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Grundfos Alpha 2 And Manifold Zoning For Radiant Floor

Building my retirement forever home and...
I would like to use Rahau manifolds with zone valves controlled by zone thermostats on the circuits of the manifold.
Q1: If I use an Alpha 2 and the zone valves close, will the Alpha 2 in Auto Adapt see a no flow or reduced flow condition and speed up to deliver more flow, or is the algorithm slow enough that it sends the pump to idle at 5 watts until a valve(s) open on a call for heat?
Q2:Can the last open zone valve close off against pumping pressure?
Q2: Do I even need a Taco Pump Controller when I can wire the zone valve end switches in parallel to the boiler on a call for heat? At 5 watts each I intend to leave the pumps on all the time during the heating season.

Thanks for any feedback in advance! HVAC guys rock!


  • mattmia2
    mattmia2 Member Posts: 3,668
    edited August 19
    What kind of boiler are you using? You can use the end switches in parallel to control the boiler and the boiler control to control the circulator(if you use zone valves with end switches). A zone controller is a good way to make it neat and organized but there are other ways to do it too.

    One of the constant pressure settings would probably be the way to go for the circulator with zone valves.

    If you are using a mod con boiler you need to maintain the minimum flow through the boiler either through primary-secondary pumping or by making your smallest zone meet the minimum flow or by using some sort of bypass.
  • Retired_guy
    Retired_guy Member Posts: 6
    Thanks for the comments mattmia2. I'm using a NTI TFT85 which has it's own internal pump for the primary loop. The secondary loop will have 3 manifolds, one for each level of the house with a Alpha 2 for each manifold. I just don't know what happens to an Alpha 2 when the last calling zone on a manifold tries to close when the zone is satisfied. I also don't think I need a zone controller with an Alpha 2 left on all the time in the Auto Adapt mode???
  • mattmia2
    mattmia2 Member Posts: 3,668
    I don't see a specific warning in the manual to not deadhead the pump, but I don't think it is intended to be deadheaded, it needs to be switched such that it is only energized when at least one zone is open.
  • Zman
    Zman Member Posts: 6,788
    My experience has been that the "auto adapt" feature does not "adapt" very well on radiant systems. I would keep it simple. Set the circ for constant pressure and turn it off when there is no call for heat. 0 watts is way better than 5 watts.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • Retired_guy
    Retired_guy Member Posts: 6
    Mattmia and Zman agree with both of you, thanks!
    To set the constant pressure selection I'm guessing I would need to open the largest circuit on the zoned manifold and select the lowest setting to match the flow?
  • duffy_4
    duffy_4 Member Posts: 72
    The Nti Tft does not come with an integral pump ,the newer TRX models do,you would still have to pipe it pri/sec. would one alpha 2 be enough for all three manifolds.? I’ve just completed Warmboard job with 3 cross manifolds located thru our 2500 sq ft home using Nti trx 120/120 gal.indirect and one alpha 2 .
  • duffy_4
    duffy_4 Member Posts: 72
    Nti has note about installing isolation relay for ecm pumps due to starting current also.