Experimental Studies on Mechanical Smoke Exhaust System in an Atrium

Mechanical smoke exhaust systems are usually required in big atria of the Far East. However, the design criteria are not clearly demonstrated to be worked out through systematic full-scale tests. There are many arguments on sizing the exhaust fans, and whether a high exhaust rate is required in an atrium is a puzzle. Atrium hot smoke tests might be required to be carried out occasionally to evaluate their performance, especially when the design does not comply with the prescriptive code in having a high-enough exhaust rate. Experimental studies on mechanical smoke exhaust systems are necessary and have been carried out. The results are reported in this paper. The measured results are also compared with the empirical equations used in designs, following NFPA-92B derived by a two-layer picture. A simple zone model reported earlier is applied to justify the results. This model is also developed based on a two-layer picture. There are significant deviations of the measured results from those predicted by the equations with a two-layer pattern. Mass exchange through the two layers in an atrium fire is suggested to be the key point. By taking the estimated mass flow rate across the two layers by experiments to be 30% of the exhaust rate under high ventilation conditions, the two-layer zone model is modified. Slightly better argument with the experiments was found for the self-developed two-layer zone model, but still there are large deviations for the NFPA-92B equations.