Auxiliary cabin heating system

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Aug 5, 2019
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I am looking to buy a 120 Ah I3. I live in the UK.

I am aware that the auxiliary cabin heating will heat up the vehicle before setting off (whilst connected to your home charging unit). My BMW garage says that this added extra will improve battery efficiency by up to 30%. The sales assistant talked about a heat pump but could not explain the dramatic improvement in battery efficiency. Is this for example in use during travel?

30% is a lot so this seems an essential extra and I wold be grateful for comments and some technical advice if possible.

Regards, George
 
A heat pump essentially runs the AC system backwards, extracting the heat from the outside air and releasing it inside. It is significantly more efficient than resistance heating (think hair dryer coils), and should absolutely be on your shopping list.

I installed a central AC system with heat pump function in the summer of 2018 here in upstate New York. It saved me over 50% compared with my heating oil bills in prior years. When it gets really cold (like 5F or -15C), heat pumps can't keep up and fall back to resistance heating...
 
I would have the heat pump if I could, but you can't get it with the REX, which I have. In my first winter with my i3 I'm finding that the cold temps (20's to low 30's) is reducing my range by about 25%.
 
mrgeorgemartin said:
I am aware that the auxiliary cabin heating will heat up the vehicle before setting off (whilst connected to your home charging unit). My BMW garage says that this added extra will improve battery efficiency by up to 30%.
This is incorrect. The battery heating and cabin heating systems are two different systems.

The battery heating system uses electrical resistance elements to warm the battery pack. Heating the battery pack in advance of departing increases the usable battery capacity (i.e., range) in cool or cold weather. This is possible only when a charging station is plugged into an i3. The heat pump option has nothing to do with battery pack heating.

The cabin can be heated or cooled in advance of departing. This is a different setting from battery pack heating and can occur even when an i3 isn't charging. The standard i3 cabin heater uses an electrical resistance element to heat a heat transfer fluid. The heat pump option adds a heat pump to the cabin heating system. This much more efficient heat pump is used instead of the resistance element to heat the heat transfer fluid until ambient temperatures drop so low that the heat pump is less efficient than the resistance element (probably doesn't happen much in a typical U.K. winter).

mrgeorgemartin said:
The sales assistant talked about a heat pump but could not explain the dramatic improvement in battery efficiency. Is this for example in use during travel?
When cabin heating is being used, the electrical power required is much less (as little as ⅓) for the optional heat pump compared with the standard resistance element. Therefore, the effect on range would be much less using a heat pump for heating.

The cost of the heat pump option is quite low, so I advise ordering the heat pump.
 
Basically, a warm battery cell versus a cold one, will allow faster and more power to be drawn off...the heat makes it easier for those electrons to move providing a bigger quantity, and they can move faster.
 
flyboy320 said:
Here is a great link that describes the difference between battery preconditioning and cabin preconditioning.

That is great info. Thanks. Personally, I really wish that BMW had given us an option to start pre-conditioning from the app or at least from iDrive. That would be very helpful for us who live in colder climates but who do not have a set departure schedule.
 
I set the departure time frequently when getting ready to use my i3. Usually I'll know the night before, or earlier in the day, so I can set it there. The logic allows for one-time, or regular departure times, and there are three slots, so if you have say a regular workweek schedule, and a different one on say Saturday and Sunday, you can fill those in in advance. In my case, I rarely have a regular schedule, but usually know early enough to get the full advantage of setting it. Of course, you could go into the car and do it, but often, using the app or doing it online may be easier. Worst case, it will take a bit over 3-hours to warm the batteries when it's quite cold out, less as it warms up outside. Cabin conditioning only starts closer to your set departure time. Even just telling it to precondition the cabin if connected will save some battery power, but not as much as getting the batteries warmed, too. Note, preconditioning the batteries will draw power, and that will start to warm the batteries all by itself, but, may also decrease the full charge. The hysteresis in turning charging back on may or may not restart charging.
 
In some markets the battery heater wires are only installed together with the heated seat option, might need to check before ordering.

I have a Rex so cant have the heat pump, the HV powered immersion heating is very quick and just uses a slug of power initially. I waws concerned it might not be suitable, because of a mild climate there has been no range shrink thru winter.
 
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