The cold reality of electric vehicles

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Vehicles powered by internal combustion engines are seldom short of excess heat. In fact, simulation software is often used by car manufacturers to find the best ways to dissipate that heat and ensure sufficient cooling airflow.

There are times when all that warmth is handy, though, like on a cold morning, when a film of frozen moisture sometimes obscures the driver’s view – something that’s been on the minds of drivers during the recent cold snap. Waste heat from the ICE can be harnessed by the vehicle’s HVAC system to clear the frost with a blast of hot air. Drivers always want to get underway quickly, so it’s important for safe vehicle operation that the vents and blowers are optimally tuned to restore visibility as soon as possible.

But what if your vehicle is one of the increasing number of electric cars hitting the streets? Generous use of the heater on a cold morning will eat into valuable battery capacity at a time of year when the vehicle’s range is already more restricted than in the summer months. In such a situation, the fastest, most energy-efficient defrosting of the windows is paramount.

Exa has been developing an extension within the PowerFLOW simulation solution that can accurately simulate the defrost process in extremely cold climates in close cooperation with its customers. The tool takes into account different ambient conditions – external temperature and wind speed both impact upon the rate of defrost – and compares the results of different HVAC settings and designs, allowing engineers to save time and money by optimizing the performance of the system, before producing a physical prototype.

Recent advances in HVAC simulation methods have enabled fast yet accurate prediction of in-car temperature changes over several hours. In the latest development, simulation considers the frost melting, subsequent evaporation or sublimation (when ice turns directly into water vapor) and moisture transport together for the first time. In a coupled simulation, its flow solver handles convection, moisture and frost, while the thermal solver takes care of radiation and conduction.

The cabin simulations can be visualized in highly realistic animations that provide a driver’s-eye view of the clearing windshield and side windows with time. Engineers can easily observe the speed and extent of the defrost, and run side-by-side comparisons of different scenarios. This is a much faster, more accurate and simpler solution than the traditional hand-sketching of defrost patterns onto a physical windshield in a climatic wind tunnel.

This defrost simulation tool will be released to selected Exa customers later this year so that drivers of new vehicles in winters to come won’t have to wait so long to get motoring in the morning – and EV owners can enjoy the benefit of a more efficient blower, while worrying less about its impact on their vehicle’s range.

February 10, 2016

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