Double facades: comfort and ventilation at an extreme complex case study

In a Dutch project the double façade became an integral part of the ventilation concepts aa well as the heating system by trying to optimize the heat gain within the cavity during spring and autumn. The study shows how variable facade parameters influence the energy flows coming through the facade, in order to optimize the indoor environment for the comfort of the individual occupant. How can the facade make optimal use of the free incoming energy flows to maximize the comfort level of the individual building occupant at minimal energy use? The type of façade described as a second skin façade is characterised by a single glass layer on the outside and an isolated façade layer on the inside. The application of the single glass layer as a second skin around the insulated layer results in an air cavity between these two layers of around 0.9 m. The property that distinguishes a second skin façade from other DSF is that it relies on natural ventilation of the cavity, in comparison to other facades which use mechanical systems to induce the airflow. The advantage of merely using natural ventilation in the façade cavity is the lower energy consumption. However, it also results in some unresolved issues which require further attention. The researched was focussed the behaviour of the highly complex shaped second skin facade of a Dutch office building, and its thermal comfort impact on the building user. During 3 weeks different measurements were done to determine the main characteristics of the glass and the cavity of the facade. A key difference between a second skin facade, as well as other climate facades, and more traditional opaque facades is its dynamic behaviour. DSF have several adjustable properties, such as the shading device and ventilation mode, and because various physical processes take place in the air cavity, these facades can show very dynamic behaviour. In case of a second skin facade this dynamic behaviour is especially of interest since its cavity airflow merely relies on temperature differences and wind effects to induce the ventilation in the cavity, resulting in very limited control and highly erratic behaviour. The complex form of the facade in combination with the large atrium and exhaust only ventilation of the offices in the case study led to a problematic thermal indoor environment.