Innovative Approaches for Heating Electric Vehicles
November 29, 2012
November 29, 2012
We’re heading into the time of year when drivers jump into their car and turn on the heater, maybe even letting the engine heat up for a minute or two before committing to grab the ice-cold steering wheel. We thought it would be a good idea to go over heating approaches within EVs and some specific challenges that they face.
When conducting the Hot Weather Webinar we touched on how large of an impact auxiliary load can have on electric vehicles and their range. This post is going to dig a bit deeper into the types of technology that manufacturers are developing to address this problem.
Heating and cooling loads are especially significant when talking about electric vehicles. The power required to make the cabin comfortable takes away from the power used to propel the vehicle, resulting in a reduced range when HVAC is used. Using Fleetcarma’s database, we found that on average about 30% of power used in an EV is not used for driving, but instead auxiliary loads such as HVAC.
Even for those without range concerns, reducing the climate control load will help with overall fuel efficiency. Allowing plug-in hybrids to maintain EV-only mode for longer, and reduce both emissions and cost while doing so.
So let’s take a look at what technology is already out there, and what we can look forward to in the near future.
Pre-heating and Pre-Cooling EVs
For EVs and Plug-in Hybrids pre-heating and pre-cooling takes advantage of the vehicle’s connection to the grid prior to a given drivecycle. With the battery fully recharged, the vehicle can be warmed up to suit the driver’s comfort level using power directly from the grid. The driver then unplugs and drives away in a warm and cozy cabin, still with a full battery. The energy required to maintain the cabin temperature will not be as high as the energy needed to heat it up initially. Pre-heating allows the driver to drain less of their EV range. A similar system works with cooling. Manufacturers have identified this as a key component in extending the electric range and systems now come equipped with apps which can remotely heat or cool a car at a particular time each day, if that car is plugged in.
Traditional electric vehicle heating involves heating up air, and then blowing that air into the cabin. Conventional vehicles use waste heat from the engine to reduce the heating load. Electric vehicles suffer in this respect as their battery is too efficient and does not generate enough waste heat to heat the cabin. Electric vehicles still heat the air using a resistance heater, and then use fans to push the warm air through the cabin. This approach to heating causes EVs to lose between 30-40% of their available range.
Up until recently, a cars climate control has been treated in the same way we would treat a house. A temperature is set, and either a heater or air conditioning turns on and fans circulate the air. Options are made available for where the air enters the car, but altogether a driver’s comfort seems based on filling the entire cabin with as uniform a temperature as possible. In order to minimize heating loads, manufactures need to think about the comfort of their occupants instead of just a temperature set point.
Heated seats have been available as a luxury trim add on for years. However in the EV market, heated seats are key to reducing heater use and extending range.
The average factory cost of heated seats is $250, without that option there is an extra $200 added on to install them afterwards. For EV and plug-in drivers these costs could be well worth it for the extra range they provide.
With a do-it-yourself kit market emerging many EV and PHEV drivers may be opting to upgrade their vehicle and maximize their range on their own.
Unlike using a resistor for generating electrical heat, a heat pump works in the same way as a household furnace. A heat pump works like a heat exchanger, transferring heat to a fluid which then circulates through ducts within the vehicle. Heat pumps are currently being developed to work on electric busses as well as a number of passenger EVs, including the 2013 Nissan Leaf released in Japan.
Heat pumps can be used for either heating or cooling the cabin depending on the time of the year and a driver’s personal preferences.
BMW discussed using an infrared heating system in an effort to cut energy use and increase range. The system would involve panels within the door and footwells and would silently deliver heat to the passengers. They estimate that with this technology the range of an electric vehicle could be extended by as much as 30%.