DE19629237A1 - Shade for building elements such as solar collectors, building fronts, windows - Google Patents

Abstract

A double layer (1,2) moves in one direction as a result of a higher temperature. A movable optical layer, positioned in front of the building element being shaded, is at least partly transparent, reflective or absorbent and has the same surface area as the building element being shaded. The double layer consists of a plastic sheet (1) stretched on one axis, and a sheet (2) of the same or similar material, such as polyamide, unstretched r stretched on two axes. Alternatively the sheet is made of reflective metal foil or an insulating layer. the optical layer is stuck to the layer (1) itself.

Description

1. Technical field of application

The invention relates to a device for temperature-dependent shading of components, e.g. B. solar collectors and building parts, TWD facades, fen window or window elements; one achieves overheating protection with too high solar radiation.

A second application is that of daylight control for window elements. A 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 developed with thermal components such as solar collectors and house facades transparent thermal insulation (TWD), as well as the trend towards "glass Architecture "ushered in, with generously dimensioned special windows or Daylight elements. In the meantime, the efficiency levels achieved are so good that For times of high irradiation, special devices are required to ensure high temperatures avert damage 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 permanent and therefore expensive materials are used (metal, glass, wood). With Series production of Kollekto is moving towards the availability of suitable technology plastic within reach, combined with a considerable drop in prices per m² of installed area.

Shading systems are used in facades and windows. An over view offers z. B. the contribution "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 from Eastern Bavaria technology transfer institute (OTTI). Tab. 1 shows a classification conceivable measures.

Static shading systems reduce the total yield considerably Dimensions or have a very small switching stroke. Dynamic systems on mechani They are expensive to buy and maintain; they also hold a high Default risk. Switchable layers (electrochromic, thermochromic, thermotropic) be can still be found in the F phase; a number of questions and problems in Zu connection with efficiency, switching stroke, long-term stability and series production are still unsolved.  

Table 1

Overview of shading measures

2.2 Light control

Pure shading is often undesirable in the window area. Diffuse light, like it z. B. offers an overcast sky, should be as unhindered as possible in the room. Direct sunlight, however, should, especially in the warm season largely reflected, partly for glare-free room lighting to care.

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

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

3. Structure of the thermal light switch (TLS)

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

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

The thermally active double layer ( Fig. 1) consists of two plastic layers ( 1 and 2 ), e.g. B. a combination of uniaxially stretched polyamide film ( 1 ) and a normal, (ie 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 concept of the switching element (see §4).

Uniaxially stretched plastics ( 1 ) have the property of increasing their constant elasticity in the stretching direction when heated (due to the temperature-dependent entropy elasticity) and thus shrinking in one direction. The isotropic layer ( 2 ) reacts only weakly to the heating. Thus, the double layer shows a voltage across the surface when the temperature changes, which changes the cylindrical curvature (principle of the bimetal thermometer). In this arrangement, a weak and thus fully reversible contraction in length 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, above normal, below overheated.

A sufficient deformation for the application over a length in the range 1-3 cm is particularly advantageous due to an extreme "mismatch", the linear expansion to achieve coefficient of performance of the two materials. But would the same high "mismatch" is also present in the transverse direction (as with the classic bimetal Element), then this geometry would not produce the desired bend but an uncontrollable shrinking.

The ontic 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.

Geometry and arrangement of the TLS element is such that the overall system in heated state absorbs less sunlight than when 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 strength and modulus of elasticity are selected so that they can maintain a horizontal rest position ( Fig. 2a), but at the same time can be bent into the shape ( Fig. 2b) without leaving the elastic stretching range . 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; but since modulus of elasticity and creep resistance in the transverse direction are much smaller than 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 overheat If necessary, keep away from the application. The arrangement of foil and backing gerprofil ensures that the light deflection be a single reflection may. This is important because of the small but inevitable Ab sorption 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 disc 3 is the outer pane of a window or collector torsion and the carrier 4 , 5 with the double membrane 1 , 2 are 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 placed in front of the Absorber itself can be attached.

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

When used as automatic daylight control ( Fig. 3), the TLS element is equipped with an optically active layer that partly reflects and partly absorbs. In the normal state (no direct sunlight) las sen, the elements most of the incident light to pass (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 to 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, it can be attached to the front or the back Double glazing show advantageous effects. Front mounting can lead to thermal coupling to the variable outside temperature, back fixation couples to the (almost) constant internal temperature.

If the TLS elements are manufactured as long, narrow elements (e.g. as strips, the length of which extends across the entire window width, the slats of which are less than 1 mm and the mutual distance of which is less than 2 mm), there is also increasing transparency possible, and thus for use at 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 in that the strips are only partially reflective or absorbent (for example 30-80%) and instead transmit the rest of the light.

An arrangement of the TLS elements transverse to the direction of natural convection, as shown in Fig. 3, can contribute to reducing the k-value, e.g. B. inside of double windows or 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. E.g. are uniaxially stretched polyamide films (15 µm thick) or polypropylene (40 µm thick) state of the art. The association with the second Layer can e.g. B. by coextrusion, gluing or simple adhesive adhesion (e.g. with paints).

The optically active component can be coated with a reflective aluminum processing (e.g. vapor deposition). It is also sufficient for non-critical applications a milky film. If the optically active component is to absorb, ei ne dark coloring 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 determined by the The degree of stretching of the anisotropic layer can be set within wide limits.

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

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. B. reflective leads out, it will produce a small shadow area in normal operation, in the overheated state. The ratio of these two areas is the optical switching stroke.

An essential feature of the invention is therefore the use of anisotropic materials lien. Ideal are z. B. uniaxially stretched polymer films as inner film: in Reckrich  they are hard (high modulus of elasticity) and have large, negative expansion coefficients targeted. In combination with e.g. B. aluminum foils (small, positive coefficients) there is a high "mismatch".

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

6th embodiment

Elements of the type outlined in Fig. 1 were produced by combining a standard self-adhesive, reflective-coated film with a uniaxially stretched polyamide film. When the temperature changed, they showed a reversible change in shape according to the prediction. (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, components or Isolate solar collectors, the latter z. B. at night or wind, and components in Winter. The double layer must then usually be turned through 180 ° be so that to isolate the insulation from the increased temperature the surface is moved away.

Claims (9)

1. Device for temperature-dependent shading of components, for. B. solar panels and building parts, TWD facades, windows or window elements, and / or for light control through window elements, characterized in that a movable layer due to higher temperature in at least one direction bare double layer ( 1 , 2 ) and one by means of the same before shading component ( 3 ) movable optical layer is provided, which is at least partially either transparent or reflective or absorbent and has an area as large as the component to be shaded, the double layer ( 1 , 2 ) made of a uniaxially stretched plastic film ( 1 ) and an unstretched or biaxially stretched film ( 2 ) of the same or a similar material, e.g. B. Po lyamide, or the film ( 2 ) consists of a reflective metal foil or an insulating layer. 2. Device according to claim 1, characterized in that on the layer ( 1 ) itself the optical layer ( 4 ) arranged, for. B. ge sticks, evaporated or applied by adhesion. 3. Device according to claim 1, characterized in 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 in that the double layer ( 1 , 2 ) curls under the influence of temperature and / or horizontally or vertically in front of the element to be shaded ( 3 ) be movable. 5. Device according to claims 1-4, characterized in 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 multiple facilities in horizontal or vertical or in arrayan regulation are provided. 8. The device according to claim 1, characterized in that when used in solar collectors as a second layer ( 2 ) an isolating layer is provided and the double layer ( 1 , 2 ) is angeord net such that the double layer of the to isolate upon exposure to temperature Element is moved away and comes to rest on the element to be insulated without the influence of temperature. 9. Use of a device according to claims 1-8 for convection suppression in solar collectors or in the space of double windows.