An innovative facade element with controlled solar-thermal collector and storage

A novel façade element is presented that forms a symbiosis of an enhanced box-type window, a closed cavity façade, and a Trombe wall. This hybrid transparent-opaque façade element features an absorbing water tank, that is installed behind a controlled shading device towards the cavity of a non-ventilated Double Skin Façade in the parapet section. To evaluate the potential impact on building performance, a transient simulation model is developed in Modelica, and calibrated by comparison with measurements on a prototype. The effect of the absorbing thermal storage on heat transfers under solar radiation is analyzed in comparison to i) conditions excluding solar radiation and ii) an empty tank. An evaluation for four European cities demonstrates that the annual heating demand can be reduced by more than 4.2%, and cooling demand by at least 6.6 % compared to a façade without thermal storage. The effect is explained not only by the increased thermal mass, but the effective modulation of solar gains by the controlled absorbing storage. The dampening of heat flow fluctuations, and the control of solar gains is a promising means to reduce installed power of HVAC installations.