AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
Abstract View
Effect of Diurnal Sunlight and Shading Patterns on Indoor Air Flow and on Human Exposure to Fine Particulates
Yan Zheng, KAI-CHUNG CHENG, Wayne Ott, Lynn M. Hildemann, Stanford University
Abstract Number: 278 Working Group: Indoor Aerosols
Abstract With the construction of tighter, energy-efficient buildings, human exposure to indoor emissions of particulates is a growing concern. Chaotic and turbulent airflow has made inhalation rates to these aerosols to be highly unpredictable, and thus a well-mixed assumption is often applied in exposure models. Sunlight patterns, however, produce a reliable heating cycle which directly affects indoor airflow patterns. As sunlight heats the top of a building, it creates an indoor temperature difference, inducing buoyancy driven flows. Strong temperature stratification impedes vertical mixing and reduces the effective mixing volume, allowing for spikes in particle concentrations near the effective height of the source. To capture this phenomenon, a series of 29 experiments were conducted in a residence in northern California. Cigarette smoke was passed through a smoke actuator and the cooled to create a non-buoyant fine particulate source to be released in the room center. PM2.5 monitors were placed every 0.25m height up to 2m and were repeated 4 times in each cardinal direction so as to account for directionality. There were a total of 16 sampling monitors and 48 sampling points for each experiment. Temperature sensors were placed every 10cm vertically for a total of 36 sampling points to obtain an accurate reading of temperature stratification. Stratification strength ranged from 0 to 15°C/m. Vertical mixing strength was quantified via Fick’s Law, yielding vertical turbulent diffusion coefficients (Kv) ranging from 3x10-4 to 4.3x10-4 m2/s. The horizontal turbulent diffusion coefficients were roughly an order of magnitude higher than the vertical coefficients. Kv was found to have a strong correlation with temperature stratification which in turn made significant impact on particle dispersion. The vertical concentration profiles showed that the maximum particle levels at the effective height of the source emissions spiked 15x higher than the vertically-averaged concentration, when comparing stratified to unstratified indoor spaces.