Concept for Adaptive Wall Elements with Switchable U- and G-Value

This contribution will present a concept for (translucent) wall elements with switchable U- and g-values. The basic concept of the element consists of an insulation panel (preferably realized by a translucent and light-guiding foam grid or in the future by transparent vacuum glazing) which is arranged inside a glazed closed cavity so that thermally driven convection around the element can either be enabled or suppressed. Supression of convection is realized by a rollable second insulation inside the cavity which can reflect incident solar radiation: If the secondary insulation is fully retracted resulting in high U and g-value and daylight being guided inside the building. By successively rolling down the insulation, convection can be suppressed and the g-value can be varied from almost unchanged to almost zero. In the case of the secondary insulation being rolled fully down, the U-value of the element is also minimal. This state is favourable in a cold winter night or during hot daytime hours in summer. The high translucence, low-U-value case is favourable in conditions where solar gains and good insulation are favourable and the translucent high-U-value case is favourable for example in a summer night to cool the building. In addition to the concept of the wall element, the need for appropriate building control strategies is discussed allowing to make optimal use of the element’s potential to save energy for lighting, cooling and heating. Demonstrators for various design generations are presented. Furthermore, the potential to include further functionalities such as thermal- or electrical energy harvesting from the element’s outer surface is addressed as well.