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Heating and cooling: Self-regulating UFH: how to control mean water temperature of flow and return

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    Posted By: ShevekYes, not intending to achieve Passivhaus certification.
    That's self evident, otherwise we would have already had 14 different threads of various different permutations on the subject from you.

    I was talking about the levels required to achieve passive house certification rather than posting the actual figures. Certification is a take it or leave it, but the levels required for certification are I believe a very good target to aim for by anyone aspiring to build a low energy house.
    • CommentAuthorShevek
    • CommentTimeAug 7th 2014
     
    So its self-evident but needed clarification.
  3.  
    I was clarifying that I was talking about the target levels one should be aiming for and not certification per se.

    One can still be aiming to achieve those levels without any intention of getting certified.
    • CommentAuthorShevek
    • CommentTimeJan 15th 2016
     
    Now that the 3rd generation Nest Protect supports modulating boilers that are OpenTherm compatible (which I believe our A325ECX is) is the Nest Protect worth considering instead of this self-regulating idea?
    •  
      CommentAuthordjh
    • CommentTimeJan 15th 2016
     
    Posted By: ShevekOpenTherm

    OpenTherm is a misnomer. It is not open, and nor is it a standard in any meaningful sense. Vendors can implement pretty much anything, so check very carefully that two products are compatible if you intend to connect them.
    • CommentAuthorSimon Still
    • CommentTimeJan 15th 2016 edited
     
    Posted By: ShevekNow that the 3rd generation Nest Protect supports modulating boilers that are OpenTherm compatible (which I believe our A325ECX is) is the Nest Protect worth considering instead of this self-regulating idea?


    It sounds like it talks OpenTherm at a pretty basic level -

    "At this time, the Nest thermostat does not directly modulate the water temperature of your boiler. The Nest Thermostat currently uses OpenTherm to tell your boiler when to turn on and off. It will tell your boiler if the temperature in your home is falling below the target temperature, and your condensing boiler will use this information to modulate internally."

    I've not looked at Nest for a while but it appeared to me that whilst it was beautifully packaged it wasn't particularly more advanced than other products -

    Drayton's thermostat controllers had an intelligent start function that 'learnt' how long your house took to warm years ago. http://www.heatingcontrolsonline.co.uk/room-thermostats-c-21.html/programmable-thermostats-c-21_31.html/hardwired-programmable-thermostats.html/acl-drayton-invensys-digistat-three-programmable-thermostat-p-395.html

    Most of the other functions of Nest work best with fast reacting heating systems in high loss houses - if you're heavily insulated with UFH there's negligible benefit in telling your heating system you're going to be late home.
    • CommentAuthorSimon Still
    • CommentTimeJan 15th 2016 edited
     
    Anyway, didn't you move in some time back? How is your heating running at the moment?

    Alec, of this parish, installed our Viessmann 222-F boiler with Weather Comp back at the end of the summer.

    However, the weather has been so warm we've not really been able to fine tune it yet.
    We actually had a frost last night (only the second since the summer) and the kitchen had dropped to 19.2C at breakfast (it's normally just either side of 20C) so we might need to extend the heating period slightly to keep it completely consistent.

    The concrete floors do seem very stable. However I'm a little puzzled at the moment as our room temperatures on the upper floors (where we have a panel system under wood so it should be faster reacting) seem to have been consistently above the flow temperatures. We've regularly been at 22C upstairs when the flow temp was no more than 21C (but the temp did seem to fall if I turned the flow to those floors off completely).
    • CommentAuthorShevek
    • CommentTimeJan 15th 2016
     
    Posted By: Simon StillAnyway, didn't you move in some time back? How is your heating running at the moment?

    LOL, we never moved out! The milestone you probably have in mind is that we finished off the outside.

    We're still doing electrical, plumbing and decorating. Slowly but surely each weekend! No UFH yet.
    •  
      CommentAuthordjh
    • CommentTimeJan 15th 2016
     
    Posted By: Simon Stillif you're heavily insulated with UFH there's negligible benefit in telling your heating system you're going to be late home.

    Exactly. There's no point. Perhaps if you were going away for a couple of weeks, but then you usually know what day you'll be back.

    However, the weather has been so warm we've not really been able to fine tune it yet.
    We actually had a frost last night (only the second since the summer) and the kitchen had dropped to 19.2C at breakfast (it's normally just either side of 20C) so we might need to extend the heating period slightly to keep it completely consistent.

    We actually had snow on the ground - shock, horror. What is your current heating period?

    The concrete floors do seem very stable. However I'm a little puzzled at the moment as our room temperatures on the upper floors (where we have a panel system under wood so it should be faster reacting) seem to have been consistently above the flow temperatures. We've regularly been at 22C upstairs when the flow temp was no more than 21C (but the temp did seem to fall if I turned the flow to those floors off completely).

    Solar gain? Or thermometer errors?
  10.  
    Posted By: djh
    Solar gain? Or thermometer errors?


    Could be solar gain but those rooms seem pretty stable at that temperature even on very overcast days. I've got a number of thermometers I've been moving around and they are all consistent with each other. It *could* be that the boiler stat is wrong and actually it's sending out water at a higher temp than it thinks it is.

    Will get my IR thermometer on the pipes.

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