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 (SF ₆) as a tracer 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 for all vehicles. Older vehicles were much less airtight than newer vehicles, a likely reflection on improved design and reduced door seal deterioration observed in the newer vehicles. HVAC systems in newer vehicles generally delivered a smaller volume of air than older vehicles under the same ventilation settings. The results are of particular interest to those involved with engineering and modelling in-vehicle environments 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/outside ratios of combustion-derived submicrometer particle concentrations were highest inside the cabins of the oldest vehicle.