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Discussion Starter #1
Since lower outside temperatures have arrived here in the northwest, the reduced range from freezing weather is quite noticeable. It has me wondering if adding some form of thermal insulation to the bottom of the battery pack may reduce the loss of range from the cold weather.

In the recent Bolt owner survey by Chevrolet, the question was asked if the option of battery insulation was offered would it be considered. To me this indicates that battery pack insulation most likely is a viable way of improving cold, and possibly hot, weather range.

Does anyone one have information on battery pack insulation and it's effect on cold (or hot) weather range?
 

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You would be better off with a coolant heater system tapped into the battery loop.
You might try a heated garage to simplify things.
 

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In the recent Bolt owner survey by Chevrolet, the question was asked if the option of battery insulation was offered would it be considered.

That's very interesting. If it were not a plausible and productive engineering topic that question certainly wouldn't have been included.

And it figures it would be plausible and productive. We're in Seattle w/the car mostly parked outside. So far I've only twice noticed battery heat kicking in, both times apparently during preconditioning. But in colder climates than here it's certain residual heat stored in the battery while plugged will have sharply diminishing benefit if the vehicle is used for any significant period of time away from the socket; radiant heat loss from a battery warmed to a particular temperature rises as whatever the battery "sees" becomes colder, while conducted heat of course also increases as the medium the battery is in become colder. Hence driving over cold pavement while cold air is vigorously circulated around the battery will strip heat at an ample rate, especially given the geometry of the battery (which tends to maximize surface area to volume). Unless the car is being driven very hard indeed, it won't need to be very cold outside (Manitoba or North Dakota-wise) before internal resistance isn't going to do the job of keeping things warm, so extra juice is going to need to be dissipated in the battery. The slower that dissipation, the less juice spent on heating and there's only one way to slow heat loss: insulation. Which of course is why we insulate such things as our houses, refrigerators etc.

And of course hot pavement is going to irradiate a battery nicely in the other direction.

Given that thermal insulation can be extremely light to the point of being a weight nonfactor to me it's odd this wasn't handled at least minimally. On the other hand there's a cacophony of demanding engineering and cost trades going on here so I guess it's understandable. I'd certainly buy an insulation option if it were offered even in our climate but that's mostly because I can't help but obsess about things like this. Which is pretty much why I own one of these cars. :)
 

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After having boldly stated above that radiant loss from the battery will be involved in "ample" loss in cold weather, back-of-the-envelope results don't actually indicate that. Figuring on 2 meters of area with half pointed at -20c surfaces and the other half at 0c surfaces (roadway and car body structure respectively) it only works out to a little over 200W, taking emissivity as 0.8 for black enamel paint. The area could be a bit more than 2 meters but not enough to nudge to "big loss."

Sadly, figuring conduction is a lift beyond the back of the envelope. Let's say it's the same as radiant, then add a fudge factor. Maybe 0.5kW continuous to keep the battery in-band in nasty cold weather? Not so bad.
 

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After having boldly stated above that radiant loss from the battery will be involved in "ample" loss in cold weather, back-of-the-envelope results don't actually indicate that. Figuring on 2 meters of area with half pointed at -20c surfaces and the other half at 0c surfaces (roadway and car body structure respectively) it only works out to a little over 200W, taking emissivity as 0.8 for black enamel paint. The area could be a bit more than 2 meters but not enough to nudge to "big loss."

Sadly, figuring conduction is a lift beyond the back of the envelope. Let's say it's the same as radiant, then add a fudge factor. Maybe 0.5kW continuous to keep the battery in-band in nasty cold weather? Not so bad.
The huge loss in heat is from convection. Drive at highway speeds and you have ambient air blowing across that 2 meter surface area at 70 mph...

Keith
 

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Well, maybe half is going to be exposed to the direct air flow. It's not an easy calculation to make, even as a rough-in.
 

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Discussion Starter #7
Here on Camano Island (north of Seattle) our 2019 bolt does regular battery heating while parked in our insulated unheated garage. Garage temperatures are typically about 50 F this time of year. I have attached a screen shot of a recent seven day (170 hrs actual) "Plug-in" to "Plug-out" with our level 2 40A Juicebox. The right scale is kW. The total for the 170 hrs was 10.1 kWh. That gives us about an average 59 watts to keep the battery conditioned at 50 F with natural air convection and radiant losses.

Heat losses while driving are going to be a much larger from the forced convection on the bottom of the battery pack. Unfortunately the under surface of the Bolt is not smooth, but a labyrinth of metal framing and recessed flat surfaces of exposed battery pack tray. This all makes for high air turbulence on these surfaces which increases heat transfer because of increased air mixing. Just adding a smooth belly pan would greatly decrease forced convection heat transfer as well as decrease aerodynamic drag. Now add additional thermal insulation between the belly pan and the battery pack for further heat loss reduction.
 

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Yeah it seems like a relatively easy lift. Maybe even as a DIY. Polypropylene or UMHW sheet from OnlineMetals, a layer of polyethylene foam between that and battery (doesn't absorb water). Even a fraction of an inch would help and per Camano Dave's points, just getting the airflow off the battery would be a big help, let alone insulation.

Eliminating flutter might be a bit of a challenge unless there's a means of fastening intermediate to edges. Neoprene insulation instead of polyethylene would help with that but at a slight weight cost.
 

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Discussion Starter #9
For the belly pan, I was thinking aluminum sheet because of it's fire resistance and ability to reflect IR in summer.

To attach the aluminum sheet, use 3M VHB foam tape. This tape is used in vehicle manufacturing in place of screws and rivets to attach body panels. Removing the belly pan would probably require destruction (severe bending) of the belly pan aluminum sheet.

As for the actual insulation, use a self-adhesive, foil faced, auto body closed cell foam sheet insulation. These also have a good fire rating and will not absorb water. The foam sheet would be applied to the actual battery tray where accessible.

All materials used need good fire ratings because the undersides of vehicles do come in contact with hot to flaming materials, think discarded burning cigarettes.

I am thinking of applying the foam insulation as a first step since it is the simplest to implement.
 

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That's good thinking, Dave.

Considering all the other flammable stuff under the car (starting with the weird "flaked and formed plastic" arch liners) I'd probably stick w/polypropylene or UMHW with an eye to being removable. A downside there is that both plastics preclude confident use of adhesive fastening without absolute assurance on the properties of adhesives employed. They're each notoriously difficult candidates for adhesives.

Using self-adhesive insulation directly on the battery tray is blindingly obvious, now you point it out. Leaving aside aerodynamics one could almost stop right there; the first iota of insulation and thermal conduction block between the metal and circulating air will have a profoundly positive effect. And so easy and lacking in mysteries about fasteners etc.

If I lived on a coastline or where salting roads is frequent I'd also be worried about rust so that's maybe another motivator to attack this, for some folks.
 

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Now that you have the cold climate situation covered, what about summer operation with that panel installed. You've blocked off the cooling factor from air movement.
You'll force the system to run hot now. Not a good idea!
 

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The system won't run hotter in summer because it's designed to maintain a thermal regime, adding or removing heat as necessary. So what's the energy cost to do that?

Radiant heat from roadways (Stefan-Boltzmann works both ways), warm air circulating around the battery increases the energy cost of battery thermal management. Meanwhile, dissipation from battery internal resistance doesn't change as a function of ambient temperature and except within a narrow ambient temperature window is going to be less significant than external heat leakage into the battery. So insulation is still an advantage. In very warm climates, advantage will only increase.

After all, we don't remove insulation from our homes during summer. :)
 

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Also per the OP it's GM that asked about the option for battery insulation, meaning some engineer is bothered enough about the lack of battery insulation to have managed to get it on a list of questions to ask of owners.

"Faced with a choice between spending money on another useless gew-gaw versus what we see as useful battery insulation, what's your preference?" Not that they'll ever put it that way. :)
 

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Discussion Starter #14
As for hot weather, do you mean ambient temperatures above optimal battery temperatures?

My guess is the thermodynamics of the Bolt are set such that the greatest energy efficiency is in a certain range of temperatures, best guess is between 65 and 85 F. This also minimizes complexity, costs and components (weight) needed. I am sure the Bolt engineering is counting on cooling the battery by air flowing over the lower part of the battery pack in the upper part of that temperature range.
The thing is in the northwest our average high temperature is about 59 F, average low is 45 F. We are probably in the optimum operating temperature range only about 10% of the time. So permanent insulation of the battery pack would be of benefit in cooler climates like here in the northwest and further north. It might also be a benefit in very hot climates.

The optimal insulation design for all climates would be an adjustable or removable insulation. For the belly pan option, being able to easily install and remove the pan would be one solution. Another belly pan solution is a design having openings that could be opened or closed either manually or automatically depending on operating conditions.
 

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I'm thinking about the evaporator and heating element in the battery cooling system, the thermal plate located below the battery and how any time due to radiant+conductive heat absorption/loss the lower pan temperature is above or below the desired temperature of the fluid circulating in the plate, that's more or less a problem, more as the delta T increases. The amount of time the ambient situation is "just right" to make a useful and significant contribution to thermal management likely isn't going to be large; the gain/loss via that path is often going to be a net drag on efficient management.

Again, the question came up on a list that is doubtless competitive in terms available space/respondent attention span and that's a very interesting "tell." At some point while this thing was being put together it was necessary get on with getting it into sales mode, which is not at all the same as saying it was completed as an engineering problem. 80:20 is everywhere, particularly for this kind of product in expert hands of engineers who know how to deploy. The survey question is indicative that it's a second-order problem to engineer on, once time and attention is available.

It's also possible that parasitic load of the car when not in use is becoming a concern, which is another valid reason to do some additional engineering on the battery thermal performance. That's going to become an issue for consumers sooner or later and possibly a point of contention in marketing. Keeping a battery warmish in cold temperatures with no insulation is actually a bit of an insane proposition.
 

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I remember this survey, and I was surprised by it. To wit, I had always thought that the "advanced thermal management" already included thermal insulation, optimized for best performance across a wide range of ambient temperatures. Consequently, I had thought, while more "padding" might be beneficial in winter, it could be detrimental in summer.

Are we to assume that GM omitted [a more substantial] thermal insulation for the battery because the Bolt was primarily intended for milder climes, like they have along the West Coast and in Western Europe? Or just omitted because they forgot in a hurry?

Whichever way, I can see that I am not the only Bolt driver who finds the winter capabilities insufficient; I used to see on average 1 Bolt/hour, almost every day, driving in Loudoun County and other near-Beltway areas - up until sometime in Nov 2018. But in the past 6 weeks or so have encountered only one Bolt.

After having boldly stated above that radiant loss from the battery will be involved in "ample" loss in cold weather, back-of-the-envelope results don't actually indicate that. Figuring on 2 meters of area with half pointed at -20c surfaces and the other half at 0c surfaces (roadway and car body structure respectively) it only works out to a little over 200W, taking emissivity as 0.8 for black enamel paint. The area could be a bit more than 2 meters but not enough to nudge to "big loss."

Sadly, figuring conduction is a lift beyond the back of the envelope. Let's say it's the same as radiant, then add a fudge factor. Maybe 0.5kW continuous to keep the battery in-band in nasty cold weather? Not so bad.
Another factor to consider: when the battery shell/pan gets wet, there must be some evaporative cooling effect, especially when the vehicle is moving.
 

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We just did a somewhat testing long trip in fairly wintry conditions, with oodles of challenges to the battery and no particular trouble. Superficially it may seem odd that people would give up on commuting but then some DC area commutes are flat insane-- a road trip, every day. Plus, there's no room for mystery or being inert by the side of the road in daily life. That kind of risk-aversion isn't too surprising when I think about it.

Would have been nice to be the fly on the wall while battery insulation was being discussed by the engineers working on this car. The battery housing itself is clearly already more expensive than ideal (starting with all those bolts and the gasket-- ai-yi-yi); I'll hazard a guess that energy losses for thermal management are low enough for the center of the Bell curve of environmental conditions that it was a matter of semi-reluctant acceptance for cost control.

When there are plenty of thousands of cars sucking down juice from the grid while parked this'll certainly be revisited, if not before.That'll be a visible wart, let alone any impact on range. The total area under the fringes of the curve is going to grow to the point it can't be ignored.
 

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Considering GM made the Bolt for the US, Korea, and other countries, I doubt they left off battery insulation thinking of only mild west coast climate use.
 

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This article on the Kona's thermal management brings together a bunch of comparative info from other implementations, including a somewhat "artistic" choice on the part of Tesla that I understand and respect even as it makes me a bit squeamish. As well, folks in the central/eastern northern tier of US states might want to take a close look at Hyundai's choices. Quite a difference at the Canadian border-- who knew the climate changed so suddenly at a line on a map? :)

https://electricrevs.com/2018/12/20/exclusive-details-on-hyundais-new-battery-thermal-management-design/

What struck me there is a reminder that at least fo the Kona's battery and some other Li variants battery warming is more important to charging as opposed to discharge. Performance loss is considered acceptable while prolonging charge times is not.

All kinds of hard choices being made.
 

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Watching Prof Kelly's vids you can see that the battery bottom case is not only double/triple wall (depending on location) but that there is an insulating pad between the heat transfer plate and the bottom case. It's pretty minimal to be sure, but it's clear that there is no direct conductive or radiative heat transfer from the battery case to the batteries themselves.
 
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