GB2068442A - Window assembly - Google Patents

Abstract

A window assembly having at least two panes of glazing material adapted for mounting in a frame reduces solar heating of a room on hot sunny days and reduces in radiant heat loss in cold weather. Accordingly, means (12, 13, 14, 15) are provided for mounting the panes (2, 3) to the frame (4) so that they are reversible therein as a body. One of said panes (3) has a higher energy absorptivity in respect of solar radiation than the or another pane (2). To one side only of the more absorbent pane (3), at least one pane face which faces another pane of the assembly bears a light-transmitting coating (6) of the material (preferably doped tin oxide) selected to reduce the emissivity of the coated face in respect of infra red radiation. <IMAGE>

Description

SPECIFICATION A window assembly The present invention relates to a window assembly having at least two panes of glazing material adapted for mounting in a frame; and concerns the thermal properties of such assemblies.

It is well known that in hot sunny weather, a room exposed to solar radiation transmitted by a window can become excessively hot and therefore uncomfortable. It is known to overcome this problem by causing the window to absorb or reflect a fairly high proportion of incident solar radiation. Such an arrangement is unsuitable in cold weather.

In cold weather, it is known to augment the solar heating effect on a room by providing its window with a pane or panes having low emissivity for infra-red radiation, whereby infra-red radiation from the room and out through the window is reduced. It is recognised that such an arrangement would normally lead to excessive overheating in hot sunny days.

It is an object of the present invention to provide a window assembly which allows reduced solar heating of a room on hot sunny days and permits a reduction in radiant heat loss in cold weather.

According to the present invention, there is provided a window assembly having at least two panes of glazing material adapted for mounting in a frame, characterised in that means are provided for mounting said panes to the frame so that they are reversible therein as a body, in that one of said panes has a higher energy absorptivity in respect of solar radiation than the or another said pane and in that, to one side only of such more absorbent pane, at least one pane face which faces another pane of the assembly includes a light-transmitting coating of a material selected to reduce the emissivity of the coated face in respect of infra-red radiation.

The invention thereby provides a reversible window assembly whose radiant energy transmitting properties are different depending on the side of the panes on which the radiant energy is incident.

The case where the low emissivity coating is located to the sunward or outdoors side of the more absorbent pane will be called the "winter orientation", and the reverse orientation, that is where the more absorbent pane is on the sunward or outdoors side of that coating will be called the "summer orientation".

Consider a theoretical window consisting of two panes of glazing material mounted in facing relation, with one of the facing pane faces including a coating which has an infra-red emissivity of 0.4, so that it reflects 60% of incident infra-red energy and, neglecting any absorption by the coating, it transmits 40% of such energy.#Let#ne pane transmit 100% of incident solar radiant energy, while the other abosrbs 50% of such energy.

The energy transmission properties of this theoretical window may, as an approximation, be considered as follows.

In the summer orientation, with solar energy incident on the absorbent pane, 50% will be absorbed there, and 50% transmitted straight through via the other pane to the interior of the room in whose wall the window is mounted. The 50% energy which is absorbed will heat the absorbent pane and will be re-emitted as long wavelength infra-red energy. In ordinary circumstances this absorbed energy would be radiated equally to both sides of the absorbent pane, and accordingly, a further 25% of the incident energy would be radiated into the room. However, because of the low infra-red emissivity coating, only a further 10% of the incident energy (0.4 x 25%) enters the room. Thus 60% of the solar energy incident on the window is transmitted when it is oriented with its absorbent pane facing outwards.

When the window is reversed into the winter orientation, again 50% of incident energy will be transmitted to the room and 50% will be absorbed to be re-radiated as infra-red energy. However, because the window is reversed so that the low infra-red emissivity coating is now on the outdoors side of the absorbent pane, most of this infra-red energy will enter the room. Accordingly up to 90% of the incident solar energy will enter into the room.

Of course these figures do not take into account any secondary reflection which takes place across the intersheet space, or the energy lost in heating the sheets, but in practice it remains true that the incident solar energy transmittance of the window will be dependent on whether the low infra-red emissivity coating is located to the sunward side of the more highly absorbent pane or vice versa.

The window assembly may be mounted to the frame in various different ways. Preferably such pane-mounting means are arranged to allow pivotal movement of the panes in relation to the frame to effect such reversing. This facilitates reversing of the window.

In preferred embodiments of the invention, said assembly includes sealing means adapted to seal the panes to the frame in either orientation.

Advantageously, said panes are secured together at their margins to form a hollow glazing panel.

This simplifies construction of the mounting and sealing means for the window assembly.

Preferably, such low infra-red emissivity coating is deposited on a face of such more energy absorbent pane. There are several reasons for preferring this feature. Firstly, this enables any other pane of the window to be made of ordinary glazing material which has not been subjected to any special treatment. Secondly, because such coating may itself absorb some proportion of incident energy, this feature entails that the less absorbent pane will be cooler and the more absorbent pane will be warmer than if the coating were applied to the less absorbent pane.Thus, in the case of a two-pane window, in the summer orientation, the cooler, less absorbent pane is directed into a room while the warmer, more absorbent pane can lose heat by conduction to the open atmosphere, whereas in the winter orientation, the warmer, more absorbent pane is protected from the open atmosphere by the less absorbent pane.

Preferably such low emissivity coating has a resistivity (measured as herein specified) of less than so nln.

Preferably the or at least one said coating has a resistivity (measured as herein specified) of less than 20 Q/CI.

In fact the values given for the resistivity of a thin light transmitting coating as envisaged by the present invention can depend on the method of measurement used. Accordingly, the following method is specified.

The coated sheet is taken and a pair of conductive strips each 5 cm long are deposited on the coated face 5 cm apart along opposite edges of a notional square. These conductive strips may be of a conductive lacquer or enamel as is well known in the art. The two strips are connected in an electric circuit and a constant current of 10 mA is passed between them. The potential differences between a point located for example at the centre of one conductive strip and a succession of positions lying on a line perpendicularly connecting the two strips and passing through that point are then plotted on a graph against the distances between those positions and that point. From the positions plotted on that graph, it is possible to obtain a straight line whose gradient is a measure of voltage drop per centimetre across the coating between the conductive strips.The value derived for voltage drop per centimetre (mV/cm) is then divided by 2 (10 mA over 5 cm) and the result is the resistivity of the coating expressed in ohms per square. This gives a more precise result than simply measuring the potential difference between the conductive strips and dividing by the current passing between them.

Preferably, said coating imparts to the coated pane face an emissivity in respect of infra-red radiation of wavelengths greater than 5,000 nm of at most 0.35, and optimally at most 0.2. This increases the difference in the energy transmissivities of the window as between its summer and its winter orientations.

Advantageously, the or at least one said low emissivity coating is a metal oxide coating. Tin oxide (SnO2) and indium oxide (In203) coatings are especially preferred.

Preferably, said metal oxide coating has a thickness of between 700 and 1000 nm. Coatings of such thicknesses give uniform light transmission, and non-uniform interference effects are largely eliminated.

Titanium nitride coatings have also been used with satisfactory results.

Preferably the or at least one said oxide coating includes a doping agent since this enables the best resistivity and emissivity values to be achieved. Such doping agent may for example be chlorine and"'orfluorine. Antimony, arsenic, cadmium and tellurium have also been used as doping agents.

A said coating may be applied to a sheet of glass for use as a window pane in any convenient manner. For example a fluorine doped tin oxide coating can be obtained by the thermal decomposition of SnOl4 and NH4F.HF or a chlorine doped coating of indium oxide can be obtained by pyrolysis of a solution of Inc3.

Considering a given orientation of a window, the transmissivity of the window in respect of visible light and indeed in respect of the total incident energy may be varied to suit customer requirements and climate conditions in the place of use by choosing a pane with an appropriate coefficient of absorption.

Advantageously, such more absorbent pane has a factor of absorption in respect of incident radiant energy which is at least twice, and preferably at least three times, that of the or another said pane.

An embodiment of the invention will now be described with reference to the accompançing drawings in which: Figure 1 illustrates a window assembly in side elevation, partly in cross-section; and Figure 2 is a section along the line Il-lI in Figure 1.

In the drawings, a window assembly generally indicated at 1 comprises two panes 2, 3 of glazing material which are adapted for mounting in a frame 4 adapted to be fixed in a window opening in a wall (not shown). In the embodiment illustrated, the first pane 2 is constituted by a sheet of glazing material, whereas the second pane 3 is constituted by a sheet of glazing material 5 and a light transmitting coating 6 which has been deposited on that surface of the glazing sheet 5 which faces the first pane 2.

The coating 6 is of a material selected to reduce the emissivity of the coated face in respect of infra-red radiation. The two panes 2, 3 have different energy absorptivities in respect of incident solar radiation.

The two panes 2, 3 are secured together at their margins by a strip of spacer material 7 to form a hollow glazing panel. The margins of the thus formed panel are secured in a channel of a panel frame 8 whose outer edge face includes a re-entrant within which strip sealing material 9 is retained by retaining lips 10. The strip sealing material 9 is provided with resilient blade portions 1 1 for making sealing contact with the window frame 4.

A pair of stub axles such as 12 are fixed to the panel frame 8 at ends of an axis of symmetry thereof so that the window assembly 1 can be reversed in the window frame 4. Each stub axle 12 is arranged for mounting in a cylindrical hub 13 (Figure 2) carried by the frame 4, the hub being of a size to co-operate with a space 14 surrounding each stub axle 12. The blade portions 1 1 of the sealing strip 9 terminate in part circular end pieces 15 arranged to make sealing contact with such cylindrical hubs.

Certain properties of particular window assemblies are indicated in the following tables. In each case the glass sheets were of float glass 6 mm thick. In fact three different coloured glasses have been tested, green glass, grey glass and bronze glass.

In the following tables, TL represents the factor of transmission of light of visible wavelengths; TE represents the factor of transmission of incident radiant energy, ignoring long wavelength infra-red radiation emitted by the sheet itself; AE represents the factor of absorption of incident radiant energy; and TET represents the factor of total energy transmission, that is, the relative intensity of the radiation of all wavelengths (including long wave-length infra-red radiation) on the two sides of the sheet. The calculation of the luminous properties was made using a radiator whose spectral composition is that of illuminant D65 as defined by the International Commission on Illumination (reference CIE 17 Section 45-1 5-145). This illuminant represents a source of daylight with a colour temperature of about 6504K.The calculation of energy properties was made using a radiator whose spectral composition is that of direct sunlight at an elevation of 300 above the horizon. The spectral composition is given by Moon's Table for a mass of air equal to 2.

TABLE 1 Single 6 mm Float Glass Sheet Glass: Clear Green Grey Bronze TL 0.882 0.710 0.416 0.481 TE 0.798 0.445 0.469 0.480 AE 0.131 0.501 0.479 0.467 TET 0.832 0.575 0;593 0.601 Two different coatings having low emissivity in respect of infra-red radiation are applied to sheets of these coloured glasses. The first coating of blue tint consists of an underlayer of bismuth oxide 10 nm thick covered by a gold layer 7.5 nm thick and a further bismuth oxide layer 10 nm thick. This coating has an emissivity of 0.26 in respect of infra-red radiation of wavelengths greater than 5,000 nm, and a resistivity of 50 52/0. The second coating, of neutral tint consists of an underlayer of bismuth oxide 1.5 nm thick, an interlayer of gold 7.5 nm thick and a top layer of bismuth oxide 5 nm thick.This coating has an emissivity of 0.26 in respect of infra-red radiation of wavelengths greater than 5,000 nm, and a resistivity of 13 SWO. The various coated coloured sheets are assembled into double glazing panels with sheets of the clear 6 mm float glass, the coating being located between the glass sheets, and these panels are tested in their summer and winter orientations.

TABLE 2 Double Glazing Panel, Internal Blue Coating (Compare Figure 1) Coloured Glass: Green Grey Bronze Orientation: Summer Winter Summer Winter Summer Winter TL 0.444 0.444 0.261 0.261 0.303 0.303 TE 0.234 0.234 0.224 0.224 0.235 0.235 AE 0.696 0.561 0.694 0.572 0.683 0.561 TET 0.307 0.560 0.304 0.558 0.314 0.560 TABLE 3 Double Glazing Panel, Internal Neutral Coating (Compare Figure 1) Coloured Glass: Green Grey Bronze Orientation:Summer Winter Summer Winter Summer Winter TL 0.482 0.482 0.282 0.282 0.327 0.327 TE 0.257 0.257 0.243 0.243 0.254 0.254 AE 0.679 0.543 0.676 0.558 0.665 0.547 TET 0.329 0.567 0.323 0.565 0.333 0.567 The values given in Tables 2 and 3 may be compared with corresponding values for a single sheet of coloured glass bearing a blue coating (Table 4) or a neutral coating (Table 5) and with values for a double glazing panel consisting of a clear glass sheet and a coloured glass sheet, neither being coated (Table 6).

TABLE 4 Single 6 mm Coloured Float Glass Sheet with Blue Coating Coloured Glass: Green Grey Bronze Orientation*: Summer Winter Summer Winter Summer Winter TL 0.499 0.499 0.293 0.293 0.341 0.341 TE 0.276 0.276 0.276 0.276 0.288 0.288 AE 0.662 0.509 0.648 0.510 0.637 0.498 TET 0.448 0.408 0.444 0.409 0.453 0.417 TABLE 5 Single 6 mm Coloured Float Glass Sheet with Neutral Coating Coloured Glass: Green Grey Bronze Orientation*: Summer Winter Summer Winter Summer Winter TL 0.541 0.541 0.318 0.318 0.368 0.368 TE 0.302 0.302 0.299 0.299 0.310 0.310 AE 0.643 0.486 0.627 0.491 0.617 0.479 TET 0.469 0.428 0.461 0.426 0.470 0.434 TABLE 6 Double Glazing Panel, One Sheet Coloured, No Coating Coloured Glass: Green Grey Bronze Orientation*:Summer Winter Summer Winter Summer Winter TL 0.631 0.631 0.368 0.368 0.426 0.426 TE 0.374 0.374 0.374 0.374 0.386 0.386 AE 0.553 0.519 0.557 0.520 0.544 0.508 TET 0.466 0.632 0.478 0.634 0.487 0.638 * For the purposes of Tables 4 and 5 the summer and winter orientations indicated are as hereinbefore defined, that is, in the winter orientation, radiation is incident on the coated face of the sheet. In practice, if such sheets were to be mounted reversibly, a comparison of the total energy transmission factors will indicate that the opposite orientations should be used. For the purpose of Table 6, the winter orientation is taken as being that in which radiation is incident on the clear glass sheet.

The effectiveness of the present invention may be indicated by a comparison of the factors of total energy transmission as between the summer and winter orientations of the glazing panels. In Table 2, the mean ratio between these factors is greater than 1.8, while for Table 3, it is greater than 1.7. For Tables 4 and 5 such mean ratio is below 1.1 while for Table 6 it is 1.3.

Four further double glazing panels are made in which the first glass sheet is clear 6 mm float glass sheet as referred to in Table 1, and the second sheet is respectively of clear, green, grey and bronze glass (also referred to in Table 1). In each case the second glass sheet was provided with a 760 nm thick coating of SnO2 doped with fluorine (F-) ions so that the resistivity of the coating was 12 Q/O and its emissivity was about 0.1 for wavelengths greater than 5,000 nm. Results of tests performed on these panels are given in Tables 7 and 8.

TABLE 7 Double Glazing Panel, One Clear Float Glass Sheet with Internal SnO2 Coating on Second Sheet Second sheet: Clear Green Orientation: Summer Winter Summer Winter TL 0.641 0.641 0;516 0.516 TE 0.446 0.446 0.280 0.280 AE 0.423 0.398 0.649 0.590 TET 0.546 0.680 0.349 0.645 TABLE 8 Double Glazing Panel, One Clear Float Glass Sheet with Internal SnO2 Coating on Second Sheet Second sheet: Grey Bronze Orientation: Summer Winter Summer Winter TL 0.302 0.302 0.349 0.349 TE 0.264 0.264 0.276 0.276 AE 0.670 0.607 0.656 0.596 TET 0.345 0.643 0.354 0.645 From Tables 7 and 8, it will be apparent that the ratio between the factors of total energy transmission of each of the panels as between their summer and winter orientations are, for the panel with the clear second sheet, 1.24, and for the other panels 1.85, 1.86 and 1.82.

Various other coating materials which may be used in the performance of the invention are set out below.

Coating Material Doping Agent Thickness Emissivity SnO2 F- ions 900 nm 0.25 SnO2 F- ions 700 nm 0.25 SnO2 Sb 400 nm 0.3 SnO2 Sb 500 nm (below 0.2) ln2O3 Cl- ions 200 nm 0.1

Claims (13)

1. A window assembly having at least two panes of glazing material adapted for mounting in a frame, characterised in that means are provided for mounting said panes to the frame so that they are reversible therein as a body, in that one of said panes has a higher energy absorptivity in respect of solar radiation than the or another said pane and in that, to one side only of such more absorbent pane, at least one pane face which faces another pane of the assembly includes light-transmitting coating of a material selected to reduce the emissivity of the coated face in respect of infra-red radiation.

2. A window assembly according to claim 1, characterised in that said pane mounting means are arranged to allow pivotal movement of the panes in relation to the frame to effect such reversing.

3. A window assembly according to claim 1 or 2, characterised in that said assembly includes sealing means adapted to seal the panes to the frame in either orientation.

4. A window assembly according to any preceding claim, characterised in that said panes are secured together at their margins to form a hollow glazing panel.

5. A window assembly according to any preceding claim, characterised in that such low emissivity coating is deposited on a face of such more absorbent pane.

6. A window assembly according to any preceding claim, characterised in that such low emissivity coating has a resistivity (measured as herein specified) of less than 50 S?/O#and preferably less than 20 Q/El.

7. A window assembly according to any preceding claim, characterised in that such low emissivity coating imparts to the coated pane face an emissivity in respect of infra-red radiation of wavelengths greater than 5,000 nm of at most 0.35 and preferably at most 0.2.

8. A window assembly according to any preceding claim, characterised in that the or at least one such low emissivity coating is a metal oxide coating.

9. A window assembly according to claim 8, characterised in that said metal oxide is tin oxide.

10. A window -assembly according to claim 8 or 9, characterised in that the or at least one said metal oxide coating has a thickness of between 700 nm and 1,000 nm.

1 A window assembly according to any of claims 8 to 10, characterised in that the or at least one said oxide coating includes a doping agent, for example selected from chlorine, fluorine, antimony, arsenic, cadmium and tellurium.

12. A window assembly according to any preceding claim, characterised in that such more absorbent pane has a factor of absorpiton in respect of incident radiant energy which is at least twice, and preferably at least three times, that of the or another said pane.

13. A window assembly according to Claim 1 and substantially as herein described.

13. A window assembly according to claim 1 and substantially as herein described.

New claims or amendments to claims filed on 22 December 1980.

Superseded claims 1-13 New or amended claims:-- 1--13

1. A window assembly having at least two panes of glazing material adapted for mounting in a frame, characterised in that means (12, 13, 14, 1 5) are provided for mounting said panes (2, 3) to the frame (4) so that they are reversible therein as a body, in that one of said panes (3) has a higher energy absorptivity in respect of solar radiation than the or another said pane (2) and in that, to one side only of such more absorbent pane (3), at least one pane face which faces another pane of the assembly bears a light-transmitting coating (6) of a material selected to reduce the emissivity of the coated face in respect of infra-red radiation.

2. A window assembly according to Claim 1, characterised in that said pane mounting means (12-15) are arranged to allow pivotal movement of the panes in relation to the frame to effect such reversing.

3. A window assembly according to Claim 1 or 2, characterised in that said assembly includes sealing means (11) adapted to seal the panes to the frame in either orientation.

4. A window assembly according to any preceding claim, characterised in that said panes (2, 3) are secured together at their margins to form a hollow glazing panel.

5. A window assembly according to any preceding claim, characterised in that such low emissivity coating (6) is deposited on a face of such more absorbent pane (3).

6. A window assembly according to any preceding claim, characterised in that such low emissivity coating (6) has a resistivity (measured as herein specified) of less than 50 S?/O and preferably less than 20 #.

7. A window assembly according to any preceding claim, characterised in that such low emissivity coating (6) imparts to the coated pane face an emissivity in respect of infra-red radiation of wavelengths greater than 5,000 nm of at most 0.35 and preferably at most 0.2.

8. A window assembly according to any preceding claim, characterised in that the or at least one such low emissivity coating (6) is a metal oxide coating.

9. A window assembly according to Claim 8, characterised in that said metal oxide is tin oxide.

10. A window assembly according to Claim 8 or 9, characterised in that the or at least one said metal oxide coating has a thickness of between 700 nm and 1,000 nm.

1 1. A window assembly according to any of Claims 8 to 10, characterised in that the or at least one said oxide coating includes a doping agent, for example selected from chlorine, fluorine, antimony, arsenic, cadmium and tellurium.

12. A window assembly according to any preceding claim, characterised in that such more absorbent pane (3) has a factor of absorption in respect of incident radiant energy which is at least twice, and preferably at least three times, that of the or another said pane (2).