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Thread: design zones with the underfloor heating controller

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  1. #1
    Automated Home Jr Member
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    Default design zones with the underfloor heating controller

    In my house the first floor is heated with the underfloor heating. The first floor has a small entrance, a big living room and a kitchen. The number of termal actuators in the underfloor heating are 5. I'm going to install the HCE80. I've read that a zone can control max 3 actuators . Is there a way to design and connect the area in the way that I would need to install only a sensor and control the first floor? Unfortunately I saw that one sensor cannot be associated to multiple zone. I'm all ears for suggestions.

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    I was thinking whether it would be possible to connect 4 or more actuators to the same zone by wiring them into a box and then connect the box to the zone 1 of the HCE80. I'm trying to find a workaround to the built-in limitation of max 3 actuators per zone which sounds very limitative. Do you have any idea?

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    Automated Home Sr Member philchillbill's Avatar
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    You should first ask yourself if you want to try and control your hall/livingroom/kitchen separately or if you realistically just treat it all as one big zone if it's open-plan vs separate walled-off rooms. I think this is what you are asking. My ground floor is 103m2 of underfloor heating split into 8 'loops', but my control of it in Evohome is just a BDR91 turning the UFH pump on/off. For me, the whole downstairs is just one zone and I ignore the fact that from a water distribution perspective, it's 8 zones/loops. If that's how you view your situation in real life, there is no value in opening and closing flow to individual loops. Just use a BDR91 to on/off the UFH pump and you're set.

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    Thanks for the exhaustive answer. I would like to treat them an one unique zone. There are no walls that separate the areas. In that case It means I do not need the HCE80? Or I need that to control the pump?

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    Automated Home Sr Member philchillbill's Avatar
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    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.

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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.

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    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.

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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?

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    I see now I understand. But then what/who will decide when my boiler must be on/off? I originally bought the BDR91 to switch on/off the boiler. Also from the manual of the BDR91 it shows to connect to the boiler. I did not know it could be used to control a pump for the UHF. I'm confused here because I come from a Google Nest thermostat that was used along with the Heat link to turn off/on the boiler so I thought since the beginning that the BDR91 would be just a switch for boiler.

  10. #10
    Automated Home Sr Member philchillbill's Avatar
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    You would use 2 separate BDR91s - one for the boiler and one for the UFH pump. The BDR is just a relay. In the case of the boiler, it switches 24V to a relay somewhere inside your boiler. For your UFH pump it would be switching the 230V mains to the pump.

    If your boiler is modern, you may be better off using the Evohome OpenTherm module R8810 instead of the simple on/off BDR at the boiler. But the UFH pump only needs on/off so that will always be a BDR91.
    Last edited by philchillbill; 8th November 2020 at 11:24 AM.

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