Experimental investigation on transient natural ventilation driven by thermal buoyancy

• Full-scale experiments are conducted to explore the transient natural ventilation.
• The surface thermal radiation delays the variations of temperature and gas concentration.
• The initial temperature difference has great effects on the transient ventilation.
• Increasing the vent area accelerates the development of the natural ventilation.
• The vent shape has little impact on the transient flow rate.

Full-scale experiments were carried out to explore the effects of the initial temperature difference between the interior and exterior and the vent characteristics on the transient development of natural ventilation driven by thermal buoyancy. Air temperature and tracer gas concentration in a test chamber were measured and the experimental results were compared with the theoretical predictions. It was found that the initial temperature difference has a large influence on the thermal stratification, the concentration distribution of tracer gas, the flow rate and the removal rate of tracer gas. The time taken to reach steady-state ventilation is shorter for a larger vent if the initial indoor temperature is greater than or equal to the outdoor temperature. For a pre-cooled room, the time taken for the ventilation to transform the airflow direction is shorter for a larger vent. Increasing the vent area would yield a greater flow rate and thus improve the efficiency of gas removal. Experimental results also show that the vent shape has little impact on the flow rate.