Today, almost all passenger vehicles are equipped with Mobile Air Conditioning (MAC) systems to provide thermal comfort to occupants. To enhance cabin cooling down rate, two approaches are possible viz. increasing the MAC system capacity or reducing heat ingress into the vehicle cabin. The first approach is likely to have a negative impact on energy efficiency. The latter approach considers the deployment of alternate passive cabin cooling technologies. Among these, the deployment of uniquely developed coatings on metal, plastic and glass surfaces of the cabin is one option. The assessment of such coatings is usually done only at severe ambient conditions (>40°C), which may not be sufficient. These coatings need to be validated across all climatic seasons of the year, for assessing their effectiveness on passenger thermal comfort.
The current work along with simulation studies, takes into account additional parameters such as the ‘feeling of hotness’ when one enters a hot-soaked cabin of a typical car not parked under the shade. Further, customer touch point surface temperatures, along with a definition of their acceptance criteria based on thermal comfort considerations, have also been examined in this work.
The proposed new and novel process consists of, defining a physical validation methodology comprising of both, objective and subjective assessments on two vehicles, viz. baseline vehicle without coating and proposed vehicle with coating on multiple surfaces. The objective assessments include a set of DoEs on both the vehicles in controlled ambient conditions in a Climatic Chamber, followed by actual real-world vehicle drives and DoEs on the road. The assessment of deterioration with dust application on the coated surfaces and sensitivity analysis with the removal of the proposed coating on some of the surfaces is also examined. Finally, a jury of experts subjectively assessed the effectiveness of the coating and ranked the, ‘critical to thermal comfort’ parameters, on a ten-point scale.
This novel methodology enables the objective and subjective assessment of a proposed coating and analysis of gaps with respect to target requirements; the primary objective being to arrive at a holistic decision on implementation for series production.