Heating & Cooling Are A Challenge For Electric Vehicles
If you are reading CleanTechnica, chances are you are a strong supporter of electric vehicles and would like to see more of them on road. Cars powered by gasoline and diesel engines are hugely inefficient. According to AAA, only about a third of the energy contained in a gallon of gasoline ever gets used to push a vehicle forward. Nearly two-thirds of that energy is turned into heat, some of which is absorbed by the coolant with the rest going out the exhaust pipe.
It’s hard to believe such a wasteful process has become the standard means of powering the world’s transportation sector, but there is good news. Some of that waste heat can be recaptured from the coolant to heat the interior of our vehicles. As wonderful as electric vehicles are, they have no stream of waste heat that can be tapped for the same purpose, which poses a challenge — how to keep EV drivers and passengers comfortable when it’s cold outside? The corollary to that is how to keep them cool when it’s hot outside?
An Electric School Bus In Alaska
According to Alaska Public Media, there is exactly one battery-electric school bus in the entire state. It transports school children in the Alaska Gateway School District, which includes the town of Tok near the Canadian border. Temperatures in the area can dip as low as -40 degrees F.
You might wonder how well the batteries in the bus function in such bitter cold conditions. Gerald Blackard, co-owner of Tok Transportation, says the bus has performed flawlessly for the past year, even in the most bitter cold weather. The one issue is keeping the interior heated. [Note: In Alaska, buses must be kept at 45° F or more. School children are required to wear warm clothing while riding back and forth to school.]
What Blackard has learned is that it takes more battery power to heat the bus than it does to drive the 30 miles a day needed to complete its route. “On January 27th, we had 38 below,” he says. “The bus’s efficiency that day was 3.46 kilowatts per mile. So this fall, in August-September, we were running between 1.4 and 1.7 kilowatts per mile. Even with a little bit of insulation on the batteries and kind of covering up the engine compartment to try to hold in as much heat as we could, we were still using more energy to heat the bus than we were to drive the bus.”
Blackard says he has been sharing the data he collects about how the bus operates with the local utility company, the University of Alaska Fairbanks Alaska Center for Energy and Power, battery manufacturer Proterra, and Thomas, the North Carolina based manufacturer of the bus. “I’m in contact with [Thomas] often,” he says, “and they’re always curious to see how things are going and making sure that it’s working properly.”
Tok Transportation uses a 10.8-kilowatt solar installation to recharge the bus, but since it uses 22 kilowatts of power while recharging, it needs to supplement the electricity from the solar panels with electricity from the local grid. A battery storage component is planned for the future when funds become available. Most of the $400,000 cost of the bus and the solar system was paid for by the Alaska Energy Authority.
About Those Rivian Delivery Vans For Amazon
This week, a loose-lipped test driver let it slip that the pre-production Rivian delivery vans being built for Amazon use up to 40% more battery power if the heating or cooling systems are turned on. Those vans are supposed to have a range of 125 to 150 miles. Subtracting 40% leaves them with only 75 to 90 miles of range.
The company acknowledged to Reuters that the testing was taking place, but cautioned that these pre-production models do not have the insulation that will be included in production vehicles. That may be true, but is seems unlikely Rivian is going to add enough insulation to the vans coming off the assembly line to make a significant difference.
Rivian is finding out what drivers of EVs already know. Activating the climate controls in an electric car means less energy will be available for moving it down the road. There’s a reason why in winter, Nissan LEAF drivers like myself use the heated steering wheel and seat warmers instead of the heater whenever possible. [The good news is, when you turn on the heat in an EV, it comes on instantly, unlike a conventional car that may need several miles of driving to warm up.]
The Takeaway
For over a century, drivers have been taking advantage of the waste heat their cars create to stay warm in winter. We never stopped to ask if such wastefulness was good for the environment. Of course it isn’t. The new age of electric vehicles is upon us and we no longer have a source of waste heat at out fingertips.
When air conditioning first became a thing for automobiles, the compressors were so inefficient they could reduce gas mileage by as much as 20%. But as gas prices went up, A/C systems became more efficient. The same thing will happen with cabin heating for electric vehicles. As usual, Tesla has been at the forefront of innovation with its Octovalve, which alone enabled a 10% increase in range for the Model Y.
Early EVs used resistance heating to warm the interior — the same 1960s technology used by electric space heaters. Electricity is passed through a coil of wire, which heats up and warms the air around it. It works, but it uses a huge amount of electricity for the heat created. In other words, it’s inefficient, just like the internal combustion engine EVs are supposed to replace.
Tesla has been a leader in improving heat pump technology for its vehicles — so much so that is may get into the business of making heat pumps for residences and commercial buildings. According to Kyle Field, Tesla redesigned the heating and cooling systems for the Model Y to reduce the inefficiencies of heating and cooling with electricity and maximize the efficiency of the vehicle’s thermal systems.
The cooling circuit was integrated into a single heating and cooling management system for the vehicle that optimizes the thermal energy flowing throughout the vehicle and integrates the Octovalve with a completely redesigned heat pump.
In the final analysis, the transportation sector will need to find new ways to control the cabin temperature of vehicles, now that it doesn’t have a ready supply of surplus heat to work with. Fortunately, Tesla is blazing a trail for the others to follow.
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