The Double Skin Facade

The largest source of air pollution in North America is the atmospheric boundary layer of a city caused by its urban canyons with pollutants produced primarily by automobiles. The pollution mix is dominated by CO, CO2, NO2, Hc and small particulates. When sufficient sunlight is available, this leads to the development of photochemical smog and secondary pollutants such as VOCs. The removal of air pollutants at the street level is normally dependent upon air temperature stratification. Free flow of the air is important to diffusing the pollution into a larger volume. “The worst conditions for dispersion occur where there is a temperature inversion and the boundary layer is stable. Turbulence is then suppressed and upward motion is effectively eliminated”(Oke 1992). The Double Skin Facade (DSF) is a facade system technology that can not only meet the needs of the building occupants for natural ventilation, thermal efficiencies, and daylighting, but also the DSF can interact with street level ventilation. Computational Fluid Dynamics (CFD) can illustrate the velocity profile for a building without a DSF and with recirculating flow at the street level simulating the boundary layer condition (Fig. 1, left). CFD was used to illustrate the velocity profile for a building with a DSF showing the flow entering through the bottom of the DSF and exiting at building roof level approximately 60 feet (Fig. 1, right).

The double skin facade can increase flow at the street level and enhance mixing at the urban boundary layer, which will assist in the evacuation of criteria air pollutants from urban canyons. This interdisciplinary approach yields the promise and expression of a building facade that serves a functional purpose beyond aesthetics, natural ventilation, daylighting, and thermal efficiency, which presents a transformative approach to building design.