Grudfos 10 gallons per min ?

[ejhills]

I have a Grundfos AF15-55f and I can't seem to get it to pump any faster than 8 gpm when my boiler spec is asking for 10-12.

Am I obsessing over the discrepancy. They spec sheet says that it can do it.
What factors are keeping this pump from doing operating faster?

Ed

 

[maple1]

Head?

 

[ejhills]

it is pushing to the bottom of the tank.
the tank is bottom fed so it is fed at by 1" at 30 psi.
the boiler supply goes up 3 feet, over 6 feet, then down 5 feet to the pump, and into the tank.
there is a reduction to 3/4" into the tank.
at the top of the take the 3/4" pressure is 40 psi
before it returns to 1" and back to the boiler.

 

[BoiledOver]

Sounds like a low head loop, shouldn't have issues. The circ is an alpha, yes? It has 3 pressure settings, 3 speed settings and automatic, yes? You have 7 choices, what are you using?

 

[ejhills]

Sounds like a low head loop, shouldn't have issues. The circ is an alpha, yes? It has 3 pressure settings, 3 speed settings and automatic, yes? You have 7 choices, what are you using?

Yes its an alfa, Im using #3.
But it only bounces between 6-9 gpm...
Low head loop... time to google...

 

[maple1]

#3 - on constant pressure side or constant speed side?

The digital readout has been noted on here as not necessarily being really accurate.

 

[maple1]

Also, why is your tank bottom fed?

 

[ejhills]

#3 - on constant pressure side or constant speed side?

The digital readout has been noted on here as not necessarily being really accurate.

the one of the left....

 

[ejhills]

Also, why is your tank bottom fed?

Heat Rises.....
The radiators also pull from the top and return to the bottom,
And the boiler supplies the bottom and returns from the top.

Is there a different case to be made for regarding stratifying the tanks in this fashion?
The water is always moving in the same direction.
So far the delta on both boiler and tanks is never more than 20.
155-180 at the most, before the fire starts back up again.

 

[maple1]

Heat Rises.....
The radiators also pull from the top and return to the bottom,
And the boiler supplies the bottom and returns from the top.

Is there a different case to be made for regarding stratifying the tanks in this fashion?
The water is always moving in the same direction.
So far the delta on both boiler and tanks is never more than 20.
155-180 at the most, before the fire starts back up again.

Yes, I think muchly so.

Most all literature I have seen (and users posting here), you feed hot to the top & pull cold from the bottom. That way the hottest is always at the top for your loads to use, and maybe more importantly the boiler is always getting fed the coolest water. Which ensures best possible boiler efficiency. (You'd need to mix to ensure boiler sees no lower than 140 - 'boiler return temperature protection'). Can't recall reading or hearing the opposite anywhere. Until now. That also sets up & preserves stratification.

I just started a fire, first one since Friday. My temps are 126 top/109 bottom. Those are at 3/4 & 1/4 from the top. I don't have a read on the temp at the very top, but the house was maintaining when we got up this morning. So was hotter than that, but certainly nearly depleted.

In a straight circulating application - with basically a non-varying load, like a boiler to storage situation - I don't think there is much advantage to using an Alpha. Well, I guess it would use a bit less electricity.

What boiler to you have? 10gpm is kind of on the high side for moving to storage.

 

[BoiledOver]

Yes its an alfa, Im using #3.
But it only bounces between 6-9 gpm...
Low head loop... time to google...

Low head loop-->Your boiler to storage loop sounds like there will not be much head built into. Unless of course you have long runs and many, many fittings, then the head will rise. As @maple1 questioned, which way are you going with the circulator, pressure or speed?

I have a Grundfos AF15-55f and I can't seem to get it to pump any faster than 8 gpm when my boiler spec is asking for 10-12.

During a storage recharge, the optimum flow rate will vary throughout the burn history. In my case, I begin on low speed which gives the loop just under 3 gpm. At the very end it needs all the high speed (12-1/2 gpm) and could use a bit more. My gpm numbers will likely be different than other users systems due to pipe length, number of fittings and circulator model, mine is Grundfos 15-58 3-speed. More pipe length and more fittings equals more head. More head means less flow. As far as the boiler specs asking for 10-12 gpm, I am not sure how that is determined, whether at optimum burn or an average.

Yes, I think muchly so.

Most all literature I have seen (and users posting here), you feed hot to the top & pull cold from the bottom. That way the hottest is always at the top for your loads to use, and maybe more importantly the boiler is always getting fed the coolest water. Which ensures best possible boiler efficiency. (You'd need to mix to ensure boiler sees no lower than 140 - 'boiler return temperature protection'). Can't recall reading or hearing the opposite anywhere. Until now. That also sets up & preserves stratification.

I just started a fire, first one since Friday. My temps are 126 top/109 bottom. Those are at 3/4 & 1/4 from the top. I don't have a read on the temp at the very top, but the house was maintaining when we got up this morning. So was hotter than that, but certainly nearly depleted.

In a straight circulating application - with basically a non-varying load, like a boiler to storage situation - I don't think there is much advantage to using an Alpha. Well, I guess it would use a bit less electricity.

What boiler to you have? 10gpm is kind of on the high side for moving to storage.

You are spot on when you say that heat rises and it does seem logical to plumb into the bottom of storage from the boiler. However there is more to the thermodynamics of a circulated liquid heating system. @maple1 is correct about the boiler feeding storage at the top. Two things about that, 1) Less mixing and better stratification in the storage vessel equals higher efficiency on the storage end. 2) Cooler temps going into the boiler allows higher boiler delta temp, higher efficiency at the boiler side. Keep in mind the 140°F minimum going into the boiler to prevent condensation within the burn chambers and flue pipe. From experience we know that 140°F cannot be achieved in the beginning of a cold start.

The boiler delta temps will change from circulator speeds and burn rate. A full on burn with incoming water temps of 160°F will get a very high delta (maybe near 30°) on low gpm. Bump the gpm up to high and the delta might drop to 20° or so. It seems that some of the lambda controlled systems can ramp circ speeds up and down depending on various inputs.

Wondering what boiler you are running and what is the controller.

 

[salecker]

Yup you need to re plumb your system.
You are working against the laws of thermodynamics which will not change, so you may as well unless you like to beat your head against a wall repeatably.

Heat Rises.....
The radiators also pull from the top and return to the bottom,
And the boiler supplies the bottom and returns from the top.

Is there a different case to be made for regarding stratifying the tanks in this fashion?
The water is always moving in the same direction.
So far the delta on both boiler and tanks is never more than 20.
155-180 at the most, before the fire starts back up again.

So if you want to see whats wrong with your system...
Heat rises to the top of your tanks where you are pulling your return water for the boiler from.Radiators return to the bottom is right because the cold water is in the bottom of the tank,where in your case it never gets to the boiler without a bunch of work.