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Thread: Evohome S Plan Plus (Plus) setup not exhibiting any Optimimal start characteristics

  1. #1
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    Default Evohome S Plan Plus (Plus) setup not exhibiting any Optimimal start characteristics

    Hi,

    I have an unusual setup with Zone valves controlling 3 CH circuits (gnd, 1st and 2nd floors, no HR92's at present), a DHW circuit and also a UFH circuit zone valve which further comprises of 4 sub UFH zones each controlled by BDR's controlling the manifold actuator. Boiler demand is wired so that any 1 of these zone valves triggers the boiler via the orange and grey end switch.

    Strange, I know, but it has by and large worked for the last few years aside from an ongoing concern that it wasn't benefiting from any optimisation. I've since confirmed this by graphing temperatures and gas useage and I can see that the boiler only ever fires at the same time or shortly after 1 or more zones set point changes above the current zone temp. With optimum start you would expect the boiler to be firing in advance of any zones set point changes, in the case of UFH you would expect that a long time ahead of this. This never happens, boiler demand always coincides with set point demand. I have reset Evohome controller and rebound all devices at least once configuring Optimum Start and/or Optimum Stop on all zones.

    I plan on introducing HR92's on a zone by zone basis and introducing a UFH HCC80 controller in due course, but in the meantime is there any fundamental reason why this setup would somehow prevent any form of optimisation? Any ideas on how to enable optimisation with this setup?

    thanks

  2. #2
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    First of all, what model of controller do you have ? It sounds like you might have an older one like the monochrome model ?

    I think you slightly misunderstand how optimal start works, and this confusion may cause you to believe it's not working.

    Optimal start works not by firing the boiler before a set point change, but rather by bringing the set point change forward.

    So for example if your set points are configured to be 5 degrees at midnight then 20 degrees at 8am, Optimal start works by changing the active set point to 20 degrees well in advance of the scheduled 8am. Subtle but important difference.

    It should also show it on the display. So if you look at your display a few minutes before a set point is due to increase, do you see the new set point applied ahead of time, with the optimisation icon displayed ? If not, it is not working.

    One other thing to keep in mind in relation to UFH, is that optimal start is disabled if the temperature is already within about one degree of the target - so if your target is 20 and the temperature is already 19 degrees it will NOT change the set point early. Not usually a problem with radiators but I've seen quite a few UFH users complain about this due to the very slow warm up times of UFH.

  3. #3
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    The controller is the colour but pre-wifi version from about 3 years ago. Optimum start and finish are enabled from the installer system-wide parameter settings menu, and then the 'optimisation' option is enabled on a per zone setting.

    Interesting re set points being brought forward, I need to double check graphing changes with the programmed schedule when I get home. However, with just a couple of exceptions a while back on 1 of the zones, I have never seen the 'OPT' icon displayed on the controller, which makes me think it hasn't been enabled correctly?

    Do I need to start again and reset and rebind everything?

    thanks

  4. #4
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    If you're graphing set points (using something like Domoticz) as I do, then you'll need to compare the actual graphed set point changes to your schedule - only then will you be able to work out what "lead time" optimal start is applying, (if any) as it will just show up on the graph as the set point changing ahead of the scheduled time.

    That's literally all that optimal start does - change the set point earlier than the schedule based on how long it thinks it will take to reach the target in time, on a per zone basis. It learns this over time.

    How many hours do you have optimisation set to ? When you enable it you can choose a number of hours - this sets a "cap" on the maximum number of hours early that a zone set point is allowed to change.

    Also - are your rooms up to temperature in time or do they not get up to temperature until some time after the set point ?

  5. #5
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    thanks so much. Can't believe I have somehow missed these optimisation icons on the controller, but looking at the changes on the graphs and you are absolutely right, I can see them shifted ahead of the scheduled times for the each floor zone.

    It gets a little less clear for the UFH zones. I've got max optimisation set to 4 hours, yet I cant see it come on more than an hour ahead of time which is not enough time to get the room up to temp. I suspect it finds these zones really hard to adjust to because they are south facing and will rapidly warm up if the sun is shining, however cold it might actually be. Without knowing the amount of sunlight coming into the zones I doubt it can really get a clear understanding of how long it takes to heat the rooms up a given amount. Having said that, from what I've read elsewhere the calculation is fairly pessimistic, so I would have expected it to err the other way, potentially overshooting when the sun is out?

    Im just using BDR's to control the UFH manifold, do you know if the dedicated HCC80 UFH controller applies a different optimisation calculation based on the fact that UFH will likely have different warmup-down characteristics? Wondering how much benefit I might get from replacing the BDR's and wiring box with the HCC80?

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    Can't answer the HCC80 question unfortunately as I haven't used one and don't have underfloor heating.

    One other thought I just had - Optimal start has two different modes you can choose - "optimal start" and "delayed start". You don't have it set to delayed start by any chance do you ?

    Delayed start simply changes the set point exactly one hour earlier than scheduled (why ??) and doesn't do any adaptive learning. To get the automatic adaption and longer lead time it must be set to optimal start and not delayed start.

    What the purpose of delayed start is I don't know - it seems pretty much pointless to me as its the same as simply offsetting your schedule by one hour...
    Last edited by DBMandrake; 16th January 2017 at 08:53 PM.

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