Boiler circ size effect

icy78

Hello all and wishing a good weekend to you!
So I have a question on the boiler circulation pumps size. I found an install today where the boiler pump had been changed from a TACO 0014 to a B&G NRF 36 which has quite different characteristics.

It seemed to me before I noticed this, that the flow at Point A, sometimes seem to be backwards. I wonder if this is possible with an oversized boiler circulation pump?
To complete the scenario I had pumps 1, 2 , and 3 off and 4 running but I found later that 4 was probably air locked at the RADS.
However point A definitely got warmer and in fact sometimes got very hot. Doesn't happen now that I installed the correct pump , and purged the rads.

I know the pumping layout is wrong but it is what it is for now.

Comments appreciated.

icy78

Here's a quick drawing

STEVEusaPA

Sure. You could have some, most or a lot of backward flow, especially if the pump is oversized. You get total backwards flow between the tees if just the boiler pump is running. I would think if the pump was too strong you may only get backwards flow thru the closely spaced tee, and your other circs may not be moving hardly any water.

icy78

Upside down sorry.

icy78

> @STEVEusaPA said:
> Sure. You could have some, most or a lot of backward flow, especially if the pump is oversized. You get total backwards flow between the tees if just the boiler pump is running. I would think if the pump was too strong you may only get backwards flow thru the closely spaced tee, and your other circs may not be moving hardly any water.


Thanks Steve. I realize there will be backwards flow between the tees. Dependant on the gpm rate at any given time. What I'm wondering is if it could get 6 feet past the CSTees and over power the zone pumps.
It seems that the boiler circ would move entirely in a ccw fashion if there was no zone flow, but given some zone flow, wouldn't water at point A have to be moving left to right? And an equal amount of boiler water also move left towards the seperator.?
BUT, if the boiler circ is oversized, does thst still hold true.
At eg. 15 fthd the nrf 36 is about 22 gpm
At. 15fthd the 0014 is about 12 gpm

(I don't know if this is actual head, no measuring points available. It's just for comparison.)

EBEBRATT-Ed

I guess technically it "shouldn't" move backwards toward A. Possibly with a lot of backward flow between the closely spaced tees some heat is migrating back to A

Zman

What type of boiler is it?
Are there check valves on the zone circulators?
The circulators pumping toward the expansion tank are not helping/

icy78

> @Zman said:
> What type of boiler is it?

Ultra 155

> Are there check valves on the zone circulators?

No unfortunatly

> The circulators pumping toward the expansion tank are not helping/
Agreed

icy78

One thing I wondered, is if with really high velocity back towards the oversized pump, the flow may overshoot and strategy in the pipe. 1.25" cu pipe.

I'd say the nrf-22 are oversized too, especially the one with 50ft of 3/4 and 6ft of 3/4 fin tube .

That one had about 6 delta T, the others about 11 DT. At 160f.

hot_rod

How close together are the closely spaced tees? Is that loop 1-1/4"?

icy78

> @hot rod said:
> How close together are the closely spaced tees? Is that loop 1-1/4"?

The tees are about 14" and yes it is 1.25" pipe.
Hmmm. They're probably too far apart.

Thinking about it last night, I know it over shot the CSTees with no zones on. That was just an experiment tho and not a typical operating senario.

(I'm sure there's ghost flow in the zones anyhow, definitely in one zone .)

DZoro

Need cv's in the zone pumps, possibly also get the boiler t's closer. But the cv's should do the trick.

hot_rod

icy78 said:

> @hot rod said:

> How close together are the closely spaced tees? Is that loop 1-1/4"?



The tees are about 14" and yes it is 1.25" pipe.

Hmmm. They're probably too far apart.



Thinking about it last night, I know it over shot the CSTees with no zones on. That was just an experiment tho and not a typical operating senario.



(I'm sure there's ghost flow in the zones anyhow, definitely in one zone .)

The more spacing (resistance) between the CST the more flow potential into the loop. You start putting that boiler pump in series with the zone pumps. Adding checks in the zone pumps may or may not solve the ghost flow. those checks are usually under .5 psi pop. That large boiler circ may still push flow into the zones.

I'd correct the tee spacing with a close nipple between AND add zone checks. Check the sizing on the zone pumps, they could be oversized even on low setting.

icy78

So Im thinking the reason it flowed back was this:
Call for heat starts zone pump.
Zone is air locked so no flow
Oversized circ pushes some flow back thru returns to supply header and from there it goes wherever it can. Like back thru another loop.

Or: boiler pump seized
Replacement pump is too big and somehow causes trickle flow thru the first zone, witch allows it to airlock.
Now boiler circ is only one running. Boiler cycles on HI limit .
At least 1 other zone satisfies on ghost flow. Others kind of stay warm. Which jives with what home owner feels in the space.
Temperature drops to 7 from mid 30s.
Trickle flow no longer satisfies and a no-heat call is generated.
Boiler circ was changed out 1 week prior. When it got colder they heard a lot of gurggling but didn't call for 2 days.

It seems the zones surely pumped better when the correct boiler circ went back in.

Lousy water quality here I'm guessing. 2 seized circulator in under 1.5 years.

icy78

> @hot rod said:
> > @hot rod said:
>
> > How close together are the closely spaced tees? Is that loop 1-1/4"?
>
>
>
> The tees are about 14" and yes it is 1.25" pipe.
>
> Hmmm. They're probably too far apart.
>
>
>
> Thinking about it last night, I know it over shot the CSTees with no zones on. That was just an experiment tho and not a typical operating senario.
>
>
>
> (I'm sure there's ghost flow in the zones anyhow, definitely in one zone .)
>
> The more spacing (resistance) between the CST the more flow potential into the loop. You start putting that boiler pump in series with the zone pumps. Adding checks in the zone pumps may or may not solve the ghost flow. those checks are usually under .5 psi pop. That large boiler circ may still push flow into the zones.
>
> I'd correct the tee spacing with a close nipple between AND add zone checks. Check the sizing on the zone pumps, they could be oversized even on low setting.

Thanks Bob.
I did install the correct boiler circ. That really helped.
Yes I'd say the zone pumps are grossly over pumping.
It also badly needs a dirt separator.

icy78

@hotrod are you saying that the oversized boiler circ could likely 'expose' the too far spaced CSTees compared to a correctly sized boiler circ?
That would sure seem logical to me and explain what I saw.

icy78

> @icy78 said:
> > @hot rod said:
> > > @hot rod said:
> >
> > > How close together are the closely spaced tees? Is that loop 1-1/4"?
> >
> >
> >
> > The tees are about 14" and yes it is 1.25" pipe.
> >
> > Hmmm. They're probably too far apart.
> >
> >
> >
> > Thinking about it last night, I know it over shot the CSTees with no zones on. That was just an experiment tho and not a typical operating senario.
> >
> >
> >
> > (I'm sure there's ghost flow in the zones anyhow, definitely in one zone .)
> >
> > The more spacing (resistance) between the CST the more flow potential into the loop. You start putting that boiler pump in series with the zone pumps. Adding checks in the zone pumps may or may not solve the ghost flow. those checks are usually under .5 psi pop. That large boiler circ may still push flow into the zones.
> >
> > I'd correct the tee spacing with a close nipple between AND add zone checks. Check the sizing on the zone pumps, they could be oversized even on low setting.
>
> Thanks Bob.
> I did install the correct boiler circ. That really helped.
> Yes I'd say the zone pumps are grossly over pumping.
> It also badly needs a dirt separator.

I will check the CSTees again for distance.
I wrote up check valves .

The pumps are single speed.

Thanks for the input everyone.

icy78

Was thinking about this some more. I'm thinking that during normal operation any one of the pumps, when running, could induce flow thru another zone by the venturi effect at the header. (Except the right hand pump maybe). Am I right about this?
If so, then I would need zone valves to isolate each zone?

Zman

Without check valves on the zones, the zone that is on will pull some water backwards through the zone that is off. You may also be getting some thermal siphoning at times.
A spring check (even the plastic ones that snap into the circ) should solve both issues.

hot_rod

A few other questions, why 160 degrees with a mod con boiler?
Is your design load 135,000, that is probably what that 155,000 is capable of.
6 feet of fin tube on one zone circ, a 3000 BTU/hr design load? That needs an awful small circulator. Can that zone be combined with another zone. I doubt that 155K boiler gets along with that micro zone alone calling

Get all the zone circulators check protected, and flowing close to their actual load, you should solve some problems.

icy78

@Zman said:
> Without check valves on the zones, the zone that is on will pull some water backwards through the zone that is off. You may also be getting some thermal siphoning at times.
> A spring check (even the plastic ones that snap into the circ) should solve both issues.

I don't see how a check will stop venturi type flow tho.?

you guys always assume that I installed this stuff that I get sent out on!

> @hot rod said:
> A few other questions, why 160 degrees with a mod con boiler?

I ran it up to 160 to check TD on the zones. This house has BB into cast iron rads and back to BB type stuff. the reset curve is 100f at 65 and 160 at 10f. Old and very sedentary people.

> Is your design load 135,000, that is probably what that 155,000 is capable of.

Design Load? what? It probably was rule-of-thumbed

> 6 feet of fin tube on one zone circ, a 3000 BTU/hr design load? That needs an awful small circulator. Can that zone be combined with another zone. I doubt that 155K boiler gets along with that micro zone alone calling
>
amen!

> Get all the zone circulators check protected, and flowing close to their actual load, you should solve some problems.

Yes there is a 6 ft base board fintube in a shed. Fed by an nrf-22.
I looked at some curves and thought the taco 003 would be the closest thing.

I still think the checks wont work because I see it a venturi thing.
Am I wrong there?

Now what happens to a 003 gpm when dumping into the same header as an nrf-22 ? I mean the head capability is quite different. Is that a problem? I just spent an hour looking for literature to explain it to me but haven't found anything.

hot_rod

Thumbs down to any venturi effect going on, in my opinion

This issue was put together to bring attention to common piping errors or glitches. Page 59 talks about common P/S mistakes.

https://www.caleffi.com/sites/default/files/file/idronics_19_na.pdf

icy78

> @hot rod said:
> Thumbs down to any venturi effect going on, in my opinion
>
> This issue was put together to bring attention to common piping errors or glitches. Page 59 talks about common P/S mistakes.
>
> https://www.caleffi.com/sites/default/files/file/idronics_19_na.pdf

Excellent! I have only had time to do a basic perusal of that entire #19, but
lots for me to learn there.
Thankyou.