MonoFlow & Pump Help

Bostopa

Hi all…back on after a few years.

So, have a B&G monoflo system with convectors…2nd floor get warm not bad first floor better…one loop for 1st & 2nd floor one pump and its a Grundfos 3 speed 15-58 pump.

So, on 2nd floor removed convenctor and installed a B&G Thermoflo Balancer wanted to see what the flow was. And what did I see…sero reading on the Thermoflo. The left side of pipe is getting hot as is the right side. Ok, so maybe the Thermoflo is stuck…removed it went to the facet put water throw it and it's working.

So, is the 15-58 pump just to small a pump for a monoflo system?

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Jamie Hall

Chances are its fine. Monoflow systems are absurdly sensitive to flow restrictions, and the water is probably just saying that that's more restriction than I like and bypassing…

Bostopa

Thanks Jamie,

But that answer doesnt really make a lot of sense to me…the 2nd floor is a bit colder, monoflo's have greater restriction and the gauge should show some kind of flow and shows zero. That does not imply fine to me.

I assume there needs to be a larger pump installed versus the existing 15-58

delcrossv

One pump for both floors? Zoned or all together?

The ones I've seen usually have B&G 100's on them. Low head, but high volume.

LRCCBJ

A monoflo system suffers from a relatively huge pressure drop at every diverter tee. The real question is whether they piped the system with 1" with either 3/4" or 1/2" takeoffs for the rads or whether they piped it in 3/4" with 1/2" takeoffs?

I can tell you from experience that the latter setup will never offer a sufficient flow rate with any of the Taco 00 pumps. I installed a Taco 011 and the system still cannot get below a DT of 27F. The Cv is just too great from the sum of six monoflo tees and the resulting flow rate is too low. The last two rads on the loop have severely diminished performance.

Bostopa

Hi DelcrossV…a few years back it did have a 100 on it…it was suggested to put a smaller 15-58 in there. But I still have the 100 and it was in real good shap…maybe I put that in there as a test. And yes one pump both floors its one loop.

LRCCBJ…so it's 11/4" main line comming off boiler goes down the middle of basement when it reaches farthest wall it branches off left and right to 1" lines. Each of those lines has the diverter tees which are 1" and the convectors are 1/2" going to them. So, each convenctor has a 1" monflo tee and the 1/2" pipe goes right to the convenctor. They are all like that.

Bostopa

Also in looking seems to me the 15-58 & B&G 100 have basically they same pump curve

LRCCBJ

https://forum.heatinghelp.com/discussion/comment/1814777#Comment_1814777

That's a good start. Now check the DT of the system after the first floor rads have fully warmed up. Also, how many diverter T's are you utilizing and what's the total length of the one loop? You could be marginal with the 15-58.

One additional question:

You have two branches with the 1" lines. Do you have an issue with ONE of those two branches versus an issue with BOTH of the two branches for the second floor? Water is going to take the branch of least resistance and this generally means you need a valve to "balance" the two branches if you wish to have equal flow in each.

EdTheHeaterMan

https://forum.heatinghelp.com/discussion/comment/1814750#Comment_1814750

Are you sure that is a zero? It looks to me like it may be at 0.5 GPM or even 0.4 GPM. That would be sending about 4000 to 5000 BTUs to that particular radiator. But the thermoFlow balancer only has increments that go down to 2 GPM. So how can you be sure it is actually at zero, and not at 0.4 GPM?

EdTheHeaterMan

https://forum.heatinghelp.com/discussion/comment/1814922#Comment_1814922

Not Exactly…

Here are both pump curves one over the other so you can see that there are portions at the higher GPM the B&G still has a significant amount of head while the Grundfos drops off. And that may be part of your problem with balance.

The Old B&G 100 has a much flatter curve. So if you are moving over 150,000 BTU of heat from that boiler to the system, you may not have enough GPM. Inversely, If you are only moving 60,000 BTUs you have too much head at high speed on that pump, you may need to drop to medium speed to get the balance you need. But if you are at 100,000 BTUs you are at about the same head and flow rate as the B&G100.

delcrossv

@EdTheHeaterMan Yep.

Swap back to the B&G and see what happens.