Transparent thermal insulation

Fig. 7: Dietrich Schwarz: house in Domat/Ems (CH), 1996

Direct gain system

The transparent thermal i nsulation is employed as an enclosing element without any wall behind. It is therefore similar to a light-permeable but not transparent window element or glass facade. The solar radiation passes through the transparent thermal i nsulation directly into the interior and is converted into heat at the various surfaces within the interior. The interior temperature changes almost simultaneously with the temperature of the surfaces. Therefore, in summer fixed or movable sunshades must be provided in order to prevent overheating in the interior.

Fig. 7: Dietrich Schwarz: house in Domat/Ems (CH), 1996

Incident solar radiation

Heat losses

Heat gains

Heat gains

Conventional insulation

Dissipation and reflection

Dissipation and reflection

Incident solar radiation

Heat losses

Heat gains

Absorber Transparent thermal insulation

Fig. 8: Transparent thermal insulation

Heat gains

Absorber Transparent thermal insulation

Fig. 8: Transparent thermal insulation

Fig. 9: Wall construction with transparent thermal insulation

Definition

Transparent thermal i nsulation functions only in conjunction with glass, which protects the i nsulation from the weather and, thanks to its transparency, admits daylight and especially solar radiation. Inside the building the light is converted into heat and contributes to the space heating requirement. In addition, transparent thermal i n-sulation reduces heat losses from inside to outside and therefore functions as a thermal i nsulation. In contrast to the majority of customary insulating products, this material also very frequently remains visible from the outside behind a pane of glass. Transparent thermal i nsulation elements are also permeable to wavelengths of the solar spectrum other than visible light and do not necessarily have to employ clear glass.

Construction (from inside to outside):

- Protective layer of glass

- Layer of insulation comprising transparent thermal i nsulation elements (dense, honeycomb-like capillary structure of transparent plastic)

- Protective layer of glass or solid i oadbearing layer, or rather absorber

How transparent thermal insulation works

Three principal forms gradually appeared in the evolution of applications for transparent thermal i nsulation. These can be distinguished according to the way in which the solar energy is used.

Fig. 10: Direct gain system

Solar wall

In the solar wall system the incident solar r adiation is converted into heat on the outside face of a solid external wall. Controlled by the insulating effect of the transparent thermal insulation material, the heat energy flows through the wall to the inside face and is then radiated into the interior. Fluctuations in the outside temperature are tracked internally but with a delay. This delay can be influenced by the material and thickness of the wall.

Thermally decoupled system

In the thermally decoupled system the incident solar radiation is converted into heat at an absorber surface isolated from the interior. The heat is fed either directly into the interior via a system of ducts, or into a heat storage medium, which can be part of the building itself (e.g. hollow floor slab or double-leaf wall), or part of the building services (e.g. pebble bed or water tank). With thermally isolated storage media the release of heat into the interior can be controlled irrespective of the absorber or storage temperature.

Fig. 11: Solar wall

Fig. 12: Thermally decoupled system

Fig. 10: Direct gain system

Fig. 11: Solar wall

Fig. 12: Thermally decoupled system

Incident solar radiation

Heat losses

Incident solar radiation

Heat losses

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