Distinguished readers will remember that we actually covered this new Ultium technology at the end of last month, when it was first announced, but it’s something I think is worth going back to, because it’s an important part of the huge efficiency problem that plagues all cars: getting some benefits out of the heat. lost.
Before I go any further, it’s important to note that electric vehicles produce less waste heat than internal combustion vehicles. For a gasoline-powered vehicle, about 25% of the chemical energy in a gallon of gasoline is directed toward moving the vehicle in the direction of its destination. The rest goes to heat dissipation, leaving the car through the radiator and exhaust and as heat into the engine compartment that seeps out. Regular friction brakes produced by non-electrified cars also produce waste heat, which literally takes the car’s kinetic energy and turns it into heat to slow the car down.
The upside? Gas and diesel vehicles can take some of this waste heat and use it to keep the cabin of the car warm. The heater core, which is essentially a small radiator, gets heated up when coolant is pumped through it from the engine, and a fan blows air through it to give you heat. Therefore, an insignificant portion of the wasted energy is put to good use.
Compare this to an EV, which converts only a little of its energy into wasted heat, and puts most of its energy toward actually moving the car down the road. When using regenerative braking (which produces some electricity rather than waste heat like friction brakes), the overall efficiency of an electric vehicle can approach 90%. That’s a great job. Not only can you use the waste heat to turn on the car’s heat as you would with a gas-powered car, but you also don’t waste a lot of energy and throw it away into the atmosphere.
But that doesn’t mean there’s no waste heat to handle in an EV. Decent electric vehicles have liquid battery cooling systems that extract this waste heat from the battery pack and dissipate it through the coolant, much like a combustion car. However, there is much less waste of heat, so there is no need for a large radiator, and the front of the car can have better aerodynamic efficiency.
Tesla and other companies that make electric vehicles are trying to take advantage of the waste heat from the battery pack. Tesla has a multi-way valve that can pump some of the hot coolant into the core of a heater or, conversely, heat up the coolant and pump it through the pack to heat up the battery cells and improve performance in cold weather.
GM’s Ultium Energy Recovery System
In a GM press release, it said, “The Ultium platform can recover and store this waste heat from the Ultium propulsion system. Furthermore, it can also capture and use moisture from inside and outside the vehicle, including body heat from occupants.”
I have to admit that at first, I was quite obsessed and was reminded of that the matrix (In this movie, AI robots use human body heat to power their civilization.) But I’m reasonably sure that GM won’t get us into a virtual world and steal our body heat, so they’d probably use another method.
So, how does a GM Ultium heat pump work?
When I tried to figure out what GM was doing to accomplish the power recovery, I couldn’t find the details. One YouTube channel interviewed an engineer at General Motors, who told viewers that there was nothing but that he was recovering waste heat and putting it to use. Other sources speculated a bit, but other than that only revamped the press release, which gave us an idea of what the Energy Recovery System does, but not how.
It was the only clue I could find here, as an engineer said that what sets the system apart is not the new parts, but how the existing parts integrate together and work together. So now I can actually make some informed guesswork rather than wild speculation.
If there are no new parts, we can rule out the idea that there is something really cool, like a thermoelectric generator, in the system. Instead, we have to assume that parts commonly found in electric vehicles are already doing the work that GM says the new system powered in its Ultium cars is doing. Since they mentioned cabin heat, that means we need to not only look at the battery cooling system, but also look at the HVAC system.
This leaves us with a liquid battery pack cooling/heating system, with liquid contact with the HVAC components. We can also assume that there is a heat pump included, as this is the most efficient way to cool and heat the cabin except for extreme cold, where resistive heating is required. But I think GM uses its heat pump like a geothermal heat pump.
A geothermal heat pump exchanges heat or cold with the ground, maintaining a constant temperature. This allows for greater efficiency than exchanging heat or cold with air, which can vary a lot throughout the year, so the heat pump itself doesn’t have to work as hard to heat or cool a home or business.
By exchanging heat between the battery pack, the power electronics (including regenerative braking heat), the coolant, and the interior of the vehicle (which may be hot or cold), the computer can determine which way to pump out the heat. If the cabin gets too hot, the heat pump can act as an air conditioner, drawing heat from the cabin air and putting it into the cooling system to pre-condition the battery pack. If the cab is cold, it can do the opposite.
If both the cab and the battery are hot, a pump may help remove the heat to both. If both are too cold, it can act as a more efficient battery pre-conditioning system (rather than resistive heat). In this way, the system can theoretically use as little energy as possible under all conditions.
But how do we use our body heat? Well, not by much, but when the cabin gets really hot, so are you! As the cabin cools down, your body heat is absorbed into the system along with other heat.
Finally, how can this energy be stored if it cannot generate electricity for the beam with excess heat? GM probably uses the same trick as the Toyota Prius to store heat: a large thermos can. If there is excess heat in the battery/cabin cooling system and there is no way to use it at the moment, the system may put some of the hot coolant away in an isolated room. Then, if hot coolant is needed to warm the cabin or the battery, they can release that heat instead of using battery power to cool it.
I could be wrong, but maybe not so much
GM can come out later and tell us all about how the Ultium heat pump system works, and it will probably differ from what I write here. But I don’t see how HVAC and refrigeration systems can do what they claim in any other way (Editor’s noteA quick Google search reveals a 2016 offering of a thermoelectric generator by a company called Evonik, whose website claims GM is one of its end customers.). However, GM can’t tell others how to make a more efficient system or that everyone does. If you work for an electric car company, don’t just do what I’m saying in this article, because General Motors may own patents on some of them.
Either way, it’s good to see that more manufacturers are taking efficiency seriously. We hope more companies will follow.
Featured image: Chevrolet Silverado EV, on a Ultium chassis. Photo by General Motors.
Do we appreciate the originality of CleanTechnica? Consider becoming a CleanTechnica Member, Supporter, Technician, Ambassador – or Patreon Sponsor.