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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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    • CommentAuthorJeff B
    • CommentTimeSep 19th 2020
     
    <blockquote><cite>Posted By: Ed Davies</cite>Some people use UFH to re-distribute solar heat from the floor areas in sunlight to the rest of the house by running the circulation pump without any heating or cooling as such. This will improve the efficiency of solar heat gain as well as the comfort in the house.

    <blockquote><cite>Posted By: Jeff B</cite>As cold air "falls"…</blockquote>Why the scare quotes? It does fall, that's what convection is: denser (usually cooler) fluid falling and displacing less dense fluid upwards.</blockquote>

    Sorry, I don't know what scare quotes means; I used inverted commas because I regarded falls in this context as a metaphor. I am aware of how convection works!
    • CommentAuthorJeff B
    • CommentTimeSep 19th 2020 edited
     
    We have discovered another low-profile UFH system - Wundatherm. It is approximately half the cost of the Lo Pro Max system and looks simple enough for DIY-ers to install. It will be used in conjunction with the existing gas boiler as all ideas of ASHP's have been discounted now on the grounds of cost.

    Thanks to all who contributed with comments in this thread.
  1.  
    Posted By: Jeff BWundatherm
    Looks interesting. Could you share roughly what price/m2 you are being quoted, and whether you were advised to lay boarding over it to carry the floor finish?
    Posted By: djhyou'd have to ask someone who does have the system
    Er - I did. If, as you say, you don't have the system, then it would be difficult for you to reply anything useful about it.
    • CommentAuthorEd Davies
    • CommentTimeSep 20th 2020
     
    Posted By: WillInAberdeenI'd heard that too, but for it to transfer a worthwhile amount of heat, the floor in the sunny area would have to be many degC warmer than the floor in the cool rooms, which would mean the room air would be too. Does that actually happen in a new house?
    I've no first-hand experience of this either but I'd think that since UFH pipes typically put heat into a slab quicker than it moves from the slab to the room (e.g., you can charge a slab overnight (8 hours, say) to produce heat for the next day (perhaps 16 hours) with only a few degrees of excess temperature in the water) it'd work reasonably well if the details are right. E.g, carpets would likely stop it.
    • CommentAuthorEd Davies
    • CommentTimeSep 20th 2020
     
    Posted By: Jeff B: “Sorry, I don't know what scare quotes means; I used inverted commas because I regarded falls in this context as a metaphor.”

    Scare quotes are quote marks used to indicate that the word is not being used in its normal sense, e.g., as a metaphor rather than that it's quoting something that somebody else said or wrote: https://en.wikipedia.org/wiki/Scare_quotes . My, rather trivial, point was only that it's not a metaphor, the denser air really does fall.
    • CommentAuthorJeff B
    • CommentTimeSep 20th 2020
     
    <blockquote><cite>Posted By: WillInAberdeen</cite><blockquote><cite>Posted By: Jeff B</cite>Wundatherm</blockquote>Looks interesting. Could you share roughly what price/m2 you are being quoted, and whether you were advised to lay boarding over it to carry the floor finish?
    <blockquote><cite>Posted By: djh</cite>you'd have to ask someone who does have the system</blockquote>Er - I did. If, as you say, you don't have the system, then it would be difficult for you to reply anything useful about it.</blockquote>

    The quote was £1040 for a 35 sq.m. area. I don't know if my son was advised to lay boarding over it (I'll check with him) but the website has videos showing floor tiles and laminated flooring being used on top.
    • CommentAuthorJeff B
    • CommentTimeSep 20th 2020
     
    <blockquote><cite>Posted By: Ed Davies</cite>Posted By: Jeff B: “Sorry, I don't know what scare quotes means; I used inverted commas because I regarded falls in this context as a metaphor.”

    Scare quotes are quote marks used to indicate that the word is not being used in its normal sense, e.g., as a metaphor rather than that it's quoting something that somebody else said or wrote:<a href="https://en.wikipedia.org/wiki/Scare_quotes" rel="nofollow">https://en.wikipedia.org/wiki/Scare_quotes</a>. My, rather trivial, point was only that it's not a metaphor, the denser air really does fall.</blockquote>

    OK, I take your point!
    •  
      CommentAuthordjh
    • CommentTimeSep 20th 2020 edited
     
    Posted By: WillInAberdeen
    Posted By: djhyou'd have to ask someone who does have the system
    Er - I did. If, as you say, you don't have the system, then it would be difficult for you to reply anything useful about it.

    I'm not sure what your point was?

    I'd heard that too, but for it to transfer a worthwhile amount of heat, the floor in the sunny area would have to be many degC warmer than the floor in the cool rooms, which would mean the room air would be too. Does that actually happen in a new house?

    And I'm confused by what you said earlier if you now say you had such a system?

    And I'm still wondering what you meant by 'many degC'?
  2.  
    Er - I did 'ask for someone who does have that system' to comment, because somebody who does not have that system, such as you, is unlikely to have anything useful to share about it, as you said.

    To transfer a worthwhile amount of heat from one room to another using the UFH, the warmest room must be warmer than the UFH water, by some number of degC. Let's call this difference 'dT'. The UFH water must in turn be warmer than the coldest room, by a similar dT, to drive the heat into that room. During ufh design, dT is often set at ~10degC or more. So one room would be warmer than the other room by 2*dT = ~20degC, which seems to me to be many degC of temperature difference between two rooms in the same house. 'Many' is defined as: 'a large number of’.

    But hopefully someone who actually has some experience doing this with their UFH will chip in their knowledge.
  3.  
    Posted By: Jeff B
    Posted By: WillInAberdeen
    Posted By: Jeff BWundatherm
    Looks interesting. Could you share roughly what price/m2 you are being quoted, and whether you were advised to lay boarding over it to carry the floor finish?
    The quote was £1040 for a 35 sq.m. area. I don't know if my son was advised to lay boarding over it (I'll check with him) but the website has videos showing floor tiles and laminated flooring being used on top.

    Thanks! We were thinking about using vinyl/lino/karndean covering to keep the floor level down. The screed or cement board ufh retrofit systems (eg LoPro Max/ LoPro 10) seem to carry vinyl directly, but the EPS board systems seemed to need another board over the top to spread out point loads, which adds to the build up height.
    • CommentAuthorJeff B
    • CommentTimeSep 21st 2020
     
    Posted By: WillInAberdeen
    Posted By: Jeff B
    Posted By: WillInAberdeen
    Posted By: Jeff BWundatherm
    Looks interesting. Could you share roughly what price/m2 you are being quoted, and whether you were advised to lay boarding over it to carry the floor finish?
    The quote was £1040 for a 35 sq.m. area. I don't know if my son was advised to lay boarding over it (I'll check with him) but the website has videos showing floor tiles and laminated flooring being used on top.

    Thanks! We were thinking about using vinyl/lino/karndean covering to keep the floor level down. The screed or cement board ufh retrofit systems (eg LoPro Max/ LoPro 10) seem to carry vinyl directly, but the EPS board systems seemed to need another board over the top to spread out point loads, which adds to the build up height.


    Not had a reply from my lad yet but I found this on the Wundatherm website:

    https://www.wundatrade.co.uk/shop/home/overfloor-retro-fit-solutions/wundatherm-underfloor-heating-boards/7mm-duo-board-system/

    It seems these Duoboards are recommended where you intend to use carpet or vinyl as a final floor finish. Will add about 7mm to the floor height. (Note: special comment about Karndean).
    • CommentAuthorEd Davies
    • CommentTimeSep 21st 2020
     
    Posted By: WillInAberdeenTo transfer a worthwhile amount of heat from one room to another using the UFH, the warmest room must be warmer than the UFH water, by some number of degC.
    They're not transferring heat from room to room, they're transferring it from slab to slab so the interface resistance between the slab and the room (which can be significant compared with other resistances in the chain between the UFH water and the room) doesn't come into play and also they're not necessarily transferring heat at the multiple kW level that UFH typically inputs at. Just taking away a hundred watts or so from the patches of floor in sunshine will do a lot to moderate the peak temperatures.

    dT is often set at ~10degC or more.
    That's way higher than numbers I've seen quoted. Typically the UFH flow temperature will only be a couple of °C above the target room temperature for a well-insulated house, and even that's only for charging the slab overnight on E7 or whatever.

    But hopefully someone who actually has some experience doing this with their UFH will chip in their knowledge.
    That would be nice but my recollection is that one of the two people who I think use this technique became a non-member of this forum following a dispute and is very unlikely to be back.
    •  
      CommentAuthordjh
    • CommentTimeSep 21st 2020
     
    Ed Davies wrote: "That would be nice but my recollection is that one of the two people who I think use this technique became a non-member of this forum following a dispute and is very unlikely to be back."

    Fortunately, his blog is still online with some numbers and drawings. At least the following pages seem to be relevant; there may be others:

    http://www.mayfly.eu/2014/09/part-thirty-three-system-details-and-the-bathrooms/
    http://www.mayfly.eu/2015/09/part-thirty-eight-heating-and-cooling-controls/

    They confirm what you say about flow temperatures.
  4.  
    His house is rather exceptional! And not a place where a retrofit underfloor heating system would be very worthwhile.
    (Edit: I'd also understood he modified it after writing those blogs to use a higher temperature to give better control)

    The rest of us need to use a mixing manifold to blend the UFH loop supplies to the optimum temperature. These are typically adjustable from 30-60degC and are often factory pre-set at 45degC - so dT=~25degC (adjustable ~10-50degC) in the notation I used above.
    •  
      CommentAuthordjh
    • CommentTimeSep 21st 2020
     
    Posted By: WillInAberdeenThe rest of us need to use a mixing manifold to blend the UFH loop supplies to the optimum temperature. These are typically adjustable from 30-60degC and are often factory pre-set at 45degC - so dT=~25degC (adjustable ~10-50degC) in the notation I used above.

    But none of that is relevant to the present conversation, which started when you responded to Ed's post:

    Posted By: Ed DaviesSome people use UFH to re-distribute solar heat from the floor areas in sunlight to the rest of the house by running the circulation pump without any heating or cooling as such.

    We're specifically talking about the no-net-heat input or output situation.
  5.  
    I'm specifically talking about Ed's more recent comment "Typically the UFH flow temperature will only be a couple of °C above the target room temperature for a well-insulated house".

    That's relevant to only very few houses with extremely low heating loads, but who for whatever reason still invested in UFH. I see that Ed was thinking of "two people", for whom moving a few hundred watts around would be a worthwhile exercise.

    I had heard of ufh being used more widely to even out temperatures, and couldn't see how that would work, but Ed's perspective of it being a very niche application makes more sense.
    • CommentAuthorEd Davies
    • CommentTimeSep 21st 2020
     
    I don't see why the success or otherwise of using circulation to distribute heat around the slab is dependent on very high levels of insulation so, no, I don't think it's a niche application. I think it'll help any time the predominant heat gain is through solar radiation falling on the floor and the floor surface is well thermally connected to the slab (no carpets or anything).

    The reason for mentioning certain well-insulated houses was only to illustrate that you can get useful heat transfer with low temperature differences.
    • CommentAuthorMike1
    • CommentTimeSep 23rd 2020 edited
     
    Posted By: Jeff BSo if my son goes for a wet UFH system powered by an ASHP, cooling the floor will reduce the room temperature more effectively than an air-to-air heat pump system? I find that hard to understand!

    One so-far unmentioned advantage of using wet UFCH for cooling is that it is effectively silent (within the building); air-to-air systems aren't, though some can be pretty quiet.

    FWIW, I was involved with a new commercial building that was experiencing overheating problems, where noise wasn't a significant issue. Modelling internal temperatures (IES environmental analysis + dynamic simulation) using the London Climate Change 2050 weather file (projected temperatures in 2050, taking into account climate change) indicated that peak temperatures and overheating would also increase significantly over the coming decades:

    - hours per year over 25°C within the building: from 184 now*, to 637 in 2050
    - hours per year over 28°C within the building: from 21 now*, to 211 in 2050
    * now = a few years ago, before the 2050 weather files were updated in 2016

    The engineer's report recommended retrofitting fan coil units (cold air blowers) hooked up to the building's existing chilled water system, either alone or in conjunction with retrofitting chilling to the existing UFCH (subject to costings, etc.). In the latter case the UFCH would be used in normal circumstances, with the FCUs being switched on during temperature peaks when the UFCH was unable to cope.

    The reason UFCH couldn't cope alone, was that it had been designed only for heating, with pipes at 300mm centres; to chill the area fully using UFCH pipes alone would have required pipes at 200mm centres. There were also some sections of pipe that would have needed modification to avoid over-chilling some areas, adding to the UFCH-chilling retrofit costs.

    Moral: design for both heating and cooling, and for the projected future summer temperatures, not for current temperature conditions.
    • CommentAuthorsgt_woulds
    • CommentTimeOct 10th 2020
     
    Hello All,

    Been a while since I last posted on here...

    I have first hand experience of the Wundatherm UFH (20mm profile - 16mm pipes - 150mm centres)

    The boards I used had aluminium spreader plates that you clipped in place before laying the pipes - I spent extra time laying layers of aluminium tape in the returns as the spreader plates only fit straight sections.

    [Wundertherm bods said this was unnecessary but my own experience proves otherwise]

    I believe their new boards are all foil faced so this is no longer necessary?

    Wundatherm also wanted the pipes laid at wider centres, but I didn't trust their output figures and also had in mind that I could reduce flow temps more easily than relay the floor... And I am thinking about future use for cooling so the reduced centres should help if I ever go down that route.

    UFH made sense at the time as I was making the kitchen and living room into one open plan space and the floor had to be screeded anyway (there was a 2inch slope from one corner to the other as well as asbestos floor coverings that I didn't want to touch)

    It was definitely the best decision we've made so far regarding the renovation of our house.

    Ive stayed in houses with full slab UFH and they've either been too hot or too cold with massive thermal inertia to overcome if the house is used sporadically.

    The overlay system in contrast is very responsive, warming up within half an hour of walking into a cold house and the heat is so much more pleasant than radiators.

    We were so pleased we did the bathroom and upper hallway as well (although learning from last time I laid an extra 20mm of tile backer insulation under the Wundertherm boards (40mm total) which has helped the system perform even better.

    I really wish we'd done the lower hallway as well! stepping from warm floor to cold back to warm is unpleasant, but too late now (does help prove to unbelievers the difference the UFH makes).

    A couple of lessons I learned:

    The heat does not travel very far from the spreader plates, so the closer you space them the more even the heat - definitely pay attention to the return loops and add extra aluminium foil wherever there is a gap.

    Think about where your toes end up! We didn't want to run under the kitchen units for obvious reasons and wundertherm designed the returns to be about 100mm outside of the cupboard faces. But see note above!
    Now when we stand at the kitchen sink to do the washing up our feet are on lovely warm floor and our toes are on (comparatively) freezing cold stone... Always run the return just under the edge of cabinets / wardrobes etc to avoid this.

    It is very easy to design and calculate the floor plans yourself once you understand the principle of the flow and return which saving time and money

    Always buy more levelling screed than you think (Wondertherm were never accurate on their calculations either and I always ended up ordering more with the inevitable delays on delivery).


    Look on ebaygumtreefacebook for people selling off cut rolls of the UFH pipe - I bought 50m for a tenner when I did the bathroom

    Likewise the plumbing parts are much cheaper elsewhere - especially abroad where this type of piping is commonly used for all plumbing works not just UFH

    If you can afford it (we couldn't) pay someone else to screed and lay the floor. Self levelling screed is easy to do but kills you. Laying 600x400 limestone slaps is difficult and kills you.
    My wife and 2yo daughter where staying with her parents in Hungary whilst I did the works - by week 6 I admitted defeat and paid a friend to help me. When my daughter met me at the airport she'd almost forgotten who I was!

    If our house extension ever gets started (a saga for another post) I will be using thin screed UFH again - we are that happy with it. We are also planning to make an airing cupboard using the Wundatherm Overlay boards for the walls and shelves
    • CommentAuthorCWatters
    • CommentTimeOct 10th 2020
     
    I have 80mm of PIR under my wet UFH and 21mm of engineered oak above it. House insulated to 2007 Building Regs.

    I find in very cold weather I need quite high flow temperatures to push enough heat into some rooms. If I was building a new house I'd put more like 150mm PIR in the floor. Don't think I would go near any of the "thin" UFH systems.

    I look at it this way.. The heat coming from the UFH will go up and down in proportion to the insulation above or below the pipes. If you have something like 10mm of insulation below the pipes and say 20mm of carpet above which way will the heat go? Yes I know thats a gross simplification.
    • CommentAuthorJeff B
    • CommentTimeOct 10th 2020
     
    sgt-woulds: thanks for your contribution, most encouraging! My son's extension is currently under construction so they are not at the UFH stage yet. I am very tempted to try it in our place (in the lounge) but my wife is not keen on the idea, not least because we have not long spent a fortune on a new wool carpet and some super-duper thermal insulating underlay! The lounge is quite big, approx 6m x 4m so you can imagine the flooring was not cheap. Maybe one day......

    Meanwhile I am looking at an air-to-air heat pump which might do just the lounge and kitchen area.
    • CommentAuthorJeff B
    • CommentTimeOct 10th 2020
     
    sgt-woulds: forgot to add that I can see only 5 of your photos in that pdf file?
    • CommentAuthorsgt_woulds
    • CommentTimeOct 11th 2020
     
    CWatters Its all a matter of use case and surface materials

    I would assume from the description you have at least 70mm of screed and then you laid an insulating material on top (Oak).

    I'm not surprised you need higher flow temps to feel the benefit and I'll bet you keep your heating on a lot longer than we do to achieve a comfortable level. This is what I experienced with other traditional UFH floors, and it's exactly what I didn't want - and I'll admit I took a lot of convincing that any thin overlay system would be so vastly different.

    I kept the rads in place for months before finally accepting they were unnecessary...

    The thin overlay boards act a lot more like vast flat radiators than traditional UFH in terms of output, warm up time is very quick but the boiler is not providing heat top up all most of the time, it's just the circulation pump running. Because the heat is truly radiative rather than convective so the whole room feels warmer than having radiators blaring out constantly we tend to set the thermostats to 18 degrees.

    With the radiators in the same space we normally had the thermostats set above 23 degrees to feel as warm. And that was before the kitchen / living room were knocked into one giant space.

    Ours is a 1960's bungalow, with a mix of uninsulated solid and filled cavity walls with 1980's dg windows (and at the moment zero insulation in the loft above the kitchen/living area whilst I sort out the loft extension) but we rarely feel cold.

    Should be amazing once the place is properly insulated a draft proofed.

    The great joy of the thin UFH is its responsiveness - we go away for an entire weekend with the heating off, come home flick on the UFH and 30 mins later toasty feet... for families and working couples who are in and out like a rude metaphor it's the perfect set up.

    But you are right, I would never wish to put UFH under carpet, nor engineered wood. What would be the point?

    Don't forget you can also use them to make radiative walls too if you really must have carpet...
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