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Thread: EvoHome Fan Control

  1. #1
    Automated Home Lurker
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    Jul 2021
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    Default EvoHome Fan Control

    Hi all,

    I had this bright idea to control the temperature under the stairs with an extractor fan, I have an evohome controller now with the latest firmware so it has the cooling option, I purchased a DT90E thermostat that came with a BDR91 relay box, everything seems to talk and bind properly, I set the zone actuator type to electric (I tried mixed, it fires the boiler up even on cooling)I set up a seperate zone on the evohome for the fan, I set this zone to cool, and set the temperature I would like it to cool to, which I thought would turn the fan off when it reached it, I must have missed something, the fan just keeps on going no matter what the temperature, I also set a schedule, that gets ignored as well, I did manage to get the fan to turn off once by matching the actual temp to the desired temp, but that seems to get ignored now for some reason.

    Any guidance would be great.

    Cheers

    Gary

  2. #2
    Automated Home Legend
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    Jul 2014
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    Default

    I thought only the BDR91T can deal with the cooling reverse demand and the BDR91 can only deal with heat demand.

  3. #3
    Automated Home Lurker
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    Jul 2021
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    Default

    That's right the BDR91T does heat and cooling demand, I just needed the thermostat to kick the fan in when it was in cool mode, didn't think the BDR91T was required, was relying on the Evohome to just send the signal at the correct temp, i.e to turn off when a low temp was reached, rather than a high one.
    This evening I have taken the Evohome out the loop, and set the DT90E into cool mode, set a low temp, and it works fine, cools the room down to the set temperature, so there must be a setting a miss on the Evohome, will keep on trying.

    Cheers

  4. #4
    Automated Home Jr Member
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    May 2021
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    Hmm I was just wondering if you could use a normal BRD91 but wire the fan using the normally closed contacts instead of the normally open (A & C).

    So lets say the set point is 20 degrees, but it's 25 degrees under the stairs, that means the BDR91 will not be energised (green LED is off), so using the normally closed contacts the fan will be on. When the temp drops to 19.5 degrees, the BDR is energised, green LED comes on but the normally closed contact goes open circuit and the fan stops. As the temp starts to rise again, when it gets to 20.5 degrees, the BDR switches off, green LED goes off, contact becomes normally closed and fan switches on.

    Would this do what you want?

  5. #5
    Automated Home Lurker
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    Cheers for that, I am pretty sure that is how the BDR91 is wired now, using A & B, will double check tonight.
    I mentioned earlier, without the Evohome controlling the DT90E stat, it works fine, so assuming the wiring is ok, I have a feeling it is to do with the heat / cool temp settings on the evohome when the zone becomes set to cool only.

    Gary

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