Alpha circ pump "GPM" readings

Dave Carpentier

My secondary circ is a Grundfos Alpha 2, model 15-55F.
I was doing some testing to see what each of my 7 loops would do for max flow.
A given loop might display a 1 or a 2.
But what constitutes a "2" ? Does that trigger at >1.5 or at > 1.9 ?
Is a "1" somewhere between 0.5 and 1.5, or somewhere between 1.0 and 1.9 ?

(Edit- Whups, it's actually an Alpha "2", confusion on my part..)

mattmia2

I doubt that it is that accurate. It is just taking a guess from the power the motor is consuming.

GroundUp

It's an educated guess, at best. If you're talking about radiant loops, a typical 250-300ft loop of 1/2" pex will only flow about .75GPM per loop on the top end with an Alpha 15-55. If 7 are running together, closer to .5 GPM. Just disregard the GPM reading on the circ

Dave Carpentier

Ah. I wasnt sure if it was an actual tach on the pump but that would imply no bypassing. A guesstimate would make sense. I get a 1 or 2 gpm on each loop, shortest is 60ft, longest is 400ft. If I open all loops, it shows 6 gpm.
When we redo the boiler piping, I would have the opportunity to install temperature or flow gauges on each loop. Do people bother with that ? For the last 20 years, I just flow-restricted the supply side zone valves (no actuators, just valves.. the actuators are on the return header) to try and 'balance' the zones by feel.
I think I saw a chart somewhere about how many 1/4 turns from closed on a manual zone valve for matching differing lengths of wirsbo.

mattmia2

Is it heating evenly? Flow meters are expensive. If you can balance it without them and the boiler is happy, no need to spend the money unless you really want to know.

Dave Carpentier

It was pretty decent balance. Like a dummy though, I reset them all while I did my tests yesterday. I should have noted the number of turns from closed.
In addition to basic flow balancing to allow for concurrent zone calls, I was thinking of how the flow speeds may affect my return temperatures now that Im moving into a modcon with a buffer tank.
I guess I dont need fancy flow or temp meters, I can just shoot the pipes with a thermal gun.

hot_rod

Slower gpm flow in the loops will lower the return temperature and increase  mod con efficiency, especially with a two pipe buffer.

However tighter delta T, higher flow makes for a more consistent flow temperature from loop beginning to end, 10-15 is not uncommon 

So you have a choice to make. Since they are easily adjusted, play around and find the best operating condition. Next winter when you have good  load conditions.

I have measured actual flow rates and have found gpm readouts on ECM circs to be as much as 80% off, under some conditions 

ScottSecor

Just for reference i have an Alpha 2 in my house that takes care of the four small hwbb zones.  The displayed gpm is pretty close to calculated flow.  The circ is only moving 4gpm (in auto adapt mode) during design conditions.  For a few days a year, I might adjust the speed to compensate for the added demand.  When only one zone is calling,  the pump display typically reads 0/1gpm and 7 watts.  Smallest hwbb zone requires .8gpm and largest requires 1.7gpm at design temp.

Dave Carpentier

hot_rod said:

Slower gpm flow in the loops will lower the return temperature and increase  mod con efficiency, especially with a two pipe buffer.

However tighter delta T, higher flow makes for a more consistent flow temperature from loop beginning to end, 10-15 is not uncommon 

That's my main flow design fault with that attached garage vs location of my utility room. The garage loop travels 15ft thru an entrance foyer (not an issue - front door and stairwell open to the upper floor) and 10ft thru a bedroom (an issue - occupant complains the room overheats during very cold days). On cold days, more zones are open and of course that garage loop slows even more, causing more heat into the passed-by rooms.

So, if I cant depend on the Alpha to give me an existing flow reading for the garage (ie, I have no idea what Im actually flowing currently) , and considering the problem, would the solution be to just put the garage on it's own fixed speed circ to keep the flow rate higher ? Design heat load is about 27k, but we do bring frozen vehicles in there a couple of times a year for repairing (not a "parking" garage) so I should probably look a bit higher. I do have a spare (20 years of service) Grundfos UPS 15-42 that can do 15ft head at 1gpm but caps out at 15.5ft.

hot_rod

Ideally you would buy 
 a circulator capable of flowing all zones and loops at the flow you need on design day. That would involve some balance valves it sounds like in your case. You could plot a system curve and lay it over the pump curve to see the Op operating point
In the bedroom could you put a throw rug over the area that over heats? A thick one would all but stop the heat output in that area.

Balancing valves are designed for exactly what you are trying to accomplish. If you know the exact flow required, buy a PIC, pressure independent valve, they work well with variable  speed delta p circs

Dave Carpentier

Insulation on top of the floor is a great idea. As I recall, the pipes were just inboard of the interior wall. Maybe even fab a custom bookcase with insulation below the bottom shelf.

Those PIC valves look cool, a set-and-forget thing. I'll probably just try to re-trim my supply side zone valves to save a few bucks, but I'll keep it in mind that they're out there.

Dave Carpentier

I think Ive been thinking wrong about my pump and how I was balancing my zones.
I run that Alpha2 (I mistakenly said it was an Alpha1 in my first post) in the max constant-pressure mode, which appears to be 12ft.
If I run the garage loop only, it says 25w. If I extrapolate that up to the curve, it's about 0.7gpm.
Am I correct in thinking that the pump will continue to provide 12ft of head (and my garage will continue to flow 0.7) as long as I dont exceed the endpoint of the constant pressure line (at about 43w or 6gpm) ?
Up to this point, I had the zones balanced based on my old constant-speed pump, so I had them restricted to allow the garage to have more flow on a multi-zone call.
Im thinking next mid-winter, I would then tweak the balancing based on zone return water temps ?