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ElectraGirl: Pre-Conditioning Explained

Saturday 3rd January 2015

What is pre-conditioning? This is the term used to describe the heating or cooling of your Electric Car interior before you need to leave your current abode.

A snow covered Leaf plugged in ready to pre-condition

A snow covered Leaf plugged in ready to pre-condition

There’s nothing nicer, when it is freezing outside, than getting into a lovely warm car. We all like it but, if you own a petrol car you cannot do this. Well, you can but you shouldn’t as you are then idling, which is, in most US states illegal – although not enforced enough. You are also creating even more pollutants in an idling vehicle than one that is being driven. To overcome the cold and the slow engine speed, a petrol car has to use even more fuel than normal to keep itself going. And, do you know who suffers the most from idling vehicles? Children do! They stand closer to the tailpipe height than adults and breathe faster than adults. An idling vehicle has higher pollutants inside the vehicle too – Yuk!!

2014 BMW i3 Remote control App

The 2014 BMW i3 App allows for on-demand or scheduled pre-conditioning

When you are pre-conditioning your EV, you can leave the garage door closed as there are no stinky fumes to stink out your garage which is an added bonus especially if you have a garage that is attached to your house. There is no worry about adding to the rise in incidents of asthma in children – yes, it is happening. You are also not damaging your cars engine as EV’s don’t have one!

You checked the weather forecast before you went to bed last night and saw that it was going to be freezing outside the next morning, you knew your EV would be cold and so will the batteries. So to have a nice warm EV ready for your departure you can either program your EV to start warming up from the settings on the car, the app on your smartphone, or the remote key fob. Some EV’s will warm their batteries first before heating the cabin, yet another benefit as warmer batteries hold more electrons and therefore you get better range. Pre-conditioning while still connected to the mains power is beneficial and results in more range as you are not using the batteries to warm the car which does eat into your range. Some EV’s can be toasty and warm to go in 15 minutes, others can take longer, depending on whether and how much they heat the batteries first. In the ActiveE, the car would heat the batteries to 20°C (68°F) first then start heating the cabin – this took around an hour in total.

Mitsubishi's i-MiEV remote Control key fob used to start pre-conditioning

Mitsubishi’s i-MiEV remote Control key fob used to start pre-conditioning

Over to my Chief Science/Technology Officer for the science behind pre-conditioning.

How can pre-warming your car be more environmentally sound than not?

To answer that, we need to look at the numbers very closely.

Let’s assume that you are going to drive in a warm car. Warming the car takes energy. Let’s assume, for example, that it takes an average car 15 minutes to warm up with its 5kW heater built in. The power used to warm up is 5kW for ¼ hr or 1.25kWh of electricity. Once the car is warmed through, the heater cuts down power to 500W or less depending upon the outside temperature. That 15 mins of driving uses 500W x ¼hr or 0.125kWh of electricity but, wait, the power used whilst we’re driving is coming off of the main battery and that’s not 100% efficient! Let’s assume 85% efficiency for charging and discharging. That means that last 15 mins of driving with the heater on actually used an extra 15% or about 0.143kWh for a total power consumption, after 15 mins of driving of 1.393kWh. That’s about $0.21 and about 1.3lb of CO2 here in New Jersey. Let’s compare that to jumping in and driving away with the heat on. That’s 15 minutes of chilly car warming up at the full 5kW and, from the less than 100% efficient batteries. So, that’s 5kW x ¼ + 15% or, 1.44kWh and that’s about $0.22 but more importantly, it’s now 1.46lb of CO2.

There are always variables, if the battery is 95% efficient it’s a wash, if the battery is charged during off-peak base-load and preconditioned on higher polluting mid-day power, it’s a wash but, it’s seldom better to heat on battery and you’ll always loose the extra miles.

In the summer we can do the reverse and cool the car the same way.

Being able to pre-condition is just one of the many great features about Electric Cars.

Are you pre-conditioning or is it just too much trouble?


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  • CDspeed

    I’ve not used mine yet, I didn’t use it in the summer the car cools down fast enough for me. And even though it’s January 3rd it was 85 degrees fahrenheit today so…………….

  • MEroller

    “warmer batteries hold more electrons”nAs a deputy Science/Technology Officier I must slighty correct this: Internal resistance (“impedance”) of Lithium-based cell chemsitries rises considerably below about 15u00b0C / 59F, thus causing higher voltage drop at a given discharge current and fooling the BMS/”fuel gauge”/controller to believe a battery is more discharged than it actually is, i.e. not as much of the (still virtually unchanged) battery capacitiy is practically usable with a cold battery.nnYes, I precondition my battery every morning that is colder than about 15u00b0C – on grid power, and ensure it heats up to 20…25u00b0C (it is already a few years and km old…) before I start my ride. And when it gets cold enough during the day that the battery temp., drops below 15u00b0C before I head back home I pre-heat the battery on it’s own power to get at least 15…20u00b0C into the battery before I need to start my climb out of the river valley where I work. Despite loosing some usable capacity the whole ride home is a LOT more spirited than when the battery only has 10u00b0C in it. Below 15u00b0C in the battery I can no longer go full blast out of the valley (at up to 65km/h), at 10u00b0C I have trouble even keeping 40km/h, and that quickly drops to 0 if the battery gets any colder.nnThis is not a car, only an electric scooter/motorcycle, so I have no additional active creature comforts that I could pre-condition, only maybe heating my gloves before I take off 🙂

    • Michael Thwaite

      +1nnnThe Roadster, which is, I think battery current limited rather than power controller limited is, in winter, with the batteries at or about a few u2103 only good for about 160-180kW of power. With the batteries all warmed up in Summer at 20-30u2103 the pack pushes out well over 200kW and that really makes a difference!

      • MEroller

        Now THAT is interesting! nBut then again: due to the very high power of the Tesla Roadster it probably stresses it’s battery to a similar, though probably a little lower extent as my scooter does (I have currents of up to 4C), so you are bound to experience some noticable power degradation over cold battery temp. too.nWhat I do NOT understand: Tesla Roadster was also tested at sub-freezing temperatures, but did they not do cold soaking tests of the battery and find out these dire effects for themselves? Adding battery heating to that pack would not have a been a great deal to them, and Model S has it too.nThe Nissan Leaf, as far as I know, does not have battery heating means to this day. The Mitsubishi i-MiEV was first lauched in moderate climate areas and only introduced to the colder climates after battery heating was added. That is such a no-brainer that I am really puzzled how even major car manufacturers overlook – maybe even by choice – the necessity of not only battery cooling, but also battery heating…

        • Michael Thwaite

          The Roadster has an immersion heater in the thermal fluid loop running round the bricks of cells. It’s wired into the charging feed and kicks in to warm the battery to a few degrees above freezing before it’ll engage charging – that can take an hour – then, it relies on internal resistance to keep it warm during charging. However, once warmed, that’s that. A lot of our Canadian friends enjoy a whole season without regenerative breaking as the Roadster cuts it completely at 0u2103 battery temp!nnnOn the flip side, owners in HK enjoy loosing a few miles range when they park their cars in the sun as, the HVAC kicks in to cool the batteries. Only problem is the HVAC cools the passengers or the battery, never both!nnnThere’s also a ‘Performance’ mode where it charges the pack fully whilst holding off the cooling to allow the pack to reach 35u2103 – that’s when they quote the full 0-60.nnnIt’s no where near as complete as the S but the Roadster does, at least do what it can to look after the batteries.

  • BenBrownEA

    wow… as I consider the i-miev (or not) I find this very helpful information. Thank you greatly.

  • Dennis Pascual

    You might want to re-run this in the summer… In Southern California, a lot of us use pre-conditioning to COOL our car when it’s really hot out.

    • Electra Girl

      I’ll make a note to do that and change it for the hotter months.

  • I routinely pre-condition my Smart ED in the winter, but never in the summer, as it’s never hot enough in the morning to matter. Frankly, the interior volume is so much smaller than other cars I’ve driven that the heating/cooling time is vastly reduced.nAgree with other posters here, that pre-conditioning on cold days allows the car to drive at full power, although in my Smart ED, it is extremely rare to get reduced power (75%), and generally only when the car has cold soaked in -10C for more than 5 hours. I’ve only once experienced reduced power to 50% when the car was -24C for 8 hours.

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