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Thread: design zones with the underfloor heating controller

  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.

  2. #2
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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?

  3. #3
    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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    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.

  7. #7
    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.

  8. #8
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    Thanks really a lot for the explaination. This helped me really a lot to design the entire system and plan the buying list.

    One more question. The BDR91 connected to the boiler when exactly will turn on/off? As far as I understand, it should turn on when no one of the zones requires to be heated and viceversa turn on when at least one of the zone needs heat. Am I right?

  9. #9
    Automated Home Sr Member philchillbill's Avatar
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    You have a typo that repeats turn on twice instead of mentioning on/off, but yes that's the idea. When you bind a BDR91 to the Evotouch, you can designate it either as a boiler relay or as a zone valve relay. The one you bind as the boiler relay will turn your boiler on/off whenever there is heat demand or when heat demand abates.

    That on/off is important to understand. It means full flame or no flame. If instead you went the OpenTherm route at the boiler with the R8810, the flame can be modulated to a percentage so it could be at e.g. 30% flame instead of just all or nothing. That can greatly reduce gas usage if your boiler supports OpenTherm.

  10. #10
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    Oh yes there is a typo. Sorry.unfortunately my boiler is electric and I do not have opentherm technology so I will simply turn off/on. Again thanks a lot

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