[Greenbuilding] infrared thermometer

[LarenCorie]

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.

Hi John;

Where does that number come from?
The sources I have checked, seem to 
all indicate between 0.90 and 0.94
(very typical of non-metallic surfaces)

http://www.infrared-thermography.com/material-1.htm
http://www.engineeringtoolbox.com/emissivity-coefficients-d_447.html
ASHRAE seems to agree with them, as does virtually every other,
that I have checked.    None seem to say 0.84

However (quote) "thermal conductivity of glass is 0.84 W m-1 K-1"

This one (link below) does encompass your number, within its
range,  but also ranges as high as 0.91 and is for temperatures
of 100-500C, with  the 0.82 apparently being for 500C.  So,
that would suggest the accuracy of a 0.90-.94 number for
the temperatures we are dealing with.

http://www.opticsinfobase.org/abstract.cfm?URI=josa-37-10-804

Am I missing something?

Thanks,
-Laren Corie-
   Natural Solar Building Design and
Solar Heating/Natural Cooling/Energy
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