Prediction of natural and hybrid ventilation performance used for fire-induced smoke control in a large single space

Abstract

This paper deals with a large single space building for smoke control when a fire happens. Two hybrid ventilations are investigated, i.e. natural ventilation through a roof opening combined with mechanical suction flow, and with mechanical jet flow. Pure natural ventilation is used as a benchmark. An experimental model was reproduced as 1/10 of the prototype. Under pure natural ventilation, the roof opening played an important role in exhausting but the smoke layer height descended rapidly. Influences of mechanical flows from sidewalls on the smoke distributions were found to be evident. Large eddy full-scale simulations were performed in which grid size of the fire-domain was determined to be 0.125 m being one half of the non-fire domain. The simulation results agreed well with the experimental ones. A total of 63 ventilation cases are further simulated, and it reveals that mass flow rates of the roof opening increase with the increase of opening area ratio or discharge velocity of inlets or heat release rate but with the decrease of exhaust velocity of outlets; under hybrid ventilation of mode 4, back-flow occurs under the roof opening when the exhaust velocity reaches up to 6 m/s, and the maximum smoke temperature and the CO concentration near the door is of the lowest indicating its best advantage in controlling the fire smoke; the smoke plume is more easily disrupted by jet flow than by suction flow. This study helps to promote the design and operation of ventilation system for large and high spaces when firing.