Abstract
In this paper, the causes of insufficient air volume of a heat- exchanging-type mechanical ventilation system installed apartment were investigated. The results are as follows: 1) Pressure-drop coefficients of the grills were excessive. 2) The blades of the exhaust fan were covered with dust and the power of that fan was less than cleaned one. 3) Pressure-drop coefficients of the filters stuffed with dust without maintenance were also excessive.