On-site assessment of the discharge coefficient of open windows

•In situ discharge coefficients of windows were measured with the flow driven by a fan and by wind.•A good agreement was obtained with the two methods.•The discharge coefficient of a side-hung casement window ranged from Cd=0.41 to Cd=0.81.•The discharge coefficient of a bottom hung casement window was Cd=0.84.•The impact of Cd of a roller shutter on a side-hung casement window was analysed.