The Truth about Electric Vehicles (EVs) in Hot Weather: a Recap from our Recent Webinar

 In Inside FleetCarma

EV HVAC Usage Heat MapOne week after our sold-out webinar on the effects of hot weather on electric vehicles we wanted to provide some quick notes for those that could not attend.

As previously outlined there are many advantages to analyzing the data from electric vehicles to determine how they perform in hot weather.  Most often vehicle manufacturers choose to roll out initial EV models in ‘hot weather’ states such as California, Arizona and Hawaii.  After gathering real world data on various EVs in a range of climate conditions, we wanted to look at how warmer weather specifically affects an EV’s range, as well as performance, so that drivers in hot weather climates can get the most out of their vehicle.   The data we looked at came from a mixture of professional and person drive cycles on a selection of 20 vehicles from our database.  The types of vehicles analyzed include the Nissan Leaf, Chevrolet Volt, Mitsubishi i-MiEV and the Ford Transit Connect.

Expanding on the Cold Weather Webinar we did in March 2012, speakers in this webinar elaborate on its bow-tie metaphor to explain the relationship between the Auxiliary Load, Component Efficiency, and Range.

What the literature indicated, and real world data confirmed, was that we could look at the important variables concerning EV performance in a way that closely resembled a bow-tie.


A Closer Look at the Bow-Tie

The bow tie shape is formed from three main lines:

Bow Tie Graph

 Describing the Bow Tie’s Curves:

The Heating and Cooling Loads Curve:

  • This line indicates that auxiliary power that is used by the climate control components
  • At cooler temperatures a higher amount is used to heat the cabin
  • At comfortable temperatures no heating or cooling is used, so the auxiliary power load bottoms out
  • At higher outdoor temperatures the air conditioning is used and the power usage rises again

The Component Efficiency Curve:

  • This line has to do with a battery’s reduced performance in cooler weather
  • As the temperature rises the component efficiency rises slightly as well

Vehicle Range: 

  • The vehicle range line is the result of the HVAC load and component efficiency
  • The line also varies due to a driver’s specific duty cycle (including driver aggressiveness and the vehicle’s map cycle).

Hot Weather Electric Vehicle Performance:

We looked at auxiliary load patterns from three very different users that all operated the same vehicle including heavy-HVAC users, light-HVAC users, and vehicles stored in heated garages.

Electric Vehicle Auxiliary Power (mostly AC)

An example of one driver’s bow tie. Range and auxiliary are both graphed on a heat map to show how the bow tie changes with increasing temperature. The ‘hotter’ colours on the heat map indicate a higher frequency of occurrences, whereas the cooler colours indicate sparse or no occurrences.

The simple bow-tie we believed to be the model going into the webinar, turned out to be 3 different bow ties that depended on the HVAC settings as well as the operator’s driving style.

In cold weather components there was a notable decrease in component efficiency, while at warmer temperatures we found a slight increase.

We noticed similar usage patterns when we looked at other vehicles such as the Nissan Leaf, and Chevrolet Volt.

For more detailed information about the effect warm temperatures have on EV performance, feel free to check out the recording of our Free Webinar The Truth About EVs in Hot Weather, available for online viewing in either video or slide format.


Download the Webinar to Find Out:

When driving range is a concern, the best strategies to mitigate the impact of climate on EV efficiency.

The potential for EVs when comparing drivers that use intense climate control and those who do not use it at all.

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