Hot water storage tanks?

[Number21]

I'm moving into a new shop with a wood stove for heat. I would like to use the stove to heat up water, which would then continue to heat the shop continuously even when the fire has long gone out. I'd like to use steel 55 gallon barrel(s) to store the hot water in. If I use a glycol based "coolant" in the barrels it would keep them from rusting and allow me to store water at above 212 degrees. I will then pump the hot water through a radiator and through another heat exchanger for my electric water heater.

My question is, how hot should I store the water? I'm not sure how much I'll need yet, but, I can always add more barrels to the system. Should I bother going much above 200 degrees?

Also, how much glycol cooling mix would I need in the barrels to keep them from rusting out? 25%? 10%?

[electrak]

10% will get you to 214F

20% will get you to 216F

30% will get you to 219F

40% will get you to 221F

50% will get you to 225F

60% will get you to 232F

Specific Heat Capacity

25% is 0.953

50% is 0.865

100% is 0.66

So as to have some safety, I would target about 180-190F. Now if you pressurize it you can go hotter, but do not use 55 gallon drums, keep them vented, and if you are using Ethylene Glycol, vent it outside, that sweet smell is antifreeze condensing in your nose, from there it goes into your blood, breathing that all day is not good.

You can get Propolene Glycol, the stuff for RV tanks, and get a crosion preventer mix. then in small amounts it's not deadly.

[BigBreaker]

Check out builditsolar.com - Gary has some great plans for hot water storage tanks.  The liners can't handle 200F but you may want to consider a lower, safer temperature.

[bob g]

if all your after is rust inhibitor, use a DCA fluid

and forget the antifreeze.

its relatively inexpensive and a pint can treat something like 10 gallons

or more.

you can get it from any heavy truck dealer, so shop around for the best price.

bob g

[scottsAI]

Alternative

Rocket stove

http://en.wikipedia.org/wiki/Rocket_stove

Better diagram of it:

http://www.permies.com/permaculture-images/1078_150/rocket_stove_butt_warmer_3.gif

Have fun,

Scott.

[gagnerargent]

I second the suggestion.

[Airstream]

Auto style anti-freeze is toxic, many dogs & other critters have sopped some up then display "drunk" or "sleepy" symptoms until their livers fail. If you are really good or have all the plumbing away from pets & such go for it; the cash-for-clunkers program put extra fluids in the recycling loop and you can probably find 55 gallon drums of used AF for about the same price as the deposit on the drum!

A non-toxic anti-freeze is Propylene Glycol and you want the "Inhibited" versions. The additives keeps the water from becoming acidic over time from heating cycles. 10% solution of an inhibited heat transfer fluid is the minimum but does not raise the boiling point. At $25 a gallon your 55-gallon drum idea will get expensive. Dowfrost is the best name in the business, the Dowfrost HD is good for above 300°F before additive breakdown so is overkill.

As to pressurizing 55gal drums?  You're nutso! Maybe think about a closed pressurized loop that dumps heat into raw water drums?

[don1]

Hey guys

I'd like to through a wench or two into the pot to help confuse the issue here.

 If you do not plan to allow the heating system to freeze you can just fill the system with water and  buy an antifreeze conditioner sold at auto parts stores. It is a pump lube and an anti rust formula.

 Also you can cut down on the number of barrels and water by filling the barrels with about 2" size crushed rock. Then fill with water. The rock being many times more dense will store a lot more BTU's  and then the water is just used as a transfer medium.

Have fun, Don

[m8e]

Water have specific heat capacity of 4.18 kJ/(kg·K) and have a density of 1 kg/dm3. Antifreeze slightly lowers both heat capacity and density.

Soapstone(one of the best stones) have 0.80 kJ/kg*k and a density of 2.86 kg/dm3.

Granite and most other stones have a smaller heat capacity and density.

Water: 4.18 kJ/(dm3·K)

Soapstone: 0.80 kJ/kg*k * 2.86 kg/dm3 = 2.3 kJ/(dm3·K)

So if you did that, you could lose almost half of the "BTU's" compared with water.

[sbotsford]

I think the easier way would be to leave the tank's unpressurized, circulate water through PEX tubing between the boiler and the tanks, putting, I don't know, 15 feet in each drum.  In the drum, add an anti-corrosion agent, and perhaps top each drum with 1/8" of mineral oil.  This will keep oxygen out of the water, reduce corrosion, and keep the water from evaporating.

If you want to keep the water hotter, dissolve salt or calcium carbide in the water.  This will also make it more corrosive.

The circulating water will have fairly small volume, so you can pressurize it reasonably safely, and/or add material to raise it's boiling point.

Check the specs on the PEX tubing.

For distributing the heat, build a styrofoam box around the barrels, and put a shuttered fan at one end, and a shutter at the other.

Quantities:

A barrel of water is nominally 55 gallons.  at 8 lbs/gallon that's 440 lbs.

If you raise the temp to 180 degrees, you'll have about 100 degrees to work with.

So a barrel will hold about 44000 BTU.  

If you have a 20 x 40 foot shop with 10 foot ceilings, you have 1200 square feet of wall and 800 sq feet of ceiling.  6 inch walls are R20, 12 inch ceiling is R40.

So the walls leak 60 BTU/F The ceiling leaks 20 BTU/F  So 80 BTU takes care of the wooden part.

10 x 10 shop door 2" thick styrofoam filled = R5.  That's another 20 BTU/F/Hr

3 x 7 people door 2" thick styrofoam is another 4.

10% wall used by window = 120 square feet at R2 (typical double pane) = 60 BTU/F/Hr

So that's 164 BTU/F/Hr

Round UP.  200 BTU/F/Hr.  Now Rule of thumb.  You'll use this much again heating air exchange.  Probably more when you're working, less when you're on coffee.  400 BTU/F/Hr.

It's -30 outside.  It's 70 inside.  So we're back to 40,000 BTU/ hour -- That's the extreme case.  So a barrel of hot water holds an hour of heat in bitter winter weather.  

Lets' loosen up a bit:

You want the shop to stay above freezing when you aren't in it.  Differential temp is now only 60 degrees, and if your detailing is any good, you're a lot closer to 200 than 400.  Under these conditions, 1 barrel is heat for 3 hours.

So: 8 barrels would let you get away with one firing a day.

If your temps are never that cold, adjust accordingly.

One other thing:  Put a big truck radiator from the local wrecking yard in the loop.

Put the fan so it blows through it on the way OUT of the box.  But the water goes through the radiator on the way INTO the box.  Now you come in in the morning, the shop is cold. Turn up the thermostat.  Fan comes on.  As soon as there is hot water in the radiator, your shop starts warming up.  When the shop is warm enough, the fan shuts off, and most of the heat goes to heating the barrels.