Converting Propane Tanks to thermal Storage.

[HappyHome]

Hello, all.

I have someone designing a new hydronic heating system for my home, and we are stuck on the thermal storage issue. The designer would like to use pressurized storage; I have a finished basement with cinder-block walls, and getting anything wider than 30" through the door will be very tricky.

I need 300 gal capacity (as a minimum) up to 550 gal capacity (ideal). I'm open to outdoor storage, but that would probably require excavating. Plus, winters here bottom out at -40, so we'd have to make extra sure of the insulation.

What ideas have people come up with for DIY storage tanks; and where can I find articles about how to make 'em?

Also: Is there a commerical option for this that is so good or so popular that people don't bother?

 

[maple1]

What can you get for LP tanks? I would have to check, but I was thinking the 100 gallon one I got for expansion is 2' diameter. I could be wrong though.

You could build an open storage tank in place, and use coils for heat exchangers. Storage would be open, but rest of system would be closed/pressurized. Insulated wood box with plastic liner, basically. Search 'American Solartechnics' - he is a member on here. Quite a few guys on here are running those - would also drastically reduce expansion tank requirements.

(Don't know what you have for a boiler, but I have 660 gallons & would love more. IMO even 550 is just adequate).

 

[Fred61]

Conventional preference on this site seems to favor pressurized storage over unpressurized which leads folks with difficult installations or space constraints to "jump through hoops" and shell out big bucks for complicated plumbing and install in less than optimal locations but I don't see the reason for it.

I have a 500 gallon unpressurized retired stainless chemical tank and if I had to do it over I would install the same set-up. All my boiler does is heat the water in the tank and all the distribution originates from that battery. I know and understand that the argument is that if the storage temperature is cold and the zones are calling the priority is the heat to the zones. I have run into that situation probably twice in the 9.5 years I've been running this with little consequence. The zones continued to produce heat albeit at a lower temperature and the only other visible result was the slower temperature rise in the tank during my daily charge session.

I don't have large expansion tanks or side arms for DHW. The two main copper coils within the tank supply all my heat and domestic hot water. Heck, just for giggles I installed a separate coil in the bottom of the tank that is hooked up to a boiler overheat zone. Because I wanted to keep the hot water make-up separate from the distribution I did install a FP exchanger so that cost me the price and operating cost of an additional circulator but that only runs during my 3 to 4 hour daily burn.

 

[peakbagger]

I have an American Solar Technics unpressurized tank. I installed it myself and the way its designed its easy to fit in a tight spot. Unlike a modified propane tank there are no potential boiler code issues. ( I don't know how Ontario treats pressure vessels)

It requires a heat transfer coil but doesn't need anywhere near the expansion tanks of a pressurized solution

(broken link removed to http://www.americansolartechnics.com/products/heat-bank-storage-tanks/)

 

[HappyHome]

Hello, Maple1 and thank you for responding! I'm getting an Econoburn EB-100 boiler, and the salesman said I could 'get by' with 300 gal, but that 500+ would be preferable. American Solartechnics is a product that I'm familiar with and I am considering using it.

I'm also in touch with a local septic tank mfgr. There's an excavator working next door throughout the summer, if I need a large enough thermal storage I may just pay them to bury a septic tank with 6"-18" of polystyrene insulation wrapped around it - in the yard under the front patio.

 

[Bad LP]

Tarm has 300 gallon tanks that are 30" diameter. ASME rated so there's no potential problems with your insurance company. I just bought 2 300 gallon tanks from them.

There is no way I'd give a single second of thought into installing tanks in the ground under any circumstances.

There is a used Solortechnics non pressurized tank for sale on the forum. It will be a few pages deep. I bought his boiler but was only interested in pressurized storage. Nice guy to deal with as well.

 

[HappyHome]

Tarm has 300 gallon tanks that are 30" diameter. ASME rated so there's no potential problems with your insurance company. I just bought 2 300 gallon tanks from them.

There is no way I'd give a single second of thought into installing tanks in the ground under any circumstances.

There is a used Solortechnics non pressurized tank for sale on the forum. It will be a few pages deep. I bought his boiler but was only interested in pressurized storage. Nice guy to deal with as well.

The Solortechnics tank might work for me. I'll have to find out where in my basement I can squeeze a tank with a 6 ft square footprint, but it's still promising.

 

[peakbagger]

AST has changed there design of the liner slightly over the years and experimented with liner materials. If you are considering a used one it would be worth given Tom the owner a call.

 

[Sparky]

Check out builditsolar.com for tank ideas
If needed I can help with making coils it is pretty easy
I had 550 gallons storage wasn't enough for my heat load
I have 1200 gallons works perfect one burn a day


Sent from my iPhone using Tapatalk

 

[Beagle Dad]

I used 120 gallon propane tanks which are 30" wide. The tanks were modified by cutting them in half and added to the middle using steel plate which was rolled into a cylinder and welded. Since the tanks were modified they are no longer certified. Here in Ontario a non ASME tank must operate at under 15 psi. Then link to the post below shows some pictures of the completed tanks

https://www.hearth.com/talk/posts/2112829/

 

[velvetfoot]

Would you have better stratification in an unpressurized tank since there is no flow stirring things up? Or, isn't that a factor with a big pressurized tank?

 

[woodsmaster]

Would you have better stratification in an unpressurized tank since there is no flow stirring things up? Or, isn't that a factor with a big pressurized tank?

Better stratification but you lose a few degrees with the heat exchager.

 

[velvetfoot]

Better stratification but you lose a few degrees with the heat exchager.

Plus I imagine the coil would be resting on the bottom of the tank. The tanks are usually not tall though.

 

[Beagle Dad]

I went through a similar process to select a storage tank system. Maximizing the storage was important and given that I have radiant floor heating which is the majority of my load with a return water temperature of 90 Deg F a tall tank would be the best fit. The solution was 4 tanks in series for a total of 920 gallons. With this configuration the BTUs stored is maximized by having the greatest temperature difference for the available mass of water. When burning once a day the bottom of the tank stays around 90F and the top varies from 175 to 165 F.

See Idronics 17 which talks about usable heat. The best way to achieve this is to keep the top of the storage as hot as possible. My system has 4) 90" tall tanks which can have up 40 Deg F difference from top to bottom. Therefore a pressurized system was selected.

http://www.caleffi.com/sites/default/files/file/idronics_17_na.pdf

 

[salecker]

Don't bury a heat storage tank in the ground.
If you can get the excavator cheep,dig out beside your basement and cut a large enough hole in the wall to get your tank inside.Then fill the hole in the wall and back fill or leave it as access to the basement with a poured retaining wall with steps,or frame walls and steps from PWF wood.

 

[Fred61]

Don't bury a heat storage tank in the ground.
If you can get the excavator cheep,dig out beside your basement and cut a large enough hole in the wall to get your tank inside.Then fill the hole in the wall and back fill or leave it as access to the basement with a poured retaining wall with steps,or frame walls and steps from PWF wood.

There are several reasons not to bury a heat storage tank including access but there is one stand alone reason not to that trumps them all. If there's any chance that moisture will come in contact with the tank it will lose it's heat to the ground.
Any moisture will draw the heat away.
This was one of the most important warnings in all the books in the early days of solar heating and storage.
Any heat lost to the earth is lost forever.

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[nhtreehouse]

While I myself would never bury an energy storage tank, the folks at Cold Climate Housing Research Center (CCHRC) in Alaska buried a 25000 gallon tank a few years back.

Here is a link to the video:

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, Inside CCHRC: Thermal storage

The idea here was to take what gassers do on a daily cycle and move it to a season cycle. That is, store solar energy in the summer and use it in the winter. I have no idea how it worked out for them.

More of a curiosity than anything else. I totally agree with the other comments - as soon as the buried tank gets wet, you're in trouble.

Chris

 

[Fred61]

They're probably still trying to get it up to temperature.

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[tom in maine]

A couple unpressurized tank comments.
Most tanks we make are 4' tall. We have made them up to 8' tall in smaller volumes. As tanks get taller, the cost rises due to increased strength requirements. That being said, 4' tanks stratify very well upon discharge. When charging they heat to one temp.
I have not see real concern with a 4' tank and the level of stratification.

Of course, if you are heating hot water baseboard, you need higher temps. But if you are heating HWBB from storage, you are compromised in using your storage to its maximum potential. Radiant panels or radiant slabs or fan convectors make a lot more sense to draw storage down for the most btu's per firing.

Our heat exchangers hang in the tank. They do not sit on the bottom. They span the bottom to the top and are used for charging and discharging heat.
We have completely transitioned to stainless steel. It is lighter, less expensive and in most cases more durable than copper.

Using our tank is analogous to using a pressure tank, there is a connection for the top of the tank and the bottom.

The big difference is you can add heat exchangers or plumbing by simply popping the top. And we can and have made a lot of size variations
to match a customer's floor space.

 

[mark cline]

I went through a similar process to select a storage tank system. Maximizing the storage was important and given that I have radiant floor heating which is the majority of my load with a return water temperature of 90 Deg F a tall tank would be the best fit. The solution was 4 tanks in series for a total of 920 gallons. With this configuration the BTUs stored is maximized by having the greatest temperature difference for the available mass of water. When burning once a day the bottom of the tank stays around 90F and the top varies from 175 to 165 F.

See Idronics 17 which talks about usable heat. The best way to achieve this is to keep the top of the storage as hot as possible. My system has 4) 90" tall tanks which can have up 40 Deg F difference from top to bottom. Therefore a pressurized system was selected.

http://www.caleffi.com/sites/default/files/file/idronics_17_na.pdf

How did you pipe to the individual tanks to balance the flow and return ? Did you use balancing valves or stepped piping . I want to configure 3 - 435 gal tanks in parallel.

 

[Beagle Dad]

How did you pipe to the individual tanks to balance the flow and return ? Did you use balancing valves or stepped piping . I want to configure 3 - 435 gal tanks in parallel.

My tanks are in series to create one every tall tank. The coldest water enters the bottom of tank 4. The boiler sends water to the top of tank 1.

 

[sardo_67]

A couple unpressurized tank comments.
Most tanks we make are 4' tall. We have made them up to 8' tall in smaller volumes. As tanks get taller, the cost rises due to increased strength requirements. That being said, 4' tanks stratify very well upon discharge. When charging they heat to one temp.
I have not see real concern with a 4' tank and the level of stratification.

Of course, if you are heating hot water baseboard, you need higher temps. But if you are heating HWBB from storage, you are compromised in using your storage to its maximum potential. Radiant panels or radiant slabs or fan convectors make a lot more sense to draw storage down for the most btu's per firing.

Our heat exchangers hang in the tank. They do not sit on the bottom. They span the bottom to the top and are used for charging and discharging heat.
We have completely transitioned to stainless steel. It is lighter, less expensive and in most cases more durable than copper.

Using our tank is analogous to using a pressure tank, there is a connection for the top of the tank and the bottom.

The big difference is you can add heat exchangers or plumbing by simply popping the top. And we can and have made a lot of size variations
to match a customer's floor space.

i was going to go for the propane tank system but the more i look the better your system seems for me, this is my first house and first wood boiler system so something i can change around later on it needed seems better to me.

i sent you guys an email

 

[Chris Hoskin]

My tanks are in series to create one every tall tank. The coldest water enters the bottom of tank 4. The boiler sends water to the top of tank 1.





View attachment 194974

Beagle, how long have you been using your set up? Is the parallel tank set up working as expected / are you pleased with the performance?

 

[warno]

I have 3) 250 gallon LP tanks plumbed together for my storage. Each tank was 29" in diameter I believe it was.

 

[sardo_67]

I have 3) 250 gallon LP tanks plumbed together for my storage. Each tank was 29" in diameter I believe it was.

View attachment 229464

that's exactly what i have been looking for, just impossible to find the tanks unless i just go and buy new ones for around 1,100 each.

so the way you have yours plumbed there is an in on the bottom and out on the top?

is that where you have them or did you move them somewhere with insulation?