itnetpro
Posts: 17
Joined: Mon Oct 05, 2015 9:47 pm

Pre-conditioning Value vs Cost

Wed Oct 21, 2015 7:57 am

So I decided to start pre-conditioning my wife Rex this morning for the first time. We have solor panels on our roof so we don't pay a dime for electricity. This is our second electric car (First Ford Focus EV) so we know the panels will produce enough energy to supply both the house and car along with enough extra to get a $100 plus credit back from PECO every year.

My concern is Value of pre-conditioning vs cost in KWh.

My wife drives:
4 days at 50 miles.
2 days at 60 miles
1 day at 70 miles

On average every week. All of theses days <Example while at work> involve an extended period of time where the car is stopped and not charging. So here is my question. Does anyone have any idea how much power is used over the 150 minutes of pre-conditioning at various temperatures. I am trying to determine if there is a real value in spending the extra KWh vs not.

I live in the North East <Philadelphia> Area. I'm trying to calculate based on average winter temperatures how much more KWh we will use per month to pre-condition. Furthermore, calculate that against the average KWh saved per trip to understand the net KWh extra power usage per month.

I know this sounds crazy but I prefer to maintain the current balance I have now where I don't pay my local utility company a dime for power generation. If for instance the net KWh usage increases by say 200 KWh per month to charge then it wold defeat the goal I am trying to achieve.

In such a scenario if my wife wants to keep her heinei warm I will have her hit the remote button 15 minutes prior to leaving to simply warm the cabin instead.

John

janner
Posts: 228
Joined: Sun Jan 25, 2015 5:24 am
Location: Bath, UK

Re: Pre-conditioning Value vs Cost

Wed Oct 21, 2015 8:01 am

If you want to save money on pre-heating the battery then set charging to finish at the same time as you want to depart. The battery heater is one kW but it's turned off during charging because charging already warms the batteries.
2015 i3 ReX Solar Orange, Loft interior world. BMW professional, 19" turbine-spoke 429 wheels, DC rapid charging, driving assistant plus.

itnetpro
Posts: 17
Joined: Mon Oct 05, 2015 9:47 pm

Re: Pre-conditioning Value vs Cost

Wed Oct 21, 2015 9:19 am

janner wrote:If you want to save money on pre-heating the battery then set charging to finish at the same time as you want to depart. The battery heater is one kW but it's turned off during charging because charging already warms the batteries.


So, heating the battery on a BMW Rex (No Heat Pump) will only consume 1KW per hour?

If this information is accurate then at most I would consume 2.5 KWh over a 150 minute conditioning period.

With that said assuming 30 days in a month that = 75 KWh.

I am already saving between 30-50 KWh per month moving from Ford Focus EV to BMW i3.

With that said I would only have to add 4-6 miles or 1 to 1 1/2 KWh range to an average trip to consume about the same I was with our Ford Focus EV.

Can anyone confirm the 1KWh consumption during battery conditioning?

janner
Posts: 228
Joined: Sun Jan 25, 2015 5:24 am
Location: Bath, UK

Re: Pre-conditioning Value vs Cost

Wed Oct 21, 2015 11:01 am

The 1kW heater came from the BMW R&D engineer at the i3 meet last weekend. It's a maximum 1kW. Would be good to have confirmation from others though.

Heating the battery on the BEV and the ReX is the same. The heat pump is for the interior.

If you're not plugged in then max 2.5kWHrs equates to 10 miles or so.
2015 i3 ReX Solar Orange, Loft interior world. BMW professional, 19" turbine-spoke 429 wheels, DC rapid charging, driving assistant plus.

jadnashuanh
Posts: 3285
Joined: Thu May 22, 2014 2:07 pm
Location: Nashua, NH USA

Re: Pre-conditioning Value vs Cost

Wed Oct 21, 2015 1:03 pm

To get maximum range, you need to set a departure time and click on precondition. Preconditioning the cabin does NOT warm the battery by default. That operation only runs for about 30-minutes. To get the full effect, you need the departure time which is what warms the battery pack up. Depending on the temperature and previous charging timeline, that could take nearly 3-hours.

On my BEV, when preconditioning the cabin, I've seen my EVSE report peaks of 20A (usually bounces between that and say about 12A). At my average 245v, that's 245*20=4.9Kw peak. It doesn't stay that high, but it does peak out there, and on preconditioning, only lasts for 30-minutes. But, if you combine that with the battery warmup from setting departure time, it might peak higher. My EVSE didn't come with a meter, but I bought a panel mount one off of Amazon and mounted it in the electrical box where my EVSE attaches...it reads volts and amps which is where I'm getting those numbers.
Jim DeBruycker
2011 535i x-drive GT, 2014 i3 BEV

i3Alan
Posts: 233
Joined: Wed Jul 09, 2014 4:08 pm

Re: Pre-conditioning Value vs Cost

Wed Oct 21, 2015 3:57 pm

janner wrote:Heating the battery on the BEV and the ReX is the same. The heat pump is for the interior.

For US i3 BEV models, the heat pump for the battery is standard. It is not available for the REX, as the REX fuel tank occupies some of the space needed for the battery heat pump components. It also has the resistive heat, but that is only used if the heat pump cannot handle the heating needs. This is one reason the BEV has less range degradation in the winter cold than does the REX.

My understanding is that the interior and battery heat pumps share a single compressor, but have separate coils/condensers. I don't know if the dual system uses the same compressor as the REX.

I thought the battery heat pump was an option for non-US BEVs.

jadnashuanh
Posts: 3285
Joined: Thu May 22, 2014 2:07 pm
Location: Nashua, NH USA

Re: Pre-conditioning Value vs Cost

Wed Oct 21, 2015 4:42 pm

I think I'm right on this...don't confuse battery heating with cabin heating...done in different ways with different components and with different settings in I-drive. You can precondition the cabin without being plugged in, but you cannot precondition the HV battery unless you are plugged in. Cabin conditioning would differ based on whether you had a BEV or a REx, but I think, battery preheating is a totally different thing. Battery conditioning only occurs if you are plugged in (to warm things), but cooling is a different story...it can occur without being plugged in to prevent damage. Cold, OTOH, will decrease the capacity of a LiOn battery, but is less likely to damage it unlike a lead acid one that, if discharged could freeze and split the case.
Jim DeBruycker
2011 535i x-drive GT, 2014 i3 BEV

psquare
Posts: 481
Joined: Wed Oct 15, 2014 5:57 am
Location: i3 REx, 225xe Hybrid UK
Contact: Website

Re: Pre-conditioning Value vs Cost

Thu Oct 22, 2015 10:55 am

Interesting topic. I was asking myself the same a while ago. Since I'm in the process of getting PV panels installed, my situation will soon be very similar.

janner
Posts: 228
Joined: Sun Jan 25, 2015 5:24 am
Location: Bath, UK

Re: Pre-conditioning Value vs Cost

Fri Oct 23, 2015 2:14 am

Since my post I've preconditioned twice and both times the readings (and kWHrs used) are consistent with a 1kW heater - ambient temperature is 10degC.

Anyone got any better / different data?
2015 i3 ReX Solar Orange, Loft interior world. BMW professional, 19" turbine-spoke 429 wheels, DC rapid charging, driving assistant plus.

jadnashuanh
Posts: 3285
Joined: Thu May 22, 2014 2:07 pm
Location: Nashua, NH USA

Re: Pre-conditioning Value vs Cost

Fri Oct 23, 2015 3:07 pm

Just for clarification, as used in the i3, preconditioning is for the CABIN. Setting a departure time is what conditions the BATTERIES. In that operation, you have the option to also precondition the cabin. Doing both means your battery is still full, at the optimum temperature, and the cabin is comfortable when you leave. This should decrease the load on the battery assuming you want to warm or cool the cabin as you drive, at least that initial conditioning period. Depending on the ambient temperature, warming the battery may or may not be beneficial, but then, it won't waste energy either, since the car just won't do it if not required. During driving, the use of power from the battery pack warms it, sometimes, enough that it takes active cooling to keep it in a safe range.

You cannot precondition the battery pack unless you are plugged into an EVSE, but you can precondition the cabin any time you wish, regardless of that. Be aware that, depending on temperature, it can take upwards of 3+ hours to condition the battery pack, while the cabin preconditioning will only run for 30-minutes. That's enough time in the winter to make it easy to remove any remaining snow or ice that may have accumulated on the vehicle, and take all of the chill out of the interior. Nice to sit on a seat that is warm and not have it suck heat out of you even if the air temp is comfortable.
Jim DeBruycker
2011 535i x-drive GT, 2014 i3 BEV

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