Experimental Evaluation of the Discharge Coefficient of a Centre-Pivot Roof Window

Windows are a component of naturally ventilated buildings. The scientific knowledge of how to estimate of airflow rates through windows is limited, especially in the case of centre-pivot roof windows. The flow through this type of windows is traditionally characterized by the orifice plate flow equation. This equation involves a discharge coefficient of the window. The value of the discharge coefficient is the major cause of erroneous estimation of airflow rates. This paper focuses on the experimental study of the discharge coefficient (CD) of a centre-pivot roof window. The measurements were performed in the energy flex house of the Technological Institute - Denmark. The discharge coefficient is evaluated for both inflows and outflows. It is concluded that the use of single value of CD for different flap opening angles is one of the cause of erroneous estimation. Likewise, the value of CD for inflows and outflows are not the same for a given pressure difference. The discharge coefficient varies with sash1 opening angle and flow direction.