Evohome - fine tuning controls

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  • Edinburgh2000
    Automated Home Guru
    • Dec 2016
    • 134

    #31
    I assume you have spring-return valves, rather than motor open/motor close (MOMO) valves. I share your frustration with the recent consolidation of heating control design such that all valves always close when there is no boiler demand, necessitating the boiler bypass and wasting energy. Even the HR92s (which are MOMO hardware) are controlled as if they are spring-return, and so close fully if there is no boiler demand. That creates a noisy opening stroke in the mornings, unnecessary valve wear and battery consumption. It would be preferable if Honeywell's control logic told the HR92s: "stay where you are", when there is no boiler demand. That way there would be only small (and quieter) adjustments when the heating cuts in again in the morning and there would be a useful destination for the boiler and pump overrun.

    But for your specific question about a "box of tricks" to keep a zone valve open, as Paul Lockenden has noted above, DB Mandrake posted a very smart wiring scheme that uses the pump demand to hold at least one valve open, which works for spring-return valves. He posted the schematic at:


    That will only work if you have only two valves (one for CH, one for DHW). If you have more valves, then you will need to create a smarter "box of tricks". I use MOMO zone valves, and I use a multi-pole boiler relay to isolate the 'close' signals to the valves, so that they will only close if there is boiler demand. That means that I will always have at least one valve open (as the boiler demand comes from the open limit switch on the valves). I wrote a rather self-indulgent lengthy piece on the shortcomings of current valves that are available for domestic use, which is at:

    Comment

    • paulockenden
      Automated Home Legend
      • Apr 2015
      • 1719

      #32
      I disagree about HR92s staying open, as each one is independent. It's schedule might have finished for the day, but it has no idea whether another zone will call for heat during the night, so it HAS to shut down.

      If the controller actually controlled things I guess it could be done differently, but the HR92s themselves actually control the zone temperatures, with the controller simply managing schedules and marshalling various individual heat demands into a single value to send to the boiler.

      Comment

      • killa47
        Automated Home Guru
        • Jan 2016
        • 123

        #33
        Originally posted by paulockenden View Post
        I think the alternative wiring scheme that (I think) dbmandrake proposed would be a better solution.
        Thank you for the referral to DBMandrake, who I always watch with baited breath.

        Originally posted by Edinburgh2000 View Post
        I assume you have spring-return valves, rather than motor open/motor close (MOMO) valves.

        But for your specific question about a "box of tricks" to keep a zone valve open, as Paul Lockenden has noted above, DB Mandrake posted a very smart wiring scheme that uses the pump demand to hold at least one valve open, which works for spring-return valves. He posted the schematic at:


        That will only work if you have only two valves (one for CH, one for DHW). If you have more valves, then you will need to create a smarter "box of tricks". I use MOMO zone valves, and I use a multi-pole boiler relay to isolate the 'close' signals to the valves, so that they will only close if there is boiler demand. That means that I will always have at least one valve open (as the boiler demand comes from the open limit switch on the valves). I wrote a rather self-indulgent lengthy piece on the shortcomings of current valves that are available for domestic use, which is at:
        http://www.wordpress-1219309-4387497...alve-actuators
        I have two CH spring-return standard Honeywell 4043 valves plus the DHW valve which happily works away. I was planning on trying to keep the Upstairs heating valve open during pump overrun because we have three towel rails plus a landing radiator upstairs all with manual TRVs, so a good natural bypass system. Plus it solves (dissipates) the WB boiler gradient limitation issue which never occurred on the previous conventionally controlled heating controller.

        I will look again at your links to see if I can fettle some fix.

        Thank you both.

        Comment

        • DBMandrake
          Automated Home Legend
          • Sep 2014
          • 2361

          #34
          If you have two heating zone valves and two separate BDR91's for them it is still possible to adapt my circuit.

          Simply wire the hot water BDR91 and first heating BDR91 as shown, then on the second heating BDR91 connect the Live, Neutral, normally closed and normally open contacts to the respective contacts on the first heating BDR91 relay. Wire the common connection of each relay independently to its respective zone valve.

          If you use HR92's for your zoning and you only have two heating zone valves because your system was originally installed as an S-Plan plus system, you don't actually need the two heating BDR91's to drive the two heating zone valves - you could dispense with one BDR91 and run both heating zone valves from the same BDR91. As both relays TPI modulate in time with each other regardless of which HR92's call for heat, having two is functionally redundant.

          The only real reason to have two separate heating BDR91's as you do now, if you use HR92's is in case the wiring for your zone valves is physically far apart - for example one in the boiler closet and one upstairs in the loft. In this case it makes sense to take advantage of the wireless transmission to bridge that gap. However if both zone valves are in the same closet or their wiring terminates near each other I would dispense with the redundant BDR91 and power both heating zone valves from the same BDR91.

          The only problem with my circuit is that it assumes your heating and hot water BDR91's are within easy reach of each other, since you are running some connections between the heating and hot water relays. If yours are in different rooms that could be a long run of cable. (But still feasible)

          My circuit also requires 3x BDR91 to work so that the boiler can be fired directly independently of the zone valves - if you only have two BDR91's you won't be able to use it. However if you currently use two BDR91's redundantly for separate heating zone valves you could rewire and rebind that redundant unit as a boiler relay to implement my circuit.

          As for your original problem with the gradient limitation - I would think that my arrangement would solve that problem for you during the TPI modulation cycle as it ensures the heating zone valve only closes when either the pump has stopped, or when there is hot water demand and the heating BDR91 has cycled off during a TPI off period. When there is no hot water demand the heating zone valve remains open as long as the pump runs, which is the key.

          It avoids the entire flow being shunted through the ABV every TPI off period. In my case it was causing the flow temperature to spike up high enough to cause kettling in the boiler, which has stopped since I modified the wiring.

          You might find that you still have a gradient limitation issue when you schedule the entire system off at once (such as the heating off action) because even though my circuit will keep the heating zone valve open for the duration of the pump overrun, if all the HR92's are closed there still won't be any flow through the zone valve. However if you have a bypass radiator you will not have a problem.
          Last edited by DBMandrake; 2 March 2017, 09:42 PM.

          Comment

          • Edinburgh2000
            Automated Home Guru
            • Dec 2016
            • 134

            #35
            Simply wire the hot water BDR91 and first heating BDR91 as shown, then on the second heating BDR91 connect the Live, Neutral, normally closed and normally open contacts to the respective contacts on the first heating BDR91 relay. Wire the common connection of each relay independently to its respective zone valve.
            That only works if you want both the CH zone valves to operate in tandem. With pump demand and DHW satisfied, both CH valves would always be open, regardless of whether there is heat demand in both zones. Thus this DBMandrake Deluxe configuration only works if you use HR92s universally and do not want to use the CH zone valves for separate temperature control of the zones overall.

            Comment

            • paulockenden
              Automated Home Legend
              • Apr 2015
              • 1719

              #36
              I always forget that some people don't have HR92s on all of their rads. I suspect others do too.

              Comment

              • DBMandrake
                Automated Home Legend
                • Sep 2014
                • 2361

                #37
                Originally posted by Edinburgh2000 View Post
                That only works if you want both the CH zone valves to operate in tandem. With pump demand and DHW satisfied, both CH valves would always be open, regardless of whether there is heat demand in both zones. Thus this DBMandrake Deluxe configuration only works if you use HR92s universally and do not want to use the CH zone valves for separate temperature control of the zones overall.
                Yes but I did specifically say if you zone using HR92's. There are two different possible configurations for heating zone valves in Evohome, and people seem to keep getting them mixed up. They are functionally very different.

                1) Heating zone valve or valves bound as heating relays in the stored hot water configuration.

                2) Heating zone valves bound as "zone valve actuators" within an individual heating zone.

                VERY different.

                In the first case you require an additional actuator (HR92's) to perform the zoning and all heating zone valves that are configured in stored hot water TPI modulate together regardless of the source of heat demand. Unless I misread, this is killa47's situation and therefore my wiring advice is relevant. It doesn't matter if there is a bypass radiator either. That radiator would have got hot before anyway. The only real difference is it may get slightly warm when the heating is off after hot water reheat finishes, as it will act as a bypass for the latent heat.

                In the second case you have something like a per floor wall thermostat with a floor being a zone, and a zone valve feeds the radiators on that floor. Because the zone valves are bound as actuators within individual zones you cannot use my wiring suggestion because they need to be able to modulate separately, unlike zone valves bound in the stored hot water configuration.
                Last edited by DBMandrake; 2 March 2017, 10:33 PM.

                Comment

                • killa47
                  Automated Home Guru
                  • Jan 2016
                  • 123

                  #38
                  Originally posted by DBMandrake View Post
                  If you have two heating zone valves and two separate BDR91's for them it is still possible to adapt my circuit.
                  I just have the one CH BDR91, both zone valves being wired in tandem.

                  Simply wire the hot water BDR91 and first heating BDR91 as shown, then on the second heating BDR91 connect the Live, Neutral, normally closed and normally open contacts to the respective contacts on the first heating BDR91 relay. Wire the common connection of each relay independently to its respective zone valve.
                  I am thinking I could do it this way if I purchase a second BDR91 to do ay you suggest.

                  If you use HR92's for your zoning and you only have two heating zone valves because your system was originally installed as an S-Plan plus system, you don't actually need the two heating BDR91's to drive the two heating zone valves - you could dispense with one BDR91 and run both heating zone valves from the same BDR91. As both relays TPI modulate in time with each other regardless of which HR92's call for heat, having two is functionally redundant.
                  Correct that I had a conventional S-Plan Plus with a 3-channel controller (two CH zones plus DHW). All worked happily. Even now, it's frustrating that I can't stop the gradient limitation. I clearly could have the two zone valves removed which would solve the problem but am reluctant to do this in case we need to change system in future.

                  The only real reason to have two separate heating BDR91's as you do now, if you use HR92's is in case the wiring for your zone valves is physically far apart - for example one in the boiler closet and one upstairs in the loft. In this case it makes sense to take advantage of the wireless transmission to bridge that gap. However if both zone valves are in the same closet or their wiring terminates near each other I would dispense with the redundant BDR91 and power both heating zone valves from the same BDR91.

                  The only problem with my circuit is that it assumes your heating and hot water BDR91's are within easy reach of each other, since you are running some connections between the heating and hot water relays. If yours are in different rooms that could be a long run of cable. (But still feasible)
                  So this not really applicable.

                  My circuit also requires 3x BDR91 to work so that the boiler can be fired directly independently of the zone valves - if you only have two BDR91's you won't be able to use it. However if you currently use two BDR91's redundantly for separate heating zone valves you could rewire and rebind that redundant unit as a boiler relay to implement my circuit.

                  As for your original problem with the gradient limitation - I would think that my arrangement would solve that problem for you during the TPI modulation cycle as it ensures the heating zone valve only closes when either the pump has stopped, or when there is hot water demand and the heating BDR91 has cycled off during a TPI off period. When there is no hot water demand the heating zone valve remains open as long as the pump runs, which is the key.

                  It avoids the entire flow being shunted through the ABV every TPI off period. In my case it was causing the flow temperature to spike up high enough to cause kettling in the boiler, which has stopped since I modified the wiring.

                  You might find that you still have a gradient limitation issue when you schedule the entire system off at once (such as the heating off action) because even though my circuit will keep the heating zone valve open for the duration of the pump overrun, if all the HR92's are closed there still won't be any flow through the zone valve. However if you have a bypass radiator you will not have a problem.
                  Doing the above with a second CH BDR91 looks like the possible way to go.

                  Thank you DBMandrake for your suggestions.

                  Comment

                  • Midori
                    Automated Home Jr Member
                    • Aug 2015
                    • 24

                    #39
                    Short Cycling on zone valve system

                    Originally posted by Midori View Post
                    This is a valid point. My Honeywell V4043H's motorised zone valves take 10 seconds to open and signal the boiler. The boiler takes around 50 seconds to do it's ignition sequence before ignition. If the zone valve micro switches are controlling the boiler then I have the same critisism. In the non-boiler relay hook up, in my view the EVO should hold the valve(s) open for a minimum of 2 to 6 minutes (user adjustable). Not a big deal EVO softwarewise, but as I understand EVO is not updateable. Proprietary delayed-close timing relays costs around £ 20 each for a DIY solution.

                    However with a "Boiler Relay" hookup and bearing in mind I presently have a binding error, I reserve my judgement until after I rewire and perform rebindings in the next couple of weeks.

                    Close time of the V4043H is 1.5 secs by the way
                    It has been well over a year since I started the thread. Here is feedback on former short cycling issue for my system (2 heating zones plus one HWS zone - boiler control by 3 x zone valves with aux valve contacts wired in parallel as boiler control contact(s) ).
                    In 2015 I purchased one multifunction timed-to-close relay and wired this between Evohome and one of the BRD relays. Setting this to 2.5 to 3.0 minutes has avoided the short cycling issue for zone valve boiler control.
                    My logic was to delay one of the heating zones by the set time period. For example if the Evo was calling for 3 mins heat on 6 minute cycles, Now Htg zone 1 calls for heat 3 minutes, and Htg zone 2 calls for heat 2.5 or 3 minutes later. So boiler has effectively had demand for 6 minutes.

                    My first thoughts were later to purchase a second multifunction relay for the 2nd Htg zone, but it was unneccessary as I had no complaint anymore.
                    Assoc IHVE; Matthew Hall Satchwell MW Kellogg CompAir; posts are personal and my own view

                    Comment

                    • G4RHL
                      Automated Home Legend
                      • Jan 2015
                      • 1580

                      #40
                      Edinburgh2000 mentions increased battery consumption with more frequent operation of the valve. I have one zone where there is more frequent operation of the HR92 than any other zone and another zone where there is the opposite, the HR92 rarely has to work. In the zone with frequent operation the batteries last the longest, about 14 months. In the zone with infrequent operation they last the shortest, about 3 months.

                      Comment

                      • HenGus
                        Automated Home Legend
                        • May 2014
                        • 1001

                        #41
                        Originally posted by G4RHL View Post
                        Edinburgh2000 mentions increased battery consumption with more frequent operation of the valve. I have one zone where there is more frequent operation of the HR92 than any other zone and another zone where there is the opposite, the HR92 rarely has to work. In the zone with frequent operation the batteries last the longest, about 14 months. In the zone with infrequent operation they last the shortest, about 3 months.
                        Something odd there. I have 12 zones and 19 HR92s. My hardest working HR92s lasted about 18 months on the supplied batteries. Three rooms that get 3 temperature changes a day but heat very rarely required battery changes in the same month: 2 years plus after installation.

                        Could life be related to pin travel/motor time as well as frequency? That said, I have read reports of HR92s used in community situations requiring battery replacement after 3 months.

                        Comment

                        • paulockenden
                          Automated Home Legend
                          • Apr 2015
                          • 1719

                          #42
                          You need to run through a few sets of batteries before deciding whether a particular HR92 is chewing through them more quickly. It's entirely possible that the first set had a rogue cell.

                          P.

                          Comment

                          • HenGus
                            Automated Home Legend
                            • May 2014
                            • 1001

                            #43
                            Originally posted by paulockenden View Post
                            You need to run through a few sets of batteries before deciding whether a particular HR92 is chewing through them more quickly. It's entirely possible that the first set had a rogue cell.

                            P.
                            Honeywell supplying rogue cells - who would believe it. A good point.

                            Comment

                            • G4RHL
                              Automated Home Legend
                              • Jan 2015
                              • 1580

                              #44
                              Originally posted by paulockenden View Post
                              You need to run through a few sets of batteries before deciding whether a particular HR92 is chewing through them more quickly. It's entirely possible that the first set had a rogue cell.

                              P.
                              In my case not a Honeywell rogue cell for all my batteries have been replaced in the time since I installed Evohome. The HR92s in my lounge, which has the most frequent "activations", give me about 14 months. A spare bedroom which has little activation and they last three months. This is quite consistent as well when I look at the log I started keeping in December 2015. New batteries were installed then and then again March 2016, June 2016, September 2016 and December 2016. I suspect they will go again this month! Perhaps it is some sort of seasonal cycle!! In other zones I get about 12 months.

                              Comment

                              • DBMandrake
                                Automated Home Legend
                                • Sep 2014
                                • 2361

                                #45
                                Three months sounds more like a faulty HR92 to me.

                                Have you tried tweaking the battery contact tension on those ones ? I've had two now where they were falsly reporting low batteries, in one case when the batteries were new!

                                Comment

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