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Thread: evohome Wi-Fi

  1. #131
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    I did notice that you can now clear errors from the logs. I think that's new?

    It hasn't done anything for my overshoots. Still going over by 2 degs in some rooms.

  2. #132
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    Quote Originally Posted by benc View Post
    It hasn't done anything for my overshoots. Still going over by 2 degs in some rooms.
    Quote Originally Posted by rotor View Post
    I have overshoots as well, and I don't understand why. Surely each HR92 is supposed to be learning the room, and should know that the radiator is too big, and should therefore restrict flow?
    Based on the fact that the heating load for each room should be individually 'designed' and 'calculated' on worst case scenario (circa 75 degrees Celsius flow temp at -4), guestimating by oversizing radiators without then reducing the designed flow temperature would in my opinion be very hard for a HR92 to control the system 100%.

    I think for the cost of these items, they do a very good job indeed. There are just too many factors and variables involved in most people heating systems (outside of the control of the HR92) for them to be perfect. If you do want perfection, when the HR92's were installed the radiators should have been replaced with ones correctly sized, the heating system flushed and the radiator valves replaced - maybe even the boiler replaced if this is oversized too.

    The HR92's in conjunction with the evohome Controller does learn and maximise what you have got to the best of their ability (this can take a while) - but they can't do miracles.

    I would suggest lowing the flow temperature of your boiler (if possible bearing in mind heating systems with hot water cylinders need to be at no lower than say 68 degrees flow temp) or balancing the heating system correctly to ensure the HR92's have the best chance of controlling the rooms they are in.

    Any chance of some pictures of these HR92's and the locations they are fitted in?

  3. #133
    Automated Home Legend paulockenden's Avatar
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    If you have rooms that overshoot one simple thing is to reduce the flow by closing the lockshield valve (other end from the HR92) slightly. Not a perfect solution, but it might help. But you're never going to reduce the thermal mass of a large radiator. Unless, perhaps, you deliberately let it half-fill with air (where you'd normally bleed it).

  4. #134
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    Quote Originally Posted by paulockenden View Post
    If you have rooms that overshoot one simple thing is to reduce the flow by closing the lockshield valve (other end from the HR92) slightly. Not a perfect solution, but it might help. But you're never going to reduce the thermal mass of a large radiator. Unless, perhaps, you deliberately let it half-fill with air (where you'd normally bleed it).
    Did you just say let the radiator fill with air Paul? If you want to promote system wide corrosion and all lol...

  5. #135
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    I too would like to see a detailed description of the setup of the rooms where the overshoots are occurring.

    At the end of the day the system can't work miracles if you have a large radiator with a large thermal mass, a high flow temperature, and (probably) a system where none of the radiators have been balanced. If the room is well insulated it would tend to make overshooting even worse.

    Our loft-conversion bedroom radiator is massively over spec'ed (by previous owners I hasten to add) and is a Type 22 of approximately 1200x750mm... Needless to say if the boiler is already up and running and I open the TRV fully for just the one minute that it takes for the radiator to fully heat and then immediately close it again, the room will suffer about a 3 degree overshoot past the previous temperature over a period of about 15 minutes purely due to the thermal inertia of the hot radiator still putting out heat...and it then take a long time to cool down.

    This kind of lopsided thermal response is what the HR92 has to try to deal with. The only way it can heat the room up quickly but without overshooting the target in such a situation is learn by trial and error how much overshoot there is and calculate how much earlier than the target temperature it should shut the valve so that the room temperature coasts towards the target as the radiator cools. (It actually progressively closes it as the target is approached but the principle is the same)

    The problem with this is that it is a delicate balance that is affected by other variables outside its control like - is the window open ? Is the door open ? Is the radiator partially or completely covered by clothes or towels ? The HR92 doesn't know... it only sees the end result of that after the fact when the temperature doesn't change in the way it anticipated, but it doesn't know why it didn't as it is not sentient.

    In our bedroom if I keep the window and door closed and put no clothes/towels on the radiator then despite the massive thermal mass of the radiator after a single day of a 2-3 degree overshoot it will get it pretty much on the dot the following day after observing the previous days overshoot and learning from it.

    However if I then cover the radiator with a towel the following day the room might overshoot by 2 degrees or so due to the slower release of heat from the radiator into the room, which upsets that delicate balance that it was maintaining. If I leave a towel on it every day it will quickly adapt (a couple of days typically) and now reach the target without overshoot. If I then remove the towel the following day it will undershoot for a day or two! Clearly it is learning and adapting the best it can with the information it has available to it.

    The more oversized the heat output of the radiator is the more "unstable" this balance will become. If the radiator was a bit smaller, or the flow temperature was lower then the system becomes less unstable and it doesn't have to rely so much on predictively turning the radiator off early to prevent overshoot.

    In our living room we have three radiator panels approx 600x600 each (double skin, no fins, yes they are antiquated) mounted around a bay window piped together as one, controlled by one HR92. Normally there is a chair in front of the middle one. Again this may be a bit oversized as it can manage a temperature increase in the room of about 6 degrees an hour at a flow temperature of 70 degrees, and that's with the lockshield valve balanced as well...

    Despite this day after day it heats up quickly without overshooting and maintains an almost flat line all evening. The day we replaced the chair with a Christmas tree (a real one) and moved the chair to obscure the 3rd panel instead of the middle one, we had a big overshoot of about 2 degrees for the first couple of days but it quickly adjusted and started hitting it's targets again. Then when the tree was removed it undershot for a day or so. Again, learning, and quickly!

    Based on how I've seen my system perform, I don't believe that it would overshoot day after day unless the heat output of the radiators was massively over rated and therefore inherently an "unstable" system from a system control point of view, or other variables were changing every day, so that it never had a steady situation to adapt to. For example doors being left open sometimes, closed others, windows the same, TV on sometimes, off other times, (a TV is a source of heat) number of people in the room changing etc.

    It's easy to forget that all sources of heat in a room count. Our living room comes up to temperature before we get home and usually the door is left closed so it reaches a very steady equilibrium with no overshoot. As soon as we put the TV on and settle on the sofa there is typically a half degree overshoot - simply due to the heat output of two people and a TV set...and it takes a little while for it to adjust to this, which it does.

    The temperature of adjacent rooms is also a factor, and one that I think the evohome does not take into account. If your living room always tries to heat to 21 degrees at 6pm but sometimes the hallway is hot at this time and sometimes it is not, then the anti-overshoot adaption would be thrown out a bit. (Obviously if the door between them is sometimes left open and sometimes not, that is also a big factor)

    In the case of a really oversized radiator, throttling down the lockshield valve a bit (measured with an IR gun at each end of the radiator) may help - it seems that balancing a system is a lost art in the days of TRV's, a lot of "heating engineers" just leave the lockshield valves fully open...
    Last edited by DBMandrake; 14th January 2016 at 12:02 PM.

  6. #136
    Automated Home Legend paulockenden's Avatar
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    Quote Originally Posted by The EVOHOME Shop View Post
    Did you just say let the radiator fill with air Paul? If you want to promote system wide corrosion and all lol...
    Would it be system wide, if the air was just in the one rad?

    OK, half fill the rad with nitrogen then!

    P.

  7. #137
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    I'd be interested in getting this new firmware. I have two controllers and a total of over 20 zones. Displaying and accountng for manual override would be a great help.

    A range extender would be the Holy grail, but for now the new firmware would be excellent. Is this being rolled out any time soon? And to those with more than one registered controller?

  8. #138
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    Quote Originally Posted by DBMandrake View Post
    I'm pleased to report that the HR92 local override now works, and pretty much in the way that I hoped it would.
    Making a local adjustment on the HR92 is now reflected on the Evotouch controller, and very quickly - typically within 5-10 seconds the new setpoint appears on the screen and within the iPhone app.
    In my testing I was able to catch it out in a couple of ways though. Not sure if these are bugs that might still get fixed or inherent limitations/restrictions in the wireless protocol:
    1) [..]
    2) If I made a manual override on an HR92, which is reflected almost immediately on the evotouch display, and I then tried to cancel the override on the evotouch within the up to 4 minute period before the evotouch sent a new setpoint update back to the HR92, eg before the local override icon went out on the HR92, then the evotouch would cancel the override from its perspective, but the HR92 would stay in local override mode and thus not revert to the non-overridden temperature.
    However if I made sure to wait until the 4 minute period was up and/or the local override icon on the HR92 had gone out (showing that the set point update had gone through) then I could successfully cancel the override on the evotouch and it would revert the HR92 back to the non-overridden temperature. I can see how this could potentially happen if the HR92 was adjusted less than 4 minutes before a scheduled setpoint change as well.

    I think what is happening here is that the evotouch will not send a message to cancel an override to an HR92 if it had not previously sent a message to set the override in the first place. EG say that the scheduled temperature was 20 and you overrode to 22 degrees on the HR92. The set point on the evotouch is now 22 degrees thanks to this new software update, but it has not yet sent any message to the HR92 to tell it to switch to 22 degrees as it is waiting for the next 4 minute interval. (It is seemingly unaware that the HR92 has been manually set to 22 even though it just received a message from it) If I now cancel the override at the evotouch, it doesn't send any message to the HR92 to set it back to 20 degrees, because it never sent it a message telling it to change to 22 degrees in the first place. Therefore the HR92 stays in local override mode at 22 degrees. This seems like it should be trivially fixable in the evotouch software by just always sending a set point message when cancelling a zone override even if the original override message never got a chance to be sent to the HR92. (What harm does it do to re-send the same set point just to make sure ?)
    Today I have seen the exact behaviour you described above. Your idea about what is actually happening fits nicely to what I observed. Good bug report! ...or room for improvement ;-)
    Did some Honeyweller already confirm this observation and acknowledge the solution you suggested?
    Evohomeclient temperatures on ThingSpeak: https://thingspeak.com/channels/79213

  9. #139
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    A possible bug yes but in practice is that a change you will really make?

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