[Greenbuilding] infrared thermometer

[jfstraube]

I just checked the ASHRAE Handbook of Fundamentals, 2009
Glass is 0.87 to 0.92.

Sorry, not sure why I had 0.84 in my head, maybe it was the thermal conductivity

Last week I was taking pictures with a $10000 Fluke IR camera (320x240 pixel photos, pretty accurate): I placed painters tape over the middle of the glass on several windows, and had the emissivity dialed in to 0.95.  Could not really see much of a difference between the glass around the tape and the tape itself.


On 2011-03-07, at 7:11 AM, nick pine wrote:

> "LarenCorie" writes:
> 
>> From: John Straube <jfstraube at gmail.com>
>> 
>>> Emissivity of glass is about 0.84, which is not far off a unit
>>> with a default of 0.90, like within a degree or two.
> 
>> ... The sources I have checked, seem to
>> all indicate between 0.90 and 0.94
>> 
>> http://www.infrared-thermography.com/material-1.htm
>> http://www.engineeringtoolbox.com/emissivity-coefficients-d_447.html
> 
> If it's 0.92 a la toolbox and 0.92Tg^4 = 0.95Tr^4, using my Raytek Mini-temp
> calibrated for 0.95, Tg = (0.95/0.92)^0.25T = 1.008Tr, a Tr = 530 R (70 F)
> reading would correspond to Tg = 534 (74 F.) If glass were 0.84, Tr = 530 R
> would correspond to Tg = 547 R (87 F.)
> 
> Nick 
> 
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John Straube
www.BuildingScience.com