Large openings such as doorways or windows are privileged places through which a large amount of air, heat and pollutant species flows. In order to predict air flow rates through these systems, a physical model which can be integrated to multizone air flow models is proposed. This model is based on the empiric determination of discharge coefficients. The discharge coefficients may have different definition depending on the hypothesis of the selected model. In order to answer that indetermination we first present the experimental facility built in a thermally controlled environment set up in CETillL, to discuss afterwards the first results obtained.