Ventilation measurements in a cinema.

This paper reports on the ventilation measurements in a cinema using the tracer-gas technique. Both the local and room air exchange efficiencies were measured. The two tracer-gas methods, "step-up" and "step-down (decay)", were used alternately when the cinema was in use to enable a continuous measurement of air-exchange efficiencies under various occupancies. The air exchange efficiencies were found to be very close to that for a perfect mixing, with little influence from the occupants. This might be due to that the cinema had a downward mixing ventilation with a large air change rate. The air exchange efficiencies were found to be lower with the decay method than with the step-up method. The results also show that the decay method was more stable than the step-up method for evaluating the local air exchange efficiencies. However, both are stable for evaluating room air exchange efficiencies. Other parameters such as the CO2 concentrations and temperatures were also measured. Due to good mixing in the cinema, the thermal stratification was found to be small. However, the difference between the CO2 concentrations in the occupied zone was found larger with higher occupancy. The CO2 concentrations were found to be higher in the occupied zone than the room-average ones.