GM: Ultium Heat-Pump System Boosts EV Range, Reduces Charge Times
Every vehicle powered by Ultium batteries incorporates efficiency-enhancing energy recovery system based on heat-pump technology covered by 11 patents.
On the same day that General Motors president Mark Reuss confirmed there will be a fully electric version of the company’s Corvette along with a hybrid model, the company released news that all its current and future EVs using its Ultium battery technology will employ a multi-patented, heat pump-based “energy recovery system” that enhances entire-vehicle thermal management.
The energy-recovery system, said engineers in a background session with media, ingests so-called “low-quality” energy, mostly in the form of heat, from various propulsion-related components – but also from the cabin and even the ambient air. Then, in a phase-change process enabled by the heat pump and an intricate collection of valves, the low-quality energy is moved “to a higher-temperature, higher-quality use,” said Lawrence Ziehr, project manager of Ultium energy recovery capabilities.
The system’s coefficient of performance (CoP) metric is measured much the same way as for residential heat-pump systems. GM engineers claim its CoP of around 4 to 5 means that for every one unit of low-value energy, the system can yield four or five times the original amount. That energy then is channeled where it can be most effective, typically to help heat the batteries or the cabin. “It’s a multi-valve system to steer the energy where you want it,” said Tim Grewe, GM’s general director, electrification strategy and cell engineering.
The system harnesses refrigeration and condensing circuits to absorb heat from places it’s unwanted – such as the vehicle’s traction motors or power electronics – and shift it to more desirable purposes. It also can take ambient air and boost its temperature when desired – significantly helping to reduce the energy taken from the batteries to provide cabin heat or heating for the batteries themselves.
By freeing the vehicle’s batteries from the need to provide heating energy, Ziehr said driving range can be extended as much as 10% (using a cabin heater in cold ambient temperatures can reduce an EV’s operating range by 35%, according to the National Renewable Energy Laboratory). Meanwhile, GM claims the energy recovery system also is able to much more quickly warm the cabin than conventional resistance heating or even the ‘heat engine’ in internal-combustion vehicles. Vehicles with Ultium batteries still will have resistance heating, but the energy-recovery system means the energy-intensive resistance heat is required to contribute less to achieving and maintaining cabin comfort.
The heat-pump energy-recovery system replaces a conventional air conditioning system that usually is separate from an EV’s heating componentry. Compared to GM’s Bolt EV that does not use the energy-recovery system, Ziehr said total HVAC system weight is roughly similar because the Bolt has separate thermal-management systems for cabin conditioning and the propulsion components.
Ziehr said the new energy-recovery system’s thermal-management optimization is one enabler of the much-promoted Watts-to-Freedom mode of the recently launched GMC Hummer EV, allowing the 4.5-ton (4082 kg) vehicle to accelerate from 0-to-60 mph (0-to-97 km/h) in around 3 sec. The system also is expected to deliver faster recharging times by using otherwise unused heat to precondition the vehicle’s battery to the optimum temperature for recharging, resulting in quicker recharging. He added that the system, managed by GM’s proprietary controls, also allowed engineers to downsize radiators and optimize the size and operating functions of other thermal-management hardware.