800 gallon solar storage, HX

hr

I inherited this solar job recently. The plan was to use 8 panels with this 800 gallon in-ground storage. The tank and panels were on the job when I took over.

We will have the tank insulated with 4" of foam and a EPDM liner inside.

I used 4" Insulseal tube to install the lines from the tank to the house.

I built this HX with 1" copper trying to keep it as low as possible in the tank.

Additional coils at the top of the tank for DHW and radiant.

The designer of this system uses a drain back system with a high temperature sumbmersible pump! Sounds workable, but I'll stay with my tried and true glycol loop on the solar.

hot rod

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Eric Johnson

I'm working on something similar

Here's one of my summer projects for a wood gasification boiler hot water storage. I'd be curious what you think, hr.

The tank is an old concrete cistern in my basement. I plan to create the 4x5x7-foot space by building a vermiculite-filled cinderblock wall in the foreground.

I think the piping scheme, as shown, is most efficient at heat recovery, but I'd appreciate any ideas or (polite) suggestions on how best to do it.

hr

On one hand

it';s nice to have the thermal storage INSIDE the heated space Any loss is in the building not the ground.

I'd be real careful to seal the lid. You probably do not want a large humidifier in the basement.

The plate HX may be the best way to go. You always get better hreat transfer with two pumped flows.

The trick in a big tank is the coils just sit in the stratified tank, not much mixing. But the copper is in direct contact with the water and it takes one less circ.

IU have seen those copper coils in large tanks pin hole after years. Perhaps a ph issue? The external HX eliminates that possibility.

hot rod

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jp_2

steel closed system

i wonder hot rod, why couldn't you use steel HX in a closed or glycol system, such as steel tubing for hydraulic systems, seems you could make much larger HX at a fraction of the cost.

Eric Johnson

Commercial tanks

The commercial tanks I've seen (like the ones that Tarm recommends) use something like 600 feet of 3/4-inch soft copper coil in the tank. At today's prices, I thought a $300 flat plate made more sense, plus it's not displacing water. Since the tank is basically picking up any excess heat not going directly into the house, I can deal with a slower rate of heat transfer, I think.

Yes, I plan to seal the lid very carefully. I think by lapping the two layers of EPDM on top of the lid and then sealing them together with either seam tape or roofing cement, the whole thing should be pretty tight. Hold it down with a couple of studs screwed down into the wood around the perimeter of the tank. I'm thinking about venting into a truck inner tube or some other flexible vessel to maybe maintain a pound or two of positive pressure to keep out dust, microorganisms and other contaminants. Yes, I remember what you told me about the stink when things go bad.

hr

Or CSST tube

it's about .40 a foot cheaper than copper.

If I were a better welder I'd consider sch. 40 steel But cold the tank be sealed O2 free?? If not I risk a rust issue.

hot rod

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LarryC

Polite Suggestion

Would it help to not have the tank inlet and discharge piping not directly above each other? Otherwise you are just short cycling the water vertically thru the tank without using the rest of the water.

jp_2

the ticket

yep hot rod,

that'd be the ticket, large diameter thin wall CSST tubing, wonder if you could get a better price if you can find it not rated for gas? and not coated either!

Eric Johnson

Something like that

That was one of my questions. What kind of spacing should I put between the pipes and does it make sense to have one going to the bottom of the tank and the other one drawing from the top?

As diagrammed, it sould work better at recovering heat from the tank than putting it in. Maybe maybe making both pipes same length would (literally) split the difference and make each function equal. And would it make sense to do that?

hr

some of the tanks at ISH

had what looked to be a corrugated stainless coil in them.

I'm not sure CSST is ratings for that use. I know the jacket strips easily.

The radiant dog in this pic has a belly full of CSST tube to warm the concrete mass. It can be looped very tightly

Years ago I did a complete staple up job with 1/2" CSST. Purely experimental, on a Heatway employees home.

I'm not sure that corrugated wall well worked in the heat transfer ability in that installation.

I suspect the fluid to wall transfer could be better with a tube like that due to the turbulance created?

I'll bet the Germans know

hot rod

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Wardner

This tank has some potential

It is all plastic including the 14,000 linear foot heat exchanger. The heated tank may need to be reinforced with a steel wrapper but one would have to know the system operating temperature. There are more pictures at eBay. Item # is 250097149349.

hr

Depends on the type of plastic

I've been told HDPE tanks should not be used over 140- 150. I tried a pallet tank, in a steel cage with a wood boiler once. It got very soft and gooey at 180. Threaded connections wouldn't hold.

The tank you show could be fiberglass. The one at ISH looked to be a 1/4" fiberglass material. Plenty of temperature and strength without a case, apparently

That tank looks very similar??

hot rod

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Wardner

Did you go to eBay?

The tank wall is Linear Low Density Polyethylene (LLDPE). 180 degrees is out of the question but 140 is probably doable with some modifications. The tank wall needs no fittings.

There are 4 manifolds with 26 tube outlets each. They are set up in a counterflow arrangement so that one circuit (pair of manifolds) flows opposite the circuit next to it. That reduces stratification. One circuit can supply heat and the other one remove it. The tank holds 1900 gallons. When used for its intended purpose, the Calmac IceBank can store 190 ton hours of refridgeration.

Ericjeeper

why not just use 1/2 pex?

I used 500 feet of pex branched out on six way manifolds.. works fine in mine
www.pbase.com/ericjeeper/solar

Bob Gagnon plumbing and heating

how is the transfer with pex, Eric?

Is it Pex-al-Pex? I checked my copper exchanger today the water from my 120 evac. tubes was 164 going into my 200 gallon tank. The tank temperature was 126 at the bottom and 130 at the top. The water temperature out of the tank was 132. It seems like the large copper exchanger is dropping off almost all of the heat. It is made out of 5- 1/2" X 60' coils, tied into 1" reverse return. Bob Gagnon

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Mike T., Swampeast MO

Do I detect a bit of Viessmann (horizontal indirect) influence in the design of that HX?

Ericjeeper

good enough to heat concrete

So therefore I figure it is good enough to heat water. If the sun shines today I will check my temps. Honestly it has been so long since I opened the door to the outhouse, I do not remember my incoming vs. outgoing temps. But I have pickups on 3 locations. Tank temp at 18 inches from top, and supply and return from the solar panels.
Plus at the cost of copper. I just could not see the extra expenses. I have close to a grand in copper above the waterline alone.But anything in the water is pex, minus the four six way manifolds.

Plumdog_2

deja vu?

I built a heat exchanger once (1976) that was similar, but it was a stack of copper "ladders" that were manifolded together with 1 1/4 supply and return and a whole pile of tees. The idea was to use a low-head pump. The concrete storage tank was poured and then built over in a crawler off to one side of the regular basement. It was sprayed on the inside with foundation sealant and then covered with backfill. Far as I know it still works.