The impact of street level particulate emissions on the energy performance of roof level building ventilation systems

Localised vehicular fine particulate matter (PM2.5) emissions in an urban canyon can influence the energy performance of a building ventilation system at roof level. This paper examines the energy demands of air filtration through an air handling unit (AHU) located in different positions and orientations on a building rooftop. A series of 3D numerical simulations examined the impact of aspiration efficiency (AE) on filter loading rates as the distance from the source increases and AHU orientation relative to ambient wind direction. The ventilation PM2.5 concentration was equal to the ambient when positioned near the windward wall of the target building. A decrease of 33% and 60% in the filter loading rate occurred at a wind speed of 7.5 m/s and 2.5 m/s at the leeward wall. There was no energy savings when the AHU is positioned on the windward side of the target building but a reduction in energy consumption of 9.8% at the centre and 19.4% at the leeward side. Comparing the effect of wind orientation for identical AHU positions on the rooftop centre resulted in a 26–35% reduction in AE when the AHU inlet is not facing into the particle laden wind and incurred energy savings of 25.8%.