EP0922829A2

EP0922829A2 - Reversible ventilated glazing system

Info

Publication number: EP0922829A2
Application number: EP98204183A
Authority: EP
Inventors: Yair Etzion; Evyatar Erell
Original assignee: Ben Gurion University of the Negev Research and Development Authority Ltd
Current assignee: Ben Gurion University of the Negev Research and Development Authority Ltd
Priority date: 1997-12-11
Filing date: 1998-12-09
Publication date: 1999-06-16
Also published as: IL122572A0; EP0922829A3

Abstract

A ventilated glazing system comprising a frame (3) suitable for incorporation in a wall element (2), which frame (3) houses at least one absorbing (5) and one clear (4) glazing component, said absorbing and said clear glazing components being spaced so as to provide an air space (6) between them, wherein said absorbing and said clear glazing components (4,5), together with said frame (3), create a substantially vertical air conduit through which air can flow from the bottom to the top, or vice versa, said frame (3) being reversible so as to permit to switch the side on which the absorbing (5) and the clear (4) glazing are positioned respective to the wall element (2).

Description

Field of the Invention

The present invention relates to the illumination and heating of buildings by solar energy. More particularly, the invention relates to a glazing system which is adjustable into two different operational forms, for use in winter and in summer, and which is further ventilated.

Background of the Invention

Glazed openings modulate the flow of energy between interior and exterior by conduction, convection and radiation. Ordinary, nearly transparent, standard double-strength sheet glass allows indoors about 87% of the solar radiation (ASHRAE (1989), 1989 Fundamentals Handbook, ASHRAE, Atlanta). This uncontrolled influx of solar energy through large glazed openings has numerous drawbacks, for example: 1) extreme overheating in the summer; and 2) visual discomforts of glare both in summer and in winter. Furthermore, direct sunlight has a deleterious effect on furniture and objects located near the opening.
The traditional response to these problems has been to incorporate shading devices, which reduce the exposed area of the glazing.
Fixed shading devices are generally installed on the exterior of the fenestration. They are usually maintenance free, but can not be adapted to changing meteorological conditions, and while blocking out direct solar radiation, have little effect on diffuse or reflected radiation.
Operable shading devices on the exterior of windows are designed to allow control of the incoming radiation at all times. They may have complex mechanisms which require maintenance or replacement, and require either user intervention to operate properly, or expensive automatic control systems.
The effect of shading devices installed on the interior of the building, such as roller shades, curtains or venetian blinds, depends on their ability to reflect incoming solar radiation back through the fenestration before it can be absorbed and converted to heat. Drapes may reduce annual cooling loads by 5-20% (Rudoy & Duran, 1975, "Effect of building envelope parameters on annual heating/cooling load", ASHRAE Journal 7:19), and serve mainly to improve visual comfort and reduce the effect of radiant energy on building occupants near the windows.
Integrated shading devices are sometimes found in the form of venetian blinds placed between the glass sheets in a double glazed unit, or between the frames of a double window (Brandle K. and Boehm R.F. (1982) "Airflow windows: performance and applications", Proceedings of Thermal Performance of the Exterior Envelopes of Buildings II, ASHRAE/DOE Conference, ASHRAE SP38.; Peck J., Thompson T.L. and Kessler H.J. (1979) "Windows for accepting or rejecting solar heat gain", Proceedings of the Fifth National Passive Solar Conference, ISES - American Section, pp. 985-989.).
All shading devices interfere with one of the main purposes of windows - the provision of visual contact with the outdoors; and since their response is based on simple geometry, they are not selective in their effect - they either block out or allow through all of the incident radiation on a given portion of the opening. The limitations of shading devices led to the development of new types of glazing materials. The new types of glazing were designed to modulate the passage of radiation by intercepting part of it. This may be done either by altering the properties of the glass itself, or by applying a coating to the surface of the material.
Currently available glazing has constant optical properties. Under changing environmental conditions, a glazing system with dynamic optical properties would be of considerable benefit. Research on "electro-chromic windows" is focused on a number of solids which display a reversible color change caused by an applied electric current or field. Oxides of tungsten, vanadium, molybdenum or titanium may be suitable for use in sol-gel glass to create a glazing system which can alter its transmissivity in response to an electric signal (Reisfeld, R. (1990), "Theory and applications of spectroscopically active glasses prepared by the sol-gel method", Sol-Gel Optics, proceedings of the SPIE International Symposium on Optical and Optoelectronic Applied Science and Engineering, San Diego, California, July 8-13, 1990) (Donnadieu, A. (1985), "Electro-chromic materials", Mat. Sci. and Eng., B3). However, electro-chromic windows are still at an early stage in their development, and it is not yet clear if or when they will be available commercially.
Therefore, although the art has been struggling with the problems described above for very many years, it has so far failed to provide a simple, effective and inexpensive solution to them.
It is an object of the present invention to provide such a solution that overcomes the drawbacks of prior art systems, in a simple and inexpensive manner.
It is a further object of the invention to provide a glazing system which can be adapted for use during summer and winter months, and which exhibits different functional properties, depending on the configuration chosen for a given month.
Other objects and advantages of the invention will be better understood from the description to follow.

Summary of the Invention

The invention is directed to a ventilated glazing system comprising a frame suitable for incorporation in a wall element, which frame houses at least one absorbing and one clear glazing component, said absorbing and said clear glazing components being spaced so as to provide an air space between them, wherein said absorbing and said clear glazing components, together with said frame, create a substantially vertical air conduit through which air can flow from the bottom to the top, or vice versa, said frame being reversible so as to permit to switch the side on which the absorbing and the clear glazing are positioned respective to the wall element.
Additional space heating is provided by long wave radiation from the heated absorbing glass into the space. When the window is rotated so that the absorbing glazing is on the exterior, the short wave solar radiation is absorbed by the absorbing glass and prevents transmission of the short wave through the transparent glass. The long wave radiation emitted is not transmitted to the space on the interior by the transparent glass, which does not permit the passage of light at wavelengths above 4 µm. Preferably, but non-limitatively, the airspace is substantially sealed at the sides.
According to a preferred embodiment of the invention, the frame holding the two glazing components is rotatable. According to another preferred embodiment of the invention, the frame holding the two glazing components is displaceable. In this embodiment, the frame may be slidably or otherwise mounted on an inner fixed frame, and can therefore by easily extracted from it, e.g., by loosening a bolt or a screw, and it can then be rotated independently of the wall element, and re-inserted in the other position into the fixed frame.
According to a preferred embodiment of the invention, the absorbing glazing is installed in a hinged sub-frame, allowing access to the glazing surfaces facing the air channel, for the purpose of cleaning.
According to a preferred embodiment of the invention the window system further comprises a fan, which can be positioned at the top of the glazing components assembly, or at its bottom. The electric fan can be powered by any suitable means, e.g., through connection to the mains, by battery or by solar energy provided, for instance, by a photovoltaic device.
The window assembly can be also rotated by remote or automatic means, and does not necessarily require human intervention. Thus, according to a preferred embodiment of the invention the assembly comprises automatic rotation or switching means for switching the sides of the glazing assembly. As said, the switching means can be remotely operated, or they can be automatically operated by actuating means which are temperature-dependent. Thus, if the temperature gradient between the room and the outside exceeds a predetermined value, the glazing can be rotated so as to obtain the opposite effect.
According to a preferred embodiment of the invention, any segment of the glazing can further be coated with a selective coating of any kind for facilitating or preventing the transmission of selected wavelengths.
Thus, in one aspect, the invention consists of a reversible frame suitable for incorporation in a wall element, holding two glazing components: transparent glazing providing a weatherproof seal, and glazing with a high coefficient of absorption, such as tinted glass. The absorbing glass is fixed at a small distance from the clear glazing, forming a space which is sealed at the sides but open at the bottom and top, through which air can flow freely. The airspace may be ventilated either by thermodynamic forces or by means of a small electric or solar powered fan. The frame holding the two glazing components may be rotated so that the absorbing glazing is either on the interior (for winter use) or on the exterior (during summer). The absorbing glazing is installed in a hinged frame, which allows access to the air channel for cleaning.
In the Winter Mode, the absorbing glazing faces the interior. Solar radiation is transmitted through the clear glazing (which faces the exterior ), and is absorbed by the absorbing glass. The absorbing glass is heated, releasing the energy to the interior by long wave radiation or by convective heating. Space heating is achieved but visual discomfort and damage to furnishings by short-wave solar radiation is reduced significantly.
In the Summer Mode, the opening frame is rotated so that the absorbing glazing faces the exterior. Most of the short wave solar radiation is absorbed by the absorbing glass, and is prevented from being transmitted through the clear glazing to the building interior. While the exterior glazing is heated, the energy absorbed by the absorbing glazing is dissipated to the outdoors by convection or by long wave radiation. The radiation it emits is not transmitted to the building interior by the clear glazing, since it is nearly opaque at wavelengths above 4µm. Space overheating is prevented and visual comfort is improved.
Throughout this description and claims, whenever reference is made to a "window", or "window assembly", it is understood that the same applies, mutatis mutandis, to any other glazed opening in the building envelope, and that the actual shape and size of the opening is not of importance. The invention is not intended to be limited to any particular type or size of glazing system, and any alternative system is thus covered by the claims of the present specification.

Brief Description of The Drawings

In the drawings:
Fig. 1 illustrates a glazing system according to a preferred embodiment of the invention, when in the summer configuration;
Fig. 2 illustrates a glazing system according to a preferred embodiment of the invention, when in the winter configuration;
Fig. 3 illustrates the flow of air in a glazing system according to one preferred embodiment of the invention, in a. the summer mode, and b. the winter mode;
Fig. 4 shows a window frame according to one preferred embodiment of the invention, together with its elements which permit it to rotate between the summer and the winter positions;
Fig. 5 shows the effect of glazing on global radiation (vertical surface parallel to glass), during the summer, in a window system according to a preferred embodiment of the invention;
Fig. 6 shows the room air temperature, in a room fitted with a window system as in Fig. 3b, compared with a reference room, during the winter; and
Fig. 7 shows the convective heat output of a channel of a window system as in Fig. 3b, during the winter.

Detailed Description of Preferred Embodiments

Fig. 1 illustrates a window system according to a preferred embodiment of the invention. Fig. 1A shows a perspective view of the window system, generally indicated by numeral 1, in mounted position within wall element 2, when the absorbing glazing is located on the outside of wall 2.
Fig. 1B shows the same arrangement, in plane front view.
Fig. 1C is a cross-section of the wall element - window system assembly of Fig. 1B, taken along the A-A plane. To the internal part of the wall element 2 there is connected a window frame 3, which supports the window system. Frame 3 must be either rotatable, or symmetric and simple to dismount, turn by 180° and replaced so that the glazing which faced out, faces in after such rotation or remounting.
Numeral 4 indicates the clear glass of the glazing system, while numeral 5 indicates the absorbing glass. An air space 6 exists between glasses 4 and 5, and air may thus circulate between them. If a fan 7 is provided, then air circulation is obtained through forced convection. If no fan is provided, an opening exists instead and air circulation is obtained by natural convection.
Fig. 1D is a top cross-sectional view of the wall element - window system assembly of Fig. 1B, taken along the X-X plane. The various system elements are clearly seen in this figure.
Fig. 2A shows a perspective view of the window system, generally indicated by numeral 1, in mounted position within wall element 2, when the clear glazing is located on the outside of wall 2. Fig. 2B shows the same arrangement, in plane front view.
Fig. 2C is a cross-section of the wall element - window system assembly of Fig. 2B, taken along the B-B plane. To the internal part of the wall element 2 there is connected a window frame 3, as described with reference to Fig. 1B.
Numeral 4 indicates the clear glass of the glazing system, while numeral 5 indicates the absorbing glass. An air space 6 exists between glasses 4 and 5, and air may thus circulate between them. If a fan 7 is provided, then air circulation is obtained through forced convection. If no fan is provided, an opening exists instead and air circulation is obtained by natural convection.
Fig. 2D is a top cross-sectional view of the wall element - window system assembly of Fig. 2B, taken along the Y-Y plane. The various system elements are clearly seen in this figure.
Fig. 3A shows in detail the radiation and air motion in a window system arranged for summer months. Solar radiation 8 incident on the absorbing glass is prevented from penetrating to the interior. As the glass warms up, it emits long wave radiation 9 to the surroundings.. Outside cool air, indicated by thick arrow 10 enters the air space 6, whether by natural convection or, if a fan 7 is present, by forced convection. Heated air, indicated by thick arrow 11, leaves the air space 6, dissipating unwanted energy to the environment.
The situation shown in Fig. 3B is similar to that of Fig. 3A, with the changes deriving from the fact that the direction of the glasses has been reversed for the winter mode. Long wave radiation, 9', which is emitted by the absorbing glass, is now emitted into the room. Cool air 10' from the room enters the air space 6, where it is heated and expelled into the room at the outlet 11'. If forced convection is used, the direction of flow of air in the air space 6 can be reversed, and heated air can be expelled at the bottom, thus contributing to the circulation of air in the room and reducing thermal stratification.
Fig. 4 shows a window frame according to one preferred embodiment of the invention, together with its elements which permit it to rotate between the summer and the winter positions. Fig. 4A schematically shows such an arrangement, in which the window 12 is permitted to rotate within its frame 13, on pivot 14. A handle 15 is also shown.
Looking now at Fig. 4B, a horizontal cross-section of the window assembly is shown, which is taken along the C-C and D-D axes of Fig. 4A. The segments indicated by "M" are part of the fixed frame 13, and the segment indicated by "N" is a part of the rotating frame of window 12. A brush sealing 16 is shown in segment M, which is customary in window assemblies. The glazing 17, already described in detail with reference to Figs. 1-3, is held in place by rubber seals 18. This type of sealing is also customary in the art.
An alternative construction is shown in Fig. 4C, in which two glazings 17 and 17' are provided, which are held in place by sealing elements 18 and 18', respectively.
Fig. 4E is a vertical cross-section of the window of Fig. 4A, taken along the F-F and E-E planes. All the elements seen in Fig. 4B are also seen in this figure, which is self-explanatory. The cross-section of the frame 13, taken along the D-D line of Fig. 4A, is also shown in Fig. 4E, for completeness' sake.
Figs. 5 - 7 show results obtained with a window system according to one preferred embodiment of the invention, as compared with a reference room, in which no such system was present.
The experimental evaluation was carried out in a test building on the campus of the J. Blaustein Institute for Desert Research at Sede-Boker. The building walls were constructed of 20 cm thick hollow silicate blocks. with 5 cm thick polystyrene insulation on the exterior and an acrylic plaster finish, painted white. The roof was a 12 cm thick concrete slab, with foamed concrete sloped to the drains. The building was insulated from the earth by 10 cm polystyrene. Interior finishes included plastered, whitewashed walls and a terrazzo tiled floor.
Each of the test rooms measured 2.7 by 3.5 m, with the long wall facing due south. The experiment was conducted on a large window measuring 1.4 by 2.1 m, at the middle of the south-facing wall. Both rooms were exposed on three sides to the ambient air, with one of the short walls common to a service space in the building interior.
The reference window had a standard aluminum frame, with fixed panes at the bottom and top, and a central section with horizontal sliding panes. The fixed panes were made of hollow polycarbonate sheet glazing, and the sliding panes consisted of 4 mm transparent glass.
In the test window, a second frame made of wood was added, on the exterior of the aluminum frame. This frame held a sheet of dark brown safety glass manufactured by the Phoenicia Co., Israel, model no. 510, parallel to the original glazing, so that an air gap 125 mm wide was formed. The glass was held in place so that openings 10 cm high at the top and bottom of the window assembly allowed free movement of air through this gap. The total thickness of this glass was 8 mm.; it had a visible transmissivity of 9% and a shading coefficient of 42 %.
1) In the summer mode, the original, aluminum-frame window was left in place, and the central, operable panes were sealed shut.
2) In the winter mode, the transparent glazing was removed from the original aluminum frame of the window. Four single-glazed wooden frames with transparent 3 mm glass were attached to the exterior of the wooden frame to create an airtight seal. The air gap formed between the absorbing glazing and the transparent exterior glazing was 50 mm wide, and was open to the test room interior by 10 cm high openings at the bottom and top.
Fig. 5 shows the effect of the glazing system, installed in the summer mode, on the penetration of solar energy into the building interior. Solar radiation was measured with Kipp & Zonen CM5 pyranometers on the exterior of a vertical, south facing wall and inside the building, 20 cm away from the center of the two windows being tested, parallel to the plane of the glass. The data indicate that noon time interior radiation levels were reduced to 5% of exterior levels, compared with 37% for standard 3 mm transparent glazing. Illuminance levels measured at the same time on a horizontal plane at 1 m height above the floor were at least 295 lux.
Fig. 6 shows the effect on room temperature of the glazing system in the winter mode on a typical winter day at Sede-Boker. Temperature was measured near the center of each of the rooms by means of three radiation shielded thermistors at heights of 50 cm, 150 cm and 250 cm above the floor. The temperature in both rooms started to rise at about 08:00, in response to solar energy penetration through the windows, declining in the afternoon, at about 16:00, as the levels of solar radiation decrease. However, the temperature in the test room, equipped with the experimental glazing system, was higher than that of the reference room, where a standard single glazed window was installed, throughout the whole day. The difference ranged from a minimum of about 1°C just before sunshine to a maximum of about 3°C in the afternoon. The difference is attributed to reduced interior reflection of short wave solar radiation during the day, and to reduced loss by conduction at night - the glazing system acted in a manner similar to double glazing, in spite of the air channel being open at the top and bottom.
Fig. 7 shows the direct energy gain produced by the glazing system in the form of warm air. The airflow through the air channel was measured by means of a hot-wire anemometer. The temperature difference between the air at the inlet of the air gap and its outlet, multiplied by the mass flow rate and the heat capacity of air gave the net convective heat output of the system. On a typical sunny day, the peak output was over 400 watts, while the total daily heat gain was approximately 2 kWh.
All the above description of preferred embodiments has been provided for the purpose of illustration, and is not intended to limit the invention in any way. Many modifications can be carried out in the system of the invention: for instance, different types and shapes of glasses can be used, many different air spaces, forced and natural convection arrangements and reversible frames can be used, all without exceeding the scope of the invention.

Claims

A ventilated glazing system comprising a frame suitable for incorporation in a wall element, which frame houses at least one absorbing and one clear glazing component, said absorbing and said clear glazing components being spaced so as to provide an air space between them, characterized in that said absorbing and said clear glazing components, together with said frame, create a substantially vertical air conduit through which air can flow from the bottom to the top, or vice versa, said frame being reversible so as to permit to switch the side on which the absorbing and the clear glazing are positioned respective to the wall element.
A system according to claim 1, characterized in that said airspace is substantially sealed at the sides.
A system according to claim 1, characterized in that said frame holding the two glazing components is rotatable and/or displaceable.
A system according to claim 1, further comprising a fan.
A system according to claim 4, characterized in that said fan is positioned at the top or at the bottom of the glazing components assembly.
A system according to claim 5, characterized in that said fan is powered by solar energy or by electricity.
A system according to claim 4, further comprising automatic rotation or switching means for switching the sides of said glazing assembly.
A system according to claim 7, characterized in that said switching means are remotely operated or automatically operated by actuating means which are temperature-dependent.
A system according to claim 7, characterized in that said glazings are further coated with a selective coating for facilitating or preventing the transmission of selected wavelenghts.