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Why Heat Pumps Are Essential For EVs When The Weather Is Cold

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If you own an electric vehicle (EV) and live in a cold weather climate, you may be concerned about winter charging capacity. But don’t despair! Your EV model probably comes equipped with a heat pump, which can help EVs retrieve anywhere from 3% to 15% of the range—up to 50 miles—otherwise lost in cold weather. Heat pumps are an important tool for EV range preservation.

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A motor produces heat when in operation; that heat is wasted energy. Internal combustion engine (ICE) vehicles tap this excess energy to help run a car’s heating and ventilation. But because EVs are much more efficient, their small amounts of wasted energy don’t comprise enough to assist the ventilation system. In fact, EVs are so efficient that three-quarters of their electricity is directed to moving the wheels. But that efficiency presents an alternative scenario when the weather turns bitterly cold, occasionally causing cold climate range anxiety.

Last week some EV owners in Chicago discovered their batteries had died in sub-zero temperatures. Other drivers moaned that charging an EV at a handful of Tesla Supercharging stations took longer than usual. Some chargers weren’t working at all in the freeze, so EV owners had their electric cars towed.

It is clear that relatively new EV drivers — and maybe some more veteran drivers who haven’t paid enough attention — needed a primer in cold weather use of their vehicles, like preconditioning and other workarounds to help boost range.

An ICE vehicle’s efficiency is around 15% lower at 20°F during city driving than it would be at 77°F. It can also drop by as much as 24% for short 3 to 4 mile trips. EVs drop 39% in mixed city and highway driving, so it makes sense to optimize the features of your EV for weather, such as our CleanTechnica colleague, Chris Boylan wrote about this week.

Yes, sub-zero temperatures can negatively affect the efficiency of an EV. EVs face a high level of energy consumption for passenger compartment heating in cold climates. Battery capacity can diminish when it is cold, reducing the average distance that can be traveled on a normal charge. Starting the EV may become more tricky in cold weather, too, as the energy consumption for heating (and it’s the same for hot weather cooling) EVs causes a decline in battery charge and driving mileage, as does turning up the cabin heating.

EVs mostly use lithium ion batteries to power their electric motors. Lithium ion batteries are very happy at temperatures between 50 degrees and 110 degrees Fahrenheit, with a commonly-accepted ideal 70 degree temperature. In freezing temperatures, lithium ions slow down and don’t hold energy very well. Thus, they generally perform worse than normal in cold climate conditions.

Yet many EVs contain heat pumps, which transfer heat from outside the car to reroute power that might otherwise deplete the battery. EV heat pumps draw air in, compress it, then use the heat from the condenser to raise the temperature in either the battery or the car’s interior. Heat pumps augment an EV’s efficiency because they transfer heat from existing sources instead of creating it.

Several EV models warm their cabins with resistive heaters, which use electricity to heat wires and then blow air over them. That process draws considerable energy from the battery. Heat pump-equipped EVs can employ the same efficient process used to warm the cabin to precondition the battery.

The coefficient of performance (COP) of a heat pump can reach 3-4 units of heat transferred for every 1 unit of electricity used.  The heat pump is 3-4 times more efficient than a resistive heater, for example, which turns 100% of energy into heat. A resistive heater has a COP of 1.

A study from Oxford University and the Regulatory Assistance Project used data from 7 field studies across North America, Asia, and Europe which shows that heat pumps are 2 to 3 times as efficient as combustion or resistive electric heating technology, even in temperatures well below 0°C (32º F). In fact they perform significantly better than their fossil fuel-based competitors even in temperatures approaching -30°C (-22º F).

Which EVs are Equipped with Heat Pumps?

In 2021, Tesla improved the Model Y by adding a new heat pump that translated to a 10% improvement in efficiency. 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. Tesla redesigned the heating and cooling systems for the Model Y to tap into the inefficiencies of heating and cooling with electricity to maximize the efficiency of the vehicle’s thermal systems.

Tesla CEO Elon Musk explained, “The solution the Tesla HVAC team came up with was to have a local heating loop. So the thing will basically just spin itself up and get hot locally before opening another valve that then tries to heat the cabin.”

Heat pumps are essentially air conditioning systems working in reverse. Heat pumps bring warm air into the car, even in sub-freezing temperatures. More importantly, as heat pumps retain heat from the batteries, they increase the range of an EV.

What other EVs have heat pumps?

  • Jaguar’s I-Pace
  • BMW’s latest i-series cars
  • Hyundai’s Ioniq 5
  • Audi’s newest e-Tron
  • Kia’s EV9
  • Nissan Ariya
  • All new Tesla models

Final Thoughts about Heat Pumps

A surge of personal transportation electrification has swept the globe in response to the existential crisis presented by climate pollution. EVs are a significant solution to the problems of environmental and energy security.

Heat pumps are increasingly recognized as a critical technology for decarbonization. A heat pump designed for operation in low temperatures (not all of them are) is quite capable of functioning just fine even when the temperature outside falls below zero.

In 2022, global sales of heat pumps grew by 11%, marking a second year of double-digit growth for the central technology in the world’s transition to secure and sustainable heating. US consumers in 2022 installed 4 million ultra-low-carbon heating and cooling heat pumps — beating out gas furnaces for the first time.

New York state is still digging trenches, laying pipelines, and installing equipment, but, instead of flammable and planet-warming gas, those pipes will carry water or other liquids that transfer heat from underground — or from other buildings and sources in the network — that can be used by heat pumps to keep buildings warm. It’s an example of adaptation that’s reimagining how we use energy, as has been the addition of heat pumps to many EV models over the past few years.

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Carolyn Fortuna

Carolyn Fortuna, PhD, is a writer, researcher, and educator with a lifelong dedication to ecojustice. Carolyn has won awards from the Anti-Defamation League, The International Literacy Association, and The Leavey Foundation. Carolyn is a small-time investor in Tesla and an owner of a 2022 Tesla Model Y as well as a 2017 Chevy Bolt. Please follow Carolyn on Twitter and Facebook.

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