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  • yngndrw
    Automated Home Jr Member
    • Mar 2018
    • 12

    EvoHome Advice

    So I've just moved into a new 5 bed house, which is over two floors and has 2 heating zones (S-Plan Plus). The boiler is an OpenTherm boiler (Logic Heat h15) but the existing thermostats and timer (ESi) are not OpenTherm compatible.

    My parents have moved in with us and my mother is home all day, so I thought that per-room zoning would be ideal for us. In the previous house we had a Nest, however when I queried them about multi-zone and OpenTherm compatibility, it looks like they can only do one or the other. My plan is now to use the EvoHome system, having a mix of smart TRVs and standard TRVs.

    Currently there is a bedroom zone (Which includes an en-suite bathroom towel radiators) with its thermostat in the largest bedroom on the second floor and a zone for the rest of the rooms with its thermostat in the ground-floor hallway.


    My plan was to put 6 smart TRVs (HR92) on the following radiators:
    - Radiator in Bed 1 (Our room, largest bedroom on the second floor - There are no other rooms on this floor other than an en-suite)
    - Main radiator in Bed 2 (Parent's room, second largest on the first floor - There is a second small radiator in this room but I was going to leave this with a standard TRV)
    - Radiator in Bed 3 (Office space)
    - Radiator in Bed 4 (Craft room for my mother)
    - Main radiator in lounge (I'll leave the second radiator with a standard TRV)
    - Kitchen (I'll leave the attached dining room radiator with a standard TRV)

    The idea for rooms with more than one radiator is to use a HR92 on the largest radiator to allow the room to call for heat, but leave a standard TRV on the second radiator so that it just assists.

    I was planning on using three relays (BDR91), one for each zone valve. (Including the hot water cylinder's zone valve) I'd also need the cylinder thermostat (ATF500DHW) which I don't believe has a relay output, hence the third zone valve.

    In Bed 1 and 2, I was going to fit a wall-mounted thermostat (T87RF2059) to make adjustment easier.

    The boiler would be controlled via the OpenTherm unit (R8810) - I don't believe it then needs any other signals, specifically the call for heat from the zone valves ?

    Obviously I'd also get the main controller, wall mounted.


    Does this setup sound right ? I don't want to spend this kind of money, only to find that it isn't going to work right for our needs.

    Thanks,
    -Andrew.
  • paulockenden
    Automated Home Legend
    • Apr 2015
    • 1719

    #2
    How many rads do you have? I’d be tempted to fit HR92s on all of them, and dispense with the zone valve BDRs for the two zones (just keep them o0en). But obviously if you have shedloads of radiators that can become expensive.

    Comment

    • HenGus
      Automated Home Legend
      • May 2014
      • 1001

      #3
      Before going firm on Opentherm, you might like to read some of the posts about Ideal boilers and Evohome/Opentherm. Opentherm is not as universally standard as some people think.

      Moreover, Evohome’s fuzzy logic is not as efficient as it could be. For example, when radiators demand heat first thing in the morning it will increase the boiler temperature to the set flow maximum temperature until all the zones are within the set temperature range. No problem with that. But, if someone plays with an HR92 in a zone later in the day, then Evohome will again demand max temperature flow until the set temperature is reached. To get maximum efficiency - lowest cost - then, in my opinion, it is best to attain and maintain rather than have variable zone temperatures.

      In your situation, a mix of HR92s and standard/electronic TRVs might work. The downside being that when any zone demands heat, then all the standard TRVs will also potentially get heat depending on the TRV setting.

      Comment

      • yngndrw
        Automated Home Jr Member
        • Mar 2018
        • 12

        #4
        Originally posted by paulockenden View Post
        How many rads do you have? I’d be tempted to fit HR92s on all of them, and dispense with the zone valve BDRs for the two zones (just keep them o0en). But obviously if you have shedloads of radiators that can become expensive.
        In total I have ten in the main zone and eight in the bedoor zone. Four of these are towel radiators in the bathrooms so they can probably be discounted (two per zone) and three are in the hallways (Main zone) so they can probably also be discounted. Eleven HR92s look to be around £600, so it should work out cheaper to get the two extra BDR91 relays if I can get away with less HR92s.


        Originally posted by HenGus View Post
        Before going firm on Opentherm, you might like to read some of the posts about Ideal boilers and Evohome/Opentherm. Opentherm is not as universally standard as some people think.

        Moreover, Evohome’s fuzzy logic is not as efficient as it could be. For example, when radiators demand heat first thing in the morning it will increase the boiler temperature to the set flow maximum temperature until all the zones are within the set temperature range. No problem with that. But, if someone plays with an HR92 in a zone later in the day, then Evohome will again demand max temperature flow until the set temperature is reached. To get maximum efficiency - lowest cost - then, in my opinion, it is best to attain and maintain rather than have variable zone temperatures.

        In your situation, a mix of HR92s and standard/electronic TRVs might work. The downside being that when any zone demands heat, then all the standard TRVs will also potentially get heat depending on the TRV setting.
        Thanks for the heads up regarding OpenTherm, I'll have a read into that.

        In terms of usage I was planning on scheduling temperatures with the intention that they would not need to be manually overridden, very much how it was when I had a Nest. Will the EvoHome manage scheduled changes better than ad-hoc changes or would it again demand the maximum flow temperature ?


        I've always read that modern boilers are most efficient when the return temperature is below a certain value. How true is this ? If it's true then the thermostat shouldn't really need to set the temperature and it should be set by monitoring the temperature of the return pipe instead. (Which could be done entirely from within the boiler) I've noticed that the Ideal h15 just goes to its set temperature each time without an OpenTherm input, so it's clearly not doing this but I've it leaves me wondering why.

        Comment

        • HenGus
          Automated Home Legend
          • May 2014
          • 1001

          #5
          Originally posted by yngndrw View Post
          In total I have ten in the main zone and eight in the bedoor zone. Four of these are towel radiators in the bathrooms so they can probably be discounted (two per zone) and three are in the hallways (Main zone) so they can probably also be discounted. Eleven HR92s look to be around £600, so it should work out cheaper to get the two extra BDR91 relays if I can get away with less HR92s.



          Thanks for the heads up regarding OpenTherm, I'll have a read into that.

          In terms of usage I was planning on scheduling temperatures with the intention that they would not need to be manually overridden, very much how it was when I had a Nest. Will the EvoHome manage scheduled changes better than ad-hoc changes or would it again demand the maximum flow temperature ?


          I've always read that modern boilers are most efficient when the return temperature is below a certain value. How true is this ? If it's true then the thermostat shouldn't really need to set the temperature and it should be set by monitoring the temperature of the return pipe instead. (Which could be done entirely from within the boiler) I've noticed that the Ideal h15 just goes to its set temperature each time without an OpenTherm input, so it's clearly not doing this but I've it leaves me wondering why.
          Rather than answer your thread point by point, I will describe my system. I have had Evohome installed now for nearly 4 years. I live in a 5 bed/19 radiator house which is divided into 12 zones. All the radiators have HR92s fitted to them. The boiler (an ATag is24) is protected by an automatic bypass valve. HW temperature control is via the Evohome HW kit connected in series with the unvented stat in the HW cylinder and controlled by a single BDR91. CH is via the Evohome controller connected to the boiler via an Opentherm Bridge. The system is configured for HW priority. The boiler parameters are set to a maximum temperature profile of 70C (TMax Set).

          I do most of my HW re-heating from 0530am. Evohome demands 90C to re-heat the cylinder but this is limited to a maximum flow temperature of 70C by the boiler settings. This does not happen with all boilers ( problem 1). CH comes on under Optimum Start conditions so from about 6.45 onwards various HR92s are whirring as the CH comes on in a particular zone. Unlike some other controls, Evohome will demand a flow temperature of 70C until all the zones are within their set temperature range (problem 2 if you are just adjusting a single zone). The boiler tries to maintain a 20C differential between flow and return but it rarely does so. Once zones reach their set temperatures, then my boiler drops back firmly into the condensing mode (having fallen from its max output of 24kWs down to 5kWs). Yesterday, when I checked the boiler, it had a flow temperature of 47C and a return temperature of 42C. More often than not, the pump was just running and the boiler had no flame. In sum, condensing does matter which is why fiddling with the HR92s is not to be recommended. I have the zones that I use set at 20C with the rest of the house at 13C from 0630 through until 22.00.

          I attach a couple of graphs which show my gas usage (yesterday) and the efficiency associated with a low flow return temperature. To make the point about not fiddling with the HR92s, the usage spike at the end of the day is associated with one zone heating our main bedroom from 15 to 19C just before we go to bed. This adjustment is set in the Evohome schedule.
          Attached Files

          Comment

          • paulockenden
            Automated Home Legend
            • Apr 2015
            • 1719

            #6
            Originally posted by yngndrw View Post
            In total I have ten in the main zone and eight in the bedoor zone. Four of these are towel radiators in the bathrooms so they can probably be discounted (two per zone) and three are in the hallways (Main zone) so they can probably also be discounted. Eleven HR92s look to be around £600, so it should work out cheaper to get the two extra BDR91 relays if I can get away with less HR92s.
            Can't help thinking that only fitting HR92s on half of your rads is a bit like driving in icy/wet conditions with two bald tyres on your car. You're going to struggle to get the level of control and (particularly) comfort that Evohome can provide.

            Other might disagree though!

            P.

            Comment

            • HenGus
              Automated Home Legend
              • May 2014
              • 1001

              #7
              Originally posted by paulockenden View Post
              Can't help thinking that only fitting HR92s on half of your rads is a bit like driving in icy/wet conditions with two bald tyres on your car. You're going to struggle to get the level of control and (particularly) comfort that Evohome can provide.

              Other might disagree though!

              P.
              i don't think that it is a question of disagreeing. i think that the decision has to be based on cost and how people use their rooms. For example, I have one room that is rarely used even when the whole family descends on us. Knowing what i know now, i would probably fit a Pegler Terrier i-temp at £18.

              Comment

              • yngndrw
                Automated Home Jr Member
                • Mar 2018
                • 12

                #8
                Originally posted by HenGus View Post
                Rather than answer your thread point by point, I will describe my system. I have had Evohome installed now for nearly 4 years. I live in a 5 bed/19 radiator house which is divided into 12 zones. All the radiators have HR92s fitted to them. The boiler (an ATag is24) is protected by an automatic bypass valve. HW temperature control is via the Evohome HW kit connected in series with the unvented stat in the HW cylinder and controlled by a single BDR91. CH is via the Evohome controller connected to the boiler via an Opentherm Bridge. The system is configured for HW priority. The boiler parameters are set to a maximum temperature profile of 70C (TMax Set).

                I do most of my HW re-heating from 0530am. Evohome demands 90C to re-heat the cylinder but this is limited to a maximum flow temperature of 70C by the boiler settings. This does not happen with all boilers ( problem 1). CH comes on under Optimum Start conditions so from about 6.45 onwards various HR92s are whirring as the CH comes on in a particular zone. Unlike some other controls, Evohome will demand a flow temperature of 70C until all the zones are within their set temperature range (problem 2 if you are just adjusting a single zone). The boiler tries to maintain a 20C differential between flow and return but it rarely does so. Once zones reach their set temperatures, then my boiler drops back firmly into the condensing mode (having fallen from its max output of 24kWs down to 5kWs). Yesterday, when I checked the boiler, it had a flow temperature of 47C and a return temperature of 42C. More often than not, the pump was just running and the boiler had no flame. In sum, condensing does matter which is why fiddling with the HR92s is not to be recommended. I have the zones that I use set at 20C with the rest of the house at 13C from 0630 through until 22.00.

                I attach a couple of graphs which show my gas usage (yesterday) and the efficiency associated with a low flow return temperature. To make the point about not fiddling with the HR92s, the usage spike at the end of the day is associated with one zone heating our main bedroom from 15 to 19C just before we go to bed. This adjustment is set in the Evohome schedule.
                Thank you, that's really helpful. As long as I don't have too many schedule changes or I batch them together so that they happen at the same time, I think I should be fine.

                Regarding problem one, does this mean that with my Ideal boiler the flow temperature would be controlled entirely via the EvoHome and would not be subject to the setting on the boiler itself ? I had a search but I couldn't find much information on OpenTherm compatibility problems. (Or I didn't understand them when I found them)



                Originally posted by paulockenden View Post
                Can't help thinking that only fitting HR92s on half of your rads is a bit like driving in icy/wet conditions with two bald tyres on your car. You're going to struggle to get the level of control and (particularly) comfort that Evohome can provide.

                Other might disagree though!

                P.
                Originally posted by HenGus View Post
                i don't think that it is a question of disagreeing. i think that the decision has to be based on cost and how people use their rooms. For example, I have one room that is rarely used even when the whole family descends on us. Knowing what i know now, i would probably fit a Pegler Terrier i-temp at £18.
                I think it will certainly work for some of my radiators, in hallways for example, but I think I'll have to have a think about exactly how I want to control it and decide based upon that. I suppose it's not too much of a hardship to add more at a later date if it becomes a problem.

                I have just realised that the ground floor hallway radiator does not have a TRV on it currently as that's where one of the thermostats is currently located so I'm going to have to drain the system and replace the valve body, so that's annoying. (I've already gotten the plumbers to fit a TRV to the upstairs radiator while they had the system drained, but forgot about the second one.)

                So lots of thinking to do before I make a decision, thank you both.

                Comment

                • HenGus
                  Automated Home Legend
                  • May 2014
                  • 1001

                  #9
                  Originally posted by yngndrw View Post

                  Regarding problem one, does this mean that with my Ideal boiler the flow temperature would be controlled entirely via the EvoHome and would not be subject to the setting on the boiler itself ? I had a search but I couldn't find much information on OpenTherm compatibility problems. (Or I didn't understand them when I found them)
                  I cannot answer that question. On my ATag, the CH manual temperature is made inoperative by the Opentherm Bridge. On the Atag, Evohome and the boiler work together to calculate what is known as the TSet Calculated flow temperature which obviously varies with Evohome demand. As I write, the boiler has a TSet Calculated Flow Temperature of 45C with a lower return temperature so I don't see the lack of manual CH control being an issue for me. On Valliant boilers, I understand that there is still manual CH temperature control. The 'problem' is that some of the parts of the Opentherm protocol are non-mandatory. Boiler manufacturers tend to configure their boilers for their own controls. For example, Atag has the Atag One controller.




                  In truth, the real problem is that UK boiler support technical teams are not that familiar with Opentherm, and if mentioned to most installers they just run a mile. (The same can be said for Evohome: they just want an install and forget type control system.)

                  Comment

                  • yngndrw
                    Automated Home Jr Member
                    • Mar 2018
                    • 12

                    #10
                    I found the same thing with Nest and OpenTherm, I called their technical support line to ask some OpenTherm questions and nobody had an answer even when they asked around. I think it's one of those things that I'll just have to take the plunge and give it a go. I might start off with just a basic system (No HR92s) and then add to it as I learn how it works.


                    One question that I have around the installation of the hot water kit is that earlier you mentioned that you have the EvoHome HW kit in series with the existing cylinder stat. My unvented cylinder is a ThermaQ Evocyl 210 which has a stat pocket going into the cylinder. There's an ESi cylinder stat mounted directly in front of the pocket with presumably its sensors going directly inside.

                    The ESi documentation suggests that there's two thermostats inside, an adjustable one and a separate 80C limit thermostat with a manual reset inside - Does the EvoTherm HW kit not fully replace both of these or do I need to find a replacement for the limit thermostat to go with it ?

                    Comment

                    • HenGus
                      Automated Home Legend
                      • May 2014
                      • 1001

                      #11
                      Originally posted by yngndrw View Post
                      I found the same thing with Nest and OpenTherm, I called their technical support line to ask some OpenTherm questions and nobody had an answer even when they asked around. I think it's one of those things that I'll just have to take the plunge and give it a go. I might start off with just a basic system (No HR92s) and then add to it as I learn how it works.


                      One question that I have around the installation of the hot water kit is that earlier you mentioned that you have the EvoHome HW kit in series with the existing cylinder stat. My unvented cylinder is a ThermaQ Evocyl 210 which has a stat pocket going into the cylinder. There's an ESi cylinder stat mounted directly in front of the pocket with presumably its sensors going directly inside.

                      The ESi documentation suggests that there's two thermostats inside, an adjustable one and a separate 80C limit thermostat with a manual reset inside - Does the EvoTherm HW kit not fully replace both of these or do I need to find a replacement for the limit thermostat to go with it ?

                      The HW Kit does not replace either of the two built in cylinder thermostats. These must not be by-passed. The HW Kit is wired in series with the existing stats. My HW Kit controls hot water in the range 55 to 60C. The cylinder stat is set at 65C. It follows that if the HW Kit fails or there is a temperature overrun (an often reported occurrence) then the cylinder stat will close off my cylinder heating at 65C. As I am sure you know, work on an unvented cylinder should normally be undertaken by a G3 qualified GSR engineer.

                      Comment

                      • yngndrw
                        Automated Home Jr Member
                        • Mar 2018
                        • 12

                        #12
                        That clarifies things a lot, I was under the impression that the HW kit replaced one of the thermostats. (The user-adjustable one) In which case, I might just fit a HR92 to replace the hot water timer and use that with the existing thermostat and valve setup initially. That saves any work on the cylinder and I'm not certain that the HW kit itself adds a huge amount of benefit for my usage, as long as enough of the radiators are calling for heat throughout the day.

                        Do you know how boilers typically work with OpenTherm and the standard call for heat signal ? I believe that normally a boiler with OpenTherm would just have the permanent live and the OpenTherm signal does all of the calling, but what if I wanted both (For example, if I wanted the radiators to call via OpenTherm and the HW via the HW zone valve's contacts) - Would this typically work okay ? (Under the proviso that all boilers will implement it slightly differently)

                        Comment

                        • DBMandrake
                          Automated Home Legend
                          • Sep 2014
                          • 2361

                          #13
                          How do you plan to use an HR92 to replace your hot water timer ? Does not compute...

                          Comment

                          • yngndrw
                            Automated Home Jr Member
                            • Mar 2018
                            • 12

                            #14
                            (Based on my understanding of S-Plan+, I need to do some tracing to find out exactly how it's been wired) So the HW "zone" is essentially five things in a chain:
                            • The HW zone in the 7 day timer
                            • The HW thermostat (User adjustable)
                            • The HW limit thermostat (Fixed at 80C)
                            • The HW zone valve
                            • The boiler (Triggered via the switch in the HZ zone valve)

                            The timer and both thermostats are in series, requiring that all three are calling for the zone valve to operate. The boiler is then triggered if any of the zone valves (HW or CH1 / CH2) are open.

                            I'm proposing to replace just the HW timer with a HR92 so that the EvoHome can decide when hot water should be available, but it would not be able to decide the temperature of it.

                            Comment

                            • DBMandrake
                              Automated Home Legend
                              • Sep 2014
                              • 2361

                              #15
                              An HR92 is a radiator controller - it doesn't have any switch contacts to connect to your zone valve. And when it calls for heat it will trigger the heating relay not the hot water relay. So again, I am confused as to why you are trying to dream up some non standard frankenstein configuration.

                              I think you're misunderstanding how the different components work together.

                              Normally with Hot water control on Evohome you have the hot water temperature sensor which sends the measured cylinder temperature back to the Evotouch controller (either insertion or strap on sensor as appropriate - insertion in your case) and the Evohome then switches on or off the BDR91 hot water relay which then opens or closes the hot water zone valve you already have.

                              You can either choose to fire the boiler from the switch contact on the hot water zone valve as you probably do now, or it is possible to add a separate boiler relay directly connected to the boiler, which is the configuration I have. (3x BDR91 in total)

                              If the hot water temperature is below the configured temperature and the hot water is scheduled to be on, the hot water BDR91 relay will turn on, at all other times it will turn off. Simple.

                              With an unvented cylinder you should always leave the limit thermostat in circuit, but you don't need to go as far as leaving the user adjustable thermostat in place, as Evohome is responsible both for setting the temperature and scheduling it. You could leave it in circuit as well and turn it up above your desired temperature as HenGus suggests but it isn't really necessary and you may not have any other usable pocket to insert the Evohome sensor if you do that.

                              So the normal method of installation would be to remove both the hot water timer and user adjustable thermostat in the cylinder, fit the insertion sensor in the adjustable thermostats old pocket, and connect the hot water BDR91 in place of both of those, leaving the high limit protection thermostat in the cylinder in series as well.

                              So you'll have BDR91 relay contacts, limit thermostat and zone valve motor all in series.
                              Last edited by DBMandrake; 14 March 2018, 05:44 PM.

                              Comment

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