The natural ventilation by thermal buoyancy in a room with small openings is determined by the equations for mass balance, energy conservation, and vertical momentum for a control volume representing the room in question and by the modified Bernouilli equation used on the inlet and outlet in order to connect indoor and outdoor conditions. Auxiliary equations are set up in order to get the solution based on density difference, temperature difference, and net heat input, respectively. The validity of the solution is discussed in relation to temperature stratification, position of neutral pressure plane, and orientation of the openings. Specific topics are discussed concerning - air velocity and ventilation capacity as affected by opening area ratio (i.e., inlet area/outlet area; size of opening areas required for ventilation capacity or required temperature difference; optimum opening area ratio; and coefficients of interest (i.e., velocity, contraction, discharge, and resistance coefficients). The set of formulas is well suited for analytical purposes and constitutes an easy-to-use method that can be programmed as an independent computer program or integrated into a simplified building energy program.

KEYWORDS: year 1995, natural ventilation, ventilation, buoyancy, calculating, computer programs, temperature stratification, orientation, windows, air speed, designing, air flow, heat flow, temperature difference