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    • CommentAuthorTheDoctor
    • CommentTimeOct 12th 2008
     
    Having all but finished our extension / part renovation, it will soon be time to programme the LPG fired wet UFH system.

    The majority of winter heat will be off a central wood-burning stove, to minimise the use of the LPG, but i am interested in the most efficient difference between daytime and nighttime temps.

    The system comes pre-programmed to 21 degrees day and 17 degrees night.
    That's way too hot for me!

    I was planning on a daytime temp of 18 degrees (which would then be tripped off as the woodburning stove would exceed this when it is running. What about night time?

    17 is 4 degrees lower than 21 - should i set nighttime at 14 degrees?

    i'd love to have it off, but apparently it is most efficient to keep a constant to reduce wasted energy bringing it back to temp.

    thoughts would be welcomed!
    • CommentAuthortony
    • CommentTimeOct 12th 2008
     
    What do you mean by most efficient? least energy use? then switched off overnight has to be that.
    • CommentAuthorTheDoctor
    • CommentTimeOct 12th 2008
     
    tony,

    agreed. but does it not then take MORE energy (in total) to bring it back to temp for the day?
    This is what i am trying to get to the bottom of.

    I am hoping that the extra insulation, central wood burning stove and large thermal mass will make this a moot point, but was keen to hear the thoughts of others.
    • CommentAuthorwookey
    • CommentTimeOct 12th 2008
     
    I don't see how it can. I've been a bit confused about this too, but so far as I can see the 'overnight set back' idea is merely so that the system can react a bit faster. I don't see how it can possibly save energy over turning it off.

    I guess if the criterion is that it must be at 20C at 8am for getting up, and it takes 2 hrs from cold (10C?) to get there then the system has to run at full blast for 2hrs to achieve that (assuming that the floor fully cooled overnight). If you set-back instead then it stays at 14C all night so only takes half as long at full blast in the morning to achieve 20 (1hr). So I guess the theory is that if the extra hours of full uses more fuel than than the 7 hours of 'low' (from midnight to 7am, in this example) then the set-back scheme will save fuel. Maybe this can happen, but normally gas boilers maximise efficiency near max output. Don't know about heat-pumps.

    Somone here must know...
    • CommentAuthortony
    • CommentTimeOct 12th 2008
     
    It cant ever happen.
    • CommentAuthorEd Davies
    • CommentTimeOct 12th 2008
     
    If the room is warmer overnight then more heat will be lost.

    The only way it could possibly be more efficient to keep unused space warm would be if the heating system was dramatically more efficient at low power than at high power. This seems unlikely and is probably the reverse of the truth in almost all cases.
    • CommentAuthorCWatters
    • CommentTimeOct 13th 2008
     
    If your house is well insulated hopefully the temperature won't fall as low as the setback temperature at night. In which the actual setback temperature (eg 10 vs 14) is slightly academic.
    • CommentAuthorTheDoctor
    • CommentTimeOct 13th 2008
     
    cWatters,

    that is what i am hoping, and will be programming it to be 'OFF' when it is not on, if that makes sense.

    I am hoping the freestanding masonry chimney central to the living area will be radiating a good chunk of heat through the night, keeping the place warm, and preventing too steep a fall in temp.

    No, the house is not passiv haus insulated, but it is well insulated, and the living area at least is fairly well draft proofed.

    We'll see!

    My question was based on the literature that comes with all of these systems, but it seems their 'lower temp, so cheaper' tag line is a non-sequiter with their operating advice
  1.  
    Could you let us know (in due course) what you work out works best for you - not frozen in the morning wise and energy consumption wise. Many thanks.
    • CommentAuthorTheDoctor
    • CommentTimeOct 20th 2008 edited
     
    it is not freezing yet, by any means, and the plan is not to use the heating on a daily basis just yet, but we did play with it from Friday am to Sunday pm, by way of a test, before it is required in earnest.

    SO, the literature said it should be "on' from 7.30 am to 11.00 pm, and then in 'setback' mode of 17 degrees through the night.

    SO, we threw out the literature!

    I programmed the thermostats to 17.5 degrees from 8.30 to 10.30, and 16.00 to 20.00, with the remaining periods at 10 degrees.

    morning one was a little chilly. The system had to work to get the slab up to temp from a standing start.
    However, once it warmed up, it got ahead of itself, and the rooms got to just under 20 degrees, even though the thermostat tripped the system off at 17.5. A bit of thermal inertia there.

    The system only engaged for about 30 minutes in the evening, as the house held the heat.

    Since Friday pm, the boiler has only been on for about an hour and a half in total, to retain the 17.5 degrees.

    Generally ,it seems that cooking heat and people are really helping, and the temperature was not below 18.5 degrees all weekend (which is plenty warm enough for me) It would take very little to nudge it to 20 degrees if required.

    The system comes on at 8.30am (if required) but this weekend there was enough latent heat to make the place comfortable - no chilly kitchen requiring heating from early on.

    With the stove going, the floor should really be a stand-by item (and a bl**dy expensive one at that!)

    My wife works from home, and the kitchen, living room and dining room (office) are all essentially one big space.

    I am really pleased that the system is not on mega-drive all the time, and hope the same can be said in January.

    The dog and kittens love the warm floors, and it is a very different feeling to radiator driven heat.


    To put it into perspective, the old part of the house - bedrooms and bathroom - have not had any heating at all since early April. It is a poorly insulated and drafty stone building.
    It is currently sitting at a steady 12 degrees. I love a cold bedroom (but i am generally on my own on this point!)

    lots of work to do at that end of the house....!
    • CommentAuthorTheDoctor
    • CommentTimeOct 20th 2008
     
    whilst the (new bit of the) house is by no means Passiv Haus, or to the insulation and draft proof levels expected of some, I put the performance of the heating in no small part down to information and ideals gleaned from this forum.

    adding an extra 10mm here and an extra 25 there to various insulation specs, and being a bit more of a draft-Nazi with the builder and myself were easy and (almost) cost neutral, and appear to be paying off.

    thanks greenies!
  2.  
    Were there any hot spots? (I know the system design is supposed to avoid these but all the same?).

    Do you have towel radiators?

    I think I'd be inclined to keep my UFH on all the time, to take the chill off the stone floors, at (say) 15C and stick a log on the fire in the evening. The problem would be the morning shower.

    I can't remember if you have the thermal store set up. A towel radiator circuit would be useful just to boost (and encourage) that getting out of bed bit in the morning or am I just complicating things too much?
    • CommentAuthorTheDoctor
    • CommentTimeOct 20th 2008
     
    there is one hotspot - where all the pipes gather toward the manifold
    there is one cold spot - where i ran out of pipe! this is very small, and disappears after a little while

    the system 'design' was by me. All in all, it worked out fine.

    setting it at 15 degrees would not have the floor warm all the time, as once it is up to temp - it switches off - regardless of thermostat temp. All the insulation under the screed does keep the surface warm for hours though, and even the following morning, it is not uncomfortable.

    no towel radiator (yet)
    the bathroom is in the cold bit of the house, so the showers are 'bracing' at the moment!

    when i've draft proofed that end of the house, the heating will be allowed on down there (a bit!)
  3.  
    Good to hear about the hotspots. I thought it would be hotter where the manifolds were situated, so 3 of them I've located in what I would like to be warm cupboards and the 4th is where I'm planning to put the cat's bed.

    I've been warned that UFH isn't the most controllable - so I'll just have to work out what constant back ground temperature is good for us.

    Can't bear cold bathrooms ...
    • CommentAuthorTheDoctor
    • CommentTimeOct 20th 2008
     
    a cold bathroom is a fairly drastic way of reducing hot water use! In and out of the shower in a jiffy!

    the UFH isnt controllable like radiators, so i will no doubt spend a lot more time fine tuning it. The key seems to be (fortunately) that it retains the heat longer than i had hoped.
    • CommentAuthorTheDoctor
    • CommentTimeOct 20th 2008
     
    we have 600x600 porcelain tiles that have a leather texture and look to them. Now that they are warm, they feel like leather too! Nice!
    • CommentAuthorJackyR
    • CommentTimeOct 20th 2008
     
    Bizarre! Leather tiles just ain't nat'ral!
    • CommentAuthorTheDoctor
    • CommentTimeOct 20th 2008
     
    exactly!

    we had visitors at the weekend who actually had to get on their hands and knees to prove to themselves it was porcelain!

    It is not really as bizarre as it sounds - they look great
    • CommentAuthorDaveK
    • CommentTimeOct 20th 2008
     
    There is no reason why UFH can't be as controllable as radiators, just that thermostats with on/off control aren't really suitable. Two methods that will give better control are:

    1. Weather compensation to adjust the temp of the boiler flow to the UFH depending on the outside temperature.

    2. Thermostats with built in proportional and integral temperature controllers. These will 'back off' the heat input to the UFH as the room approaches the set point and avoid the overshoot you are experiencing. This is achived by changing the amount of time the zone valves are open. For example, if the room temp was 2deg below setpoint the zone valve might be open for 20 mins in a 30 minute period. As the room temp rises to say 1deg below setpoint the zone valve would be open for maybe 15 mins in a 30 minute period. The amount of time the zone valve is open over a period of time is constantly calculated by the controller maintaining the room temperature at the setpoint.

    Option 2 gives excellent control but is obviously much more expensive than a simple on/off thermostat.
    • CommentAuthorTheDoctor
    • CommentTimeOct 21st 2008
     
    thanks for that, Dave

    I think i will set the temp lower to resolve any overshoot.

    It didnt come on at all yesterday. the whole area dropped a total of 1 degree in 24 hours. Of course, winter isnt here yet, but that is encouraging
  4.  
    DaveK - could you describe how 1 (weather compensation) works in more detail please, is this just an intelligent widget of some description?
    • CommentAuthorDaveK
    • CommentTimeOct 21st 2008
     
  5.  
    Googling 'chronostat' (a word picked up from DaveK's link above) showed me a whole new world of widgets when it came up with a company called syxthsense. I have more reading to do but it sounds like they sell widgets that you can programme to put the heating on when you're still stuck in traffic getting home.

    Googling 'weather compensation' was less useful. Perhaps this is something you have to have in a boiler (and I'm thinking in terms of very primitive boilers ie back boiler on a wood burning stove + solar evac tubes).
    • CommentAuthortony
    • CommentTimeOct 22nd 2008
     
    weather compensation is an external thermometer which controls boiler power -- the idea is that the colder it is outside the more power is needed from the boiler.

    These are very common on commercial buildings and almost non existant domestically.
    • CommentAuthorDaveK
    • CommentTimeOct 22nd 2008
     
    Weather compensation is most commonly built into the boiler to modulate the boiler power as tony says (some Viessmann boilers for example), however the same effect can also be achived with non weather compensating boilers using a purpose supplied controller and 3-way valve. Not sure how efficient these are with condensing boilers, maybe not in condensing mode as long due to higher return flow temps????

    Mrswhitecat, you could also look at the heatmiser website if you need to control your heating away from home.
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