When winter storms left hundreds of drivers stranded and stuck on I-95 in Virginia for hours, some people questioned what would have happened if the cars were electric vehicles (EV) given EV batteries' susceptibility to temperature extremes.
Alex Lauer put it to the test, sitting in a Ford Mustang Mach-E for 12 hours in temps ranging from 13-24 ℉ degrees. Even after 12 hours of operating time with the vehicle’s HVAC system fully engaged for a comfortable interior temperature, his EV battery had a 75% charge and a range of 132 miles, performing much better than its ICE counterparts under similar conditions.
Despite a sometimes pessimistic public view of EV performance in cold weather, the results of Lauer’s impromptu experiment are no accident and shouldn’t come as a surprise. EVs are designed with efficiency in mind and are often performance tested at temperatures down to -40 degrees Fahrenheit.
What makes this possible is sensor technology integrated into an EV’s design.
One such component contributing to improved battery efficiency is EV heat pumps. Considered a new tool for increased battery life, EV heat pumps are providing the alternate route for improved efficiency and range.
In the world of EV design, electric cars with heat pumps are relatively new. Many major manufacturers have quickly embraced heat pumps as an alternative to resistive heaters.
Bringing a new level of optimized power conservation to a vehicle, heat pumps are proving themselves as an important addition to EVs. Heat pumps for climate control represent efficiency in action, as they leverage the by-product of normal operation (heat) and use an EV’s existing systems for climate control.
The shift toward using heat pumps as a means of cabin climate control flips the model of heating used by vehicles with an internal combustion engine. Without the waste heat generated by combustion, an EV has to create heat using alternate means.
A heat pump in an EV works as an air conditioner in reverse and uses a system with two loops. The first loop moves a cooling medium (coolant or refrigerant) around a component — in this case the EV battery — with tubing connected to a “cold plate” attached to the battery array. Excess heat that is captured is then moved by the coolant pump into a liquid-to-liquid heat exchanger into the second loop, where heat is released by an evaporator and redirected into the cabin as a heating source in cold weather. Furthermore, through the use of new combinations of flow control and expansion valves, the refrigerant that normally cools the cabin can be flowed in reverse to add heat to the cabin in cold weather.
Heat pumps create an improved and more efficient use of power, which increases battery life by reserving more power and extending range. Rather than using a battery’s energy to generate new electric heat for passenger comfort, an EV is able to conserve power or use it for other comfort items, such as heated seats and steering wheels.
To use heat pumps effectively to increase battery life, the system uses refrigerant pressure and temperature sensors. Both pressure and temperature sensors help control enthalpy (internal energy plus pressure and volume). This helps create a high coefficient of performance to produce a maximum amount of heat exchange using a minimum amount of energy.
More specifically, pressure and temperature sensors help the vehicle regulate the thermal management system, and, by extension, the cabin’s climate for heat with precise control.
Controlling pressure in a thermal management system – and thereby the expansion and compression of cooling fluids – requires this high level of precision. It impacts how all elements of both loops, such as the expansion valves and the condenser, function in moving refrigerants in liquid and gas under different pressures through the system. Compression of refrigerant gas releases heat from the refrigerant into the environment, while expansion of the gas extracts energy from the environment. By changing the direction of flow and controlling the location of the compression or expansion cycles, the same refrigerant and controls can provide both heating and cooling of the cabin within the same hardware.
The precision control relies on understanding the pressure and temperature of this refrigerant at various critical control points within the system. In heat pump systems such as those used in Tesla’s Octovalve design, the precision controls driven by accurate sensing increase the range of the vehicle by over 10% in cold weather over the standard heating loop.
In addition, these sensors help the vehicle manage how these elements are using power to achieve the necessary high coefficient of performance. It all leads to more efficient use of available power to extend the battery’s life per charge, as well as range.
While cold temperatures can reduce the driving range for some EVs by as much as 40%, thermal management systems using heat pump technology and sensors can recover a significant amount of energy loss.
Visit our EV/HEV Sensor Resource Hub to learn more:
EV heating and cooling systems are a far cry from those in internal combustion engines and the stress it puts on the vehicle, but heat pumps and their accompanying sensors are an important component in thermal management for improving performance.
While heat pumps don’t eliminate the impact of cold weather on battery life, they do allow EVs to make better use of available energy than their internal combustion engine (ICE) counterparts.
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