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Thread: Evohome hybrid system possible?

  1. #11
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    Default Evohome hybrid

    Quote Originally Posted by bruce_miranda View Post
    There is nothing stopping you from having both a timer and/or the Evohome both triggering the boiler. There was a time when I was using a traditional timer to determine the house heating time and then using Evohome to just control the smart TRVs within that time slot. The down side with this is that its not then a smart TRV, in that it can't turn on the boiler. But you can have this setup running in tandem, so both Evohome and the timer can fire the boiler.

    The BDR91 can also be wired to allow the Evohome or a timer to fire the boiler.
    Sorry to resurrect an old post, but I'm just about to invest in evohome. To get the hybrid functionality that's mentioned above, I'm assuming you'd use a BDR91 with the NC utilised, So common would go to the boiler NC would go to the timer and NO would be the demand live from evo home.

    Or is there another way ??????

    Thanks

    Paul

  2. #12
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    What is the timer controlling, that Evohome isnt?
    It also depends if your boiler needs a 230V Live feed to fire or uses volt free contacts.
    You could just terminate the timer output and the Evohome's BDR91 output at the boiler. Or as you say, loop the timer through the BDR91, making use of the NC terminal in the BDR91 for firing the boiler via the timer and then the NO is used when Evohome needs to fire it up.

  3. #13
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    Thanks for the prompt reply, to fess up its not actually a timer I'm using, but I thought it may be the simplest way to ask the question.

    The boiler is a WB greenstar 24i system boiler that uses a 230v live to fire.

    What I currently have is downstairs a 8 zone UFH system that has its own wiring centre, so a call for heat is a single live feed to the boiler, upstairs are rad's, it was set up by a guy 'in a rush' as a y plan, so the upstairs rads only come on when the downstairs UFH system calls for heat.

    I didn't want to splash the cash to go wireless on the UFH system and change 8 stats and a wiring centre, so thought if I put the HR92's on the rads upstairs and find a way to use the UFH call for heat to fire the boiler, it would save me about 800 ( the cost for wireless stats and UFH centre. It wont give me wireless control downstairs, but it would be better than having to strip out the plumbing to fit extra zone valves everywhere !

    Then I can upgrade the UFH to wireless as at later stage when funds allow.

  4. #14
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    Is the UFH genuinely zones or just 8 outputs on a manifold? A lot of people confuse the two. For a proper UFH zone, the pipework under the floor needs to just be under the single zone and you need to be able to shut doors in it etc. And then each actuator on the manifold will need to be controlled separately.
    If the UFH is just a single zone then you dont need to use the Evohome UFH controller, you just need a single BDR91 and a TR87.

    However if you have a proper zoned wired UFH system then you actually shouldn't need strip that out. And in your case there is a lot to be gained by going down the hybrid route because your radiators will finally be able to call for heat when they need it, independently of the UFH. Just make sure you have an ABV on the boiler rather than assuming one of the radiators is playing that role.
    Last edited by bruce_miranda; 31st October 2019 at 01:22 PM.

  5. #15
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    Thanks Bruce, yes 8 zones controlled by 8 stats ( 10 manifold outputs). The hybrid route looks like a good intermediate step, I'll check on the ABV, although I do have 2 uncontrolled towel rads and the boiler does modulate, if that helps.
    Last edited by Paul M; 31st October 2019 at 01:57 PM.

  6. #16
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    I would keep the hybrid system in forever, you are unlikely to gain payback in changing over. Also IMHO UFH zones don't benefit as much from smartening. They don't react fast enough. A properly timed setpoint UFH zone is sufficient.

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