Message Board Thread - "Heat lost calculations"

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Heat lost calculations jjb 4/15/2011
Dear Flir,

I am trying to analyze heat loss through a window/door on buildings. I took pictures of buildings outside. The R-value and U-value do not seem correct. I am not sure what values I need to place for atm.,rel., temperature. An example picture is attached.

Thanks,
jjb
 
Re:Heat lost calculations Gary Orlove 4/29/2011
I would be VERY VERY VERY CAUTIOUS about trying to make heat transfer and R value measurements from the outside of a building. There are just too many uncontrolled variables to deal with.

R or U value measurements are only valid when a system is in steady state. Buildings are never in steady state, but if you do your data collection extremely carefully, you can achieve quasi-steady state data. This usually involves taking your data from the inside when conditions outside are overcast (and have been for several hours) to reduce solar loading.

I can’t tell from the data you have supplied whether the thermograms were taken at night and under what weather conditions. Your T reflected temperature value is most definitely not correct, when the exterior air temperature is 46 F. The emissivity for glass is also incorrect, it should be about 0.8 to 0.88 depending on the glass and dirt buildup.

We teach how to do this type of analysis in our Level I - Thermal Imaging for Energy Audits - Certification Course, http://www.infraredtraining.com/courses/weatherization_certification.asp
 
Re:Heat lost calculations dandersen 5/1/2011
To add to what Mr. Orlove pointed out, you are using an area tool. This is averaging several window/door components that are not the same “e” or “p”. There is even a railing in the way.

You said “I took pictures of buildings outside.”
Does this mean you didn’t do anything on the inside?

There is a set of measurements and adjustments you must make to determine R/U Values.
The hardest is to determine the emissivity of the window.

This is a Level II exercise, though Scott Wood covers this quickly (for wall evaluation, not glass) in Building Science. I recommend this training before you attempt this evaluation in the field. As Gary pointed out, this is a difficult task “at best” .

It is best used as a “like comparison” evaluation.
 
Re:Heat lost calculations Mobius01 5/1/2011
jjb wrote:
ir,

I am trying to analyze heat loss through a window/door on buildings. I took pictures of buildings outside. The R-value and U-value do not seem correct. I am not sure what values I need to place for atm.,rel., temperature. An example picture is attached.

Thanks,
jjb
First off, in my opinion, you dont need to do quantitative analysis for these types of scans unless the customer specifically wants some numbers. All you need is qualitative scan for heal loss analysis.
 
Re:Heat lost calculations LKO 5/5/2011
jjb wrote:
ir,

I am trying to analyze heat loss through a window/door on buildings. I took pictures of buildings outside. The R-value and U-value do not seem correct. I am not sure what values I need to place for atm.,rel., temperature. An example picture is attached.

Thanks,
jjb
I have a question for Mr. jjb. What kind of software have you been using for this evaluation. I am a MW Flir camera user so I am not familiar with LW cameras FLIR software if this is part of it.
 


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