Hot Water Storage

[Nofossil]

I think I may have posted this picture somewhere, but it's not in this thread. I used an 880 gallon stainless tank from a local stainless scrap dealer / fab shop. I think I paid $350 for it. I put in three HX coils:

1) Domestic hot water preheat (cold well water gets heated on it's way to the hot water heater).
2) EKO boiler / zone coil with rectangular hard copper grids top & bottom.
3) Solar panel rectangular hard copper spiral.

The EKO / zone coil is bidirectional. When th EKO is heating it, it flows top-to-bottom driven by the EKO's circulator. It acts as another zone, in effect. When it's being used to provide heat, it flows bottom-to-top, driven by its own circulator. In that mode, it's effectively another heat source plumbed in parallel to the EKO and the oil boiler. Description of the plumbing here.

It's enclosed in an insulated 'doghouse' under the deck just outside the boiler room.

More description here.

 

[pbvermont]

why is everyone building elaborate concrete and wood-based structures for storing large volumes of water? Why is no one using the variations on the method that the Tarm heat storage tanks are made from? Its essentially several 4'x8' aluminum sheets riveted end to end and forming a large circular tension ring, insulated w/ foam foil board and lined w/ epdm. All materials available at local home-building supply store and EASILY moved and put together. AND in whatever size that fits your needs.

 

[Eric Johnson]

That's a good idea. I think the answer (at least in my case) is twofold: 1.) I assume that anything that costs $3,000+ from a vendor is going to cost at least half that for me to build. That sounds like an erroneous assumption from what you say. And, 2, sometimes these projects can get out of control: Let's see, I've got a concrete tank in my basement already, all I need is some foam board insulation and a liner. It turns out to be a little more complicated than that, but once you get started, you really don't want to start from scratch. Recently, I've also wondered about using a small above ground pool.

So welcome to the Boiler Room, pbvermont. Have you actually built a tank this way? If so, how much did it cost?

 

[Nofossil]

why is everyone building elaborate concrete and wood-based structures for storing large volumes of water? Why is no one using the variations on the method that the Tarm heat storage tanks are made from? Its essentially several 4'x8' aluminum sheets riveted end to end and forming a large circular tension ring, insulated w/ foam foil board and lined w/ epdm. All materials available at local home-building supply store and EASILY moved and put together. AND in whatever size that fits your needs.

From your screen name, I'm assuming that you're from Vermont as well. I would like to welcome you as a forum member and as a fellow Vermonter. Where are you, if I might ask?

To answer your question for my situation, I needed more water storage than I could accomplish with a round tank. I actually needed more than I did accomplish with my oval tank, but that's life.

 

[pbvermont]

Thanks for the welcome. I have been reading many of the posts here for several months, and have benefitted greatly.
I live in Washington Co. in Vermont. I am presently installing a 1979 Buderus woodboiler (83K BTU) of which I have 3 in number (in various states of repair...2 were free and the good one was $400).
And yes, I built my own heat storage tank for $700 worth of materials from my local lumber store...no wood, no concrete, in the manner described in my previous post. It is 4' tall and 7.5' in diameter (approx 965 gal), insulated w/2" of foil-foam board under, around and on top. Lined w/ .45mil epdm "pond-liner"/roofing material. It has 3/4" copper pipe for lid support. This includes the pvc plumbing bits for the pass-through plumbing for my eventual hookups. It's essentially an indoor, above-ground swimming pool that sits in my basement, under the cellar-stairs. This price does NOT include any heat exchange element.
I'm going to depart radically from anything I've encountered on this site, (because I can, having the "item" I need) and install a 200 gal. heavy-walled old, copper boiler-tank INSIDE my main heat-storage tank. Essentially a tank-in-tank heat exchanger. Unlike a coil-in-tank that others are working with. This will be a closed system, boiler to copper tank for heat IN, and reverse flow from copper tank to CI radiators for heat OUT.
My system like others on this site is somewhat designed around the principal components I have "garnered."
I could use some help planning my piping and circ. sizing and placement etc.

 

[Eric Johnson]

Sounds like an interesting project. I really admire the innovative ideas people come up with when it comes to setting up hydronic wood-fired heating systems. Reminds me of the logging business--everyone innovates to accommodate their situation. As you probably know, some of us have thought about using cast iron radiators for in-tank heat exchange. Pretty cool idea with the tank; kind of a similar approach. Does it have tapping top and bottom? How much does it weigh? At today's scrap prices, that's got some value.

 

[pbvermont]

I've certainly thought of its scrap value, but it is a thing of beauty from a bygone industrial era that I don't want to destroy. It has found a new useful home. It has tappings all over it. Six, to be exact. Sizes ranging from 3/4" to 4". I am about to move it into the "swimming pool" and guess that it weighs in the 4-500 lb. range. I'll be ramping and rolling it up on top of the "pool", then head scratching, and figuring a way to lower it in(prob. a couple of come-a-longs hanging from basement ceiling joists).

 

[Nofossil]

I love the intersection of technology and old-fashioned scrounging.

In this case, I'd be a little worried about the effectiveness of heat exchange between the two tanks. Lots of the water in both tanks would be some relatively far away from the HX surface, so you'd have to depend on convection to spread the heat. I haven't got the energy at this moment to compare surface area with other designs.

 

[pbvermont]

My inner tank has roughly 48 sq. ft. of copper surface area. More than 180' of 3/4" copper pipe does, that I know is rated to transfer 39,600 BTU/hr. at 4.5 gpm. What's wrong w/ relying on convection currents? I'm not sure why you say "much of the water in each tank is not near convection surface." Is this not also true of coil systems?

 

[leaddog]

:wow: guess that it weighs in the 4-500 lb. range

The last scrap copper I took in I got $3.00 a pound. If that thing is 4500lbs that would buy you a complete heating set up with storage. I run into some good deals with scrap but not that good.
I do think it will do the job for you but make sure you have some cold water return protection for the boiler as it would take a long time to get all that water up to temp when it was doen on heat.
leaddog

 

[Nofossil]

My inner tank has roughly 48 sq. ft. of copper surface area. More than 180' of 3/4" copper pipe does, that I know is rated to transfer 39,600 BTU/hr. at 4.5 gpm. What's wrong w/ relying on convection currents? I'm not sure why you say "much of the water in each tank is not near convection surface." Is this not also true of coil systems?

Thanks - saved me the effort of doing the math. Math on Saturday mornings doesn't always happen.

There's nothing wrong with relying on convection - that's how indirect hot water heaters work, also. My only question is how well this configuration accomplishes it. Coils spread the surface area over a larger volume.

I'll gladly admit that I don't know the science - please take my question as curiosity rather than criticism. I'm truly interested in how this works.

 

[pbvermont]

Sorry, my bad typing. I meant "in the 400-500 lb. range." It doesn't weigh 4500 lbs. Yes I will put cold water return protection on it, thanks. The boiler will have its own preheat loop w/ a Termovar valve and dedicated circulator. I hope that generally, once I get the big tank temp up, the little one will just need to boost it now and then.
Nofossil. Thanks for your critique and questions. Its all grist for the mill. Dialogue can help towards greater knowledge. Again, because I HAVE this tank, and its a LOT of copper, I am interested in using it. Being the scrounger that I am, there's no way I can go out a buy comparable amounts of copper at this point.
I believe Eric said a while back that anything (metallic) with a lot of surface area, in the storage tank, is going to exchange heat. How it does it, exactly are all finer points of thermo and fluid dynamics.
Two types of smaller indirect tanks are made to go next to regular oil and gas boilers for DHW: coil-in-tank, and tank-in-tank. Mine is just a large version of tank-in-tank.

 

[WRVERMONT]

Another crazy Vermonter. I like the copper tank within your swimming pool concept. Useing what you have is efficiency in itself.

 

[hkobus]

I love the "pool" idea. I the round shape has more strength to begin with. Not sure if I like aluminum, but roofing steel is high tensile, easily riveted and cheap (cover-sheets are very cheap if you don't care about color) I am thinking about using load ty-down straps, with ratchets to tension the outside.
My question is, how do you make a round liner from EPDM. I have seen the tape they use to attach flat surfaces, but I would think you would have to deal with some creasing where the sides meet the bottom. Any experience on this anyone? I appreciate any thoughts here, thanks.

Henk.

 

[pbvermont]

I actually didn't use aluminum. I used 4x8 sheets of Tuff-liner, readily avail. at the lumber store for $35/sheet. It's white and has a nubby surface and is used around here to line the walls of milking parlors, food processing rooms. I overlapped the sheets 4" at the ends, put construction adhesive between and a double row of large autobody rivets. Your idea of reinforcing tension straps is a good idea, but when you put these materials together you may see that they would be overkill. Save them for a better purpose.
As for the Epdm liner in a round container. Not a problem. I bought 15' square pondliner on the internet for the inside of the tank, AND a 10' square piece to make a lid. These were standard sized pieces that were...ON SALE! They are heavy. The inside liner weighed 65 lbs. I just draped the 15' piece in the tank, tucked it well around the bottom joint with my feet, and here's the trick for the side-walls....made lots of regularly spaced small pleats.(consult a seamstress or tailor). These pleats are "pinned" on the top edge with 8 or 10d gal. or alum. nails punched through the liner into the foam insul. Trim the excess rubber around the edge. Then cut your top "lid" piece using a great big compass. Make sure you don't undersize it. It needs to go all the way out over the edge. It gets sealed to the tank liner w/ silicone caulk. Done.

 

[Eric Johnson]

I stapled my liner into the wooden toprails on the top perimeter of my concrete tank. Silicone the joint where the liner used for the lid and the liner used for the tank meet.

 

[ISeeDeadBTUs]

Greenwood does not sugest storage ?

Nick

I have the GW with no storage, other than the amount in the oil boiler 20 gal(?) and the DHW tank 50gal.

I am thinking pretty seriously about going to a two-coil 160gal DHW tank to replace the 50-plate HX, and eventually incorporate solar. We haven't had the sub-zero nights with all 6 radiant zones calling yet, but last year they tended to overwhelm the GW. But I think I calculated already that 160 gal of 160 deg water only gives me a buffer of like 20 minutes? Anyway, since the dog and I NEED it cool to survive, the tank don't go in until I figure out how to move the stand-by losses outside once it warms up outside.

And a warm basement does mean a warm house - within reason! I set my walk-out basement stat at 65 deg, keep my DHW between 135-145 deg. The standby losses keep the basement warm, thanks to concrete and polystyrene insulation . . . oh, and dirt!! But trust me, ones it gets sub-zero at night and max of 20 during the day, the basement slab will start circulating.

Jimbo