About that climate hit....

[jmueller065]

I've been wondering how the FFE figures out the range hit to use when you turn on the heater. I think I've figured it out...
http://jamiegeek.myevblog.com/2014/02/01/about-that-climate-hit/

 

[dmen]

Curious, jmueller- on Monday morning, did you turn on cabin heater right when you left the garage with a preconditioned vehicle, or 15 minutes later when the windshield was freezing up? How about on Saturday? I'm assuming from the blog post that it was right away both times. I ask because I don't see the same heated-range prediction behavior in my car.
I run cabin heating on some drives and not on others as well, often in patterns as well-- more heating on weds-fri when I drive the kids to school and on weekends, less on mon-tues when I drive alone-- but I don't see big differences in the degree of impact based on recent heater use patterns.

As far as I can tell, the range reduction due to cabin heating is affected by: outside temp(obviously), cabin temp at the time heater is engaged (pretty obvious too), and recent driving pattern. That last effect is a kind of reverse to what happens in warm weather. When I've been driving more open highway and light traffic for several trips, heating takes a smaller hit, like 30% or 70 mile range down to 50. But when I've been driving in very slow stop-and-go traffic for a few trips (when I'd get sub-200wh/mi in summer), the cabin heating can take 50% or more off! This sucks, but it makes sense. If I drive slower, I'm in my car for more time to go a set distance. All the while the heater's running. Since the motor is using less power at slower speeds, the heater is taking a larger piece of the battery pie.

So, I think the car uses outside/inside temperature info and heater settings to guess how much power the heater will be pulling, and uses recent average driving speed to guess how long the heater can run at that power alongside the motor's guessed-at power draw before the battery depletes. I think it takes that time and speed data to come up with the range when heat's on.

 

[jmueller065]

Curious, jmueller- on Monday morning, did you turn on cabin heater right when you left the garage with a preconditioned vehicle, or 15 minutes later when the windshield was freezing up? How about on Saturday? I'm assuming from the blog post that it was right away both times

You are correct: it is right away. I've found that if I wait until the window is icing up then heat is required. If I immediately turn on defrost on LO and low fan it prevents the window from fogging and subsequently icing--even with the really frigid temps (<0). Granted it means that the cabin does get colder as the drive progresses.

Good points: it's possible that what I'm seeing appears learned from history but is actually table or formula driven?

 

[WattsUp]

Also remember that, even if the "climate hit" were computed using a fixed formula (say, -10%), the hit would appear to be different simply based on the currently estimated range remaining.

For example, with 76 miles of range estimated, a climate hit of 10% will lop off 7.6 miles. But, with only 10 miles of range, exactly the same hit will only lop off 1 mile.

 

[jmueller065]

I've attempted to quantify this by recording the hit every morning before I drive away. To be consistent: I always take the same route for my commute (both ways), I drive at the same time every day, on the last drive of the day I turn off the climate controls (so that it is off in the morning when I start the car), the battery is always full (and has shown a range close to 70 miles) and the car is preconditioned to 85F for the morning commute. I can't control for: the weather, the traffic, and what the car does (see below).
For each day this week I recorded the outside temp as read on the MFT screen, the precondition state of the car, and the mileage hit when I initially turned the climate system on with LO/Low Fan/Defrost (sitting in the driveway before driving).
If the hit was formulaic I would expect the hit to track up and down (or stay constant) with regards to the outside temperature (e.g. if it was colder I would expect a greater hit than when it was warmer). If the hit was based on prior electricity usage by the climate system I would expect the hit to trend downwards throughout the week as I'm not using the heater as much as on the weekends. If the hit is based a little on driving habits I'd expect it to be somewhere in between the two above (but not show a consistent downward trend).
What did I see so far in 4 days?

Outside     Preconditioned   Status Hit
     6F          No*           -17
     7F          Yes           -11
    20F          Yes            -7
     0F          Yes            -4

Granted this is only 4 days worth of data but you can see a clear downward trend (upward trend? they are <0 numbers) in the status hit. I was really expecting a bigger hit this morning with the 0F temperatures out.

* = For some reason the car decided it didn't want to precondition itself on Monday (it was having problems syncing up the go times over the weekend and that may have contributed to the issue). In this instance I remote started the car and let it sit for 5 minutes (while still plugged in) and thus this datapoint may have a higher status hit than normal if the car didn't account for the fact that it was plugged in when I remote started it.

4 datapoints isn't really statistically significant but this is the kind of thing I've been observing all winter with the car which led me to think that the status hit is based on prior climate usage.

 

[dmen]

Interesting, jmueller- I didn't realize you are seeing a drop in predicted range even when activating the climate control system at LO defrost, without the heater engaged. I thought you were seeing the trend in how much range drops with the heater activated.
My range does not drop at all when I go from climate off to climate LO-defrost. Do you have A/C on? Otherwise, I'm not sure why your car's range would drop at all in this situation.

Basically if I have the temp set to 60 or LO, the range doesn't drop at all, whether on auto or specific fan speed, any combo of floor/dash/defrost vents, and A/C off. But if I turn the climate temp setting to 61 or higher, the range drops, like I said, anywhere from 30 to 50 percent. It seems to be an all-or-nothing thing: whether on auto or a specific fan speed, floor/dash/defrost vents activated, even Max Defrost, the range drops to the same number at that particular instance.

 

[WattsUp]

Basically if I have the temp set to 60 or LO, the range doesn't drop at all

Mine does (that is, when selecting defrost) when the external temperature is low.

Also, I think the defrost engages A/C whether you otherwise have it on or not. And when it does, it does NOT change the display to indicate that A/C is on -- but you do see the drop in range.

 

[jmueller065]

My sequence is: Hit the Fan "Down" button to turn on the climate, turn the knob to LO (if it isn't already there) and then hit the defrost button--the A/C has been off since October. After that sequence I see the range hit (typically as soon as I turn it on I see the range hit and it doesn't change while changing the settings).

I don't think the A/C runs with it on defrost, at least in these low temps... -2F this morning, simply because the Climate graph doesn't act like it did with the A/C running. With the temp set to LO the Climate graph stays at 0, if I turn it up to 60 or 61 the Climate graph will PWM control the heat (e.g. I'll see it go to the 5kW+ value for a little bit, then off, then back on, off, on, etc.). During the summer when using the A/C the Climate graph would stay at some intermediate level for a while then gradually drop off as the car came down to the set temp.

It is possible that it would run the A/C on defrost to cool the air--but there isn't any need to cool the air here!

 

[WattsUp]

My sequence is: Hit the Fan "Down" button to turn on the climate, turn the knob to LO (if it isn't already there) and then hit the defrost button--the A/C has been off since October.

Interesting.. with mine, seemingly depending on what phase the moon is in, or whether I've done an MFT reboot lately, simply turning on the climate (even via the fan LO button with temp already set to LO) can sometimes decide to turn on the A/C, regardless of whether it was on or off before. I often find myself turning off A/C that I didn't request.

 

[dmen]

My sequence is: Hit the Fan "Down" button to turn on the climate, turn the knob to LO (if it isn't already there) and then hit the defrost button

Huh. When I do the same thing, my range remains whatever it was with the climate control off. If temperature setting wasn't initially at LO, the range drops with the touch of the first fan button, but when I turn knob down to LO, range comes back to the starting position. Is the climate fan powered by the high voltage battery? In better weather, I seem to get equally low efficiency numbers with or without the fan running on low speed so I guessed it was powered by accessory battery.