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Thread: HR92's and BRD91 Guidance Please

  1. #1
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    Default HR92's and BRD91 Guidance Please

    Hi all,

    Just jumped into the evohome! Ive just moved into a new build which has a 2 zone splan + system.

    I have installed 2 BRD91's that controll the 2 zone vales (for upstairs and downstairs) a Boiler relay and a Hot water Kit. Evohome controller controlling downstairs and a Y87RF controlling upstairs.

    Now my question......

    Can i mix HR92's with the Upstairs BRD91. I have 4 HR92's but 6 rads. So i wanted the Upstairs thermostat to control the 2 rads that do not have HR92's.

    So can i program the evohome controller to open the BRD91 when the different HR92's call for heat?

    EG

    Bedroom 1 calls for heat > opens Upstairs BRD91 (Boiler fires from Boiler relay) > Bedroom 1 reaches setpoint > BRD91 closes (Boiler stops firing)
    Bedroom 2 Calls for heat > opens the same upstairs BRD91(Boiler fires from Boiler relay) > Bedroom 2 reaches setpoint > BRD91 closes (Boiler stops firing)

    So how many zones can a single BDR91 be binded to?

    The theory is there but will the evohome work this way?

    Hope my explanation is clear

    Thanks


    Jay

  2. #2
    Automated Home Legend
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    Default

    No, you can't configure the system to do what you're hoping to.

    You cannot "assign" different HR92 controlled zones to your two S Plan heating zone valves and expect it to open only the "correct" heating zone valve - the system doesn't work that way.

    If you have an S Plan + system (a hot water zone valve and more than one heating zone valve) then you bind all of the heating zone valves to the heating zone valve function in the stored hot water configuration. (NOT to a particular zone)

    This means if any HR92 calls for heat both heating zone valves will be opened, as there isn't a way to tell it which zone valve a given HR92 belongs to. If you have any uncontrolled radiators they will heat up when any other zone calls for heat. In an HR92 installation you are expected to have HR92's on all radiators you want controlled/zoned.

    If you only want a two zone, zone valve controlled system with no HR92's this is possible - you can use the controller and Y87RF as two thermstats for two zones, configure those zones as "zone valve" actuators (eg bind the BDR91's for the zone valves in the zone configuration instead of hot water) and control your existing zone valves. You would need to configure the stored hot water section in the hot water zone valve only mode so that it didn't expect a 3rd "overall" heating zone valve.

    Now the system will control those two zone valves based on those two temperature sensors but of course you will only have two controllable zones.

    However as soon as you add any HR92's into the mix you have to abandon the above scenario, bind your two zone valve relays as heating zone valves in the stored hot water configuration (NOT in the individual zones) and bind HR92's to the zones instead - and you will need an HR92 for every radiator that you want to control and zone. A hybrid approach like you suggest isn't possible.

    If you have HR92's on all radiators you don't even need your heating zone valves anymore - the can be latched open and disconnected, only a hot water zone valve is required then. Or you can leave them in service controlled by the BDR91's bound as heating zone valves in the hot water configuration. It doesn't make a lot of difference either way as they will both always open together when any HR92 calls for heat.

    Hope that makes sense.
    Last edited by DBMandrake; 27th December 2016 at 08:37 AM.

  3. #3
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    Thanks DBmandrake, It is as i thought then.

    I have, as you've suggested abandoned the HR92 approach for the moment and set up 2 zones with a Hot water function. Better get saving for more HR92's!

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