Large hot water storage tank for my HS T
Im going to start building a large hot water storage tank fed from my HS Tarn wood boiler. I dont have any info on it but from what I can find out so far it might be in the 145,000 to 175,000 btus range.
my tank will be 4w x 8L x4H with 4 in foam on bottom and 6ins on walls and top with 3/4 50ftcoil for water comming from wood boiler and a 50 ft coil from my oil fired boiler with the circulators feeding heat up into the house. Ill use a 60 mil rubber liner used for ponds and roofs.
Its going to be reinforced with steel 1 1/2 in u beams (the type that are used to hang ductwork heating and air conditioning units up hanging from ceilings .. in warehouses and lg box stores hotels etc. Ill post pics once I get under way so far ive only been getting supplies . havent cleared the space in my basement yet thats next. let me know if any of you guys have had any or done anything like this and please give me advice or feedback. thanks Vic
Carpentry and remodeling
Vic Vardamis
Bangor Me
Replies
This is a non pressure tank? Sounds like a GREAT idea ... gives you lots of options. I looked at the TARM once for a house I designed. Didn't check your size ... how many gallons are you talking about (too lazy to calc it right now)? It sounds like a large tank ... but I don't know your house size/load, either. You live in the cabboose in the picture?
... Did the calcs ... that's roughly 1,000 gallons of water. If you store it up to say 160 degF and use it down to around 110 degF ... you have energy storage of 400,000 + Btu's If your house heating load is say 50,000 Btuh, this provides about 8 hours of energy storage ... VERY roughly. So the tank doesn't seem overly large, now. Do you know anything about your load? The TARM system may allow storage up to say 180 degF ... not sure.
Now that I think about it ... storing heated water may require a special tank ... maybe someone else can jump in here. Maybe the only criteria is a high temp pressure relief??? It's a little late, ... thinking out loud here. I think even non pressurized tanks may need to be ASME rated or some such (i.e. you may not be able to just go build a tank). Don't recall when a tank needs to be 'rated' and for what uses, etc. If the tank is not sealed, it may not have to be rated ... but if your system is a sealed/closed system, it may need to be rated ... someone help us here!
Food for thought.
from my calculations it is about 1000 gals but due to my adding more foam it would be a littoe less about 960 gals + or -Carpentry and remodeling
Vic Vardamis
Bangor Me
FYI - a 4 x 4 x 8 tank inside dimensions is about 950 gallons. You add 6" of insulation to that (assuming you are using your plywood module to build the box) ... and you end up with just under 500 gallons (3 ft x 3 ft x 7 ft insulated w/ 6 inches). I think this calc is right. Bigger difference than I might think. Insulation takes up a lot of volume.
Anyway 1,000 gallons gives you 550,000+ Btu storage at 180 deg storage and roughly 110 degree use/return temp. 500 gallons gives you just under 300 KBtu energy storage.
For mild temp days ... you may have a week's worth of storage ... not knowing your load.
Sounds like the tank issue is a non issue. I'd have a tendency to look for a tank I could just buy ... an used tank ... but maybe you have problems w/ fitting in through the basement door? That's always a tough one.
Good luck ... have fun doing it. Take pics and post them.
Dog Boy,
I have interviewed several people who have tried to do what you are doing. In every case they have had problems with leaks.
Your original post does not clearly explain how you are building the tank. Poured-in-place reinforced concrete? Fiberglass-lined plywood? Something else?
3/4 in PT plywood steel reinforced bolted at corners steel strapping about every 16 ins screwed etc braces from floor to ceiling 6 ins of foam inside with a rubber membrane liner with no seams. rubber inside folded in corners and pulled up over top edges strapped, glued and screwed. Insulated lid, rubber foam and 1/2in plywood spray foam to seal top to tank. But not pressurized, pipe in side above water line and access door on top to get at water to test ph balance and check piping. My wood boiler runs at about 175 to 190 degrees so I think it will send enough hot water into it for most days with 1 good fire. I load about 7 10in round logs at about 24 ins per load and it can burn at a hot fast burn for about 4 to 5 hours with a good bed of hot coals for another 2 to 3.
I think my real savings will be those days that are 40 to 55 degrees and on colder days I would load it at least 2 to 3 times but that would be at least half over the winter. Now I'm not expecting using half of what I would use but I wouldn't be unhappy if I did. This tank is similar to the design HS Tarn shows on there new web site that's made in Liberty Maine and made with the same materials in a kit they sell except I'm using PT plywood and 6 ins of foam instead of 4 like they do, there's is 6' x 6' and 4' tall approx the same size tank but I don't have the space for it to take up that much room from a wall.it will be built on cement pads on 6x6 pt beams every 16" and covered with 2x8 decking tight fit. and screwed and bolted to that with steel around bottom edge so no blowout . I think it should be fine it will be beefier then an above ground pool by far. Any leaking would be from rubber breaking down and everything I see shows its very stable for up to 25 years plus. The tank would be running temps of 175 or less. If more then I would have to add another loop to get rid of access temps or just shut down the boiler. the only thing I might change in building it would skip the 6x6 beams and cover the floor under it completly with cement blocks but still have decking under plywood and braced. .... there some more info for now. Carpentry and remodeling
Vic Vardamis
Bangor Me
Vic,
Eric Doub of Boulder, Colorado built a similar tank out of concrete. He used EPDM rubber to waterproof his tank, but the EPDM failed the first time he installed it. Here's what was written about his experience (September 2006 issue of Energy Design Update):
"Doub’s biggest headache has been his storage tank. Worried about leaks, he decided at the last minute to change his original tank design (a concrete tank coated on the inside with a spray-on truck-bed liner). For increased waterproofness, he installed a layer of 40-mil EPDM rubber on top of the spray-on liner. Soon after the tank was filled with water, however, it began to leak, so Doub drained the tank and removed the EPDM. The useless truck-bead liner left a bumpy surface on the inside of the tank. To create a smoother surface, Doub installed a layer of ½-inch polyisocyanurate insulation on the tank’s walls and floor, covering the rigid foam with two layers of 60-mil EPDM. “We spent about $10,000 for the tank,†said Doub. “If I had to do it again, I would not install the type of tank we have in our basement. It’s a potential Poseidon Adventure.†"
I hope yours works! Good luck!
There was a company in MD that was building holding tanks under the home. There was an episode on This Old House years ago when Bob Villa was still on. They said the homes would be 30 or 40% more efficient. They used the water to run a forced hot air furnace.
I would think it would be better to run in floor heating tubes. You would have a lower temp to circulate and should allow the system to be more efficient.
just a thought ....
http://www.builditsolar.com
Everything you need to know.
He has built your tank, all the details are there.
Great site for solar info.
Joe H