Researchers at the Fraunhofer Institute for Solar Energy Systems have developed a solar thermal facade element. The heat collected with it is used to raise the flow temperature for air-water heat pumps. The background to this is the fact that these heat pumps require an outdoor unit. This is either located next to the building or - in the case of multi-storey residential buildings, for example - integrated into the facade.
Architectural aesthetics
However, not all properties have space for such an outdoor unit and integration into the facade is aesthetically questionable. The developers at Fraunhofer ISE have solved this problem with their heat collectors.
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These consist of an ultra-high performance concrete (UHPC) and can be architecturally designed as glazed or unglazed facade cladding elements. The elements are criss-crossed by channels through which a solar fluid flows. There, the heat from the sun and the environment is collected and transferred to the heat pump circuit via a heat exchanger.
Collecting more heat
The multiple branched fractal structure of the channels increases the amount of heat that can be collected. This reduces the amount of energy that the heat pump has to expend to raise the temperature of the heat source to the necessary temperature of the heating circuit. It also means that any shape can be provided with a uniformly flowing duct network. "According to our simulations, the available facade areas in new buildings or renovated existing buildings can be sufficient for this purpose," says Michael Hermann, head of the research project at Fraunhofer ISE.
Two different variants developed
Together with industrial partners, the Freiburg researchers have also developed a manufacturing process based on a membrane vacuum thermoforming process. They can be prefabricated and integrated into ventilated curtain facades and, in the future, also into thermal insulation systems or sandwich panels. They are planned in two different versions. An unglazed version is suitable as a heat pump source, for domestic hot water preheating or for swimming pools.
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Similar to conventional facade elements made of UHPC, it can be freely designed in terms of structuring and colour. The glazed elements are additionally provided with spectrally selective layers. Similar to classic solar thermal collectors, they are then suitable for domestic hot water heating and heating support, as they reach higher temperatures. (su/mfo)
