Engines produce plenty of waste heat that can be used to warm the air in the cabin and keep things comfortable. The inherently greater efficiency of an electric powertrain means less wasted energy, but it also means that the battery has to be used to power a resistive heater to produce that warm air – electrical energy could otherwise be used to propel the vehicle, which is one of the reasons why electric vehicles have a significantly shorter driving range in cold weather.
“It requires as much energy to heat the interior of a car on a cold day as it does to drive at a constant speed,” said Susan Stevenson, General Motors benchmarking engineer for heating, ventilation and air conditioning systems.
The Volt has several features designed to minimize the drain on the lithium ion battery while still affording occupant comfort. The exclusive OnStar MyLink smartphone app or the MyVolt.com website can remotely start the Volt and warm the cabin while it is still plugged in and drawing power from the grid, leaving the battery with a full charge to maximize the electric driving range.
“The coldest weather I’ve experienced so far with my Volt was 18 degrees during a drive to the Poconos and I’ve had no complaints,” said Jeffrey Kaffee, the first retail customer to take delivery of a Volt in mid-December. “Most of the time I just use the Eco mode instead of the Comfort mode and it’s been no trouble whatsoever.”
Less energy is consumed maintaining the cabin temperature than heating it up, but even on the road the Volt has more to contribute. Heated seats available on the Volt require less energy to keep passengers warm and comfy than it does to heat the full volume of air in the car.
The Volt also can use the engine to generate some extra heat and electrical energy in sub-freezing temperatures. In sub-freezing temperatures, the engine will periodically cycle on and off, heating the coolant to create a reservoir of thermal energy that is then used to warm the cabin air.
Using engine heat this way enables faster window defrosting and rear seat heating than taking energy from the battery. Under light driving loads, the engine and generator also can put some electrical energy back into the battery during these heating cycles to extend the electric driving range.
“Volt drivers in Southern California will likely never experience this in their day-to-day commute, but if they pack up their gear and head into the mountains for some skiing, they will appreciate the enhanced cabin comfort made possible by this unique powertrain” said Andrew Farah, vehicle chief engineer for the Volt.
Even with all of the energy optimizations, the same mechanical factors that lower fuel mileage for traditional vehicles contribute to a shorter electric driving range in winter. Cold temperatures increase the viscosity and resistance of lubricants in transmissions and axles while roads covered in snow or slush increase rolling resistance causing the powertrain to work harder and drain the battery.
But the Volt’s engine generator dramatically reduces the fear of being stranded. When the lithium ion battery is depleted, the industry-first extended range capability allows the car to continue on for up to 340 additional miles.
“Volt engineers spent many frigid weeks in places like Kapuskasing, Ontario and Fairbanks, Alaska testing and calibrating the climate control system to make sure that drivers and passengers remain comfortable while still enjoying plenty of gasoline-free electric driving even in the harshest winter weather” said Farah.