Design & SimulationJuly 6, 2021

Address Challenges in Vehicle Cabin Air Quality with SIMULIA Solutions

Indoor Air Quality and Air Filters With increasing emissions, risks of pandemics…
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Vijaisri Nagarajan

Indoor Air Quality and Air Filters

With increasing emissions, risks of pandemics and rising population globally, vehicle air conditioning units are not only responsible for our comfort anymore; they also ensure our safety.

Air quality inside the vehicle cabin depends on the surrounding air and the Heating, Ventilation and Air Conditioning (HVAC) unit performance. According to some studies, as much as half of the pollutants inside the car come directly from the vehicle ahead; furthermore contaminants released by sick occupants or even taken in from the surrounding air are becoming a growing concern.  The HVAC unit must ensure that all occupants are kept safe whilst meeting performance and efficiency imperatives – with regulations requiring a full redesign of the HVAC to reduce polluting refrigerants use by 80% by 2047. This is a big challenge for vehicle Original Equipment Manufacturers (OEMs) and their suppliers, and they are looking into several ways to improve the HVAC and air filter performance to provide clean air with reduced contaminant spread inside the cabin. This must be done without considerably increasing manufacturing costs or affecting passenger experience.

The air filter is one of the most important but underrated components in any vehicle heating and cooling HVAC system. The filter is often located behind the glovebox inside the HVAC unit. It traps the airborne debris entering the vehicle HVAC unit, thereby providing clean cabin air and protecting the HVAC equipment. There are many types of air filters available in the market. Not all air filters clean with the same level of efficiency. Depending on the level of clean air required, the incoming air travels through one filter with higher efficiency, or through several filters. An example of contaminant removal process is shown in Figure 1.

The Minimum Efficiency Reporting Value (MERV) often determines the efficiency of the filter and its performance. It defines the air filter’s ability to block particles between 0.3 and 10 microns. MERV ratings are from 1 to 16 with higher values indicating higher particle trapping efficiency. In vehicles, High Efficiency Particulate Air (HEPA) filters are widely used. As per the government regulations, HEPA filters must remove 99.97% and 99.95% of contaminants in the US and Europe, respectively.  Figure 2 shows different contaminants filtered by HEPA filters with different MERV ratings.

solver with Particle Modeling is used to model the flow behavior, contaminant transport, accumulation on the air filter and pressure drop  for different filter ratings and positions. The filter design simulation is integrated into our cabin comfort simulation framework. In the HVAC simulation, the contaminants are injected into the system through a prescribed boundary condition. The filter is modeled as a particle screen which controls the particle opening size and pass through fraction for different filter types and ratings. It provides the user with insights about filter/system efficiency and models the effects of clogging from contaminant accumulation either uniformly or non-uniformly. Figure 5 shows the HVAC geometry with particle screen and flow path:

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