Patent Application
20100139195
This invention generally relates to an insulating spacer and in particular to an insulating spacer for creating a thermally insulating bridge between spaced-apart panes in a multiple glass panel window unit, for example, to improve the thermal insulation performance of the unit. This invention also relates to methods of making such an insulating spacer.
An important consideration in the construction of buildings is energy conservation. In view of the extensive use of glass in modern construction, a particular problem is heat loss through glass surfaces and glazed building envelopes. One solution to this problem has been an increased use of insulating glass units comprising basically two or more glass panels separated by a sealed dry air space. Sealed insulating glass units generally require some means of mechanically separating the glass panels by a precise distance, such as by rigid spacers.
The spacers historically used are rectangular channels made of steel, aluminum or some other metal, with an internal desiccant to adsorb moisture from the space between the glass panels and to keep the encapsulated sealed air space dry. Tubular spacers are commonly roll-formed into the desired cross sectional shape. Steel spacers are generally considered the cheapest and strongest option, but aluminum spacers are easier to cut and form into non standard window shapes such as semicircles. Aluminum also provides lightweight structural integrity, but it is more expensive than steel. Metal spacers are manufactured by PPG of Pittsburgh, Pa. Spacers made entirely of plastic or from a combination of metal and plastic, termed warm edge spacers, have also been used to a limited extent. Manufacturers of these types of spacers include EdgeTech I.G., Inc. of Cambridge, Ohio and Swisspacer of Kreuzlingen, Switzerland.
There are specific factors that influence the suitability of the spacer material or design for use in high performance windows. Of most importance are the spacer's heat conducting properties and the spacer material's coefficient of thermal expansion. To date, metal has been the most widely used spacer material even though as a material it has a number of disadvantages in both of these areas. First, the thermal conductivity of metal is unacceptably high for use as a spacer. Since a metal spacer is a much better conductor of heat than is the glass or the air space between the panes of glass, its use leads to the rapid transfer of heat between the inside glass pane and the outside glass pane resulting in heat dissipation, energy loss, moisture condensation and other window assembly performance shortcomings. For example, in a sealed insulated glass unit, heat from within a building tries to escape in winter, and it takes the path of least resistance. The path of least resistance is around the perimeter of a sealed window unit, where the metal spacer bar is located. Metal spacers contacting the inner and outer panes of glass act as conductors between the panes and provide an easy path for the transmission of heat from the inside glass panel to the outside panel. As a result, under low temperature conditions in winter, condensation of moisture can occur inside the insulating glass or on the surfaces of the inner glass panel. Also, heat is rapidly lost from around the perimeter of the window, often causing a ten to twenty degree Fahrenheit temperature drop at the perimeter of the window relative to the center thereof. Under extreme conditions in winter, a frost line can occur around the perimeter of the window unit. These conditions undermine the energy efficiency of the window, and ultimately, the energy efficiency of the building itself.
A second important feature of the spacer material is its coefficient of thermal expansion. The coefficient of expansion of commonly used spacer materials is much higher than that of glass. Any difference in thermal expansion causes problems in the form of glass stress, seal shear and failure, or spacer damage. For example, the coefficient of linear thermal expansion for steel is twice that of glass (17.3×10−6 inches per degrees K. versus 8.5×10−6 inches per degrees K.). This difference is particularly critical in climates that have large changes in temperature. As a result of such changes in temperature, stresses do develop at the interface between the glass and spacer bar and in the perimeter seal. This often results in damage to and failure of the sealed insulating glass unit, such as by sufficient lengthwise shrinkage of the spacer to cause it to pull away from the sealant and therefore cause premature failure of the insulating glass unit. Many window units tend to fail due to such stress cracks or loss of seal resulting in water vapor condensation which is deposited inside the panes and observed as window fogging. Such a condition results in a warranty callback and a window replacement.
Although the issue of thermal expansion is important to window durability, the most common spacer material commercially used in the manufacture of such insulated glass units has been metal due to cost and a lack of viable alternate materials.
U.S. Pat. Nos. 4,222,213 and 5,485,709 disclose additional composite spacers. Both patents disclose a thin plastic insulation which is in contact with one glass surface and thereafter fitted by contact pressure or friction over a portion of a conventional extruded or roll-formed metal spacer or plastic/metal composite. The plastic insulating overlay can be formed over a conventional extruded metal spacer and from an extrudable thermoplastic resin. However, the force fit and the bi-material construction of such a spacer can result in separation of the two components with changes in temperature due to the different thermal expansion coefficients of the metal and the plastic and again allow for substantial thermal bridging across the structure. These features are undesirable.
Descriptions of additional composite window unit spacer designs can also be found in U.S. Pat. Nos. 6,035,602, 6,581,341, 6,989,188, 6,136,446 and 7,270,859.
Accordingly, what is needed is an insulating spacer which creates a thermally insulating bridge between spaced-apart panes in a multiple pane, insulated glass unit which overcomes the above-noted drawbacks.
It is an object of the present invention to provide an improved thermally insulating spacer for a multiple pane, insulated glass unit which solves or overcomes the drawbacks noted above with respect to conventional spacers.
It is another object of this invention to create a thermally insulating bridge to reduce heat transfer from one pane of the window (glass or polyester film) to another through the insulating spacer of the present invention. This invention thus keeps the inner pane of material (glass or polyester film) several degrees warmer than it might otherwise be in the winter, while preventing condensation that otherwise may occur. This invention also improves the thermal efficiency of the window unit.
It is another object of the present invention to provide an insulating spacer with a coefficient of expansion approximately equal to that of glass.
It is another object of the present invention to provide an improved composite insulating spacer which has the features necessary for a spacer relating to water vapor transmission, gas permeability, ultraviolet light resistance, dust containment, desiccant containment and ease of handling as well as the ability to be manufactured to precise dimensional tolerances.
It is still another object of the present invention to improve the speed and yield of high performance window fabrication by providing a spacer that is easily handled, cut to precise lengths, and placed onto its host materials.
The present invention provides an insulating spacer for spacing apart panes of a multiple pane window unit, for example, and for defining an insulated space between the panes. The insulating spacer comprises an assembly of selected materials that encapsulate an aerogel composite core, specifically a fiber reinforced aerogel (FRA). The spacer may consist entirely of an FRA and a resin or hot melt adhesive hardener, an FRA core, a structural stiffener and a UV resistant wrap, such as shrink tubing, woven or polymer wrap, or some combination of these materials.
Fiber reinforced aerogels (FRA) have the lowest thermal conductivity value of any material currently used in building construction. They have thermal conductivities of 12 to 18 mW/m-K, where “mW” is milliwatts, “m” represents meter, and K is degrees Kelvin. By comparison, metals such as copper, aluminum, and stainless steel have much higher thermal conductivities of 36,000 mW/m-K, 20,400 mW/m-K, and 12,000 mW/m-K, respectively. Even closed cell foams designed for thermal insulation such as expanded polystyrene and polyisocyanurate have thermal conductivities of 32 and 24 mW/m-K, respectively. In addition to their low thermal conductivity, FRAs exhibit good moisture and water vapor resistance. The FRA is hydrophobic with excellent resistance to moisture. The material's series of nanopores embedded into a fibrous matrix form a tortuous gas-resistive network that resists vapor penetration, condensation and ice crystallization. FRAs also exhibit good dimensional stability and structural integrity over a broad range of temperatures. Typically available FRAs have a range of service temperatures over 200 degrees C., which is greater than that required for the building envelope. Across the service temperature, the FRA remains flexible and is not subject to contraction, thermal shock or degradation from thermal cycling as are foams. Last, FRAs have a coefficient of thermal expansion similar to that of glass. The result is that once these materials are bonded together there are no additional stresses due to temperature change. Therefore, the present invention improves the thermal performance of the insulated glass units along the edge of the assembly where unwanted heat transfer is a particular problem.
The construction of such fiber reinforced aerogel materials suitable for construction applications is disclosed in U.S. Pat. No. 6,068,882, by Jaesoek Ryu. This patent is hereby incorporated by reference herein in its entirety, and will be referred to as “Ryu”. Described in general process steps, the fiber reinforced aerogel (FRA) is prepared by impregnating a fibrous matrix with an aerogel precursor solution so that a liquid phase is placed around every fiber and then, without aging of the precursor solution to form a gel, supercritically drying the impregnated matrix under conditions such that substantially no fiber—fiber contacts are present. The fibrous matrix consists of a nonwoven felt or blanket. The fibers are generally oriented in a parallel fashion. Fibers often consist of PET or a PET and fiberglass blend with a diameter of 100 microns or less, preferably with diameters between 5 and 20 microns (see Ryu, 5: 15-65, and Table I for further examples). Commercially available examples of suitable fiber matrix materials include Q-fiber by Johns Manville, Inc. Of Denver, Colo., Nicalon by Dow Corning of Midland, Mich., and Duraback by Carborundum of Niagara Falls, N.Y. Supercritical drying is achieved by heating the autoclave to temperatures above the critical point of the solvent under pressure, e.g. 260° C. and more than 1,000 psi for ethanol, generally in the range of 1 to 4 hours (see Ryu, 10: 16-17). The resulting composite insulation contains aerogels distributed substantially uniformly throughout the fibrous matrix. This general process is discussed in detail below.
To fully obtain the benefit of the composite configuration, each fiber within the fibrous matrix is completely surrounded by aerogels such that all fiber to fiber direct contact is avoided. The substantial absence of fiber to fiber contacts is accomplished by a combination of (1) selection of compatible fibrous matrices and aerogels, (2) impregnation of the fibrous matrix with an aerogel sol so that the liquid phase surrounds every fiber, and (3) controlled aerogel processing procedures. Products utilizing this technology are commercially available from Aspen Aerogels of Northborough, Mass. in the manufacture of their Spaceloft, Cryogel, and Pyrogel products.
In the process of the FRA manufacture, the principal synthetic route for the formation of aerogels is the hydrolysis and condensation of an alkoxide. Major variables in the aerogel formation process are the type of alkoxide, solution pH, and alkoxide/alcohol/water ratio. Control of these variables permits control of the growth and aggregation of the aerogel species throughout the transition from the “sol” state to the “gel” state during drying at supercritical conditions. For low temperature applications, the preferred aerogels are prepared from silica, magnesia, and mixtures thereof (Ryu, 6: 1-17).
After formation of the alkoxide-alcohol solution, water is added to cause hydrolysis so a metal hydroxide in a “sol” state is present. Techniques for preparing such aerogel “sol” solutions are well known in the art. (See, for example, S. J. Teichner et al., “Inorganic Oxide Aerogel,” Advances in Colloid and Interface Science, Vol. 5, 1976, pp 245-273, and L. D. LeMay, et al., “Low-Density Microcellular Materials,” MRS Bulletin, Vol. 15, 1990, p 19).
Next, the fibrous matrix may be placed in an autoclave, the aerogel-forming components (metal alkoxide, water and solvent) added thereto, and the supercritical drying then immediately commenced. Supercritical drying is achieved by heating the autoclave to temperatures above the critical point of the solvent under pressure, e.g. 260° C. and more than 1,000 psi for ethanol.
Following a dwell period (commonly about 1-2 hours), the autoclave is depressurized to the atmosphere in a controlled manner, generally at a rate of about 5 to 50, preferably about 10 to 25, psi/min. Due to this controlled depressurization there is no meniscus in the supercritical liquid and no damaging capillary forces are present during the drying or retreating of the liquid phase. As a result, the solvent (liquid phase) (alcohol) is extracted (dried) from the pores without collapsing the fine pore structure of the aerogels, thereby leading to the enhanced thermal performance characteristics.
A commercially available fiber reinforced aerogel product is Spaceloft, manufactured by Aspen Aerogels of Northborough, Mass. To date, fiber reinforced aerogels have been used as interlayers over stud framing in walls, thermal clothing, and cladding for pipes and ducts. In U.S. patent application Ser. No. 12/124,609 filed May 21, 2008 (attorney docket M-17193) and assigned to the same assignee as the assignee of this invention, Tinianov discloses a fibrous aerogel assembly for use as a spacer in window insulated glass units, but does not address the dust mitigation, water vapor management, low heat transfer, and manufacturing issues as treated in the present invention. patent application Ser. No. 12/124,609 is hereby incorporated by reference in its entirety.
As will be appreciated by those skilled in the art, in addition to the multiple glass or polyester film (or more specifically biaxially-oriented polyethylene terephthalate (PET), commonly referred to as Mylar or Melinex) panes and the aerogel spacer, the complete insulating glass unit assembly may employ polyisobutylene (PIB), butyl, hot melt, or any other suitable sealant or butylated material as a sealant and adhesive to bond the perimeter of the insulated glass unit. Sealing or other adhesion for the insulating spacer is necessary both to ensure the structural integrity of the window unit, but also to act as a gas and water vapor barrier isolating the ambient atmosphere from the atmosphere within the insulated glass unit for the service life of the window. These sealing needs may be achieved by providing special adhesives, e.g., acrylic adhesives, pressure sensitive adhesives, or hot melt adhesive. Multiple sealant layers may be used. By providing at least two different sealing materials as is described below, the result is that discrete and separate sealing surfaces are in place to protect the spacer. This is useful in the event that one seal is compromised. The sealant materials may be embedded within one another.
In addition to the flexible, thermally insulating spacer, the assembly may include an additional vapor barrier about the rear face of the insulated glass unit. Regarding the vapor barrier, it may be a plastic film or tape, a metallized film or tape, metal tape or other material well known to those skilled in the art.
A better understanding of these and other advantages of the present invention, as well as objects attained for its use, may be had by reference to the drawings and to the accompanying descriptive matter, in which there are illustrated and described preferred embodiments of the invention.
a to 2h show in cross-section alternate embodiments of encapsulated insulating spacers of the type shown in
Throughout the views, like or similar reference numerals have been used for like or corresponding parts.
A second physical attribute of the layer system consisting of materials 112 and 114 is that of dust and desiccant containment. The fiber reinforced aerogel 110 is a composite impregnated with many small particles of about 1 to 400 mm. Whenever the core is flexed or otherwise disturbed, it will shed these particles in the form of a fine dust. Dust migrating to the viewable area of a window is unacceptable. In addition to dust from the aerogel core 110, materials 112 and 114 must also encapsulate the window desiccant. This can either be accomplished as an external wrap around a desiccant material or as a hot melt adhesive with desiccant incorporated into the glue itself. Desiccant comes in two forms for window use, either as small spherical pellets of approximately 1-5 mm diameter or as a powder. These desiccant materials are available from Delta Adsorbents of Roselle, Ill.
A third requirement is that the material layers 112 and 114 add rigidity to the core 110 to ease handling and to provide the ability to manufacture the composite insulating spacer to precise dimensional tolerances. Without sufficient rigidity, the panes may have imprecise spacing relative to each other which may impact the thermal performance and visual appeal of the insulated glass unit. In the embodiment illustrated in
A final requirement of the material layer 114 is that of ultraviolet (UV) light resistance. In this case, the attribute of UV resistance signifies that the material will not crack or disintegrate, thereby allowing particles to shed into the viewable window area, over the twenty year life of the window.
The layers 112 and 114 may be permanently applied such as by direct adhesion to the four surfaces 102, 104, 106 and 108 using a commercially available adhesive such as Super 77 Spray manufactured by 3M of St. Paul, Minn. Alternately, the core 110 may be wrapped by a non-woven fabric which is welded to itself in a seam along the outer face 108 forming a sleeve. The thicknesses of layers 112 and 114 may be varied between about 2 to 50 mm to best suit the thermal, structural, and product cost needs of the assembly.
In one embodiment, layers 114 as shown in
a through 2h show in cross-section further embodiments of the spacer 100 as illustrated in
One embodiment of the invention consists of a spacer as shown in
As stated above, the U-factor is a measure of a system or assembly's thermal transmission or the rate of heat transfer through the system. Therefore, the lower the U-factor, the lower the amount of heat loss, and the better a product is, at insulating a building. In the present application, the U-factor is measured in units of Btu/(hrFt2° F.) (British thermal unit per hour, per square feet, per degree Fahrenheit), where 1 Btu/(hrFt2° F.)=5.666 W/(m2 K) (Watts per meter squared, per degree Kelvin). Conversely, R-value is a measure of thermal resistance, and is the reciprocal of the above mentioned U-factor, i.e. R-value=1/U-factor. The units of the R-values reported in this application are therefore, hrFt2° F./Btu (with “R-values” defined according to the insulation resistance test set forth by the American Society for Testing and Materials in the Annual Book of ASTM).
Other instances of the embodiment disclosed above have been modeled using THERM, to demonstrate further the improvement in the thermal performance of the system introduced by the present invention. The embodiment used for the testing is illustrated in
Table I corresponds to a window structure where the leftmost component 602 is a ⅛ inch thick “Cardinal 272 Low E” pane and the rightmost is ⅛ inch thick “clear glass”, a common window material sold by OldCastle Glass, Cardinal Glass and others. Components 604 were PET polyester film SC75 manufactured by Southwall Technologies of Palo Alto, Calif. The three voids 606 of the insulated glass unit 600 were filled with Krypton gas (90%), a typical thermal insulator. The window frame 612 used in this embodiment was a fiberglass frame (model 325, with a 1⅜ inch deep insulated glazing unit pocket depth) manufactured by Inline Fiberglass of Toronto, Ontario. A detailed description of Table I follows.
Case 1 corresponds to prior art, using the 6 mm steel tube spacers mentioned above. Case 2 corresponds to the embodiment of case 1, except with spacer 2 being replaced by the spacer embodied in
Table II corresponds to a window structure different from that of Table I in that only one of the components 604 is present, so only 3 panes and 2 spacers are involved. Also, the window frame in this case corresponds to model 325, 1″, from Inline Fiberglass, Toronto, Ontario. All other components and materials are the same as in the structure of Table I. Cases 6 through 10 were modeled with this configuration, with case 6 corresponding to prior art, and case 10 corresponding to the two steel spacers in the structure being replaced with aerogel spacers. A detailed description of Table II follows.
Case 6 corresponds to prior art, using the 6 mm steel tube spacers mentioned above. Case 7 corresponds to the embodiment of case 6, except with spacer 2 being replaced by the spacer in the embodiment of
Other embodiments of this invention will be obvious in view of the above descriptions.
