Thermally Insulating Structure

FIG. 1 is an end oblique view of a window made according to the invention.

FIG. 2 is a graph of heat transfer versus pressure for a gas.

FIGS. 3A and 3B are partial end oblique views of alternative embodiments of the window of FIG. 1.

FIG. 4A-4E illustrate five different cross-sectional shapes for edge seals.

FIG. 5 shows a further configuration for edge seals.

FIG. 6 is a partial end oblique view of a metal panel as an alternate embodiment of the window of FIG. 1.

Referring now to FIG. 1, an insulating window 2 is shown to include first and second panes of glass 4, 6 separated by spacers 8 and sealed along their edges 10, 12 by edge seals 14. Glass planes 4, 6 will preferably have at least one low emissivity coating on at least one of their surfaces. Edge seals 14 and first and second panes 4, 6 define a main insulating region 16 therein. Edge seals 14 in the preferred embodiment are made from edge spacers 18 of a low thermal conductivity material to help reduce conduction losses between first and second panes of glass 4, 6 along the edge seals, although edge spacers 18 could alternatively be made of more common, higher conductivity materials such as metal or glass. Likewise, spacers 8 are also preferably made from a low thermal conductivity material and it can also be configured with narrowed portions to restrict thermal conductivity.

When edge spacers 18 are made of a gas permeable material, such as many plastics, edge spacers 18 are covered on at least one of their surfaces 20 with a low permeability film, such as aluminum, to help prevent migration of gases. The regions between panes 4, 6 and external of surfaces 20 are filled with a protective material 21, such as silicone, polysulfide or polyisobutylene. Such materials provide a protective, water-resistant coating for the adjacent vacuum seals, and also contribute mechanical strength in maintaining the proper positioning of glass panes 4, 6. Adhesion between edge spacers 18 and panes of glass 4, 6 is by layers of sealant 22. Sealant 22 is preferably a low vapor pressure, low gas permeability adhesive, such as Torr Seal brand epoxy sealant of Varian Associates, Inc., Vacuum Products Division, of Palo Alto, Calif. Since glass panes 4, 6 exhibit low (substantially no) gas permeability, window 2 defines an enclosure having low gas permeability.

Insulating region 16 is filled with a gas at a pressure at which convective heat losses are substantially eliminated. As shown in FIG. 2, in which the heat transfer rate between two surfaces is plotted against gas pressure, an initial portion 24 of plot 26, called the convection range, shows a decreasing energy loss with the reduction in gas pressure. The intermediate portion 28 of plot 26, called the conduction range, is almost flat. That is, in conduction range 28 the energy loss between the surfaces remains about constant as the gas pressure is reduced. The final portion 30 of plot 26, called the Piriani range, illustrates the reduction in energy loss with the further reduction in gas pressure caused by the reduction in the conduction component of heat transfer.

Radiation heat transfer can be reduced by the use of a low emissivity film 27 on the inner surface of pane 6. Film 27 could also be placed on the inner or outer surfaces of panes 4, 6 or suspended between the panes.

The present invention contemplates the provision of a low thermal conductivity gas within main insulating region 16 at a moderately low pressure, that is in a conduction range 28, so that the convective components of heat transfer have been substantially eliminated while the conductive components have not. The actual shape of curve 26 will depend upon the kind or composition of the gas (which includes vapors) used and the window pane spacing. For example, conduction range 28 may start at about 100-200 torr for a particular gas at a one-inch spacing but could be as high as 400 torr for a one-half inch spacing. By using a one-inch thick insulating region 16 and minimizing radiation heat transfer between panes of glass 4, 6 and conduction heat transfer along spacers 8 and edge seals 14, it is expected that window 2, using trichlorofluoromethane as the low thermal conductivity gas at a pressure of about 100 torr, would have an R-value of about 15. This would be a great improvement over even the best of commercially available windows.

The invention has generally been described in terms of a flat, dual glazed window having a one-inch spacing. Of course other spacings can be used, and, as shown in FIG. 5, curved glass panes can be used also.

An L-shaped evacuation tube 31, typically made of copper, is used to evacuate air from region 16 and fill it with a low thermal conductivity gas under moderate vacuum. One leg 32 passes through a sealed opening in edge spacer 18 while the other leg 33 lies near surface 20 and between panes 4,6. After the vacuum is achieved, leg 33 is mechanically sealed shut at its outer end. (The region surrounding tube 31 may be cleared of material 21 to permit later access to tube 31.)

In time, or due to a defective seal, interior 16 may rise in pressure sufficiently to make a substantial reduction in the thermal efficiency of window 2. If it is desired to reevacuate and re-fill region 16, the sealed end of leg 33 can be opened by simply snipping it off. Other, typically more elaborate, methods for re-evacuating and refilling region 16 can also be used.

Referring now to FIG. 3A, an alternative embodiment of window 2 is shown with like elements having like reference numerals. Window 34 includes an edge seal 36. Edge seal 36 includes inner and outer spacers 38 and 40 constructed similarly as are edge spacers 18. Edge seal 36 creates a buffer region 44 between edge spacers 38 and 40. Buffer region 44 is preferably filled with the same low conductivity gas as in main insulating region 16. However, other low conductivity gases, or air under vacuum, could also be used in buffer region 44, as described more fully below. Also, evacuation tubes 31 could be used for the initial and supplemental evacuation and filling of region 44 as well as region 16, though said evacuation tubes are not illustrated for the sake of clarity.

Similarly, FIG. 3B shows an alternative embodiment of window 2 with a dual buffer edge seal 36. Edge seal 36 includes inner, intermediate and outer spacers 38, 40, 42 constructed similarly to edge seal 18. Edge seal 36 creates an inner buffer region 44 between edge spacers 38 and 40 and an outer buffer region 46 between edge spacers 40, 42. Buffer regions 44, 46 are preferably filled with the same low conductivity gas as in main insulating region 16. However, other low conductivity gases, or air under vacuum, could also be used in buffer regions 44, 46, as described more fully below. Also, evacuation tubes 31 could be used for the initial and supplemental evacuation and filling of regions 44, 46 as well as region 16, though said evacuation tubes are not illustrated for the sake of clarity.

Regions 44 and 46 can be placed at the same low pressure as region 16. Doing so should dramatically decrease the rate at which ambient air enters main insulating region 16 thus helping to keep main insulating region free from air, with its higher thermal conductivity, and help to keep the pressure low. Alternatively, one or both of buffer regions 44, 46 can be placed at a pressure higher than the low pressure within region 16 to reduce the pressure differential between the ambient air and the particular buffer region. Increasing the pressure within a buffer region 44 or 46 would also help to dilute any air which may enter the buffer region so that less air would enter into main insulating region 16. For example, one may wish to place inner buffer region 44 at the same low pressure as main insulating region 16, so to eliminate the tendency of gas within either region to enter into the other, and place outer buffer region 46 at the same pressure as the ambient atmosphere. This would substantially eliminate the tendency for the ambient atmosphere and the gas in outer buffer region 46 to mix because of the similarity of pressures. The main pressure differential would be across intermediate sealing panel 40. However, migration of gas from region 46 to region 44 would be migration primarily of the low conductivity gas so to help keep inner buffer region 44 and thus main insulating region 16 free from higher conductivity air.

Buffer regions 44 and 46 can also contain air under vacuum as a means of reducing contamination of the main insulating region 16 with high thermal conductivity atmospheric gases. Edge seals 36 can also comprise a mixture of low conductivity gases and air under vacuum in their design. For instance, buffer region 44 could contain a low conductivity gas while region 46 could contain air under vacuum. Of course, multiple buffer seal designs containing three or more regions can be constructed in a similar manner to the seals depicted in FIGS. 3A and 3B; such seal designs could contain many possible combinations of low conductivity gases at various pressures, as well as air under vacuum.

Edge spacers 18 may have configurations other than the flat one shown in FIGS. 1, 3A and 3B. FIGS. 4A-4E illustrate various cross-sectional shapes for spacers 18a-18e. An advantage of spacers 18a, 18b and 18d is that they each provide extended surfaces 48a, 48b and 48d facing the interior surfaces of panes 4, 6 so to provide a longer migration path for air migration.

The effectiveness of the invention depends in large part upon the effectiveness of the edge seals. Although existing sealants are satisfactory, improvements in the area could provide substantial benefits. For example, and referring to FIG. 5 an edge seal 50 is shown to include a generally I-beam shaped spacer 52 having a central protrusion 54 extending between panes 4, 6. This arrangement creates an extended, U-shaped migration path 56 and also uses atmospheric pressure to force spacer 52 against the edges 10, 12 of panes 4,6. Both of these aspects help to increase the sealing effectiveness of seal 50. Edge seal 18d provides similar benefits as edge seal 50. Note that the sealant applied between spacers 18a-18e and 52 and panes 4, 6 has not been shown in FIGS. 4A-4E and FIG. 5 for sake of clarity.

The invention can be used with transparent silica aerogels which incorporate a low thermal conductivity gas at conduction range pressures. (Aerogels are a bonded network of tiny silica spheres which create a rigid material which is transparent and which traps gases in pores smaller than the mean free path of the gases. See Solar Energy Materials 7 (1983) North-Holland Publishing Company at pp 393-400.) Since the aerogels can contain up to 97% gas by volume, such a structure may be able to combine the advantages inherent with the present invention and the advantages inherent with aerogels.

The present invention can be used much as the conventional window it replaces. Insulating windows 2, 34 can be used in place of conventional dual pane windows. The insulating value will be determined at least partially by the distance between panes 4, 6 so that modification may need to be made if conventional window frames are to be used to accommodate the thicknesses of window 2 which, for increased insulation, would typically be thicker than conventional double pane windows.

Referring now to FIG. 6, an insulating panel 60 is shown to include first and second panels 61, 62 separated by spacers 63 and sealed along their edges 64, 65 by edge seals 66. Panels 61, 62 are preferably made of a metal such as sheet steel, but may alternatively be made of metal/plastic laminates, plastic or ceramic. Edge seals 66 and first and second panels 61, 62 define a main insulating region 67 therein. Edge seals 66 in the preferred embodiment are made from edge spacers 68 of a low gas permeability, low thermal conductivity material to help reduce conduction losses between first and second panels 61, 62 along the edge seals. Edge spacers 68 could alternatively be made of more common, higher conductivity materials such as stainless steel or glass. The regions between panels 61, 62 and external to spacer 68 are filled with a protective material 69, such as epoxy, silicone, or polysulfide. Adhesion between edge spacers 68 and panels 61, 62 is by layers of sealant 70. Sealant 70 is preferably a low vapor pressure, low gas permeability adhesive, such as Torr-Seal brand epoxy. Alternatively, sealant 70 may be a welded or brazed metal seal if panels 61, 62 are metal, resulting in even lower rates of gas permeation into main insulating region 67. Buffer regions as in FIGS. 3A and 3B can similarly be incorporated into the design of panel 60.

Radiation heat transfer is reduced by the use of low emissivity films 71 such as thin reflective metal foils of aluminum, thermally separated by poor conducting glass fiber paper 72 such as 475 Tempstran 110 manufactured by Manville Corp. of Denver, Colo. Only two such films 71 are shown for sake of clarity, although multiple films are advantageous. Alternatively, low emissivity films 71 and glass fiber separator 72 can be replaced by using polyester film which has been aluminized. Since radiative heat transfer is a function of the number of low emissivity film, but not of their spacing, films 71 may be placed anywhere within main insulating region 67. A particular advantage of placing films 71 within the main insulating region 67, as opposed to adjacent to panel 62 as shown, is that convection currents of the insulating gas or vapor are reduced.

Other modifications and variations can be made to the disclosed embodiments without departing from the subject of the invention as defined in the following claims. For example, desiccants to absorb water (to maintain thermal insulation properties) can be used in spaces 16, such as adjacent edge seals 14, or incorporated in the spacers.