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Thread: Evohome - poor temperature regulation

  1. #41
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    Understood, but the question I am asking is whether the HR92s act independently of the controller? Assume valve open and temp rising. Controller communicates with HR92, and temp is 1 degree below target. Two minutes later local temp reaches target. Does the HR92 just close the valve or does it have to wait until it next speaks to the controller?

  2. #42

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    Quote Originally Posted by HenGus View Post
    Understood, but the question I am asking is whether the HR92s act independently of the controller? Assume valve open and temp rising. Controller communicates with HR92, and temp is 1 degree below target. Two minutes later local temp reaches target. Does the HR92 just close the valve or does it have to wait until it next speaks to the controller?
    The Hr92 reads the surrounding air. Not the temp of the water/rad etc. Two mins to reach target temp would be unlikely. In a typical room you are looking at 1-2 degrees per hour. (assuming no bodies/heat additions etc).

    But in answer to your question - it will close the valve. The Hr92 is in full control of the valve. The evohome makes temp requests/commands only
    getconnected.honeywell.com | I work for Honeywell. Any posts I make are purely to help if I can. Any personal views expressed are my own

  3. #43

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    Quote Originally Posted by erik View Post
    What you're describing is a typical accidental overshoot. Heat being put into the radiator causing an overshoot AFTER the system has already adapted to the rising temperature (closed the valve). However, I think what we're seeing is a valve that doesn't actually close untill there's a huge overshoot already. I wouldn't call that an accidental overshoot, but a orchestrated overshoot. I think greyhound actually said it doesn't close untill 1.5 degree above setpoint. That's way too late. Unless his room temperature rises 1.5 degree in 10 minutes or so, because that might be too short for the system to adapt in time, but I doubt that's the case. My guess is that the HR92 got more than enough time to close earlier, but chose to remain open untill way above setpoint.


    what do you expect to happen when it hits 17? The valve opening shortly to stay on or just above 17 and closing in time to prevent creating another overshoot? I expect it to build up the same huge overshoot again to be honest. Which is silly.


    so why is the valve open anyway when the temperature is already above setpoint and it's not asking for heat? This will cause these overshoots when another zone heats up all the time, especially if it's not aware what other zones are doing (why not?!). Seems like a bad design decision?


    No. Just no. An antique Honeywell Round performs at least 5x better in keeping a constant temperature than Evohome, that's fact. You can show any certification you want, but it's not going to change what we're seeing in the home.



    Anyway, this was just your response to 1 of the 2 issues greyhound was reporting:


    What about this one?

    Any comments on that?

    Erik - I am sorry to correct you but I am not sure you fully understood what I am saying -

    so why is the valve open anyway when the temperature is already above setpoint and it's not asking for heat?

    It is asking for heat - even at 17 degree it will be asking for heat - albeit in controlled amounts

    what do you expect to happen when it hits 17?

    The HR92 will perform as it did before at the beginning of this virtual scenario - working to balance the heat available and modulating the water flow.

    No. Just no. An antique Honeywell Round performs at least 5x better in keeping a constant temperature than Evohome, that's fact. You can show any certification you want, but it's not going to change what we're seeing in the home.

    No it doesn't - you are expecting a 0.2 degree of control which is industrial scale and would never been achieved within residential controls.

    Zones will first call for heat when they are at or less than the set point. But once called, zone will continue to call for heat all the way up to 1.5 degrees over the set point


    Same answer as above if the zone is at setpoint it will continue to trickle heat into maintain the setpoint, above the setpoint the valve will shut. It does not call for heat. As mentioned it will be probably be around the +0.5 mark.

    I think greyhound actually said it doesn't close untill 1.5 degree above setpoint.

    If it really did close 1.5 degrees above setpoint, then a room temp even greater would be experienced. Any temp reading on the HR92 has had the action long time ago against it (like light from our sun, what you see is 7 mins old, bad metaphor but hopefully helps) . So if the rooms do reach a max temp of 18.5 then the HR92 would have operated in the past to reach this max point.

    Erik - if you give your consent we can share the findings and data found in your open case with us with the rest of the forum to help illustrate the above?
    Last edited by Rameses; 13th March 2015 at 08:47 PM.
    getconnected.honeywell.com | I work for Honeywell. Any posts I make are purely to help if I can. Any personal views expressed are my own

  4. #44
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    No it doesn't - you are expecting a 0.2 degree of control which is industrial scale and would never been achieved within residential controls.
    do you think I'm making this up? The degree of control I'm expecting is in the same ball park as a dirt cheap and very old Honeywell Round. But it's doing 5 times worse instead. Again: I'm not making this up. This is what I see happening right under my eyes. Why would Evohome not be able to achieve at least close to the same degree of control? I can tell you why. Because it NEVER skips a 10 minute cycle, or two, even though it clearly should sometimes. It just keeps putting in more heat every 10 minutes, even though it's clearly not needed.

    I'm telling you what the problem is. I'm telling you under what circumstances it's happening. I'm telling you the reason why it happens. And still Honeywell is unable to recognize it. It's absurd. And I'm not alone. There's people like greyhound who are seeing the exact same dumb behavior as I am seeing.

    if the zone is at setpoint it will continue to trickle heat into maintain the setpoint, above the setpoint the valve will shut. It does not call for heat. As mentioned it will be probably be around the +0.5 mark.
    NOT TRUE. The valve WILL stay open and it WILL call for heat, every 10 minutes. Come over to my house. Take a look. See what it does. It doesn't do what you're saying. Reinstall it, do whatever you want to it. It won't change. Especially in thermostat modus, it will easily go more than +1.0 (1.5 actually) above setpoint. In zoning modus using HR92's, it's going to be around 0.7 over setpoint untill it stops asking for heat. Still not acceptable.

    It is asking for heat - even at 17 degree it will be asking for heat - albeit in controlled amounts
    In greyhound's example it wasn't asking for heat, as far as I understood. The temperature was still above the setpoint of 17.

    The HR92 will perform as it did before at the beginning of this virtual scenario - working to balance the heat available and modulating the water flow.
    maybe greyhound can test to see if that's really the case. I think there's a good chance it will go to 18.5 again before closing.

    If it really did close 1.5 degrees above setpoint, then a room temp even greater would be experienced.
    Well, I'd like to have greyhound confirm it. But let's say it happens at 1.0 degree above setpoint instead of 1.5 above. Still very bad performance.

    Erik - if you give your consent we can share the findings and data found in your open case with us with the rest of the forum to help illustrate the above?
    I would like to receive these findings and data myself first please. As far as I know, Honeywell is testing the Evohome thermostat modus behavior in a test setup (a simulation with just Evohome and BDR91, an outside temperature of 18 and a setpoint of 20). How's that going? Maybe you can share that data? If its BDR91 ever skips a 10 minute cycle, could you please make sure to record it on film? Because it would be a unique moment and the first time ever I would see it.
    Last edited by erik; 14th March 2015 at 12:22 AM.

  5. #45
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    We have had many postings about temperatures and over runs, some getting a little irate but it seems to me many are saying the same thing, albeit in a different way. So often that happens and you see discussions getting heated yet both sides are saying similar things and don’t realise it! I decided to check my system again this morning and bore myself to death in the process. (and probably you!). I monitored two rooms. My lounge which is set to 20 at 06:40 on a Saturday and my kitchen which is set to 18 at 07:30 in both cases after overnight settings of 10.

    In each case I noted what the TRV said the temperature was and what the Control Panel (CP) said. The CP was often reading a higher temperature than the TRV and not just momentarily. It cannot be the communication delay as if the latter it would read a lower temperature until it got its next message. Therefore it seems the TRV is sending a different temperature reading to the CP or perhaps the display is not as spot on as the actual sensor in the HR92,

    I also noted separately when the boiler came on and off. I had to sit in the kitchen for the duration so that I could hear it. Below is listed the times, TRV and CP readings for each room and a note of what the boiler was doing.

    I also found that the boiler was not switching off frequently because the TRVs were telling it to but because the heat had reached the maximum for the boiler and the cut out was operating i.e. Evohome was not switching the boiler off but its own cut out was. I found it out by a simple check of turning the thermostat up on the boiler with the immediate result it came on.

    Also toward the end at 06:30 my hot water comes on, the boiler fired up and stayed on for longer to heat the hot water but the controlled rooms did not get any hotter.

    Other zones I did not touch and none came on, valves remained closed until about 07:10 when a couple opened up. They are set to 18 at 07:30, they read 16.5 and optimisation was operating. Radiators in the those zones got hot but my two test ones (kitchen and living room) did not alter despite they being close to temperature. The boiler did not then immediately come on despite this and I assume because it's thermostat was overriding it. The pump was on.

    What does it tell me? I am sure others will make more of this than I do. I am not a systems expert etc. just a humble user but it seems to me what I am getting is what one would expect. Evohome is controlling things; it is creating a balanced heat where required, when one zone wants heat and another is near to it in temperature it is not getting warmer when it should not; they are staying off when told to be off. Warm up is a gradual process hindered only by the boiler's thermostat cutting out. I am sure that if I opened up all 11 zones and/or disconnected the boiler thermostat Evohome would control things such that the boiler does not cycle so frequently, except the water in the system might get hot!

    Concern has been expressed at constant cycling. As can be seen below, until really the required temperature was obtained there was much cycling of my boiler. But I repeat that most of this was due to the water temperature causing the boiler stat to switch off. However, the pump remained on hence the radiators continued to heat up as was required.

    Is this no different to my having electric panel radiators? Once the desired temperature has been obtained they switch off but could repeatedly then come on and off to maintain the temperature. In a previous house I owned I at one time had all electric heating. Panel radiators. It was highly efficient and economic. They would come on until the set temperature was reached and then off. Thereafter you could hear them clicking on and off to maintain that temperature. Just what you would expect. Just what I expect with any central heating system, except with a water filled system it is a boiler that goes on and off.

    It seems to me my Evohome system is working as it should. More than likely it will be more efficient at some future time when my boiler packs up and needs to be replaced - current boiler is 17.5 years old and a non condensing type.

    I have in a previous posting queried whether optimisation needs finer tuning. I think it still could be better but after this check I think it operates better than I thought. I still have the conundrum of it coming on exactly 60 minutes before the allotted time to heat up one room but for other zones it seemed to come on only 20 minutes before. Again 60 minutes before the set time it switched a zone off and had I not been going out the room probably would have cooled too much. I still think optimisation needs some fine tuning. It has not learned as I expected it would (it is 8 weeks + since all was set up).

    Results. First temperature is the TRV reading CP is what the Control Panel displayed.

    Living Room
    05:40*Optimisation started - room set for 20 at 06:40
    05:40 16
    05:58 16.5 CP 17*
    06:04 17 CP 17.5
    06:09 17.5 CP18.5
    06:12 19 CP 19
    06:17 19.5 CP 19.5
    06:18 19.5 CP20 – room at set temperature after 38 minutes.
    06:20 20 CP 20
    06:25 20 CP 20.5
    06:28 20.5 CP 21
    06:31 21 CP 21
    06:34. 21.5 CP 21.5
    06:38 21.5 CP 22
    06:46 22 CP 22
    07:00 Optimisation applying again. Room to be 18 at 08:00. Checking the HR92 it clearly had a message to be at 18 now.
    Thereafter stopped increasing and remained at 22 but touching radiator could feel it was off. The pump was running as other zones being heated but this zone was not affected by that. However, a room thermometer at waist height read 19.5. No doubt t was throttling back to be at 18:00 by 08:00. I see nothing wrong with this.

    Kitchen
    05:45 Kitchen 15 (night time setting10) manually (via CP) increased to 20
    05:48 Kitchen valve receives set temp of 20
    05:58 15.5 CP 16*
    06:08 16.5 CP 17.5
    06:15 18 CP 18
    06:17 18 CP 18.5
    06:19 18 CP 19
    06:20 valve adjust heard 18 CP 19
    06:23 19 CP 19.5 Valve adjust heard.
    06:24 19.5 CP 20
    06:26 valve adjust 19.5 CP 20 (could hear restricted flow into radiator)
    06:29 20 CP 20
    06:30 valve adjust ? Closing 20 CP 20
    06:33 20 CP 20.5 no sound of water flowing in radiator ? Valve off
    06:37 20.5 CP 20.5
    06:40 valve adjust - ? Further closing - no sound of water flow anyway. 20.5 CP 20.5
    06:46 21 CP 21
    Thereafter did not go above 21 but settled back to 20.5 and touching radiator could feel it was off. Gradually it settled at 20 until the next set point (07:30 – 18)

    Boiler
    05:40 On
    05:55 Off
    06:00 On
    06:01 Off
    06:02 On
    06:03 Off
    06:05 On
    06:06 Off
    06:07 On – I increased the temp setting for boiler. Clearly boiler cutting out not Evohome causing it.
    06:10 Off
    06:11 On
    06:12 Off
    06:13 On - after putting boiler on maximum
    06:16 Off
    06:18 On
    06:19 Off
    06:20 On
    06:21 Off
    06:23 On
    06:23 Off
    06:30 On HW comes on at 06:30 Starting temp 45
    06:40*Off HW now 58 (set to 60)
    06:45 On
    06:46 Off
    06:47 On
    06:48 Off HW 61

    Answer, to use an oft used expression, I think Evohome does “what it says on the tin.”

  6. #46
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    you're asking for 20. It's delivering 22. It didn't say that on my tin.

    Also, if you will keep the same setpoint in a zone for a day (and close all other zones to prevent them from influencing the result), you will probably see it going from setpoint to setpoint + 1 and back to setpoint and back to setpoint + 1 etc. all day.

    If you do the same experiment with a old Honeywell Round thermostat, it will probably do a much better job in keeping temperature constant.

    Your heating is very very quick by the way. It doesn't slowly build up a huge overshoot like it does for me. It very quickly builds up a overshoot, more like a true accidental overshoot. Less orchestrated than in my case. The circumstances are very different and therefor hard to compare.

  7. #47
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    Quote Originally Posted by erik View Post

    Your heating is very very quick by the way. It doesn't slowly build up a huge overshoot like it does for me. It very quickly builds up a overshoot, more like a true accidental overshoot. Less orchestrated than in my case. The circumstances are very different and therefor hard to compare.
    "And there is the rub" bit of Shakespeare! Different set ups, different properties, different construction. My house has always heated up quickly - even long before Evohome. It was good from day one for that and got better when we replaced the double glazing and installed cavity insulation.

  8. #48
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    Additional note -optimisation.

    This morning I noticed that of three zones all at the same temperature, optimisation came on for two of them an hour before the set point (07:30) - in each case to get them up from a starting temperature of 15 to 18. Puzzled as to why not the third zone as this is the hall and it takes longer to warm up than other zones. Yesterday morning optimisation started heating that zone 20 minutes before the set time. This is the reverse of what I would expect - surely those that take longer to heat up come on sooner with optimisation? No doubt the remaining zone will start to come on at 07:10.

    Addendum 07:07 - it came on 25 minutes before at 07:05.
    Last edited by G4RHL; 15th March 2015 at 07:07 AM.

  9. #49
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    Quote Originally Posted by Rameses View Post
    @ All

    I will try to explain.

    At 17 degrees there will still be demand - albeit low. (unless its 17 degrees outside) - so this means that whilst the system has achieved 17 degrees, this does not mean it’s off, for instance the boiler will be operating a water temp of 30 and the Hr92 valves will be open 20 % for example - this keeps the room at your set point - whilst keeping boiler burn to a minimum and energy into the system.

    < at this time the important thing here is Hr92's are open taking the throttled heat>

    If you increase Zone A to 20 degrees you are then making a 100% heat call - which will make the boiler turn up to 70 degrees (dependent on boiler and demand for heat from the rest of the house)- which will go around the 'circuit' - at this point your Zone A valve will more than likely be fully open - but your Zone B valve will still be opened slightly from the previous (and current) operation of trying to keep 17 degrees.

    Zone B will get some heat temporally - and the valve WILL close once it sees that the temp is rising in a way that will jeopardise the 17 degree set point. An amount of heat delivered to the radiator before the valve closes is causing the short temporary overshoot. This is typical and consistent to what you are experiencing with the 1.5 degree ‘overshoot’ but this is both short term and not requiring any more energy that has already been created into the support Zone A. Left alone the zone will go back to 17 degrees. NB: Some customers have incorrectly sized radiators for the room, ie too big or designed, and this can amplify this problem, with a larger mass to cool.

    Please note that if your 17 degree Zone B was set to 10 degrees (ie not calling for heat) – this would not occur as the valve would be fully closed when the heat is injected into the system.

    The Hr92 is designed to operate within its own surroundings it will always find the balance to provide set temperature in the room independently from call for heat from other zone. But the process of finding this balance takes time and it has no awareness of what the other zones are asking for, choosing to operate on what it can experience within the room.

    The zoning system behaviour described above is in contrast to traditional systems where the whole house would rise in setpoint and radiator valves were static and not dynamic in their operation.

    We are sure of the capability of the Hr92 as recently we received EUBAC certification (independent third party testing) endorsing its capability to exercise control, and is best in class with a AA rating.
    Attachment 506

    I hope this goes a little to explain the behaviour you are observing. Yes there are possible areas for improvement getting even tighter control, but right now these are not possible within this product and as we are demonstrating this is significantly better than previous controls on the market. We are listening – we do read this feedback –and we will aim to improve our products over time.
    Hi Rameses

    Okay I can see that IF the 'zone B' zone valve were operating as you say, then the zone B radiator would be cool, and any transient increase in air temperature would be short lived and not affect the thermal comfort of the room since the radiative temperature of the surroundings would be fairly unchanged and indeed the thermal mass would soak up the tiny bit of extra heat. However, the Zone B radiator was running at full bore, hot, for the hour that Zone A was calling for heat. Until Zone B reached 1.5 degrees over, when it closed.

  10. #50
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    A picture is worth 1000 words.
    Please see my sketch of how a single zone heating behaviour works.
    Clipboard02.jpg
    This is not from data, but just to illustrate it.

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