Design of natural ventilation by thermal buoyancy with temperature stratification.

A set of formulae for natural ventilation by thermal buoyancy is derived for a room with two opening and with a linear temperature stratification. The formulae are based on the fundamental flow equations, and they cover air velocities, temperature differences and ventilation rates in relation to opening areas, opening position, net heat input, building geometry, and temperature stratification. The temperature stratification can simply be taken into account by introducing a stratification factor E and by using the mean difference between indoor and outdoor temperatures. The validity of the formulae is discussed as well as specific topics concerning design and control. The use of the formulae is illustrated on an atrium.