Energy saving potential of night ventilation: Sensitivity to pressure coefficients for different European climates

The suitability of night ventilation to reduce the cooling demand in buildings can be evaluated by coupling Airflow Network Models to Building Energy Simulation tools. To estimate wind-induced ventilation, pressure coefficients (Cp) on the building envelope are key inputs, as well as local wind speed and direction. Cp data obtained by primary sources such as measurements or CFD simulations are considered the most reliable but can be difficult to obtain. An easy alternative are Cp secondary sources, such as databases providing literature data correlations. Therefore an issue arises regarding the choice of the source of pressure coefficients. This paper investigates the effects of Cp from primary and secondary sources on the predicted energy saving potential of night ventilation of an isolated office building for several European climates and some relevant design conditions and simulation parameters. Different Cp sources produce a dispersion of Cp data and differences in the calculated night ventilation rates up to 15%. Contrary to what might be expected, these differences influence only marginally the resulting passive cooling effects. Overall a stronger impact is observed for the colder climates, where higher temperature differences occur between desired indoor temperature and night-averaged outdoor temperature. Finally, for the building under study, the choice of the Cp source appears less crucial than the choice of other building simulation parameters, such as the internal Convective Heat Transfer Coefficient. This study can support building designers towards accurate energy simulations of naturally ventilated buildings.