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Can thermal imaging be used to evaluate window glass performance?
07-01-2018, 08:05 PM
Post: #1
Can thermal imaging be used to evaluate window glass performance?
Hello-- We are trying to troubleshoot a cooling problem in a glass room. There is a question about whether the glass or the HVAC system, or both, is the problem. I would like to use a C3 camera to help diagnose the issues but am not sure how to get accurate readings. There is a flat glass sloped ceiling, a curved glass clerestory below it, and flat vertical windows. The glass on the ceiling has Low E coatings on surface 2, and the windows have Low E coating on surface 3. In addition, there is an applied UV film on the interior of all the glass.

The room gets very hot on sunny days (which is the problem we are trying to solve), making reflected and ambient heat significant issues as well.

As en example, attached is a pic of one wall of windows and doors at about 11am on a clear 84 degree day in NYC. The cooler door glass on the right has NO interior film and the Low E coating on surface 2 (unlike all the other vertical glass adjacent to it, which has it on surface 3 and an applied film). How useful is this kind of reading? Is it accurate? Can it be used to show anything generally if not specifically (accurately)? How can thermal imaging best be used in these conditions?
[attachment=364]
Thanks for your help!


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07-02-2018, 09:08 AM (This post was last modified: 07-02-2018 09:09 AM by JKEngineer.)
Post: #2
RE: Can thermal imaging be used to evaluate window glass performance?
A few observations:
The fact that you are seeing the furniture, etc., in your image shows that you are getting mixed readings of radiation from the glass and from the outside and from the reflected interior.
The cooler readings on the right panel are similar to those of the wall below the windows. I believe that what you are seeing is the reflection of the room T in the door.
As shot, I would have difficulty accepting these as temperature readings, rather than radiation readings.

There are methods to set the near surface of the glass to be highly emissive in order to get readings of T. These will affect the temperature locally (and should only be done locally), but should nevertheless give better results. You should consider doing that if you wish to use the IR camera to get readings.
You could consider using a contact thermocouple to get readings of T.
You could also consider using a heat flux meter to determine what the loadings are. Given the suspicion of solar loading, this might have limited application.
Some thought about the impact of the various coatings and the interaction of the surface of application needs to be done.

I'd be willing to have a conversation with you if you want to reach out to me.

A heads up: I am also in NYC, and might offer to do paid consulting with you. ;-)

Jack

Jack Kleinfeld, P.E.
Kleinfeld Technical Services, Inc.
1-718-884-6644
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07-02-2018, 06:08 PM
Post: #3
RE: Can thermal imaging be used to evaluate window glass performance?
Thanks for the response, Jack. The cooler glass in the pic on the right has NO applied film AND the low E coating on a different surface than the adjacent glass, so although it COULD be measuring a reflected temp, it could also have a significantly different characteristics with regard to heat...

Thanks for the offer of a call. I may take you up on that tomorrow if I can get out of meetings long enough...

Best,
T.
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07-03-2018, 03:40 AM
Post: #4
RE: Can thermal imaging be used to evaluate window glass performance?
The image uses MSX which makes it extremely difficult to make any valid conclusions. The furniture in the image is mainly coming from the MSX feature which is being overlaid onto the thermal from the visual camera. In this case MSX is unhelpful.
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