Hi
I have completed an overheating report for a block of apartments with a large amount of glazed areas we have modeled glazing with a g-value of between 0.72 and 0.43. I understand there will be some impact on the light transmittance but not sure how noticeable between these two figures it would be?
I am hoping someone might be able to help or point me in the right direction, thanks in advance.
g value and light transmittance
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RossThompson87
- VE Professor
- Posts: 202
- Joined: Mon Feb 13, 2012 8:56 am
Re: g value and light transmittance
Hi,
That is possibly more of a question for a glazing manufacturer.
It is possible to achieve low g-values whilst maintaining high light transmittance, but it gets expensive.
A few years ago I contacted Pilkington and they gave me free samples for many of their solar control products. They also have a selector program which lets you build up the window and gives u-value, g-value, LT etc.
I also tried to get some £/m2 data but manufacturers aren't keen on giving this out!
I hope this helps
Ross
That is possibly more of a question for a glazing manufacturer.
It is possible to achieve low g-values whilst maintaining high light transmittance, but it gets expensive.
A few years ago I contacted Pilkington and they gave me free samples for many of their solar control products. They also have a selector program which lets you build up the window and gives u-value, g-value, LT etc.
I also tried to get some £/m2 data but manufacturers aren't keen on giving this out!
I hope this helps
Ross
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andysadler
- VE Newbie
- Posts: 6
- Joined: Tue Aug 27, 2013 3:07 pm
Re: g value and light transmittance
Thanks that is a great help. I have asked a couple of manufactures and am awaiting there reply.
Re: g value and light transmittance
Pilkington Spectrum is a proggie on their website which will give you the LT figures and the g value's for all combinations of their glass. I think 66/33 offers the best performance whilst maintaining good light transmission. ie 66 LT and 33 g. Its a useful program and St Gobain offer Calumen which is similar and can be downloaded from their site.
My only gripe is that this information is usually for the full unit. ie double glazed. IES in their wisdom requires it for each pane. ie energy transmission (g) and reflectance (the absorptance calculated as a diff between these.) I find it difficult to replicate manufacturers data with what IES reports and it usually requires a bit of fudging for me to get the IES to match the manufacturers data and requires me using g's and reflectances that differ from what the manufacturers states in order to get the same overall data.
Ordinarily this is not an issue. But with other parties scrutinising the information you provide, any discrepancy gives them a path to giving you a hard time. I'd like to see IES address the glazing tool to make it more user friendly or at least to incorporate more manufacturers glazing within their library. After all, they know their tool better than anyone.
My only gripe is that this information is usually for the full unit. ie double glazed. IES in their wisdom requires it for each pane. ie energy transmission (g) and reflectance (the absorptance calculated as a diff between these.) I find it difficult to replicate manufacturers data with what IES reports and it usually requires a bit of fudging for me to get the IES to match the manufacturers data and requires me using g's and reflectances that differ from what the manufacturers states in order to get the same overall data.
Ordinarily this is not an issue. But with other parties scrutinising the information you provide, any discrepancy gives them a path to giving you a hard time. I'd like to see IES address the glazing tool to make it more user friendly or at least to incorporate more manufacturers glazing within their library. After all, they know their tool better than anyone.