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Particularly in the case of an upcoming renovation, two birds can be killed with one stone: Façade collectors, e.g. as a ventilated façade, enable on the one hand an architecturally high-quality and designable façade with the necessary thermal protection. On the other hand, the collectors can serve as a noiseless source for a heat pump. These synergies usually lead to high cost efficiency.

The number of heat pumps installed in Germany is growing and growing, and with it the knowledge of what is important when switching to a heat pump system. An air-source heat pump is cheap to buy and can be installed almost anywhere. Although the outdoor air units are getting more and more quiet, they are not completely silent and they must be placed somewhere, preferably not next to the neighbour's living room window. This is where the German Technical Instructions on Noise (TA-Lärm) come into play. 
A ground or groundwater heat pump is usually more ecological and more efficient, but you have to have the space and the possibility to drill probes or wells or to lay a ground collector. 
But what to do if this space is not available?
(A publication on source availability can be found here: https://bit.ly/42aPwki)

Architecturally designable fluid-flow façades can offer a visually appealing alternative. Like PVT collectors, these absorb heat from the environment and from the sun and make it available to a heat pump as a source. Depending on the thermal efficiency and temperature level achieved, the heat from the façade elements, or façade collectors, can also be used directly. In a series of research projects, Fraunhofer ISE has developed and investigated elements made of ultra-high performance concrete (UHPC) that can be flowed through.  These elements can form the basis of various façade collectors, but also of thermally active elements in the interior. These TABSOLAR® collectors will soon be used for the first time in a demo building.

UHPC is suitable as a material for façade collectors for various reasons: On the one hand, very high spans can be achieved with low material thickness. The material is also so dense that it is impermeable to water. This means that the fluid channels can be formed directly into the UHPC without additional materials. Good for later recycling. On the other hand, very diverse, fine structuring and different colour shades can be applied to the surface. UHPC is already being used as passive façade cladding.  
Whether these collectors made of concrete can ultimately be the basis for ecologically beneficial and economically competitive systems is something I investigated in my doctoral thesis.

In my thesis, I investigated the energetic and ecological potential of unglazed façade collectors made of UHPC as a source for a heat pump. Using component and system simulation, I determined the electricity demand of different collector and reference systems based on a typical apartment building in Germany. Using a detailed material analysis, I was able to determine the primary energy demand and CO2 emissions over the entire life cycle. I used the ecoinvent database to evaluate all relevant system components.