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Thread: design zones with the underfloor heating controller

  1. #21
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    Quote Originally Posted by philchillbill View Post
    To control the pump, all you need is a BDR91. No need for the HCE80. You can bind that BDR91 as a zone controller to the Evotouch and when there is heat demand for the zone it will simply turn the UFH pump on to add heat to the circulating water in the floor. The Evotouch can act as the temperature sensor for the UFH zone.
    Hi
    This is exactly what I want to do. When you say add the BDR91 as a zone controller, do you mean add it in the same way as you would add a HR91/92 into a zone, but then select the Evotouch (or other wireless roomstat) as the temperature sensor?

    Will that then use the new BDR91 to switch on the UFH pump, but also call the existing BDR91 connected to the boiler in order to send hot water into the UFH?

    At times I want the UFH to be off. Would the pump not running keep hot water from entering the loop, or could I use a spare honeywell motorized valve and connect that to the new BDR91 also? That way the motorised valve and the pump would both be run when the new BDR91 is switched on, and remain shut to heated water when it is off.

  2. #22
    Automated Home Sr Member philchillbill's Avatar
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    Quote Originally Posted by Ansaar View Post
    Hi
    This is exactly what I want to do. When you say add the BDR91 as a zone controller, do you mean add it in the same way as you would add a HR91/92 into a zone, but then select the Evotouch (or other wireless roomstat) as the temperature sensor?
    Yes, that's correct.

    Will that then use the new BDR91 to switch on the UFH pump, but also call the existing BDR91 connected to the boiler in order to send hot water into the UFH?
    Yes, the boiler-BDR91 responds to heat demand, as always.

    At times I want the UFH to be off. Would the pump not running keep hot water from entering the loop, or could I use a spare honeywell motorized valve and connect that to the new BDR91 also? That way the motorised valve and the pump would both be run when the new BDR91 is switched on, and remain shut to heated water when it is off.
    You should not need the motorised valve. The UFH manifold is designed in such a way that water circulating as a result of the boiler-pump being active will not circulate in the floor unless the UFH pump is on. The top bar on the manifold 'short circuits' the UFH circulation in this case.

  3. #23
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    Fantastic!. thankyou for your very quick response. My evotouch controller is not being used as a temp sensor in any of the radiator zones, so its free. I guess all I need to buy is another BDR91.

    Im going to leave two radiators in my large UFH lounge. This is to get the room temp up to speed quicker in the colder mornings. I know theres an issue with the rads getting the room temp first, and the ufh not having time to even warm up the screed. My plan is to set the two radiators as a zone, but make the set point around 2 or 3 degrees below optimal. The UFH zone will have the optimal setting. So the radiators will get the room out of freezing temps, but leave a little temp for the UFH to keep calling for heat until its optimal.

    Given the evohome is a learning system, do you predict any complications with it thinking my UFH zone is super quick or too efficient at heating the room?

  4. #24
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    The only drawback you need to be aware of is that a BDR91 performs TPI, regardless of how it is used. This means that it will turn the UFH on/off more frequently than is necessary.

  5. #25
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    Why is that a drawback? Isnt TPI and evohomes logic designed to try and make sure the room doesnt overshoot the desired temp or get too cold? The old thermostats i had simply were a binary on and off, and either made the house too hot or too cold.

    My boiler is a Worcester CDi (around 9 years old). its not opentherm, but it does regulate the rate at which it heats the water quite well (presumably sensing the return temp). Ive set the max temp to 65c, which i believe is the most efficient for a condensing boiler.

    all in all, im winning plenty from the days my one analogue thermostat heating the entire house based on the hall temperature

  6. #26
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    although one concern i have is that the UFH BDR91 turns off (before the optimal temp is reached) anticipating it will get there. that however turns off the circulating pump in the UFH, in which case the whole circulating/mixing of hot water stops. That will make the ufh not reach the optimal temps.

    Is there a UFH pump that continues to operate for a few minutes after the instruction to stop is received? or is that a standard for all pumps (regardless of them being used in UFH or not?)
    Last edited by Ansaar; 23rd December 2020 at 09:52 PM.

  7. #27
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    Bruce, I just found your post from 2014 about literally the above.

    Did you find a solution to your UFH pump switching off when the BDR91 stops calling?

    Also, you mentioned using proportional pressure in the pump. I thought "constant differential pressure" is recommended for UFH systems. Im looking at the DAB Evosta 3 as an option.

  8. #28
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    I guess you can install a pump overrun timer on your UFH pump.

  9. #29
    Automated Home Sr Member philchillbill's Avatar
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    Won't the warm floor continue to heat the room even when the circulation stops? It represents a gigantic mass containing substantial heat (vs a small mass at a higher temperature = a radiator). Sure it won't perform any miracles but I'd wager leaving the pump on for 'a few more minutes' wont really make that much difference in real life.

  10. #30
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    True, and I'm hoping I wont need an overrun on the UFH pump. But my electrician buddy says he knows how to do it easily enough. So if I find it to be a problem and need to wire in 5 mins overrun or so, good to know it can be done.

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