Best material to insulate batteries? Best R-value?

[justinm001]

Winter's here and I'm starting on insulating my batteries and RV water tanks. I have a tank heater pad sandwiched between 2 batteries and plan to wrap them completely in some form of insulation and looking for something about 1inch thick.

Since its not house insulation and I'm not concerned with weight I'm wondering what the best material is? So far I've found Vacuum Insulation Panel (VIP) with an R-value around 45. The panisonic U-vacua below looks to be R60 and $50 for a 24x22" sheet so would fit the bill but would be like a grand if I want to insulate both battery banks, both tanks and the bays they hold.

https://www.digikey.com/en/products/detail/panasonic-industrial-devices-fbd/CNRZZB78600/9558503

Since LFP batteries just need holes for cables and no venting or anything is there another material that might be a better R-value. I could enclose the entire thing in wood but apparently most wood only has a R-value around 1.4. I'm curious about forms of plastics and their R-value, expecially types that can be molded or extruded and I could have a box built.

Is there any battery box thats designed for 1-2 rack mount LFP batteries with a R-value over 50?

I'm curious to see how efficiently I could keep a battery warm. Say I want to keep a rack battery at 40degrees and its 20 degrees out. How long could it keep itself warm with 1kwh of usable power? Anyone know the calculation and how to compare different types of materials, not just construction materials?

 

[sunshine_eggo]

You can actually calculate based on R-value:

Keeping batteries cool-low tech

Has anyone taken temp readings inside a styrofoam cooler on a hot day? I’m interested in how temps track. For example, let’s stipulate something like a 100F day and 70F night. I’d suspect that the temp inside a cooler would be buffered from the outside highs and lows. E.g.: it would be...

diysolarforum.com

 

[justinm001]

You can actually calculate based on R-value:

Keeping batteries cool-low tech

Has anyone taken temp readings inside a styrofoam cooler on a hot day? I’m interested in how temps track. For example, let’s stipulate something like a 100F day and 70F night. I’d suspect that the temp inside a cooler would be buffered from the outside highs and lows. E.g.: it would be...

diysolarforum.com

Sweet! I think my maths right
-6c outside
4c inside
16sqft total (2 rack batteries)
R60
((-6-4)*16)/60 =.5333 watt hours. 12.8Watts/day 384 per month and 4672 per year. So a 5kWh rack battery would last roughly 1 year in 20deg temps fully enclosed with a consistent temp of 40F/4C

 

[Symbioquine]

When you start asking about "Best R-value", my mind goes to vacuum based insulation strategies. Almost certainly impractical, but fun to think about. In practice, this is why you need the math @sunshine_eggo is pointing to. Engineering is almost never about "best" - but "good enough".

Either you're trying to keep some residual heat in for some amount of time or your trying to see how much heating power is required to keep up in a steady-state scenario. For future readers, that's the question to answer for any given system - not what's "best" in general.

 

[ElectricIslander]

For BEST R-Value you might look into the vacuum panels that Symbioquine mentions, or into aerogel based panels.

The off-shore off-grid sailing community has much discussion of high performance insulation for home-made low power freezer/fridges on yachts (search the Cruisers Forum for threads on these search terms).

Both vacuum panels and aerogels have significantly higher R-values than the commonly available foams and you don't need very much to insulate a battery.

 

[sunshine_eggo]

Looks like the migration axed a couple posts.

There's an error on the linked post:

Watts = ((T2 - T1) * A) / R

T2 = outside temp, °C
T1 = inside temp, °C
A = area of surface, m^2
R = R value of surface.

R should be RSI, which is 5.68X higher than R, so should be:

Watts = ((T2 - T1) * A) / ( R / 5.68 )

T2 = outside temp, °C
T1 = inside temp, °C
A = area of surface, m^2
R = R value of surface.

@justinm001 please re-run your calcs. They're off. You used sq-ft, not sq-m, and the answer is Watts, not W-h.

Try 2" pink foam board from Home Depot, R-10.

 

[HRTKD]

My two LiFePO4 batteries are encased (top and sides) in the standard rigid foam insulation you can buy from Home Depot. I also insulated my 120 gallon fresh water tank to about R-19 with the same stuff. So far so good.

 

[Tomthumb62]

Not sure of the R-value, but my Powerurus came packed in a semi rigid foam “case”. The battery sits in the foam case and a perfect fitting foam lid goes on top. The foam is softer than styrofoam but not as soft as open cell foam. It’s some kind of closed cell foam.

I have no need for it just now but I’m going to keep it around should I ever need to insulate the battery.

 

[gotbeans]

Rock wool is made from slag of steel production. It catches fire at several thousand degrees (very safe)
Mineral wool is similar but can be made from molten spun rock, slag from steel production, or any other minerals
both virtually cannot catch fire.. If that's any worry of yours. You should use one of those. They're available all over. You can put a blow torch on them and nothing will happen to confirm.

Cellulose also has very heavy soaking process of flame retardant. It's the second most flame resistant but also probably terrible to work with to do around batteries.

Pink foam board is the best foam board and also is "fire retardant" it'll still melt though, as will every foam except thermal spray/treated foam but that's the treatment spray protecting it. Also resistant to most weather and molds etc. It's used in pool/hot tub more than others

Fiberglass just melts

If you want spray foam to just "fill everything" like you say, you can get

FROTH-PAK Low GWP 620 Spray Foam Sealant Kit 12031908 - The Home Depot

FROTH-PAK Spray Foam Sealant is a 2-component, quick-cure polyurethane foam that fills penetrations and cracks in rim joists, roof wall junctures and around pipes and ducts greater than 2 in. and less

www.homedepot.com

or

FROTH-PAK Low GWP 650 Spray Foam Sealant Insulation Kit 12031907 - The Home Depot

FROTH-PAK Spray Foam Insulation is a Class A Fire Rated 2-component, quick-cure polyurethane foam that fills cavities, penetrations and cracks in rim joists, roof wall junctures and around pipes and ducts

www.homedepot.com

red one is more but it has some more ratings on it, including fire retardant etc

-----------------------------------

If you want a giant pack of something you can get https://www.lowes.com/pd/ROCKWOOL-C...th-Sound-Barrier-15-25-in-W-x-47-in-L/3610406 which will give you half your R value you're after.

Or just use a few pink foam boards (only home depot carries them) https://www.homedepot.com/p/Owens-C...Foam-Board-Insulation-Sheathing-45W/100320352
cost adds up but there you can easily see it'd be 10 inches thick to get your R50 (since the boards are 2 inches R10)
This product is extremely easy to cut and you can use a variety of tools but the easiest is a very small toothed saw like a japanese style pull saw or a hacksaw just with the blade. Sawzaw makes a huge mess and hot knife stinks and also shrinks the product

Personally for your R50 I'd do a concrete board structure for the internal space to get the size right. Wrap it with rock wool and then make the outside look nice with whatever.. wood etc.

I'm curious to see how efficiently I could keep a battery warm. Say I want to keep a rack battery at 40degrees and its 20 degrees out. How long could it keep itself warm with 1kwh of usable power? Anyone know the calculation and how to compare different types of materials, not just construction materials?

I've already done this and you only need like 20 watts of power and <R10 so if you're actually wanting to do R50 you probably don't need heating at all

Reptile Heating Pad To Keep LFP Batteries Warm?

There has been a few discussions on self heating LFP or using external heaters and it occurred to me I used to have an iguana and used a small pad heater in the tank that actually got very warm and used low watts. So I looked for them on Amazon and they have lots of models big and small and...

diysolarforum.com

If it's windy against your battery you want a wind barrier on the outside of the insulation or it'll pierce through it and cool faster... literally anything. Plastic, wood, concrete board etc. Sounds like your batteries might be outside idk

For BEST R-Value you might look into the vacuum panels that Symbioquine mentions, or into aerogel based panels.

The off-shore off-grid sailing community has much discussion of high performance insulation for home-made low power freezer/fridges on yachts (search the Cruisers Forum for threads on these search terms).

Both vacuum panels and aerogels have significantly higher R-values than the commonly available foams and you don't need very much to insulate a battery.

Aerogel also should be non-flammable until thousands of degrees.. but it probably has an insane cost lol
but yea I think that'd win, I don't think anything is more insulative than aerogels are (that we've discovered yet)

 

[justinm001]

Looks like the migration axed a couple posts.

There's an error on the linked post:

Watts = ((T2 - T1) * A) / R

T2 = outside temp, °C
T1 = inside temp, °C
A = area of surface, m^2
R = R value of surface.

R should be RSI, which is 5.68X higher than R, so should be:

Watts = ((T2 - T1) * A) / ( R / 5.68 )

T2 = outside temp, °C
T1 = inside temp, °C
A = area of surface, m^2
R = R value of surface.

@justinm001 please re-run your calcs. They're off. You used sq-ft, not sq-m, and the answer is Watts, not W-h.

Try 2" pink foam board from Home Depot, R-10.

Thanks for the update. I think these calcs are correct although its early. SOK batteries are 17.5x7x18.25in so 2 of them with 1 inch spacing between is 17.5x15x18.25in 6 panels would be 319.375 sqin or 43.46575 sq-m. If someone could double check my math and I can update all the calculations.

((40-20)*43.46575)/(10/5.68)=493.77 watts which seems extremely high using R10

				Cost per day				Cost per month
R-value	Watts	W Per Day	W Per mo	0.1​	0.3​	0.5​	1​	0.1​	0.3​	0.5​	1​
5​	987.5418​	23701​	711030.1​	2.3701​	7.110301​	11.8505​	23.701​	71.10301​	213.309​	355.5151​	711.0301​
10​	493.7709​	11850.5​	355515.1​	1.18505​	3.555151​	5.925251​	11.8505​	35.55151​	106.6545​	177.7575​	355.5151​
15​	329.1806​	7900.335​	237010​	0.790033​	2.3701​	3.950167​	7.900335​	23.701​	71.10301​	118.505​	237.01​
20​	246.8855​	5925.251​	177757.5​	0.592525​	1.777575​	2.962626​	5.925251​	17.77575​	53.32726​	88.87877​	177.7575​
25​	197.5084​	4740.201​	142206​	0.47402​	1.42206​	2.3701​	4.740201​	14.2206​	42.66181​	71.10301​	142.206​
30​	164.5903​	3950.167​	118505​	0.395017​	1.18505​	1.975084​	3.950167​	11.8505​	35.55151​	59.25251​	118.505​
35​	141.0774​	3385.858​	101575.7​	0.338586​	1.015757​	1.692929​	3.385858​	10.15757​	30.47272​	50.78787​	101.5757​
40​	123.4427​	2962.626​	88878.77​	0.296263​	0.888788​	1.481313​	2.962626​	8.887877​	26.66363​	44.43938​	88.87877​
45​	109.7269​	2633.445​	79003.35​	0.263344​	0.790033​	1.316722​	2.633445​	7.900335​	23.701​	39.50167​	79.00335​
50​	98.75418​	2370.1​	71103.01​	0.23701​	0.71103​	1.18505​	2.3701​	7.110301​	21.3309​	35.55151​	71.10301​
55​	89.77653​	2154.637​	64639.1​	0.215464​	0.646391​	1.077318​	2.154637​	6.46391​	19.39173​	32.31955​	64.6391​
60​	82.29515​	1975.084​	59252.51​	0.197508​	0.592525​	0.987542​	1.975084​	5.925251​	17.77575​	29.62626​	59.25251​

But could be correct as lastnight I had a space heater set on low (500w) pointed right at a battery in my front 12v bay and the temp still dropped to 28.2 while the 48V bay with all the tanks and water heater was 49. I also was running 25amps from shore, through the inverters to charge my tesla and the heaters and such so might have added additional heat. The 48V battery bms reported 50 was its low so thats good.

I put $1 per kwh considering many here might be using a genny and costs likely are even higher. Even an efficient generator is over $1/kwh in fuel alone and genny maintenance is close to $1/kwh.

From this I'm showing R10 vs R30 would save $23.70 per month so for a 3 month winter it'll be $75 per year in savings. With this info I'm thinking about getting some 1in VIP boards that are custom sized to overlap the edges, wrap in cold temp real duct tape then get some 1in home depot foam board cut overlapping opposite edges and wrap in real duct tape. Leave a gap in the VIP panels on one side for the battery cables then cut out the foam board for the cables.

I'm still not convinced the VIP panels are the most efficient material. I'm surprised there isn't some silicone or plastic or some metal/stone that isn't much better at insulating. Weight isn't really a concern and if the numbers above is correct then its well worth a couple hundred for things to last.

 

[sunshine_eggo]

43 sq m is the equivalent surface area of 20 400W solar panels (about 2m^2 each).

17.5*18.5 = 319.375 sq-in = ONE of the six sides of the cube.

Morning coffee is not working yet, so I'm just going to multiply that by 6 rather than figure out the smaller sides:

1,916.25 sq-in = 1.24 m^2

that should change your number from 494W to 14W with R-10.

 

[yabert]

that should change your number from 494W to 14W with R-10.

Wow! it's so easy to heat a well insulated battery.
Really low energy needed.

 

[wme]

Lots of choices here...https://learnmetrics.com/insulation-r-value-chart-per-inch/

 

[HRTKD]

The first time I checked on my system in my RV after a heavy snow storm left about 10" of snow on the panels, I was very surprised at how little the state of charge dropped to keep the batteries warm without getting anything from solar. I checked about five days after the snow storm.

 

[pvgirl]

Those vacuum insulated panels can not be cut, and must be protected from damage. The vacuum is provided by what is basically a sealed myler type bag, if cut, punctured or other wise damaged, the vacuum will be lost, and most of the insulating value would be lost.

 

[magnet creek]

The question is easier than the answer. The problem is (in practice) that by only looking at the material you overlook the actual enclosure package. I assume You are probably not going to enclose the front and therein lies the problem. In order to calculate the R value of the enclosure as a whole, you would need to calculate the weighted average of the insulated and uninsulated area (which is only insulated by air).
Since the (uninsulated) front covers 10-15% of the total enclosure you pay quite a penalty for not insulating the front. Compare it to acoustic insulation It is a bit like leaving your window open in a well-insulated building; you still hear street noise.
So, yes, you can look for the absolute best material, but it may be better to look at a practical application that insulates the whole enclosure AND is easy to remove, presumably you do not want the insulation to be there in summer.
I used 1" Polyiso board around the 2 server rack batteries on all sides without the front, placed the batteries in a Dewalt shelf (Thanks @Will Prowse for the hint), and insulated the area in the shelf on 4 sides. Nice and toasty/

 

[yabert]

Lots of choices here...https://learnmetrics.com/insulation-r-value-chart-per-inch/

Really interesting chart. Especially the new/used 5-10 years value for some material.
Sad they don't include the poor value of the Polyiso when temperature drop.

 

[justinm001]

43 sq m is the equivalent surface area of 20 400W solar panels (about 2m^2 each).

17.5*18.5 = 319.375 sq-in = ONE of the six sides of the cube.

Morning coffee is not working yet, so I'm just going to multiply that by 6 rather than figure out the smaller sides:

1,916.25 sq-in = 1.24 m^2

that should change your number from 494W to 14W with R-10.

converting inches to meters is apparently different than sq-in to sq-m so 1711.25sq-in is 1.10403005 sq-m although 1711.25in is 43.46575 meters. oops.

				Cost per day				Cost per month
R-value	Watts	W Per Day	W Per mo	0.1​	0.3​	0.5​	1​	0.1​	0.3​	0.5​	1​
5​	25.08356​	602.0055​	18060.17​	0.060201​	0.180602​	0.301003​	0.602006​	1.806017​	5.41805​	9.030083​	18.06017​
10​	12.54178​	301.0028​	9030.083​	0.0301​	0.090301​	0.150501​	0.301003​	0.903008​	2.709025​	4.515041​	9.030083​
15​	8.361188​	200.6685​	6020.055​	0.020067​	0.060201​	0.100334​	0.200669​	0.602006​	1.806017​	3.010028​	6.020055​
20​	6.270891​	150.5014​	4515.041​	0.01505​	0.04515​	0.075251​	0.150501​	0.451504​	1.354512​	2.257521​	4.515041​
25​	5.016713​	120.4011​	3612.033​	0.01204​	0.03612​	0.060201​	0.120401​	0.361203​	1.08361​	1.806017​	3.612033​
30​	4.180594​	100.3343​	3010.028​	0.010033​	0.0301​	0.050167​	0.100334​	0.301003​	0.903008​	1.505014​	3.010028​
35​	3.583366​	86.00079​	2580.024​	0.0086​	0.0258​	0.043​	0.086001​	0.258002​	0.774007​	1.290012​	2.580024​
40​	3.135445​	75.25069​	2257.521​	0.007525​	0.022575​	0.037625​	0.075251​	0.225752​	0.677256​	1.12876​	2.257521​
45​	2.787063​	66.8895​	2006.685​	0.006689​	0.020067​	0.033445​	0.06689​	0.200669​	0.602006​	1.003343​	2.006685​
50​	2.508356​	60.20055​	1806.017​	0.00602​	0.01806​	0.0301​	0.060201​	0.180602​	0.541805​	0.903008​	1.806017​
55​	2.280324​	54.72777​	1641.833​	0.005473​	0.016418​	0.027364​	0.054728​	0.164183​	0.49255​	0.820917​	1.641833​
60​	2.090297​	50.16713​	1505.014​	0.005017​	0.01505​	0.025084​	0.050167​	0.150501​	0.451504​	0.752507​	1.505014​

So R-10 would use 300w per day or 9kw per month vs R-30 at 100w per day or 3kw per month. Few bucks more per month.

 

[justinm001]

Those vacuum insulated panels can not be cut, and must be protected from damage. The vacuum is provided by what is basically a sealed myler type bag, if cut, punctured or other wise damaged, the vacuum will be lost, and most of the insulating value would be lost.

Thank you!

 

[justinm001]

The question is easier than the answer. The problem is (in practice) that by only looking at the material you overlook the actual enclosure package. I assume You are probably not going to enclose the front and therein lies the problem. In order to calculate the R value of the enclosure as a whole, you would need to calculate the weighted average of the insulated and uninsulated area (which is only insulated by air).
Since the (uninsulated) front covers 10-15% of the total enclosure you pay quite a penalty for not insulating the front. Compare it to acoustic insulation It is a bit like leaving your window open in a well-insulated building; you still hear street noise.
So, yes, you can look for the absolute best material, but it may be better to look at a practical application that insulates the whole enclosure AND is easy to remove, presumably you do not want the insulation to be there in summer.
I used 1" Polyiso board around the 2 server rack batteries on all sides without the front, placed the batteries in a Dewalt shelf (Thanks @Will Prowse for the hint), and insulated the area in the shelf on 4 sides. Nice and toasty/

You're correct but I'd also want to insulate the front of the battery as I'd hope I wouldn't need to get in there and if so I can easily replace the tape. Also with rack batteries the front is where the bms is and there's a decent sized air pocket with another metal panel. I'd think this wouldn't be as big of an issue to leave open as the heat would need to travel through the battery to escape. Similar to leaving a window open in the winter in like a bathroom but the bathroom door closed so it doesn't affect the house nearly as much.