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Thread: Is my plan going to work?

  1. #1
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    Default Is my plan going to work?

    Hello all, first time poster, stumbled across this forum less than a week ago and have learnt a huge amount from browsing already – thanks.

    I have a plan for my heating and HW setup; I’d appreciate the hive-mind’s thoughts on whether it will work or not.

    Current set up: Worcester Bosch Greenstar condensing boiler feeding a typical S-plan with one zone valve for the radiators and another for the HW tank. All wired connections, other than an old RF thermostat/controller for the heating.

    Proposed: Evohome controller running
    • Same HW set up (not using a CS92 to cut equipment costs – I can always add it later).
    • Isolate the existing radiator loop zone valve, mechanically set it open, leave it in situ.
    • HR92s on all radiators.
    • Fit new zone valve to a branch off the radiator loop, which will feed a single zone wet underfloor mixer/pump/manifold (so no manifold actuator required).
    • BDR91 on UFH zone valve, bound to the main controller as thermostat.
    • BDR91 on the boiler so that the HR92s and UFH can call for heat.

    It is not normally good practice to fit UFH to the radiator loop, everything that I can find says to put in a dedicated zone valve and flow/return pipework. This makes sense if there is a single zone valve that allows flow to all radiators; you would not be able to have the UFH on unless all the radiators were on too.

    I want to avoid this so that I don’t have to rip up bits of the house, which will save some labour cost (that I can spend on EH bits instead…). If I use HR92s to give every radiator its own zone valve, then it becomes feasible. If a radiator needs heat, it will call for it, fire the boiler and open itself. If the UFH needs heat, it will call for it, open its zone valve and start its pump. Concurrent activity should be possible.

    Right?

    Thanks in advance for your thoughts.
    Last edited by wafu1983; 22nd March 2018 at 09:08 PM. Reason: Removed a mistake!

  2. #2
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    For what it's worth my original system was s-plan DHW + CH with zone valve for each driving boiler.

    A couple of years ago I added a 2 zone UFH in an extension

    The UFH controller (not H/well) requests heat from the boiler when it runs the pump. This was wired in parallel to the DHW and CH zone valve orange wires so any one of the three can request the boiler. There's no need for a zone valve for the UFH because the UFH pump is effectively a valve.

    So now I've upgraded to Evohome.
    I've added HR92s to all the rads (with a couple of bypass towel rails)

    I've left the DHW on the old timer ( I don't see that the CS90 really gives you anything other than remote control)
    The two zone valves and UFH are still controlling the boiler in the same way. I just have a BDR91 controlling the CH valve.
    The UFH is currently outside Evohome control (Don't see the value of 200 for H/well controller refit)

    The reason I've left the CH zone valve is to prevent the radiator circuit seeing hot water cycle when the UFH calls for heat (it takes longer for the UFH to heat up than the radiators)

    It's working just fine.

  3. #3
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    I have done something similar to what you propose with UFH. I have a valve on the heating circuit controlled by a BDR91 bound to the controller. I also have a room thermostat in the UFH room, also bound to the controller. All other rooms have HR92s.

    I'm intrigued, how you are going to get the BDR91 on the HW circuit to operate from the old thermostat?

  4. #4
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    Quote Originally Posted by wafu1983 View Post
    Hello all, first time poster, stumbled across this forum less than a week ago and have learnt a huge amount from browsing already – thanks.

    I have a plan for my heating and HW setup; I’d appreciate the hive-mind’s thoughts on whether it will work or not.

    Current set up: Worcester Bosch Greenstar condensing boiler feeding a typical S-plan with one zone valve for the radiators and another for the HW tank. All wired connections, other than an old RF thermostat/controller for the heating.

    Proposed: Evohome controller running
    • Same HW set up, controlled through a BDR91 that switches the zone valve, which is wired to the boiler to call for heat (not using a CS92 to cut equipment costs – I can always add it later).
    • Isolate the existing radiator loop zone valve, mechanically set it open, leave it in situ.
    • HR92s on all radiators.
    • Fit new zone valve to a branch off the radiator loop, which will feed a single zone wet underfloor mixer/pump/manifold (so no manifold actuator required).
    • BDR91 on UFH zone valve, bound to the main controller as thermostat.
    • BDR91 on the boiler so that the HR92s and UFH can call for heat.

    It is not normally good practice to fit UFH to the radiator loop, everything that I can find says to put in a dedicated zone valve and flow/return pipework. This makes sense if there is a single zone valve that allows flow to all radiators; you would not be able to have the UFH on unless all the radiators were on too.

    I want to avoid this so that I don’t have to rip up bits of the house, which will save some labour cost (that I can spend on EH bits instead…). If I use HR92s to give every radiator its own zone valve, then it becomes feasible. If a radiator needs heat, it will call for it, fire the boiler and open itself. If the UFH needs heat, it will call for it, open its zone valve and start its pump. Concurrent activity should be possible.

    Right?

    Thanks in advance for your thoughts.
    You'll find the the UFH pump will starve the radiator circuit. It needs dedicated flow and returns from the boiler to work properly.

  5. #5
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    Quote Originally Posted by mtmcgavock View Post
    You'll find the the UFH pump will starve the radiator circuit. It needs dedicated flow and returns from the boiler to work properly.

    For clarification the feed/return for the UFH in my system branches near the boiler close to the CH zone valve. It's not part of the rad loop.

  6. #6
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    Petep,

    So you must have flow/return pipes going to the UFH pump from before the CH zone valve, so your radiator circuit is, as you say, separate. A tough option for me as the boiler is miles away from the UFH site.

    I'm also guessing you use the Evohome controller as a thermostat to switch your CH zone valve (and fire the boiler)? I'm planning on not having a thermostat at all for the radiators, just using the HR92s instead.

  7. #7
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    Ian,

    Good spot, mistake on my part, I'm not going to get a BDR91 to switch the HW circuit. I won't need to because it's all hardwired in.

  8. #8
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    Quote Originally Posted by wafu1983 View Post
    Petep,

    So you must have flow/return pipes going to the UFH pump from before the CH zone valve, so your radiator circuit is, as you say, separate.
    See my comment above

    Quote Originally Posted by wafu1983 View Post
    A tough option for me as the boiler is miles away from the UFH site.
    My boiler is in the loft on one side of the house. My UFH is on the ground floor on the other side. It' couldn't be further away

    Quote Originally Posted by wafu1983 View Post
    I'm also guessing you use the Evohome controller as a thermostat to switch your CH zone valve (and fire the boiler)? I'm planning on not having a thermostat at all for the radiators, just using the HR92s instead.
    That's irrelevant. The Controller collects all the demands from the HR92s and uses the greatest value to send demand to boiler/zone BDR91. The controller does this whether or not it's the temperature reference for a zone.

    As it happens I do use the controller as a thermostat in a room with two HR92 radiators but that's because I think it's a better place to measure the temperature in that room.
    Last edited by petep; 22nd March 2018 at 09:37 PM.

  9. #9
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    Quote Originally Posted by mtmcgavock View Post
    You'll find the the UFH pump will starve the radiator circuit. It needs dedicated flow and returns from the boiler to work properly.
    Starve it in terms of what? Pressure? Flow? Temperature?

  10. #10
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    Quote Originally Posted by petep View Post
    My boiler is in the loft on one side of the house. My UFH is on the ground floor on the other side. It' couldn't be further away
    How did you run the flow/return to your manifold? Did you just rip up bits of the house, or box it in somewhere?


    Quote Originally Posted by petep View Post
    The Controller collects all the demands from the HR92s and uses the greatest value to send demand to boiler/zone BDR91. The controller does this whether or not it's the temperature reference for a zone.
    Great, sounds like exactly how I want to use them.

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