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    •  
      CommentAuthorfostertom
    • CommentTimeApr 8th 2017 edited
     
    Posted By: djhI doubt they're recommending lowering minimum temperatures
    I wasn't particularly suggesting that - maybe is, maybe isn't, depending. But those fixed minimum recommended temperatures, applicable everywhere in all seasons, are old thinking presently being challenged.

    Why
    Posted By: djhI don't have much respect for Ms Roaf's thinking
    •  
      CommentAuthordjh
    • CommentTimeApr 8th 2017
     
    Posted By: SteamyTeaI know someone that built to passive house standards who has found that using a single circuit UFH system is useful for redistributing solar gain around the house

    It's a technique recommended in that New Zealand book somebody posted a link to.
    •  
      CommentAuthorfostertom
    • CommentTimeApr 8th 2017
     
    It's only going to distribute long-term averaged imbalances, like hours- or day-long - no good at all for sudden peaks like sun coming in, firing up a woodburner, cooking, leaving a door open.
    •  
      CommentAuthordjh
    • CommentTimeApr 8th 2017
     
    And what's the problem with that? Isn't that just what you need?
    • CommentAuthorgyrogear
    • CommentTimeApr 8th 2017 edited
     
    We bought a house with central heating.

    I then proceeded to take it out.

    Having been there and got the tee-shirt, I feel "magnanimous" enough to want to install some electric radiant at the house core = under a concrete staircase (thanks in particular to mucho assistance from Present Site !)

    This will consume 1.6 kWh/day for a planned 130 days.
    (compared with previous 27 kWh/day :shocked: of (retired) electric radiant floor), which I consider a fair trade-off...

    Much talk of the envelope on here, and rightly so, but don't ignore the poor old house core !

    Also, unless I did not read right, nobody yet replied concerning ability to cool the house in summer with the passive slab. As I understand it, the slab will take care of itself (and do the cooling...) because the cold northern back of slab (back of house) ought to "transfer coolth" (meaning, absorb heat...) from the exposed southern bit (which ought not to be too "deep" due to high sun angles anyhow)
    or something like that... Just leave enough overhangs to control for summer sun
    and good luck with the build !

    gg
    • CommentAuthorringi
    • CommentTimeApr 8th 2017
     
    Posted By: fostertomIt's only going to distribute long-term averaged imbalances, like hours- or day-long - no good at all for sudden peaks like sun coming in, firing up a woodburner, cooking, leaving a door open.


    A cool floor that is exposed to the incoming sun (no carpets) would help take up the heat and with the correct color tiles would stop most of the heat being reflected into the rest of the room. (But I like carpets!)
    •  
      CommentAuthorfostertom
    • CommentTimeApr 8th 2017 edited
     
    Posted By: djhAnd what's the problem with that? Isn't that just what you need?
    Wd feel unresponsive, not doing anything perceptible to even out local peaks and troughs as they arise.
    •  
      CommentAuthordjh
    • CommentTimeApr 8th 2017
     
    Posted By: fostertom
    Posted By: djhAnd what's the problem with that? Isn't that just what you need?
    Wd feel unresponsive, not doing anything perceptible to even out local peaks and troughs as they arise.

    I'm sorry? What do you want? The sun shines through the windows into the room where you're sitting and you not only don't expect to feel it but you don't WANT to feel it? And you think the building is faulty if you do feel it?
    •  
      CommentAuthorfostertom
    • CommentTimeApr 8th 2017
     
    sigh - nothing to do with the building's faulty, but a feature of a massive/wet redistribtion system compared with a fast-responding system. If that's OK i.e. not perceptibly relieving sudden local overheating as it happens, then it's fine.

    So what's to disrespect about Ms Roaf's writing?
    •  
      CommentAuthorSteamyTea
    • CommentTimeApr 8th 2017
     
    Posted By: fostertomcompared with a fast-responding system
    Starting to sound a bit magical, can you explain how it works a bit more.
    •  
      CommentAuthorfostertom
    • CommentTimeApr 8th 2017
     
    MHRV air doesn't move thermal capacity fast enough to be useful for redistribution but a hypothetical high-vol air system (can't imagine what, in this day and age) would have at least some instant effect in moving heat peaks away as the arise, incl instant-cooling massive surfaces experiencing solar radiation. By contrast, a UFH-based redistribution system would be the extreme opposite of instant effect.
    •  
      CommentAuthorSteamyTea
    • CommentTimeApr 8th 2017
     
    Umm, you would have to shift a lot of air though, which would make it drafty.
    Try putting some numbers to the
    Posted By: fostertomhypothetical high-vol air system
    and see what pans out.
    I suspect that a slab with pipes it will work just as well. For any given time of year, you know where there is likely to be a problem, so only a matter of making sure there is pipework to carry the energy away in those locations.

    You mentioned a similar idea several years ago, I suggested that you make up a physical model, that should satisfy you to its validity (or not).
    •  
      CommentAuthorjoe90
    • CommentTimeApr 9th 2017
     
    Posted By: gyrogear

    Also, unless I did not read right, nobody yet replied concerning ability to cool the house in summer with the passive slab. As I understand it, the slab will take care of itself (and do the cooling...) because the cold northern back of slab (back of house) ought to "transfer coolth" (meaning, absorb heat...) from the exposed southern bit (which ought not to be too "deep" due to high sun angles anyhow)
    or something like that... Just leave enough overhangs to control for summer sun
    and good luck with the build !

    gg


    Our old friend Jeremy Harris has reverse engineered his ASHP to provide cool water which cools his passive slab when needed and he also leaves the circulation pump running during the day to even out his floor temps from south to north whether the heat pump is running ( hot or cool) or not.
    • CommentAuthorgyrogear
    • CommentTimeApr 9th 2017
     
    Posted By: joe90he also leaves the circulation pump running during the day to even out his floor temps


    NICE ! However, a passive solar slab would not need the pump...

    cf. https://riversonghousewright.wordpress.com/about/16-passive-solar-radiant-slab/

    gg
    •  
      CommentAuthorfostertom
    • CommentTimeApr 9th 2017
     
    What a clear, well written and informative article - and only one of many on the site - v gd, hours of reading there - thanks.

    An intriguing mention within
    "to combine the structural floor with the thermal mass, design it to be earth-coupled to make the house frost-proof, and perhaps integrate a radiant floor central heating system, is the height of design elegance: using one element to serve multiple essential functions" -
    earth-coupling, a favourite of mine - however doesn't seem to feature further in this article's slab discussion.
    • CommentAuthoranth.payne
    • CommentTimeApr 9th 2017 edited
     
    Posted By: SteamyTeaI know someone that built to passive house standards who has found that using a single circuit UFH system is useful for redistributing solar gain around the house (imagine a sun heated hotspot). He just pumps the water around, no heating or cooling. You can of cause use a heat pumpp for cooling if you rally need to.

    I am a fan of basic DHW, so a simple well-insulated cylinder and E7, though it would be nice to use a heat pump, it really depends on your water usage, if you don't use much, a 200lt cylinder at 50°C will do you. A PV system that cost £4-5k, will currently buy you about 20 years worth of E7 hot water.

    You can get films for windows that can reduce the solar gain, they can be retrofitted if you find there is a problem.

    You have not mentioned ventilation. In an airtight house you will need a good system. Generally a pure mechanical ventilation and heat recovery system is not good enough to 'heat' a house, there is too little mass air flow.
    You may want to explore a larger system that can contribute to space heating. It does depend on your layout and budget.

    Building a house is more arithmatic and basic engineering than science.


    Thanks SteamyTea - some useful points there... I think I'm convinced to install UFH, which can then used to heat, redistribute solar gain and even cool... sounds like it ticks all boxes!

    Totally agreed on the hot water, and think that will be the plan. I think we'd ultimately get an ASHP, so may also use this to preheat DHW, and top with an element if necessary. Just need to decide on a suitable size tank.

    Also, the films - I used this in an office environment and it worked well. Hoping that clever architectural design will combat the need.

    It's a balancing act at the end of the day. If we want beautiful expansive glass we need to deal with the consequences one way or another...

    Glad you raised ventilation as I've been pondering this. I'm really against ducted options! To me they feel unhygienic and harbours for dust. I really like the ductless options... and then promote good air flow throughout the house, which should also help with heat distribution?
    • CommentAuthoranth.payne
    • CommentTimeApr 9th 2017 edited
     
    Posted By: gyrogear
    Also, unless I did not read right, nobody yet replied concerning ability to cool the house in summer with the passive slab. As I understand it, the slab will take care of itself (and do the cooling...) because the cold northern back of slab (back of house) ought to "transfer coolth" (meaning, absorb heat...) from the exposed southern bit (which ought not to be too "deep" due to high sun angles anyhow)
    or something like that... Just leave enough overhangs to control for summer sun
    and good luck with the build !
    gg


    Thanks gg- hopefully it should all balance out if I take the approach with UFH too? It makes sense that the passive slab is going to be the biggest thermal mass of the build
  1.  
    Ok I give up on the quotes which seem not to be working...

    Fostertom I take your points about localise short term temp changes, but isn't that impossible to avoid in day to day living? Not sure that's something you can design in. Cooking will generate heat for example. The only way to mitigate this is do something short term to combat it (i.e. Open a window)
    •  
      CommentAuthordjh
    • CommentTimeApr 9th 2017
     
    Posted By: anth.payneOk I give up on the quotes which seem not to be working...

    You need to select 'Html' instead of 'Text' to 'Format comments as'. You can go back and edit the format of your existing comments.
  2.  
    Thanks for the tip... never even noticed the option
    •  
      CommentAuthorSteamyTea
    • CommentTimeApr 9th 2017
     
    Posted By: anth.payneCooking will generate heat for example. The only way to mitigate this is do something short term to combat it (i.e. Open a window)
    What the kitchen extractor is for, not sure how they work with any sort of MVHR though. And they are noisy.

    While on this subject.

    Posted By: anth.payneI'm really against ducted options! To me they feel unhygienic and harbours for dust.
    I think with the correct filters, and maintenance, this is not a problem. My only concern with a ducted system is that it takes up a lot of space, so has to be designed in right from the start.
    I hear a lot of talk about the ductless sorts, but there seems to be a lot of confusion about them i.e. area they work effectively over, maintenance, BC approval.
    I think they have to be oversized, just like any ventilation system, and a HP fo that matter.
    • CommentAuthortony
    • CommentTimeApr 9th 2017
     
    Pretty much every Passive House has ducted ventilation, the majority heating choice in North America is ducted hot air, many homes in Europe have ducted ventilation and all the big hotels do too.
  3.  
    Most of the living space is open plan. It's only the bedrooms which is where we'd spend any time. So that why I'm hoping ducteless might be sufficient

    But never thought of BC... will need to check that.
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