Storage Tank Heat Exchanger - Would this work?

[Mushroom Man]

After lurking for months, developing a basic understanding; I'm coming out. Last week I picked up a gasification boiler (Orlan EKO 60) and I need to install it over the next few months.

I'll be heating a 2700 sq.ft. house and a 2000 sq.ft. basement with 11 ft. ceilings. Additionally, I need to heat a 500 sq.ft. MushRoom in the barn this winter. There are plans to heat up to 6500 sq. ft in the barn over the next two years. A driveshed, garage and small animal barn are future heating considerations and that's why I purchased a fairly large capacity wood boiler.

My question to the brain trust relates to the storage tank that I am contemplating.

I have decided to build a 1000 U.S. gallon cement block tank. Three sides of the (future) tank are already built-in (basement walls). I intend to insulate the walls using styrofoam and bubble wrap and then line it with fiberglass, made from a marine epoxy resin.

The heat exchanger is potentially very time-consuming and expensive. Most people seem to be using copper spirals as a HX.
My question is whether an old oil tank could be used instead of copper coils. Would it work?

 

[Willman]

line it with fiberglass

I would rethink the FG lining. There is a post detailing the process to use FG by an airplane builder. It needs to be high heat cured to withstand high heat without deforming.
Will

 

[Mushroom Man]

Good suggestion on re-thinking the fiberglass.

I found some information on the website of a supplier of fiberglass as follows:

High Heat Resistance:
Fiberglass cloth has excellent heat resistance at relatively low cost. Fiberglass cloth retains approximately 50% of room temperature tensile strength at 700°F (371°C); approximately 25% at 900°F (482°C); with a softening point of 1555°F (846°C) and a melting point of 2075° F (1121 °C).

 

[EricV]

Hi Tim

Welcome to the forum, lots of good guys here with lots of good info.

I have had a part time boat shop for 15 years so I have some experience with epoxy. Most regular epoxy will start to soften at 140f. so unless your using a special high heat resin it won't work.

as far as using a tank my guess (and the real experts will chime in shortly) that there may not be enough surface area for heat transfer. the smarter guys here can do the math and tell you how much surface area on coils vs a tank.



Eric

 

[Mushroom Man]

Thanks Eric for your informed answer.

If fiberglass won't resist the heat, I wonder what could be used to cover polyurethane foam.

I have planned to line the inside of the tank with insulation (rather than insulating outside the tank) because three walls of the tank are existing exterior walls of the basement.

Some people have used liners, but I have been repeatedly told, by vendors of the liners, that the 180 degree heat will harden the liner material, make it brittle and in that state it will break.

I have also been so warned by vendors of spray-foam products that the material will not handle 180 degree water.

I heard of a sealer called uSeal that is made to cover masonry (blocks). It allegedly will hold back water but I am unsure whether it will work with the heat load. I will still be left with an insulating problem and I certainly don't want to excavate to insulate.

 

[free75degrees]

I just had a thought...
epdm can get quite close to 180*, I think it is safe to 170*. What if you were to put some water resistant or water tolerant insulation into the water, just inside the epdm. As long as it can provide a 10 degree drop in temp so that the epdm is protected to 170* you would be fine. Polystyrene comes to mind, although you'd have a heck of a time egting it to stay underwater. I wonder if there are any insulations that would be ok underwater and that would become water logged so as to get dense enough to stay submersed.

I know this may sound stupid, but think about a wetsuit - it is basically neoprene that becomes completely soaked throughout with water and it still manages to keep the user warm by trapping body heat.

 

[Dune]

Ordinary concrete is not waterproof, however, there are waterfroof cements avaiable. So, you could line your tank with bubble wrap, then styrofoam, or some other more apropriate foam, then parge the inside of the tank (over the foam), with two layers of waterproof cement. Don't forget the bottom of the tank. Also there are resins which can handle 180f. If you go with the parge method, use a layer of s.s. mesh in the first coat of cement.

 

[EricV]

I used the Firestone 60 mil liner. It has properties to keep it from getting brittle and good to 175. I figure they are conservative with the numbers so I figure 180 is no problem.

here is a linkwith info on the firestone brand

(broken link removed to http://www.justliners.com/EPDM.htm)

 

[EricV]

another link

(broken link removed to http://www.justliners.com/tisepdm.htm)

 

[Mushroom Man]

So many great ideas and information. Thanks to all.

My wife had a pretty good idea. Why not use porcelain floor tiles, she said. They'll hold back water and heat. They are fired at 1800 degrees in their creation. I have some questions about the cost and the grout longevity but the grout could be sealed I'm sure. The tiles can go over the insulation rather easily.

She is a potter who has worked with porcelain and she knows its qualities. She says stoneware would work too, but said to avoid earthenware or terra cotta tiles which can crack easily and absorb moisture.

If I don't care how ugly the pattern is (and I don't care, of course, for this application) I might be able to get a break on the price. Most people want pretty ones for their floors and walls.

If my calcs are correct, it might be a cheap solution.

I'm still looking for a cheaper solution than copper spirals but I may never find one. A flat plate heat exchanger is sometimes used as an effective alternative to a sidearm hx; so I'm trying to apply the same logic to the tank. My idea of using the old oil tank seems to have met with resistance here because it might have inadequate surface area and a rusty surface. It is a pretty good sized tank (250 gallon), relative to the 1000 gallon tank size and could be painted with stove paint to eliminate the rust issue. It is free and an eyesore in the field that I'll have to bury somewhere, if I don't recycle it. While it would probably be less effective than copper coils at transferring heat, I'd like to know by how much the methods differ.

Does anyone know how to calculate the effectiveness of the tank as a HX versus the copper coil method.

 

[Nofossil]

Oil tanks are not designed as pressure vessels. Even the relatively low pressure that most boilers operate at is likely too much, and if you run potable water through it you will definitely have more than one problem:

1) Tank blows up like balloon
2) Nasty taste of fuel oil in your lemonade
3) Tank will rust due to continuous supply of dissolved oxygen in fresh water.

Tiles are waterproof, but grout isn't, and pressure is likely to cause enough stress to create a small crack or two.

I'd go with EPDM, keep an eye on it, and hope for the best. EPDM will be able to stretch as your insulation compresses. There's a surprising amount of force at the bottom of a storage tank.

 

[Tarmsolo60]

the oil tank will not stand up to the pressure in the system. I know there is only 12 pounds psi but they are not made for pressure applications.

 

[Tarmsolo60]

Oil tanks are not designed as pressure vessels. Even the relatively low pressure that most boilers operate at is likely too much, and if you run potable water through it you will definitely have more than one problem:

1) Tank blows up like balloon
2) Nasty taste of fuel oil in your lemonade
3) Tank will rust due to continuous supply of dissolved oxygen in fresh water.

Tiles are waterproof, but grout isn't, and pressure is likely to cause enough stress to create a small crack or two.

I'd go with EPDM, keep an eye on it, and hope for the best. EPDM will be able to stretch as your insulation compresses. There's a surprising amount of force at the bottom of a storage tank.

Hmmm, looks lke you beat me to it

 

[Willman]

Search the old posts for Sparke. he is using another material for his tank that is higher temp rated.

Will

 

[WoodNotOil]

I believe the STSS tanks, like the ones Tarm sells, uses an EPDM liner. This suggests that longevity in high temp situations has been tested for a while in their applications. Yes, there is a temp limit, which is why open storage systems require more total gallons to store the heat. Pressurized systems operate at higher temps, so less storage is needed. There are custom liner places that have materials that can go up to 300*, but they are cost prohibitive. I used a flate plate for my exchange and I get stratification in the tank equal to the delta T on the tank side of the hx, about 20* when charged and widens if left to stratify further. Copper coils probably can give better strat than that, but would have cost a lot more. There are advantages and disadvantages no matter which method you choose.

Make sure to check the temp ratings of insulation before planning to use them. Polyiso has a good temp rating and high R-value per inch. Here is a link: http://www.engineeringtoolbox.com/insulation-temperatures-d_922.html

 

[Mushroom Man]

Points well made.

So, no oil tank. OK. Are copper coils the only solution then?
Are flat boxes of other materials possible solutions?

For the tank, I too distrust the grout; but I think there might be an effective sealer in the marketplace. I mentioned a product called U-Seal. Some of its qualities are: waterproof, heat resistance to higher temps (more than what I will go to), roll on, bonds to masonry. Is grout "masonry?

I haven't operated a boiler with storage but I suspect that the temperature can get higher than 180 and that is when I might ruin a liner and maybe more.

 

[Willman]

Is grout “masonry

Cement based grout is not waterproof. Spectra lock grout is an epoxy product that is waterproof but the temp limit is the problem, also quite spendy. The major problem with tile or coatings is the expansion and contraction of these products. Sparke bought some different high temp liner and has it in his tank. Check it out. Not sure what it is.
Will

 

[Mushroom Man]

The suggestion in this thread that holds the greatest appeal to me is Dunebilly's idea of using several layers of reinforced waterproof cement over the insulation layers. Temperatures are unlikely to be an issue with that approach and it seems like a cost effective solution. I have increased the tank size (conceptually) to 1337 US Gallons.

I am still not sure why I need a heat exchanger inside that tank. OWBs circulate the water in their hot water storage tanks. Why can't I. One European gentleman in another thread circulates water into and out of storage, has done for decades and has suffered no excessive corrosion issues. He claimed that most people in his area don't use heat exchangers in their storage tanks and a few added oil to the water to ensure that corrosion remained under control. Can anyone explain why pressurized systems are better. I just don't get it. There is a lot of expense associated with those coils of copper.

To all who have rendered their assistance thus far...Thank you!

 

[pybyr]

Pressurized systems operate at higher temps, so less storage is needed.

that's true only if your unpressurized storage is, as has usually been true to date, with STSS, and site-built liner-type tanks, dependent upon a floppy liner (EPDM & etc) to seal in the water, within some kind of other structure to physically support the floppy liner.

I'm going to be the guinea pig on a 409 stainless rectangular tank, with bolted Buna joint-ed seals and Sikaflex caulk rated for 190 continuous, 250 intermittent, F, at all the joints.

Not sure I am always going to try to push it to or near 212 F, (actually, water probably boils less at my elevation of about 1200 ft above sea level) but one of the reasons I am trying to blaze this trail is to create an option of a tank that can be brought into an existing structure in carry-able, fit-through-door pieces, and yet is not constrained by the temperature/ leak-worry limitations of the "floppy lined" unpressurized tanks.

 

[jebatty]

I assume you are moving from a pressurized boiler to an unpressurized tank. Boiling point of water at 15 psi is about 250 degrees, so your boiler should be able to handle probable 225 output to push tank to near 212. I would be concerned about getting so close to boiling, as you may be getting gas bubbles in or around the heat exchanger, and to get the whole tank near 212 this probably is a certainty, as the hx needs to be hotter than 212. I see boiling water around the hx and lower temps around the tank.

My gut tells me an interesting experiment with some serious safety issues.

 

[rone57]

I knew the guy who created one of the first systems when developing the R2000 home concept. His heat storage system was to buy a used stainless milk truck tank. He buried it 6 ft underground outside his house and ran an in-out system back to the boiler.

He also supplement the heat by using black corrugated steel facing south with 1//2" gap sealed and covered in used office glass. Water was circulated with a secondary pump.

The advantage is that the tank was relatively cheap, designed to handle the heat and pressure, no rust, and since it was buried underground it maintained the heat.