concrete solar storage tank

Karl_Northwind

So I'm bidding a combination wood boiler/solar heating system for a greenhouse. 

I'm considering using a concrete tank for my heat storage.  they've been pretty widely used around here for solar water storage (think large unpressurized tank with copper coils in it)



the below grade appeal is there, as is low cost, and ease of insulating, flat surfaces taking well to sheets of polyiso foam and all that.



they seem to have handled 150-160 for a number of years in solar applications just fine, but what about 200F for an extended period?  What about cycling from 120 to 200F every day?



does anyone have a suggestion?  I can spray waterproof the interior to keep moisture migration to a minimum, but what else should I think about? 



What's the protocol/etiquette on cross posting a link to this thread on another Wall Page (radiant heating?)



thanks

Karl

Charlie from wmass

Concrete water tanks

I tend to be involved with are for storage of cold water. They need to be made with higher density concrete is my understanding. Will this tank be buried or above grade inside? I am looking for a similar idea so I will be following this thread. I have a customer with no storage and a wood boiler. I think this is the area to post for this question. But you can cut and paste you question into the radiant forum too. The consumers do it all the time.

hot_rod

tried it twice

first in my shop as a wood boiler buffer. It cracked the first week so I removed all the coils and tried to seal it. I ended up putting an EPDM liner in it. Over the summer it grew some sort of mold or bacteria and ended up stinking, finally abandoned it.. It makes a good watering trough for the cattle however.



I took over a solar job with an underground tank. Insulated it inside and out and used a liner. But I think the high springtime water table sucks away a lot of BTUs. You really need to assure it stays dry under all conditions. I don't know I would trust spray foam to waterproof it for 20 years. I'm seeing insects boring into all the various foams around here. Probably a nice toasty place to hole up for the winter



Also a huge delta T between the tank and surrounding ground even below frost level. I suspect 6- 12" of foam to really keep the heat in. The problem is qualifing all this. I suppose you could BTU meter it and compare it to above ground, inside, insulated tanks of the same size?



I'm not sure I would try another. I like my above 500 gallon pressurized former LP tank best of all the methods I have tried.



I suspect a nice professionally built tank like Tom up in Maine builds would be the way I would go for an un-pressurized tank.



It's just too hard to correct problems in an underground tank.



I know Bob's up in WI is a big advocate of underground concrete. He figures solar is "free" heat and leaking a bit isn't a huge deal. I visited his shop and it is a super simple, well priced method. I like his custom, ground mount racking system. 2" galvanized steel square tubing, as I recall 10 foot on center piers. Tek screw the collector feet to the tube with a cordless impact driver.



hr

Unknown

chapo polyethylene plastic

on the outside of the buried tank would provide a vapor barrier between the tank & the ground. Styrofoam seems to be the board insulation of choice to use under radiant slabs.

Karl_Northwind

insulation

The additional insulation is not a problem, as the site is sand, ands the ease of insulating a square tank is better than the round fibreglass tank that is the other optiopn. The plus of the fibreglass is that I can put it in the heated space, and catch the bleed heat, and I can get one in the 2500 gal size I want. And get it guaranteed for 200f continuous.

Thee plus of the concrete is less inside space used, and the cost factors.

I want the best option, and would use toms tanks in a heartbeat if I could get 2000 or more gallons. Ill email him and see what he says.

hot_rod

getting to

and maintaining 200F in a tank fired by wood may be a tough go. Hitting 180- 185 is fairly easy that last 20F takes some diligent fire tending. And that last 20 is a very slow gain.



But I would recommend you find a liner material rated for that temperature continously.



hr

Steve Fontas

.

Karl, couldn't you bury the fiberglass tank? We bury them all the time here (gasoline), yes they are double walled but still, I would think you could bury it. No?

Karl_Northwind

buried fibreglass

Honestly it never crossed my mind.

at this moment the garn 2000 is winning, when you consider that it's easier to get to 200F, we'll be distributing the heat via fan convectors, and the price of direct (read ASME Pressurized) storage.



by the time we buy the storage, the 2 boilers we're looking at are even price wise, and by the time we consider the BOS installation time, I think the all in one storage and burner characteristics of the garn are winning.  and I like the heavy iron and long service life of the garn, and I can do my distribution and control on a pressurized system with all the usual lack of issues rather than having to deal with any real amount of open system.



I'd love to hear people try to convince me one way or the other.  I will leave the gassification boiler nameless at this point except to say that it's a long term high end brand.   I don't know of another boiler with the characteristics of the garn, so It's kind of hard to reference it without naming a brand. 



it will be interfaced with solar thermal, with the solar dedicated to a separate tank that can also be charged with the wood after the solar day is done.  and the solar tank will be the first one discharged.  definietly down to 100F by the end of the night most if not all of the year.



once this project is signed, I'll share more details.



thoughts?

thanks

Karl

Mark Eatherton

Avoid concrete...

We had a housing project here in East Denver, that incorporated solar thermal into the foundations of the home. Each and every one of them failed due to expansion/contraction to the point that they had to be completely eliminated and replaced. The solar was abandoned at that point.



The only problem I can see with the use of the Garn is freeze protection. If the occupants are not home, and its extremely cold, and the fire goes out, how does one protect the storage vessel from freezing conditions?



If one opts to use glycol, it is going to have some $ignificant fir$t co$ts, and then continuing ongoing maintenance cost due to the open/unpressurized nature of the storage vessel.



In using a different type of biomass generator, i.e. Tarm, the required quantity of glycnoids would be significantly less, but then you lose useable storage space in the area where the open pressure storage tank would be located.



The Tarm we installed at a non profit day camp here in the Rockies had two coils in the tank. Input, and extraction (actually 2 extraction coils, one for DHW preheat and one for space heat.) Last word I'd heard was that they'd reduced their LP consumption by around 60%.



BTW, don't be bashful about naming names, unless you perceive some sort of problem with defamation...



Fortunately, this web site is not like some other non profit sites that don't want to offend their members. (Spelled RPA).



ME

Karl_Northwind

tarm or froeling

the gasification boilers we were/are considering



this is actually for a 24/7 greenhouse operation, where there will be no "down time" and everything will be in a heated space. 

the huge storage is to be able to bank heat during non use times (read daytime) and use it all night. 



K

hot_rod

corrosion protection

is one area to keep an eye on with any open system. I would certainly have a plan in mind for an expensive product like that.



My other thought with the Garn is having a flue into your heat storage. I suspect there is some addition loss up that flue?



As far as I can tell that brand has a loyal following and properly applied and maintained it is a unique heat source.



hr



hr

Karl_Northwind

horizontal

we're planning on venting it thru a horizontal vent into their recommended barrel with a 1/4" spark arrestor screen.  so while there may be some heat loss, it will most likely be minimal, as there is no rise. 



garn provides water testing services and analysis and a customized treatment regime for their product.  I wonder how many regular OWB manufacturers actually deal with that? 



as far as I know, their original boilers from the mid 80's are still running.  or that was a few years ago, but that's hard to beat. 

unfortunately, it seems with lots of the other OWB's, about the time you've saved the 7-10K they cost, they're about done for.  of course there is a huge difference when things are properly maintained. 



cheers,

karl

NRT_Rob

I don't like unpressurized boilers

they all require water treatment and with 2000 gallons+ of storage like the garn, that's a serious issue, you either have to dump it all and redo it every few years or get yourself a 2000 gallon bucket for the periodic draindown and service the Garn requires.... at this point I am viewing unpressurized boilers as "corner cutters" that generally are cheating by making a portion of their cost hidden in the maintenance and upkeep. I prefer the ones that put it up front...



I would vastly prefer a pressurized boiler and an unpressurized tank with a coil in it. then you don't need ASME rated tanks, water treatment, and you have a fully pressurized hydronic system.