GB1577129A

GB1577129A - Insulating structures and a method of insulation

Info

Publication number: GB1577129A
Application number: GB49381/76A
Authority: GB
Original assignee: RAMA INT
Current assignee: RAMA INT
Priority date: 1975-12-02
Filing date: 1976-11-26
Publication date: 1980-10-22
Also published as: IT1072119B; AU2005776A; CH614482A5; BE848959A; NL7613370A; FR2333910A1; ES453842A1; DK540176A; BR7608037A; DE2654272A1; AU503094B2; JPS5276764A; NO764094L; SE7613471L; ES460453A1; FI763463A

Description

(54) IMPROVEMENTS IN OR RELATING TO INSULATING STRUCTURES AND A METHOD OF INSULATION (71) We, RAMU INTERNATIONAL, a Partnership organized under the Law of the State of Connecticut, United States of America of 75 Pheasant Drive, New Canaan, Connecticut, 60840, United States of America do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to insulating structures and to a method of insulation.

Conventional construction of dwellings, office buildings, schools, and other like buildings provides walls with a space between the inner and outer wall surfaces.

In order to achieve acceptable comfort levels in cold climates and for fuel economy this "dead air" space has been found to impart important insulating qualities. Windows are constructed in the same general way with double panes and an insulating "dead air" space between them.

Heat is lost through such a construction, however, when the construction is subject to a temperature gradient such as when heating a house in cold weather. Heat is lost by the three well known mechanisms of cenvection, conduction, and radiation. Of these the largest factor is convection in which process air circulates picking up heat from a warm surface and giving up heat to a cold surface. This convection heat loss has been conventionally greatly reduced by the use of lightweight nsulation materials placed in the air space between the inner and outer wall surfaces such as the use of fibre batts made from a variety of fibres.

While this insulation system greatly hinders the convective movement of air thus largely eliminating convection as a heat loss mechanism, heat loss by conduction is increased.

In windows the use of such insulating materials cannot be accomplished but it has been found that a minimum of convection takes place if the two panes of glass are positioned close enough together. For many years such thermo-insulating glass windows have been used in which two panes are sealed about their edges in a suitable frame in close proximity to each other sufficient to provide the requisite "dead air" space. The system is not perfect, however, and there is heat loss through such windows. With a modern trend towards more and larger windows, heat loss through windows has tended to dominate the heat losses from dwellings. The total heat loss from dwellings due to the windows as well as the heat loss per unit area of windows far exceed the losses through other parts of the walls when they are properly constructed.

An object of the present invention is to provide an improved form of insulating structure and an improved method of insulation.

According to the present invention there is provided a thermally insulating structure for insulating a first zone from a second zone and comprising a pair of elements for positioning between said first and second zones with the first element of said pair adjacent said first zone and the second element of said pair adjacent said second zone, said pair of elements being arranged in spaced apart relation to provide an interelement space, first passage means for permitting fluid flow from the first one into said inter-element space, second passage means for permitting fluid flow from the second zone into said inter-element space simultaneously with said fluid flow from said first zone into said inter-element space, and third passage means for permitting both of said flows from said inter-element space to pass to the first zone, the arrangement being such that, in use of the structure with a temperature differential existing between said first and second zones, first and second fluid flows pass from said first and second zones through said first and second passage means, respectively, into said inter-element space, and then from the inter-element space through said third passage means in contact with one another to said first zone, without any substantial mixing of said first and second flows over a substantial part of their passage through the inter-element space.

In a peferred aspect the invention provides a thermally insulating structure for insulating a first zone from a second zone and comprising a pair of elements for positioning between said first and second zones with the first element of said pair adjacent said first zone and the second element of said pair adjacent said second zone, said pair of elements being arranged in spaced apart relation to provide an inter-element space, first passage means for permitting fluid flow from the first zone into said interelement space, second passage means for permitting fluid flow from the second zone into said inter-element space simultaneously with said fluid flow from said first zone into said inter-element space, the arrangement being such that, in use of the structure with a temperature differential existing between said first and second zones, first and second fluid flows pass from said first and second zones through said first and second passage means, respectively, into said inter-element space and then pass through said inter-element space in contact with one another without any substantial mixing of said flows with one another, and third passage means for permitting passage of both of said first and second flows into said first zone after passage through said inter-element space.

According to a further aspect of the invention there is provided a method of thermally insulating a first zone from a second zone comprising providing a space between said zones, which space is separated from said zones, introducing a first fluid flow from said first zone into said space, introducing a second fluid flow from said second zone into said space, and passing both of said fluid flows in contact with one another into said first zone, said flows being simultaneously moved through said space in a laminar manner so that said first and second fluid flows pass through the major portion of said space without any substantial mixing of said fluid flows and without creating any substantial convection currents in said defined space.

The invention is particularly applicable to walls and windows in which two substantially parallel elements in the form of panels are arranged vertically between a first zone and a second zone and spaced apart to provide a space between the pallets. The panels may be glass in the case of windows, and in the case of walls they may be made from any number of a variety of construction materials such as gypsum board, wood or synthetic panelling and the like for the inner panel and a sheathing, siding, shingles or the like for the outer panel. The inner panel has one or more openings adjacent the top thereof and an additional opening or openings adjacent the bottom thereof.

The outer panel has an opening or openings adjacent the upper end only thereof if the invention is to be used only in the heating of the building. A wall means in the form of deflector is positioned in the interelement or inter-panel space adjacent the top opening(s) in the outer panel to deflect cold air entering the inter-panel space downwardly. The deflector also serves to prevent any mixing of the flows cold and warm air in the upper portion of the interpanel space.

Cold outside air enters the inter-panel space through the opening(s) near the top of the outer panel and flows downwardly along the inner surface of the panel. Warm air adjacent the ceiling area of the interior of the building enters inter-panel space through the upper opening in the inner panel and moves downwardly along the inner surface of the inner panel under the influence of the downwardly moving cold air. There is no substantial mixing of the warm and cold air as they move downwardly, but rather there is a laminar flow that keeps the warm and cold air substantially separate. At the bottom both the warm and cold air exit from the inter-panel space into the interior of the building through the lower opening(s) of the inner panel.

The flow of the warm air downwardly along the inner surface of the inner panel utilizes the heat in the warm air to maintain the inner panel warm. Similarly, the flow of cold air downwardly along the inside of the outer panel maintains that panel cooler and as such the warm air does not give up its heat to the outer panel and the colder outside environment. Also, because the warm air does not contract the cooler outer panel, there is no condensation produced on the inside of the outer panel as would be the case if a convection process were operating rather than the laminar flow that takes place with the invention. Savings in fuel are obtained since the excessively heated air adjacent the ceiling is used to warm the inner surface of the inner panel and a more even floor-to-ceiling temperature is achieved.

Embodiments of the invention will now be described by way of example, with reference to the accompanying drawings in which: Fig. 1 is a schematic cross-section view taken along the line 1-1 of Fig. 2; Fig. 2 is a vertical elevation, schematically showing a window embodying the invention as viewed from inside the building and with parts broken away; Fig. 3 is a cross-sectional view similar to Fig. 1 but showing a cross-section through a frame-type wall utilizing the invention; and Fig. 4 is a view similar to Fig. 3 but showing the invention as modified for use when the interior of the building is being cooled.

Referring to Figs. 1 and 2, an insulating structure comprises a double glass-paned window generally indicated by the reference numeral 10 has upper and lower frame members 12 and 14 respectively and side frame members 16 and 18. Mounted in spaced relationship within the frame members 12-18 are first and second window glass sheets 20 and 22 constituting first and second elements enclosing an inter-element space 42. An elastic sealing member 24 within each of frame members 16 and 18 embraces the lateral edges of the first glass sheet 20 and seal the same within the vertical frames 16 and 18. Within the lower frame 14 and the upper frame 12 there is no comparable sealing element. However, in order to support the first glass sheet 20 within the frame member 14 and to prevent movement between the frame member 14 and the first pane 20, there may be provided small spaced holding or spacer elements 26 between the bottom edge of the first sheet 20 and the frame 14. If desired similar spacing and securing and holding elements 28 may be provided at the top edge of the pane 20 within the top frame 12.

Within the side frames 16 and 18 and also within the bottom frame 14 is a sealing member 30 which embraces the lateral edges and the bottom edge of the second glass sheet 22. There is no sealing member for the glass sheet 22 within the upper frame 12 although spaced securing and holding members like members 26 and 2 8 may be provided for the upper edge of the second glass sheet 22 if desired. Between the first glass sheet 20 and the second glass sheet 22 is disposed a wall means in the form of a deflecting member 32 supported in any suitable way from the upper frame member 12.

For example, if the frames are of extruded aluminium, the deflector member 32 may be extruded integrally with the upper frame member 12 or any suitable material such as a sheet of acrylic or glass may be secured to a flange 31 extruded integrally with the upper frame member 12 or mounted by any other suitable means.

As best shown in Fig. 1, the construction provides a first opening 36 providing first passage means between the upper frame member 12 and the upper edge of the first glass sheet 20. Similarly, the construction just described provides for a third opening 38 providing third passage means between the lower frame member 14 and the lower edge of the first glass sheet 20. If no securing and holding elements 28 are provided, the first opening 36 will extend uninterrupted along the upper edge of the first sheet 20 (from left to right as shown in Fig. 2). If the securing and holding members 28 are utilized, they will be very small in comparison to the length of the upper edge of the first glass sheet 20 and will divide the first opening 36 into a plurality of openings. Similarly, the lower holding and supporting elements 26, if used, are small and divide the lower second opening 38 into a plurality of openings. It will be appreciated that if the sealing member 24 in the side frames 16 and 18 has sufficient frictional engagement with the interior of the frames 16 and 18 as well as with the lateral edges of the first glass sheet 20, then, in that event, the supporting and holding elements 26, 28 will not be necessary.

As described, the construction also provides for a second opening 40 providing second passage means extending along the top edge of the second glass sheet 22.

As shown in Fig. 1, the excessively heated warm air in the interior of the structure adjacent the ceiling (in the area denoted 34) passes through the first opening 36 up and over the top edge of the first blass sheet 20 and into the inter-panel space 42. The colder air on the outside of the structure passes through the second opening 40 up and over the top edge of the glass sheet 22 and then downwardly between the deflector 32 and the second glass sheet 22. In Fig. 1 the cold air flow is shown by dot-dash arrows and the warm air flow by the solid arrows.

As shown by the arrows in Fig. 1 initial contact between the warm air from inside the building and the cold air from outside the building is prevented at the top by the deflector 32. The cold air does not mix with the warm air to any substantial extent but does entrain it sufficiently to cause it to flow downwardly in a laminar flow, as shown in Fig. 1. At the bottom of the inter-panel space 42 both flows of air exit into the room through the third opening 38 along the bottom edge of the first glass sheet 20. Only as the two flows of air enter and pass through the third opening 38 and enter the room does any substantial mixing of the two air streams begin to take place.

As the cold air flows downwardly in the inter-panel space 42, it is at all times the flow of air that is in contact with the inner surface of the outer second glass sheet 22 thus preventing contact between the warm air flow and the outer second glass sheet 22.

By thus preventing contact between the warm air flow and the outer second glass sheet 22, heat loss to the second sheet 22 and thus to the outside is avoided as well as condensation on the inner surface of the second glass sheet 22. As the warm air flows downwardly in the inter-panel space 42, it is at all times the flow that is in contact with the inner surface of the inner first glass sheet 20. The heat of the warm air flow thus warms the inner first glass sheet 20 and helps to maintain a much more even temperature from the floor to the ceiling in the room as well as on the first glass sheet 20 itself. Since there are no convection currents circulating in the inter-panel space 42, loss of heat by convection is substantially eliminated. In addition, the laminar flow substantially eliminates heat loss by conduction. As such the structure of this invention achieves a far higher thermal insulation value than in previously known conventional constructions.

In Fig. 3 there is shown a cross section through a conventional frame wall construction, which cross-section has been taken between two vertical studs. As shown, the wall comprises a header member 112 and a plate 114 with studs 118 extending vertically between the plate 114 and the header 112. Secured to the inner surface of the frame 112, 114, 118 on the interior of the building is a first panel 120 which may be conventional wood panel, gypsum board, or a lath and plaster construction. First and third openings 136 and 138 providing first and third passage means extend along the top and bottom respectively of the first panel 120. Conveniently, these first and third openings, 136 and 138 may extend the full distance between adjacent studs or may extend the full width of the first panel 120 over several studs. Suitable ceiling and base mouldings 116 and 124 respectively may be provided to cover the first and third openings 136 and 138 for aesthetic purposes.

On the outer surface of the frame 112, 114, 118 is shown a second panel 122. While only one layer is shown for the second panel 122, it will be appreciated that this may compromise several layers as in any conventional construction. For example, it may have a layer of sheathing overlaid with tar paper, plastics sheet material or the like with a final siding layer. Whatever the construction, there is provided along the upper edge of the second panel 122 a second opening 140 providing second passage means. The second opening 140 may be hidden from view and provision made to prevent rain, snow, and the like from entering through the second opening 140 by use of a suitable moulding such as that shown largely schematically at 126. Within the inter-panel space 142 there is provided a deflector 132 of any suitable material such as wood, plywood, sheet metal, plastics; or the like secured to and supported by either the header 112 or the stud 118, or both. Cross-braces, fire-stops, or the like must be avoided between the vertical studs since they would interfere with the laminar movement of the air. It will be appreciated that the wall section shown in Fig. 3 functions in the same manner as the window shown in Fig. 1 and the operation of which is described above. Excepting for the openings deliberately provided the panels should be sufficiently air tight to prevent other infiltration which would create undesirable convection.

Fig. 4 shows a construction similar to that shown in Fig. 3 with the same parts indicated by the same reference characters except for the addition of a prime (') after the numeral and in which the construction is designed for use when the interior of the building is being cooled, and the exterior environment is hot relative to the interior.

The construction shown in Fig. 4 has second opening 140' in outside panel 122' at the lower end of the inter-panel space 142' rather than at the top as was the case in the construction of Fig. 3. Additionally deflector 132' is located at the bottom of the inter-panel space and a protective hood or moulding 126' is positioned above second opening 140' in substantially the second same manner as the protective hood 126 with respect to the opening 140 as shown in Fig. 3. It should also be noted that in this arrangement the lower opening 138' provides the first passage means whilst the upper opening 136' provides the second passage means.

The solid arrows in Fig. 4 indicates the flow of warm outside air through the second opening 140' into the inter-panel space 142' and upwardly along the inner surface of the panel 122'. During this movement it draws with it the cooler air from the interior of the building which enters into the space 142' through lower opening 138' where it moves upwardly along the inner surface of the inner first panel 120' and exists through the upper opening 136'. The warmer outside air also exits through the upper opening 136'. This flow is essentially the reverse of that described above with reference to Fig. 1 and Fig. 3 in that the cold interior air accumulating along the lower portion of the room at the floor serves to cool the first panel 120' as it moves upwardly therealong.

The laminar flow of the two streams of air prevents the cooler stream from contacting the relatively warm second panel 122' thus avoiding pickup of heat therefrom by either convection or conduction.

It will be understood that windows can be similarly constructed with the outside opening adjacent the bottom as shown in Fig. 4 rather than at the top as shown in Fig. 1 and with the deflector relocated at the bottom as well.

Still further, the outer panels 22, 122, 122' may, if desired, be constructed with both upper and lower openings with provision made to close either the top or the bottom opening depending upon whether the interior of the building is being cooled or heated respectively. Also, two deflectors such as the deflectors 32, 132, 132' may be provided with one located at the top as with deflectors 32 and 132 and the other located at the bottom as with deflector 132'. In such a construction it is preferably to provide some mechanism to move the deflectors to a position where they will not obstruct the laminar flow in the inter-panel space. That is to say, that when the building is being heated and the upper opening is being utilized its associated deflector will be positioned as shown in Figs. 1 and 3 while the lower opening is closed and its associated deflector moved out of the way, such as by pivoting the deflector against is associated support. When the building is being cooled, the lower deflector would be positioned as shown in Fig. 4, the lower opening would be open and the upper opening closed. The upper deflector would then be pivoted or otherwise moved out of the way.

In windows constructed in accordance with this invention either or both of the inner and outer glass sheets 20 and 22 respectively may be so mounted as to be movable or removable to permit access to the inner facing surfaces for washing and cleaning.

It is also contemplated that the opening or openings through or at the outer panel may be screened or provided with filter to prevent insects or debris outside the building from entering the inter-panel space.

Still further, one or both of the inner facing surfaces of the panels may be lined with a sheet such as plastics sheet or aluminium foil when the invention is applied to a frame wall as in Figs. 3 or 4 in order to reduce friction losses along the panels that might tend to slow the air movement. Such, of course, is not necessary with the glass sheets in the window embodiment of the invention.

The size of the openings and the distance between the inner and outer panels can vary within wide limits and depend, in part, on whether filters and screens are used and the prosity thereof. It is only necessary that the openings and inter-panel space be so dimensioned as to avoid convection currents being created. For the same reason obstruction in the inter-panel space must be avoided.

EXAMPLE 1.

Two rooms of a house were used for comparison tests. Both rooms had similar outside exposure and window area. The construction was on a concrete slab with concrete outside walls. The control room had a conventional frame construction on the inside of the concrete walls with gypsum board mounted on the interior side of the frame to provide the walls of the room.

Between the gypsum board and the concrete wall there was located in the usual manner 4 inches of glass fibre insulating batt. The test room also had gypsum board but it was mounted by means of vertically disposed furring strips i.e. relatively thin strips used for mounting wall panels on walls directly to the concrete wall. The furring strips were an actual 3/4 of an inch in thickness (throughout their length) and as such the inner surface of the gypsum board was spaced 3/4 of an inch from the concrete wall. Slots 1/16 inches wide were left at the top and bottom of the gypsum board thus allowing communication between the room and the interior wall space at both the top and the bottom. In addition a 1/16 inch wide slot was provided above the top of the concrete wall which slot allowed communication between the space between the gypsum board and the concrete wall and an unheated plenum above the ceiling of the room. An 8-inch wide (measured vertically) deflector was provided at the top of the space between the concrete wall and the gypsum board to separate the room derived air from the plenum derived air.

Both rooms were operated for a period of three years and the temperatures both inside and outside were continually monitored as was the electrical power consumed in heating the rooms. The results were evluated by comparing the actual heat loss of each room with the expected heat loss calculated from standard empirical tables. Calculations for the control room were made for the room as actually constructed. The actual and calculated heat loss values for the control room were always within 5% of one another.

Calculations for the test room were made on two different bases. The heat loss was calculated for the test room for its actual construction (uninsulated in the conventional way). When these calculated values were compared with the heat loss actually experienced in the room when the slots were closed it was found that the actual and calculated heat losses were then quite close.

The calculations were also made as if the test room had been insulated in the same way as the control room. The actual heat loss experienced in the test room (with all three slots open and operating) when compared with these calculated values demonstrated that there was generally 45% lower heat loss actually experienced in the test room than the calculated loss based upon the room being insulated. These measurements and calculations were carried on routinely throughout the three-year period with the same results.

It was also discovered that the system functioned quite well without the deflection panel at the top of the inter-panel space until the temperaure differential between the inside and the outside was reduced to about 12"C. By use of the deflector panel it was discovered that efficient operation was achieved over the entire temperature range experienced.

EXAMPLE 2.

A double window was constructed in accordance with Fig. 1 by mounting two sheets of window glass in standard extruded aluminium frames. The air flow slots were provided by eliminating the gasket or sealing material at the top and the bottom of the inner glass sheet and at the top only of the outer glass sheet. This provided slots approximately 1/16 inches wide where the sealant was eliminated. Thermocouples were then installed both in the inside air and in the outside air as well as on both surfaces of both glass sheets.

For experimental purposes the slots were then temporarily sealed and the temperature difference was measured across each of the glass sheets. When the outside slot alone was sealed, the temperature gradients across each of the glass sheets remained approximately the same as when all the slots were sealed but condensation developed on the outside sheet which resulted from contact with the warm, moist, inside air. Smoke tracings indicated a downward flow between the two glass sheets.

When all slots were open including the outside slot, the air moved downwards in a very uniform laminar flow. No condensation developed and the temperature gradient across each of the glass sheets was reduced. The temperature gradient across the outside glass sheet was reduced virtually to zero.

WHAT WE CLAIM IS: 1. A thermally insulating structure for insulating a first zone from a second zone and comprising a pair of elements for positioning between said first and second zones with the first element of said pair adjacent said first zone and the second element of said pair adjacent said second zone, said pair of element being arranged in spaced apart relation to provide an inter-element space, first passage means for permitting fluid flow from the first zone into said interelement space, second passage means for permtting fluid flow from the second zone into said inter-element space simultaneously with said fluid flow from said first zone into said inter-element space, and third passage means for permitting both of said flows from said inter-element space to pass to the first zone, the arrangement being such that, in use of the structure with a temperature differential existing between said first and second zones, first and second fluid flows pass from said first and second zones through said first and second passage means, respectively, into said inter-element space, and then from the interelement space through said third passage means in contact with one another to said first zone, without any substantial mixing of said first and second flows over a substantial part of their passage through the inter-element space.

2. A thermally insulating structure for insulating a first zone from a second zone and comprising a pair of elements for positioning between said first and second zones with the first element of said pair adjacent said first zone and the second element of said pair adjacent said second zone, said pair of elements being arranged in spaced apart relation to provide an inter-element space, first passage means for permitting fluid flow from the first zone into said interelement space, second passage means for permitting fluid flow from the second zone into said inter-element space simultaneously with said fluid flow from said first zone into said inter-element space, the arrangement being such that, in use of the structure with a temperature differential existing between the said first and second zones, first and second fluid flows pass from said first and second zones through said first and second passage means, respectively, into said interelement space and then pass through said inter-element space in contact with one another without any substantial mixing of said flows with one another, and third passage means for permitting passage of both of said first and second flows into said first zone after pas

Claims

**WARNING** start of CLMS field may overlap end of DESC **. calculations were carried on routinely throughout the three-year period with the same results. It was also discovered that the system functioned quite well without the deflection panel at the top of the inter-panel space until the temperaure differential between the inside and the outside was reduced to about 12"C. By use of the deflector panel it was discovered that efficient operation was achieved over the entire temperature range experienced. EXAMPLE 2. A double window was constructed in accordance with Fig. 1 by mounting two sheets of window glass in standard extruded aluminium frames. The air flow slots were provided by eliminating the gasket or sealing material at the top and the bottom of the inner glass sheet and at the top only of the outer glass sheet. This provided slots approximately 1/16 inches wide where the sealant was eliminated. Thermocouples were then installed both in the inside air and in the outside air as well as on both surfaces of both glass sheets. For experimental purposes the slots were then temporarily sealed and the temperature difference was measured across each of the glass sheets. When the outside slot alone was sealed, the temperature gradients across each of the glass sheets remained approximately the same as when all the slots were sealed but condensation developed on the outside sheet which resulted from contact with the warm, moist, inside air. Smoke tracings indicated a downward flow between the two glass sheets. When all slots were open including the outside slot, the air moved downwards in a very uniform laminar flow. No condensation developed and the temperature gradient across each of the glass sheets was reduced. The temperature gradient across the outside glass sheet was reduced virtually to zero. WHAT WE CLAIM IS:

1. A thermally insulating structure for insulating a first zone from a second zone and comprising a pair of elements for positioning between said first and second zones with the first element of said pair adjacent said first zone and the second element of said pair adjacent said second zone, said pair of element being arranged in spaced apart relation to provide an inter-element space, first passage means for permitting fluid flow from the first zone into said interelement space, second passage means for permtting fluid flow from the second zone into said inter-element space simultaneously with said fluid flow from said first zone into said inter-element space, and third passage means for permitting both of said flows from said inter-element space to pass to the first zone, the arrangement being such that, in use of the structure with a temperature differential existing between said first and second zones, first and second fluid flows pass from said first and second zones through said first and second passage means, respectively, into said inter-element space, and then from the interelement space through said third passage means in contact with one another to said first zone, without any substantial mixing of said first and second flows over a substantial part of their passage through the inter-element space.

2. A thermally insulating structure for insulating a first zone from a second zone and comprising a pair of elements for positioning between said first and second zones with the first element of said pair adjacent said first zone and the second element of said pair adjacent said second zone, said pair of elements being arranged in spaced apart relation to provide an inter-element space, first passage means for permitting fluid flow from the first zone into said interelement space, second passage means for permitting fluid flow from the second zone into said inter-element space simultaneously with said fluid flow from said first zone into said inter-element space, the arrangement being such that, in use of the structure with a temperature differential existing between the said first and second zones, first and second fluid flows pass from said first and second zones through said first and second passage means, respectively, into said interelement space and then pass through said inter-element space in contact with one another without any substantial mixing of said flows with one another, and third passage means for permitting passage of both of said first and second flows into said first zone after passage through said inter-element space.

3. A structure as claimed in Claim 1 or Claim 2 in which said structure includes wall means arranged in said inter-element space for initially preventing the first and second fluid flows from mixing substantially in said inter-element space in use of the structure.

4. A structure as claimed in any one of Claims 1 to 2, in which said structure includes means for initially guiding the fluid ffow from said second zone along the surface of said second element that faces said first element.

5. A structure as claimed in Claim 4, wherein the guiding means comprise wall means arranged in said inter-element space.

6. A structure as claimed in any one of Claims 1 to 5, in which said elements are positioned, in use of the structure, at an

angle to the horizontal.

7. A structure as claimed in Claim 6, in which said elements are positioned, in use of the structure, in substantially vertical planes.

8. A structure as claimed in any one of Claims 1 to 7, in which said elements are disposed substantially parallel to each other.

9. A structure as claimed in any one of Claims 1 to 8, in which each of said passage means for permitting fluid flow comprises an opening in or adjacent a respective one of said first and second elements.

10. A structure as claimed in Claim 9, in which the openings of the first and third passage means are spaced apart.

11. A structure as claimed in Claim 10, in which the elements are disposed at an angle to the horizontal, in use of the structure, and one of said first and third passage means openings is above the other of said first and third passage means openings.

12. A structure as claimed in Claim 10 or Claim 11, in which the opening of the second passage means is positioned above the lower of said first and third passage means openings.

13. A structure as claimed in any one of Claims 1 to 12, in which said elements are glass sheets.

14. A structure as claimed in Claim 13, which is a window.

15. A structure as claimed in any one of Claims 1 to 12, which comprises at least part of a wall of a building.

16. A structure as claimed in any one of Claims 1 to 15, in which the arrangement is such that, in use of the structure between a warm first zone and a cold second zone, first and second fluid flows will pass from said first and second zones through said first and second passage means respectively, into said inter-element space, and then from the inter-element space through said third passage means in contact with one another to said first zone, without any substantial mixing of said first and second flows over a substantial part of their passage through the inter-element space.

17. A thermally insulating structure according to Claim 1, substantially as described hereinbefore with particular reference to Figures 1 and 2 or Figures 3 and 4 of the accompanying drawings.

18. A method of thermally insulating a first zone from a second zone comprising providing a space between said zones, which space is separated from said zones, intoducing a first fluid flow from said first zone into said space, introducing a second fluid flow from said second zone into said space, and passing both of said fluid flows in contact with one another into said first zone, said flows being simultaneously moved through said space in a laminar manner so that said first and second fluid flows pass through the major portion of said space without any substantial mixing of said fluid flows and without creating any substantial convection currents in said defined space.

19. A method as claimed in Claim 18 in which, when said first zone is warmer than said second zone, and said space extends between said zones at an angle to the horizontal, the introduction of said first and second fluid flows into said space takes place adjacent the top of said space.

20. A method as claimed in Claim 19 in which, when said first zone is cooler than said second zone and said space extends between said zones at an angle to the horizontal, the introduction of said first and second fluid flows into said space takes place adjacent the bottom of said space.

21. A method of thermally insulating a first zone from a second zone according to Claim 18 substantially as described hereinbefore with particular reference to Figures 1 and 2 or Figures 3 and 4 of the accompanying drawings.