Measurement of cross-ventilation rate in urban multi-zone dwellings

Abstract

Cross ventilation can effectively improve air quality with larger ventilation rate than single-sided natural ventilation. The measurement of ventilation rate is critical for research on indoor environmental maintenance and air quality control. This investigation compared four methods of obtaining the cross ventilation rate in a residence, including direct measurement by the tracer-gas-decay method, and indirect measurement with ultrasonic anemometers, from the wind speed at a reference position, and from the differential pressure between two sides of the residence. Furthermore, measured wind speed in the direction normal to the opening was used to analyze the unsteady and non-unidirectional flow characteristics, and the airflow consistency σ was found to be in the range of 50%–98%. The results show that when σ > 90%, the internal airflow was close to unidirectional flow, and the ventilation rates in all rooms were similar. As the ratio σ decreased, the error between the measured and calculated ventilation rate at the openings increased. When σ < 70% with severe non-unidirectional flow, the presumed ventilation volume based on the measured wind speed at one opening had a large deviation from the measured ventilation rate at the other. We then calculated the volume of air intake and outflow at the same opening. On the basis of volume conservation, the exchange ventilation rates between internal rooms were obtained by the tracer-gas-decay method combined with ultrasonic anemometers to measure the wind speed at the openings of the multi-zone dwellings. Therefore, single tracer-gas-decay method with ultrasonic anemometer at the openings can measure the cross ventilation rate and obtained the ventilation rate between internal rooms of the multi-zone residence.