Active envelopes - essential in urban areas?

Today, the development of new technologies to improve building envelope performances ishighly encouraged and provides a clear challenge for designers and researchers. In thiscontext several typologies of active envelopes have become very popular. The paper startswith an overview of the history and the performances of active envelopes in the context ofurban design. With these considerations in mind we will analyse the performance of the activewindow system of the DVV-headquarters downtown Brussels.This paper presents experimental data and a model to quantify the physical properties ofactive envelopes. The experiments clearly demonstrate that workmanship and design have animportant impact on the results: the performances, predicted at the design stage, are notalways achieved after construction. For instance the DVV Case Study reveals that airtightnessand the use of frames with thermal break are extremely important. The attention is also drawnto the importance of a correct split between the convection and radiation when predictingthermal performance, the unclear meaning of the equivalent U-value and the Solar Heat GainCoefficient and the importance of the absorption of short wave radiation in the cavity.