Energy consumption of Climate (and Preconditioning?)

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DougTheMac
Posts: 240
Joined: Mon Sep 17, 2018 7:50 pm
Location: Suffolk UK

Energy consumption of Climate (and Preconditioning?)

Post by DougTheMac » Mon Apr 15, 2019 12:51 pm

I did a test yesterday to establish the energy consumed by "Climate" and/or battery preconditioning.

The short answer is it takes about 1.1kW to maintain 22degC cabin temp with an ambient of 6degC, ie 16degC differential.

The methodology was that the car was parked in the open, not connected to a charger, and I repeatedly set the "Climate" in motion using the App, recording the %SoC with the App every c30mins or so when I restarted the Climate.
The Climate Set Point was 22degC. Ambient temperature was c-1 when I started, warming up (?!!) to a pretty steady 5-7degC (tho' the car was in weak sunshine latterly). The test ran for 16 cycles spread over 10hr (I didn't always restart immediately).
The loss of %SoC per hour was very linear after the first 1.5 hr, at a very constant 1.35%/hr, corresponding to a steady 1.1kW power consumption if we assume 100%SoC is 82.5kW-hr
There was an "initial hit" for the first 1.5hr of an extra 3.65% SoC or 3kW-hr (ie an extra 2.4% SoC loss per hour in addition to the "steady state"). I'm assuming this is a mixture of the energy needed to get the car up to temperature in the first place, and the fact that the ambient was significantly lower at the start. The latter is not enough to explain this quite large "initial hit", so I assume that most of this is going into latent heat of the car (and batteries?).
It has never been clear whether "Preconditioning" and/or "Remote Climate" do anything to warm up the batteries if the car is not connected to a charger. It would seem from this quite large (3kW-hr) figure that the batteries might indeed be being warmed too.

One would expect the steady-state power consumption to be roughly linear with temperature differential.

To put the ss consumption in context, if you get 240 miles range at a steady 60mph that's 4hr. The Climate will consume 1.1*4=4.4kW-hr in that time which is 5.3% of your battery, reducing your range by c13 miles. Roughly tallies with JLR's "Range Calculator" which shows a loss of 8-10miles range between AC Off and On at "motorway" driving.

To be borne in mind, and emphasising what we all know by now, that the range is penalised by cold weather. But the effect of cold weather on the batteries is much greater (more power needed to keep them warm), as shown in the JLR calculator. So, it's not worth freezing your b****cks off for 4 hours to get 8-13 miles further!

It does answer one question I've had at the back of my mind for a while. Last winter (2018), lots of people were stuck in cars overnight in the UK because of snow. (Our EU friends will find this hard to understand, but a couple of cm of snow on a major road in UK will cause a truck to skid and block the road for many hours...) In an ICE, you can keep your engine running to generate heat. In an EV, how long can you keep warm for? Well, if we assume outside temp -5 and inside (to be tolerable) +15, that's a 20degC differential, so probably around 1.4kW. So, as long as you have c20% SoC when you get stuck, you will stay warm for 12hr, though you may need a towtruck when the snow gets cleared! And don't get stuck in a snowdrift with low %SoC!!!

I ought to get a life, really; p'rhaps I retired too soon? :roll:
HSE Silicon Silver Pano Air+AD Oyster since 1Mar19
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TeslaDriver
Posts: 22
Joined: Sat Apr 13, 2019 11:02 am
Location: United Kingdom

Re: Energy consumption of Climate (and Preconditioning?)

Post by TeslaDriver » Mon Apr 15, 2019 2:22 pm

DougTheMac wrote:
Mon Apr 15, 2019 12:51 pm
The short answer is it takes about 1.1kW to maintain 22degC cabin temp with an ambient of 6degC, ie 16degC differential.
As an additional data point Bjorn has videos of rapid charging where toggling Climate off increases charge rate by 1~2kW, so "same"
To be borne in mind, and emphasising what we all know by now, that the range is penalised by cold weather. But the effect of cold weather on the batteries is much greater (more power needed to keep them warm), as shown in the JLR calculator. So, it's not worth freezing your b****cks off for 4 hours to get 8-13 miles further!
When non EV people ask me about this my answer is that in slow traffic (when impact of Climate power consumption is greatest) I have no range anxiety - on a day when I have to drive into town for an hour each way at <10 MPH nether range nor climate is going to be an issue - and on a day when I am driving at 70 MPH the percentage, 5% as you calculate, would only be an issue in extreme range conditions, and I don't cut it that fine :)

Getting stuck in the snow is the same problem for ICE and BEV ... if you didn't have much fuel to start with you are going to start freezing before you get rescued :( ... Bjorn has videos of sleeping in his car in Norwegian winter - perhaps easier to keep warm than an ICE in that regard? I've slept in a parked ICE on an overnight journey to ski resort. After a couple of hours (engine off) the biting cold prevented any further sleep, so definitely not possible to sleep for 6+ hours ... whereas a BEV with "camper mode" would be just fine :)


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