Dynamic simulations to develop a natural ventilation concept for an office building

The Sustainability Group of the University of Luxembourg defined for their new buildings a
maximum thermal end-energy of 14 kWh/(m3a) and an electricity consumption for HVAC
and lighting below 6 kWh/(m3a). Therefore it was necessary to avoid active cooling loads and
mechanical ventilation in the offices and small lecture rooms.
The well insulated and air-tight façade, including special outside shading elements which were designed as a grid over the complete building envelope, was an essential given architectural element of the building. Therefore further external shading devices were not applicable. The only possibility to have an influence on solar gains was to optimize the window size, the glazing type and potentially an internal shading device. Furthermore, to prevent the risk of overheating during the summer period, it was necessary to reduce the internal gains from lighting and IT-equipment.
Hence detailed dynamic simulations using TRNSYS and TRNFLOW were done to evaluate the thermal comfort without air-conditioning and mechanical ventilation. The effects of optimizations like a state-of-the-art lighting control system or a window-based night ventilation, as well as the influence of the effective thermal inertia of the building were analyzed. The assumed natural ventilation rates were calculated by combining TRNFLOW and TRNSYS simulations and by the software LESOCOOL.