pressurized storage tank piping to the top with hot or to the bottom with hot?

[2.beans]

I installed two 500 gallon propane tanks hooked in parallel. The supply from my wood boiler goes in the top of each tank and the return to the wood boiler is off the bottom of each tank via dip tubes. The supply for the house is off the top of each tank and the return from the house is to the bottom of each tank via dip tubes. All the piping is equally is equally spaced across the top of tank. It's been running for about a month and seems to work great, but would it work better if my supply from my wood boiler went to the bottom of the tanks and returned to the wood boiler off the top? I may just swap the lines to try it for awhile, but if anyone has any experience or opinions on this, it would be much appreciated. Thanks

 

[2.beans]

anybody out there?

 

[leaddog]

If you run the supply into the bottem you will mix the water more and loose any stratification. also if your tanks get down in temp it will take longer to get hot water to your house as you will be slowly heating all the water. By putting the hot water at the top the hotter water tends to stay at the top.
leaddog

 

[Nofossil]

Leaddog has it right. You want maximum stratification - coldest water to the boiler return, hottest water to the house for heating.

 

[kenny chaos]

For maximum stratification, would it be better to run the two tanks in series instead of parallel?

 

[Nofossil]

For maximum stratification, would it be better to run the two tanks in series instead of parallel?

I haven't seen the plumbing diagram, but if it were me I think I'd do exactly that - plumb them in series. If I could, I's stack them one above the other as well.

Tanks plumbed in parallel and sitting next to each other would likely equalize so that the tops were the same temp and the bottoms were the same temp. That means that if you managed to get one tank more stratified than the other, it would equalize by itself.

 

[2.beans]

We plumbed the tanks so the supply from the wood boiler goes into the top of each tank, and all the piping is exact equal length. The return to the wood boiler is from the bottom of the tank and all the piping is at equal length. We put temperature gages on the inlet and outlet from each tank and my inlet temps are equal as well as the outlet temps. Ins at 180, outs at 160. I realize stacking the tanks would have been better, but I didn't have the room to stack the tanks and I didn't want the 10,000 lbs confined to a 3X10 area. The supply to the house is from the top of each tank with all the piping the exact same length from each tank and the return goes to the bottom of each tank again with the piping each at equal lengths. It seems to work really well, I just want to make sure that the supply from the wood boiler should go into the top of the tanks.

 

[Nofossil]

Yes - hot goes in and out the top of the tank(s), cold goes in and out the bottom.

 

[Grapenut]

For maximum stratification, would it be better to run the two tanks in series instead of parallel?

I haven't seen the plumbing diagram, but if it were me I think I'd do exactly that - plumb them in series. If I could, I's stack them one above the other as well.

Tanks plumbed in parallel and sitting next to each other would likely equalize so that the tops were the same temp and the bottoms were the same temp. That means that if you managed to get one tank more stratified than the other, it would equalize by itself.

So, we're really looking for a storage tank that stands vertically (space permitting) rather than horzontally? That would maximize stratification.

 

[twofer]

Sorry, I'm a bit of a newbie and a little confused here.

First, the pressurized tank is to have four connections??? Two up top for the hot water supply and two on the bottom for the cold water return? Also, when the house calls for heat and the boiler is not running does the pump then reverse the flow? Because it seems that if it didn't reverse then the cold water from the bottom of the tanks is what would be supplied.

 

[Nofossil]

Here's a simple schematic showing on possible way to do it. The number of connections depends on the tank, but the important idea is that you want maximum startification - hottest water at the top.

 

[twofer]

Here's a simple schematic showing on possible way to do it. The number of connections depends on the tank, but the important idea is that you want maximum startification - hottest water at the top.

But it seems like if the boiler isn't running then you're taking cold water off the bottom of the tank and then dumping on the top before it gets sent to the zones. I'm having a heck of a time wrapping my head around this.

 

[Grapenut]

For maximum stratification, would it be better to run the two tanks in series instead of parallel?

I haven't seen the plumbing diagram, but if it were me I think I'd do exactly that - plumb them in series. If I could, I's stack them one above the other as well.

Tanks plumbed in parallel and sitting next to each other would likely equalize so that the tops were the same temp and the bottoms were the same temp. That means that if you managed to get one tank more stratified than the other, it would equalize by itself.

So, we're really looking for a storage tank that stands vertically (space permitting) rather than horzontally? That would maximize stratification.

Nofossil, Not to sound redundent, but if we are looking for maximum stratification, the ideal configuation would be a tall thin tank, as opposed to a short fat tank. Right? If so, is it worth the time to build legs to stand a 500 gal propane tank up vertically? I've priced a number of used pressure tanks and although I've found several 1000 gal vertical tanks for 2k to 3.5k, propane tanks are much cheaper.

 

[Ron Lloyd]

For maximum stratification, would it be better to run the two tanks in series instead of parallel?

I haven't seen the plumbing diagram, but if it were me I think I'd do exactly that - plumb them in series. If I could, I's stack them one above the other as well.

Tanks plumbed in parallel and sitting next to each other would likely equalize so that the tops were the same temp and the bottoms were the same temp. That means that if you managed to get one tank more stratified than the other, it would equalize by itself.

So, we're really looking for a storage tank that stands vertically (space permitting) rather than horzontally? That would maximize stratification.

That’s an interesting idea. The building that I’m putting my Tarm 60 in has a 12’ ceiling. So, two (or even three) 500 gallon tanks, standing on end, would take up less floor space than one 1000 gallon tank lying down. This may be totally crazy but take a look at this drawing.

Sorry the link I attempted to insert here did not work.

Let's try this. Click on the link below and then the link in the center of the page labeled "piping diagram 1".

http://ronlloyd.embarqspace.com/

In this configuration (with the tanks standing on end) could you theoretically get tank #1 to 190 degrees in its entirety? The boiler would be far less likely to idle because it would always be drawing from the coldest water in the entire system. I realize that when the boiler circulator is running you would be putting the coldest water from the bottom of tank 1 into the top of tank 2 and the coldest water from the bottom of tank 2 into the top of tank 3. The reverse would occur when the zone circulators were running. This may not be ideal in terms of maintaining stratification in each tank, but the very hottest water would still always be in tank 1 and the coldest in tank 3. I imagine each tank would also need to be insulated from its neighbor to maximize stratification across the three tanks.

Ron

 

[MrEd]

I couldn't open your document, but seems to me that if you are aiming for stratification, having 3 tanks (or 2) one on top of the other is better than 3 tanks vertical - if you have just a single tank, vertical probably would be better. I am keeping mine horizontal, thats a lot of weight to try and keep straight up and down...

 

[Northwoodsman]

I just ordered an EKO 40 and purchased (2) used 500 gallon propane tanks. I had planned to weld rings to the bottom of the propane tanks and stand them up vertically but after what has been said I am thinking that if I stacked them one on top of the other that would provide the best stratification possible. Additionally, wouldn't it make sense to come in the bottom on one side of the tank and go out the top at the opposite end of the same tank, thus again maximizing the stratification process? I have yet to pour my concrete foundation/slab and thus I could make it a few inches thicker in the areas that would bear the additional load.

On another note, are there any precautions I need to take before cutting/welding on the tanks (to add the proper size fittings in the best location)? I have power washed them to the best of my ability and according to the local salvage yard where I purchased them from they just take off the valves when they get them, "AIR" them out for a few weeks and use the Oxy/Acet torch and cut them into pieces without any problems?

Thanks,

Brian

 

[Grapenut]

Brian,

I agree, if I go with propane tanks, I think I will stack them also. Putting the inlet and outlet at opposite ends of the top and bottom tank also makes sense to me. Anyone who has done this: how have you built a cradle to stack the tanks?

I've cut propane tanks with a torch. Prior to cutting I've always filled them with water overnight, and then drained. I'm still here, so I guess it works.

Rob

 

[jebatty]

FWIW, my previous setup used three 275 gal tanks in series. They were mounted side by side. Result was each tank would stratify, but great temperature variation between the tanks. Mounting them vertically, one on top of the other, would have solved the multiple stratification problem, but the engineering and logistics of doing this was beyond my willingness to undertake.

I think this would work OK with low temp radiant, but not if you needed 140+ or so water moving into your system, unless the boiler also was operating. If I had to do over again, I would do a parallel setup, equal piping, in an attempt to get equal hot water into and out of each tank, same with the returns.

Same result could be accomplished without going the equal piping route with a manual set balancing valve on each tank. Open or close some for each tank to get approximate same result. Once set, don't need to adjust again.

Since moved to 1000 gal single LP tank mounted horizontal.

 

[Nofossil]

Here's a simple schematic showing on possible way to do it. The number of connections depends on the tank, but the important idea is that you want maximum startification - hottest water at the top.

But it seems like if the boiler isn't running then you're taking cold water off the bottom of the tank and then dumping on the top before it gets sent to the zones. I'm having a heck of a time wrapping my head around this.

In the system I posted, think of it this way:

- There are three circulators, each with a check valve to prevent reverse flow.

- If there's heat demand, the secondary loop circ (on the right) runs, drawing hot water from the top of the tanks, pushing it through the zone(s), and returning it to the bottom of the tanks.

- If either boiler is operating, the circ for that boiler is on, drawing water from the bottom of the tanks, heating it, and returning it to the top of the tanks.

- If a boiler is not operating, there is NO flow through that boiler.

If a boiler is operating AND one or more zones is calling for heat, then a boiler circ and the secondary loop circ will both run. Depending on the relative flow rates, you may get excess hot water from a boiler going into the top of the tanks as well as feeding the secondary loop. You might also get no flow in or out of the tanks.

The idea is that the tanks isolate the control logic. Zone demand simply turns on the secondary circ. An operating boiler simply turns on its own circ.

The only additional logic that you might need is an aquastat that turns on the oil boiler if there is demand and the top of the storage is not hot enough.


Standing tanks on end would probably improve stratification, but I think that legs and fittings are arranged so that horizontal mounting is easier.

 

[twofer]

Thanks nofossil, I definitely get it now.

 

[Nofossil]

I'm glad if this helps. I'll reiterate my standard warning:

This is a simplified drawing. I think it might make a bit more sense in an actual implementation to connect the boiler and secondary loops with a 'T' fitting that also goes to the tank. That way, hot water wouldn't have to pass through the tank on its way to the secondary loop.

I also don't show any recirculation loop on the wood boiler to provide inlet temperature protection for the boiler.

Bottom line - this is for illustrative purposes. Don't mistake this for an actual system design. There are lots of folks here with more experience and knowledge than me when it comes to the details of plumbing design.

 

[deerefanatic]

Primary/Secondary all the way folks...... Solves boiler shock forever....

It cost's more money to get started with (trust me on this one!!) but it is sooo worth it from everything I've read...... I'm building my own boiler so I can have the money to do the primary/secondary stuff.