Range declining with cooler temperatures

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Daveion
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Post by Daveion »

Scratch said.
"Ok, I apologise in advance for this question. Is there any point in preheating except to jump into a warm cabin? If the battery only warms itself when the car is in motion, then the longer the journey, the more efficient the drive will be? No?"

It seems that this is the main benefit but I still believe on heat pump models there is a degree of battery heating taking place. The secondary coils firstly deliver heat to the cabin. Any residual heat in the system either passes directly via the batteries or via a heat exchanger to the battery system.
The article describes that. I cant see that being held back in pre heating.
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monkeyhanger
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Post by monkeyhanger »

Daveion wrote: Mon Nov 29, 2021 6:44 pm Scratch said.
"Ok, I apologise in advance for this question. Is there any point in preheating except to jump into a warm cabin? If the battery only warms itself when the car is in motion, then the longer the journey, the more efficient the drive will be? No?"

It seems that this is the main benefit but I still believe on heat pump models there is a degree of battery heating taking place. The secondary coils firstly deliver heat to the cabin. Any residual heat in the system either passes directly via the batteries or via a heat exchanger to the battery system.
The article describes that. I cant see that being held back in pre heating.
There are a few contradictory review comments to that article that suggest that the claims that the heat pump can heat the batteries and cabin interchangeably are untrue.

Also the claimed ability to heat the cabin with excess heat from the battery pack is largely useless if you think about it - When would the battery pack get too hot and need to dump some heat? In the winter when you want a warm cabin? No, in the Summer, doing motorway speeds - warm ambient temp with high rate of discharge.

Its all academic for most of us as we don't have the heat pump, and given that those that do are lucky to see 5% efficiency gains (an extra 5-10 miles range) and yet its established that heat pumps use about half the energy of resistive electrical heating for the same effect. If the heat pump was able to do the heating duties for both systems, interchangeably or simultaneously, you'd be seeing about 15% Winter loss worse case, not 30%. The needs of the 2 systems are way out of balance with each other, with battery heating needing around of 8kWh per hour at around freezing until warm vs a brief spell of less than 2 kWh for cabin heating and a fraction of that to maintain the desired temp once there.

It just doesn't add up that the heat pump heats the batteries when needed.

For scratch's question at the top of the quote, assuming you're going fast enough on your longer journey for the battery discharge to generate enough heat to maintain the desired battery temp, once warm, that one long journey is going to be far more efficient than loads of short journeys. Here's a slightly simplistic example (with minimal cabin heating) with figures taken from this weekend's driving at around 0-2C and mixed journey lengths,

150 mile journey @70mph with first 20 miles heating the battery and the rest of the way heating itself with heat generation in discharge may see the first 20 miles @ 2.5 miles per kWh and the other 130 miles at 3.6kWh, overall 3.4kWh.

8 x 19 mile journeys, all at 2.5 miles per kWh, battery heating always on for the depletion of the battery
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Post by dodge »

What I saw today would suggest heating of the cabin is much more than 2kW at lower temps (around zero C). I used the car from cold, but left the cabin heating off and it was using 5kW, which I assume was battery heating. When I put the cabin heating on it was at 10kW, so 5kW for cabin heating. I didn’t test how long it stayed at this level, but it shows the draw when cold from both systems can be significant. Screen shot was taken after a short trip to collect the kids from school.

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Post by Deleted User 192 »

Scratch wrote: Mon Nov 29, 2021 6:11 pm
Ok, I apologise in advance for this question. Is there any point in preheating except to jump into a warm cabin? If the battery only warms itself when the car is in motion, then the longer the journey, the more efficient the drive will be? No?

Yes there is a point.

If you pre-heat the cabin while the car is charging, the energy taken from the battery for the heater is replenished.
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Post by itsjon »

Scratch wrote: Mon Nov 29, 2021 6:11 pm
scott28tt wrote: Mon Nov 29, 2021 5:51 pm
itsjon wrote: Mon Nov 29, 2021 5:00 pm

Im confuzed now .... yup, I assumed using the battery heated it up.

Scott said "There is no battery pre-heat yet, something VW need to offer"

??????? Unless it has a battery heater that only works when the car is on the move ????

There is no option to pre-heat the battery while it is plugged into a charger, which would be how you would maximise range (the subject of this thread)

Once you're driving the car, the battery management system will use battery power to heat the batteries - this is good if you're driving a long way as the efficiency gained should be greater than the energy used by heating, but it's not good at all when you're only making a short journey.

Hopefully that makes sense.
Ok, I apologise in advance for this question. Is there any point in preheating except to jump into a warm cabin? If the battery only warms itself when the car is in motion, then the longer the journey, the more efficient the drive will be? No?
I'm not sure but I agree ! ... only benefit seems to be a warm cabin.
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Post by monkeyhanger »

dodge wrote: Mon Nov 29, 2021 10:51 pm What I saw today would suggest heating of the cabin is much more than 2kW at lower temps (around zero C). I used the car from cold, but left the cabin heating off and it was using 5kW, which I assume was battery heating. When I put the cabin heating on it was at 10kW, so 5kW for cabin heating. I didn’t test how long it stayed at this level, but it shows the draw when cold from both systems can be significant. Screen shot was taken after a short trip to collect the kids from school.

5kWh.heating for the cabin? You'd melt your plastic interior ducting and vents putting air that hot through the vents and likely crack a cold windscreen too. A 3kWh fan heater does an amazing job of heating a room in a house, let alone a small car cabin. If that cabin heater is rated higher than 3kWh, I'd amazed, it's probably no more than 2 kWh. How high did you put your temp setting to?

How big is an ID3 interior?.Maybe 6 or 7m3 (3m long x 1.6m wide x 1.4m tall approx)? A 2kWh heater would gave that from 0 to 24C in a few minutes.
Last edited by monkeyhanger on Tue Nov 30, 2021 9:09 am, edited 1 time in total.
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Post by daesimpso »

monkeyhanger wrote: Tue Nov 30, 2021 6:38 am
5kWh.heating for the cabin? You'd melt your interior ducting and vents putting air that hot through the vents and perhaps crack a cold windscreen too. A 3kWh does an amazing job of heating a room in a house, let alone a small car cabin. If that cabin heater is rated higher than 3kWh, I'd amazed, it's probably no more than 2 kWh. How high did you put your temp setting to?
Not sure about how Dodge got their figures, but I turned on the remote cabin preheat yesterday at 0C whilst plugged in to charge and my smart meter showed an increase of about 5KW, so that seems to be similar.

It does sound like a hell of a lot for such a small space.

What I didn’t check, as the preheat had finished by the time I got in car, was if it put the heated window, mirror, seats and steering on. That would make the figures make sense.
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Post by monkeyhanger »

I just did the same school run as yesterday - ambient a balmy 9.5Crather than 0C, no cabin heating, 3.1 miles per kWh. That vastly reduced need for battery heating has had a massive effect on efficiency.
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Post by dodge »

That 10kWh/h reading was taking while stationary. If moving it would read in miles/kWh.

My point was that the figures suggest a 5kW draw for cabin heating, given it was at 5kWh draw with cabin heating off - I’m not saying it does that for any more than a few minutes, but I think what a lot of people are seeing is very inefficient short journeys in winter and this seems a contributing factor. This seems to have been acknowledged by VW in the recently shared FB post - they claim to be addressing short range winter efficiency in future SW updates.

I also have an Ioniq 5 and do see the climate take a few kW in the early parts of a journey, but haven’t seen as high as 5. VW’s German efficiency wants to get you to temperature very quickly it seems!

Neither cars have heat pumps.
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Post by dodge »

Similar to monkeyhanger it’s much milder here today - 8.5 degrees measured in the car. As a test I turned the car on but remained stationary with no cabin heating; the battery heating did start even with the higher outside temps, but was just a few minutes at 5kW and then turned off leaving a draw of just 0.3kW which can be attributed to the car electronics.

I suspect the best thing to do to stop the battery heating is to actually drive the car :)
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Post by itsjon »

any consensus / conclusions yet ?

If the pre-heating option draws significantly more power compared to a tiny electric wall wart style ceramic style heater then its plausible to assume something much bigger is making use of the energy.

Or - the process is inefficient.

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Post by Daveion »

Im not sure that pre heating the cabin is comparable with that type of heater.
What we see from the threads is that heating can account for maybe 2-5 kW and that is not unreasonable when you think of the mass you are heating up and the amount of glass that is not double glazed like a house.
The heater you are showing has a capacity of 0.5kW. That incidently looks good for what it is.
I don't think the heating system is inefficient. I think it has a high initial current draw and energy consumption though which may be revisited in SW updates.
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Post by Daveion »

Just thought I would a note.
When I turn the heating on I get around 20 mile immediate reduction in range. That equates to about 5kW. These numbers we see in the threads fit well together.
All the more reason to pre heat plugged in.
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Post by sidehaas »

20 miles is approx 5kWh, that says nothing about the power draw in kw. The power draw to consume 5kwh depends entirely on how long it is operating at that power for.
5kW seems extremely high for cabin HVAC.
Re: the battery preheating, has anyone actually tried the suggestion I gave up thread to go out and turn on with the car on/off button while still plugged in, or knows for definite whether it would work?
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Post by monkeyhanger »

I'd agree that the suggestion that the ID3 has a cabin heater that can draw 5kWh is unfeasible to me. The ducting couldn't take air that hot and neither could the windscreen (strong heating inside with a 0C outside surface temp is a recipe for disaster.

The Golf GTD has a 1.5kWh auxiliary heater to take care of cabin heating until the engine warms up (and doesn't pull any combustion derived heat until the engine is warm) and can then divert combustion derived heat to the cabin. No reason to believe the ID3 would have a more powerful heater for the cabin.

2kWh cabin/8kWh battery array heating I could believe, but 5kWh each? I really don't think so.
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Post by Daveion »

sidehaas wrote: Tue Nov 30, 2021 12:24 pm 20 miles is approx 5kWh, that says nothing about the power draw in kw. The power draw to consume 5kwh depends entirely on how long it is operating at that power for.
5kW seems extremely high for cabin HVAC.
Re: the battery preheating, has anyone actually tried the suggestion I gave up thread to go out and turn on with the car on/off button while still plugged in, or knows for definite whether it would work?
4 miles/kW The initial draw could well be 5kW.
Not sustainable maybe but the figure the car initially reports and that is when the range drops 20 miles. I dont think we have seen any average consumptions in kW from the heater. My point was that the car reports 20 mile reduction in range.
Its a 3 phase 400 volt system so an initial 5KW take up is not impossible if the heater operates on all 3 phases. Does anyone know if the heater is single or 3 phase?
Scott seems sure there is no battery pre heating.
Yesterday I preheated the cabin on a 1C morning plugged in for 30 mins. The green bar was only on half measure when I drove off and took 15 minutes or so to reach normal length. I would have thought if any battery preheating had taken place that would have appeared a little different.
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Post by steviebabes »

I had ours on charge yesterday, outside temperature about 4 degrees. charging at 7kWh giving 23 MPH. When I switched on aircon including screen heating this dropped to 17 MPH, a 26% decrease. Not sure if my maths is correct but this means the cabin and screen heating has 'stolen' 1.82 kWh from the battery. This sounds about right to me.
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Post by Daveion »

After the initial surge I agree.
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Post by sidehaas »

Daveion wrote: Tue Nov 30, 2021 2:08 pm
sidehaas wrote: Tue Nov 30, 2021 12:24 pm 20 miles is approx 5kWh, that says nothing about the power draw in kw. The power draw to consume 5kwh depends entirely on how long it is operating at that power for.
5kW seems extremely high for cabin HVAC.
Re: the battery preheating, has anyone actually tried the suggestion I gave up thread to go out and turn on with the car on/off button while still plugged in, or knows for definite whether it would work?
4 miles/kW The initial draw could well be 5kW.
Not sustainable maybe but the figure the car initially reports and that is when the range drops 20 miles. I dont think we have seen any average consumptions in kW from the heater. My point was that the car reports 20 mile reduction in range.
Its a 3 phase 400 volt system so an initial 5KW take up is not impossible if the heater operates on all 3 phases. Does anyone know if the heater is single or 3 phase?
Scott seems sure there is no battery pre heating.
Yesterday I preheated the cabin on a 1C morning plugged in for 30 mins. The green bar was only on half measure when I drove off and took 15 minutes or so to reach normal length. I would have thought if any battery preheating had taken place that would have appeared a little different.
Sorry, don't wish to be pedantic but your car doesn't do 4 miles/kW, it does 4 miles/kWh. The distinction is important. One is an instantaneous power draw and the other is a quantity of energy (power * time.)
If the aircon drew 5 kW the whole time (just for illustration) then it would draw 5kWh *per hour* of driving. Let's say you run your total 58kWh battery out in approximately 3 hours of driving (a reasonable estimate?) - then a 5kW heater would reduce total battery capacity by 15kWh (or just over 25%) not by 5 kWh. The longer you were driving around with a 5 kW heater running the bigger the total impact would be.
A 20 mile reduction in range is somewhere between a third and a half of the above, but I'm not sure that's a good indicator anyway because you don't know what efficiency the car is assuming in it's range calculation and whether it makes any assumptions about how long you might have the heating on for, there are loads of unknowns. Hope this all makes sense. I have seen various videos and posts by people who actually monitored kW draw and most suggested numbers like monkeyhangars.
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Post by ProstetnicVogonJeltz »

Battery capacity is lower at lower temperatures, and you're also having higher loads such as headlamps and heating. The range indicator can be misleading and seems to be based on recent performance rather than a theoretical range (which is good in a way). You may also see the remaining range "stuck" around the 70 mile mark for a while (I've driven 20 miles without it changing). I tend to watch the battery charge level and base my decisions on that.
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