AUTOMOBILE HVAC SYSTEMS: AIR FLOW, LEAKAGE AND THEIR EFFECTS ON IN-VEHICLE AIR QUALITY

We have sought to accurately quantify automobile HVAC air flow rates in four passenger vehicles,under a range of different ventilation settings and speeds. We used Sulphur Hexafluoride (SF6) as atracer gas, coupled with a portable doser/sampler system to quantify flow rates and leakage.Results of this work indicate a linear increase in HVAC air flow rate with increasing vehicle speed forall vehicles. Older vehicles were much less airtight than newer vehicles, a likely reflection on improveddesign and reduced door seal deterioration observed in the newer vehicles. HVAC systems in newervehicles generally delivered a smaller volume of air than older vehicles under the same ventilationsettings.The results are of particular interest to those involved with engineering and modelling in-vehicleenvironments and associated HVAC systems, especially in relation to pollutants. For example,subsequent air quality assessments in the same fleet of vehicles indicated that the inside/outsideratios of combustion-derived submicrometer particle concentrations were highest inside the cabins ofthe oldest vehicle.