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Thread: Evohome: living room getting warmer when warming other room!!??

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  1. #1
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    Default Evohome: living room getting warmer when warming other room!!??

    I don't know what to do anymore...

    The Evohome system seems to be stupid, not able to control logically.

    Situation:
    Living room: SET: 19C, MEASURED: 19.5 VALVE % on touch display: 18%

    So I want to heat up my Study: the system is heating up the boiler.
    So far so good...


    BUT NOW the living room is also getting hotter because the HR92 does not close!
    touch display reading of living room valve remains on 18% (on HR92 valve position is 42%)

    Living room is heating up, 1 degree above SET temp of 19C and valve is not closing yet

    What is going on???

    I think I have had it with this system, I can return it until jan 31 unless someone has some suggestion??

    I do hope on some help, missing things I did not though of
    Thanks!


    DOMOTICZ SCREEN DUMP:

    here you see overshoot in STUDY when living room is heating AND overshoot in LIVING ROOM when study is heating up
    Last edited by wwjd1924; 22nd December 2019 at 01:36 PM. Reason: adding picture

  2. #2
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    This sounds like normal activity to me so I'm not sure why you are concerned. I currently have all my ground floor room temperatures set to 21 degrees. Once it has achieved that temperature in the early morning, most of the radiators are either slightly on, or off, and the circulating water temperature drops back to a lower temperature that is sufficient to keep the temperature at 21 degrees. Each room is differant and it depends on the outside temperature.

    If I increase one room to a higher temperature, then the boiler is activated and the water heats up as would be expected. That higher tempertaure water flows through all the other slightly open radiators heating them and the room slightly until they turn off fully and things have settled down again.. I would expect this to happen and have no issues with it at all. Am I wrong?

  3. #3
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    Thanks for explaining! This confirms what I observed.

    But the problem for me is that the 'slightly heating' of the rooms with no heating need is at least 1 degree. that is a lot (I think) and enough for my wife to complain.
    If I don't fix this I will be banned and spent the nights in the chicken coop and it's cold out there!!

    What I don't understand is this: the system 'knows' the boiler is heating up and the living room is already 0.5C over the set-point. Radiator valve is still somewhat OPEN
    WHY would the system not close the living room valve...?

    But if that is normal behaviour than I have to return to the old situation.

  4. #4
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    Quote Originally Posted by wwjd1924 View Post
    I don't know what to do anymore...

    The Evohome system seems to be stupid, not able to control logically.

    Situation:
    Living room: SET: 19C, MEASURED: 19.5 VALVE % on touch display: 18%

    So I want to heat up my Study: the system is heating up the boiler.
    So far so good...

    BUT NOW the living room is also getting hotter because the HR92 does not close!
    touch display reading of living room valve remains on 18% (on HR92 valve position is 42%)

    Living room is heating up, 1 degree above SET temp of 19C and valve is not closing yet

    What is going on???
    How long have you had the system installed ? It has a "learning" process where it learns the characteristics of your radiator valve, radiators and room characteristics. This can take a few days to a week or so to adapt, so if you've only just installed it it will not yet be optimised for your system.

    Also, what is your flow temperature set to ? If it's set too high for the weather then some interaction between rooms in inevitable if the set point changes suddenly in a different room causing the boiler flow temperature to increase suddenly.

    When you say the temperature is overshooting by one degree are you sure the room temperature is actually overshooting by this much ? Are you going by the temperature reported on the Evohome, and if so are you using the HR92 as the sensor for the zone or a separate wall sensor ?

    Or are you measuring it separately with another thermostat ? If you're going by the reading on the Evohome and using the HR92 as the sensor then it's normal for the temperature reading to fluctuate a little bit as the reading is influenced by the heat directly from the radiator, however the true room temperature will not be varying nearly much.

    For example an HR92 reporting an overshoot of one degree as measured at the HR92 itself is typically a true room overshoot of only about 0.2 degrees.

    Quote Originally Posted by wwjd1924 View Post
    Thanks for explaining! This confirms what I observed.

    But the problem for me is that the 'slightly heating' of the rooms with no heating need is at least 1 degree. that is a lot (I think) and enough for my wife to complain.
    If I don't fix this I will be banned and spent the nights in the chicken coop and it's cold out there!!

    What I don't understand is this: the system 'knows' the boiler is heating up and the living room is already 0.5C over the set-point. Radiator valve is still somewhat OPEN
    WHY would the system not close the living room valve...?

    But if that is normal behaviour than I have to return to the old situation.
    If the room needs some heat to maintain the required temperature then an HR92 will always be slightly open. If it closed completely the room would fall below the set point and need to be heated up again, causing continuous fluctuation of the temperature.

    If another zone suddenly switches on and causes the boiler flow temperature to increase a lot then the HR92 for this zone will be unaware of this. The first it will know is when the room temperature starts to overshoot slightly (usually 0.5 degrees or less) and at that time it will close the valve slightly to compensate.

    This is normal operation. If your flow temperature is excessively high or your radiators are very large you might get one degree or more overshoot - in those conditions consider reducing your boiler flow temperature a bit. A lot of people run their boiler unnecessarily hot year round and this will magnify both overshooting and interaction between rooms.
    Last edited by DBMandrake; 24th December 2019 at 08:50 PM.

  5. #5
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    Hi,
    what seems to be general opinion, which I have read and noticed by monitoring the data that I log on the system. The Valves will operate/stay open up to Set point plus 1.5'C, so whether the boiler relay is on or off the HR92/80 will be open up to 100% if valve temperature is below set point +1.5'C.

    If you only have one zone demanding heat. You will find that temperature control is excellent, and setpoint will be maintained very well.

    If a second zone then demands heat this is when you can get overshoot.

    Because the second zone is demanding heat the boiler relay stays on until the second zone is at temperature then shuts off and goes into a on off cycle as per your touch screen hourly timing cycle 3/6/9/12 etc.

    Your first zone will not close until set point +1.5'C is reached. It will proportionally close up to +1.5C.

    Once both zones are at Setpoint then they will both find there happy spot for valve open %, and temperature regulation should be excellent.

    If a third zone starts demanding then the overshoots can happen again.

    See a made up table below to give example of 1 zone working and then 2 zones.



    ROOM A ROOM B
    Boiler Relay Status Set Hr92 Temp Valve Position Set Hr92 Temp Valve Position
    Room A Needing Heat On 18 16 100 15 17 0
    Room A Needing Heat On 18 16.5 100 15 17 0
    Room A Needing Heat On 18 17 100 15 17 0
    Room A Needing Heat On 18 17.5 100 15 17 0
    Room A Needing Heat On/Off 18 18 50 15 17 0
    Room A Needing Heat On/Off 18 18 40 15 17 0
    Room A Needing Heat On/Off 18 18 33 15 17 0
    Room A Needing Heat On/Off 18 18 25 15 17 0
    Valve position changing to optimise for room Room has no heat demand so valve stays closed while Room A is working as need
    Room A & B Needing Heat On 18 18 25 20 17 100
    Room A & B Needing Heat On 18 18.5 15 20 17.5 100
    Room A & B Needing Heat On 18 19 8 20 18 100
    Overshoot Period stops at Set+1.5 = Valve Closed
    Room A & B Needing Heat On 18 19.5 0 20 18.5 100
    Room A & B Needing Heat On 18 19.5 0 20 19 100
    Room A & B Needing Heat On 18 19 0 20 19.5 100
    Room A & B Needing Heat On 18 18.5 0 20 20 100
    Room A & B Needing Heat On/Off 18 18 25 20 20 25
    Room A & B Needing Heat On/Off 18 18 22 20 20 20
    Room A & B Needing Heat On/Off 18 18 15 20 20 12
    Room A & B Needing Heat On/Off 18 18 7 20 20 8


    When you have multiple zones changing setpoints at different times you can get alot of overshoots that you can notice temperature that is not desired.

    This is the system, although not perfect, it is still pretty good and alot more comfortable in the house.

    I would prefer to have the Setpoint +1.5 to be variable to my choice. lets say +0.5'C. I do not know why honeywell do this. Maybe to maximise boiler heat efficiency. Maybe to minimise the valve movements for battery life. I'm not sure and it is the worst part about evohome to me and it is annoying when you get to 1.5C overshoot when it is a zone that makes it uncomfortable.

    Still the system is still excellent as whole and better than a load of mechanical TRVs and 1 Stat to manage them all.

    This has been posted about for 5-6 years and honeywell dudes have never really never acknowledge that it is pretty crap, or given a reason for why it is +1.5'C. Lots of irate users, this should be a easy fix but they do no fix. If its to save battery life. I would happily change batteries every year if I could have a smaller differential.

    Hope this helps

    Frank

  6. #6
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    Quote Originally Posted by frankmalia View Post
    Hi,
    what seems to be general opinion, which I have read and noticed by monitoring the data that I log on the system. The Valves will operate/stay open up to Set point plus 1.5'C, so whether the boiler relay is on or off the HR92/80 will be open up to 100% if valve temperature is below set point +1.5'C.

    If you only have one zone demanding heat. You will find that temperature control is excellent, and setpoint will be maintained very well.

    If a second zone then demands heat this is when you can get overshoot.

    Because the second zone is demanding heat the boiler relay stays on until the second zone is at temperature then shuts off and goes into a on off cycle as per your touch screen hourly timing cycle 3/6/9/12 etc.

    Your first zone will not close until set point +1.5'C is reached. It will proportionally close up to +1.5C.

    Once both zones are at Setpoint then they will both find there happy spot for valve open %, and temperature regulation should be excellent.

    If a third zone starts demanding then the overshoots can happen again.
    What you say is basically true (a large set point change in another zone can cause an overshoot in unrelated zones) however it is not as bad as you describe on most Evohome installations. On my system the overshoot is rarely more than 0.5C, (measured with an independent table top thermometer) so it's not true that because the proportional zone is +/- 1.5C that the overshoot will also necessarily be 1.5C.

    The radiator controller does not require the temperature to overshoot by 1.5C before it will fully close - it can also close inside the +/- 1.5C proportional band - this depends on the previously learnt characteristics of the room and ambient conditions. It depends how much heat the room requires to maintain the set point.

    If you get large overshoots (>0.5C) in a zone when another zone comes on it almost certainly means that either your flow temperature is too high, the radiators in the zones that are overshooting are oversized, or the valve bodies don't suit the HR92 and therefore the heat into the room is difficult to control accurately.

    This means that when the flow temperature suddenly increases due to the demands of another room the room heats up so quickly that the system doesn't get time to respond - remember HR92's only make an adjustment to their valve about once every 4 minutes. Within that 4 minute period if a large radiator heats up to a very high surface temperature then it can put a lot of heat into the room that will cause an overshoot even if the HR92 closed completely on the next 4 minute interval due to the large thermal mass of the radiator. This is the essence of the problem.

    Another possible issue relating to this is mismatching of radiators in different zones. The ideal situation is that to maintain a comfortable temperature in each zone that the required flow temperature is approximately the same. This would require larger radiators in large rooms and smaller radiators in small rooms etc..

    If radiators in some zones are oversized and those in other zones are undersized you have a situation where as soon as the zone with the undersized radiator calls for heat due to a schedule change it is going to demand a high (perhaps 100%) heat demand from the boiler which will then cause other zones to overshoot.

    One way to detect this problem is to set all rooms to a similar temperature like 20C and wait until they are all stable and then have a look at the heat demands for each zone in the installer menu - if they're wildly different then there could be a radiator sizing mismatch issue. It only takes one zone with an undersized radiator that struggles to reach the set point to cause issues.

    See a made up table below to give example of 1 zone working and then 2 zones.

    [...]

    When you have multiple zones changing setpoints at different times you can get alot of overshoots that you can notice temperature that is not desired.
    The table you show above shows a clear problem with your system that needs fixing - specifically the compatibility of your valve bodies that the HR92's are attached to.

    You show Room A stabalising at 18C with a valve position of 25%, then when Room B comes on the temperature of Room A starts rising and overshoots 1.5C. This should not happen.

    The HR92 is designed with the assumption that <= 30% valve pin position means the valve is closed. Below 30% valve pin position the HR92 will not call for any heat. Please see the following graph I created some time ago to show the relationship between HR92 valve positions and heat demand called for from the boiler:



    So if your valve still lets water through the radiator significantly below a position of 30% you will have the problems you describe. This is because when Room A was the only one calling for heat it reached equilibrium with the boiler not running (25% valve position calls for 0% heat demand) however the valve is still allowing water through.

    That means when Room B calls for heat Room A is allowing water to flow through the radiator so it will continue to heat up when it shouldn't.

    What kind of valve bodies do you have, and do you use Stroke 0 or Stroke 1 mode ? If you use the default Stroke 0 mode it might be worth switching your HR92's to Stroke 1 mode. After you do this, remove the HR92's, turn the black wheel anti-clockwise and refit them to trigger a valve pin recalibration.

    After this it will take maybe a day or two for the HR92's to learn the new characteristics in Stroke 1 mode. If you're still finding that the radiators keep flowing below 30% indicated pin position you might want to consider different valve bodies.

    This is the system, although not perfect, it is still pretty good and alot more comfortable in the house.

    I would prefer to have the Setpoint +1.5 to be variable to my choice. lets say +0.5'C. I do not know why honeywell do this. Maybe to maximise boiler heat efficiency. Maybe to minimise the valve movements for battery life. I'm not sure and it is the worst part about evohome to me and it is annoying when you get to 1.5C overshoot when it is a zone that makes it uncomfortable.
    I think you're misunderstanding what the proportional band is for. If you shrink the proportional band to only +/- 0.5C you will actually cause more overshoots, because as soon as the room went 0.5C under the set point the radiator would fully open which would almost certainly cause an overshoot in response. A wider proportional band would give smoother temperature control not a narrower band.

    Your comment about minimising movements for battery life makes me think you're confusing proportional band with deadband. There is virtually no deadband in the HR92. Even a measured temperature change of about 0.1C will result in a slight movement of the motor controlling the valve position.
    Still the system is still excellent as whole and better than a load of mechanical TRVs and 1 Stat to manage them all.

    This has been posted about for 5-6 years and honeywell dudes have never really never acknowledge that it is pretty crap, or given a reason for why it is +1.5'C. Lots of irate users, this should be a easy fix but they do no fix. If its to save battery life. I would happily change batteries every year if I could have a smaller differential.
    Sorry but I really think you're misunderstanding the situation. Some interaction between zones when schedules change is unavoidable with a system like this where the flow temperature is affected by all zone heat demands, however an overshoot of 1.5C is not normal, nor does the +/- 1.5C proportional band have anything to do with this, and making it smaller would be counter productive.

    In your case I'm fairly confident that the issue you're seeing will be one or more of flow temperature too high, oversized radiators or valve bodies whose opening threshold do not match what the HR92's expect.

    While an HR92 will fit any valve with an M30x1.5 thread that doesn't mean it will work well with all of them. I actually got rid of my old peggler bulldog valves as I was having the same problem you seem to be having - they were still allowing water to flow with a valve pin position as low as 12-15% and this was upsetting the control algorithms of Evohome (which expect water to stop flowing below 30%) and causing large temperature overshoots when other zones were scheduled on very similar to what you describe.

    I don't have that issue anymore now I'm using Honeywell Valencia valves, however as I reported in another thread I did find I have to use Stroke 1 to get the best control with them as they have a very long travel pin compared to some other valve bodies.
    Last edited by DBMandrake; 3rd January 2020 at 02:23 PM.

  7. #7
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    Isn't that just as bad if it did this? Your living room temperature would then drop and it would become cold? You can't have your cake and eat it!

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