The effect of upstream buildings on near-field pollutant dispersion in the built environment

This paper examines the effects of near-field pollutant dispersion characteristics of upstream buildings in the built environment and compares them to the ASHRAE 2007 model. Wind tunnel simulations were performed for nine different building configurations for three exhaust momentum ratios (M) and three stack heights (hs). The effect of spacing (S) between the buildings and stack location from the upwind edge of the emitting building (X) were also investigated. Measurements of gas concentrations were performed on the roof and leeward wall of the emitting and upstream buildings. Data show that within the recirculation zone a change in along wind dimension of the upstream building has a negligible effect on the dilution of emissions from the downwind building. However, spacing between buildings and the height of the upstream building were found to be critical parameters in assessing plume dilution. The plume geometry is largely governed by the upwind dimensions of the upstream building. ASHRAE (2007) predicts lower dilution for all cases examined, leading to conservative or very conservative design. However, the ASHRAE 2007 cannot model the effect of upstream buildings, thus further investigation of its formulations is required. Guidelines for placement of intake and stack on the roof of the building to avoid problems of re-ingestion are discussed.