Designer’s façade: new concepts of solar building envelopes
Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings.
With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections.
The first product concept consists of strip-shaped heat pipe collectors which are variable in length and which can be attached flexibly. The heat pipe concept is designed to enable all alignments, including in the horizontal direction. Due to the particular connection to the heat collector, researchers anticipate that a reduced thermal resistance will be possible. The collector connection is provided in the form of a heat pipe which engages in a form-fit manner with a corresponding extruded collection duct.
It also enables an infinitely variable, flexible distance of the individual heat pipes, thus further contributing to the individualization of the application. “The strip collector combines a high level of efficiency with architectural design diversity”, says Dr.-Ing. Christoph Maurer, Head of Team Solar Thermal Facades, at Fraunhofer ISE. “Classic materials such as wood or plaster, structures and colours can be used in the area between the glazed collector strips.”
The second product concept is a solar thermal blind which for the first time enables the energetically optimal regulation of the energy flows through the façade. In order to achieve this effect, blind slats can be used with spectral selective coating. Heat is transported via a heat pipe from the slat to the side collection duct. If external blinds are not required or are not possible, blinds are already now being inserted between two glass panes. “These blinds reach high temperatures, which increase the cooling requirement of the building. The solar thermal blinds can move just as freely as a normal blinds, but at the same time, they deliver heat and reduce the amount of energy entering the interior of the building”, says Maurer.