Flow resistance for different types of windows in the case of buoyancy ventilation

• Measured mass flow rates are theoretically examined by the Bernoulli equation.
• Flow resistance coefficient ζ are determined for each type of examined window.
• The flow resistances increase linearly with the area of the window opening.
• For symmetric windows types the flow resistance coefficients are virtually identical.
• Triangular openings have a smaller flow resistance than polygonal openings.

In a previous paper [1] we have quantified the buoyancy driven mass flow rates for different types of windows that result from a temperature difference of 1 K between the two spaces that are separated by the window in question. For the examined windows it was possible to relate the opening rate to the resulting mass flow by a logarithmic function. This paper draws on these results and shows how to further develop them to basic flow parameters and thus to generalize the outcomes to arbitrary situations. The most important flow parameter in this context is the flow resistance ζ of the window opening. This flow resistance is quantified for the examined window types and the results show that the flow resistances are virtually identical for the majority of the tested window openings. In addition, the flow resistance is linearly and positively dependent on the size of the window opening. With these results, mass flow rates can easily be calculated for windows under buoyancy ventilation in thermal building simulations.