This study aims to propose a measurement method of vent cap airflow resistance through an examination of pipe models using realistic airflow rates, test methods including measurement methods and test conditions that refer to the results of previous tests including flow capacity tests. Next, using these factors, the airflow resistance coefficients and equivalent pipe lengths of vent caps of exposed and embedded types, most commonly available types, were calculated based on applied pipe diameters to provide new, practical data for ventilation design. Lastly, typical vent caps were selected, based on said airflow resistance coefficients as indexes, and were attached respectively to the top of the vent pipe of an actual high-rise building drainage stack system to examine the influence of the vent cap airflow resistance on the flow capacity. Experiments were carried out with the focus on these three aspects, and the following has been achieved.
(1) By setting airflow rates that were generated during drainage load experiments using the high-rise/super high-rise drainage stack system, airflow resistance pipe models of horizontal header and vertical and horizontal single types and a test method have been proposed. The airflow resistance coefficients ζ and equivalent pipe lengths L of 38 commercially-available vent caps of exposed and embedded types have been calculated.
(2) The results of airflow resistance tests indicate that the average airflow resistance coefficient ζ corresponding to the average applied pipe diameter is 3.0 with the exposed type and 5.5-7.5 with the embedded type. As for the equivalent pipe lengths L, the difference between the maximum and minimum values corresponding to the applied pipe diameters is approximately ±2[m] with the exposed type and approximately ±6-11[m] with the embedded type. Although there is some variation due to difference in shape, etc., when regarding the average equivalent pipe length L corresponding to the average applied pipe diameter as an equivalent pipe length L for practical application, it is approximately 11[m] with the exposed type and approximately 21-27[m] with the embedded type.
(3) Flow capacity experiments were carried out, according to SHAPE-S218, on the high-rise building drainage stack system using six vent caps of different common types, in different shapes and with different airflow resistance coefficients ζ. The flow capacity was measured to be 2.0[L/s] with both the exposed type and the embedded type, which was very similar to the flow capacity with the bellmouth used in the experiments. There was no variation in the flow capacity caused by the airflow resistance coefficients ζ.
(4) The calculation results of airflow resistance coefficients ζ and equivalent pipe lengths L show that there is only slight variation between the measurements obtained from the airflow resistance pipe models in the laboratory and the measurements obtained from the flow capacity experiments that were carried out outdoors. Therefore, it is considered that the calculation results of airflow resistance coefficients ζ and equivalent pipe lengths L from the outdoor flow capacity experiments can be used as practical design data, provided that the influence of external disturbance is similar.
