Cast Iron Boiler Buffer Tank Plumbing ?

billyboy

Am thinking that hot water out from cast iron boiler should go into buffer tank bottom.
Return from buffer tank top should go back to boiler input.
This will mix the buffer tank, increasing it's effective capicity, & return hotter water to cast iron boiler.
Yes or No ?

billyboy

Hatterasguy said:

If the boiler SWT is 180F and the DT on the system side is 20F, the SWT on the system side will be 160F and the RWT on the system side will be 140F and the RWT on the boiler side will be 160F.

That's very close to my system design requirements.

Will use Tekmar 256 to control BT temps. based on ODR.

BT is Rheem ST120 has 4x 2" ports, 1 on top & 3 in bottom 1/3

billyboy

Boiler is Burnham ESC5 & can handle 120* return.

BT top port is for system supply.

Any suggestions on using ports better?

billyboy

My mistake, there are only 2x 2" ports in bottom 1/3 of tank.

I will call the 2" port on top of tank #1, then the middle #2 & the bottom #3

All pipes are 1-1/4"

I have welded in a flow diverter plate into a 1-1/4" x 1-1/4" x 2" bullhead tee.

Boiler supply & system return could both go into port #2.

The port #3 could return to boiler.

billyboy

Thanks! Hatterasguy

House is my sons new place, 3,000ft2, in Crested Butte Colorado.
9,500' altitude design -20*F

I want the boiler heating the BT & the system drawing it down to be asynchronous with each other.

With a 20* delta set on the Tekmar 256, & derating boiler 2% each 1,000' boiler should have a minimum burn time of about 13.5 minutes with no system load, much longer -20*F

hot_rod

If you have time this Thursday tune in at noon central time. we will be presenting a 1 hour webinar on Thermal Buffering and Storage. It will be archived also, if you cannot make it by on Thursday.

Idronics 17 will be out next week and the pdf at www.caleffi.com

There are a few different ways to pipe a buffer tank, depending on your system and expectations.

Sounds like you have a typical DHW storage tank with two connections near the bottom, one up top.

A two pipe connection method would accomplish your goal and help stratify the tank. There are a few critical piping details with two pipe.

4 port as Hat mentioned is better if you needed hydraulic separation, you don't, nor does that tank allow it, easily.

hot_rod

But you don't need the buffer if the boiler is matching the load. Once the load circ drops off the boiler loads the tank. Then the boiler will fire again when the tank drops. The tank could be "unloaded" via ODR.

Ideally the boiler circ would be V/S and track the load and the boiler output would modulate also. Lochinvar, paired with a mini Magna can do that, if then load requires that much pump.

The load circ could also be a delta P type, depending on zoning.

No issue with two circs, they would both be sized to the load they are moving. They could be different capacity circs also.

There are a half dozen ways to pipe buffer tanks, this is just another option.

billyboy

The system load would only match the boiler at about -25*F

Also, the difference in this boiler's efficiency between return temperatures of 120* & 160* would be VERY small.

Show me some real data, please.

I don't need for the buffer tank to stratify, as a modcon would.
I have read with purposeful de-stratification a buffer tank would act larger & always return water to boiler that is above condensation.

My system design won't allow for direct return to boiler.

4 zones, 2 medium-high temperature & 2 low temp. slab.

All 4 have independant continuous circulation (Alphas on low)
& have thermostat controlled zone valve injection.

The 2 slab zones use a "dumb" mixing down valve (as Siggy calls them) of about 30* below the Tekmar 256 ODR controlled buffer tank temperature (for the high temp. 2 zones).

1 Taco Viridian pump provides all zone valves with the proper water temperature. It pushes into buffer tank (to suck on the mixing valve)

billyboy

BTW, thanks for the discussion guys.

HR, I have watched lots of your Caleffi youtube vids & respect your expertise.

I will be sure to watch & study your BT webinar. (if you can, please include some cast iron boiler stuff)

PS. After messing with unreliable modcons at high altitude on LP, I won't install another up here.

billyboy

Boiler:

Burnham ESC5, 104,000 BTU Output Cast Iron Gas Boiler (High Altitude) ESC5NI-TH

sealed combustion wall vent & adjustable post-purge

Zman

I am curious as to what models have given you what kind of trouble at altitude? Aside from some harmonic noises I have found Mod/Cons work really well.
I have never seen an atmospheric boiler (with built in power vent) with a 2% altitude deration. I would double check with US boiler, I am of the understanding that that is physically impossible in that type of boiler. That boiler design would normally have a 4% deration.
Carl

billyboy

Install instructions, Page 58
"ESC boilers built for altitudes greater than 4,999 feet above sea level do not need to be re-orificed. The ESC
boiler “H” Model has been certified to operate in atmospheric conditions from 5,000 to 10,000 feet above sea
level. Input is naturally derated approximately 2% per every 1000 feet above sea level.
The ESC boiler is available in two (2) altitude Models: The “S” Model 0 to 4,999 feet above sea level, and the
“H” Model 5,000 to 10,000 feet above sea level."

billyboy

HTP Polaris: fail to fire, frequent igniter replacement, & very noisey fan, junk
WM Ultra 155: fail to fire & mixture problems, HX starting to leak
TT Solo60: fail to fire, foghorn noise on fire when bouncing off the bottom.

billyboy

what's wrong with this?

billyboy

billyboy said:

I have welded in a flow diverter plate into a 1-1/4" x 1-1/4" x 2" bullhead tee.

This would be used in the bottom 2" input port.

billyboy

Boiler would heat BT under control of Tekmar 256.

During that or after, system would pull heat out of BT.

billyboy said:

My system design won't allow for direct return to boiler.

4 zones, 2 medium-high temperature & 2 low temp. slab.

As I said, I can't do direct return from slab zones, too cold for boiler.

billyboy

Yes, Hatt, glad U see it.

billyboy

Long, hot (no boiler condensation), efficient burn times
(13.5 min. up to possibly 60 min.)

Rich_49

billyboy said:

HTP Polaris: fail to fire, frequent igniter replacement, & very noisey fan, junk
WM Ultra 155: fail to fire & mixture problems, HX starting to leak
TT Solo60: fail to fire, foghorn noise on fire when bouncing off the bottom.

American water heater manufactured the Polaris , Not HTP . HTP had the Voyager .

billyboy

Yep, twas a HTP Voyager

billyboy

What about my diagram ?

billyboy

Other experts R welcome to review my plan.

billyboy

I'm a novice, have never done cast iron boiler & buffer tank.

In my house, I have a 4 port Lochinvar Sunsaver 80 gal. BT.
Has a flat plate HX between (TT Solo60 / system) & BT.
BT is also my DHW.

System can run during a boiler burn cycle or after by pulling heat back out through HX.

Works great, usually about 30 minute boiler burns.

billyboy

Here is bullhead tee that I welded in a flow divider so the 2 pumps don't fight each other.

billyboy

I will install a Caleffi Dirtmag on return to boiler, will have 5 ECM pumps, so want water to stay clean.

Harvey Ramer

I don't like the way you show the piping for the tank. With your current piping arrangement, it is physically impossible for the boiler to deliver it's full rated output to the system while the demand is for high temperature. (assuming a normal 180° high limit). It is infact, nothing more than closely spaced tees that are reversed.

hot_rod

billyboy said:

Here is bullhead tee that I welded in a flow divider so the 2 pumps don't fight each other.

One for top and bottom connections?

billyboy

HR, just bottom, as that is where the 2 flows would hit head-to-head, I have read that this would cause pressure pulsations back to pumps.

billyboy

I think that 2 pumps pulling out of a bullhead tee would not be much of a problem?

hot_rod

It's a practice that has always been discouraged, running two flows into one another, on the "run" of a tee. A nipple with two tees or one tee and an elbow has been the common approach.

When we design hydraulic separators the criteria is generally the barrel size is 3 times the diameter of then pipes connected to it. That allows enough "room" so the velocity drops below 1 fps and does not cause flow balance issues. The math is a bit more. complex in the larger sizes, above 2" connections. We have fluid modeling software for that in Italy, similar to what is show in the link below.

It's the same on the return as the supply, really same flow rate same reasoning. I think the diverter would help, in both fittings, like a suction diffuser on large pumps.

There have been attempts to model that behavior, with enough computing power, time, knowledge, and the proper software it is probably doable.

Some "light" reading on the subject here.

http://www.uvm.edu/~pdodds/teaching/courses/2009-08UVM-300/docs/others/2007/vasava2007a.pdf

billyboy

Thanks HR

billyboy

1st: the math is WAY over my head.

2nd: the flows studied are a few cm/s
Hydronics are usually ft/s , much faster, so much higher head loss. But trends may continue ?

For combining flows at tee: fig 6.3 & 6.4 about 3 Pa @ 3cm/s

For dividing flow at tee: fig 6.7 & 6.8 about 2 Pa @ 3cm/s

Sooo, about 50% more head loss combining flows at tee ?

Also no mention of: pulsations due to turbulant clashing water momentums.

hot_rod

my experience with "pumped" bullheaded flows has been un-predictable flows depending on when the circs start and their flow rates.

Maybe just come out with a 2" or larger nipple and tee and ell either direction. I know this method works without a problem.

With your diverter tee, It would be interesting to put flow meters on both branches and watch what happens, as pumps cycle on and off. What are the expected flow rates for the two directions?

billyboy

1 pound force/square inch [psi] = 6894.7572798677575 pascal

billyboy

New plan:

billyboy

8 gpm on both sides, system & boiler.

8 x 22 DT x 500 = 88,000 btu/h

billyboy

Of course system side flow will vary based on load.

hot_rod

Basically what you are trying to do is build a hydraulic separator with that diverter tee concept. You need it on both ends of the tank.

We explain the workings of that separation concept in Idronics 15. Here are a few of the graphics.

When designing that "common space" the goal is to have flow velocities less that 1/2 fps.

We are concerned with two velocities in the design. The velocity through the ports, and the velocity inside the barrel. Both can be tweaked in the design.

Probably if you waded through that paper I linked above you would find about the same final answer.

Some of the seps I see in the magazines make me scratch my head. Short skinny barrels do not a separator make. I wonder if they design and flow test those?

The concern for a homemade fitting is how to know if it is working, or how well. With your potential for two 8 gpm flows, I guess you want at least a 4" center section.

A bullhead fitting with one or the other side flowing is not as bad, with both sides flow, and one possibly varying, I suspect weird things may happen.

RobG

I can definitely see some strange flow patterns going on with that setup. If you have the time to play with it I would love to find out the results.

hot_rod

I started building a clear plastic version, but without all the dimensions, not sure what it would prove?

With this clear P/S fitting I made for this display, you can see how flow goes in two directions as I vary speed of the circs. The QuickSetters indicate the flow rates.

The upstream flow actually hugs the inside wall of the tube in a thin, flat stream.

billyboy

Thanks for input