Insulating glass with capacitively coupled heating system

#1. Field of the Invention

#The present invention pertains to a heated glass system and insulating glass units, and more particularly, to a sheet of low emissivity glass with a resistive coating which is connected to a power source. A capacitor is coupled to the resistive coating to increase the impedance and control the power dissipated by the coated glass. When used in an insulating glass unit for commercial freezer and refrigeration doors, the heated glass prevents condensation from forming on the doors.

#2. Summary of Related Art

#The above, as well as 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 in the light of the accompanying drawings in which:

#FIG. 1 is a circuit diagram of the heated glass system of the present invention;

#FIG. 2 is a circuit diagram of a heated glass system with two capacitors and a four position switch;

#Referring now to FIG. 1, the heated glass system 10 of the present invention is shown in schematic form. A sheet of glass 12 is coated with a microscopically thin coating of a transparent, conductive material 14. The coating material 14 may be tin oxide, indium tin oxide, zinc oxide, or other similar coating. The coating may be fabricated in a production line using a pyrolytic process, such as atmospheric chemical vapor deposition, or some 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 approximately 0.84 to less than 0.50. The preferred range for the hemispheric emissivity is 0.15 to 0.43 for pyrolytic low emissivity glass. Other processes can be used to provide a low emissivity glass with hemispheric emissivity as low 0.01. The sheet resistance of such a conductive coating for low emissivity glass is typically less than 20 ohms per square. The low emissivity glass can be produced cost effectively on a high volume production line and provides improved thermal properties.

#However, the low sheet resistance prevents direct connection of the low emissivity glass 12 to the power source 16. The power source 16 is a single phase supply and in the U.S. is rated at 60 hertz and 115 volts. At a sheet resistance of 11 ohms per square, for example, a direct coupling to a 2.times.6 door connected for maximum resistance of 33 ohms provides 400 watts of power or 33.3 watts per square foot. Such power dissipation density is too high for freezer and refrigerator door applications.