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Heating and cooling: Super insulated dwellings

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  1.  
    • CommentAuthorowlman
    • CommentTimeJul 25th 2019
     
    Heat waves are supposed to become more intense and more frequent as GW bites.
    Super insulation obviously works fine in the winter, but is it in danger of turning our dwellings into hotboxes in Summer?
    I arrived home late last night and the outside temperature was 16.5C In spite of windows and roof-lights being open and a oscillating fan on, and a relatively open plan interior, the living room was at 26C.
    When I finalise the duct-work to my A2A system, hopefully it'll be a thing of the past.
    • CommentAuthortony
    • CommentTimeJul 25th 2019
     
    Are you shading the windows externally to cut out solar gain?
    • CommentAuthorowlman
    • CommentTimeJul 25th 2019
     
    To some extent yes, Tony, but a total daytime close-down no.
    If windows are open during the day then circulating inside air temperature reaches a balance with outside. Come evening and the insulated solid structure it seems can't loose that heat quickly enough. Fans help of course, but obviously not enough.
  4.  
    Ours is aiming for Passivhaus certification in the next few months and is 'super insulated' as a result. Whilst the overheating criteria are achieved in our PHPP model (predicted to 'overheat' above 25 degrees about 5% of the year), this does mean that most of the time lately we're at about 24 degrees internally. Technically below the threshold, but not what you'd call 'cool'.

    The only way to keep it any lower than that has been to totally shade the windows - what you call a total daytime close-down, and then do a night purge.

    Worth mentioning that the MVHR has been making a big difference to perceived humidity, which in turn makes it feel relatively cooler than outside.

    All in all, much more comfortable in practice than our previous developer-box rental (lightweight timber, fast to heat up in summer and lose heat in winter) in similar weather conditions. The only buildings that are any cooler are probably thermally massive stone.

    I do think that as a nation we'll end up changing behaviour patterns to match warmer (and cooler) climates out of necessity. Most of what I've described above is no different to closing shutters etc. that vernacular architecture in other climes has been doing for centuries.
  5.  
    I find keeping windows closed and closing curtain keeps the house cooler, espcially on the sunny side.
    my house isnt super insulated , just the loft. Planning to EWI the walls this month with 200mm

    I lived in Cordoba, Spain for a bit. they use external shutter or closed windows, curtain to reduce internal heat there in the summer. the idea of opening the windows during the day is a no no to most of the residence there
    (those without air con of course)
    .
  6.  
    Posted By: jamesingramin the summer. the idea of opening the windows during the day is a no no to most of the residence there

    That is what we do - when it is warmer outside than in - all windows shut, when it is cooler outside than in -windows open.

    We have a high thermal mass house and we have found that adding EWI made the coolth last a lot longer in the summer, although if we have a prolonged heat wave the internal temp. does creep up.

    We don't have much solar gain and no MVHR
    • CommentAuthortony
    • CommentTimeJul 26th 2019
     
    Yes, insulation keeps the heat out too, high mass inertia helps a lot to increase comfort by reducing speed of temperature swings
    • CommentAuthorgyrogear
    • CommentTimeJul 26th 2019
     
    Posted By: Peter_in_Hungarywhen it is cooler outside than in -windows open.

    We have a high thermal mass house and we have found that adding EWI made the coolth last a lot longer in the summer, although if we have a prolonged heat wave the internal temp. does creep up.


    +1

    Having a crawlspace or cellar and a whole-house fan and external blinds also helps substantially.

    gg
  9.  
    I've seen a lot of passive houses have roof or porch overhangs or have boxes around the windows that provide shade in summer, but are angled to allow direct sunlight through the windows when the sun is lower in winter. Other alternatives are to introduce trees for shading, though this might take a few years to grow big enough if you've got a new build.

    Our house is nicely shaded by three huge beech trees to the south of our property. Shade in summer and heat and light in winter once the trees lose their leaves. The shade, coupled with the thick stone walls and heavily insulated roof often sees us wearing jumpers in the house in summer as it gets quite chilly. I'm looking forward to installing a MHRV with summer bypass to help bring warmer air in from outside and heat us up!
    • CommentAuthorCharli
    • CommentTimeJul 26th 2019
     
    My house is by no means super-insulated, it has 50mm of internal insulation and double glazed windows that are all north-facing. Windows kept closed in the day. Yesterday outside temperature was 34C, indoors was a lovely 24C! The temperature does creep up over an extended heat wave (like last year), but that's a 10C difference to the neighbours house (semi-detached to mine but with no insulation and single glazing).

    Insulation definitely worth it!
    •  
      CommentAuthordjh
    • CommentTimeJul 26th 2019
     
    Posted By: Pile-o-StoneI'm looking forward to installing a MHRV with summer bypass to help bring warmer air in from outside and heat us up!

    Decent MVHR units don't do that. If the air outside is warmer than inside, it automatically turns off the bypass, precisely to avoid warming the house. You'd need to manage the bypass manually, which would get to be a real pain, I imagine. Far simpler just to open the windows, no?
    • CommentAuthorsam_cat
    • CommentTimeJul 26th 2019
     
    If you superinsulate, good air tightness and covered in solar... Why not add Aircon? It could run for 'free' during the bright sun (powered by SolarPV) so less/no concern around the 'green' factor, and being superinsulated it wouldnt take much to cool to a comfortable temperature.

    Are there MVHR that can tie into aircon/use the thermal transfer to keep the COOL inside?
  13.  
    Posted By: sam_catAre there MVHR that can tie into aircon/use the thermal transfer to keep the COOL inside?


    Ours is a Paul Novus system. We recently got confused as to why the bypass wasn't closed in hot weather, until we realised that the heat exchanger was effectively using the coolth in the outgoing air from our house to cool the fresh air coming in. When the temp outside dropped again, the bypass turned on so that the relatively warm air was then kicked out without transfer.

    No link to aircon, but you can definitely count on MVHR to use your house's thermal properties to best effect!
    •  
      CommentAuthordjh
    • CommentTimeJul 26th 2019 edited
     
    Posted By: Doubting_Thomasbypass wasn't closed

    I think you mean open. Or was closed.
    •  
      CommentAuthordjh
    • CommentTimeJul 26th 2019
     
    Posted By: sam_catIf you superinsulate, good air tightness and covered in solar... Why not add Aircon? It could run for 'free' during the bright sun (powered by SolarPV) so less/no concern around the 'green' factor, and being superinsulated it wouldnt take much to cool to a comfortable temperature.

    An aircon costs money and resources and shouldn't be necessary if the property is insulated and shielded to keep out excessive solar gain. So pretty much 100% waste from a green point of view.
    • CommentAuthorbhommels
    • CommentTimeJul 26th 2019
     
    Perhaps it would go down well with the eco bling crowd if you called it a heat pump?
    •  
      CommentAuthordjh
    • CommentTimeJul 26th 2019
     
    In an office, a heat pump to provide cooling sometimes makes sense, but in a house?
    • CommentAuthorCerisy
    • CommentTimeJul 27th 2019
     
    I'm considering couple of a/c units run from a PV array. Our elderly MVHR unit has a useless summer bypass system so I switch the whole thing off during hot days and rely on natural ventilation when the temp drops. We will replace the units shortly. All unshaded windows upstairs have solar powered shutters which we keep shut and use heavy curtains downstairs.

    However as we are getting on now - 70 next year - these high temp events are getting very difficult to bear and I can only see a/c as the answer. At least using a PV array to power them + our electric car, makes it less of an environmental concern.
  19.  
    Posted By: sam_catAre there MVHR that can tie into aircon/use the thermal transfer to keep the COOL inside?


    Genvex produce a MVHR with built in EASHP that can heat or cool the supply air. The amount of air delivered through the ducting is a lot less though than can be delivered with an air to air HP.
    • CommentAuthortony
    • CommentTimeJul 27th 2019
     
    I have one but almost never need to use either function,
    • CommentAuthorowlman
    • CommentTimeJul 27th 2019 edited
     
    Posted By: djhIn an office, a heat pump to provide cooling sometimes makes sense, but in a house?


    And why not Dave? If it's OK to put in and A2W heat pump for winter comfort heating why is it not OK to install an A2A heat pump to do that, plus have the added facility to reverse and provide occasional Summer comfort cooling.
    The install costs are possibly less than UF heating and/or exchanging radiators for larger capacity ones. Run the whole lot on Solar PV as sam_cat says and it's a win/win.
    •  
      CommentAuthordjh
    • CommentTimeJul 27th 2019
     
    Because there are other, passive ways to eliminate the need for cooling in our climate - basically shading. The energy and materials used to manufacture the PV panels and the energy generated by the PV panels can then be used for something that does require an active electrical solution.

    One of the principal failings of the current regulatory regime is the notion that you can somehow achieve goodness by adding additional renewable energy generation to a building. The building should first be designed to minimise the energy it requires and it should be measured against that underlying energy demand. Energy generation is a separate thing. You can't net one off against the other.
    • CommentAuthorgyrogear
    • CommentTimeJul 27th 2019
     
    Posted By: djhThe building should first be designed to minimise the energy it requires and it should be measured against that underlying energy demand.


    +1

    gg
    • CommentAuthorowlman
    • CommentTimeJul 27th 2019
     
    In a perfect world and new build I'd agree, but that's not the world we inhabit, and existing properties built to different standards and design often don't lend themselves to either IWI or EWI or external or internal shutters, before we consider the personal financing of such measures or local planning restraints.
    • CommentAuthortony
    • CommentTimeJul 27th 2019
     
    I like the idea of measuring energy demand
  26.  
    <blockquote><cite>Posted By: djh</cite><blockquote><cite>Posted By: Pile-o-Stone</cite>I'm looking forward to installing a MHRV with summer bypass to help bring warmer air in from outside and heat us up!</blockquote>
    Decent MVHR units don't do that. If the air outside is warmer than inside, it automatically turns off the bypass, precisely to avoid warming the house. You'd need to manage the bypass manually, which would get to be a real pain, I imagine. Far simpler just to open the windows, no?</blockquote>

    I undertsand where you're coming from but if summer bypass is turned off, then it means the heat exchange is on, which means that the house still warms up because while the cooler exhaust air will cool the warmer incoming air, the MHRV is not 100% efficient, so the house will be warmed a little with incoming air.

    With opening windows, I guess the options depend on whether you live in a high crime area and you're out all day and whether you want filtered air because you live in a high pollen or high pollution location? Plus an open window is good for ventilating around the window, and perhaps the interior if you can get a cross wind though the house (if there is any wind on a hot day), but it can't hope to compete with air ducted to the interior of the house by a ventilation system. As we have solar, and this is summer, the MHRV would be running on free energy.
    •  
      CommentAuthordjh
    • CommentTimeAug 2nd 2019
     
    Posted By: Pile-o-StoneI undertsand where you're coming from but if summer bypass is turned off, then it means the heat exchange is on, which means that the house still warms up because while the cooler exhaust air will cool the warmer incoming air, the MHRV is not 100% efficient, so the house will be warmed a little with incoming air.

    If the temperature outside the house is warmer than the temperature inside the house then the house will warm up by heat passing through the walls and the windows as well as to a tiny amount by ventilation air cooled by an MVHR. That is basic physics and the only way to avoid it is to use some active cooling, such as evaporating water or installing an air-conditioner.

    Plus an open window is good for ventilating around the window, and perhaps the interior if you can get a cross wind though the house (if there is any wind on a hot day), but it can't hope to compete with air ducted to the interior of the house by a ventilation system.

    Open windows usually have a much greater impact on interior temperatures than any ventilation system, whether HRV or not. The air flow through windows are just so much greater. The areas of windows are much larger than ventilation ducts, and the flow rates are much larger. Ventilation systems are designed not to cause drafts. Windows almost always cause noticeable drafts, either from wind pressure or thermal passive stack effects.
    • CommentAuthordickster
    • CommentTimeAug 6th 2019
     
    With the luxury of a new build and 300mm blown recycled paper insulation and not many burglars, hot weather dealt with as follows: windows and roof open when cooler outside, opposite and curtains drawn when hotter outside. Low mass house, so cooling effect quicker.

    Only gets tricky with continuous hot weather over maybe 3-4 days.

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