A mechanical ventilation model is proposed, independent of spatial coordinates, consisting of pure air injection and polluted air extraction (double method). Through finite differences, the oxygen percent vs. time is computed for different intake and exhaust conditions, including one with simple pure air injection as a particular case. Results show that exit opening area is a critical parameter in the effectiveness of the simple method, and under certain conditions, the oxygen level can be kept a long time, and it is easy to compute.
indoor mechanical ventilation; double and simple methods; independent of spatial coordinates
