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Thread: Honeywell evohome and OpenTherm integration

  1. #41
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    Quote 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; 2nd August 2017 at 10:55 AM.

  2. #42
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    Quote 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:

    http://uk.grundfos.com/content/dam/U...eet%201214.pdf

    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; 2nd August 2017 at 11:21 AM.

  3. #43
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    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!

  4. #44
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    Quote 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):

    https://getconnected.honeywell.com/e...L01%201216.pdf

    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; 2nd August 2017 at 01:50 PM.

  5. #45
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    Quote 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):

    https://getconnected.honeywell.com/e...L01%201216.pdf

    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.

  6. #46
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    Quote 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?

  7. #47
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    Quote 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.

  8. #48
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    Quote 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.

  9. #49
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    Quote 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
    https://theevohomeshop.co.uk/content...vohome-with-it

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

  10. #50
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    Quote 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):

    https://getconnected.honeywell.com/e...L01%201216.pdf

    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.

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