Food Grade Drum For Hot Water Storage

[toadshade]

I am starting my research on building a solar water heater. My main question for now is the water storage container. I am a welder and appreciate steel or especially stainless steel but no matter how much I know how to build a stainless vessel, it is still extremely expensive. As of now my system will be an indirect (closed loop) glycol system heating the supply tank with a three way bypass with a tankless water heater in high demand situations. I plan on regulating the tank to 150 degrees F for now (adding more storage in the future if I am heating water that efficiently). So given those temperatures, I see no reason not to use a food grade polyethylene barrel for my storage container. The water will not be consumed so it is not a safety concern. A shower would be the only real contact and I do not, nor have I ever, drank my shower water ?. I will have a copper or stainless coil on the roof and I was thinking a PEX coil inside the container. And I will spray foam the container. As long as I can keep the storage container sealed, then I do not see any reason why I cannot use the food grade drum over a very very expensive stainless drum. I searched the forum for a little while assuming I could not be the first person to bring this up, but I could not find any discussion on this topic.

 

[rodrick]

how about a old hot water tank find one that somebody upgraded to a more efficient tank and was still good or the electric side is toast

 

[toadshade]

I briefly thought about that but I would rather not use one for a number of reasons. But one of the main reasons is the awkward size in my limited space. But regardless, it would eventually need to be replaced now and then. The plastic is durable, easy to work with, and very easy and cheap to replace.

 

[Rednecktek]

What kind of capacity are you looking for? Food grade steel drums are pretty cheap and you can weld right to it for fittings and such. Plus, they most often have removable lids which makes life easy for access and inspections.

Bigger? Liquid totes. Smaller? Propane tank.

 

[Bluedog225]

Keg?

 

[toadshade]

Stainless steel drums are around $300 each and not easy to find so it would involve travel and/or delivery. So I would rather avoid that if I can spend $15 on a plastic drum and pick one up just about anywhere. I am looking for about 50 gallon capacity which is perfect for a drum. I thought about welding a few kegs together and mounting it sideways for space restrictions. But all of that is a lot of work if a plastic drum will work for this purpose. I just want to know if there are drawbacks to a plastic drum, or more specifically, if it is a downright bad idea for some reason I am not aware.

 

[HighDesertOffgrid]

HDPE has a melting point of 266F. Should be fine.

 

[Rednecktek]

Gluing fittings to a round surface is a PITA, but doable.

 

[toadshade]

I agree but I will be using mechanical fittings for the entire project from the lid.

 

[bstump]

Not "cheap", but this is actually made for the job. I have one between my geo unit and my heat pump water heater. My geo recirculates ("desuperheater") and excess heat goes to the water in the storage tank as it pumps through.

https://www.menards.com/main/plumbing/water-heaters/hot-water-storage-tanks/richmond-reg-120-gallon-hot-water-storage-tank/st120/p-1444452203469-c-8691.htm?tid=-4485638087405679350&ipos=1&exp=true

 

[toadshade]

I really would love something like that but I am such a build it myself person since I have the tools, I cannot make myself buy something like that if I can build it myself. Regardless, I bet that tank is steel and might have to be occasionally replaced? If it is stainless, then I'd say the cost is probably a great deal in a package like that. I would even be willing to buy something similar if I could be convinced that a $15 drum with some pex fittings and spray foam isn't going to perform in exactly the same way. And I am not trying to be a smartass or argumentative. I joined this forum because I honestly want to know of any drawbacks to this idea.

 

[Mart Hale]

I ran into this document thought I would share it, I also have been looking at thermo storage, only I am now testing sand. But I also like to look at all projects to get another idea.

 

[jimi PV-T]

I made a thermal store out of an IBC,just used 3/4 tank connectors like you'd have on a water storage tank for flow and return .IBC will take boiling water but there's little chance of you boiling 1000 litres. We had underfloor heating pipes connected to the other side of tank with a mixing valve to keep it under 35 degrees Celsius.
I was going to drop a coil of pipe into the IBC to act as a heat exchanger for domestic hot water,one connected to main and the other to your hot tap but I'm told there's a risk of leginellas disease if it you don't get it up to 60 degrees Celsius now and again