Thermally active rear-ventilated façades: Numerical modelling and experimental validation

Thermally activated façades represent a promising approach to assist or substitute conventional heat pump sources such as air or geothermal energy and therefore enable the use of non-fossil heat generation for buildings. Rear-ventilated façades have a beneficial structure for thermal activation. The design and optimization of such façade systems require simulation models, that are able to predict their thermal performance for various geometries and materials. Modeling approaches so far are limited to only specific designs and applications. Furthermore, there are no suitable models for the interaction between the thermally activated cladding elements and the ventilation space of rear-ventilated façades. In this paper a general approach for the numerical simulation of thermally activated façades is presented and experimentally validated. The modelling approach is based on finite element simulations of the thermally activated façades. It enables the estimation of the thermal performance for a wide range of geometries, materials and design methods with short computational times. Additionally, we carried out measurements on a large-scale thermally active test façade and characterized the heat transfer mechanisms in the ventilation space in order to accurately describe the thermal behavior of activated rear-ventilated façades. We compared the simulation results to the results of laboratory performance measurements of 6 different single-module façade prototypes with varying designs and materials to validate the simulation model. The performance curves from the simulation and measurement showed a good agreement and the expected annual gross thermal yield at an operating temperature of 15°C could be reproduced with a deviation of less than 3.5 % for 5 out of 6 prototypes. In a second step, we carried out the comparison for the large-scale active test façade under real weather conditions and with the previously characterized model for the heat transfer in the ventilation space. Again, the performance curves between simulation and measurement showed a good correspondence. The simulation predicts the annual gross thermal yield from the measurement with an absolute deviation of less than 10 kWh/m 2 a and a relative deviation of less than 6 % for operating temperatures of 0°C, 15°C and 30°C.