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Water storage options....

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by tuolumne, Dec 18, 2007.

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  1. tuolumne

    tuolumne New Member

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    I hope some of the forum readers will share any experiance with pressurizes storage systems. I got another quote today for an open vessel 822 gallon (STSS) storage system with 3 180' coils. Those coils were $330 each when I got a quote a while back, but now they're $975 each. That makes the total bill for tank and coils around $4800, not including controls etc. There will also be a shipping fee of close to $500. It seems I can do a lot with those sort of funds in the way of pressurized storage.

    Question 1 - Is there any other effective means to heat an open vessel? The pair of 180' coils is rated somewhere around 11 GPM. I've heard of flat plate heat exchangers. Could this be submerged to do the job? A 20 GPM flat plate heat exchanger (I know nothing about them) can be had for $200 from pexsupply. The picture makes them look more like a "fluid in a pipe" to "fluid in a pipe" exchange. Would fintube coils (like a tankless coil) be more effective or cheaper than the plain copper coils? What else is there?

    Question 2 - I have not inquired locally, but a quick web search says a 1000 gallon propane tank would be around $2000. A large expansion tank would be under $1000. This is still far cheaper than option 1. Is anyone doing this? Are other tanks out there (such as various plastic varieties) rated to take the pressure? Would the high temperatures affect plastics?

    It is not the cost of the STSS tank that is hard to swallow, but the cost of the heat exchangers. Any ideas would be great.

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  2. Eric Johnson

    Eric Johnson Mod Emeritus

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    True enough about the high cost of copper.

    I think you can use a flat plate heat exchanger if you have a good design. I considered it, but decided to go with a DIY rigid copper hx instead. There are pros and cons, but nothing that you wouldn't be able to work around with enough information, I don't think.

    If I had it to do all over again, I'd take a closer look at pressurized hot water storage. $2 a gallon sounds a little steep. I've heard that the going rate for used propane tanks is closer to $1 a gallon.

    As to expansion, Joe Brown has an interesting thread around here detailing how to make an expansion tank out of a hot water heater vessel with some instrumentation that I'm guessing would cost you less than $1,000, depending on the amount of work you were willing to do yourself.

    So it's not as bleak a picture as you're probably thinking. Dig around the site a little more and you might find some answers. Hopefully somebody will drop in with a perfect solution, though I'm guessing a collaborative effort is more likely. More fun, too.
  3. tuolumne

    tuolumne New Member

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    If the flat plate exchanger is installed outside the tank, I would nead another pump to circlate storage water. This seems to simplify things even more, since this pump provides the control for when I'm dumping heat into storage. Total cost for heat exchange and this bypass control is still less than $300. Any comments?
  4. Nofossil

    Nofossil Moderator Emeritus

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    I'd consider using the flat plate exchanger the way you're describing - one loop consisting of the tank, circulator, Joe's hot water heater based expansion tank, and one side of the heat exchanger. The other loop would be your existing hydronic system. Isolating the storage tank would help keep things simpler and would allow you to drain / depressurize / service either loop without affecting the other. I also worry about the corrosion potential of the amount of dissolved oxygen in 2000 gallons of water.

    The only wrinkle is that you'd like to draw from the bottom of the storage tank and return to the top when you're heating it, and vice versa when you're drawing heat from it. That would require a little more complexity, but would deliver better performance.
  5. Tarmsolo60

    Tarmsolo60 Feeling the Heat

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    those are exactly me feelings from a previous storage tank thread. even buying soft L and building them like I did is pricey. I'm interested to see how eric's design works, aside from trying to salvage something from a junkyard for a submersible heat exchanger i'm not sure what the answer is. I had thought of the flat plate before I built my Hx but had concerns about even heat distribution in the tank. what can you get 3/4 soft L for, the exchangers are pretty easy to build.
  6. BrownianHeatingTech

    BrownianHeatingTech Minister of Fire

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    Flat plates have a great deal of efficiency. I wouldn't even contemplate bare copper pipe.

    Either go with a flat plate or, if you want to eliminate that extra pump, use finned copper to get a lot more transfer efficiency out of a smaller amount of the copper.

    That can be things like baseboard element, but I'm looking into cleaning and recycling coils from air conditioners. Huge surface area. But they should be properly cleaned to removed the residue of refrigerant oil that will be in the pipes.

    Joe
  7. Eric Johnson

    Eric Johnson Mod Emeritus

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    I thought long and hard about doing it that way. In fact, that's the way I have it piped at the moment, I just never got beyond that point. In the end, I wasn't confident that it would work. So, I decided to go with something else that I'm not confident will work.

    I'm a little confused about what you're asking about. Seems to me you're looking at two alternatives: pressurized storage with an old propane tank (no hx needed), and using a nonpressurized tank with an external flat plate heat exchanger instead of an in-tank coil. Nofossil seems to be combining the two somehow.

    Anyway, I'm going to focus on the flat plate/nonpressurized option. You need a couple of diptubes in the tank. The question is where do you position them? If you have one drawing from the top and the other one drawing from the bottom, your system is going to be good at one thing (storage or recovery) and not very good at the other. One way around that is to somehow reverse the flow through the tank/hx, depending on what you're trying to accomplish at the moment. I have a diagram of one way to do that, below. Other thing to consider is that you'll probably wind up with a mixed tank instead of a stratified one. That matters, but I don't know, as a practical matter, how much.

    The other thing to consider is the pump on the unpressurized (tank) side. Those circulators don't run for very long without water. The problem with pumping an unpressized water source with little or no water above it (think about that for a minute), is that you risk cavitation to the pump's impeller, which will ruin it, as well as running out of water to the pump, which will also ruin it in a matter of minutes. Ideally, you would have some sort of reservoir sitting over the pump providing a modicum of pressure and a substantial supply of spare water. For the sake of the pump, I'd seriously consider putting a low-water cut-off switch above the pump as well. And you might want to consider a bronze pump (or pumps) on that side of the equation.

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  8. tkirk22

    tkirk22 New Member

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    If any of you guys want to take a ride to VA, I know of a couple stainless tanks for sale. One was in the 300 gallon range and the other is 1000 or 1200 gallons. He wants a buck a gallon.

    You might be able to find a similar deal through a local farmer.
  9. BrownianHeatingTech

    BrownianHeatingTech Minister of Fire

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    The mixing will occur even with a stratified tank - for example, as you take heat out of the top of the tank, the water will cool and fall, being replaced by warmer water that was just below it.

    The key to greatest efficiency is for that to happen at exactly the rate that you are extracting heat. Never going to actually achieve that goal, but the closer you get, the better the efficiency.

    Using an external heat exchanger, you can try to minimize the the "mixing" by using a small pump and a large heat exchanger, relying on heat exchanger surface area, rather than a high water flow rate, to achieve heat transfer.

    Or you can skip the whole reversing deal and just install a big pump and mix the tank, so you work based on the average water temp, not the stratified temp. Lower efficiency, but simplified installation.

    Joe
  10. tuolumne

    tuolumne New Member

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    It seems to me that "injecting" the storage water at the bottom of the tank and removing it from the top would be best. Won't the warmer water move to the top? If the pump is below the tank water level will that minimize the low water problem?
  11. rreihart

    rreihart New Member

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    Kirk, I assume you're talking about unpressurized tanks. If pressurized, I'd be interested in a 300 gallon size.
  12. Burn-1

    Burn-1 Feeling the Heat

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    Eric,

    Tim Brown at Windy Ridge sells these Kaukora accumulator tanks from Finland to go with the Kaukora boilers he sells. They're pressurized but pretty expensive, I think the 400 gallon one is about ~$3,500 or almost $9/gallon!. The natural draft downdraft small boiler he sells is only about $2,800 or so. It's a nice oval setup to go through doors and a tall shape with top and bottom fittings to get good stratification.
  13. Eric Johnson

    Eric Johnson Mod Emeritus

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    Not only that, but it's an "Energy Storage Battery." Makes about as much sense as most Finnish translations. Some of my friends from Finland speak what I call "Finnbonics," i.e., "You must to ski!" Sub in the words "sauna" and "drink" and that about sums up my exposure to Finland.

    I'll have to try to talk Tim into bringing one of those boilers up to our show in Essex Jct. next May. Either that or stop in and check one out next time I get through Tamworth.

    Is it similar to the other Euro gasifiers, Burn-1?
  14. tkirk22

    tkirk22 New Member

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    They are thin wall so suppose they would be for an unpressurized use. Sorry for the confusion.
  15. Burn-1

    Burn-1 Feeling the Heat

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    The one I saw on his floor is this ECOPUU 25, only abour 85k BTUs and given the forums preferences for common naming conventions I would call it a downdraft boiler. There is a secondary air intake and maybe some light off in the turbulators but no forced draft. It also only takes up to 14 inch wood which might affect some people's choice. The other boilers in the line are here and a couple these I would call gasifiers although in Finnbonics it's 'reversed combustion technique'. But none of these are near the BTU's of some of the bigger Orlan and Atmos models.
  16. verne

    verne Member

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    Im going to use a 1000 gal propane vessel with eko 40 . Ive spoke to cozy dave and zennon. both agree this would match well.
    As long as you have room for the 16'long x 40" tank I cant see why it wouldnt be the most cost effective. I put a wanted add on my local freecyle .org for propane tanks and got a few replys . allthough i have decided on a new tank for ease of delivery etc.
    the best price on new vessel is $1600 delivered. as for exspansion i was told to use a 40 gal expansion tank and set the bladder at 8 lbs. by zennon. other folks have stated that an 80 gal would be a better size . either way Amtrol Extrol 44, 62,86 gal range from $420-$520, Amtrol Therm-x-trol 44,62,86 gal $ 518- $ 585.Also i think dave told me $375. In the big picture of things $2000
    -$2500 seems affordable for heat storage .
  17. Eric Johnson

    Eric Johnson Mod Emeritus

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    Not to mention the "improved and powerful driving water coil" in the 40KW version.
  18. Grover59

    Grover59 Member

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    This thread answered some of my questions, my direction that I am going in now is the dip tubes in the tank, I have thought about stratiication but I don't think it is a big deal. I already have a flat plate HX on the boiler loop to the oil fired boiler so I don't have to shut anything down to tie this in. I was going to use the same loop to the heart Hx to both charge up the tank and then pull heat out by reversing the flow. This would allow me to use the existing baseboard with the existing circulator on the oil fired boiler. However knowing that I would need to have a higher tank temp to really make the baseboard work and decrease the useable BTU's in the tank, I decided to use a total separate loop, to a water to air heat exchanger to use forced hot air. This means that I would use 4 dip tubes in my tank, now after doing more reading and thinking, my best approach would be to use radiant floor heat from my tank. This would have to be the staple up type, and I believe that this would be the best way for me to go.
    Atl this time I have everything in place to do the forced hot air, so for now I will do that, but I will be spending the rest of this winter installing the radiant floor heat. I am in no rush, when I am all done I will be able to put heat to the house with the baseboard or the forced hot air or the radiant floor heat.

    Steve
  19. Nofossil

    Nofossil Moderator Emeritus

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    Of course, you might still want to insulate it. I spent a couple hundred bucks on that as well :-(
  20. tuolumne

    tuolumne New Member

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    verne - what is your source for the expansion tanks; those prices seem a bit better than what I've found to date. I haven't yet checked with my local F.W. Webb. Pressurized storage sure seems to simplify things from a piping and control standpoint.
  21. verne

    verne Member

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    I think the numbers I gave you came from plumbersurplus.com. Hope that helps
  22. sparke

    sparke Minister of Fire

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    When you go with a premade tank, like a used propane tank. Do you still need Heat xchangers? If my wood and oil are hooked up in parallel? Or can you just have a closed loop from tank to wood boiler?

    By the way, I just spoke to Dave from Windy Ridge. He is very helpful. If I can figure out the storage tank situation, I will buy one of his boilers...
  23. Eric Johnson

    Eric Johnson Mod Emeritus

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    Which boiler are you looking at?

    You don't need heat exchangers. That's the beauty of pressurized hot water storage. You just have 1,000 more gallons of water in your system, so it's a self-storing, closed loop.

    What you do need is a lot of expansion tank capacity. That much water heating and cooling requires a much bigger pressure tank than a normal hydronic heating system. Something on the order of 40 to 80 gallons seems to be considered appropriate.
  24. sparke

    sparke Minister of Fire

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  25. jebatty

    jebatty Minister of Fire

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    I am using a 30 plate, 5" x 12" HX, with 1" in/out ports, on my Tarm Solo Plus 40. The HX cost just over $200 on Ebay. The boiler loop powered by its own pump uses antifreeze, and the storage loop powered by its own pump is about 800 gallons of water (3 - 275 gallon old fuel oil tanks in series, got them for $125). The tanks are vented and not pressurized. I have a diversion to a unit heater for immediate heat when needed. Otherwise, the three steel tanks function as large radiators and provide heat without any blowers, fans, etc. All of this is installed indoors in my wood-working shop (20' x 40' x 10'), poorly insulated. The HX takes all the heat the boiler can deliver with less than a 5 degree temperature drop, in other words, 160F into the HX and 155F or more out to storage. A surface mount thermostat on the boiler return line turns on both pumps when the return temperature reaches 150F, and both pumps shut down when return temperature falls to about 140F. This occurs only when the boiler has burned its wood load. In about 8 hours of burn time, with outside temperatures around 10F, the water storage will be brought from about 80F to about 150F. The steel storage tanks, acting as radiators, then heat the shop for 1 to 3 days depending on outside temperature.
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