Dealing with solar gain

[HughF]

The house in question: 1946 end of terrace, block + block, 50mm filled cavity (chopped and blown fibreglass)

 

South facing, non shaded. The issue is that in summer, the constant solar gain on the southern aspect means that the walls are now a storage heater and it’s pretty nastily hot in there. Luckily I just leave and go to my rural property in Dorset which is sheltered and made of sticks.

 

We’re up to dpc on a rear extension that will remove half of this aspect from the direct sun, moving the solar gain into the extension, which I’m hoping will be manageable through the better standard of construction.

 

But apart from ewi, what are the options for managing the solar gain and subsequent heating of the remaining exposed wall section, the upstairs…. I’m going for 3G on the extension and will be changing the upstairs bedroom windows for 3G too.

Edited June 26, 2023 by HughF

[SteamyTea]

Will need a lot more data.

Which wall is becoming a 'storage heater' assuming that the south facing wall is mostly windows and doors i.e. front of the house.

What sort of areas?

How does the internal temperature correlate with the outside temperature?

How is the roof orientated and how well insulated?

[Conor]

What colour are the walls? If unpainted, or a dark colour, paint them white. The 3G will make a big difference. Otherwise you can introduce shading - trees, climbing plants etc.

[HughF]

29 minutes ago, SteamyTea said:

Will need a lot more data.

Which wall is becoming a 'storage heater' assuming that the south facing wall is mostly windows and doors i.e. front of the house.

What sort of areas?

How does the internal temperature correlate with the outside temperature?

How is the roof orientated and how well insulated?

South facing walls, the whole ‘back ‘ of the house. There are four windows, all 1800x1200 (ish), all 10yr old upvc.

 

downstairs is a kitchen and a sitting room. The front of the house (north facing just has a sitting room downstairs and the hall/stairs).

 

House is painted white, roof is 300mm of insulation (with a bit of it compressed because the loft is boarded around the hatch).

 

Now that it’s had a month of sunshine on it, it seems to be consistently stable at ‘hot’ temperatures internally.

[SteamyTea]

3 minutes ago, HughF said:

South facing walls, the whole ‘back ‘ of the house. There are four windows, all 1800x1200 (ish), all 10yr old upvc.

Is the east or west wall the end.

By the time the sun is on a west wall, the OAT is pretty high.

 

My house temperatures have be high this last week, even with the OAT temperature dropping to 15°C last night, the house was 23°C this morning.  I have a jumper on at the moment.

[HughF]

The west wall is the end wall. 
 

 

We’re about to start the ball rolling (slowly) on a double height side extension to replace that single skinned outhouse. But that might be 3yrs away, planning/financing/dno depending.

Edited June 26, 2023 by HughF

[HughF]

I put my hand on the inside pane of the downstairs windows yesterday afternoon, they were ‘quite hot’… so I’m assuming the issue is related to the glass as much as the walls.

 

Hence my desire to go for 3G in the extension.

 

 

[SteamyTea]

That is quite a lot of surface area to get hit by the afternoon sun.

You could try a some solar reflecting paint.

https://www.rawlinspaints.com/home/roof-paints/solar-reflective-paints/551-coo-var-solar-reflective-paint-white.html

 

Putting a hand on a window is really showing how powerful the sun is.  I still have my winter secondary glazing in place, so in effect, triple glazed windows.  I am not sure if it is helping or hindering.  Hindering I think, but that may be because I can only open two windows now, one upstairs and one downstairs.  Leaving it as it is as I am collecting data and can do some analysis later.

When we had the heat warning last year (first time it had happened in Cornwall) I found a just closing the curtains made no difference.  The year before 2021, when in my location it was even hotter, I tin foiled the windows, that made a 10°C difference.  So maybe cover the top half of the windows in tin foil to reflect the excess solar energy.

But I think your problem is the wall.

[HughF]

1 hour ago, SteamyTea said:

That is quite a lot of surface area to get hit by the afternoon sun.

 

But I think your problem is the wall.

Thanks for the input. Appreciate it.

[eandg]

You'll notice a huge difference with new 3G - I am really surprised how little solar gain appears to come in (only a very marginal temperature difference) through south facing windows in our build compared to the old 2G in current home. 

[Sparrowhawk]

2 hours ago, SteamyTea said:

The year before 2021, when in my location it was even hotter, I tin foiled the windows, that made a 10°C difference.  So maybe cover the top half of the windows in tin foil to reflect the excess solar energy.

Did you tin foil the inside or outside of the windows?

[SteamyTea]

14 minutes ago, Sparrowhawk said:

Did you tin foil the inside or outside of the windows?

Inside

[Radian]

Grow a virginia creeper on the wall. It won't take long to establish itself. It's self supporting on little suckers so no need for trellis. I grow one up a south facing wall to keep the inside cool in summer. Seems to work.

Once in a while I cut it down at the top to stop it going over the roof. Overdid that a bit last time. Also trying a new look letting it go over the chimney!

 

[SteamyTea]

16 minutes ago, Radian said:

Seems to work.

I did an experiment where I grew some grass in a tray and compared the temperatures to a similar tray with just dirt in it.

No real difference I seem to remember.

https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=7304&page=1

 

There is a lot of talk in the 'eco' world about it, but little evidence to back it up.

I do like the look of it though, walls are a good size canvas and need to be decorated.

I have a lizard and a butterfly on mine.

 

Edit

Just reread what I wrote 12 years ago.

Seems I compared a roof tile and grass, with the soil making the difference, not the grass.

Edited June 26, 2023 by SteamyTea

[MikeSharp01]

2 hours ago, SteamyTea said:

Just reread what I wrote 12 years ago.

Seems I compared a roof tile and grass, with the soil making the difference, not the grass.

You have come a long way Charlie Brown

[SteamyTea]

17 minutes ago, MikeSharp01 said:

You have come a long way Charlie Brown

Feel I am going backwards. Was in my 40s then, now late 20s.

[Radian]

5 hours ago, SteamyTea said:

I did an experiment where I grew some grass in a tray and compared the temperatures to a similar tray with just dirt in it.

No real difference I seem to remember.

Just pointed an IR thermometer at a bit of wall behind the creeper and at the cleared area directly above... currently 5^oC cooler behind the creeper. Now charging the FLIR attachment for my phone to try getting a full image (it's ALWAYS flat when I go to use it). I'm not sure if it will be so representative as the emissivity of the stone will be different to the foliage.

[SteamyTea]

2 minutes ago, Radian said:

currently 5^oC cooler

The physics days it should shield the wall from direct light, and as leaves absorb the red and blue light, they should heat up. As they are mostly water, quite a lot of energy is absorbed.

But then, depending on the plant type C3 or C4, they transpire, mostly water vapour and a little oxygen, and a lot of nitrogen, so that shifts the energy balance somewhat.

Also, plants are piss poor at converting sunlight into biomass, generally 0.25%. which leaves a lot of energy just passing though, one way or another.

I am not sure how easy it is to calibrate for different emissivity, probably very complicated and needs special kit, though there may be general numbers that are good enough.

[Radian]

3 minutes ago, SteamyTea said:

The physics days it should shield the wall from direct light, and as leaves absorb the red and blue light, they should heat up. As they are mostly water, quite a lot of energy is absorbed.

 

Transpiration should be the principle process here. The fact that the air can flow freely behind the leaves as well as them shading the wall makes them an ideal sunshade.

 

[Mr Punter]

I think that the solar gain will be via glazing, not walls.

[HughF]

55 minutes ago, Mr Punter said:

I think that the solar gain will be via glazing, not walls.

I guess we’ll find out when we replace the 2g with 3G on the south facing area of the house.

[Radian]

3 hours ago, Mr Punter said:

I think that the solar gain will be via glazing, not walls.

 

13 hours ago, HughF said:

South facing walls, the whole ‘back ‘ of the house. There are four windows, all 1800x1200 (ish), all 10yr old upvc.

 

That's a fair amount of gain for sure. Reflective backed blackout blinds can help to an extent - which was my first step in combating our problem. Solar gain through the glazing will also drive up the temperature of the inner blocks and add to the problem if it's allowed into the interior. All the masonry is then absorbing and re-emitting the thermal energy at a maximum probably right when you least want it - when you're trying to get some sleep. Our problem has also got noticeably worse this year since we had the cavities filled with EPS. Seems I picked a bad time to go overboard with cutting back the creeper.

[HughF]

4 minutes ago, Radian said:

 

 

That's a fair amount of gain for sure. Reflective backed blackout blinds can help to an extent - which was my first step in combating our problem. Solar gain through the glazing will also drive up the temperature of the inner blocks and add to the problem if it's allowed into the interior. All the masonry is then absorbing and re-emitting the thermal energy at a maximum probably right when you least want it - when you're trying to get some sleep. Our problem has also got noticeably worse this year since we had the cavities filled with EPS. Seems I picked a bad time to go overboard with cutting back the creeper.

Well, hoping that the single story (pitched roof) rear extension that we’re cracking on with will reduce the exposure of the lower level to the sun. The extension is 150 cavity, full fill, thermalite inner skin. It will also have slab cooling.

 

So that leaves the upstairs on the south aspect. New windows and a couple of fan-coil units?

 

I guess it’s one of the downsides to a block/block build with solid internal walls. My timber framed shack in purbeck stays lovely and cool. Although it is freezing in winter.

 

Edited June 26, 2023 by HughF

[SteamyTea]

The reason I say that the problem is the wall, not the window(on the west side in the photo) is that there is a lot of area, the window is quite small.

At this time of year, even west facing glazing is reflecting a lot of light as the sun is still quite high in the sky,

we have also had high temperatures and lots of sunshine for 3 weeks now.

I have picked Dorchester as an example.

The solar is measured in the horizontal plain, so only noon is close to correct, either side of that, more power from the sun will be hitting the walls (if I feel up to it I shall look at the solar angles and do a bit of trigonometry, but I have a busy day tomorrow, maybe others can do it)

Assuming your west facing wall starts to get a decent amount of light on it from 1 PM, then since the beginning of the month, there has been a mean of 375 W.m^-2 hitting it, peaking mean is 579 W.m^-2.

The mean afternoon temperature, when the sun is out, has been 21°C.  The night temperature has been 14.8°C, the morning till 1 PM temperature has been 16.7°C.  The daily mean of the period has been 17.8°C.

 

To see how things changed over the month, here are some more charts, but week based.

Week 22 is the first week of June.

 

Week 23

 

Week 24 (gone off the scale a bit)

 

Week 25

[joe90]

Vertical solar panels, use all that solar gain 🤷‍♂️