AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
Abstract View
Mixing and Distribution of a Point Source Pollutant in a Chamber with Two Airflow Conditions
MATTHEW VANNUCCI, U.C. Berkeley, Civil and Environmental Engineering Dept
Abstract Number: 593 Working Group: Indoor Aerosols
Abstract The mixing rate of an air pollutant from an indoor source is a significant contributing factor to occupant exposure. In a residence with natural ventilation the mixing rate of pollutants from indoor sources is strongly influenced by the relative temperature of the walls and floors to the air. This ongoing study correlates the mixing time of an instantaneously released bolus of carbon dioxide (CO2) in a sealed 1.75 m^2 chamber with independently controlled surface temperatures of the walls. Opposing walls are symmetrically heated and chilled to create a natural convection with no net heat flow, while chilling the floor and heating the ceiling create a stable thermally stratified condition. Six real-time CO2 sensors are used to measure the mixing time and are calibrated in situ with co-located syringe sampling points.
It is not yet known how the mixing time varies with wall temperature in natural convection systems, but for other sources of mixing, such as forced convection, mixing times correlate well with the cube root of mechanical power. For a natural convection system it is hypothesized that the mixing time will decrease with increased wall to average air temperature differences, while for a thermally stratified condition the opposite may hold true. We will also investigate a single sensor’s ability to estimate human exposure under these conditions by measuring the spatial variability of CO2 concentration on a horizontal plane. This estimate is done using an array of syringe sampling points located on a plane 2/3 of the height of the chamber, roughly equivalent to the breathing zone in a full-scale room, in conjunction with the real-time sensors. Understanding the spatial distribution of airborne pollutants can be utilized to develop improved source control strategies and enhanced distribution of ventilation air with the aim to mitigate occupants’ exposure.