Ventilation system performance of vertical exhaust common-duct in a multi-story house.

Ventilation performance of a vertical exhaust common-duct installed in a multi-story house was analysed using model experiment and computer simulation. Pressure losses at the flow junctions in the vertical common-duct were investigated using the model experiment. The pressure distributions along the vertical common-duct in three different multi-story houses of 5, 15 and 25 stories, respectively, were calculated by the computer simulation. The results are as follows: (1) The pressure losses in the converging flow at the junctions in the vertical common-duct were expressed by approximate equations with two ratios, namely, the ratios of the velocity of airflow and the sectional area of the vertical common-duct to those values of the branch duct. (2) The pressure loss in the converging flow at the junction through the vertical common-duct was positive in the case of the T-type junction. But the pressure loss in the case of the elbowtype junction was negative, which means that the elbow-type junction increases the pressure in the common-duct and may cause a reverse flow from the vertical common-duct to the apartments, especially those in the upper stories. Therefore, the T-type junction should be used in order to prevent such reverse flow. (3) It is possible to keep the difference between the static pressure in the common-duct and the outside pressure small by controlling the rotational speed of the exhaust fan mounted at the top of the vertical common-duct.