided for the freezer doors. Such a unit of double sheets of glass (emissivity of 0.15, air space of 1.27 cm) will have an R value of 3.33. The addition of argon gas between the glass sheets increases the value of R to 4.0. The use of a single low emissivity glass produced in a high volume production line can provide significant benefits to the manufacturers of freezer doors and refrigerators. The cost of Coated glass for use in heated doors will be significantly reduced and the thermal performance of the glass will be improved. The use of low emissivity glass with a standard coating for high volume production is the key to cost savings. However, there is a significant problem with the use of low emissivity glass for heated glass applications. Low-emissivity glass has low resistance, so the continuous direct connection of the glass to an energy supply will produce too large a power density. In addition, the correspondence requirements of resistance have made such an application difficult. The control systems, which depend on the detection of temperature and / or humidity, have not provided acceptable results. Such sensors do not directly detect the condensation on the surface of the glass sheet and provide only an approximation of when the condensation will form. Such systems do not have the sensitivity or accuracy necessary to control the energy to a coated glass sheet in applications of insulating glass. A low cost control system, with acceptable performance capabilities, is necessary to allow the use of low emissivity glass in units of insulating glass doors. Applicants have developed an insulating glass unit with a capacitively coupled heating system, for continuous operation. A capacitor is coupled between the power supply and the coating of the glass, to supply the desired reduction of current and the dissipation of energy for continuous operation. A simple type of low emissivity glass can be used for a variety of door sizes and power supplies by changing the capacitance in the control circuit. The details of the coated glass and the control system are disclosed in the US application, also pending, Serial No. 08 / 779,470, the disclosure of which is incorporated herein by reference. The present invention involves a control system which uses an optical sensor for the direct detection of condensation, instead of the indirect temperature and relative humidity method. The sensor Optical provides improved detection of the condensation of the glass surface to facilitate the intermittent application of energy to the coated glass. A variety of control systems have been developed in the prior art for heated glass applications and insulating glass units. Transformers have been used to reduce line voltage to heated glass, as shown in US Patent 4,248,015 to Stromquist et al. Transformers are an unacceptable solution, because they are bulky and expensive. External ballast resistors (also shown in '015) have been used, but they are large and generate unwanted heat. Transformers have also been used to overcome a problem that frequently occurs when using a coated glass with a fixed resistance, directly connected to a power source. If the humidity in a facility can be higher than expected, when the system was designed, possibly due to the variation of stations, the energy density of the doors may be insufficient to prevent condensation from occurring.

Because the energy density is established by a fixed sheet glass resistance, expensive impulse transformers have been installed to increase the voltage, in order to correct the problems of condensation. Control systems using triac circuits have been developed to vary the voltage applied to a heated glass sheet, an example of which is shown in U.S. Patent No. 4,260,876 to Hochheiser. Hochheiser detects the difference in the surface temperature of the glass and the dew point temperature of the ambient air and uses a complex solid-state switch to control the current. However, complex triac phase control circuits can cause charges to the power line that have high peak currents and high harmonic content. Additionally, triac circuits cause large amounts of electromagnetic interference (EMI). These triac circuits that reduce harmonic distortion and EMI have been taught, for example, by Callahan et al., In U.S. Patent No. 5,319,301. However, such triac circuits are complex, expensive and only limited effectiveness in the reduction of ridge currents. Reiser et al (U.S. Patent No. 5,347,106) discloses a control system for heating a mirror, to prevent the formation of condensation. The coating is divided into separate conductive elements with one or more marking lines, in order to control the length of the conductive path. Heaney, in US Patent No. 4,127,765, teaches that several doors can be wired in series. Heaney also reveals the use of sensors to detect ambient temperature, dew point and relative humidity to control energy to coated glass. In a previous patent (US Patent No. 3,859,502), Heaney discloses a relative humidity sensor and a controller for controlling the energy to the glass based on the relative humidity level. Humidity is detected based on the variable impedance of the resistive component or electrode. Sensors for detecting relative humidity and / or temperature are disclosed in U.S. Patent Nos. 4,277,672, 4,350,978 and 4,827,729. The sensors of the Temperature alone, where the glass is maintained at a specified temperature, does not provide accurate control, since the dew point is dependent on both temperature and humidity. Systems with both temperature and humidity sensors have not provided the accuracy or response time necessary to efficiently operate the insulating glass units with the heated glass. Technology has been developed in the automotive industry to detect moisture on a windshield and control the automatic operation of windshield wipers. Cleaner control systems have employed a number of different technologies to detect the moisture conditions encountered by a vehicle, including conductive (which detect variable impedance), piezoelectric, and optical sensors. Optical sensors operate on the principle that a beam of light diffuses or deviates from its normal path by the presence of moisture on the outer surface of the windshield. Systems employing optical sensors have the unique advantage that the detection facility (i.e. disturbances in an optical path) is directly related to the Observed phenomena (ie disturbances in the optical path that makes the vision, which, in this case, is the condensation observed by the person in the door of the freezer). Thus, optical systems generally have an advantage over other sensor technologies, in that they are closely related to the problem correlated by the wipers in a windshield or by heating the glass in an insulating glass door unit. McCumber et al. (U.S. Patent No. 4,620,141) discloses an automatic control circuit for activating a sweep of the wiper blades in response to the presence of water droplets on the outer surface of a windshield. Devices that detect rain to control the windshield wipers of a vehicle, as described by McCumber et al, and Teder (U.S. Patent Nos. 5,059,877 and 5,239,244) include a box-like housing mounted on the interior surface of the windshield. The presence of moisture on the surface of the windshield changes the reflection of light at the air-glass interface, and this change in reflected light is processed electronically and used as the signal to activate the windshield wipers. In the present invention, optical sensors can provide improved detection and control, to eliminate condensation and facilitate the use of low emissivity glass. The sensor housing in an optical moisture sensor should securely couple the glass and the optical coupling to the glass, so it will effectively remove the interface between the emitters-light detectors and the glass surface from an optical point of view. In optical humidity sensors, the light from the emitter is directed by a guide element in the glass at an angle of approximately forty-five degrees with respect to the glass. The light is then reflected by the outer surface of the glass at approximately a forty-five degree angle and is directed by a guide element in a detector. Water or other condensation on the surface of the glass affects the overall transmittance of the optical path between the emitter and the detector. When the angle of entry of the light beam in the glass is greater than fifty degrees, a loss of the signal It happens frequently. When the entry angle is less than forty degrees, a loss of sensitivity occurs and the sensor is not able to properly detect the moisture in the glass. Consequently, it is essential that the angle of entry of the light beam from the emitter enters the glass at approximately forty-five degrees. Examples of optical sensor mounting configurations to achieve a forty-five degree angle between the optical axis of the emitter and the glass windshield, are disclosed by Noack (U.S. Patent No. 4,355,271), Bendicks.

(U.S. Patent No. 5,323,637), Larson (U.S. Patent No 4,859,867), and Stanton (U.S. Patent No. 5,414,257). Teder, one of the present applicants, has a pending application (EUA, Serial No. 08 / 653,545, incorporated herein by reference) which discusses the configuration of an optical sensor in greater detail. In addition to mounting the optical moisture sensors on the glass, several control circuits have been developed in the windshield wiper application to process signals from an optical moisture sensor and generate a control signal. Teder (US patent ,059,877) involves a control circuit for a windshield wiper system, which is designed to drive the wiper blades at a rate dependent on the level of precipitation encountered, but which also addresses the problem of noise associated with shifts in the windshield. ambient light level. Several automotive glass applications use less expensive conductive sensors instead of optical sensors. Conductive sensors are formed on the glass sheet to measure the humidity on the surface of the glass and are based on the principle that the moisture located on the surface, between two electrodes, will vary the impedance between the two electrodes. U.S. Patent Nos. 3,902,040, 4,032,745 and 4,127,763 disclose electrical systems used in the automotive glass industry for heaters. US Patent No. 3,968,342 discloses a car-coated glass with a pair of electrodes attached to the surface of the glass sheet. The current through the coated glass is activated and disconnected in response to variations in electrode resistance, caused by condensation. , The electrodes they are mounted on the outer surface of the glass sheet, so that these electrodes corrode frequently or deteriorate in use, which adversely affects the accuracy of the control system. In summary, the cost, complexity and other problems associated with sensors and energy conversion circuits have prevented manufacturers from realizing the cost benefits of using a standard low-emissivity glass in heated insulator glass for freezer doors and other apps. Optical sensors provide an accurate system for moisture detection, but these optical sensors have not been used in conjunction with the low emissivity glass coating on an insulating glass unit.

SUMMARY OF THE INVENTION According to the present invention, a glass heating system is provided for use in insulating glass units, including a coated, low emissivity glass sheet, at least one humidity sensor mounted on the coated sheet of glass, and a control system connected to the humidity sensor, to control the energy to the coated glass. Low-emissivity glass is economical to produce and provides superior thermal properties. However, low emissivity glass has a low sheet resistance, so that direct connection of the coated glass to a standard 115 volt power supply will generate too much heat for most insulating glass applications, such as freezer doors. The sensor detects condensation on the glass surface to selectively supply energy to the coated glass to eliminate condensation. The control circuitry provides a switch to connect and disconnect power to the coated surface of the glass, based on the signal from the sensor. Multiple sensors can be used on a single sheet of glass. A microprocessor can be added to the control circuitry to provide circuit synchronization and variable power control. When condensation is detected by a sensor in the microprocessor controller, a high level of Current can be provided to the coated glass to supply an inrush of energy to immediately clean the window. The energy is then reduced to a lower level to keep the glass at an elevated temperature for a specified period of time. When both the innermost sheet of glass and the outermost sheet of glass are provided with a conductive coating, the sensors are placed on both sheets of glass. The humidity sensor is mounted directly on the glass sheet. The preferred sensor is an optical moisture sensor, which can be mounted between the two sheets of glass in an insulating glass unit. The sensor detects the presence of condensation on the outer surface of the glass and generates a signal to control the transmission of energy to the coated surface. The energy is delivered to the coated surface of the glass sheet only when moisture is detected on the surface of the glass by the sensor. Low-emissivity glass, with its low resistance, can be used because the energy is selectively supplied to the glass sheet when condensation is detected. The Excessive power, which will be generated by a continuous supply of energy to the low emissivity coating on the glass, is avoided by the use of the sensor and the control to selectively supply the energy. Low-emissivity glass has improved thermal characteristics, which improve the efficiency of an insulating glass unit of the freezer or refrigerator with the heated glass system. The improved thermal characteristics allow the use of double-pane glass doors instead of triple glazed doors in many applications, to insulate the glass units. In a two-leaf insulator glass unit, for a freezer door, the innermost glass sheet has an exposed surface facing the inside of the freezer cabinet and an unexposed surface. The outermost glass sheet has an exposed surface that faces the environmental conditions and the surface without exposing face to face with the other unexposed surface. This unexposed surface of the outermost sheet will be coated. The unexposed surface of the innermost sheet of glass can also be coated to prevent condensation forming on the innermost sheet when the door opens. The circuit board for the control circuit can be mounted in the enclosure for the sensors or it can be mounted on a circuit board in the frame of the insulating glass unit. The spacing between the two glass sheets is 19 mm, which provides enough space to mount the optical sensors between the glass sheets. The assembly of the sensors inside the space enclosed between the two leaves, provides a clean environment and protects the sensors from damage. An object of the present invention is to use low emissivity glass for an insulating glass unit. Such glass has a low resistance and good thermal properties for insulating glass applications. Low-emissivity glass can be produced in a production line for a relatively low cost. A further object of the present invention is to develop a low-cost control circuit for supplying the desired energy dissipation for the heated glass. A direct connection of the coated surface from glass to a power supply produces too much energy dissipation. A control system is provided with optical sensors mounted on the coated glass sheets to optically detect condensation. The power can be disconnected until the condensation is detected. When the condensation is detected, the energy is turned on to heat the glass. A further object of the present invention is to provide two levels of energy or variable energy to the coated surfaces. When the sensors detect humidity and turn on the power, a high level of energy can be provided for a short period of time, to immediately clean the window. A lower level of energy can be maintained for a period of time to keep the glass clean. Another object of the present invention is to mount the sensors in the space between the two sheets of glass in an insulating glass unit. The sensors are mounted conveniently between the glass sheets. Instead of having the sensors mounted externally to measure the temperature and relative humidity, these sensors are protected in the enclosed space. The combination of low-emissivity glass and a control circuit with optical sensors mounted in the enclosed space, provides a low cost and efficiently heated glass unit for use in insulating glass units, such as freezer doors and refrigerators, and other applications of heated glass.

BRIEF DESCRIPTION OF THE DRAWINGS The foregoing, like other advantages of the present invention, will become readily apparent to those skilled in the art from the following detailed description of a preferred embodiment, when considered with reference to the accompanying drawings, in which: Figure 1 is a schematic block diagram of the electrical circuit for a heated glass system of the insulating glass unit, with the optical moisture sensors of the present invention; Figure 2 is a perspective view of an insulating glass unit with a frame and two sheets of glass; Figure 3 is a cross-sectional view of an insulating glass unit, showing an optical sensor and a conductive coating on both glass sheets; Figure 4 is a cross-sectional view of an optical sensor mounted on a glass sheet of the insulating glass unit; Figure 5 is a schematic block diagram of the control circuit for the optical sensor of the heated glass system; Figure 6 is an electrical schematic diagram of the optical sensor and the control circuit system; Figure 7 is a series of waveforms showing the operation of the optical sensor; and Figure 8 is a schematic block diagram of the control circuit of an insulating glass unit, with a microprocessor.

DESCRIPTION OF THE PREFERRED MODALITY Referring now to Figure 3, the heated glass system 10 of the present invention is shown schematically. A sheet of glass 12 is coated with a thin coating microscopically of a conductive, transparent material 14. The coating material 14 may be tin oxide, indium tin oxide, zinc oxide, or other similar coatings. The coating can be manufactured in a production line that uses a pyrolytic process, such as an atmospheric chemical vapor deposit, or some other alternative process. The glass 12 may also include a color suppression layer (not shown), which is applied in a similar manner. The coating 14 reduces the emissivity of the glass 12 from about 0.84 to less than 0.50. The preferred range for hemispherical emissivity is 0.15 to 0.43 for low emissivity pyrolytic glass. Other processes can be used to supply a low emissivity glass with hemispherical emissivity as low as 0.01. The sheet resistance of such conductive coating for low glass Emissivity is typically less than 20 ohms per square. Low emissivity glass can be produced with cost effective in a high volume production line and provides improved thermal properties. However, the low resistance of the blade prevents the continuous direct connection of the low emissivity glass 12 to the power source 16. This power source 16 is a single phase supply and in E.U.A., it is rated at 60 hertz and 115 volts. A sheet resistance of 11 ohms per square, for example a direct coupling to a 61x183 cm door connected for the maximum resistance of 33 ohms, supplies 400 watts of power or 33.3 watts per 929 cm2. Such energy dissipation density is too high for freezer and refrigerator door applications. Electric power is supplied from the power source 16 through the conductor 18 to the busbars 20. These busbars 20 are attached to the jacket 14 to ensure electrical contact between the busbars 20 and the cover 14. The busbars 20 , which are frequently named as Band electrodes are preferably placed along the opposite edges of the glass 12, so that current flows through the coating 14 between the bus bars 20 to prevent the dissipation of desired energy in the form of heat. In order to reduce the energy dissipation of the coating 14 on the glass 12, a controller 24 is used to selectively change the connection and disconnection of the energy, to prevent condensation from forming on the surface of the glass 12. A sensor 22 it is placed on the glass sheet to detect the formation of condensation on the glass 12. The preferred sensor 22 is an optical sensor that uses the emitters and light detectors to directly detect the condensation on the surface of the glass 12. The sensor optical 22 is connected to the controller 24 which includes the interrupting capabilities for connecting and disconnecting power from the power source 16 to the coated surface 14. When condensation is detected by the optical sensor 22, the energy is activated. When no condensation is detected, the controller 24 disconnects the power, so that this energy is only supplied to the coating 14 when the condensation is detected on the glass 12. Figures 2 to 4 show a typical freezer door formed by an insulating glass unit 26, having a heated glass system, with an optical sensor 28 connected to a controller 30. This insulator glass unit 26 includes a frame 32 and two sheets of glass. The innermost piece of glass 34, which faces the freezer cabinet, may be uncoated (Figure 4) or coated (Figure 3). If the freezer unit has a problem with the formation of condensation on the inner surface of the door, when the door is opened, the insulating glass door unit will often include a coating 38 on the innermost 34 glass. The outermost glass 36, which faces the user in the store, is provided with a conductive coating 38, as described above. This conductive coating 38 is preferably a low emissivity coating, which can be produced economically in line. The coating 38 is applied to the unexposed surfaces 42, 44 of the respective glass sheets 34, 35. The coating of the Unexposed surfaces reduces any deterioration or damage to the surface when the insulating glass unit 26 is in use. The glass sheets 34, 36 are installed in the frame 32 in a known manner for the insulating glass doors. The frame 32 is made of extruded aluminum or other similar frame material. The glass sheets 34,3 6 are kept separated by a spacer 40 and sealed to form an insulating glass unit 26. The space 52 between the two glass sheets can be filled with argon gas or another transparent gas, to increase the insulator value of the unit. An energy cord 46 is used to ground to transport energy to the insulating glass unit 30. The two insulated conductors 48 from the energy cord 46 are connected to the busbars 50 at the opposite ends of the glass 36. The busbars 50 they are attached to the cover 38 to ensure electrical contact between these bus bars 50 and the cover 38. The power cord 46 is connected to the insulating glass unit 30 at one end of the frame 32 in a known manner. He conductor 48, electrically connected to the busbar 50 at the opposite end of the frame 32, is secured to the frame 32 and extends along the edge of the glass sheets 34, 36. In Figure 4, a more detailed drawing of a typical sensor 54 is shown mounted in the space 52 between the glass sheets 34, 36. This optical sensor 54 is secured to the unexposed surface 44 of the outermost glass 36. The sensor housing 56 must be securely coupled to the innermost surface 44 of the glass 36 and can be optically coupled to the glass 36, so as to effectively remove the interface between the light emitting-detectors and the glass surface from an optical point of view. The sensor housing 56 is fixed to the coating 38 on the surface 44 by means of an internal adhesive layer 58. This adhesive inner layer 58, double-sided, is made of silicone or other similar flexible plastic material. The optical sensor 54 includes an emitter 60 with the lens 62 and the detector 64 with the lens 66 mounted on the circuit board 68. In operation, the light beam 70 is emitted from the emitter 60 and travels through the glass 36 in an angle of forty-five degrees. The light beam 70 is reflected internally completely outside the outer surface 74 of the glass 36, so that the reflected beam 72 is detected by the detector 64. If there is any condensation 74 or moisture of any kind on the outer surface 72 , some of the beam 70 of light escapes and the resistance of the reflected light beam 72 is reduced. The signals to the emitter 60 and from the detector 64 are transported through the conductor 78. The mounting of the sensor 28 between the glass sheets 34, 36, in an insulating glass unit 26, protects sensor 28 from adverse environmental factors. The optical sensor 28 is ideally suited for detecting condensation on the exposed surfaces of the glass sheets 34, 36, although the sensor 28 is placed in the enclosed area 52 of the insulating glass unit 26, because no exposure to the Humidity or environmental conditions is required for optical measurements. The control circuit system for the controller 24 is shown in Figures 5 and 6. The power cord 46 and the conduit 48 provide power to the 80 power supply of controller 30 An isolation transformer is not required in this application. The energy is delivered to a capacitor C6 that stores energy, by means of a rectifier D3 and a resistor R18 of voltage drop. A Zener D4 diode prevents the voltage across the capacitor from exceeding 24 volts. Considerable ripple of the supply is present in the previously regulated voltage, but this does not adversely affect the circuit. The three-terminal SI regulator also regulates the voltage to supply a 12V (Vcc) cleaning source. The resistors Rll and R12 supply a reference voltage (Vref), nominally 2.2 V. The oscillator 82 (Ul, Rl, R2,, C1, C2) receives energy from Vcc and produces a series of pulses at the output of the oscillator 82 The emitter 60 is an infrared emitter and is connected to the output of the oscillator 82 by means of a current limiting resistor R3, which results in a series of pulses of current through the emitter 60. The current in the emitter 60 causes that it emits a corresponding pulsating infrared beam of light 70. The cycle of operation could consist of a pulse in time of 50 microseconds and a pulse out of time of 10 milliseconds. This results in an average duty cycle of 0.5% and a carrier frequency of 100 hertz. The oscillator 82 includes a section U2A of a square analog switch, a resistor R4, and a capacitor C3, to supply a delayed gate signal. The divergence of the beam 70 of light is reduced by the lens 62, which is used to collimate this beam of light. The emitter is arranged on an entry axis of forty-five degrees with respect to the glass 36. The parallel rays of the light beam are optically coupled in the glass by the internal layer 58 of adhesive. The handsets of the light beam 70 are internally reflected completely outside the outer surface 74 of the glass 36. The rays of the light beam 70 entering the glass 36 are reflected again as a reflected light beam 72. This beam of reflected light 72 converges by the lens 66 associated with the detector 64. The rays of the reflected light beam 72 collide with the photodiode of the detector 64. This detector 64 is also arranged at an angle of forty-five degrees and includes a filter of daylight, what blocks all light except infrared light from the emitter 60. Other optical configurations are known in the prior art and will also be suitable for the insulated glass unit 26 of the present invention. The use of optical sensors provides accurate detection of moisture on glass surfaces. The sensors can also be mounted on the unexposed surface of the glass and remain protected in the space between the two sheets of glass. The detector 64 produces a pulsed current waveform in response to the pulsatile reflected beam 72 which strikes the detector photodiode 64. This detector 64 will include a photodiode, a phototransistor or other optical device to produce a signal. The presence of condensation 76 or other moisture on the outer surface 74 of the glass 36 will cause a reduced reflected beam 72, which results in a lower output signal. The detector 64 is connected to the inverting terminal of an operational amplifier 84 (U3A). The operational amplifier 84 is configured as a transimpedance amplifier to simplify the current from the detector 64 and convert the current signal to a voltage signal. The output of the amplifier 84 is coupled by the capacitor C5 and the resistor R7. that prevent sudden changes in direct current, caused by ambient light, from passing through the circuit. The amplifier 84 is named A synchronous demodulator 86 is connected to the amplifier 84 and converts the output of the amplifier 84 to a DC signal by mastering the output of the amplifier 84 during a sample interval provided by the gate signal from the oscillator 82. The slight delay of the signal The gate prevents the time rise of the detector current from having any effect on the signal. The mastered signal charges the capacitor C4 sampler by means of resistor R. Capacitor C4 and resistor T perform a relatively long time constant, and several pulses may be necessary for capacitor C4 to become charged to a steady state level. Other signal processing circuits for detecting moisture on the glass by optical sensors are known in the art. The present circuit of process is a relatively inexpensive circuit to achieve acceptable control. The output of the synchronous demodulator 86 is connected to the inverting input to a second operational amplifier 88 (U3B). The amplifier 88 e is configured to operate as a comparator. The comparator section can be half a double operational amplifier, such as type LM358 and the transimpedance amplifier uses the other half. The non-inverting input of the comparator is connected to a reference formed by the resistor R15 and the resistor R14, with the resistor R13 forming some hysteresis. In the absence of humidity, the demodulated level (5 volts) is above the reference level (3.8 volts) and the output of the comparator amplifier 88 is low (less than 1 volt). in the presence of humidity, the demodulated level falls below the level of the comparator, causing the output of amplifier 88 of the comparator to increase significantly (more than 11 volts). The output of amplifier 88 of the comparator is connected to the input section of an opto-isolator triac 90. This opto-isolator triac 90 is activated when the voltage output of the amplifier 88 is high. The optic-isolator triac 90 is connected to a power triac 92, which is configured to be activated when the opiate-isolator triac 90 is activated. An opto-isolator circuit, which incorporates the detection circuitry that crosses the zero, can also be replaced by the triac 90. Various interruption configurations can be used to supply not only the complete energy directed through the coating 38 for heating 36 glass, but also reduced energy for a long time operation. When moisture is not present, the triac opto-isolator 90 and the power triac 92 remain outside and no current flows through the cover 38. When the power triac 92 is driven, the power is transmitted to the bus bars 50 and through the cover 38 in the glass 36. The glass 36 is heated and the condensation 76 is removed from the surface 74 of the glass o36. When the condensate 76 is cleaned, the power triac 92 is turned off until moisture is detected. The hysteresis of the comparison circuit ensures that the power triac 92 is completely disconnected.

Figure 7 shows the operating waveforms for the previous mode of the controller 30. The emitter current 100 and the gate signal 102 are cycled at adjusted intervals. The detector current shows the output waveform of the present non-condensing detector 104 and with the present condensation 106. The corresponding waveform of the demodulated output 108 and the state 110 of the electronic switch are shown for non-detection and detection of condensation. The components of the controller 30 can be mounted on the sensor circuit board 68. In the alternative, the components can be mounted on a circuit board 94 secured to the frame 32. A conductor 48 of the power cord 46 provides power to the supply 60. A short conductor 96 extends from the circuit board 94 to the bus terminal 50. This circuit board 94 may be mounted at either end of the insulating glass unit 26. In addition, the emitter 60 and the detector 64 can be mounted on the circuit board 94 and the light tubes (conductors) can be used to couple the light beams inside and outside the enclosed area. The light tubes provide the desired angles for the transmission of light from the emitter 60 to the glass and back to the detector 64. The light tubes are clear and provide less obstruction of sight than the enclosed housing 56. In order to to achieve the desired thermal insulating properties, argon or other gases can be used within the space 52, between the glass sheets 34, 36. The holes 98 in and around the spacer 40 are covered with a sealant, to properly seal the internal space 52 inside the insulating glass unit 30. If light tubes are used, the openings in the spacer 40 for the light tubes can be effectively sealed. A number of different control circuits can be used in the controller 30. The main requirements of the circuit are to process the output from the detector 64 to control the interruption of the energy to the coating 38 on the glass 36. The synchronizing circuits can be added to operate the triac 92 switch for a specified period of time, after detecting the condensation. Different comparator circuits can be used to generate a signal to activate a switch. Additional examples and details of the process signals to and from the emitter and detector of an optical sensor and the operation of the control circuit system can be obtained from U.S. Patent Nos. 4,620,141, 5,059,877, 5,239,244 and 5,262,640. To the extent any of such details may be necessary to complete the descriptions and estimates necessary for the purposes of the present application, they are considered incorporated herein by reference. In Figure 8 the controller 30 includes a microprocessor 112, to provide various control capabilities. This microprocessor 112 supplies the functions of the oscillator and the boundary comparison circuit. The insulating glass unit 26 is provided with multiple sensors 28 and the multiple signal process is effectively handled by the microprocessor 112. This microprocessor 112 also detects the level of rest, adjusts the appropriate threshold level and provides the time and estimate circuits. Several control algorithms can be used to control interruption operations and provide more detailed operating cycles. For example, the repeated cycle of connection-disconnection for a short period of time may be inconvenient. The microprocessor 112 counts the number of times the energy is activated during a specified period of time. If the energy is activated too frequently (three times in one minute, for example), the microprocessor detects such an occurrence and supplies the transmission of energy to the coating 38 for an extended period of time (ten minutes). Another control feature that can be easily incorporated into the microprocessor 112 is the control of a switch device with full power and reduced power capabilities. When condensation is detected, the microprocessor provides an initial full-power application to the coating 38 to clean the condensate as quickly as possible. After applying the full power for a period of time, the microprocessor 112 controls the interruption to a Application of reduced power, for a prolonged period of time. The insulating glass unit 26 may be provided with multiple sensors 28 mounted on the unexposed surface 44 of glass 36. The microprocessor 112 supplies a comparator circuit for processing multiple signals. Since the condensation is not uniformly formed on the entire outer surface 74, multiple sensors 28 will typically ensure an immediate supply of energy, to eliminate condensation. When the condensation 76 is detected by one of the sensors 28, the power switch 92 can be activated to pass current through the coating 38. The condensation 76 will first be formed on the exposed surface 74 of the outermost glass 36 and consequently this glass The outermost will be heated in an insulating glass unit 26 However, the condensation 116 may also form on the exposed surface 114 of the innermost glass 34, such as when the door is opened for a period of time. The unexposed surface 42 of glass 34 may also have a conductive coating 38 applied to heat the glass 34. When both glass sheets 34, 36 have the conductive coating 38, energy can be applied through a single switch 92 for simultaneous heating of the glass sheets 34, 36. Since condensation will form more frequently on the exposed surface 74 of the outermost glass 36, it may be preferable to use a separate switch 92 for each glass sheet 34, 36. Figure 3 shows the two sensors 28 placed between the glass sheets 34.3 6. Figure 8 shows the microprocessor 112 for processing multiple sensors 28 and two switches 92 to independently control the energy to the conductive coating 38 on the glass sheets 34, 36. One of the benefits of the insulating glass unit 26 of the present invention is the improved insulator value. The lower the hemispherical emissivity of the coated glass sheet 36, the better the insulator value (R value) of the insulating glass unit 30. The preferred hemispherical emissivity is below 0.50. Low-emission pyrolytic glass, which is suitable for On-line production, can achieve hemispherical emissivity in the range of 0.10 to 0.20. Low-emissivity pyrolytic glass is preferred, due to the low production cost. Other low emissivity glasses, such as multilayer glass with electronic coating, can be used to achieve a hemispherical emissivity below 0.10. Any low emissivity glass can be used in the insulating glass unit 30 of the present invention. Due to the lower emissivity and the resulting improvement in the insulating capabilities, an insulating, two-leaf glass unit 26 can achieve comparable insulator values than a three-leaf door, without low emissivity glass. A double glazed door with a low emissivity glass can achieve R values of 4.0. The improved R value will keep the outermost glass up to five degrees warmer than the uncoated units of triple sheets of glass, which will also reduce the need to apply heat to the glass. The two-pane glass door of the present invention will typically provide significant savings in cost and weight, when It is compared to a sheet of triple sheets of glass in applications of the door of a freezer. When the low emissivity glass is connected directly to a power source, the blade strength is unacceptably low. This low resistance results in a level of current and heat dissipation in the coated surface 38, which is too high for direct and continuous power connection for freezer or refrigerator door applications. By adding the sensors 28 and a controller 30 to the system, the low-emissivity glass 34, 36 can be selectively heated only when the condensation has formed on the glass 34, 35. Since energy is not continuously applied to glass 34, 36, general power dissipation is acceptable for insulating glass units 26 used as freezer or refrigerator doors. The heated glass system 10 and the insulating glass unit 26 of the present invention allow the use of low emissivity glass, which includes low emissivity pyrolytic glass. The use of such glass provides a number of advantages, which include the low cost, improved thermal performance, improved coating uniformity and good product appearance. Using an optical sensor to detect the optical condensation condition on the surface of the glass, it provides an exact device to control the heating of the glass to eliminate condensation. In an insulating glass unit, the sensors are conveniently mounted in the space between the glass sheets. This mounting configuration is convenient from the point of view of space and provides excellent protection of the sensors from adverse environmental factors, such as humidity and dust. The control circuit system, which includes a microprocessor, can be conveniently mounted on a circuit board in the frame of the insulating glass unit. Since the present invention does not require continuous heating of the glass by direct connection to the power source, the resistance of the coating does not have to be changed for each different door design. The same coated glass can be used in all door designs by the manufacturer of the units of insulating glass. The ability to directly detect condensation on the glass and operate only when this condensation is detected, facilitates the operation of the door undry, normal and humid conditions

Claims (22)

1. A heated glass system, for heating a surface of a glass sheet, this heated glass system comprises: a glass sheet, having a generally rectangular configuration; a transparent, conductive coating applied to the surface of the glass sheet, this coating has a hemispherical emissivity less than 0.50; a pair of busbars, mounted along the opposite edges of the glass sheet, and electrically connected to the conductive coating, these busbars each include a connector, for coupling the busbar to an energy supply and forming a circuit through the conductive coating; at least one sensor, mounted on the glass sheet, to generate a control signal, in response to moisture formed on the glass sheet; and a control circuit, electrically connected to the busbars and to a sensor, for selectively transmitting current through the conductive coating, in response to the control signal from this sensor.

2. The heated glass system, defined in claim 1, wherein the conductive coating is tin oxide.

3. The heated glass system, defined in claim 1, wherein the conductive coating is indium tin oxide.

4. The heated glass system, defined in claim 1, wherein the conductive coating is zinc oxide.

5. The heated glass system, defined in claim 1, wherein the conductive coating has a hemispherical emissivity in the range of 0.15 to 0.43.

6. The heated glass system, defined in claim 5, wherein the conductive coating is a pyrolytic coating of low emissivity.

7. The heated glass system, defined in claim 1, wherein the sensor is an optical sensor, optically coupled to the glass sheet.

An insulating glass unit, which comprises: a first glass sheet and a second glass sheet, each including an unexposed surface and an outer surface; a conductive coating, applied to the unexposed surface of the first sheet of glass; a frame, secured around the periphery of the first and second sheets of glass, to hold these sheets of glass in a parallel, spaced relationship, with the unexposed surfaces facing each other and creating a space therebetween; A pair of bus bars, mounted along the opposite edges on the surface does not exposed from the first glass sheet and electrically connected to the conductive coating, these bus bars each include a connector for coupling the bus bar to an energy supply and forming a circuit through the conductive coating; at least one sensor, mounted on the first sheet of glass, to generate a control signal in response to moisture formed on the outer surface of the first sheet of glass; and a control circuit, electrically connected to the busbars and the optical sensor, to selectively transmit the current through the conductive coating, in response to the control signal from the optical sensor.

9. The insulating glass unit, defined in claim 8, wherein the sensor is an optical sensor, mounted on the unexposed surface of the first glass sheet and placed in the space between the first and second glass sheets.

10. The insulating glass unit, defined in claim 8, including a conductive coating, applied to the unexposed surface of the second glass sheet, a pair of bus bars, mounted along the opposite edges on the unexposed surface of the second glass sheet, and electrically connected to the conductive coating, these busbars each include a connector for coupling the busbar to the power supply and forming a circuit through the conductive coating, at least one optical sensor, mounted on the unexposed surface of the second glass sheet, and placed within the space between the first and second glass sheets, to generate a control signal, in response to the moisture formed on the surface external of the second glass sheet, and a control circuit, electrically connected to the busbars and the optical sensor on the second glass sheet, to selectively transmit current through the conductive coating on the second glass sheet, in response to the control signal from the optical sensor.

11. An insulating glass unit, which comprises: a first glass sheet and a second glass sheet, each including an unexposed surface and an outer surface; a conductive coating, applied to the unexposed surface of the first glass sheet, this conductive coating has a hemispherical emissivity less than 0.50; a frame, secured around the periphery of the first and second sheets of glass, to hold these sheets of glass in a parallel, spaced relationship, with the unexposed surfaces facing each other and creating a space therebetween; a pair of busbars, mounted along opposite edges on the unexposed surface of the first glass sheet and electrically connected to the conductive coating, these busbars each include a connector for coupling the busbar to a power supply and forming a circuit through the conductive coating; at least one optical sensor, mounted on the first glass sheet and placed in the space between the first and second glass sheets, to generate a control signal in response to moisture formed on the first glass sheet; and a control circuit, electrically connected to the busbars and the optical sensor, to selectively transmit the current through the conductive coating, in response to the control signal from the optical sensor.

12. The insulating glass unit, defined in claim 11, wherein the control circuit includes a microprocessor.

13. The insulating glass unit, defined in claim 11, including a plurality of optical sensors, mounted on the unexposed surface of the first glass sheet and placed within the space between the first and second glass sheets.

14. The insulating glass unit, defined in claim 11, wherein the conductive coating has a hemispherical emissivity in the range of 0.15 to 0.43.

15. The insulating glass unit, defined in claim 14, wherein the conductive coating is a pyrolytic coating of low emissivity.

16. The insulating glass unit, defined in claim 11, including a conductive coating, applied to the unexposed surface of the second glass sheet, this conductive coating has a hemispherical emissivity less than 0.50 and includes a pair of busbars mounted to along the opposite edges on the unexposed surface of the second glass sheet and electrically connected to the conductive coating, these busbars each include a connector, to couple the busbar to the power supply and form a circuit through the coating conductive, at least one optical sensor, mounted on the unexposed surface of the second glass sheet and placed within the space between the first and second glass sheets, to generate a control signal in response to the moisture formed in the outer surface of the second glass sheet, and a control circuit, electrically connected to the busbars and to the optical sensor on the second glass sheet, to selectively transmit the current through the conductive coating onto the second glass sheet, in response to the control signal from the optical sensor.

17. The insulating glass unit, defined in claim 11, wherein the control circuit is mounted on a circuit board and this circuit board is placed in the frame.

18. The insulating glass unit, defined in claim 17, wherein the sensor includes an emitter mounted on the circuit board, with a glass tube extending to the unexposed surface of the glass, and a detector mounted on the circuit board, with a glass tube that extends to the unexposed surface of this glass.

19. The insulating glass unit, defined in claim 11, wherein the control circuit transmits energy for a period of time, in response to a signal control that indicates that moisture has formed on the outer surface of the first sheet of glass.

20. The insulating glass unit, defined in claim 11, wherein the control circuit transmits energy for a first period of time with full power and a second period of time with reduced energy, in response to the control signal, which indicates that moisture has formed on the outer surface of the first sheet of glass. twenty-one,. A refrigerated cabinet door, adapted to be mounted movably on this refrigerated cabinet, this door comprises: a first sheet of glass, adapted to be placed adjacent to the environment of the refrigerated cabinet, and a second sheet of glass, adapted to be placed adjacent to the interior of the refrigerated cabinet, each includes an unexposed surface and an exterior surface; a conductive coating, applied to the unexposed surface of the first sheet of glass,

This conductive coating has a hemispherical emissivity less than 0.50; a frame, secured around the peripheries of the first and second sheets of glass, to maintain these sheets of glass in a parallel, spaced relationship, with the unexposed surfaces facing each other and creating a space therebetween; a pair of busbars, mounted along opposite edges on the unexposed surface of the first glass sheet and electrically connected to the conductive coating, these busbars each include a connector for coupling the busbar to a power supply and forming a circuit through the conductive coating; at least one optical sensor, mounted on the first glass sheet and placed in the space between the first and second glass sheets, to generate a control signal in response to moisture formed on the first glass sheet; Y a control circuit, electrically connected to the busbars and the optical sensor, to selectively transmit the current through the conductive coating, in response to the control signal from the optical sensor.

22. The refrigerated cabinet door, defined in claim 20, wherein the conductive coating has a hemispherical emissivity in the range of 0.15 to 0.43.