Pressurized or open storage

[NCFord]

I am trying to decide whether to install a 500 gallon pressure tank or about 1000-1500 gal open storage. I only have the space for one short stubby 500 gallon propane tank or use the same space to build open storage that could be 1000-1500 gallons. I have an econoburn 100. I will not have any loads except a heat exchanger in my forced air duct and I will plumb my DHW with the intial install or later.(I have a gas tankless now and still trying to find the best way to plumb it) I know for the open storage I will simply have a closed system to my boiler and then another closed system to the heater loop. My biggest question which will give me the longest heating times. I think the press. system in more efficient than the open storage. I think if I had to chose between a 500 gallon pressure vs 500 gallon open storage I would use the pressure system, but I can't figure it out considering the increase capacity of the open system.

Also, what temp. does the open storage tanks usually get up to?

Side note: My storage tank either press. or open will be outside attatched to my workshop in a very well insulated enclosure. I also live in North Carolina. House square footage is 1500 sq. ft.

Any advise would be helpfull, as once I figure this out I can design my system.

Thanks

 

[tom in maine]

Our unpressurized tanks are usually heated to 180F. They can go up to 200F. We now double line everything we make.
The liner, if it does deteriorate, would become brittle over time. This would mean it could crack if moved.
Since our tanks are not normally moved, this is not an issue. I have not had any liner embrittle over time.
Double lining also insures if there was embrittlement, the second liner would not be brittle since it was not exposed to hot water for much of its life.
I have never seen any of our liners fail due to embrittlement. The current liner we manufacture is material that we have
had in service for almost 30 years.

We have had folks boil our tanks. This is undesirable due to the noise, not any major issue with liner or tank breakdown.

A single heat exchanger is used to move heat in and out of the tank. Plumbing is the same as if this was a pressure tank.
There are other threads that offer the issues related to both types of tanks.

 

[NCFord]

Thanks,
I was planning on building my own open storage w/ EPDM, even knowing that it will need replacing at some point...its just cheap. One thing I am considering is adding solar to the storage tank year around to help with heat in winter and perhaps provide enought heat in summer for DHW, though I am not sure if I can heat 1000-1500 gals with solar and still heat my DHW without adding additional plumbing.

 

[kopeck]

Just a warning, EPDM doesn't like to go over 170 deg F from what I've read.

Not an issue for solar but I like to see my tank (I have one like what Tom was describing above) to about 175 deg F with my wood boiler on colder nights.

When it's warmer out I only heat the tank up enough to get me through the day. Right now that's two small loads and the tank usually tops out around 165 - 170. When it get a bit warmer I'll switch to one bigger load a day, and so on.

K

 

[Karl_northwind]

With the solar in the summer, you may only want to use the solar to heat the top 1/4 of the tank, so you keep a hundred or 2 gallons in the 120-140 range, rather than keep 500 gallons 100 F. put your DHW preheat coil in that top 1/4 of the tank so It gets the highest temps.

karl

 

[NCFord]

thanks Karl. That might work for the main heat exchanger going to my furance as well ... maybe mount that one horizontal in the tank?

 

[bmblank]

I would avoid horizontal loops, or any where the pipe would be going up-down-up-down. Its an air-lock nightmare.

 

[NCFord]

good point