WO1997004207A1

WO1997004207A1 - Device for providing shade for construction elements as a function of the temperature

Info

Publication number: WO1997004207A1
Application number: PCT/EP1996/003194
Authority: WO
Inventors: Harry Wirth
Original assignee: Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V.
Priority date: 1995-07-21
Filing date: 1996-07-19
Publication date: 1997-02-06
Also published as: DE19629237A1; DE19629237C2

Abstract

The invention concerns a device for providing, depending on the ambient temperature, shade for construction elements such as solar collectors and parts of buildings, e.g. transparent thermal-insulation facades, windows or parts of windows, and/or for guiding light through parts of windows. The device has a double layer (1, 2, 3) which moves in at least one direction when the temperature rises and an optical layer (4) which is moved by the double layer in front of the construction element to be shaded, at least part of the optical layer being transparent or reflecting or absorbing and the area of the optical layer being as large as the construction element to be shaded.

Description

DESCRIPTION

Device for temperature-dependent shading of components

1 . Technical application area

The invention relates to a device for temperature-dependent shading of components, e.g. Solar collectors and parts of buildings, TWD facades, windows or window elements; one achieves overheating protection in the event of excessive solar radiation.

A second application is that of daylight control for window elements. Another application is the insulation of solar collectors.

2. State of the art and current problems

The energetic potential of the sun as a source of heat and light has stimulated the development of thermal components such as solar collectors and house facades with transparent thermal insulation (TWD), as well as ushering in the trend towards "glass architecture" with generously dimensioned special windows or daylight elements. In the meantime, the efficiencies achieved are so good that, at times when there is a high level of irradiation, special devices are required in order to avert high temperatures and possible damage to the system. 2.1 OVERHEATING

There is currently no suitable device for protecting solar collectors against overheating; therefore only high temperature-resistant and therefore expensive materials (metal, glass, wood) may be used in the entire structure. With the availability of a suitable technology, the series production of plastic collectors is within reach, combined with a considerable drop in prices per square meter of installed space.

Shading systems are used in facades and windows. An overview of this offers e.g. the article "Shading Devices on Buildings - Optical and Thermal Effects" by A. Raicu, H.R. Wilson and V. Wittwer from the "Innovative Lighting Technology in Architecture" series of the East Bavarian Technology Transfer Institute (OTTi). Tab. 1 shows a classification of conceivable measures.

Static shading systems reduce the total yield considerably or have a very low switching stroke. Dynamic systems on a mechanical basis are expensive to purchase and maintain; they also harbor a high risk of failure. Switchable layers (electrochromic, thermochromic, thermotropic) are still in the R&D phase; a number of questions and problems relating to efficiency, switching stroke, long-term stability and series production are still unsolved.

Shading systems

STATICALLY DYNAMIC

Switching effect through switching effect due to change outside the system

independently controlled externally

Blinds

Roof overhang Vegetation Roller blinds immobile slats thermotropic layer movable slats

Mirror profiles TLS electrochromic layer

Liquid crystals

Tab. 1: Overview of shading measures

2.2 CONTROL OF LIGHT

Pure shading is often undesirable in the window area. Diffuse light, e.g. offering an overcast sky should enter the room as freely as possible. Direct sunlight, on the other hand, should be largely reflected, especially in the warm season, and in part should ensure glare-free room lighting.

The demand for active light-directing window elements is great, but the products currently available can only ever meet part of the requirements. Electrically adjustable slats are complex, simple infrared-active coated panes cannot react to different irradiation conditions.

The object of the invention is to provide a device for shading solar collectors, parts of buildings, windows or window elements or for To create light control for window elements that does not require external energy, reacts automatically and is easy to implement. According to the invention, this object is achieved by claim 1. Advantageous configurations of the device are characterized in the subclaims.

3. Structure of the thermal light switch (TLS)

The intended large-area switching effect is achieved through the collective switching process of many neighboring TLS elements.

A TLS element consists of a thermally active double layer and an optical component.

The thermally active double layer (Fig. 1) consists of two plastic layers (1 and 2), e.g. a combination of uniaxially stretched polyamide film (1) and a normal (i.e. unstretched or 2-axis stretched) film of the same material (2). The two layers stick together. Whether the double layer is transparent, reflective or absorbent depends on the overall design of the switching element (see §4).

Uniaxially stretched plastics (1) have the property of increasing their constant elasticity in the stretching direction when heated (because of the temperature-dependent entropy elasticity) and thus shrinking in one direction. The isotropic layer (2) reacts only weakly to the heating. Thus, when the temperature changes, the double layer shows a voltage transversely to the surface, which changes the cylindrical curvature (principle of the bimetal thermometer). In this arrangement, a weak and thus fully reversible length contraction of the layer (1) is sufficient to change the shape of the element to a large extent. Fig. 1 shows the principle of thermoelastic deformation, the normal state at the top and the overheated state at the bottom. A deformation over a length in the range 1-3 cm which is sufficient for the application can be achieved particularly advantageously by an extreme "mismatch" of the coefficients of linear expansion of the two materials. However, if the same high "mismatch" were also present in the transverse direction (as in the classic bimetallic element), this geometry would not result in the desired curvature, but in an uncontrollable shrinkage.

The optical component is deformed or moved by the deformation of the thermally active double layer. Deformation is achieved when the thermally active double layer (Fig. 1) is given an additional reflective or absorbent coating. Movement is achieved when the thermally active double layer has an extension that does not deform itself, but changes its orientation due to the deformation of the double layer. This extension can be an extension of the layer (1) or the layer (2) from Fig. 1, or consist of another plastic or metal. The extension is reflective or absorbent coated or formed. However, it is advantageous if the entire surface curves in one direction, as shown in Fig. 1.

The geometry and arrangement of the TLS element is such that the overall system absorbs less sunlight when heated than when it is cold.

Fig. 2 shows a self-regulating sun protection system. Rectangular profiles 4 with strings 5 form the carrier. The strips 6 are aluminum foils, the thickness and modulus of elasticity of which are selected so that they can maintain a horizontal rest position (Fig. 2a), but at the same time get into the shape without leaving the elastic stretching range (Fig. 2b ) let it bend. Uniaxially stretched plastic foils are laminated on the underside of the aluminum foils. These contract when the temperature increases in the stretching direction and deform the aluminum foil elastically (Fig. 2b). In the stretching direction, these plastic films show a modulus of elasticity that is many times higher than in the transverse direction or in the unstretched state; the tendency to creep is also reduced dramatically. With these requirements, the aluminum foil can be held in the curved shape for a long time. In the transverse direction, the stretched film shows a different thermal expansion than the aluminum film; since the modulus of elasticity and creep resistance in the transverse direction are much smaller than in In the longitudinal direction, the stretched film adapts to the thermal expansion of the aluminum film in the transverse direction and the deformation of the laminate proceeds as desired.

Due to the deformation at elevated temperature, sunlight can be kept away from the application in the event of overheating. The arrangement of the film and the carrier profile ensures that the light deflection requires only a single reflection. This is important because of the slight but inevitable absorption and self-heating of the film.

In the absence of insolation and low outside temperatures (winter, at night), the laminate cools down to such an extent that it deforms in the opposite direction (Fig. 2c). The aluminum foil thus reduces the heat radiation exchange between the interior and the cold outer pane and thus improves the k-value of the arrangement.

Advantageously, the pane 3 is the outer pane of a window or collector and the supports 4, 5 with the double membrane 1, 2 are located in the space between the outer pane and the inner pane, not shown.

4. Properties of the thermal light switch

In the case of the collector, the reflective TLS elements can also be attached in front of the absorber itself.

When used in the window area (e.g. overhead glazing), the absorber is replaced by a second glass pane, in the case of the building facade the wall is arranged instead of the absorber or e.g. a transparent thermal insulation wall in front of the facade.

When used as automatic daylight control (Fig. 3), the TLS element is equipped with an optically active layer, which partly reflects and partially absorbed. In the normal state (no direct sunlight), the elements allow a large part of the incoming light to pass through (Fig. 3a). However, if the sun is shining, the partial absorption of the optically active layer leads to heating of the element. As a result, the element changes into the heated state; the new shape (Fig. 3b or Fig. 3c) reflects partly on the ceiling, which creates an advantageous light distribution in the room, and partly on the outside, giving off excess energy.

Depending on the objective, an attachment to the front or rear pane of the double glazing can have advantageous effects. Attachment at the front can lead to thermal coupling to the variable outside temperature, rear fastening couples to the (approximately) constant inside temperature.

If the TLS elements are produced as long, narrow elements (for example as strips, the length of which extends over the entire window width, but whose slat widths are less than 1 mm and the mutual distance of which is less than 2 mm), it is also increasingly possible to see through and therefore an application for windows at eye level. The smaller the width, the less the straight view through the strips is disturbed (Fig. 3a); ideally, they are only visible as lines to an observer near the window. A further improvement in transparency can be achieved by reducing the contrast, for example by only partially reflecting or absorbing the strips (e.g. 30-80%) and transmitting the rest of the light.

An arrangement of the TLS elements transversely to the direction of natural convection, as shown in Fig. 3, can contribute to reducing the k value, for example in the interior of double windows or of solar collectors. 5. Manufacture of the thermal light switch

The uniaxial stretched layer can be provided as a film or fiber; many standard thermoplastic plastics such as polyethylene or polypropylene can be stretched. For example, are uniaxially stretched films made of polyamide (15 // m thick) or polypropylene (40 μm thick) state of the art. The bond with the second layer can e.g. through coextrusion, gluing or simple adhesive adhesion (e.g. in the case of paints).

The optically active component can be produced by a reflective aluminum coating (e.g. vapor deposition). A milky film is also sufficient for non-critical applications. If the optically active component is to absorb, a dark color is used.

Adhesion to the pane is achieved with glue, or with light manufacturing of the elements by (independent) adhesion, or as shown in Fig. 2.

The extent of the thermal deformation and the switching point can be set within wide limits by the degree of stretching of the anisotropic layer.

The shape of the element in the normal state can be determined by thermoforming.

Insulated elements as well as elongated strips of approx. 1 - 5 cm can be used as geometry. By appropriately orienting the layers, the shape change for special applications can be extended to two dimensions, comparable to opening a flower (see Fig. 5). Such an arrangement increases the optical switching stroke. If the TLS element e.g. is designed to be reflective, it will produce a small shadow surface in normal operation and a large shadow surface in the overheated state. The ratio of these two areas is the optical switching stroke.

The essential feature of the invention is therefore the use of anisotropic materials. For example, uniaxially stretched polymer films are ideal as the inner film: in stretching they are hard (high modulus of elasticity) and have large, negative expansion coefficients. In combination with eg aluminum foils (small, positive coefficients), a high "mismatch" results.

In the transverse direction they have positive coefficients of expansion and are "soft" so that they can (as required) follow the expansion of the outer film without tension and there is no transverse deformation.

6th embodiment

Elements of the type outlined in Fig. 1 were produced by combining a commercially available self-adhesive, reflective-coated film with a uniaxially stretched polyamide film. When the temperature changed, they showed a reversible change in shape as predicted. (The last developed model showed no irreversible deformation after any of the tests; it only occurs at very high temperatures, e.g.> 100 ° C, when the material begins to soften.)

The device can also be used according to claim 9 to isolate components or solar collectors, the latter e.g. at night or wind, and components in winter. The double layer must then generally be arranged turned through 180 °, so that the insulation is moved away from the surface to be insulated when the temperature is increased.

Claims

claims

1. Device for temperature-dependent shading of components, e.g. Solar collectors and building parts, TWD facades, windows or window elements, and / or for directing light through window elements,

characterized,

that a double layer (1, 2) which can be moved in at least one direction as a result of the higher temperature and an optical layer which can be moved by means of the same in front of the component (3) to be shaded is provided, which is at least partially designed to be either transparent or reflective or absorbent and has the same area as the component to be shaded, the double layer (1, 2) consisting of a uniaxially stretched plastic film (1) and an unstretched or biaxially stretched film (2) of the same or a similar material , e.g. Polyamide, or the film (2) consists of a reflective metal film or an insulating layer.

2. Device according to claim 1,

characterized,

that the optical layer (4) itself is arranged on the layer (1), for example glued, vapor-deposited or applied by adhesion.

3. Device according to claim 1,

characterized ,

that the optical layer is an extension of one of the two layers (1, 2,) or of another material.

4. Device according to claim 2,

characterized,

that the double layer (1, 2) curls under the influence of temperature and / or can be moved horizontally or vertically in front of the element (3) to be shaded.

5. Device according to claim 1-4,

characterized ,

that the double layer is approximately as long as the width of the component (3), but is only a width of 1 to 5 cm.

6. Device according to claim 5,

characterized,

the width is only up to 2 mm.

7. Device according to claim 1-6,

characterized,

that several devices are provided in a horizontal or vertical or in an array arrangement.

8. Device according to claim 1,

characterized,

that when used in solar collectors, an insulating layer is provided as the second layer (2) and the double layer (1, 2) is arranged in such a way that, when exposed to temperature, the double layer is moved away from the element to be insulated and without the effect of temperature the element to be isolated comes to rest.

Use of a device according to claims 1-8 for convection suppression in solar collectors or in the space between double windows.