Honeywell evohome and OpenTherm integration

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  • dty
    Automated Home Ninja
    • Aug 2016
    • 489

    #46
    Originally posted by The EVOHOME Shop View Post
    I am using an OpenTherm monitor from here - http://otgw.tclcode.com/otmonitor.html
    Richard,

    Where did you get that from? I've gone through the "click here to pre-populate a basket of components" link, but it appears that supplier doesn't ship to the UK. Did you get a pre-built one, or find a different supplier of components?

    Comment

    • top brake
      Automated Home Legend
      • Feb 2015
      • 837

      #47
      Originally posted by blowlamp View Post
      When I fitted a Lyric T6R to the inlaws' Intergas combi earlier this year, I don't remember seeing any option to set CH maximum temperature.

      I wouldn't get too excited by the Lyric - remember that at its heart it is still a TPI controller that seems to 'convert' to OpenTherm like Evohome does and as such will act similarly. In fact there is a discussion on this site that details the high flow temps & boiler cycling a user experienced with his Lyric.
      both evohome and Lyric T6 are self learning fuzzy logic controllers - the control is either TPI Cycle rate / run time or OT Modulation depending on whether you connect to TPI or OT terminals

      so your comment 'at its heart it is still a TPI controller' is factually incorrect, sorry

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

      Comment

      • blowlamp
        Automated Home Sr Member
        • Apr 2017
        • 98

        #48
        Originally posted by top brake View Post
        both evohome and Lyric T6 are self learning fuzzy logic controllers - the control is either TPI Cycle rate / run time or OT Modulation depending on whether you connect to TPI or OT terminals

        so your comment 'at its heart it is still a TPI controller' is factually incorrect, sorry

        hope this makes sense?

        I wrote that based on what I'd read here about how it is believed Evohome works when controlling an OpenTherm boiler. This being that Evohome works out a boiler on/off ratio for the current set of conditions (as per TPI), which is subsequently converted to a suitable modulation level and/or flow temperature before being passed onto the boiler. My apologies to Honeywell if this isn't the case.

        I'd be interested to know if Lyric uses a proportional band technique for regulation and does the T6 thermostat directly monitor & control CH flow & return temperatures for modulation under OpenTherm, or does it use the air temperature at the unit?

        Cheers.

        Comment

        • top brake
          Automated Home Legend
          • Feb 2015
          • 837

          #49
          Originally posted by blowlamp View Post
          I wrote that based on what I'd read here about how it is believed Evohome works when controlling an OpenTherm boiler. This being that Evohome works out a boiler on/off ratio for the current set of conditions (as per TPI), which is subsequently converted to a suitable modulation level and/or flow temperature before being passed onto the boiler. My apologies to Honeywell if this isn't the case.

          I'd be interested to know if Lyric uses a proportional band technique for regulation and does the T6 thermostat directly monitor & control CH flow & return temperatures for modulation under OpenTherm, or does it use the air temperature at the unit?

          Cheers.
          have a read of this great explanation


          any remaining questions i'll be happy to answer :-)
          I work for Resideo, posts are personal and my own views.

          Comment

          • blowlamp
            Automated Home Sr Member
            • Apr 2017
            • 98

            #50
            Originally posted by StephenC View Post
            Indeed - it was finding this out that made me realise that actually it wasn't just Viessmann locking you in to their controller, but that Nest, as you've found have the ability to control this when driving via OpenTherm as well. I'm still unhappy with Viessmann though, and Nest is not really comparable with retrofit zoning to be fair.

            I believe the only way Honeywell could change this is via (optional) demand based offsets (i.e. reduce demand percentages sent to R8810 by NN%) as the R8810 is the system device that deals with flow temps. Evohome controller deals in demand percentages. Demand % gets translated to flow temp on R8810 itself. I'm not sure how this would work in practice, and may have an adverse effect on the rest of the temp range.

            I would imagine it will take their next-gen product to supercede both the Evohome controller and R8810 Opentherm bridge to be able to add this option in somehow.


            I believe the Honeywell Lyric has a newer all-in-one receiver On/Off and also Opentherm control box (R4H810A):



            Does anyone know if the max ch flow temp can be set with the Lyric?

            This is physically different and also in the spec sheet details encryption for the RF transmission (which I don't think Evohome has?). So likely a new generation of product aimed at retrofit multi-zone I would think cannot be too far away that may (or may not) resolve this issue by providing the optional OT spec config on the controller.

            @blowlamp - it would be good to get some of your feedback on the Nest v3 driving OpenTherm by the way (in a separate thread).

            I'd like to know as well and would love to oblige, but it turned out that her boiler doesn't have OpenTherm, just on/off I'm sorry to say.
            I thought about trying it with my own system, but it's still a bit too warm to be messing around with the heating.

            Comment

            • rotor
              Automated Home Guru
              • Aug 2015
              • 124

              #51
              Originally posted by The EVOHOME Shop View Post
              Modern condensing boilers are designed to have a flow and return differential of 20 deg C. Condensing boilers require a return water temperature of below 55 degrees C to be at their most efficient. So designing a heating system to operate at 70 deg C flow and 50 deg C return will guarantee efficient operation.

              When measuring the differential, this is done at the radiators - ideally 70 in and 50 out. The obvious downside of this is where the existing system was designed as an 82/71 system, the radiator sizing would have been specified much smaller than if they had been sized for a condensing boiler at 70/50. So if everything was to remain the same as before with a 70 degree flow temp, this will give less heat output to the room. If you increase the temperature of the flow, you will bring the boiler out of condensing mode.

              My advice is if you replace the boiler and it was an old standard efficiency boiler, the radiators should be looked at and correctly sized for efficient operation of the new boiler.
              Thanks again. Another question: if each radiator is a different size, how can they all give 20 degrees drop? Wouldn't a bigger radiator drop a lot more than a smaller one?

              Comment

              • paulockenden
                Automated Home Legend
                • Apr 2015
                • 1719

                #52
                Originally posted by rotor View Post
                Thanks again. Another question: if each radiator is a different size, how can they all give 20 degrees drop? Wouldn't a bigger radiator drop a lot more than a smaller one?
                That's what balancing is all about.

                Comment

                • HenGus
                  Automated Home Legend
                  • May 2014
                  • 1001

                  #53
                  A quick google search shows that even installers cannot agree on the required temperature drop across radiators. Historically, it was 20F which equates to 11C but many rounded it down to 10C. Some installers are adamant that it should now be 20C and others think that anything between 10C and 20C is just fine - and these people are the professionals.

                  I know that Richard is keen to maximise efficiency; however, given that the condensing/non-condensing saving is stated to be in the order of 3%, why would any homeowner want to go to the expense of having new radiators installed? Given that the 3% saving is on kWhs/year consumed, my saving would be 10000 x 3% or 300kWhs which equates to an annual saving of £8.93 per year on my present tariff. What am I missing?

                  Comment

                  • dty
                    Automated Home Ninja
                    • Aug 2016
                    • 489

                    #54
                    Originally posted by HenGus View Post
                    A quick google search shows that even installers cannot agree on the required temperature drop across radiators. Historically, it was 20F which equates to 11C but many rounded it down to 10C. Some installers are adamant that it should now be 20C and others think that anything between 10C and 20C is just fine - and these people are the professionals.
                    More to the point, you might not be able to practically increase the size of your radiators for physical/aesthetic reasons. Many of mine are type 11 or type 21, so I can at least update them to type 22. However, many of them are also imperial sizes, so the physical/aesthetic issues still exist.

                    Originally posted by HenGus View Post
                    I know that Richard is keen to maximise efficiency; however, given that the condensing/non-condensing saving is stated to be in the order of 3%, why would any homeowner want to go to the expense of having new radiators installed? Given that the 3% saving is on kWhs/year consumed, my saving would be 10000 x 3% or 300kWhs which equates to an annual saving of £8.93 per year on my present tariff. What am I missing?
                    I have just finished the first full year in our new house. My usage for the year was approximately 65,000kWh. So in my case I'd be looking to save about £33 since I'm only paying 1.69p/kWh. Even on your tariff it would mean £58. As you say, hardly worth it for the cost savings.

                    I will be looking to upgrade my radiators, but mostly from a comfort perspective... some of my rooms heat up very slowly at the moment.

                    Comment

                    • DBMandrake
                      Automated Home Legend
                      • Sep 2014
                      • 2361

                      #55
                      Originally posted by HenGus View Post
                      A quick google search shows that even installers cannot agree on the required temperature drop across radiators. Historically, it was 20F which equates to 11C but many rounded it down to 10C. Some installers are adamant that it should now be 20C and others think that anything between 10C and 20C is just fine - and these people are the professionals.
                      Achieving a drop of 11 degrees is difficult on very small radiators, (such as mini hallway types) let alone 20 degrees, so I doubt whether a house with a wide variety of radiator sizes can achieve 20 degrees on the smallest radiators in practice. You have to restrict the flow to the small radiator so much that it can hardly heat up while it is achieving a large temperature drop.
                      I know that Richard is keen to maximise efficiency; however, given that the condensing/non-condensing saving is stated to be in the order of 3%, why would any homeowner want to go to the expense of having new radiators installed? Given that the 3% saving is on kWhs/year consumed, my saving would be 10000 x 3% or 300kWhs which equates to an annual saving of £8.93 per year on my present tariff. What am I missing?
                      Where did you get a figure of 3% for efficiency increase for a condensing boiler ? If it was only 3% it wouldn't be worth the hassle - it would be lost amongst the noise of daily/weekly/monthly variations in the weather...

                      A quick google suggests "at least" 10-12% increase in efficiency when condensing, which seems more likely. Also just compare the efficiency of older non-condensing boilers with a modern condensing boiler - 70-75% is typical for a non-condensing boiler such as mine, over 90% is typical of a condensing boiler in condensing mode - eg about a 25% improvement in efficiency. Granted, some of that will be improvements in heat exchanger/burner design etc but a lot of it must come from the actual condensing process.

                      So 3% doesn't sound right to me at all, unless it is an average figure that takes into account what percentage of time the boiler is likely to be in condensing mode in a "typical" system, if so, that's not the right figure to use in this context. We want to know the efficiency increase when it is condensing, vs when it is not for the same boiler and system.
                      Last edited by DBMandrake; 3 August 2017, 11:02 AM.

                      Comment

                      • blowlamp
                        Automated Home Sr Member
                        • Apr 2017
                        • 98

                        #56
                        I think that in days of old balancing was more important to ensure each radiator got its fair share of water.

                        When I put in my system, I didn't spend too long fussing over balancing, I just made sure the lockshield valve allowed adequate flow through the radiator, whilst being sure it restricted it enough for the sake of directing water to the other radiators in the system.

                        In use, I feel the balancing is done in real-time by the TRVs, as they constantly modulate the circulation.
                        Last edited by blowlamp; 3 August 2017, 05:51 PM.

                        Comment

                        • dty
                          Automated Home Ninja
                          • Aug 2016
                          • 489

                          #57
                          Originally posted by blowlamp View Post
                          I think that in days of old balancing was more important to ensure each radiator got its fair share of water.

                          When I put in my system, I didn't spend too long fussing over balancing, I just made sure the lockshield valve allowed adequate flow through the radiator, whilst being sure it restricted it enough for the sake of directing water to the other radiators in the system.

                          In use, I feel the balancing is done real-time by the TVRs as they constantly modulate the circulation.
                          My installer shares this view, but I'm not convinced. This overlooks the early morning heat up where it's conceivable that the majority of radiators will be calling for heat (especially during the winter). Without a reasonably well balanced system, some radiators will get hot and some won't. I guess Evohome will eventually compensate by starting the more distant radiators earlier in the optimum start window. Maybe.

                          Comment

                          • blowlamp
                            Automated Home Sr Member
                            • Apr 2017
                            • 98

                            #58
                            Originally posted by dty View Post
                            My installer shares this view, but I'm not convinced. This overlooks the early morning heat up where it's conceivable that the majority of radiators will be calling for heat (especially during the winter). Without a reasonably well balanced system, some radiators will get hot and some won't. I guess Evohome will eventually compensate by starting the more distant radiators earlier in the optimum start window. Maybe.
                            Which is why I put this:

                            "When I put in my system, I didn't spend too long fussing over balancing, I just made sure the lockshield valve allowed adequate flow through the radiator, whilst being sure it restricted it enough for the sake of directing water to the other radiators in the system."

                            Comment

                            • HenGus
                              Automated Home Legend
                              • May 2014
                              • 1001

                              #59
                              Originally posted by DBMandrake View Post
                              Achieving a drop of 11 degrees is difficult on very small radiators, (such as mini hallway types) let alone 20 degrees, so I doubt whether a house with a wide variety of radiator sizes can achieve 20 degrees on the smallest radiators in practice. You have to restrict the flow to the small radiator so much that it can hardly heat up while it is achieving a large temperature drop.

                              Where did you get a figure of 3% for efficiency increase for a condensing boiler ? If it was only 3% it wouldn't be worth the hassle - it would be lost amongst the noise of daily/weekly/monthly variations in the weather...

                              A quick google suggests "at least" 10-12% increase in efficiency when condensing, which seems more likely. Also just compare the efficiency of older non-condensing boilers with a modern condensing boiler - 70-75% is typical for a non-condensing boiler such as mine, over 90% is typical of a condensing boiler in condensing mode - eg about a 25% improvement in efficiency. Granted, some of that will be improvements in heat exchanger/burner design etc but a lot of it must come from the actual condensing process.

                              So 3% doesn't sound right to me at all, unless it is an average figure that takes into account what percentage of time the boiler is likely to be in condensing mode in a "typical" system, if so, that's not the right figure to use in this context. We want to know the efficiency increase when it is condensing, vs when it is not for the same boiler and system.
                              Efficiency doesn't appear to fall off a cliff if the boiler isn't condensing. I have been looking at a number of condensing boiler efficiency graphs this morning which show, for example, a condensing boiler with a return temperature of 55C with a boiler efficiency of 87% which reduces to 85.5% with a return temperature of 70C. A boiler efficiency of 99% is only achieved when the flow return temperature is 10C. The extra savings come from the fact, as far as I can see, that the heat exchanger is bigger; there is usually some form of modulation and no pilot flame.

                              Going from the theoretical to the practical. Looking back over the month of July 2016, my old boiler consumed an average of 10.74kWh per day. Last month, my daily average was 6.8kWhs with HW selected on for a similar period of time. Given that the boiler slowly cranks up to 70C when cylinder heating, it would only be in condensing mode for some of the time. The efficiency saving is high at 36%: I suspect that a lot of this is down to the fact that there is no pilot flame burning in the boiler for 24 hours a day.

                              Edit:

                              The graph in this article is typical of what a google search reveals:

                              https://vintagegreenhome.wordpress.com/2012/10/17/are-you-getting-the-maximum-energy-savings-from-your-condensing-boiler-fall-is-a-great-time-to-check-your-settings-to-find-out/
                              55C = 131F

                              70C = 158F
                              Last edited by HenGus; 3 August 2017, 03:45 PM.

                              Comment

                              • The EVOHOME Shop
                                Site Sponsor
                                • Dec 2014
                                • 483

                                #60
                                Originally posted by rotor View Post
                                Thanks again. Another question: if each radiator is a different size, how can they all give 20 degrees drop? Wouldn't a bigger radiator drop a lot more than a smaller one?
                                I think I've started something here... The thread is about OpenTherm and evohome, but this is one small factor. There is a lot more importance in the heating design and its at this point you will discover the gaps in your knowledge.

                                So, lets get to the basics...

                                Each room in your house has a certain heat loss (based on heat loss calculations for that room) and the rooms heat loss is calculated based on say a -4 degrees C outside temperature. The radiator is then sized based on the heat loss of the room, but using the design characteristics that you want.

                                So say I want a 70 degree C flow and 50 degree C return (ideal conditions for a condensing boiler). This gives you a Mean Water Temperature (MWT) of 60 degrees C. Say then you want the room to be 21 degrees C, this then gives you a Mean Water to Air Temperature (MW-AT) difference of 39 degrees C (60 - 21 = 39). As all radiators are tested for their output at a MW-AT of 50 degrees C you have to recalculate the radiator size. To give you some perspective, a MW-AT difference of 50 degrees C would mean an 81 degree C flow temp, 20 degree C differential (so a 61 degree C return temp which is above condensing temps) at a required 21 degree C in the room air temp.

                                So if I give the example of a Stelrad Compact 600mm x 1000mm Double Panel Radiator (K2). It has an output of 1732 Watts at a MW-AT difference of 50 degrees C (most will state DT50*C in a radiator book). If it was now to be used with a system running with a MW-AT of 39 degrees C (70/50) the actual radiator output would now only be 1204 Watts, some 30.48% too small! You would now need to have a radiator some 30% bigger in output verses the old radiator, as its output in Watts was was originally sized for a MW-AT of 50 degrees C.

                                If you were just to swap a condensing boiler into a house where the original radiators were sized for a boiler designed with a 82 flow and 71 return (MW-AT difference of 56 degrees at an air temp of 21 degree C), then the original radiators would actually be some 36.76% too small...

                                Pump selection (including pump speed selection based on the index circuit) and system balancing must be done with caution, as flow rates to the radiators are directly calculated on the heat output of the radiator and this is expressed in kg/sec (or can also be expressed as litres/sec, as 1 kg of water is equivalent to 1 Litre of water). For example, a room requiring a 2000 Watt radiator would need a correctly sized radiator at 70/50 to obtain the correct output, but would also need a flow rate of 0.024 kg/sec in order to supply enough energy to that particular radiator to obtain its output.

                                I can go on, but hopefully the above shows there is much more behind heating design than a thermostat controlling the room by relaying the information back to the boiler...
                                Last edited by The EVOHOME Shop; 4 August 2017, 10:13 AM.

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