Honeywell evohome and OpenTherm integration

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  • HenGus
    Automated Home Legend
    • May 2014
    • 1001

    #31
    Originally posted by The EVOHOME Shop View Post
    As Hengus has said, the tests he did were performed for 3 weeks during April and his heating system isn't necessarily correctly designed or balanced for a condensing boiler. In my opinion there are various ways OpenTherm can be used to achieve heating control strategies and it is understanding this aspect that I am most interested in.

    At the end of the day the OpenTherm Protocol Specification does not require the 'master' to do every OpenTherm command and because of this, the boiler manufacturers should make their boilers capable of modifying the settings that the controls are not required to do. By Viessmann not allowing these settings available, they are in essence forcing people to buy Viessmann's own controls or an OpenTherm controller that is capable of this. In my opinion this is damaging to the OpenTherm brand as people will start seeing 'incompatibilities' with some OpenTherm products and this is no fault of the manufacturer that has produced them.



    OpenTherm doesn't require the system to be designed and correctly balanced for it. The heating system design specifies how the system should operate and condensing boilers require a 20 degree differential between flow and return. Most design for 75/55 but you can design the system at a lower temp (70/50 for instance) to aid condensing effect (you would need to increase radiator sizes to use lower temps). The fact is that the heating installer is the expert here and if they feel the new boiler is not capable of maintaining a designed temperature differential of 20 degrees because the radiators are undersized, they should advise that they are changed.

    I am using an OpenTherm monitor from here - http://otgw.tclcode.com/otmonitor.html
    Thanks Richard. I have no reason to doubt the knowledge/experience of my installer. He came with a TB recommendation. He looked carefully at the house size, radiators etc and calculated that I could get away with an 18kW system boiler. We went for a 24kW boiler because of the 250L cylinder re-heat requirement.

    Are you using an HGI 80?

    Comment

    • The EVOHOME Shop
      Site Sponsor
      • Dec 2014
      • 483

      #32
      Originally posted by HenGus View Post
      Thanks Richard. I have no reason to doubt the knowledge/experience of my installer. He came with a TB recommendation. He looked carefully at the house size, radiators etc and calculated that I could get away with an 18kW system boiler. We went for a 24kW boiler because of the 250L cylinder re-heat requirement.

      Are you using an HGI 80?
      No problem, I am sure your installer was good but I am just re-iterating that the system should be designed correctly to remain efficient no matter what demand is being thrown at the boiler.

      I am using the 80 to monitor zone temps, IDS software to monitor the Intergas boiler and OpenTherm monitor to look at thermostat commands... I am trying to give the best feedback to the customers that choose OpenTherm and it would be poor of me if I didn't understand everything that happens (hence I have setup the facility to do this and also train installers here on OpenTherm).

      top brake has asked for feedback and specific cases where there are issues with evohome and OpenTherm. I am trying to help differentiate between OpenTherm 'issues' and system design/boiler specific issues.

      You have to bear in mind that to be an OpenTherm thermostat, you do not have to have every OpenTherm control parameter the 'master' can have. This then creates 'issues' when the manufacturer of the boiler knows this and uses this to their 'benefit', knowing only their controls satisfy their requirements (because they have not allowed the installer/user to modify the settings).

      This manufacturer behaviour is not in the sprit that OpenTherm was developed and quite frankly upsets me. Any manufacturers I find doing this will be named and shamed and I will have a recommend list and an avoid list on The EVOHOME Shop based on 'compatibility'.
      Last edited by The EVOHOME Shop; 1 August 2017, 12:06 PM.

      Comment

      • blowlamp
        Automated Home Sr Member
        • Apr 2017
        • 98

        #33
        It would be less hassle for Honeywell to update their software to include a CH maximum setting and more convenient for the customer.

        Comment

        • HenGus
          Automated Home Legend
          • May 2014
          • 1001

          #34
          Originally posted by The EVOHOME Shop View Post
          No problem, I am sure your installer was good but I am just re-iterating that the system should be designed correctly to remain efficient no matter what demand is being thrown at the boiler.

          I am using the 80 to monitor zone temps, IDS software to monitor the Intergas boiler and OpenTherm monitor to look at thermostat commands... I am trying to give the best feedback to the customers that choose OpenTherm and it would be poor of me if I didn't understand everything that happens (hence I have setup the facility to do this and also train installers here on OpenTherm).

          top brake has asked for feedback and specific cases where there are issues with evohome and OpenTherm. I am trying to help differentiate between OpenTherm 'issues' and system design/boiler specific issues.

          You have to bear in mind that to be an OpenTherm thermostat, you do not have to have every OpenTherm control parameter the 'master' can have. This then creates 'issues' when the manufacturer of the boiler knows this and uses this to their 'benefit', knowing only their controls satisfy their requirements (because they have not allowed the installer/user to modify the settings).

          This manufacturer behaviour is not in the sprit that OpenTherm was developed and quite frankly upsets me. Any manufacturers I find doing this will be named and shamed and I will have a recommend list and an avoid list on The EVOHOME Shop based on 'compatibility'.
          Thanks Richard. I know that you are doing your best to sell Evohome/Opentherm but it is hardly surprising that most installers run a mile when third-party smart controls are mentioned, Given the marginal savings benefit of Opentherm over a BDR and weather compensation, I just wonder how long it would take the average house owner to recover the cost of changing an established heating system into something that is ideally configured from an Evohome/Opentherm point-of-view?

          Comment

          • The EVOHOME Shop
            Site Sponsor
            • Dec 2014
            • 483

            #35
            Originally posted by blowlamp View Post
            It would be less hassle for Honeywell to update their software to include a CH maximum setting and more convenient for the customer.
            I am sure this is something they could consider, but like I said its not an OpenTherm requirement.

            Originally posted by HenGus View Post
            Thanks Richard. I know that you are doing your best to sell Evohome/Opentherm but it is hardly surprising that most installers run a mile when third-party smart controls are mentioned, Given the marginal savings benefit of Opentherm over a BDR and weather compensation, I just wonder how long it would take the average house owner to recover the cost of changing an established heating system into something that is ideally configured from an Evohome/Opentherm point-of-view?
            Hengus, I'm not trying - OpenTherm has the capability to be best plug and play solution. Plus OpenTherm isn't a compromise, where using weather comp on a boiler and a BDR91 as a boiler relay switching the boiler is (some zones may not get to temp unless the WC curve is set correctly).

            I am used to modifying cars and you can't just upgrade a turbo without remapping the engine - effectively adding a condensing boiler to a existing standard efficiency heating system where the rads have been sized for 82/71 will mean you will not get the best results (OpenTherm controlled or W/C controlled). Radiators will be generally undersized when swapping for a condensing boiler, due to an existing higher flow temp and higher return water temp (Mean Water Temperature (MWT) would be 76.5 deg C with 82/71 verses 60 deg C with 70/50).

            Does that make sense? You will have the same efficiency issue with a condensing boiler upgrade, irrespective of the control type (ON/OFF or OpenTherm or W/C).
            Last edited by The EVOHOME Shop; 1 August 2017, 02:53 PM.

            Comment

            • HenGus
              Automated Home Legend
              • May 2014
              • 1001

              #36
              @Richard - what you are saying makes some sense; however, .....

              Myth 3

              "Condensing boilers need larger radiators."

              Although a marginal benefit of about 3% (in terms of heating capacity) can be achieved by coupling a condensing boiler with oversized radiators, it proves impractical and not that cost-efficient as one might expect. Thus, one shall not worry about the appropriateness of operating a condensing boiler with standard size radiators, all the more so when most of the current heating systems have already integrated large radiators.

              Source: Green Match/EST/Building Regs

              Comment

              • rotor
                Automated Home Guru
                • Aug 2015
                • 124

                #37
                Originally posted by The EVOHOME Shop View Post
                I am used to modifying cars and you can't just upgrade a turbo without remapping the engine - effectively adding a condensing boiler to a existing standard efficiency heating system where the rads have been sized for 82/71 will mean you will not get the best results (OpenTherm controlled or W/C controlled). Radiators will be generally undersized when swapping for a condensing boiler, due to an existing higher flow temp and higher return water temp (Mean Water Temperature (MWT) would be 76.5 deg C with 82/71 verses 60 deg C with 70/50).
                Hi Richard, would you mind explaining a little bit more? When you say 70/50 do you mean 70C flow and 50C return (measured at the boiler)? And I assume these measurements are taken while the house is already at the correct temperature, i.e. the heating system is "maintaining" temperature, not running flat out to heat up the house.

                Comment

                • The EVOHOME Shop
                  Site Sponsor
                  • Dec 2014
                  • 483

                  #38
                  Originally posted by HenGus View Post
                  @Richard - what you are saying makes some sense; however, .....

                  Myth 3

                  "Condensing boilers need larger radiators."

                  Although a marginal benefit of about 3% (in terms of heating capacity) can be achieved by coupling a condensing boiler with oversized radiators, it proves impractical and not that cost-efficient as one might expect. Thus, one shall not worry about the appropriateness of operating a condensing boiler with standard size radiators, all the more so when most of the current heating systems have already integrated large radiators.

                  Source: Green Match/EST/Building Regs
                  If radiators are sized for a higher temperature output boiler (standard efficiency boiler) they will be undersized when the new boiler requires a lower flow temperature (condensing boiler) - this is a fact not a myth.

                  Originally posted by rotor View Post
                  Hi Richard, would you mind explaining a little bit more? When you say 70/50 do you mean 70C flow and 50C return (measured at the boiler)? And I assume these measurements are taken while the house is already at the correct temperature, i.e. the heating system is "maintaining" temperature, not running flat out to heat up the house.
                  Yes, no problem.

                  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.

                  Comment

                  • DBMandrake
                    Automated Home Legend
                    • Sep 2014
                    • 2361

                    #39
                    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.
                    I've often wondered how much an automatic bypass valve interacts with a condensing boiler and spoils its ability to condense, especially if pump speeds, radiator sizing and ABV pressure setting are not optimised.

                    It seems to me that on most systems with a fixed speed pump and an ABV, if the pump has sufficient delivery for a large number of radiators (say 10+) that when only one or two radiators are flowing in a zoned system, that there must be significant flow through the ABV that raises the return flow temperature into the boiler considerably (since it is blending hot water directly out of the boiler that hasn't passed through any radiators) and thus prevents efficient condensing despite the radiators themselves achieving their designed 20 degree drop. Is this the case ?

                    Does this mean a variable speed pump is preferred for best efficiency with a condensing boiler in a zoned system where there may be times when one or two zones have high output but other zones are scheduled off ? (Which in a fixed speed system would result in high flow temperature to meet the demand from those zones, but also high return temperature due to the high ABV flow)

                    I wonder if many condensing systems with fixed speed pumps and ABV's have the ABV set too low - I've often seen people say on here theirs is set as low as 0.2 bar which seems quite low to me, and at least on my system that results in significant flow through the ABV even with many radiators open which is not really necessary. (I have mine set to about 0.4)

                    Just pondering...
                    Last edited by DBMandrake; 2 August 2017, 09:33 AM.

                    Comment

                    • dty
                      Automated Home Ninja
                      • Aug 2016
                      • 489

                      #40
                      Originally posted by DBMandrake View Post
                      Does this mean a variable speed pump is preferred for best efficiency with a condensing boiler in a zoned system where there may be times when one or two zones have high output but other zones are scheduled off ? (Which in a fixed speed system would result in high flow temperature to meet the demand from those zones, but also high return temperature due to the high ABV flow)
                      I had this conversation with my heating guy yesterday. I really need an ABV because I have HR92s on every rad and am concerned about the situation where the demand is removed (say when the overnight setback kicks in), but the pump overrun is on. He said to just take the HR92 off one of the towel radiators. I mumbled about wasting heat - especially when the bathroom is already warm or during the middle of the day when warm towels aren't required, and he said:

                      "No one has shown the industry how to commission an abv with a modulating pump yet."

                      As I understand it the two end up fighting each other. With only low demand and one or two valves open, the resistance is quite high and the pump ramps up its output pressure. This can cause the ABV to open which reduces the resistance. So the pump ramps down the pressure which makes the ABV close again. And repeat. Obviously, setting the ABV quite high would prevent this, but in my system I need high pressure to get hot water from the boiler at one end of the house to the study at the other end via the 1st floor and 15mm pipes.

                      Comment

                      • HenGus
                        Automated Home Legend
                        • May 2014
                        • 1001

                        #41
                        Originally posted by DBMandrake View Post
                        I've often wondered how much an automatic bypass valve interacts with a condensing boiler and spoils its ability to condense, especially if pump speeds, radiator sizing and ABV pressure setting are not optimised.

                        It seems to me that on most systems with a fixed speed pump and an ABV, if the pump has sufficient delivery for a large number of radiators (say 10+) that when only one or two radiators are flowing in a zoned system, that there must be significant flow through the ABV that raises the return flow temperature into the boiler considerably (since it is blending hot water directly out of the boiler that hasn't passed through any radiators) and thus prevents efficient condensing despite the radiators themselves achieving their designed 20 degree drop. Is this the case ?

                        Does this mean a variable speed pump is preferred for best efficiency with a condensing boiler in a zoned system where there may be times when one or two zones have high output but other zones are scheduled off ? (Which in a fixed speed system would result in high flow temperature to meet the demand from those zones, but also high return temperature due to the high ABV flow)

                        I wonder if many condensing systems with fixed speed pumps and ABV's have the ABV set too low - I've often seen people say on here theirs is set as low as 0.2 bar which seems quite low to me, and at least on my system that results in significant flow through the ABV even with many radiators open which is not really necessary. (I have mine set to about 0.4)

                        Just pondering...
                        @DBMandrake. You raise some interesting questions/

                        My boiler manual states the following:

                        Quote: The boiler has a self-adjusting and self-protecting control system for the load. This involves checking the temperature difference between the flow and return water.

                        If the installation resistance is higher than the value stated, the control system will adjust the load until a
                        temperature difference between flow and return water is reached that is acceptable for the control system.

                        When the temperature difference still remains too high the boiler will switch itself off and wait until the high temperature differential between the flow and return water has decreased again. Unquote

                        The flow rate and resistance figures are 910Litres/hour and 250mbar.

                        It would seem, to me at least, that without any smart controls the boiler would do what is needed to achieve the 20 degree drop.

                        Edit:

                        I have just run through the manual again and it says that the ABV has to be set such that the pump can overcome the resistance: fair enough. A flow of 910Litres/Hour equates to a Honeywell ABV setting of just under 4: my ABV is set at 3.5 (0.35mb). I may tweak it up a bit before the CH goes back on.
                        Last edited by HenGus; 2 August 2017, 09:55 AM.

                        Comment

                        • DBMandrake
                          Automated Home Legend
                          • Sep 2014
                          • 2361

                          #42
                          Originally posted by dty View Post
                          I had this conversation with my heating guy yesterday. I really need an ABV because I have HR92s on every rad and am concerned about the situation where the demand is removed (say when the overnight setback kicks in), but the pump overrun is on. He said to just take the HR92 off one of the towel radiators. I mumbled about wasting heat - especially when the bathroom is already warm or during the middle of the day when warm towels aren't required, and he said:

                          "No one has shown the industry how to commission an abv with a modulating pump yet."
                          To me, having no uncontrolled (bypass) radiators is a benefit/feature that can be implemented with a system like Evohome where every zone has an equal ability to call for heat. The hallway radiator was originally the bypass radiator in our system, I now have an ABV and all radiators including hallway have HR92's.

                          A perfect case in point is our upstairs bedrooms aren't insulated as well as they should be and we're more or less forced to schedule those rooms on (to about 18) through the night in the winter, especially with a toddler now who isn't as accepting of cold nights and thick blankets as we are... if I had a bypass radiator that hallway radiator would be running all night long in the winter - very wasteful.

                          One thing is for sure - if you have a fixed speed pump and HR92's on all radiators there MUST be some sort of automatic bypass. If the system has a variable speed pump then I'm not sure - can the pump modulate right down to zero flow without harming itself or the heat exchanger in the boiler ? I suspect boilers provided with internal modulating pumps probably have a safety bypass inside them that may be enough for pump overrun for a few minutes, but that's speculation.
                          As I understand it the two end up fighting each other. With only low demand and one or two valves open, the resistance is quite high and the pump ramps up its output pressure. This can cause the ABV to open which reduces the resistance. So the pump ramps down the pressure which makes the ABV close again. And repeat.
                          I think you have that backwards actually.

                          If you look at the graphs provided with the pumps, variable speed pumps (at least the Grundfos one I have - in its variable speed mode, which I don't use) actually reduce the pressure when the flow is restricted. For example:



                          On the first graph flow volume is on the X axis and pressure on the Y axis. The black trend lines are in the fixed speed mode, and you can see what you would expect there - as the flow rate is restricted (to the left) the pressure increases until it reaches the maximum the pump can produce. However in the variable speed mode (red lines) the curve slopes the opposite way - lower flow rate (due to reduced numbers of radiators being open) will reduce the pressure not increase it. (Or more precisely when it senses reduced flow it reduces the speed to effect an overall drop in pressure, instead of letting the pressure rise, like it normally would)

                          So the problem with combining an ABV with variable speed would be - below the pressure threshold where the ABV would open everything works fine, when radiators are closed and flow is low the pump would run slowly at low pressure, as radiators open and the flow increases so does the pressure, at some point the ABV threshold will be met and it will start to open and provide an "easy" flow path, the pump will sense this as if more radiators opened, run the pump faster, increase the pressure and cause the ABV to open further.

                          In effect you have a runaway situation where once the ABV starts to open it makes the flow easier which makes the pump speed up and increase pressure further. Soon the pump will be running at full speed and the ABV will be fully open.

                          Again I'm not an expert but I think that if you had a modulating variable speed pump and an ABV you'd want to set the ABV pretty high (maximum ? 0.6 bars) so that it only acts as a safety pressure relief valve and doesn't open at all under normal operating conditions. Let the pump modulate as it is designed to.
                          Last edited by DBMandrake; 2 August 2017, 10:21 AM.

                          Comment

                          • blowlamp
                            Automated Home Sr Member
                            • Apr 2017
                            • 98

                            #43
                            I'm tasked today with installing a Nest v3 thermostat for an elderly neighbour.

                            I thought I'd check out what specific OpenTherm settings are available when used as such and it seems there are two: DHW temperature and CH maximum flow temperature.

                            So come on Honeywell - go with the flow!

                            Comment

                            • StephenC
                              Automated Home Guru
                              • Feb 2017
                              • 102

                              #44
                              Originally posted by blowlamp View Post
                              I'm tasked today with installing a Nest v3 thermostat for an elderly neighbour.

                              I thought I'd check out what specific OpenTherm settings are available when used as such and it seems there are two: DHW temperature and CH maximum flow temperature.

                              So come on Honeywell - go with the flow!
                              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).
                              Last edited by StephenC; 2 August 2017, 12:50 PM.

                              Comment

                              • blowlamp
                                Automated Home Sr Member
                                • Apr 2017
                                • 98

                                #45
                                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.
                                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.

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