After driving ICE vehicles all your life it's easy to take for granted that heating a car is "free" and has no effect on range or MPG. But it's only free in the sense that the car is throwing away 80% of the energy in the fuel as waste heat into the environment year round even when you don't want heating, and in the winter you can capture say 10% of that to warm the interior and then still throw the other 70% away.white exec wrote: ↑19 Oct 2018, 08:14Electric buses and warmth
Came across some articles on this issue last week, looking at how to keep all-electric battery bus interiors acceptably warm (or cooled).
What was interesting was that the driving range (155mi_250km/day+) was not an issue with currently available vehicles, but heating remained so. A whole variety of solutions on offer (from old friends like Valeo and Webasto, amongst others). Interesting figure: using the traction batteries for interior heating would require an additional 2000kg of batteries to be carried.
http://www.eliptic-project.eu/news/are- ... sion-buses
https://www.busworld.org/uploads/exhibi ... -buses.pdf
So it's free if you don't mind throwing away 70-80% of the fuel you buy year round... The efficiency of an electric drivetrain is so high (90% is typical including battery, inverter and motor) that there isn't enough waste heat to heat the interior any significant amount - no EV that I'm aware of tries to use drive train or battery heat to heat the cabin, although a few will use the drivetrain waste heat to warm the battery in cold weather to bring the battery up to more efficient temperature.
So you end up having to use your precious traction battery energy to run the heater as well, and this can reduce range by anywhere from about 10% to 30% depending on heater system design. On the plus side, in the summer when you don't need heating there is no additional waste heat being pumped out, so your summer driving is as efficient as it could be.
A surprising number of EV's still just use resistive heaters - which fall into two broad categories. PTC water heater or fan heater.
My Ion uses the old fashioned PTC water heater approach using a conventional heater matrix. This is probably because it's based on a petrol car that was originally designed with a heater matrix. Instead of completely redesigning the heating and cooling system they essentially fitted a 5kW 360 volt PTC water heater which heats a glycol coolant loop that is pumped around the heater matrix and PTC heater. Maximum temperature is about 60 degrees so the coolant loop is not pressurised and it doesn't do anything else other than the heater. (There is a separate coolant loop for the motor and drive inverter which goes through the radiator at the front)
Simple, very reliable and safe, and it works, but very slow to respond as you have a huge thermal mass of the PTC heater, a loop of coolant and the heater matrix itself. So the heater takes a good 5 minutes to fully heat up in the morning (although that's still quicker than an idling ICE first thing in the morning) and is very slow to respond to increases or decreases of the temperature knob - which can take several minutes from when you turn the temperature up or down until you notice a significant change.
There is probably some efficiency loss in having to heat the thermal mass of everything up, because when you get to your destination and leave the car there is still a large thermal mass sitting there hot wasting that stored energy. If you turn the heater off earlier before reaching your destination it stops the coolant pump so you still can't extract the latent heat from the PTC unit. Definitely not my choice of heater.
Some EV's use what is essentially identical to a mains operated fan heater, where you have coils of nichrome wire running directly from the ~360v traction battery heating the airflow as it goes through the ducts. The advantages of this system are super fast response time, (turn the heater on and it is hot in seconds, so you could have your window thawed out in the morning in minutes with no engine running) and very low thermal mass. (not much latent heat loss after turning the heater off and leaving the car)
The disadvantage is probably in making this safe - for safety reasons you'd have to be very careful about bringing the high voltage for the heater element into the cabin, most likely the heater box is located in the "engine bay" to avoid bringing high voltage into the cabin. You do also rely a lot on your pollen filter - the last thing you want is bugs, dirt, dust etc getting into your high voltage element causing shorts, catching on fire etc... Likewise water from a leaking scuttle getting into it would not be good. Another possible problem might be burnt dust smell that you get on some fan heaters that have sat unused for a long time.
The third approach is to use a heat pump, which can increase the coefficient of performance by up to about 3 - so you can get the same cabin heat from 1kW that a resistance heater would need 3kW for. A heat pump can bring the range penalty in winter down from 25-30% to more like 10-15%. The disadvantage is heat pumps don't work well in very low temperatures (below about -10C) so still need a resistance heater to work in conjunction with it at very low temperatures. Not really a problem in the UK though, mainly an issue in places like Canada.
Heat pumps are just AC's running backwards of course so make a little bit of noise and do eventually wear out or break down whereas a PTC or fan heater style heater basically lasts forever.
Interestingly while new Leaf's, Hyundai Ioniq and Kona and many other EV's have heat pumps either as standard or as options, Tesla have decided to stick to fan heater style resistance heaters. Not entirely sure why, but it means that a Tesla will lose more range as a percentage in winter than an EV with a heat pump.