One facade, three functions, and a new way to measure all of them

A prefabricated timber facade that integrates heating, cooling, and ventilation in a single modular unit can reduce its effective thermal transmittance by more than two thirds compared to the same assembly without active components. That is one of the findings of a new study by researchers at Eurac Research's Institute for Renewable Energy, in collaboration with the Faculty of Engineering at the Free University of Bozen-Bolzano, Ecoloop, and MCI – The Entrepreneurial School in Innsbruck, published in the journal Buildings.

The facade in question belongs to a category of active prefabricated systems designed for the energy renovation of existing buildings. Rather than relying solely on insulation, these assemblies embed an HVAC unit directly within the facade structure, delivering fresh air, heat recovery, and space conditioning without requiring invasive work inside the building. While such systems have attracted increasing research interest over the past decade, their thermal behavior as complete assemblies had not been rigorously characterized before.

To fill that gap, the team built a full-scale prototype of the facade at the Facade System Interactions Lab of Eurac Research in Bolzano and monitored it over six months under real outdoor conditions. The experimental data were then used to develop, calibrate, and validate a three-dimensional finite element model in COMSOL Multiphysics, tested against measurements from winter heating, summer cooling, and HVAC-off scenarios. The model achieved a mean absolute error below 0.6 K at all 10 surface temperature measurement points across all three validation cases.

"The standard methods we use to evaluate wall thermal performance were designed for static, passive building elements. An active facade behaves differently depending on its operating conditions, and that complexity needed to be addressed with both experimental rigor and a new way of expressing performance," said Ingrid Demanega, researcher at Eurac Research and co-author of the study.

Because the facade is intended for retrofit applications on buildings with widely varying existing wall constructions, the team extended the analysis to five different existing wall thermal resistance values and subdivided the facade surface into characteristic areas — supply duct zone, recirculation/return duct zone, HVAC unit zone, and passive undisturbed area — each assigned its own performance indicator. This subdivision forms the basis of a simplified calculation tool, HeTheP (Heating Thermal Performance), designed to support practitioners in design workflows.

The research was carried out within the EU Horizon 2020 INFINITE project (Grant Agreement 958397).