Domestic hot water off of a tarm with pressurized storage.

[MrEd]

OK, finally did it. Plunked down my cash for a tarm after debating the issue (with myself) for the past 5 years...for me, a 3 year payback at most.

Question is, I am planning on pressurized storage (2 500 gallon propane tanks), and currently I have a oil boiler with hot water on demand off the boiler...what is the optimum way to use this pressurized storage to give me DHW all year round?

-Thanks.

 

[Nofossil]

Others will doubtless chime in, but with the current price of oil, on-demand DHW from a boiler seems pretty much a losing proposition. There's a good deal of standby loss from the boiler itself, and most of them have to fire pretty often when you're using hot water.

Are you planning on burning wood from time to time to keep the storage hot during the summer? If so, you'll want REALLY good insulation to keep your standby losses reasonable. Many folks use wood during the winter and electric/oil/propane/natural gas/solar during the summer.

With pressurized storage, there are three basic ways to get heat from storage into your DHW:

1) Use and indirect DHW tank (Superstor or equivalent) and circulate water from storage through the internal coil in the DHW tank as needed to maintain DHW temperature.
2) Use a flat plate HX and a pair of circulators. Circulate water from the storage on one side of the HX, and circulate water from the DHW tank on the other side. Run circs as needed to maintain DHW temperature.
3) Thermosiphon. If you can mount your DHW tank above your storage, then you can set up a sidearm HX alongside of the storage and connect the other ports to the top and bottom of your DHW tank. It won't transfer a lot of BTUs per hour, but it will keep your DHW at the same temperature as the top of your storage.

The first option requires an indirect DHW tank (one with an internal coil) Options 2 and 3 would work with any type of DHW tank, including electric, indirect, gas, or whatever.

The propane / natural gas on-demand DHW heaters are really good. You might just consider one of those and ignore the storage during the summer.

 

[MrEd]

Yes, I am planning to run the boiler for DHW in the summer, as infrequently as possible. Also would like to hookup a solar loop someday if I can figure it in so I don't have to burn wood at all in the summer.

Any idea how much oil/$$$ I am wasting using on-demand off the boiler? It does run a lot...

Which of the three options do you think is best? Besides the almost $1100 for a super-stor tank, it seems like a good option - even if I didn't have a wood boiler (i.e. replacing the on-demand with a superstor zone off the boiler).

 

[Nofossil]

Yes, I am planning to run the boiler for DHW in the summer, as infrequently as possible. Also would like to hookup a solar loop someday if I can figure it in so I don't have to burn wood at all in the summer.

Any idea how much oil/$$$ I am wasting using on-demand off the boiler? It does run a lot...

Which of the three options do you think is best? Besides the almost $1100 for a super-stor tank, it seems like a good option - even if I didn't have a wood boiler (i.e. replacing the on-demand with a superstor zone off the boiler).

I use solar on mine - haven't used oil yet this year, though I might have to in the next few days (no sun), I didn't realize the Superstor was so expensive. I got mine 20 years ago. You can estimate your oil usage by timing how long it runs. I probably uses around 1 gallon per hour of run time. Pretty typical numbers are 20-30 gallons per month for a family of four for oil fired hot water.

The superstor is really nice in that you can heat your hot water from oil, wood, or storage with pretty minimal effort. At that price, though, I'd be looking at electric with external HX of some sort.

 

[Ron Lloyd]

Hi all. I have been reading here for several weeks and now that I ordered my Tarm Solo Plus 60 it is time to start asking some questions. This thread is germane to what I intend to do. I would prefer to go with a pressurized storage system but I also want to get my domestic hot water from this system. I am going to look at a 1000 gal. propane tank this afternoon. The guy I’m going to see buys, restores and resells all sorts of pressure vessels. I explained to him that I would like to place a hx “inside” the tank for my domestic hot water. I described my theory that a hole could be cut in the tank and then weld a flange around the circumference of the hole to bolt a lid to. He said he didn’t see any problem with this at 30 psi. My question is would the integrity of the tank be compromised as soon as a hole was cut into it? Obviously the hole would be as small as possible to accommodate the hx and the flange and lid would have to be thick steal. He said he could do these modifications for a fee. Is this a really crazy idea? Any input would be appreciated.

Thanks
Ron

 

[Nofossil]

Hi all. I have been reading here for several weeks and now that I ordered my Tarm Solo Plus 60 it is time to start asking some questions. This thread is germane to what I intend to do. I would prefer to go with a pressurized storage system but I also want to get my domestic hot water from this system. I am going to look at a 1000 gal. propane tank this afternoon. The guy I’m going to see buys, restores and resells all sorts of pressure vessels. I explained to him that I would like to place a hx “inside” the tank for my domestic hot water. I described my theory that a hole could be cut in the tank and then weld a flange around the circumference of the hole to bolt a lid to. He said he didn’t see any problem with this at 30 psi. My question is would the integrity of the tank be compromised as soon as a hole was cut into it? Obviously the hole would be as small as possible to accommodate the hx and the flange and lid would have to be thick steal. He said he could do these modifications for a fee. Is this a really crazy idea? Any input would be appreciated.

Thanks
Ron

I haven't done it yet, but I'm thinking a sidearm-style double tube HX installed next to a pressurized tank could be used to get heat out via thermosiphoning - no pumps, no controls. I'm dying to try it. I think it would work well for maintaining heat in a DHW tank. Could also be used to transfer heat in from a solar panel.

 

[Ron Lloyd]

Thanks nofossil. I considered going that route but if I can get the HX inside I would prefer to do that. The guy I visited yesterday at Fisher Services showed me how he would accomplish this. He would cut a 6” or 8” hole in the propane tank then weld a corresponding 6” or 8” pipe coupling to the tank over that hole. The HX would be tapped and threaded through the “plug” that would then thread into that coupling. I had no problem finding 6” and 8” couplings (and even larger) on internet searches but I can’t find a plug that large. Maybe he has a source.

The next problem is finding a HX that will fit through a 6” opening or at least an 8” opening. I’m going to experiment with flexible copper to see if I can coil my own HX with that tight of a radius. He said he could easily pressure test the tank to more than double it’s intended pressure after all the welding. This guy has quite an operation. He has dozens of tanks on hand (at various stages of repair) and appears to have a lot of experience at modifying them. What he would do to a tank for me is not dissimilar to a number of modified tanks that he showed me at his shop.
.
Ron

 

[Nofossil]

Thanks nofossil. I considered going that route but if I can get the HX inside I would prefer to do that. The guy I visited yesterday at Fisher Services showed me how he would accomplish this. He would cut a 6” or 8” hole in the propane tank then weld a corresponding 6” or 8” pipe coupling to the tank over that hole. The HX would be tapped and threaded through the “plug” that would then thread into that coupling. I had no problem finding 6” and 8” couplings (and even larger) on internet searches but I can’t find a plug that large. Maybe he has a source.

The next problem is finding a HX that will fit through a 6” opening or at least an 8” opening. I’m going to experiment with flexible copper to see if I can coil my own HX with that tight of a radius. He said he could easily pressure test the tank to more than double it’s intended pressure after all the welding. This guy has quite an operation. He has dozens of tanks on hand (at various stages of repair) and appears to have a lot of experience at modifying them. What he would do to a tank for me is not dissimilar to a number of modified tanks that he showed me at his shop.
.
Ron

That sounds really good. If you're trying to fit the HX through a 6" hole, you almost have to go with finned tubing to get enough surface area. Don't know where you can buy it, but I've seen it. Maybe your tank guy could get some. Given the cost of copper, perhaps stainless would be a good option. I've seen really good looking finned stainless.

 

[steam man]

I have a few minutes to kill so let me help you out here. I wouldn't try to thread anything that big and expect it not to leak. My suggestion is to take a 6" or larger flange and have it welded to a pipe 6" or so long and have that welded to the hole in your tank. The heat exchanger can be made using a blank flange of the same diameter and drilling holes and welding it for your exit pipes. Obviously a gasket would be slipped over the heat exchanger and used between the flanges. Looking at one of my supply catalogs I notice that W&O;Industrial Supply makes custom heat exchangers similar to that and will make it with finned tube of various materials. You may be able to find a ready made heat exchanger that you can adapt your tank to. Its a common design. The only caveat is sizing the exchanger for the right amount of heat transfer.

 

[Ron Lloyd]

Thanks for the advice steam man. I don’t see any reason why my guy could not weld the pipe to the tank instead of a coupling but I can not visualize what you mean with these flanges. I absolutely do not want this thing to leak so would you be able to provide me with a link to a supplier of the flanges that you describe? Might this be close to what you are talking about?

(broken link removed to http://www.anvilintl.com/ps_pipefitting/index.php?PCAT=34)

Thanks
Ron

 

[Ron Lloyd]

I think I see what you’re saying now steam man and I like it.

(broken link removed)

So now I’m thinking why not a 12” hole, pipe and flange that would accommodate a larger diameter HX.

Ron

 

[MrEd]

Unless someone can talk me out of it, I think I am going to purchase a SuperStore SSU-60, indirect fired water heater as a zone off of my existing oil boiler. Then, the tarm will provide the heat to the oil boiler and thus it will never fire. Besides the $1100 cost, I don't see the drawback and at todays oil prices thats only 225 gallons I need to save.

 

[Nofossil]

Unless someone can talk me out of it, I think I am going to purchase a SuperStore SSU-60, indirect fired water heater as a zone off of my existing oil boiler. Then, the tarm will provide the heat to the oil boiler and thus it will never fire. Besides the $1100 cost, I don't see the drawback and at todays oil prices thats only 225 gallons I need to save.

I use a 40 gallon SuperStor and I've been very happy with it. I've added some complexity (solar, preheat, superheating, oil heat scavenging) - here's a writeup.