[Bldg-sim] measurement of SHGC in the field

Nathan Brown nathan at coolshadow.com
Mon Nov 13 11:50:00 PST 2017


Hi Charlie —
Thank you for correcting my oversight about Tsol vs SHGC! They are not the same, and I was forgetting about the inward flowing fraction of absorbed energy component of SHGC.
Best,
Nathan

Nathan Brown, BEMP, LEED AP ~ Associate
LOISOS + UBBELOHDE
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1917 Clement Avenue, Building 10A
Alameda,CA 94501 USA
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510 521 3800 VOICE
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www.coolshadow.com <http://www.coolshadow.com/>
> On Nov 13, 2017, at 11:42 AM, D. Charlie Curcija <dccurcija at lbl.gov> wrote:
> 
> Please note that SHGC is not equal to solar transmittance. Even if you would be able to make perfect Tsol measurement in the filed, that could be way off in predicting SHGC. This is because, SHGC consists of two parts, one is Tsol (directly transmitted solar radiation and the other is inward flowing fraction of absorbed solar energy in the window. For the most part inward flowing fraction is NOT small and it depends on the glazing and framing configuration. In its extreme, single glazed tinted glass would have SHGC more than twice than Tsol and often triple Tsol.
> 
> Charlie
> 
> On Mon, Nov 13, 2017 at 11:29 AM, Nathan Brown <nathan at coolshadow.com <mailto:nathan at coolshadow.com>> wrote:
> Hi Chris —
> 
> A bit more reading shows that the LiCor Pyranometer is not designed for SHGC: the manual says the following:
> 
> “The spectral response of the Li-200 does not include the entire solar spectrum, so it must be used in the same lighting conditions as those under which it was calibrated. Therefore, the LI-200 should only be used to measure unobstructed daylight. It should not be used under vegetation, artificial lights, in a greenhouse, or for reflected solar radiation”
> 
> The solar radiation getting through the glass is obstructed, so the LiCor should not be used for measuring SHGC and I’d probably look elsewhere if the measurement is important enough to verify in the field.
> 
> Best,
> Nathan
> 
> Nathan Brown, BEMP, LEED AP ~ Associate
> LOISOS + UBBELOHDE
> - - - - - - - - - - - - - - - - - - - - - - - - - - -
> 1917 Clement Avenue, Building 10A
> Alameda,CA 94501 USA
> - - - - - - - - - - - - - - - - - - - - - - - - - - -
> 510 521 3800 <tel:(510)%20521-3800> VOICE
> 510 521 3820 <tel:(510)%20521-3820> FAX
> - - - - - - - - - - - - - - - - - - - - - - - - - - -
> www.coolshadow.com <http://www.coolshadow.com/>
>> On Nov 13, 2017, at 11:06 AM, Nathan Brown <nathan at coolshadow.com <mailto:nathan at coolshadow.com>> wrote:
>> 
>> Hi Chris —
>> 
>> The LiCor manual shows that the pyranometer is sensitive to wavelengths between 390 nm to 1100 nm. That means the LiCor misses most of the UV (and longer near IR). So the LiCOr is not perfect by any means, but it’s pretty good, given the coverage of the visible and shorter end of the near IR, which represent most of the energy in solar heat gain. So it’s a matter of how precise you need to be - LiCor gets you most of the way there, but you may need something more robust depending on the application. My instinct says that it’s good enough for telling the difference between 0.4 and 0.6 SHGC.
>> 
>> Best,
>> Nathan
>> 
>> 
>> 
>> (from https://heatisland.lbl.gov/sites/all/files/Solar%20Energy%20Spectrum.jpg <https://heatisland.lbl.gov/sites/all/files/Solar%20Energy%20Spectrum.jpg>)
>> 
>> 
>> 
>> Nathan Brown, BEMP, LEED AP ~ Associate
>> LOISOS + UBBELOHDE
>> - - - - - - - - - - - - - - - - - - - - - - - - - - -
>> 1917 Clement Avenue, Building 10A
>> Alameda,CA 94501 USA
>> - - - - - - - - - - - - - - - - - - - - - - - - - - -
>> 510 521 3800 <tel:(510)%20521-3800> VOICE
>> 510 521 3820 <tel:(510)%20521-3820> FAX
>> - - - - - - - - - - - - - - - - - - - - - - - - - - -
>> www.coolshadow.com <http://www.coolshadow.com/>
>>> On Nov 13, 2017, at 2:10 AM, Chris Yates <chris.malcolm.yates at gmail.com <mailto:chris.malcolm.yates at gmail.com>> wrote:
>>> 
>>> Hi Nathan
>>> 
>>> Does the li-cor measure short enough wavelengths? I thought a lot of the uv was < 400nm. I guess that most "selective coatings" have quite a big crossover to the visible range in their reflectivity - hence the slight green or blue hues. So, I can imagine that missing some of the uv-b isn't too big a deal.
>>> 
>>> Both responses are super interesting. Thank you very much!
>>> 
>>> Chris
>>> 
>>> On Fri, Nov 10, 2017 at 6:54 PM, D. Charlie Curcija <dccurcija at lbl.gov <mailto:dccurcija at lbl.gov>> wrote:
>>> At LBNL, in collaboration with University Federal Santa Catarina (UFSC), Brazil, we have designed partable window energy meter that measures SHGC in the filed. The instrument is not yet commercialized, but two companies are exploring commercialization (D&S and EPDT). In a mean time, UFSC can manufacture unit for you. I can supply you with contact information if you are interested. Also, attached link to US DOE newsletter about the instrument: https://energy.gov/eere/articles/us-brazil-collaboration-leads-innovative-device-reduces-energy-use-buildings <https://energy.gov/eere/articles/us-brazil-collaboration-leads-innovative-device-reduces-energy-use-buildings>. 
>>> 
>>> Charlie
>>> 
>>> On Fri, Nov 10, 2017 at 10:07 AM, Nathan Brown via Bldg-sim <bldg-sim at lists.onebuilding.org <mailto:bldg-sim at lists.onebuilding.org>> wrote:
>>> Hi Chris —
>>> 
>>> That instrument won’t do it, because it is not sensitive to infrared. More than half of irradiance is in the near IR (aka solar infrared). You need a pyranometer (LiCor is our go-to <https://www.licor.com/env/products/light/pyranometer.html>, or an Eppley <http://www.eppleylab.com/instrument-list/standard-precision-pyranometer/> for critical measurements, although that is probably overkill for this). I would measure vertical irradiance just inside and just outside the glass under direct sunlight. Here in the Bay Area, there is a tool lending library that will loan a pyranometer. Perhaps you can find a similar source closer to you.
>>> 
>>> Best,
>>> Nathan
>>> 
>>> Nathan Brown, BEMP, LEED AP ~ Associate
>>> LOISOS + UBBELOHDE
>>> - - - - - - - - - - - - - - - - - - - - - - - - - - -
>>> 1917 Clement Avenue, Building 10A
>>> Alameda,CA 94501 USA
>>> - - - - - - - - - - - - - - - - - - - - - - - - - - -
>>> 510 521 3800 <tel:(510)%20521-3800> VOICE
>>> 510 521 3820 <tel:(510)%20521-3820> FAX
>>> - - - - - - - - - - - - - - - - - - - - - - - - - - -
>>> www.coolshadow.com <http://www.coolshadow.com/>
>>>> On Nov 10, 2017, at 3:08 AM, Chris Yates via Bldg-sim <bldg-sim at lists.onebuilding.org <mailto:bldg-sim at lists.onebuilding.org>> wrote:
>>>> 
>>>> Dear all
>>>> 
>>>> We are trying to get a reasonable estimate for SHGC in the field.
>>>> 
>>>> Our project is a retrofit of a relatively recent build that has overheating problems. No records exist of the original glazing spec.
>>>> 
>>>> The glazing has a slight green tint; i.e. the "look and feel" of a fairly modern spectrally selective product with g-value (sorry SHGC) of about 0.4. However, a team member has now produced some records indicating this is significantly higher (more like 0.6).
>>>> 
>>>> Does anybody have any experience or know of any research relating to this?
>>>> 
>>>> I was thinking of something like this, taking measurements on the horizontal and vertical plane inside and out: https://www.uv-light.co.uk/meters/irradiance-and-exposure/ <https://www.uv-light.co.uk/meters/irradiance-and-exposure/>
>>>> 
>>>> Our saint gobain rep tells me their spectrographic equipment is 50,000 GBP - a bit out of our price range! (They've offered to test a sample for us!).
>>>> 
>>>> Cheers
>>>> 
>>>> Chris
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>>> -- 
>>> --------------------------------------------------------------------------
>>> D. Charlie Curcija, Ph.D.                     Tel: (510) 495-2602 <tel:(510)%20495-2602>
>>> Lawrence Berkeley National Laboratory         Fax: (510) 486-4089 <tel:(510)%20486-4089>
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>>> 
>> 
> 
> 
> 
> 
> -- 
> --------------------------------------------------------------------------
> D. Charlie Curcija, Ph.D.                     Tel: (510) 495-2602
> Lawrence Berkeley National Laboratory         Fax: (510) 486-4089
> Windows & Envelope Materials Group            Cell:(510) 604-8668
> 1 Cyclotron Rd., MS 90-3111                   Email: dccurcija at lbl.gov <mailto:dccurcija at lbl.gov>
> Berkeley, CA 94720                            Web: http://windows.lbl.gov/ <http://btech.lbl.gov/>
> --------------------------------------------------------------------------
> 
> 

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