How about Simple and CHEAP storage

[Vinced]

Hello,
I have a conventional OWB and would like to add storage to it. I have a 500 gallon tank, old diesel fuel tank cleaned and drained. My OWB is a pressurized system and I'd like to make it non-pressurized storage. My Idea for a bare bones cheap storage would be to build a oversized sidearm heater for my 500 gallon tank and let the tank heat by thermalsiphoning. My current piping layout is primary/secondary system and I would just plump my oversized sidearm in the primary curcuit. The main reason I would like to add storage is to get away from cycling and try to burn 1 complete hot fire a day. Right now I get 12 hour burn times in the coldest weather, but would be great to have just one long fire a day. I've had my OWB for a year now and I've lurked around here for over 2 years. I'm just trying to do this without spending a bundle. Please don't tell me I need 2 pumps, plate heat exchanger, controller, mixing valves, and etc. Just give me your opinion on why this would or wouldn't work.
Thank you, Vince

 

[Eric Johnson]

Hi Vince. I'm from Coloma originally.

I think it would work, but you'd have to watch your water treatment pretty carefully, as old fuel tanks are made from pretty thin gauge steel and not designed to hold water. I think you might need a pump to increase your heat transfer into and out of the tank. Maybe one on each end. But that's not a big deal. I'd go with something like 1" pipe for the inner tube and maybe 2" for the shell. You might want to try black iron instead of copper. I haven't priced copper lately, but I doubt its price has dropped all that much.

 

[WoodNotOil]

You might try putting in an anode like they use in hot water heaters to slow the erosion of the steel. As Eric said fuel tanks are sometimes rather thin. I am sure 500 gallons will cause less idling, but it may be too small to eliminate it altogether. That depends on a lot of factors like btu of boiler, heat loads, the btus your sidearm can can transfer, etc.

 

[tom in maine]

I would suspect that the heat exchanger you are describing will not handle the full load. It might be enough to heat the tank over some time.
It will not move all the heat the boiler can generate, especially with passive flow (without pumps)

You certainly can try it, but I would keep an eye out for a deal on the plate heat exchanger and pumps you are probably going to need.

 

[mtnmizer]

Hi Vince. I'm from Coloma originally.

I haven't priced copper lately, but I doubt its price has dropped all that much.

The spot price is up about 30% this year, last I checked around $1.70/lb/10K lots. Locally
around a buck and a quarter. I don't know how prevalent it is, but in this local
all service entrance lines are done in soft K copper. A plumber I know sold
me all the 3/4" K I needed for a storage tank at scrap price. It was left over 20-30ft
pieces from jobs. It came in about a buck/lb to me. Currently working on a tubing
roller to do it correctly.. Check around your local plumbing shops for scrap
copper.... MM

 

[Vinced]

Ok,
I'm a welder/ fabricator and I have access to alot of aluminum scrap. By oversize sidearm I was talking about a 6" outer tube with maybe 4ea 1" tubes inside. Basicly scale up the sidearms used for domestic water heaters. Copper prices have dropped quite a bit from when I last priced it in September of last year. I was going to try some epoxy paint on the inside of my tank to see if that would stop corrosion.
If I did decide to get a plate exchanger and pumps does anyone have a simple layout of how to hook it up. I've read the simple storage posts on the top of this page, but still can't figureout how I would tie it into my system without replumping the whole thing.
Vince

 

[Duetech]

I have a sidearm on my dhw tank and it works but the amount of flow through the domestic side by siphoning is really slow compared to a pump by a ratio of X minutes compared to 1 1/2 hours. I think you would need several of the over-sized sidearms to equal the output of one pump. What you need to know is the average flow rate that thermal siphoning creates and build your sidearm/s to match the flow rate generated by a pump. As well you will need to know the reverse flow rate and resulting thermal transfer rate of your sidearm/s in order to extract the stored heat in a sustainable volume. Just by conjecture I do not think that a sidearm with a one inch center will exceed 1/2-1 gallon per minute IF it will do that much.

 

[WoodNotOil]

If I did decide to get a plate exchanger and pumps does anyone have a simple layout of how to hook it up. I've read the simple storage posts on the top of this page, but still can't figureout how I would tie it into my system without replumping the whole thing.
Vince

If you can attach a diagram of your current piping, we can help you figure it out.

 

[Fred61]

I am in the process of building a storage tank from a 500 gallon fuel tank. I had the junk yard cut off one end before I picked it up. I wasn't there when they did the cutting but I suspect there was some liquid in it that went somewhere. I didn't want to know where it went. When I got it home, I took one of those large propane torches to it and burned or evaporated everything that was left in it. The joint was the most difficult to clean because the perimeter overlapped about three inches and was only welded on the outside, of course. After burning, I washed it thoroughly with strong detergent and water. This exposed all the rust and pits. There were many. I didn't have access to a sandblaster nor could I find anyone that would do it at a reasonable price so I ground the whole surface, paying particular attention to the pits (big job). When it was completely "shiny" I coated it with a high temp. epoxy that's made particularly for coating tanks. It's good for about 300* wet. Not just any epoxy paint will do. Oh! forgot!! I purchased a kneadable epoxy and filled the joint and around where the tappings were welded in. This material was also good for about 300*.

I wouldn't be concerned with strength. My sidewalls measure .017" with the epoxy. That is far thicker than swimming pool sides. I'm using the tappings for temp probes and circulation tubing. I even installed a water level sight glass and coated all bulkhead fittings with epoxy. All other connections are above the water line (heating coil supply and return, etc.). I am, at this time, constructing a cover which consists of a piece of polyiso. covered with a piece of the above ground pool side that I abandoned screwed to a piece of plywood. The sheet metal will also be coated with the epoxy and will be exposed to the condensation. I think the plywood is isolated from the heat enough with the 2" polyiso. between it and to heat. I will then add more insulation on top.

I have not insulated the tank yet, as I want to get all my plumbing done first, check for leaks and then fill the tank so it will take it's own desired shape before insulating.

I won't tell you, at your request, that you need pumps, etc. You'll find that out on your own. I did have one thought though. What if you soldered about a 10 guage copper in a spiral pattern around the inner tube of your sidearm. Anybody think the turbulance it creats would be an advantage over smooth pipe?

I'm going to be heating the tank water with a flat plate HX and I've installed 200 feet of 3/4' copper for recovery for heat and DHW. I also had an old copper coil laying around from another job and laid it in the bottom and will be using it for my overheat loop.

Edit: Came back and read this. Put my decimal point on the wrong side of the "0". Should be 0.17" sidewall thickness!

 

[Vinced]

First off, has anyone thought that this sidearm would be heating the tank from say 130 degrees to around 170-180 degrees instead of a dhw heater that is heated to 180 degrees and then gets about 45-65 degree water dumped into it the replace the discharged hot water? I know thermal siphoning is not fast at all, but remember it will only take a long time to bring the tank up to temp but after that it only has to raise it about 40-50 degrees.
Fred61, what brand of epoxy paint and putty did you use? I also cut one end of the tank off and will use it on its side. You said 200ft of 3/4" copper coiled into you tank, is that used for charging and drawing heat off the tank?
Woodnotoil, can you suggest a simple program to draw a diagram of my system? I've just started playing with SketchUp and have it half drawn, but I'm having a hard time getting it drawn the way I want (bear with me I'm learning).

 

[WoodNotOil]

First off, has anyone thought that this sidearm would be heating the tank from say 130 degrees to around 170-180 degrees instead of a dhw heater that is heated to 180 degrees and then gets about 45-65 degree water dumped into it the replace the discharged hot water? I know thermal siphoning is not fast at all, but remember it will only take a long time to bring the tank up to temp but after that it only has to raise it about 40-50 degrees.

The closer the two temp get, the longer it takes to transfer the heat. Those last 20* take the longest to pick up unless you have an abundance of heat hx. There will also likely be a differential between boiler tank and temp that can't be surmounted. Usually around 10*, but varies based on the hx.

 

[Fred61]

Vince,
The epoxy I used is #641 epoxy coating from http://www.epoxy.com/ I'm sure this guy doesn't manufacture his products but having been in the adhesives business in the past, I only wish I could have found the suppliers that he has. This stuff is not cheap! I purchased the two gallon kit (1 gal. part A and 1 gal. part B) for about $250.00. He recommends applying it with a brush or roller but it is so viscous it pulls the nap right off the roller and does not spread very well with a brush. I found a better way to apply it. Used one of those spreaders (about 6 or 7 inches) that they use for applying body putty to automobiles. Be sure to mix it well! Also it has a high surface tension and tends to have pin holes. Two or three coats are needed to make sure you have coated all the drop-outs. In the industry, they use some sort of static electricity generator to locate pin holes.

The putty is from http://www.epoxygator.com/ It is their steel stick Epoxy.

I'm using a flat plate HX to charge the tank and the copper coil to retrieve for the DHW and heating loop. I have a unique situation. When I installed my radiant system I worked with http://www.radiantcompany.com/ Their installations usually heat with a large domestic hot water heater and run line pressure through the system. Works well! When I decided to use a wood boiler, that's when I discovered that the radiant loop did not have oxygen barrier. so I am running the domestic and heating loop off the storage through the copper HX. What I did was run two coils in parallel splitting at the return and then tying them together where they exit the tank with ball valves to balance the output of each. I theory, this slows down the flow so the water in the coil spends more time in the hot water bath.

 

[Vinced]

Thanks for the info on the epoxy paint and putty. I knew it was going to be expensive, but I got my tank for free from a buddy. It will still be less money then building one from wood and using a pond liner and it should last longer.

 

[Duetech]

Vince,
The other thing about storage is (not only the heating) but...the extraction of the stored heat. Getting thermal siphoning to supply enough heat to "reheat" the sidearm flow, which is pumped, is going to require a high degree of flow rate to supply the thermal transfer to fulfill any demand for heat. Isolating the boiler, which will probably start cooling at about the same time the storage tank starts supplying the demand for heat, adds a level of sophistication in plumbing and controls that has not as yet been mentioned. The boiler itself will start depleting heat from storage and would certainly tax the longevity of the storage supply not to mention the sidearms ability to supply the thermal transfer demand. Heating the storage tank will probably work to a high degree if you are patient and the tank is insulated beyond anyone's business but getting that heat back out to heat your home is where the sidearm is going to show it's weakness.

 

[Vinced]

Cave2k, that makes sense to me. I was wondering how the drawing of heat off the storage tank via the sidearm was going to work. I think it would be just another heat load and I don't think it would transfer it back into the system properly.

 

[Duetech]

Cave2k, that makes sense to me. I was wondering how the drawing of heat off the storage tank via the sidearm was going to work. I think it would be just another heat load and I don't think it would transfer it back into the system properly.

Since the sidearm would heat your house via convection or thermal siphoning it wouldn't work because the transfer rate of the side arm has to be very fast (equal to the pumped rate) to meet the demand and sidearms don't work that way. The water that the sidearm gets its heat from is pumped at a high rate, compared to the flow rate of the water that is being heated, and causes the thermal siphoning by surface contact and heat transfer. The side arm would essentially be working backwards, compared to the storage tank heating process, when trying to heat the home. The result would be that the house wouldn't get warmer and would cool as a result. The tank would get cooler but actually not as fast as the house. Also the amount of time it would take to heat the storage tank via a sidearm would be huge and would probably suck your wood pile into non-existence.

 

[Der Fuirmeister]

Cave2k, that makes sense to me. I was wondering how the drawing of heat off the storage tank via the sidearm was going to work. I think it would be just another heat load and I don't think it would transfer it back into the system properly.

Vince, What did you end up doing with the aluminum tank. I'm considering an aluminum tank as well, but I'm planning to use PEX tubing for a heat exchanger because I have so much of the stuff laying around. That way I won't need to worry about corrosion with copper coils / aluminum either.

 

[WoodNotOil]

Cave2k, that makes sense to me. I was wondering how the drawing of heat off the storage tank via the sidearm was going to work. I think it would be just another heat load and I don't think it would transfer it back into the system properly.

Vince, What did you end up doing with the aluminum tank. I'm considering an aluminum tank as well, but I'm planning to use PEX tubing for a heat exchanger because I have so much of the stuff laying around. That way I won't need to worry about corrosion with copper coils / aluminum either.

Sparke did a pex hx in his plywood epdm tank and I think he said it worked. Keep in mind you need about 3x as much pex as you would copper because it transfers heat less efficiently. You will have to build a frame to support the coils so that they stand up in the tank. Also, keep in mind all of that pipe displaces more water, so you actually have less storage capacity that way. Not a problem if you size the tank larger so that the water left over after displacement is sufficient for your needs. I abandoned the pex route for those reasons and used a flat plate hx with dip tubes instead.

 

[Vinced]

I never built the aluminum tank. The company I work for builds in aluminum and I can get a good buy on the materials for a aluminum tank at scrap price. I still have my steel fuel tank that I plan on using for storage and I haven't decided how to setup my storage yet, but I have all summer to figure it out.

 

[tom in maine]

If you never do anything else in building your own tank, do not use aluminum either as a tank of a heat exchanger, unless you are prepared to replace something expensive. Something will corrode, I will guarantee it.

Use either copper or pex (should be 3-6x more than a similar copper hx) or use plate hx.
You will save yourself a LOT of grief.

 

[Der Fuirmeister]

I never built the aluminum tank. The company I work for builds in aluminum and I can get a good buy on the materials for a aluminum tank at scrap price. I still have my steel fuel tank that I plan on using for storage and I haven't decided how to setup my storage yet, but I have all summer to figure it out.

This past few weeks I looked at the costs / advantages / disadvantages of tanks types.......... used SS insulated milk tanks, EPDM home made, pressurized steel LP tanks and aluminum. I decided to go aluminum with PEX HX and PEX piping. Like you I can get aluminum cheap. Right now with the cost of aluminum down I can build an 1100 gal. tank for less than $1000. That's with 5052 alum., which is the type used in boat fabrication and aircraft fuel tanks. I've read on this web site the HX rates of copper range from 2x to 6x that of PEX. Based on the heat clacs for in-floor radiant, I'd tend to agree with the lower end or 2x the amount required compared to that of copper. Here are the issues that were considered in my design.....an aluminum tank is just $200 more than EPDM tank, aluminum can handle 200 plus degree water, will last multiple times longer than EPDM, the PEX HX I will use is 1/4th the cost of copper HX for a given HX output and I have a lot of PEX laying around. For me it makes sense.

 

[Vinced]

Hey,
Let me know if you need help with your aluminum tank fabrication. I'm just outside of Wausau and have aluminum wirefeed and tig welding capabilties at my home shop. Do you plan on a pressurized or open tank. If open I think I would coat the inside to keep it from coroding. Just my 2 cents.
Vince

 

[Der Fuirmeister]

Hey,
Let me know if you need help with your aluminum tank fabrication. I'm just outside of Wausau and have aluminum wirefeed and tig welding capabilties at my home shop. Do you plan on a pressurized or open tank. If open I think I would coat the inside to keep it from coroding. Just my 2 cents.
Vince

Open tank. I appreciate the welder offer, but I need to weld it place (in the room it's going into). That was another consideration in tank type that eliminated use of propane tanks and insulated milk tanks. Wouldn't fit through the 36" doorway. The EPDM (plywood sides etc.) would be made in place. But I've been told the EPDM liners will only last from 3-8 years.

Just this week I started to look into marine grade 5086 and 5083 aluminum, but not sure it's needed or worth the additional cost above the 5052. I might just go to .190 in a 5052 instead. I've also considered painting the tank interior with epoxy paint. At work we use the same paint they use on water towers. What they use is a high zinc solids epoxy, top coated with a UV resistant urethane. This may not be what you'd want on aluminum, but they have other epoxy types which could work. What I need to talk to the paint rep about is how the epoxy types will hold up to 200 degrees, and the expansion of aluminum. I don't suspect any problems and will probably paint the interior for added protection.

Another option is to use a cathodic protection system. They use these on buried steel tanks that have been in service for 40-60 years. A steel tank with the correct cathodic protection would easily last my life time. But there is a cost trade off to buy and run these active systems. Passive anodes are used in hot water heaters (and the Garn boiler). No perfect answer.........

I'm also considering a two tank system. One tank for hot water pre-heat which will be heated by the wood boiler in winter and pex tubing solar collector in the summer months. The other tank will be used for wood boiler heat storage in the winter and summer geothermal cooling with a horizontal ground loop system again utilizing PEX tubing. In WI the soil temps down 8 feet don't really change from 50 degrees all year. The same heat exchanger in my forced air furnace that we'll use for winter heating will be used for cooling in the summer. It will need to be larger than required for heat, and I accept the fact that it will not be large enough for cooling on those 100 degree days to keep the house at 72. But we rarely hit 95 in WI and it's really really cheap to run. And you'd be surprised at how cheap to install and run compared to the usual freon type that suck money out of your pocket to run and have serviced every other year to charge up. With a properly sized horizontal loop system, 50 degree water will keep the house at 72-74 when it's 90 outside, running on the little 1.2 amp Taco pump instead of the 28 amp freon compressor. The added cost to install over a standard freon system is paid for in 2-3 years. The less I need to pay for heating and cooling the sooner I can retire.......

If I get 30 years out of the tanks, more than likely I won't be around or won't care when they start leaking anyway.

 

[Vinced]

That is an interesting concept, using water cooled by the low ground temperature to cool your home. A few years ago I saw a website that had plans on how to do this accept it used 8" pvc pipe buried at least 6ft deep and they buried it in a large grid in your yard. They circulated air and tied it into the forced air heating system. They also said that the 50 degree or so air helped the heating system in the winter also. At the time I was building my house and it seemed very doable. The problem was I didn't have the equipment to dig the trenches and it would have costed quite a bit to hire it out. I now have my own backhoe and would like to look into a type of cooling system since I never put A/C in my house. I would like to read up on this if you have any websites or info on this concept.
Vince

 

[Der Fuirmeister]

That is an interesting concept, using water cooled by the low ground temperature to cool your home. A few years ago I saw a website that had plans on how to do this accept it used 8" pvc pipe buried at least 6ft deep and they buried it in a large grid in your yard. They circulated air and tied it into the forced air heating system. They also said that the 50 degree or so air helped the heating system in the winter also. At the time I was building my house and it seemed very doable. The problem was I didn't have the equipment to dig the trenches and it would have costed quite a bit to hire it out. I now have my own backhoe and would like to look into a type of cooling system since I never put A/C in my house. I would like to read up on this if you have any websites or info on this concept.
Vince

It should work well with the boiler system storage, although you can use it alone (direct from loops to furnace) with a forced air furnace and not have any storage. The storage concept should give better cooling with a reduced field and larger HX. Right now Obama is giving away money for geothermal systems and other forms of renewable energy. And WI is doing the same.

Here you go.....

http://www.alliantenergygeothermal.com/index.htm

http://www.informedbuilding.com/Geothermal/Main16/Types-of-Geothermal-Ground-Loops/

(broken link removed)

http://en.wikipedia.org/wiki/Geothermal_heat_pump