Analysis of the Excergy Transfer and Efficiency of Buoyancy-Driven Ventilation

Based on the second law of thermodynamics, this paper investigates buoyancy-driven ventilation (BV) in respect of exergy analysis. One-dimensional assumption is adopted and a computation procedure of muti-zone model, based on conservation laws of mass, momentum and energy, is established for simulation purpose. A novel index evaluating performance of ventilation is defined. A high-rise building with a tall atrium is selected as a case study. The schematic of exergy transfer of BV is presented, together with that of mechanical ventilation (MV) as a comparison. Results from simulations indicate that flow exergy, warm exergy and mechanical work are the driving forces to promote ventilation, but have different conversion ways., and the exergy efficiency of BV is very poor due to great external exergy destruction, but that of MV is 100%. This conclusion can enable designers to use BV with caution when some sort of high grade energy is used to promote ventilation.