Grundfos alpha

NRT_Rob

anyone else having problems getting the alpha to display charted flow rates under conditions that should allow for it?



I have one here in my shop. when I open up my 36 one hundred foot loops, I should be able to peg the pump at max flow for each setting. Instead I can't even get it to report more than 7-8 GPM.



be curious to know if anyone else is seeing anything like that.

Eastman

Is there a

check valve?

heatpro02920

Did you try it

in fixed high?  Do you have more than 10 feet of head? I use them on primary loops all the time and they have no problems ramping up there...

NRT_Rob

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yes, we've tried fixed high. with all the loops I can find twisted wide open it's topping out at 7 GPM. I have something like 45 one hundred foot loops of 1/2" pipe, in six manifolds all with 1" copper feeds. I should be double that flow... easily.



some of the loops may be airbound... 2nd floor radiant ceiling that's been shut off for quite awhile. but still. 36 solidly operating loops... and flow meter readings not agreeing with the alpha. I've seen THAT before, but the alpha was the one that was right in that case.

heatpro02920

Hmmm...

Take another alpha off the shelf and try it, if they both say 7 there must somehow be around 10ft of head in the system....  Do you have a flow meter?  on fixed high these things scream, how many watts does it read, I believe on fixed high the alpha in my basement reads 42 watts... and pumps around 15 gpm

NRT_Rob

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43 watts. flow meters on every loop (but not necessarily extremely accurate ones).



we'll switch it out tomorrow and see if it's the pump... can't see where we would get 10 feet of head with 7 GPM here at all. that's barely 1 GPM per manifold...

heatpro02920

weird

I would try another pump, 7 gpm and 43 watts is way off, I will check mine later and see what it reads, but If I remember correctly it is up around 15 when its above 40 watts...  Mine is just on the primary loop of a solo 175, but I know when I install alphas on hydro systems I use the auto adapt and they are always around 8 watts and 3 gpm, we did one on a 1 1/4 venturi system and I was curious to see where it auto adapted to, it ended up around 30 watts and 7gpm... 

I would try another one, what are the flow meters addding up to?

NRT_Rob

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we use lots of these. this is odd. I would never use autoadapt though.. hate that setting! too unpredictable.



flow meters are way over what the pump is reporting... I've got about 6 GPM just on one manifold on the flow meters here... about what I would expect. I would expect the constant pressure modes to be maxing out on their max flow and the fixed speed modes to likewise top out their curves here. 6 sets of one inch feeds with nothing but one hundred foot half inch loops on it....



we'll see if the switch does it in the morning. will report back.

CMadatMe

Rob, What Is

Your delta-t across the loops and what water temp are you running? 100' loop of 1/2" Pex has a head loss of .2 @ 120 degree water temp. That's your 7gpm/36 loops...

NRT_Rob

hmm.

we could crank up the heat source and check for a DT for sanity. no load and no running heat source today... had a client with this issue and tested on our system and got this result...

NRT_Rob

mystery solved

we did have a zone valve in line. It has enough Cv that it shouldn't be a problem, however we have it in "manual open" mode which actually isn't open quite as much as "really open". when I bypassed the zone valve flow shot up to max.



pump is good. injection zone valves, not so much.