Combating Solar Gain

[Deejay_2]

12 hours ago, Iceverge said:

I guess your first buildup was something like this.

 

I calculated a U value of 0.188 and a phase shift (decrement delay) of 6.7hrs.  This isn't a great number and may have added to your overheating. 

 

 

A better option for heat protection. Similar U value but a phase shift of 12.8hrs. Notice the much less extreme swing for internal surface temperature in the summer. This makes overheating easier to control.

 

On a cold winters day both roofs will perform the same against the cold.  

The website I used was. It's worth having a play. 

https://www.ubakus.com/en/r-value-calculator/?

 

It includes this importance sentence in the blurb there too. 

 

"For a proper summer heat protection, materials with a high heat storage capacity should be used, ideally in combination with an outer insulation. In addition, the direct sun exposure through windows must be reduced to an acceptable level by shading means, e.g. outer blinds, roller shutters or sun sails"

 

 

 

 

Wow, that information is so useful.  It looks as though it's another case of specifying suitability for the winter months, with no thought given for the extreme heat in the summer months.  WE used an architectural technician last time and we followed his specification - however, the "retired" RIBA architect we are currently using has not offered any advice either.  It may be a case of "you get what you pay for".    I'm going to research the information you have given - many thanks for going to all that trouble - it's not something I would have considered and as can be seen from my post, I have been concentrating on the windows and shading.   

[Iceverge]

It's a part of the issue, mostly in room in roof designs. 

 

It's difficult to get a handle on this without playing with some kind of overheating calculator. The effect of mainly poor glazing choices become more obvious then. 

[RandAbuild]

We made the mistake of concentrating on insulating for winter rather than summer. Having a SSE facing rear has contributed to high levels of solar gain in the summer months. Our large hall and landing window is non-opening and can easily raise the inside temperature to 32deg.

 

We have now finished installing an electric pergola for the kitchen and electric solar blind for the hall. These both operate from the Somfi app and coupled with the Velux have made things much more controllable.

[Adsibob]

On 08/09/2021 at 12:20, ProDave said:

Triple glazing does not increase solar gain.  Fit triple glazed windows from a good manufacture.

This isn't always true (at least not the first sentence). If you use a good manufacturer, then it probably is true, but distinguishing between "good" and "bad" in this area is a minefield. I had assumed Velux was a "good" manufacturer, but the devil is in the detail and it depends on the spec. For example, take Velux's Integra GGL range. Some of these rooflights come as 3G and others as 2G. If you look at the spec of the 66 model (which is 3G) and compare it to the 60 model (which is 2G) the 3G has a solar gain value of 0.52 whereas the 2G has a solar gain value of 0.3. So in this instance the 3G is letting in 73% more heat than the 2G model (52% versus 30%). I mistakenly specified the 3G thinking it would be better, but it's not. Compare the two tables on page 3 of the attached, which shows the 3G model uses slightly thinner glass and different gas.

 

 

 

 

Velux download.pdf

[Dan F]

9 hours ago, Adsibob said:

This isn't always true (at least not the first sentence). If you use a good manufacturer, then it probably is true, but distinguishing between "good" and "bad" in this area is a minefield. I had assumed Velux was a "good" manufacturer, but the devil is in the detail and it depends on the spec. For example, take Velux's Integra GGL range. Some of these rooflights come as 3G and others as 2G. If you look at the spec of the 66 model (which is 3G) and compare it to the 60 model (which is 2G) the 3G has a solar gain value of 0.52 whereas the 2G has a solar gain value of 0.3. So in this instance the 3G is letting in 73% more heat than the 2G model (52% versus 30%). I mistakenly specified the 3G thinking it would be better, but it's not. Compare the two tables on page 3 of the attached, which shows the 3G model uses slightly thinner glass and different gas.

 

 

 

 

Velux download.pdf 848.27 kB · 0 downloads

 

The model you are referring to looks like it has "solar protection" (or so it says on the next page).  2G with solar protection is almost certainly going to have lower solar gain than 3G.

[Adsibob]

41 minutes ago, Dan F said:

 

The model you are referring to looks like it has "solar protection" (or so it says on the next page).  2G with solar protection is almost certainly going to have lower solar gain than 3G.

But if you look at that table, in the row above the row that talks about “solar protection” there is a “solar gain” row. And that says that there is less solar gain on the 60 model (which is 2G) than on the 66 model (which is 3G).