thermal storage (wood boiler related)

[[486]]

any of you guys running anything for a large amount of storage?
The idea being then you only need to fire the boiler with a full draft every other day (or whatever) rather than continuous firing with a choked down fire. Leaving the house without relying on propane or electric backup heat. Shit like that.

I know they make tanks, sorta like an electric water heater without the elements in it, but that seems too easy/expensive. I was thinking something more like an IBC tote full of boiler-temp water.

another idea that's way interesting from a technical perspective is wax batteries. You got what is essentially a heat exchanger with one side full of high-melting-point wax. The magic of the system is that the phase change of the wax freezing lets off a shitload of heat at a steady temperature.
Water dropping a couple degrees only releases a little bit of thermal energy, but dropping the wax across its melting point has many times the energy released. Meaning you wouldn'd need nearly as much heated mass to store the same energy.
Heat exchanger would be an open-topped drum with a loop of a couple hundred feet of pex held inside, suspended in there so there aren't as many dead spots as wax doesn't conduct heat too good.

The only big trouble is the cost of the wax. Been thinking about calling all the local thrift stores to see if they could save all the broken/unsaleable candles they get as donations, but they've probably already got someone buying them up. Haven't called any of them yet though.

as said, any of you with wood boilers doing any of that sorta shit?

 

[Muckin_Slusher]

How about fat? Is there some byproduct of farming or slaughter that you could use?

Does bacon grease go rancid? Would it matter?



You've always got interesting problems!

 

[Pony_Driver]

Cheap is a disease, but this sure is interesting. Fat will go rancid, but tallow (rendered organ fat) ought to last a LONG time. Especially if it is sealed.

 

[dave_dj1]

There are many people who have added a couple thousand gallon tanks in their basements as storage from their outside wood boiler. Personally it would be a giant PIA to have to make a fire every other day and tend to it for a charge. I have a Heatmor and it's really efficient in my opinion. It only holds 114 gallons. I burn only dry wood. Years ago I had a vision of building a new house and burring a 2000 gal insulated tank. I forget all the math now but by my calcs at the time I would only need a fire once a week (modest house)
Check out a Garn wood boiler, basically a firebox in a large tank of liquid.

 

[ExWrench]

Probably doesn't help with "cheap" (or practical at the DIY level ), but Glauber's salt is good for thermal storage.
I dig the wax idea - relatively inexpensive way to take advantage of phase change at reasonable temperatures.

Does wax expand before melting?
You may need a container with drafted walls to avoid splitting your drum & waxing your basement.
If you let molten metal solidify in a full crucible, 9x/10 you just bought a crucible.

 

[[486]]

good fucking god fifth try posting this
everywhere else is fast, for whatever reason you hit the quote button here and it takes five fucking minutes to load

You've always got interesting problems!

Cheap is a disease, but this sure is interesting.

inorite?
always rather spend a couple extra days doing wierd shit rather than the couple days at work to buy a solution

see also:
running backup generator coolant through the loop to scavenge the heat from that
and
having a separate loop with a heat exchanger and pump that's got actual good antifreeze in it to pre-heat the car with those spit-swapping quick connects
heat exchanger just to keep the coolant separate, as the boiler loop is probably gonna get garbage glycol from the drain pans at work, distilled to get all the worst poop out of it

Does wax expand before melting? You may need a container with drafted walls to avoid splitting your drum & waxing your basement.

it does shrink a lot when it solidifies, figure an HDPE drum would be plenty flexible to deal with it

 

[tracyb]

Cheap is a disease, but this sure is interesting. Fat will go rancid, but tallow (rendered organ fat) ought to last a LONG time. Especially if it is sealed.

i dont think tallow ever goes bad. the rudder flanges on most of the Wa state ferries are packed in about 50 gallons of tallow. everytime they are serviced, we would catch as much as we could when cutting the side plates offs, filter it, and put it back in when done. these where open top and not sealed.

 

[[486]]

Shit right I forgot to reply to that.
tallow seems to have a melting point of around 120f whereas paraffin can be had up to around 165f
120 seems to be around where you run the water after the mixing valve, where the hot side of the loop you would want to run as close to boiling as you could in order to get more thermal storage
ideally it'd be something that melts at like 190f but good luck finding something like that, then good luck getting it for cheap

the "cheap" side of things keeps making me lean more toward just sticking a few IBC totes in the basement and running them full of boiler-temperature water, as even 50 gallons of paraffin wax ain't all that cheap

 

[Poke]

My neighbor strung together a bunch’s used/free water heaters. So his boiler would heat 3-4 water tanks at a time. He wrapped them in heavy insulation. He captured a ton of heat from his wood boiler.

 

[larboc]

It's too bad steam is so hard to deal with at a residential scale.
I've always thought a free CL hot tub would be a good option to store heat if the top could be made to seal well.
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[xjmark]

It's a much smaller setup than what you're looking for, but this 50 gallon suprerstor tank was bought used and cheap. I don't use the woodstove much anymore, but when I did, it heated the main shop and pumped water out to fan coil units in one the front garage bays, and into the house. Water temp was controlled with a digital 0-10vdc signal to the air damper actuator. Usually ran it 180-190*.

When I was going to spend part of the day in the shop, I'd run the system without the tank. When it was a weekend project, I'd open the valve to the tank which works off of stratification. The pump was only used for the main loop. When the tank was in the picture, it acted like a thermal flywheel to smooth out the water temp fluctuations, and gave you more time between stove feedings.

If you keep your eyes open for used water storage tanks, I'm sure you can find them for cheap/free since many places are converting to the small wall hung water heaters.

 

[[486]]

It's too bad steam is so hard to deal with at a residential scale.
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it does have cool side benefits like running a generator off of it so you can sell the electric if you're set up for that with solar panels
there's just the "you gotta monitor it the entire time or you end up blown up and boiled at the same time"

I don't think it has a large advantage in thermal storage though, as while you've got the phase change transition there the density of steam goes way down, so you would need a very large vessel for it

 

[sdmuleman]

Wax benefit seems overrated. Yes, you get lots on energy from heat of fusion, but at a somewhat low temperature - 120-140*f, and specific heat is about half of water. Going from 190*f to 105*f, wax only stores about 70% more energy per gram than water, and most of that heat is released at a lower temperature than is really useful for heating. Add in water having higher density, and if you add 50% to your water tank size you'll achieve the same result. Plus, wax expands considerably when liquid, so the different is even smaller if you look at liquid phase density. Further, getting a meaningful amount of heat storage requires hundred of lb of wax - not easy or cheap. Nor does the idea of large quantities of hot wax seem like a particularly safe thing to have around. Far far easier just to have more water tankage, and also eliminates the need for heat exchangers.

Bigger problem is heat loss. Uninsulted tote is going to loose so much heat to be practically useless unless it's very large. Used water heaters are a better solution because they already have good insulation.

 

[[486]]

Going from 190*f to 105*f, wax only stores about 70% more energy per gram than water,

Thanks for doing the math on that, man
I'm really bad at math

now it's between craigslist free section water heaters (probably a recipe for lots of leaks) or just totes in the basement with insulation packed around them
iirc water heaters only got a couple inches of fiberglass or pour in foam around the tank, nothing amazing so far as insulation

 

[[486]]

seriously you probably saved me weeks of effort, never mind the expense, thanks man

 

[RusM]

i dont think tallow ever goes bad. the rudder flanges on most of the Wa state ferries are packed in about 50 gallons of tallow. everytime they are serviced, we would catch as much as we could when cutting the side plates offs, filter it, and put it back in when done. these where open top and not sealed.

You work for ferries? Also, gross!

 

[[486]]

While looking up tallow I found out that they used to use it for frying fries and such but don't any more
I'd post that in the "things ain't how they used to be" thread, but those snowflakes've already admonished me for that sorta shit

 

[YotaAtieToo]

I skipped a lot of this, but where the fuck do you guys live that a giant vat of hot animal fat wouldn't attract a ton of animals?

Also, in for the tech.

 

[tracyb]

You work for ferries? Also, gross!

how'd the tugboat gets aids?
it was rear-ended by a ferry

on the repair crew, local ship yard.
imagine having a 1/4" steel vat of solid tallow. you have to cut the sides off with an o/a torch and melt the rest off with a weed burner. nasty, gross... doesn't begin to describe it. unbolting the flange involved a 4' breaker bar, on a hand cut socket, hooked to a 10k lb chainfall over tightened. then taking turns beating on it with Monday (Monday; a 25lb hammer)

 

[Microtus]

A little outside the box but if you already have the boiler, could you tie it into a gaht type system instead of using passive heat from a greenhouse? Two separate closed loop systems to store and transfer heat underground.

 

[87manche]

how'd the tugboat gets aids?
it was rear-ended by a ferry

on the repair crew, local ship yard.
imagine having a 1/4" steel vat of solid tallow. you have to cut the sides off with an o/a torch and melt the rest off with a weed burner. nasty, gross... doesn't begin to describe it. unbolting the flange involved a 4' breaker bar, on a hand cut socket, hooked to a 10k lb chainfall over tightened. then taking turns beating on it with Monday (Monday; a 25lb hammer)

a new meaning to "a case of the mondays"

 

[Provience]

i'm planning on running water for thermal storage, a couple large sealed tanks, whatever amount i need to take a full hot load from a wood furnace at max capacity without exploding is the goal.

wax is an interesting idea, haven't heard of that one

 

[larboc]

I'd looked at this awhile back when I was considering converting from my indoor hot air wood furnace to an indoor boiler and decided I would need so much space it wasn't quite worth it, especially given the hassle of starting new fires vs. just keeping one going. Would be handy in the shoulder seasons, but at the time being the ROI on the effort still isn't worth it for me.

Some numbers:
25 million BTU/cord for decent firewood. In the shoulder seasons I probably burn 1/2 cord a month, dead of winter 2 cords/month. That's 2 to 8 bulk cubic feet per day= 0.4 to 1.6 mil/btu per day.
I figure to have it be of value I'd need the system to be able to provide heat for at least a day.
The usable temp range of hot water would be about 120-190F=70F delta T.
8.3lbs/gal of water
8.3*70F=600 BTU/gallon
So to carry a day's worth of heat I'd need 700 to 2800 gallons to provide heat for 24 hours.
That's beyond what I could practically store with free water heaters.
Obviously I'd need less and less as the outdoor temps are warmer and I think that's the only time it would be worth it. For those times of year there's enough thermal inertial in my house and basement that I still don't know that it would be worth the hassle.

 

[Sterlingfire]

I'd looked at this awhile back when I was considering converting from my indoor hot air wood furnace to an indoor boiler and decided I would need so much space it wasn't quite worth it, especially given the hassle of starting new fires vs. just keeping one going. Would be handy in the shoulder seasons, but at the time being the ROI on the effort still isn't worth it for me.

Some numbers:
25 million BTU/cord for decent firewood. In the shoulder seasons I probably burn 1/2 cord a month, dead of winter 2 cords/month. That's 2 to 8 bulk cubic feet per day= 0.4 to 1.6 mil/btu per day.
I figure to have it be of value I'd need the system to be able to provide heat for at least a day.
The usable temp range of hot water would be about 120-190F=70F delta T.
8.3lbs/gal of water
8.3*70F=600 BTU/gallon
So to carry a day's worth of heat I'd need 700 to 2800 gallons to provide heat for 24 hours.
That's beyond what I could practically store with free water heaters.
Obviously I'd need less and less as the outdoor temps are warmer and I think that's the only time it would be worth it. For those times of year there's enough thermal inertial in my house and basement that I still don't know that it would be worth the hassle.

Shit, how many sq ft you heating? 2 cord a month is pretty nice considering where you are. I burn +/- 3 cord a weekLots of wood cutting for me... near 60 cord a year

 

[Poke]

Shit, how many sq ft you heating? 2 cord a month is pretty nice considering where you are. I burn +/- 3 cord a weekLots of wood cutting for me... near 60 cord a year

3 cord a week is physically impossible to burn in a home under. 10,000 square feet unless you don’t have walls or a roof. Safe assumption you don’t know what a cord is.

60 cord would heat a neighborhood. Lol

 

[larboc]

Shit, how many sq ft you heating? 2 cord a month is pretty nice considering where you are. I burn +/- 3 cord a weekLots of wood cutting for me... near 60 cord a year

1600 above ground, 1700 basement that's 1/4 exposed.

Umm, what are you calling a cord?
I burn 8-10 cord a year. Cord=4'x4'x8' stack of wood=128 bulk cu. ft.

 

[larboc]

3 cord a week is physically impossible to burn in a home under. 10,000 square feet unless you don’t have walls or a roof. Safe assumption you don’t know what a cord is.

60 cord would heat a neighborhood. Lol

That's about like adding a 8"x24" round of firewood every hour. Yea, neighborhood territory. I'd guess he's confused on what a cord is, he could mean face cord (typ. 16"x2'x4') which is ~1/3 a cord.

 

[[486]]

Shit, how many sq ft you heating? 2 cord a month is pretty nice considering where you are. I burn +/- 3 cord a weekLots of wood cutting for me... near 60 cord a year

my neighbor goes through 20 a year, little house and a 40x60, thought that was excessive
you ever heard of insulation?

I suppose it helps the math on my end that I'm planning mostly earth-sheltered shit, where I can easily just bury a foot of EPS foam all around it

 

[Sterlingfire]

3 cord a week is physically impossible to burn in a home under. 10,000 square feet unless you don’t have walls or a roof. Safe assumption you don’t know what a cord is.

60 cord would heat a neighborhood. Lol

face cord. I should've read more closely
Btw, my home is 5k sq ft, my shop is 2400 sq ft with 14' sidewalls, so not far off 10k sq ft when you consider the shop with not great insulation and 14' walls with a 17'-6" peak...

1600 above ground, 1700 basement that's 1/4 exposed.

Umm, what are you calling a cord?
I burn 8-10 cord a year. Cord=4'x4'x8' stack of wood=128 bulk cu. ft.

Yeah yeah I'm dumb, face cord... now that that's cleared up, i burn 4 cord a month, still double what you do, but also have well over double the sq ft.
What boiler you using? I rebuilt mine and it's far more efficient than it was last year.

 

[larboc]

face cord. I should've read more closely
Btw, my home is 5k sq ft, my shop is 2400 sq ft with 14' sidewalls, so not far off 10k sq ft when you consider the shop with not great insulation and 14' walls with a 17'-6" peak...



Yeah yeah I'm dumb, face cord... now that that's cleared up, i burn 4 cord a month, still double what you do, but also have well over double the sq ft.
What boiler you using? I rebuilt mine and it's far more efficient than it was last year.

Generic "Humble" 70's indoor hot air add on furnace in series with an oil furnace. I've also got a Jensen indoor wood/coal boiler that isn't hooked up. Rule of thumb around here is that an outdoor wood boiler will use about 2x what an indoor boiler/furnace will use, is your boiler outdoors?