Discussion on design of make-up air rate of mechanical smoke exhaust systems

The mass flow rate of smoke exhaust and make-up air in the smoke exhaust room is equal, but the temperature is not equal, and the greater the temperature difference, the greater the difference between the volume flow rate of smoke exhaust and make-up air. At present, in engineering practice, the make-up air rate is generally designed according to 50% of the exhaust smoke volume flow rate at the lower limit of the specification, which has nothing to do with the exhaust smoke temperature. According to the requirements of GB 51251-2017 Technical standard for smoke management systems in buildings, the average temperature of smoke layer in the large space with a clear height of more than 6 m needs to be determined by calculation, and can be adjusted by changing the depth of the smoke storage bin. It can be seen from the calculation that different smoke exhaust temperatures can be obtained under different combinations of working conditions. At this time, the proportion of the make-up air rate to the exhaust volume flow rate is 45% to 81%.