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Alpha Pumps Don't Work?

RobinInCali Member Posts: 33
I have a radiant floor system with two zones. Zone #1 is 1800 square feet of staple up joist ex, and Zone #2 is 900 square feet of slab on grade (a basement). I was using 2 Grundfos 15-58 3 speed pumps, Zone #1 set on the fastest speed, and Zone #2 set on the slowest speed. The house heated fine and I was happy enough with this system. No problems.

(Each pump is installed on a 3/4" copper circuit running to Pex, and each zone came off a 1.25" copper manifold, feeding back into a second manifold the same way. The zones are equally spaced on the outgoing side and the incoming side.)

When one of the pumps started making loud noises, I thought about putting in Zone Valves to save on electricity, but instead, I bought into the idea that multiple circuit pumps were a better idea. Since I'd had good luck with that already, replaced both Zones with Alpha pumps, thinking I'd still save electricity.

But the Alpha pumps don't seem to move the water, and therefore, do not heat the house when they're set on Auto. If I set them on Auto, my house stays chilly at best. Sure, I can heat the house with the Zone #1 is set on high speed, and the Zone #2 is set on middle speed, but the "Auto Adapt" setting on the Alpha just doesn't circulate the water. And even when the speeds are set higher, I am not getting the same performance I got with the 15-58 pumps.

The read-outs on manual aren't any higher than 3 GPM, and on auto adapt, it's like 0-1gpm. When only one zone is on, you can get the pumps up to 5 GPM at the high speed.

I know by the specs that the old 15-58 pumps moved water much faster, at up to 17 GPM. They also gobbled up electricity.

I tossed out the old loud 15-58 pump, and gave away the other one. So should I go buy some new 15-58s? I need my warm house back.

I cannot believe these Alphas don't work, and I can't seem to find the answer anywhere else. Any ideas? I wonder what the issue really is, here.


  • Harvey Ramer
    Harvey Ramer Member Posts: 2,221
    Auto Adapt is not the right setting for your application. It is designed for TRV controlled systems. Set your pumps to the lowest fixed speed that heats the house adequately. You will still save on electricity.
  • hot_rod
    hot_rod Member Posts: 16,317
    yep, chose the speed that heats the zone, it will still consume 1/2 or less power than the 15-58.

    The Auto Adapt is for a system that is zones with valves or TRVs.

    Don't trust the gpm readout, set the speed to the setting that moves sufficient flow.

    Curious as to why the 15-58 were a problem, they run almost silent when purged properly and running on the curve.

    6 gpm is about all you want to flow thru 3/4" copper tube, I doubt you were moving 15 gpm with the 15-58?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • RobinInCali
    RobinInCali Member Posts: 33
    edited May 2015
    Thanks for the comments. I do have to bring in that old chestnut of an issue--pump speed and flow--do you all think that maybe I need a stronger pump? The 15-58 on high speed worked better than this Alpha on high speed, so would an even stronger pump like a 26-99 heat the space better? In other words, if I move more hot water, faster, with more head, would the floor put out more heat?

    Sorry for the possibility that these are dumb questions. Thanks for entertaining me.

    (And btw, the 15-58 "went" because of bad bearings or something; it wasn't a problem other than that. It sure seemed to heat the space quicker.)
  • Zman
    Zman Member Posts: 7,330
    The Alpha has an identical curve to the 15-58..When selecting the fixed speed settings you should not see a change in performance, just a savings in electricity.
    I agree that auto adapt does not work well for radiant. Either the constant speed or the constant pressure setting will work better.
    Keep in mind that, unless your system was carefully designed, when the concrete slab is cold, the upstairs zone will have trouble keeping up.
    Another possibility is that some air was introduced when the circulators where swapped. Air trapped in some of the loops would also account for the reduced performance.
    If you have the means to measure the supply and return temps on the loops, this will help diagnose.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • RobinInCali
    RobinInCali Member Posts: 33
    May I now ask... Since the whole idea was to save electricity anyway, should I replace the Alpha pumps with zone valves, then use one Alpha as the primary pump, and the other as the secondary pump?

    Carl, I have a temperature differential of 15-18 degrees, which is more than the 15-58 was--it was about 10.

    As for air, I thought I did a pretty good job of purging the air, but still was thinking of putting on an additional Spirovent. I've read they work great and I have a couple leftover from an old job.

    I also changed the expansion tank--forgot to mention that. I charged it and it appears to be working. Perhaps that could be a factor?

    To answer the other issue raised, the concrete slab has always been the EZ part to keep warm. That zone usually runs only two hours a day to keep a constant toasty temperature of around 68-69. The insulation is excellent. The joist portion is more of a pig, I have to run 4-6 hours in the morning, and 4-6 hours in the evening.
  • Paul48
    Paul48 Member Posts: 4,469
    Can you post a picture of the pump installation? It's rare for the bearings to fail.
  • Steve Thompson (Taco)
    Steve Thompson (Taco) Member Posts: 200
    If you intend on zoning with circs an ECM circ will actually draw more electricity than a zone valve (our Zone Sentry is 4 watts) - but less than a standard old style "AC" circ.

    I think the bigger picture is how to modulate the flow through a zone to potentially save electricity and increase system efficiency/comfort vs a constant or improperly controlled ECM circ.

    As delta P only reacts to changes in "push back" on the impeller the only proper solution is delta T that will react on the zone load or zone temperature differential. There is no impeller push back change in a zone circ application so, at least to me, a delta P control strategy makes little sense.

    Please remember, this is an unbiased viewpoint as we now have both delta T and delta P.
    Rich_49Bob Bona_4