Evo home + 4 zone valves

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  • ads_green
    Automated Home Lurker
    • Mar 2017
    • 6

    Evo home + 4 zone valves

    Hi All,

    I used Evohome several times before to great success and looking to upgrade my new property. It's a bit different as it has quite a "industrial" heating setup but I was hoping it could be used pretty easily.
    I'm happy with the DHW setup so will leave that alone.

    The property is split over four flours and each has it's own physical zone valve located near the boiler and a conventional thermostat located in the landing.
    The boiler has built in cycling protection so I'm not worried there.

    The easy answer would be to manually lock open all the zone valves and then use a BDR relay for the boiler linked to an evohome controller and fit HR92's everywhere for zoning.
    I'd prefer not to do this as the property is reasonably large and pumping all zones for a single HR92 requesting heat is a massive overkill. Also the boiler room is a significant distance away from the property and I suspect the signal would also be blocked - so any rewiring in the boiler room is tricky at best. The pipework from the boiler to the property is 28mm so represents a reasonable amount of water to pump for a single radiator requesting heat.

    The next option would be to replace the existing thermostats with 4 x BDR relays and setup up 4 zones with zone's BDR linked to its zone valve. This would "ok" (but not ideal) as it means I can't further subdivide the floors into zones that can demand heat.

    One option would be to implement the 4 BDR's and override the rooms that I don't want to use (spare room for example). Then if needed bring them back into sync when occupied. It's "ok" and works for a couple of floors but the ground floor has rooms with very different heat profiles so it's not ideal.

    Now I know I can bind a single BDR relay to multiple controllers so yes it could be solved with additional evohome controllers but this feels like quite an expensive option and frustrating if this can't be achieved with a single controller and multiple zones.
    If it were possible (but I suspect it is not) to have a single BDR relay bound as an actuator to multiple evohome zones then it could be achieved.

    Just trying to get a little more control within the physical zone - if you could map the same physical BDR relay on the same Evohome Controller to multiple controller defined "virtual" zones (as a zone valve actuator) then job done.

    So for example in the evo home controller "Zone 1" could be the lounge (physical pipework Zone Valve 1) and then "Zone 2" could be the kitchen and dining room (also physical pipework Zone Valve 1).
    Thus if you could wire the physical zone valve for that floor to a single BDR but configure both virtual zone 1 and zone 2 to use the same relay actuator as the zone valve then it'll work perfectly. What I'm not sure of is that last step of mapping the same BDR relay to two virtual zones on the same evohome controller.

    Am I missing something obvious? I'm struggling to find a method to achieve this and I don't see why it should be so difficult!
  • paulockenden
    Automated Home Legend
    • Apr 2015
    • 1719

    #2
    Originally posted by ads_green View Post
    I'd prefer not to do this as the property is reasonably large and pumping all zones for a single HR92 requesting heat is a massive overkill.
    You wouldn't be, but this seems to be a very common misconception.

    If all of the HR92s in one of your (valved) zones are closed then no water will flow, despite the zone valve being open.

    P.

    Comment

    • ads_green
      Automated Home Lurker
      • Mar 2017
      • 6

      #3
      Originally posted by paulockenden View Post
      You wouldn't be, but this seems to be a very common misconception.

      If all of the HR92s in one of your (valved) zones are closed then no water will flow, despite the zone valve being open.

      P.
      Interesting... It was my belief that radiators are plumbed in parallel... so the feed of the radiator is linked to the flow from the boiler and the exit of the radiator linked to the return back. As such if all radiators are fully switched off then the flow/return circuit would still pump water around.
      Is it a case then that the last radiator is effectively the end of the loop so if it is switched off too then as the water has nowhere to go and can't compress then that zone wouldn't flow as it would back up to the manifold where the zone valves are....

      If so then yes that gives some options...
      - Manually latch open all the zone valves.
      - Take three of the four zone thermostats and simply disconnect or set to minimum.
      - On the last one, replace with a BDR relay and set as the boiler heat demand.
      - Zone as required.

      Perfect! I must try it!

      Comment

      • dty
        Automated Home Ninja
        • Aug 2016
        • 489

        #4
        Originally posted by ads_green View Post
        Interesting... It was my belief that radiators are plumbed in parallel... so the feed of the radiator is linked to the flow from the boiler and the exit of the radiator linked to the return back. As such if all radiators are fully switched off then the flow/return circuit would still pump water around.
        Is it a case then that the last radiator is effectively the end of the loop so if it is switched off too then as the water has nowhere to go and can't compress then that zone wouldn't flow as it would back up to the manifold where the zone valves are....
        Correct. The flow is not linked to the return except through radiators. So if all the radiator valves are closed, the water has nowhere to go.

        Now... you still might have your pump on, and that would be bad. So I strongly suggest a modulating pump and a bypass of some kind, such as an automatic bypass valve, or an uncontrolled radiator somewhere.

        Comment

        • paulockenden
          Automated Home Legend
          • Apr 2015
          • 1719

          #5
          They are usually plumbed in parallel, as you suggest.

          Something like this:



          As you can see, there's no direct connection from red to blue except via a radiator, so if all of the TRVs are closed there's no flow-path for the water to take.

          having said that, occasionally systems may be plumbed differently, so do check!

          Comment

          • ads_green
            Automated Home Lurker
            • Mar 2017
            • 6

            #6
            Thanks all - I will check... I haven't found a radiator with only a manual valve though so I won't put out the bunting just yet!

            There is a bypass fitted already for the pump but this was added very recently so there must be somewhere of dealing with this.

            Comment

            • ads_green
              Automated Home Lurker
              • Mar 2017
              • 6

              #7
              Arg! Towel Rails!
              We have combined units that support hot water from the heating circuit with electrical backup...
              I suspect these are acting as the manual loops for the circuit - each floor has one.

              Easy option would be to close them off and use the electric feed if required.

              Comment

              • ads_green
                Automated Home Lurker
                • Mar 2017
                • 6

                #8
                Doh... The kitchen has a kick board heater that is plumbed into the heating circuit with no isolator valves.

                Every other floor can work ok but it's looking like back to plan A (not going to disassemble the kitchen to re-plumb it!)

                Is it possible to have the same BDR bound to a single evo home controller but used as a zone valve in multiple evo home zones?

                Comment

                • paulockenden
                  Automated Home Legend
                  • Apr 2015
                  • 1719

                  #9
                  Sounds like you've bought a bit of a castle! Separate boiler house?

                  Does it have a moat? ;-)

                  Comment

                  • ads_green
                    Automated Home Lurker
                    • Mar 2017
                    • 6

                    #10
                    I suspect castles have easier plumbing!

                    But yeah, the boiler is about I guess just over 50m away from the main house in it's own little brick building with the main house I guess maybe 6,000 sq/ft ish over four floors.

                    I suspect that if I can't bind a BDR to multiple zones then I think it's going to be multiple evo home controllers.

                    Comment

                    • paulockenden
                      Automated Home Legend
                      • Apr 2015
                      • 1719

                      #11
                      I suspect you're going to need opentherm (with always on lower flow temps) rather than BDR91 (with it's short pulses of hot water) because one BDR cycle might not be enough to get the hot water from the boiler house to the house, especially if the pipes are really fat.

                      It'll be interesting to hear whether Evohome can cope in a property like that.

                      P.

                      Comment

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