Translucent wall elements with switchable U ‐ and g ‐value

This contribution will present a concept for translucent wall elements with switchable U ‐value and g ‐value. The basic concept of the element consists of an translucent 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 in a way that thermally driven convection around the element can either be enabled or suppressed. Suppression of convection is realized by a rollable second insulation which at the same time is reflecting incident solar radiation: If the secondary insulation is fully retracted resulting in high U ‐value 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 winter. 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 when no strong energetic separation of interior and exterior conditions is needed. While the rollable insulation element is a rather delicate structure, it nevertheless can be used as a shading device independent of external wind conditions as it is safely housed inside the glazed wall element. In addition to the concept of the wall element, the need for appropriate building control strategies allowing to make optimal use of the element's potential to save energy for lighting, cooling and heating and demonstrators for various design generations of the element are discussed. Furthermore, the potential for including further functionalities such as harvesting thermal or electrical energy from the element's outer surface is addressed as well.