Cooling battery cabinet in shed

[t3kn0f1l3]

I am in the later design stages of a small geothermal cooling loop for an insulated battery cabinet that is located in an outbuilding (shed). After reading through some other threads, I don't find one dedicated to the idea I have in mind, although curiouscarbon gives some pics that illustrate the components of the idea here: https://diysolarforum.com/threads/diy-geothermal.26639/ - please correct me if I just did not find the dedicated thread.

Some givens for my case:

I dug a small, shallow 'well', 1 foot in diameter, about 4 or 5 feet down into the clay ground. The water table is really high, so about 3 feet of this 'well' is underwater (at least right now).

The 'well' is ~3' from the shed, so maybe 4' from the battery cabinet.

(My thought here is: use an efficient, low-draw pump to circulate water through a small car radiator and into a heat exchange coil inside this shallow 'well'. A fan then pulls air through the radiator and into a 4" duct in the battery cabinet and exhausts out the top (another 4" duct). I'm playing with the details in the late design stage now, and am wondering if others have done something similar. If so, would you be willing to share what has worked/not worked.)

Main purpose:

I intend this loop to keep my NMC batteries cool(ish), esp. during the heat waves we get - up above 40 C (104F) as daytime high for several days in a row.

(The night time temps get down to mid 20's in these cases, but like others, I'm expecting temps to get worse going forward)

At this point, the battery box, with the ducts, is almost finished - insulation is R20 (4" of xps) all around (except for ducts) - I am currently figuring out the doors.



Things I'm wondering about:

-I'm thinking of using a 16' copper lineset for a mini split, just b/c I have it on hand. (The lineset has a 1/4" copper and a 1/2" flexible copper tube). Does using maybe both tubes in parallel make sense, just because I have the material on hand? Or, should I use only 1 dia. If so, would it make more sense to use a longer length than 16' for the heat exchanger?
-what should the total volume be of the water in the closed-loop system?
-anyone have an idea of what to use for the radiator - maybe a small car radiator - I need to integrate it into 4" metal ductwork by fabricating a sheet metal box, I think. . . . but am open to suggestions
-I have just started wondering if it would make sense to make the air duct a sealed loop rather than constantly bringing in fresh air at the bottom left and exhausting at the top right. Any thoughts?
-I have some ideas about a pump, but would appreciate feedback on sources for pumps, but esp. on flow rate specs:

curious carbon suggested https://coldandcolder.com/collections/featured-products/products/12v-micro-water-pump and also https://www.amazon.com/bayite-BYT-7A006-Heater-Circulation-Discharge/dp/B0196WL55G/, which has twice the pumping capacity.

I've also been looking here: https://www.ussolarpumps.com/product-category/circulating-pumps/

The main spec I'm trying to figure out is flow rate. I'm thinking maybe I should get something that allows me to adjust the flow rate so I can trial-and-error it?

In any case, I'll maybe leave it here for now. If you've done anything like this, I'd love to know what worked/what didn't work, etc. I'll post some more pics once I can get a few decent and recent ones, probably in a day or so. Also, please let me know if I've left out relevant details.

 

[FilterGuy]

I have considered, but not done what you are doing. I am very interested in how it works out for you.

A few thoughts.

Think about condensation on your radiator. If the radiator is cool and the air is humid, there is a very good possibility you will hit the dew point and get condensation. The main thing to think about is how to collect it and route it out of your box. (It is probably not a good thing if it drips on your battery. ) The other thing about condensation is that you might start growing mold and mildew. Having a copper radiator would help eliminate growing new life forms.

-I have just started wondering if it would make sense to make the air duct a sealed loop rather than constantly bringing in fresh air at the bottom left and exhausting at the top right. Any thoughts?

That would be better at keeping things cool and would help reduce any condensation. (After the internal air drys out, the condensation will slow down or stop)

The main spec I'm trying to figure out is flow rate. I'm thinking maybe I should get something that allows me to adjust the flow rate so I can trial-and-error it?

I can't give any advice on flow rate, but it seems to me that more is better. Consequently, I am not sure adjustable is better. If you think you might need 'X' flow rate and then buy something that can give you a range around 'X', why wouldn't you just run it at its max value all the time? If you are going to run it at max value, why not just buy one that is fixed at that value?

Also, when looking at pumps, head pressure is important too. Since you will be running it through 16' of tube and a radiator, there is going to be a fair amount of back pressure. It has been a while, but back when I was designing industrial water filter systems I had to look up the characteristics of the pipes to understand the pipe pressure loss and then use the pump's pressure vs Volume charts to determine the flow rate.

 

[t3kn0f1l3]

Thanks for the suggestions, Filter Guy.

Yes, I'm worried about condensation. The best solution I have so far is to put a pan under the radiator and run a drain hose out the side of the shed - just gravity-fed, similar to a heat pump drain tube.

If I make a closed air loop, rather than just venting to the inside of the shed, I should probably insulate that loop of duct, too, so I don't get condensation there.

I'd put a container of desiccant like CaCl or SiO2 inside the cabinet to dry out the air when the cabinet is opened. I'd have to replace that from time to time, but probably worth it.

My flow rate question comes from thinking about the time the coolant spends in the heat exchanger. Maybe I'm over-thinking it, though.

Thanks for the suggestion to look at pump head pressure and resistance values/back pressure for different pipe materials/sizes. V. helpful. Hadn't considered that.

 

[ArkCabinMan]

With respect, you're making the geothermal concept application way too complicated by introducing water piping and heat exchangers into the design.
Too many variables and too many points of potential failures.
For one thing, water is not going to be an efficient heat exchange medium, given the tiny diameter line set tubing and tiny water pump you mentioned, which cannot move enough water to do the job.
Probably would be way more effective and simple, to dig a trench a couple feet deep, into which to lay 8" corrugated plastic tubing, connect the tubing to your vents in the battery cabinet, with a squirrel cage to force air through the tubing and through the battery cabinet, taking advantage of the geothermal cooling effect.
Summing up, why set up a complicated, inefficient water-driven cooling system, when simple geothermal airflow probably would do the job?

 

[Steve_S]

Ground Temp below 4' is usually around 50F +/- a bit depending on soil type & exposure. Dig your hole 4' deep, 4' in diameter, then a coil of PEX "in clean sand, have 6" above & below the 3/4" or better 7/8" pex! Run the Pex back to "shed" using a small low flow 12V Pump that can feed an Automotive "Heater Core" no need for a radiator and voila. Alternately, you could do a Radiant System in this manner and plumb the PEX into the flooring BUT do have a layer of foam insulation with foil under it IF wood frame floor, or embed in Concrete (minimum 4" thick) with from under it.

My House is Radiant Floor Heated using a Frost Protected Slab Foundation. When I build my Powerhouse I did the same thing by embedding PEX into it's FPSF Slab for future use. My intention was not for cooling through but rather Heating because in summer the PH never get's that warm due to the Thermally Broken wall structure but in winter it does get to -35C/-31F outside and I intended to use Passive Solar Heating with heating panels on the roof.

 

[Risky Rob]

Is the well water clean enough to circulate through a radiator? Does it contain particles or minerals that might be a problem? A system with large diameter pipes might work better. Would evaporative cooling work in your climate?

 

[t3kn0f1l3]

With respect, you're making the geothermal concept application way too complicated by introducing water piping and heat exchangers into the design.
Too many variables and too many points of potential failures.
For one thing, water is not going to be an efficient heat exchange medium, given the tiny diameter line set tubing and tiny water pump you mentioned, which cannot move enough water to do the job.
Probably would be way more effective and simple, to dig a trench a couple feet deep, into which to lay 8" corrugated plastic tubing, connect the tubing to your vents in the battery cabinet, with a squirrel cage to force air through the tubing and through the battery cabinet, taking advantage of the geothermal cooling effect.
Summing up, why set up a complicated, inefficient water-driven cooling system, when simple geothermal airflow probably would do the job?

Thanks ACM, good suggestion. I take your point about over complicating the thing.

In my application, the water table is really high, so even a 2' trench would put the air tubing under water half the time. This means it would take a beating through the freeze/thaw cycles in winter here - (our winters get to - 30C). For instance, I put in a fence 5 years ago, took pains to make all posts plumb, and buried them 5' down with 1/2 yard of concrete per post. Some of the posts are already way off - it's almost comical. Also, I've read (I have no experience here) two problems with air cooled systems: 1. they can leak, filling with water 2. they produce mould. Again, I could be wrong about this - just what I've read. Maybe it would still work to do air-cooled, but I figured a water cooled would take advantage of the high water table and be easy to dismantle for season changes. Sounds like using larger dia. heat exchanger in the ground would be best, though. I'll avoid the smaller of the copper lineset tubes and maybe upgrade to something entirely different . . .

 

[t3kn0f1l3]

Is the well water clean enough to circulate through a radiator? Does it contain particles or minerals that might be a problem? A system with large diameter pipes might work better. Would evaporative cooling work in your climate?

Last time I checked, the well water is clear at the top, but a bit cloudy at the bottom - I covered the bottom end of the vertical 1' dia. tube with landscape fabric before submerging/burying it, so I'm not sure what's getting thru. I should take another look to be sure before proceeding, since your suggestion would let me avoid a heat exchange coil altogether The pump would have to be able to handle some silt, so I'll check to see if that's a problem.

I haven't looked at the evaporative cooling option. Our heat waves are normally pretty humid. A quick search (https://en.wikipedia.org/wiki/Evaporative_cooler) makes me think this option could work, but in dry regions.

Looks like I should be considering larger diameter pipes and ignore the smaller stuff.

 

[t3kn0f1l3]

Ground Temp below 4' is usually around 50F +/- a bit depending on soil type & exposure. Dig your hole 4' deep, 4' in diameter, then a coil of PEX "in clean sand, have 6" above & below the 3/4" or better 7/8" pex! Run the Pex back to "shed" using a small low flow 12V Pump that can feed an Automotive "Heater Core" no need for a radiator and voila. Alternately, you could do a Radiant System in this manner and plumb the PEX into the flooring BUT do have a layer of foam insulation with foil under it IF wood frame floor, or embed in Concrete (minimum 4" thick) with from under it.

My House is Radiant Floor Heated using a Frost Protected Slab Foundation. When I build my Powerhouse I did the same thing by embedding PEX into it's FPSF Slab for future use. My intention was not for cooling through but rather Heating because in summer the PH never get's that warm due to the Thermally Broken wall structure but in winter it does get to -35C/-31F outside and I intended to use Passive Solar Heating with heating panels on the roof.

Your setup sounds good. Unfortunately for me, my shed is done, slab and all, and I did not do this - never thought I'd want to insulate the whole shed. I'm hoping my 1' dia., ~4' deep well will work for the battery cabinet (16" x 3' x 4' - interior), but I guess I'll see. Yes, a heater core. That's about the right size. Thanks for the suggestion!

 

[400bird]

This is interesting, I wish I had a water table like that, I could never make it work here.

If you can get down deep enough to reach a constant temperature, you could use it to maintain the battery summer and winter.

Also, I'd try a combination of both ideas. Push batter cabinet air through the tubing/heater core in your well. In the summer you'd push hot air into the well and get cooler air back out. In the winter, you'd push cold air in and get slightly less cold air out.

With 4" of foam insulation and good air sealing, it shouldn't take much in the summer. I'd expect the same in the winter, but your delta temps (ground 50 f vs desired 60-70 f) won't drive much temperature movement.

That said, if you can't move enough heat around with direct air, you could go to pumping water into a heat exchanger at each end. It's not like whatever you choose is permanent, you may end up tweaking it depending on how it works.

 

[Daddy Tanuki]

-anyone have an idea of what to use for the radiator - maybe a small car radiator - I need to integrate it into 4" metal ductwork by fabricating a sheet metal box, I think. . . . but am open to suggestions

PM me your mailing address, I can ship you a 10" x 8" heat exchanger (free) (you pay shipping USPS only) from a juice bar machine that would probably be fine and dandy. if you needed something larger than that I would suggest either a motor cycle radiator or a K jidosha radiator, The K car is slightly larger than a motorcycle one.

 

[Daddy Tanuki]

I was considering something similar but found out that at least in my location a simple 4" chimney flue in black out the top of the battery shed was enough draw to keep the batteries at 26-27c or below. inside the battery shed it come out about 3inches below the roof so not 100% optimal but it works, you can stand on a ladder and feel the air moving. I forget who suggested i try this first but it was a good call, the chimney pipe is stainless and normally stainless with no paint.

I simply painted it BBQ black and the natural convection from the pipe itself draws the air from the battery shed and then heats it a bit hotter in the pipe causing it to continuously draw fresh air into the shed. In the winter I will plug it with a Styrofoam plug. at the end is a cleaning plug that normally points down, i put it sideways so I can stuff a plug in the pipe via that cleaning plug

Edit: it was a comment by @FilterGuy about trying just a black painted chimney pipe.


.

 

[FilterGuy]

I was considering something similar but found out that at least in my location a simple 4" chimney flue in black out the top of the battery shed was enough draw to keep the batteries at 26-27c or below. inside the battery shed it come out about 3inches below the roof so not 100% optimal but it works, you can stand on a ladder and feel the air moving. I forget who suggested i try this first but it was a good call, the chimney pipe is stainless and normally stainless with no paint.

I simply painted it BBQ black and the natural convection from the pipe itself draws the air from the battery shed and then heats it a bit hotter in the pipe causing it to continuously draw fresh air into the shed. In the winter I will plug it with a Styrofoam plug. at the end is a cleaning plug that normally points down, i put it sideways so I can stuff a plug in the pipe via that cleaning plug


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View attachment 110478

Heat chimneys are great for a passive airflow system! Where do you draw the fresh air from? Do you have an earth tube to cool the input air?

What part of the world are you in? What are your temperature extremes?

 

[Daddy Tanuki]

Heat chimneys are great for a passive airflow system! Where do you draw the fresh air from? Do you have an earth tube to cool the input air?

What part of the world are you in? What are your temperature extremes?

Japan northwest flanks of Mt. Fuji.
night to hottest part of day: Winter -17°c ~ 5°c. Summer 17°c ~ 35°c
box is 1/2" plywood with 4" of blue foam with another 1/2" of plywood on all walls floor, and ceiling. box was sealed tight and in the summer i would open the door about 1" and lock it in place with a set screw to keep things cooler.

Now door is closed and air comes from below and out the chimney.

copy paste form other thread:

It works. I put this in in late May and my battery box temp never went above 29°c. In the past it had went as high as 38°c and on average it hovered around 35°c. Now with the chimney stack installed it hovers around 27°c which is an average 6-7°c drop.

in the winter I will use the cleaning plug on the chimney pipe to stuff a foam plug in it to prevent heat loss.

no earth tube, just drawing cooler air from under the 40' container that forms the basis for the shop. if you look at the photo you can see a container on the left side, there is an identical unit on the right. they both have about 8" of clearance below the containers.

this is just a 4" chimmeny pipe with rain/critter hat and a 90° cleaning elbow. but it definitely dropped my box temps immensely. My magnum and 4 morningstar controllers puts out some heat while powering the split pack, fridge, and freezer 24-7. for about $50.00 in parts and a spray can of BBQ flat black, it was a very cheap and very effective mod. thanks for the idea on the other post.

edited symbols next to temperatures for clarity

 

[Daddy Tanuki]

gratuitous shot of 100 A/h at 54.9 volts charging. I run my A/C 24-7 to prevent mold from the high humidity here in Japan

 

[t3kn0f1l3]

Ken, these are some awesome alternatives. Thanks for sharing and please everyone, keep any more ideas coming! Since there are so many different specific cases, like having cool air from under the container shop, having the battery box exposed so the heat chimney concept can work, etc., I think it's helpful maybe to gather a list of different options for cooling the batteries.

I absolutely love the elegance of this design!

 

[Daddy Tanuki]

Ken, these are some awesome alternatives. Thanks for sharing and please everyone, keep any more ideas coming! Since there are so many different specific cases, like having cool air from under the container shop, having the battery box exposed so the heat chimney concept can work, etc., I think it's helpful maybe to gather a list of different options for cooling the batteries.

I absolutely love the elegance of this design!

honestly Thank @FilterGuy I had thought about fans and whatnot, but he suggested this and I tried it. it is working damn well so far, i just had to figure a way to plug it up in the winter which with the cleaning plug its easy... stuff some phone and rags into it come november.

 

[FilterGuy]

Thank @FilterGuy

Actually, credit goes back to the US National park service. Back in the 60s (maybe 70s), they gave a huge contract to a company to come up with a solution to smelly outhouses. What the company came up with was to use a really large black vent pipe from below that is exposed to the sun....and it worked. The smell went up through the chimney.... not through the seat. (There was a bit of backlash about spending so much money for such a simple solution.....but I figure that if it works no one can complain) It turns out that the pipe did not even need to be exposed to the sun because the heat of the decomposing waste was enough to get the convection current flowing.

When I heard that story I was impressed with the simplicity of the solution and realized it could be used in many places....but never had a place to use it. Since then I have heard of solar chimneys in relation to earth tubes so when the conversation came to batteries it seemed like a good solution to suggest.......so, I guess you could claim it was a shitty suggestion.

 

[t3kn0f1l3]

So, I'm back at it now after a break to deal with other things. Here's a sketch of the plan I've settled on (described above) and some pics on progress so far. I've got the air loop roughed in and will be roughing in the water loop in the next day or so. Thanks much to @

Daddy Tanuki for sending me the water-air heat exchanger, which is now enclosed in the duct. ​

 

[Daddy Tanuki]

So, I'm back at it now after a break to deal with other things. Here's a sketch of the plan I've settled on (described above) and some pics on progress so far. I've got the air loop roughed in and will be roughing in the water loop in the next day or so. Thanks much to @

Daddy Tanuki for sending me the water-air heat exchanger, which is now enclosed in the duct. ​

View attachment 157408View attachment 157409View attachment 157410View attachment 157411View attachment 157412

who makes the circulator pump? (link please!) I have some ideas for some simple space heaters and need a pump that will flow for the same sized heat exchanger like what I sent you.