Evohome (again)

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  • davegilsenan
    Automated Home Lurker
    • May 2016
    • 5

    Evohome (again)

    Hi All,
    I've bought an Evohome controller/DHW kit/radiator valves.
    For some reason the evohome doesn't seem to be able to control 2no 2 port valves and zoned areas? The S-plan diagram in the manual says the whole home controlled under the same time and temp settings if using an S-plan.

    Next best is a single 2 port valve on the DHW and HR92's on all the rads. That's OK (apart from hot water circulating through the heating circuit when the DHW is calling for heat) but there is no wiring diagram for the junction box for this type of set up. Can anyone help or am I missing something.

    Thanks,
    Dave.
  • DanD
    Automated Home Ninja
    • Feb 2016
    • 250

    #2
    The S-plan diagram in the manual says the whole home controlled under the same time and temp settings if using an S-plan.
    Are you referring to the Figure 2 sample set-up at the bottom of page 42 in the instructions? If so, this is just a simple illustration of a set-up without any HR92s. You mention radiator valves in the kit you bought, do you mean the HR92 radiator controllers? If you have these then you can still use the set-up in Figure 2 and when a least one of the HR92 radiator controllers needs heat the CH zone valve will open and the boiler will fire. In addition, the Evohome controller can act as a thermostat to create an additional zone linked to the zone valve.

    The Evohome system is very flexible and supports many different types of set-ups. I have an S plan set-up similar to yours and I decided to put HR92s on all rads and latched the CH valve open, this set-up allows the use of the 'Boiler Relay' function. Have a search on the forum and you'll find a lot of discussion on this topic. Some prefer the S plan set-up retaining both zone valves, others use the 'Boiler Relay' function. The choice is yours!

    Dan

    Comment

    • top brake
      Automated Home Legend
      • Feb 2015
      • 837

      #3
      Originally posted by davegilsenan View Post
      Hi All,
      I've bought an Evohome controller/DHW kit/radiator valves.
      For some reason the evohome doesn't seem to be able to control 2no 2 port valves and zoned areas? The S-plan diagram in the manual says the whole home controlled under the same time and temp settings if using an S-plan.

      Next best is a single 2 port valve on the DHW and HR92's on all the rads. That's OK (apart from hot water circulating through the heating circuit when the DHW is calling for heat) but there is no wiring diagram for the junction box for this type of set up. Can anyone help or am I missing something.

      Thanks,
      Dave.

      Dave if you can sketch out your system it will help us to give you advise.
      I work for Resideo, posts are personal and my own views.

      Comment

      • davegilsenan
        Automated Home Lurker
        • May 2016
        • 5

        #4
        Thanks for the replies.

        DanD - Thanks for confirming what I hoped. Keep the 2no 2 port valves and put HR92's on the rads. Any valve calling for heat will open the heating 2 port valve.

        top brake - at the moment I haven't actually got a system as the house is being rebuilt. I'm just planning what to do.

        Is the s-plan and HR92's on the radiators the best way to go?

        Comment

        • davegilsenan
          Automated Home Lurker
          • May 2016
          • 5

          #5
          Sorry, another question.....
          If I went for the configuration in Fig 4 of the manual i.e. 1no 2 port valve on the hot water side, it shows a junction box but there is no wiring diagram for this. Any ideas where to find it?

          Comment

          • DanD
            Automated Home Ninja
            • Feb 2016
            • 250

            #6
            Hi,

            Here's a link to the wiring diagram I created for my Figure 4 set-up. It's just a simplification of Figure 9 in the manual with the CH valve and pump removed (as I have a system boiler with internal pump). Note my follow-up post in the linked thread indicating that the wiring was even simpler than the diagram as a couple of the connections could be made internally in the BDR91s rather than looping all the way back to the junction box.



            Really happy with my Evohome system set-up using HR92s on all radiators. If you go this route, have a search on the forum about Automatic Bypass Valves (ABV) as it's really important to ensure that your system has one to function OK when all HR92s close and the boiler/pump need to overrun to dissipate heat. My system already had one installed with the bypass diverting to the DHW cylinder which was great. Totally off-topic, but the only slight downside of my Evohome installation is how obsessed I've become monitoring my entire home !

            Dan

            Comment

            • Gairloch
              Automated Home Lurker
              • Jun 2016
              • 4

              #7
              Originally posted by davegilsenan View Post
              Hi All,
              I've bought an Evohome controller/DHW kit/radiator valves.
              For some reason the evohome doesn't seem to be able to control 2no 2 port valves and zoned areas? The S-plan diagram in the manual says the whole home controlled under the same time and temp settings if using an S-plan.
              Yes, I agree - it seems one of the biggest oversights in the evohome system not to provide a proper facility for pump overrun in the S-plan scheme or most of the others where the boiler and pump are powered together. To do it properly would require 3 wireless relays, giving control of the boiler fully independent of the pumps and valves. However, it seems to me that if all radiators have wireless controllers on them, the problem can be partially remedied with minimal changes to wiring by driving the pump via the zone valve switches, as is usual in S-Plan, but driving the boiler directly from the boiler wireless relay.

              So that's as per figure 9 wiring except that the boiler live goes to terminal 5 instead of terminal 10.

              When there is any heat demand from a radiator evohome puts the boiler relay on, so the boiler is switched on, and opens the HTG zone valve which in turn starts the pump. If hot water is called for both relays are activated by evohome, so both zone valves open and the boiler and pump are powered. (If in fact only water heating is required, the individual radiator HR92 valves will be closed anyway, so nothing will circulate in the CH even though the valve is open.)

              If the evohome wants a period of pump overrun after water heating, it powers only the DHW relay and only the pump and HW valve operate, but not the boiler, so circulating residual boiler heat through the HW cycling.

              An additional benefit is that the pump runs only if at least one of the valves is open, so it can't find itself pumping against a closed circuit as can otherwise happen if a valve burns out or sticks shut, which are the most common modes of failure.

              Now shoot me down in flames!
              Last edited by Gairloch; 21 June 2016, 10:44 PM.

              Comment

              • top brake
                Automated Home Legend
                • Feb 2015
                • 837

                #8
                Originally posted by Gairloch View Post
                Yes, I agree - it seems one of the biggest oversights in the evohome system not to provide a proper facility for pump overrun in the S-plan scheme or most of the others where the boiler and pump are powered together. To do it properly would require 3 wireless relays, giving control of the boiler fully independent of the pumps and valves. However, it seems to me that if all radiators have wireless controllers on them, the problem can be partially remedied with minimal changes to wiring by driving the pump via the zone valve switches, as is usual in S-Plan, but driving the boiler directly from the boiler wireless relay.

                So that's as per figure 9 wiring except that the boiler live goes to terminal 5 instead of terminal 10.

                When there is any heat demand from a radiator evohome puts the boiler relay on, so the boiler is switched on, and opens the HTG zone valve which in turn starts the pump. If hot water is called for both relays are activated by evohome, so both zone valves open and the boiler and pump are powered. (If in fact only water heating is required, the individual radiator HR92 valves will be closed anyway, so nothing will circulate in the CH even though the valve is open.)

                If the evohome wants a period of pump overrun after water heating, it powers only the DHW relay and only the pump and HW valve operate, but not the boiler, so circulating residual boiler heat through the HW cycling.

                An additional benefit is that the pump runs only if at least one of the valves is open, so it can't find itself pumping against a closed circuit as can otherwise happen if a valve burns out or sticks shut, which are the most common modes of failure.

                Now shoot me down in flames!
                The heating zone valve is not required if the system is multizoned

                Ref Fig 4

                The fitment of an automatic bypass is recommended.
                I work for Resideo, posts are personal and my own views.

                Comment

                • Gairloch
                  Automated Home Lurker
                  • Jun 2016
                  • 4

                  #9
                  Originally posted by top brake View Post
                  The heating zone valve is not required if the system is multizoned

                  Ref Fig 4

                  The fitment of an automatic bypass is recommended.
                  The CH valve is performing an essential function as an isolating relay between the pump and the boiler - that's the whole point of this mod - to allow the pump to run under command of the DHW relay without also firing the boiler when the boiler wireless relay is off during an overrun.

                  Of course the heating zone valve is superfluous (literally!) from the water circulation point of view if all rads/zones have their own controlled valves anyway, but in my scheme to allow hot water overrun pumping in an S-plan the valve is being used for its electrical function.

                  The valve could be replaced by a simple electrical relay to provide the isolation needed to allow the pump to run independently of the boiler, but the water valve with relay contacts is there already when retrofitting an S-plan, so my suggestion was to use the heating valve just as the required isolating relay.

                  Yes a bypass is usually recommended, and is present in my current case, but may not actually be necessary with an evohome system since the boiler will only be fired up if either at least one zone is calling for heat (and therefore at least one zone valve is open) or if DHW heating is required, in which case the DHW valve will be open.

                  The bypass may nonetheless be handy on a system that has a lot of radiators with a powerful pump, to cater for the over-pressure that might occur if just one zone needed heat and the pump was a bit over-sized for just one zone/rad.

                  However, while the bypass is a good backup option in all cases, a better design solution is to use an 'intelligent pump' such as Grundfos Alpha that will step down its power according to pressure and flow rate. They are a relatively low-cost drop-in replacement that doesn't even require a drain down compared with adding a bypass valve.

                  But what about my basic idea of separating the pump and boiler to allow evohome's overrun function to work, which the recommended wiring scheme doesn't. Do you see any problems with it?

                  Alex
                  Last edited by Gairloch; 21 June 2016, 11:32 PM.

                  Comment

                  • paulockenden
                    Automated Home Legend
                    • Apr 2015
                    • 1719

                    #10
                    Interesting mod - I think it sounds sensible.

                    P.

                    Comment

                    • davegilsenan
                      Automated Home Lurker
                      • May 2016
                      • 5

                      #11
                      I think I'm in over my head.......

                      Comment

                      • DBMandrake
                        Automated Home Legend
                        • Sep 2014
                        • 2361

                        #12
                        Originally posted by Gairloch View Post
                        Yes, I agree - it seems one of the biggest oversights in the evohome system not to provide a proper facility for pump overrun in the S-plan scheme or most of the others where the boiler and pump are powered together. To do it properly would require 3 wireless relays, giving control of the boiler fully independent of the pumps and valves. However, it seems to me that if all radiators have wireless controllers on them, the problem can be partially remedied with minimal changes to wiring by driving the pump via the zone valve switches, as is usual in S-Plan, but driving the boiler directly from the boiler wireless relay.

                        So that's as per figure 9 wiring except that the boiler live goes to terminal 5 instead of terminal 10.

                        When there is any heat demand from a radiator evohome puts the boiler relay on, so the boiler is switched on, and opens the HTG zone valve which in turn starts the pump. If hot water is called for both relays are activated by evohome, so both zone valves open and the boiler and pump are powered. (If in fact only water heating is required, the individual radiator HR92 valves will be closed anyway, so nothing will circulate in the CH even though the valve is open.)

                        If the evohome wants a period of pump overrun after water heating, it powers only the DHW relay and only the pump and HW valve operate, but not the boiler, so circulating residual boiler heat through the HW cycling.

                        An additional benefit is that the pump runs only if at least one of the valves is open, so it can't find itself pumping against a closed circuit as can otherwise happen if a valve burns out or sticks shut, which are the most common modes of failure.

                        Now shoot me down in flames!
                        It might just be my opinion, but I really don't see it as the job of the Evohome system to manage pump overrun ?

                        That is an implementation specific detail for your boiler and system design. It's the Evohome's job to call for heat from the boiler and if necessarily control zone valves to direct that heat either to radiators or hot water. (With the heating zone valve only being necessary if not all radiators have HR92's)

                        This can be done with a two relay S-Plan config where one relay calls for CH and one calls for HW, or a 3 relay config where you also have a separate boiler demand relay instead of relying on the zone valve switches to fire the boiler.

                        If your boiler or system needs pump overrun then generally the boiler will already have a pump overrun timer or thermostat built in or your system will already have an external timer.

                        Originally posted by Gairloch View Post
                        The CH valve is performing an essential function as an isolating relay between the pump and the boiler - that's the whole point of this mod - to allow the pump to run under command of the DHW relay without also firing the boiler when the boiler wireless relay is off during an overrun.

                        Of course the heating zone valve is superfluous (literally!) from the water circulation point of view if all rads/zones have their own controlled valves anyway, but in my scheme to allow hot water overrun pumping in an S-plan the valve is being used for its electrical function.

                        The valve could be replaced by a simple electrical relay to provide the isolation needed to allow the pump to run independently of the boiler, but the water valve with relay contacts is there already when retrofitting an S-plan, so my suggestion was to use the heating valve just as the required isolating relay.
                        Instead of all this hackery, why not just use an off the shelf pump overrun timer instead of an expensive BDR91 ? On my old system I retrofitted a pump overrun timer using an MRT16-REM, which is available for about £25 - a good deal cheaper than a £55 BDR91:

                        Contact us today for your free 242 page catalogue packed full of the latest branded products


                        Spec sheet:



                        It is also available in a potential free relay version if your wiring requires it.

                        The time delay can be set to anywhere between 1 second and 2 hours... I have mine set to about 3 1/2 minutes at the moment. It's mainly there to prevent kettling in the boiler every time TPI cycles the boiler off - with the overrun there is time for latent heat in the heat exchanger to be distributed to the radiators before stopping the pump, which also improves the efficiency of TPI.

                        Yes a bypass is usually recommended, and is present in my current case, but may not actually be necessary with an evohome system since the boiler will only be fired up if either at least one zone is calling for heat (and therefore at least one zone valve is open) or if DHW heating is required, in which case the DHW valve will be open.
                        I wouldn't count on that if I were you. This is the perception that many people have but it does not match the reality of how the system operates. For starters, when HR92's close (for example when set points change to 5 degrees) the HR92 does not send a zero heat demand until after it has finished closing, and it takes up to 30 seconds for the valves to fully close. So even if there is no pump overrun, when the heating is scheduled to go off the pump will end up pumping into a dead end for up to 15 seconds or so which is enough to cause a lockout or a leak for that matter. If there is deliberate pump overrun then obviously there must be a bypass of some sort.

                        Also, HR92's don't always know exactly at what position your TRV valve bodies open - especially if the valves are a bit sticky and not consistent in their operation. It's been my experience that the boiler relay will sometimes be cycled on for a few minutes when none of the radiators are flowing, because one or more HR92's aren't sure exactly where the opening points of the valves are, meaning that the valve is actually closed rather than slightly open. Without a bypass this will cause you an issue.

                        Other's may disagree but IMO if you have a fixed speed pump and an HR92 on every radiator you must have an ABV if you don't want to experience problems. From a system efficiency point of view its silly not to have one anyway.
                        The bypass may nonetheless be handy on a system that has a lot of radiators with a powerful pump, to cater for the over-pressure that might occur if just one zone needed heat and the pump was a bit over-sized for just one zone/rad.
                        Again, from my experience an ABV is beneficial even if one radiator is fully open - I have 9 radiators and my ABV set to a relatively high 0.5 bars for various reasons, and the valve still flows even with (only) one radiator fully open. Without it the differential pressure would be rather high. And no, the pump speed is not set to high, it's on medium - with it on low the boiler short cycles due to insufficient flow.
                        However, while the bypass is a good backup option in all cases, a better design solution is to use an 'intelligent pump' such as Grundfos Alpha that will step down its power according to pressure and flow rate. They are a relatively low-cost drop-in replacement that doesn't even require a drain down compared with adding a bypass valve.
                        Variable speed pumps are not a drop in replacement for boilers that were not originally designed for them - although they solve the problem of excessive differential pressure you now have the problem of insufficient flow rate through the boiler, where the boilers minimum flow rate in litres per minute will not be satisfied. This will cause overheating of the heat exchanger, short cycling, or lockout.

                        In another thread you'll find Richard from the evohomeshop advising against retro-fitting an 'intelligent' variable speed pump to a system not designed for it, and I have to agree.

                        I replaced a faulty Grundfos pump on my system with a new UPS2 15-50/60, which supports three fixed speeds and three 'intelligent' variable speeds - of course I tried the variable speed mode and it was completely useless on my system - even with all radiators open (which is where variable speed pumps run at maximum speed) there was not sufficient flow to prevent short cycling of the boiler. It might be partly due to the fact that most of my radiators are microbore and thus have too high a flow resistance for a variable speed pump but even if that wasn't the case the flow rate through the boiler would have been too low when few radiators were open.
                        But what about my basic idea of separating the pump and boiler to allow evohome's overrun function to work, which the recommended wiring scheme doesn't. Do you see any problems with it?
                        It seems to me that fitting a standard pump overrun timer where the system doesn't already have one is much cheaper and more logical than trying to hack that functionality onto an additional BDR91, especially when the Evohome software doesn't actually support such operation at the moment.
                        Last edited by DBMandrake; 22 June 2016, 10:31 PM.

                        Comment

                        • Gairloch
                          Automated Home Lurker
                          • Jun 2016
                          • 4

                          #13
                          Originally posted by paulockenden View Post
                          Interesting mod - I think it sounds sensible.

                          P.
                          Thanks Paul - I've set a system up like that today and will see how it goes.

                          Comment

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