Friday, December 17, 2010

Can I take a Cold Cabin?

The short answer is yes.  Ever since I've been looking into Electric Vehicles (EVs), I have been trying to do things counter-intuitive for a standard Internal Combustion Engine (ICE) to make me more comfortable for the switch to an EV.  Today I tried Cold Cabin Driving.  Cold Cabin driving is based on the idea that heating the entire cabin of an EV is very energy expensive.  For instance, the Nissan LEAF is said to have only 62 miles of range (100 km) at 14℉ / -10℃ outside temperature in stop-and-go traffic at 15 mph / 24 kmph:

Winter, urban stop-and-go, traffic jam: 62 miles

Speed: Average 15 mph
Temperature: 14 degrees
Climate control: On
Though the average speed is only 15 mph with stop-and-go traffic, the 14-degree temperature means the heater is doing a lot of work so you spend considerable time and energy heating your car rather than moving forward. Despite these conditions, it would still take more than 4 hours to run out of charge!

The reason for this abysmal drop in range is not specific to the LEAF and indeed is a common problem of all EVs.  In an EV, the engine does not generate much heat — it works by the more powerful force of Electromagnetism — so it can't take advantage of engine heat generated through the inefficiency of an ICE to otherwise efficiently heat the cabin.  Instead, an EV must use some form of active heating to generate the desired cabin climate, such as the heating coil and radiator used in the Nissan LEAF.  The operative point here is with climate control on.  However, one could conceivable drive with reduced (in the LEAF's ECO mode) or no climate control at all to achieve greater ranges under those conditions; driving using this technique is an example of hypermiling.

Hypermiling is the process of driving in such a way as to get the most bang for your buck, the most distance for a fixed amount of fuel.  It is possible to hypermile a standard ICE vehicle, an EV or a hybrid, however the techniques differ slightly for each one.  In the case of cabin heat, the ICE is using small explosions of fuel to drive the car forward, thus producing wasted energy through the heat dissipated by the reaction.  Thus, in an ICE, using the heater is actually more fuel efficient because normally the air used to cool the engine is just sent outside the vehicle to be lost.  By filtering it and sending it instead into the cabin, you're actually making use of heat energy that would otherwise be wasted.

Contrarily in an EV, it's expensive to heat a cabin.  In fact, it's a lot easier to just heat the driver through heated seats and steering wheel and a thermal blanket.  This is because heating via conduction through the seats and steering wheel is more efficient than heating by radiation from the atmosphere.  And the thermal blanket helps by keeping that extra heat in.

Now my current ICE doesn't have a heated steering wheel or thermal blanket, but it does have heated seats.  So I hopped in my car, turned the cooler down low and flipped on the heated seats to see how I fared during my commute.  I then repeated it this morning for an even colder test run.  And my verdict?  Bring on the LEAF!

But, I should point out one caveat: the Cold Weather Trims are so far not being offered on the 2011 LEAF.  The Cold Weather Trim is handy because it adds the Heated Seats and Steering Wheel and Thermal Blanket to the LEAF, which is required to fulfill the use-case specified in this experiment.  It is my sincere hope that, having to wait an extra 8 months for my car, when my appointed hour miraculously does arrive, I'll be allow to ordering the Cold Weather Trim for my very own Nissan LEAF.