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    • CommentAuthorCX23882
    • CommentTimeMay 27th 2017
    In the ever-moving goalposts of improving efficiency and summer comfort, the solar window screens have pretty much solved day-time overheating issues, but now I notice that as it gets to late-evening, the two rooms at the north end of the building begin to heat up. Thermal imaging shows the exterior walls (north-west facing) are a few degrees warmer than the ceiling, floor, internal partition walls or north-east exterior wall. This occurs at a time where the outside temperature has begun to drop.

    The walls are traditional 60s/70s construction - i.e. plain red bricks, cavity (retrospectively filled with blown-in mineral fibre), then concrete block, with a plaster finish.

    Due to orientation, the wall gets direct sun for late-afternoon until it falls below the trees and surrounding properties. Is the problem that the sun is hitting the dark-coloured bricks, heating them up far above ambient/shade temperatures, and they then continue to release the energy even after the sun has gone down and temperatures drop?

    What I'm getting to, is would there be any noticeable benefit in battening out and then cladding the wall with white shiplap? It wouldn't look too out of place on the property, and isn't particularly expensive either. The goal being to prevent solar radiation from hitting the bricks directly; instead it would be absorbed by a white PVC or timber surface, with a ventilated void behind it.

    I wasn't considering adding EWI, but could possibly add some insulation - after all, the uPVC door panels with only around 15mm of polystyrene insulation bonded to them seem to do a good enough job of avoid solar heat gain.

    The other option would be a pergola or carport fitted over the full length, but I assume it would need to be quite large to provide appropriate shading, due to the orientation.
    • CommentAuthorgoodevans
    • CommentTimeMay 27th 2017
    I reckon that would work - in effect a solar screen for the walls (sun drenched walls are significantly warmer than ambient). The better the ventilation the better the effect. (the colour however would play little part in the equation).
    • CommentAuthorgyrogear
    • CommentTimeMay 27th 2017 edited
    Posted By: CX23882The other option would be a pergola or carport

    or perhaps some tallish vegetation and leafy stuff - something to prevent direct radiation by casting some shade.

    (I get the same phenomenon, it is amazing how far north the sun comes of an evening, these days !). (My solution is drafting - I open the roof lights and pull in full basement air...); and opening N/W bedroom windows & dropping outside (electric) shutters...

    If the summer heat can get in then the winter heat can get out. So if you are going to do some remedial work then cladding with a rear ventilation gap would probably resolve the summer problem but do nothing for the winter loss.
    EWI would do both!
    • CommentAuthortony
    • CommentTimeMay 27th 2017
    If you do it and it sounds good to me, you would need to meet building regs and have to add insulation.

    Sounds to like the supposed CWI might not be there
    • CommentTimeMay 27th 2017
    Before taking any action, check the diagnosis! Get out your IR thermometer (you do have one? If not then get one) and measure the actual temperatures on the various surfaces. Then you can work out where the problem is coming from. Your description is way too vague to draw any conclusions.

    Colour doesn't affect things much, contrary to common sense. Shiny is more reflective, and so is white until it accumulates a bit of dust. But you need special surface treatments to really lower emissivity. A ventilated screen would reduce insolation. But is there a problem? What are the numbers?
    • CommentAuthorCX23882
    • CommentTimeMay 27th 2017
    Thanks for the replies.

    I agree, I need to take some measurements of surface temperatures both sides of the wall. I do have a non-contact IR thermometer, in addition to the Flir, so next time there is a problem day I'll take a few readings (today was warm but overcast and stormy in the afternoon, and I didn't experience any warm walls).

    I'm not going to rush into anything just yet. It isn't a huge issue other than a handful of days of the year. But just want to get a plan of future improvements. Maybe it is worth biting the bullet on a proper EWI install.
    • CommentAuthormw116
    • CommentTimeMay 30th 2017
    Would it be worthwhile setting up a 'temporary' screen - nothing fancy, say a tarpaulin or similar to shade the wall and see if it makes a difference?
    • CommentAuthorSigaldry
    • CommentTimeMay 30th 2017 edited
    If the dwelling has cavity wall insulation and a reasonable amount in the roof, then most of your problems are likely to be around controlling solar gains and night time purge ventilation.

    Solar shading over southerly facing glazing might be an option (from a pergola or similar), or just ensuring you shut curtains/blinds during the day on hot days.

    Likewise try and get rid of heat accumulation from during the day, over the night.

    A few ideas to consider in: https://www.bre.co.uk/filelibrary/Briefing%20papers/116885-Overheating-Guidance-v3.pdf

    edited for typo and so it makes sense!
    • CommentAuthorCX23882
    • CommentTimeJun 4th 2017
    Still haven't had any more days where it has been clear and sunny in the late afternoon, and even with highish shade temperatures, no overheating inside. I'm not seeing much temperature drop overnight though.

    Night time purge ventilation is difficult for security and pet escape reasons. Would a high speed extractor such as the Manrose MF200 providing 238l/s be of any use. An inlet could be mounted to a plywood or perspex panel that clips into some mounts fitted to the euro groove in the windows. Effectively a high speed version of positive input ventilation, that is mounted temporarily. Whilst the flow rate seems good, is an axial fan appropriate?
    • CommentAuthorgyrogear
    • CommentTimeJun 4th 2017 edited
    Posted By: CX23882I'm not seeing much temperature drop overnight though

    does this mean climate-wise, or dwelling-wise ?

    Accessory question: how would you summarize your dwelling from the point of view of thermal mass: much, not much ? Perhaps a brief summary of the structure might help (types of walls and floors, insulation types, presence of underfloor voids (cellar, crawlspace, basement etc.).


    Posted By: CX23882Would a high speed extractor such as the Manrose MF200 providing 238l/s be of any use

    High speed extractors make a lot of noise! A big(er) large dia. slow fan would be much better.
    • CommentAuthorCX23882
    • CommentTimeJun 4th 2017 edited
    Posted By: gyrogeardoes this mean climate-wise, or dwelling-wise ?

    Dwelling-wise. Over the past week, my typical day-night air temperature swings measured in a south-west room have been a minimum 20C at around 7am rising to a maximum of 23C/24C at around 8pm, with the rate of increase between 7am and 8pm being a similar gradient to the decrease between 8pm and 7am.

    Interior air temperatures (degC)
    30/5 21 / 20
    31/5 22 / 20
    01/6 24 / 22
    02/6 23 / 22
    03/6 22 / 21

    Unfortunately I don't have an exterior temperature monitor, but the recorded temperatures on Accuweather show temperatures have been a maximum of 21 to 23C, and lows of 10 to 14C.

    Accuweather (degC)
    30/5 20 / 12
    31/5 21 / 8
    01/6 23 / 12
    02/6 21 / 14
    03/6 20 / 10

    My peak temperature is generally 1 degree higher than the Accuweather max temperature for that day, which I suppose isn't actually that bad, given that I'm working from home all day, with windows either closed or a couple on the "locked-open" position. The bigger problem seems to be that I'm not getting rid of enough of the heat at night - one possibility might be walls/floor getting heated up during the day, and then releasing that heat well into the evening, and my rate of ventilation isn't enough to offset that.

    It looks like there is a lag of around 4 hours between peak exterior air temperature, and interior peak air temperature (and similar lag for minimum exterior for my minimum interior).

    Posted By: gyrogearAccessory question: how would you summarize your dwelling from the point of view of thermal mass: much, not much ? Perhaps a brief summary of the structure might help (types of walls and floors, insulation types, presence of underfloor voids (cellar, crawlspace, basement etc.).

    Typical British construction.
    Walls: standard 60s/70s cavity, red brick outer leaf, concrete block inner leaf (no idea of density), wet plastered, filled with blown-in mineral wool. Concrete block partition walls.
    Roof: concrete tiles, bituminous under-felt, ventilated (but still 60C attic temperatures on a sunny day), 300mm mineral wool over ceiling
    Floor: concrete ground bearing slab, no insulation, vinyl plank over thin foam/metallic underlay
    Windows: 80% solar screens externally, rigid PVC vertical blinds internally, 4+20+4mm non-low-e glazing, average 30% window to floor-area ratio per room.

    Posted By: Peter_in_HungaryHigh speed extractors make a lot of noise! A big(er) large dia. slow fan would be much better.

    I'll have to look at what else is available. The 200mm Manrose fan doesn't appear to have much difference between its 3 speeds - they only give the RPM which varies between 2000RPM and 2700RPM, and curiously the same noise level for all speeds.
    • CommentAuthorgyrogear
    • CommentTimeJun 5th 2017
    <blockquote><cite>Posted By: CX23882</cite>Concrete block partition walls.</blockquote>

    Sounds very useful - how much of these actually "see" the sun ?

    <blockquote><cite>Posted By: CX23882</cite>average 30% window to floor-area ratio per room.</blockquote>

    This sounds absolutely ginormous to me !
    To my reckoning you have about twice too much glass !

    per robert riversong:
    Too much glass can mean:

    • overheating even in the dead of winter
    • overchilling at night
    • too little privacy
    • too little usable wall space
    • too much glare and shadow
    • too little sense of enclosure and security

    Could you consider having a bare concrete floor ?

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