"Figure 4" installation vs. Y-plan

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  • SimonW500
    Automated Home Jr Member
    • Feb 2015
    • 21

    "Figure 4" installation vs. Y-plan

    Hi,

    Please forgive my lack of knowledge here! I have an Evohome retrofitted to my Y-plan system, however am now looking a changing a few things around and I read through these forums the "figure 4" installation is considered optimum - that is the heating circuit always on (though flow restricted by every radiator having a Evohome valve with a single 2-way valve, thus definitely requires a bypass valve) and relay to introduce HW on demand.

    My question is WHY is this optimal? Perhaps naively I would've thought the Y-plan setup with the 3-way value would be better as at any given time the system can provide heating OR hot water OR heating and hot water.

    The only obvious advantage I can see is within the Evohome software: for whatever reason when setting up as Y-plan the configuration options to set boiler cycle and run times are not available, this despite the fact the Evohome still has exclusive control over the boiler (even in setups like mine which incorporate pump overrun it still has exclusive control over demand).. I don't see why this 'logic' / 'limits' cannot be used for Y-plan setups (eg. don't cycle boiler more than x times an hour and don't run boiler for less than x minutes)?

    Quite possibly missing something - maybe on both on the optimal pipework/valve setup AND a good reason why the above can't be configured for Y-plan - look forward to being educated!

    Thanks.
    Last edited by SimonW500; 1 March 2015, 06:22 PM.
  • top brake
    Automated Home Legend
    • Feb 2015
    • 837

    #2
    Originally posted by SimonW500 View Post

    The only obvious advantage I can see is within the Evohome software: for whatever reason when setting up as Y-plan the configuration options to set boiler cycle and run times are not available, this despite the fact the Evohome still has exclusive control over the boiler (even in setups like mine which incorporate pump overrun it still has exclusive control over demand).. I don't see why this 'logic' / 'limits' cannot be used for Y-plan setups (eg. don't cycle boiler more than x times an hour and don't run boiler for less than x minutes)?

    Quite possibly missing something - maybe on both on the optimal pipework/valve setup AND a good reason why the above can't be configured for Y-plan - look forward to being educated!

    Thanks.
    For the reason you identified Fig 4 is optimal for new installations. Modern high efficiency boilers may benefit from adjusting the cycle rate, particularlupy oil boilers. It also means that the hot water zone valve is only powered when hot water is required, meaning it will last longer.
    It's basically less parts so inherently easier to install.

    Hope this makes sense?
    I work for Resideo, posts are personal and my own views.

    Comment

    • SimonW500
      Automated Home Jr Member
      • Feb 2015
      • 21

      #3
      Originally posted by top brake View Post
      For the reason you identified Fig 4 is optimal for new installations. Modern high efficiency boilers may benefit from adjusting the cycle rate, particularlupy oil boilers. It also means that the hot water zone valve is only powered when hot water is required, meaning it will last longer.
      It's basically less parts so inherently easier to install.

      Hope this makes sense?
      For new installations I can fully follow the less parts / simpler design logic. Yet for existing installations, I still cannot understand the benefit of rejigging a working Y-plan system (perhaps the answer is there isn't one?).

      Also re. setting boiler cycle and minimum runtime settings I still cannot see why this couldn't be configured for a Y-plan (other than the software currently doesn't allow it) - am I missing something?

      (thanks in advance)

      Comment

      • jonstatt
        Automated Home Guru
        • Feb 2015
        • 111

        #4
        Originally posted by SimonW500 View Post
        For new installations I can fully follow the less parts / simpler design logic. Yet for existing installations, I still cannot understand the benefit of rejigging a working Y-plan system (perhaps the answer is there isn't one?).

        Also re. setting boiler cycle and minimum runtime settings I still cannot see why this couldn't be configured for a Y-plan (other than the software currently doesn't allow it) - am I missing something?

        (thanks in advance)
        I don't see why the options couldn't be provided for either S-plan or Y-plan. I think the issue is that the EVOHOME controller likes to separate "boiler control" from "heat" or "water" controls. So if you have a set-up where there is only a single relay that basically is there to cycle the boiler regardless of whether it is heat or water, then you get these options. But in the event of multiple BDR91s, these options are gone. It is a limitation of the programming but it could be enhanced.

        Comment

        • top brake
          Automated Home Legend
          • Feb 2015
          • 837

          #5
          Originally posted by SimonW500 View Post
          For new installations I can fully follow the less parts / simpler design logic. Yet for existing installations, I still cannot understand the benefit of rejigging a working Y-plan system (perhaps the answer is there isn't one?).

          Also re. setting boiler cycle and minimum runtime settings I still cannot see why this couldn't be configured for a Y-plan (other than the software currently doesn't allow it) - am I missing something?

          (thanks in advance)
          Originally posted by jonstatt View Post
          I don't see why the options couldn't be provided for either S-plan or Y-plan. I think the issue is that the EVOHOME controller likes to separate "boiler control" from "heat" or "water" controls. So if you have a set-up where there is only a single relay that basically is there to cycle the boiler regardless of whether it is heat or water, then you get these options. But in the event of multiple BDR91s, these options are gone. It is a limitation of the programming but it could be enhanced.
          without a BOILER RELAY you do not have control over the cycle rate and minimum runtime

          if this level of control is required you need to install as Fig 4
          I work for Resideo, posts are personal and my own views.

          Comment

          • jonstatt
            Automated Home Guru
            • Feb 2015
            • 111

            #6
            Originally posted by top brake View Post
            without a BOILER RELAY you do not have control over the cycle rate and minimum runtime

            if this level of control is required you need to install as Fig 4
            That's how it is today....but Honeywell "could" enhance this through a firmware update to offer these options for s-plan and y-plan configurations as well.

            Comment

            • SimonW500
              Automated Home Jr Member
              • Feb 2015
              • 21

              #7
              Originally posted by top brake View Post
              without a BOILER RELAY you do not have control over the cycle rate and minimum runtime

              if this level of control is required you need to install as Fig 4
              Seems Jon and myself are angling at the same question!

              Following a Y-plan installation, requiring 2 wireless relays to fully control both sides, the Evohome still has full and exclusive control over boiler demand and therefore COULD control cycle rate and minimum runtime. My question is therefore validating my understanding / trying to understand WHY this currently isn't an option (a decision made on a Friday afternoon perhaps?!).

              Comment

              • SensibleHeatUK
                Moderator
                • Feb 2009
                • 228

                #8
                Originally posted by SimonW500 View Post
                Seems Jon and myself are angling at the same question!

                Following a Y-plan installation, requiring 2 wireless relays to fully control both sides, the Evohome still has full and exclusive control over boiler demand and therefore COULD control cycle rate and minimum runtime. My question is therefore validating my understanding / trying to understand WHY this currently isn't an option (a decision made on a Friday afternoon perhaps?!).
                If you add a third BDR to your S or Y-plan setup, registered to Evo as a Boiler Controller (re-wiring the boiler demand signals appropriately), then you can have control over the boiler too. It is simply that most installations are not set up this way, either for cost reasons (although an extra BDR is not a massive cost increase in relatively terms), or because the system has been installed with as little disruption to the existing wiring as possible.
                Sensible Heat
                SensibleHeat.co.uk

                Comment

                • SimonW500
                  Automated Home Jr Member
                  • Feb 2015
                  • 21

                  #9
                  Originally posted by SensibleHeatUK View Post
                  If you add a third BDR to your S or Y-plan setup, registered to Evo as a Boiler Controller (re-wiring the boiler demand signals appropriately), then you can have control over the boiler too. It is simply that most installations are not set up this way, either for cost reasons (although an extra BDR is not a massive cost increase in relatively terms), or because the system has been installed with as little disruption to the existing wiring as possible.
                  Yes I figured as much - thanks for the confirmation - indeed a route I may go down.

                  However, this is more a 'fudge' to work within the artificial software limitations of the current Evohome options right? As Jon and myself state these options could (in theory) be simply updated to work as-is?

                  Further, are you able to comment on my original question re. efficiencies of figure 4. vs. Y-plan? If I am moving things around with my wiring I might as well consider moving the plumbing arrangement around as well.. if of course there is a benefit?

                  Thanks!

                  (nb. equally happy to be wrong.. I'm just trying to further my understanding as opposed to hammer home a point/agenda!

                  Comment

                  • thepook
                    Automated Home Jr Member
                    • Jan 2015
                    • 32

                    #10
                    Originally posted by SensibleHeatUK View Post
                    If you add a third BDR to your S or Y-plan setup, registered to Evo as a Boiler Controller (re-wiring the boiler demand signals appropriately), then you can have control over the boiler too. It is simply that most installations are not set up this way, either for cost reasons (although an extra BDR is not a massive cost increase in relatively terms), or because the system has been installed with as little disruption to the existing wiring as possible.
                    But as I have found out, if you install this way with three BDRs, then neither zone valve BDR is necessarily operated at the same time as the Boiler Demand BDR. So if you did this on an S-plan, the boiler demand could effectively be calling heat and pumping straight through an automatic bypass. On a y-plan it is less of an issue, as the valve will be held in the last port of call. Evo is not designed to work in this way according to Top Brake; see this post here: http://www.wordpress-1219309-4387497...ll=1#post21263

                    Comment

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