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Thread: Keeping the Zone Valve BDR91 open longer for UFH

  1. #1
    Automated Home Legend
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    Jul 2014
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    Default Keeping the Zone Valve BDR91 open longer for UFH

    I have my UFH configured as a Zone Valve and I use a BDR91 as my actuator. The BDR91 opens a motorised zone valve, which in turn starts the UFH pump.
    I don't have a Boiler Relay because I use OpenTherm. I still have no idea if the System Parameters will affect my BDR91 Zone Valve or that is only meant for the Boiler Relay.
    It would have been better if I could switch off the TPI for this BDR91, but I can't.
    Hence I would like to keep that BDR91 switched ON for as long as possible each time it is switched on by TPI. The reason being, my UFH pump is an adaptive pump and ramps up slowly on power on. So each time the TPI cycle kicks in, it goes through its start up routine.
    Cycle Rate is 3 per hour with a Min On Time of 1 min. What do I set this to, to keep the BDR91 ON for longer?

  2. #2
    Automated Home Sr Member
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    Sep 2018
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    Default

    I used to have a setup like yours but upgraded to an HM80 mixer valve, which is far superior for single zones, eliminating the overshoots I saw with the BDR91. It doesn’t use TPI but learns the appropriate flow temperature setting.

    The system parameter for Cycle Rate does impact BDR91 TPI behaviour but if I recall correctly Min On Time does not.

    With my system I initially had a Cycle Rate of 3. Although this means a longer ON time it also of course results in a longer OFF time too at partial demand. I found a Cycle Rate of 6 to perform better.

    My pump can be set to adaptive but the manufacturer’s recommendation for UFH is constant speed mode.

  3. #3
    Automated Home Legend
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    My UFH uses a GRUNDFOS UPM3 AUTO L and just reading the manual it appears that for almost 5 years I've not realised that my installer has forgotten to change the default setting of the pump from Proportinate Pressure to Constant Pressure! I seem to have 3 options of Constant pressure curves. Any idea how to decide which one I should use?

  4. #4
    Automated Home Legend
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    Default

    Also, am I to use Constant Pressure or Constant Speed in an UFH installation?

  5. #5
    Automated Home Sr Member
    Join Date
    Sep 2018
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    64

    Default

    Constant Pressure, probably with the minimum curve setting/speed required to achieve your designed manifold flow rate.

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