[Bldg-sim] measurement of SHGC in the field

Mon Nov 13 11:06:22 PST 2017

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
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> On Nov 13, 2017, at 2:10 AM, Chris Yates <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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