Stock material or miscellaneous articles – Sheet including cover or casing – Including elements cooperating to form cells
Reexamination Certificate
2002-07-19
2004-03-02
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
Sheet including cover or casing
Including elements cooperating to form cells
C428S116000, C428S034000, C428S119000, C428S220000, C428S402000, C428S403000, C428S426000, C428S446000, C428S689000, C428S702000, C428S913000, C359S350000, C359S359000, C359S591000, C359S596000, C359S614000, C427S162000, C427S164000, C427S165000, C427S209000, C427S221000, C427S230000, C264S176100, C264S177120
Reexamination Certificate
active
06699559
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the field of glazings and glazing systems, including windows, skylights, atriums, and greenhouses. More specifically, it relates to honeycomb transparent insulation materials that are used as components in glazing systems.
BACKGROUND OF THE INVENTION
Honeycomb transparent insulation was first developed in the early 1960's in order to enhance the insulation value of glazed systems, with minimum loss of light transmittance. Honeycomb transparent insulations are transparent-walled honeycombs, with open-ended cells whose axes are oriented parallel to the normal vector of the plane of the glazing. Honeycomb transparent insulation materials achieve high light transmittance because the cell walls are perpendicular to the plane of the glazing, and thus, any light that reflects from the cell wall continues in the forward direction. Thus these materials avoid the reflection-loss penalty that is incurred when extra glazings are inserted in the standard plane-parallel orientation.
Honeycomb transparent insulation materials provide insulation value by suppressing both convection and radiant heat. Honeycomb transparent insulation materials are typically made from transparent plastics such as acrylic, polycarbonate, or polypropylene. They are manufactured by a number of different techniques, including capillary bundling, extrusion, and film-fabrication. Their properties (such as light transmittance, insulation value, rigidity, weight, etc.) strongly depend on how they were manufactured. Examples of honeycomb transparent insulations are InsolCore®, a film-based transparent insulation made by Advanced Glazings Ltd., Nova Scotia, Canada, Kapillux®, a capillary-bundled transparent insulation made by Okalux Kapillarglas Gmbh. of Marktheidenfeld-Alffeld, Germany, and AREL®, an extruded transparent insulation made by Arel Energy Ltd., Yavne, Israel. The mechanisms by which heat transfers through honeycomb transparent insulation materials are well understood. They are well-described in the technical literature (“Coupled Radiative and conductive heat transfer across honeycomb panels and through single cells”, K. G. T. Hollands et al., Int. J. Heat Mass Transfer v.27, n.11 pp. 2119-2131, 1984, “An approximate equation for predicting the solar transmittance of transparent honeycombs”, K. G. T. Hollands, K. N. Marshall, and R. K. Wedel, Solar Energy, v.21 pp. 231-236, 1978). Like many other thermal insulators, honeycomb transparent insulations work by dividing an air gap into spaces that are too small to support free convection. It has been found, both experimentally and theoretically, that honeycomb cells with a hydraulic diameter on the order of 1 cm are sufficiently small to suppress free convection. (“Dimensional relations for free convective heat transfer in flat-plate collectors”, K. G. T. Hollands, Proceeding of the 1978 Annual Meeting, ASES/ISES, Denver, Colo., vol. 2.1 pp 207-213, 1978). Thus an appropriately-designed honeycomb transparent insulation material does a thorough job of creating a dead air layer. Using smaller cells provides little improvement in suppressing the non-radiative portion of heat transfer, but does increase the amount of material required to manufacture that honeycomb transparent insulation.
To achieve maximum insulation value, a material must suppress radiative heat transfer in addition to conduction. The rate of radiant heat transfer through a honeycomb transparent insulation depends on the thermal-radiative emissivity of the boundary (i.e. the sheet(s) of glass or plastic adjacent to the honeycomb), the thermal-radiative emissivity of the cell wall, and the aspect ratio of the cell (defined as the ratio of the cell's hydraulic diameter to its length) .
Boundary emissivity is generally a function of the glazing system in which a transparent insulation is used, and not a function of the transparent insulation material itself. Thus, for the sake of simplicity, the scope of background discussion will be limited to systems with high-emissivity boundaries, on the order of 0.9, such as are common for surfaces of glazing materials such glass or sheet plastics of thickness 0.030 or more. However the present invention can be used in glazing systems with other boundary emissivities.
To improve the radiant suppression (and therefore improve the insulation value) of a typical honeycomb transparent insulation made with plastic walls which are partially transparent to thermal radiation, it is necessary to do one of the following: (1) increase the aspect ration of the honeycomb; or (2) increase the emissivity of the cell walls. To accomplish option (1), it is necessary to either use a smaller cell diameter or a larger cell length (i.e. overall honeycomb thickness). But both of these modifications mean extra material usage and cost—material content increases with the inverse square of the cell diameter, and in proportion to the honeycomb thickness. Also, practical limitations may discourage greater thickness: for example, finished glazing units made of such insulation sandwiched between glass may be too thick to work with existing framing systems. Thus, Option (2), increasing wall emissivity, is attractive, and forms the basis for the present invention.
For materials and geometries typically found in honeycomb transparent insulations, cell-wall emissivity is a function of wall thickness and the type of material from which the wall is constructed. Present honeycomb transparent insulation materials are almost exclusively made from plastics such as polypropylene, acrylic, and polycarbonate, with typical wall thicknesses of 0.001″ to 0.005″, and have non-optimal wall emissivities (typically 0.15 to 0.40). As a result, present honeycombs have non-optimal ratio of performance to material content. This situation could be remedied by simply increasing wall thicknesses, but this is undesirable because the material content increases, raising the cost and weight.
Thus it is highly desirable to use a material that is inherently a strong absorber of thermal-infrared radiation. Inorganic materials such as glass or silica are highly-attractive materials for making transparent honeycombs, having excellent clarity and high emissivity for small thicknesses (a layer of glass thickness of 0.0003″ has an emissivity of about 0.85). However, such materials are inherently difficult to work with in typical honeycomb geometries, and this has prevented the development of optimal glass honeycombs. Plastics, despite their imperfect radiative properties, are much easier to work with, and thus are the material of choice for today's commercial honeycomb transparent insulation.
Composite materials made with finely-divided inorganic fillers in plastic resins are commonplace in today's material technologies. Glass-filled thermoplastic resins are readily available to plastic processors, where typically the glass has been added to alter the elastic modulus or other physical properties of the plastic. Diatomaceous earth and calcium carbonate are regularly added to plastic resins when processing into plastic film in order to provide anti-block properties.
The addition of finely-divided inorganic fillers to plastic to create plastic film with enhanced infrared absorption is known. An example is ‘infrared-blocked’ polyethylene film for covering greenhouses, such as ‘Duratherm’ (AT Plastics, Toronto, Canada). A number of additive concentrates are readily available for creating such films. An example is Ampacet additive concentrate Product 10021 B-U (Ampacet Corp, Tarrytown, N.Y.) which contains a high percentage of Kaolin, a fine white silicate clay that does not absorb visible light but effectively absorbs infrared radiation, in a linear low-density polyethylene/ethylene vinyl acetate carrier. The presence of Kaolin typically interferes with the passage of visible light by increasing scattering (i.e. haze). Any haze in the wall of a honeycomb transparent insulation material will reduce the light transmittance via backscattering, and this
(Marks & Clerk)
Advanced Glazings Ltd.
Boss Wendy
Jones Deborah
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