Buffer tank install

Rich Swatton_2

Just installed buffer tank with Siggy's new design.
Used a Modcon munchkin MC80 boiler with a 45 gallon buffer tank.
System Runtal panel radiators home run feed and return to manifolds.
Installed exact same system using conventional piping
This piping arrangement uses the full capacity of the tank
Has anyone used this design yet.

hot_rod

I know of a few others in progress, anxious to hear results.

It is a common Euro method, I have no doubt it will perform as expected, and in many cases better than a 4 pipe method.

kcopp

How large should the tapings be? it says short and generous.....1 pipe size bigger?
That design you could use a std electric water heater... huge savings in price.

hot_rod

The goal is to drop the head loss in that section as low as possible. That is the basis of how a hydraulic separator works.

In the Caleffi separators we get down to about a .43, zero is not possible. Rule of thumb for separators is the barrel is 3 times the diameter of the pipe connection. That changes a bit on larger seps.

You could add all the possible GPM flows in that section and use a pipe sizer chart to see what the fps is with different sizes.

Unless you buy a custom tank, 2" is about the largest I have seen. That will dictate the header pipe dimension, pretty much.

I'd caution against a 3/4 connection, it could cause enough pressure drop to eliminate the separation required for it to work.

Zman

Why would you use a mixing valve with one low temp zone and a mod con boiler?

If you run an on/off differential of 20 degree, the 45 gallon tank would store 7,506 BTU's. That's without stratification.

The Munchkin will modulate down to 24,533 BTU/HR.
If the system had no load at all, It would run for about 18 minutes on low fire then turn off.
What else could you ask for?

If you go hotter so that you would need the mixing valve, you stop condensing and lose efficiency.

njtommy

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Rich Swatton_2

Yes I increased the pipe size and didn't use a mixing valve. I have 2 installations one with conventional piping and one with this design. The new design uses the total mass of the tank. Works much better than the conventional way. Flow is equal to system flow.

SWEI

kcopp said:

That design you could use a std electric water heater... huge savings in price.

We're looking at using NOS electric water heaters for this on a couple of projects. Time to look for some 1" NPS dies, methinks.

1" Schedule 40 hits 2 FPS around 5.5 GPM. Some kind of custom swage nipple would be ideal for this.

hot_rod

I bought Swage nipples online, available in various metals. It will ease that transition, but still a small hit for that small diameter connection.

Shown below are a 2 X 1-1/4" resin coated galv, and 1-1/4 X 1" bronze.

The bronze is what were installed in the Munchkins to give you an 1-1/4 connection into the small tube HX ports.

I offer these for installers that want to reduce the 2" ports on a ThermoCon tank with a nice flowing one piece transition.

Had a call from a contractor that had installed some solar tanks with 3/4" water connections in a commercial building.

The inspector wanted number showing that those 3/4 port sizes on the 3 RR piped tanks would not be an issue with DHW building flow.
There is no real practical way to put an exact number to that pressure drop in a 1" section of tank, that I have found?

SWEI

Seems like there might be a small market for a custom piece here -- something with a 1" NPS end, two 1" NPT ports, and perhaps a thermowell.

Eastman

@Rich Swatton

How does the control system work?

hot_rod

SWEI said:

Seems like there might be a small market for a custom piece here -- something with a 1" NPS end, two 1" NPT ports, and perhaps a thermowell.

I've searched for that also. Something like this S&R Tee.

Caleffi Italy has a lot of versions of this brass manifold.

VelvetFoot

Hi. I have a buffer tank, but I am using that with a modulating (to 30%) pellet boiler. It works great, even with my oil boiler which I am using now, given the price of pellets. I can see using a buffer tank with an pellet or even oil boiler to limit the number of starts. I'm not sure that's really needed with a mod/con gas boiler, is it? Is there a real need to extend run times? On another note, my relatively expensive Froling Energy tank has a stainless coil in it for dhw-my experience is that it provides hot water down to pretty cool buffer tank temps.

hot_rod

It really depends on what you are trying to accomplish. One buffer tank sizing guideline is how the smallest load matches to lowest turndown of a modulating heat source.

Pellet boilers almost always benefit from some buffer, in the above case.

Wood and pellet boilers are very high mass and usually high water content, they run best and most efficiently with long burn cycles, a lot of flywheel working for, or against you.

VelvetFoot

Another advantage of the buffer tank, is that it might be able to absorb enough heat so that another zone can turn on and the boiler supply that load. The thing is, with this arrangement (and I have a similar one), as far as I can tell, the buffer tank will not lose any heat while the boiler is supplying the zone-the buffer tank will start up where it left off. It might be better if the buffer tank got depleted somewhat while the boiler was still running, but I wouldn't know how to do it.

The flywheel is also exacerbated by the fact that pellet, and wood (big time) are not on/off, like that gas boiler.

hot_rod

The buffer tank can get depleted when the boiler is running if the load of the system exceeds what the boiler can provide. Maybe a undersized condition like below design water conditions, or a large cold mass, like a concrete radiant slab calls on and over-powers the system.

With two pipe buffer tank arrangements, both can be adding to the system. if the tank has enough energy, and the boiler adds some additional, both add to the system requirement.

Control logic comes into play. If the tank has enough energy to supply the load, deplete that then allow the pellet to light off.

Or when the load is satisfied, allow the boiler to run and load or post purge into the tank.

njtommy

So I would assume a two pipe would be better for fan coils units do to faster hot water response?
my buffer tank just came in the other day. Was going to pipe it 4 pipe till @hot rod 2 pipe is better for faster hot water.

hot_rod

I think two pipe is better all around. For quicker start up, the least amount of interaction with the mass in the tank would be benificial. Short, large diameter nipples and a large reducing Tee to provide a hydro-separator in those fittings.

kcopp

hot rod said:

I bought Swage nipples online, available in various metals. It will ease that transition, but still a small hit for that small diameter connection.

Shown below are a 2 X 1-1/4" resin coated galv, and 1-1/4 X 1" bronze.

The bronze is what were installed in the Munchkins to give you an 1-1/4 connection into the small tube HX ports.

I offer these for installers that want to reduce the 2" ports on a ThermoCon tank with a nice flowing one piece transition.

Had a call from a contractor that had installed some solar tanks with 3/4" water connections in a commercial building.

The inspector wanted number showing that those 3/4 port sizes on the 3 RR piped tanks would not be an issue with DHW building flow.
There is no real practical way to put an exact number to that pressure drop in a 1" section of tank, that I have found?

I suppose a 1" close nipple and a coupling would be ok.

VelvetFoot

This buffer topic is interesting. I would think you'd like to keep the heat inventory in the buffer to a minimum, so as to maximize its excess heat absorption potential. Therefore, modulating down the boiler should be the first thing to occur, before shunting heat to the buffer tank, which should also be at a minimum level to prolong run time.

The way my system is now, when the buffer tank is getting loaded, the boiler is going at 100% (initally). I'm thinking, since there is no hurry, because I want to extend run time, why not start it at 30% to the buffer? I don't think that's possible to control though with my boiler.

I wonder if replacing the B&G Vario Ecocirc boiler circ with the Auto version would help? It could match the flows of the zone pumps to eliminate excess flow to the tank when the zones are on, but I don't know how the pump reacts in the case when both are turned off. Even if the flow is slow, I'm not sure the boiler temp would go up, and the modulation as well.

Perhaps a Thermomix type bypass around the tank so that flow is bypassed until a certain high-ish temperature is reached. The boiler would modulate down with the higher temperature, but might not be that smooth when the valve opens.

This is all a thought experiment though, and I am probably viewing it through the prism of my zone circs system, vs, radiant, although long boiler run times would also be a goal there, I imagine. I'm liking the bypass idea though.

hot_rod

Buffers can serve multiple functions, with most wood fired boilers they are pretty much full speed ahead, they perform best and most efficiently run hot and gasifing.

Ideally the boiler would be sized close to the building load, but there are not a wide selection of sizes. So the buffer can smooth out the on/ off and fire building steps. It also allows that coast period. For the most "coast" you want to load and stratify the tank as much as possible.

If your boiler can modulate down to 30% and still provide the best and highest efficiency, maybe low 80% on gasification boilers, sure you could slowly load.

That could be done nicely with a ∆T circulator, be sure you have boiler return protection of course.

Perhaps the best info on tanks, piping and controls are at this link, a guide that John Siegenthaler put together for NYSERDA. It takes you through all the steps.

http://www.nyserda.ny.gov/-/media/Files/EERP/Renewables/Biomass/biomass-hydronics-training.pdf