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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

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    • CommentAuthordelprado
    • CommentTimeMar 9th 2018
     
    Continuing my education, I was interested to read that passiv haus or ultra low energy buildings are not huge fans of UFH, because unlike radiators, they cannot push air around the house to where it needs it. Is that correct from your experience?

    So for example if you lived in a bungalow and your heat loss was 1000w (inc ventilation and thermal bridge loss, ie everything), you could put a single 1000w radiator in and it be miles away from cold spots in the house and it would do its thing, whereas if you have a single UFH heating room of 1000w (would be hard to achieve but for purpose of example), then it wouldnt do the same?

    Thanks
    •  
      CommentAuthordjh
    • CommentTimeMar 9th 2018
     
    Posted By: delpradoContinuing my education, I was interested to read that passiv haus or ultra low energy buildings are not huge fans of UFH, because unlike radiators, they cannot push air around the house to where it needs it. Is that correct from your experience?

    I haven't read that anywhere, and have several times seen the opposite. Radiators don't 'push' air anywhere, they just allow thermal convection; so does UFH although somewhat differently.

    So your question is a strawman proposal. Is it yours or did you really read it somewhere?
    • CommentAuthordelprado
    • CommentTimeMar 9th 2018
     
    I read it here, and it makes sense to me given that convection will produce an air current, whereas (a heat source which is primarily) radiation will not?

    "Radiators make for a cheap heating system, but are also an excellent match for a Passivhaus. Thanks to triple glazed windows you can put them where you like in a room as there are no downdraught comfort issues. Individual room control with Thermostatic Radiator Valves (TRVs) allows the system to respond to solar and internal heat gains, which provide a far greater fraction of the heating than in a conventional building.

    Radiators can also provide buffering for the minimum output of a gas boiler or heat pump: the thermal mass of the radiators allows the boiler fl ow temperature to rise gradually even though the boiler may be generating 4 or 5 times the amount of heat the building needs. Then when the boiler stops fi ring the radiators continue to release heat to the rooms.

    Warm radiators generate convective air movement, which helps move heat around a house. This and the high levels of insulation mean you don’t need radiators in every room.

    Underfloor heating certainly works in a Passivhaus, but is an expensive option since it is a radiant source and you need to install it in every room you want to be warm. This then means that the system can be far too powerful for the heat load – and needs careful control to avoid overheating. If you can keep the floor temperature down to a degree or two above room temperature however, the heat output will be self limiting – once the room is warmer than the floor it will stop heating the room"

    http://howtopassivhaus.org.uk/heating-systems
    • CommentAuthordelprado
    • CommentTimeMar 10th 2018
     
  1.  
    I'm trying to work out the logic. I suspect it only works for Ultra Low energy houses, as any sort of "normal" house, you'd get one warm room and everywhere else cold.
    Even in a passivhaus, you'd still need to leave all the doors open?
    It must be something to do with the convection from the radiator causing air to circulate, so it rises to the ceiling and causes a very definite circulation pattern.
    With UFH, where you have a whole barely warm floor, you wont get anyhting like the same circulation patterns.

    I think.
  2.  
    Also, as a thought, if you really only need 1 or 2 kW of heating, for overall install costs and even long term simplicity, a couple of simple electric heaters are going to be massively simpler, easier, etc. etc. than a UFH install.
    • CommentAuthorKenny_M
    • CommentTimeMar 10th 2018
     
    From an experience, rather than any theoretical knowledge I have on the subject, I would say that it's hard to see one radiator heating different rooms, unless its open plan. In my previous house I had a stove, with an ecofan on it. I'd leave both doors open and the stove room would heat up and the rest of the house stay mostly cold. The stove with fan could be called assisted convection, as the fan is drawing cold air up behind and over the top of the stove, but very little of that heat went out of the doors into the other rooms.

    My understanding of why underfloor heating works is that the heat is concentrated where the body is, rather than being sent first to the ceiling and travelling around the room before it gets to the body. But I could be completely wrong about that, just seems to be what makes sense to me, or maybe I have read somewhere.
    • CommentAuthordelprado
    • CommentTimeMar 10th 2018
     
    I suppose a supplementary question is to turn it on its head, how do passiv haus work if the heat is not distributed around the home of its own accord somehow?

    A passiv haus is simple an air tight house with lots of insulation. Through a mixture of ventilation and diffusion whatever heat is contained within it is slowly lost through the walls like any other house. Just because it has tonnes of insulation, I don't understand how everywhere gets evenly heated without even heat sources throughout the house?
    • CommentAuthortony
    • CommentTimeMar 10th 2018
     
    Come and see if you like. Anywhere there is a temperature difference heat will flow. As you say all houses loos heat. With highly insulated homes the losses are less so everything inside the insulated envelope gets to roughly the same temperature.

    When the heat losses are higher warmers tools tools heat to cooler rooms which in turn loose heat to outside. In poorly insulated homes these rooms become uncomfortably cold, hence the need for central heating.
  3.  
    Posted By: delpradoI suppose a supplementary question is to turn it on its head, how do passiv haus work if the heat is not distributed around the home of its own accord somehow?

    A passiv haus is simple an air tight house with lots of insulation. Through a mixture of ventilation and diffusion whatever heat is contained within it is slowly lost through the walls like any other house. Just because it has tonnes of insulation, I don't understand how everywhere gets evenly heated without even heat sources throughout the house?


    Most PH have MVHR which is how air along with heat is moved around the house. If it's set up correctly there's no reason why one part of the house should be warmer than another unless of course there is a high heat source in one area of the house, which isn't a good idea in a PH.
    • CommentAuthordelprado
    • CommentTimeMar 11th 2018
     
    My understanding is that MVHR does not move hot air around house at all.

    Tony - that doesnt answer the question, how does the air move around the house? Are you saying its diffusion through the air from warmer spots to colder spots internally?

    Look at that Norwegian studfy though, it seems to suggest bedrooms stayed cold
    •  
      CommentAuthorfostertom
    • CommentTimeMar 11th 2018
     
    Posted By: delpradoMy understanding is that MVHR does not move hot air around house at all.
    It does, not enough to notice in a 'normal' house, but enough to even things out in a lo- or zero-demand PH.
  4.  
    Posted By: delpradoMy understanding is that MVHR does not move hot air around house at all.


    My experience is the opposite. I heat my house using warm air produced by the EASHP in my Genvex Combi185 and because the heating requirement is so low it's very effective.
    •  
      CommentAuthordjh
    • CommentTimeMar 11th 2018
     
    Posted By: PeterStarckMy experience is the opposite. I heat my house using warm air produced by the EASHP in my Genvex Combi185 and because the heating requirement is so low it's very effective.

    I use a post-heater on our MVHR. But to be fair heated supply air is slightly different since that's supplied to all habitable rooms, generally, which makes the problem a little easier. However I agree with what Tom said as well.
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