# IR Thermometer - Windows Edition



## szmaine (Feb 4, 2011)

Just got and IR thermometer. Boy, what a great little gadget In addition to discovering that my Rutland stove top thermometer is surprisingly accurate, +/- 10*, I've spent some time poking around the house with it to address weatherization issues.

I am stunned by what i have learned about my windows. 

I have a few different configurations. All are old wood double hung, but about 60% of them have the old style wooden storms - the kind you have to take down and pop in screens if you want to open the windows in the summer. The previous owner had rigged these with a layer of sturdy plastic stapled around the edge that faces toward the inside went the storm is installed. I thought that was a pretty good idea so after I painted them I redid them with better plastic that wasn't like looking through a coating of vaseline.

Two downstairs windows and all of the upstairs windows are aluminum storms, make sense - someone got sick of swapping them out every year. All of the upstairs windows I've done up with 3M shrinky plastic. Two downstairs I didn't bother.

Here are my IR results for temperature drop (rough average) on the window system relative to the wall beside it. All were done later in the evening so the the sun would not skew my numbers.

Old style storms with plastic, -5*

Aluminum storms with 3M, -10*

Aluminum storms only, -15*

Quite an eye opener Other things certainly have a effect too - both the window quilts I made for my daughters room and a shade pulled over an old style window showed no temperature difference relative to the adjacent wall.

Anyone want to post their window info? Could be interesting.


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## begreen (Feb 4, 2011)

Craig should here shortly to post the Mac edition. LOL

Where are you reading? Off the glass or the wood casing of the window?


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## szmaine (Feb 4, 2011)

Yeah, thought it might sound like that but I thought in the future I might want to do a Walls Edition or a Perfect Popover Edition...  

I am measuring on the glass.


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## henkmeuzelaar (Feb 5, 2011)

szmaine said:
			
		

> Just got and IR thermometer. Boy, what a great little gadget In addition to discovering that my Rutland stove top thermometer is surprisingly accurate, +/- 10*, I've spent some time poking around the house with it to address weatherization issues.
> 
> I am stunned by what i have learned about my windows.
> 
> ...




Always enjoy these kinds of reports. Please keep them coming!!

One problem with this "Windows Edition" of your planned measurement series, however, is that the type of IR thermometer you are using is basically not suitable for measuring the surface temperatures of plastic, glass or other materials that may be partially (or completely) transparent at the wavelength(s) used by the thermometer. Also, many glass and plastic surfaces tend to be fairly reflective, another problem for IR thermometers, though not as serious as transparency (unless you have a true mirror surface; e.g. when people us aluminum-coated mylar sheet as a heat-loss barrier.

Some very good advice regarding IR temperature measurements on various types of surfaces and materials can be found here. In case you would like to have a more detailed technical reference than that; you might also want to consult this article. 

Henk


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## szmaine (Feb 5, 2011)

PyMS said:
			
		

> Always enjoy these kinds of reports. Please keep them coming!!
> 
> One problem with this "Windows Edition" of your planned measurement series, however, is that the type of IR thermometer you are using is basically not suitable for measuring the surface temperatures of plastic, glass or other materials that may be partially (or completely) transparent at the wavelength(s) used by the thermometer. Also, many glass and plastic surfaces tend to be fairly reflective, another problem for IR thermometers, though not as serious as transparency (unless you have a true mirror surface; e.g. when people us aluminum-coated mylar sheet as a heat-loss barrier.
> 
> ...



Hi Henk - I was sort of hoping you " Clean Windows=More Heat" geeks might show up. ;-) 
I was following that a bit, but it got way over my head..
Before I go slogging through that very intense article you linked..

Don't you think the exercise is worthwhile as an operationally defined method? As long as I use the same IR unit the differences I measured are still a valid comparison of the different approaches to weatherization I have in my home ie. any error in measurement is equal across the board...
or do you think that the layers of plastic have significantly different reflective qualiuties that might render the performances differences I posted null and void? 

I did think of other potentially problems with my approach if others did the same test and were comparing their results to mine...
I think the drop would vary with outside temperature, ie someone doing measurements at a different outside temp would draw incorrect conclusions about the performance of their windows vs mine if that is not accounted for...

your thoughts? dum it down!


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## sesmith (Feb 5, 2011)

szmaine said:
			
		

> PyMS said:
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## charly (Feb 5, 2011)

szmaine said:
			
		

> Just got and IR thermometer. Boy, what a great little gadget In addition to discovering that my Rutland stove top thermometer is surprisingly accurate, +/- 10*, I've spent some time poking around the house with it to address weatherization issues.
> 
> I am stunned by what i have learned about my windows.
> 
> ...


  I agree, my IR gun showed my Rutland thermometer to be quite accurate too. Plus I found the hotest part on my stove top to place my Rutland thermometer. I had it in a area on the top of my stove that was 150 degrees cooler than the hottest spot. IR gun has certainly been handy, as I see you've been busy as well. My hat's off to Rutland for making such a simple accurate thermometer.


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## szmaine (Feb 5, 2011)

The emissivity of my IR is set at 0.95
Glass, paper, paint and plastics all hover around this value.

http://www.engineeringtoolbox.com/emissivity-coefficients-d_447.html


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## henkmeuzelaar (Feb 5, 2011)

Hi szmaine,

The first of the two articles is not "intense" since you could simply skip the theory and scroll directly to the last paragraphs dealing with measurements on different type of materials, including plastics and glass.

I think you make a very good point about using it perhaps as an "operationally defined method". I can't remember how many times I have had to resort to that myself (and not only for temperature measurements) in order to try and save the day.   When it comes to inaccuracies caused by reflective surface properties, I think you could certainly do that as long as you compare surfaces differing only by tens, rather than hundreds, of degrees (which can cause the emissivities of these surfaces to change fairly dramatically, as shown in a graph at the end of the second, more highly technical, article.

With transparent materials such as plastics and glass (or various combinations thereof), however, the biggest problem really is to avoid measuring background radiation from outside the house. Not knowing what type of window (if any) the detector in your particular thermometer has, nor what the precise transmittances of your glass and plastic sheets are, you might simply try to temporarily block all outside radiation with a piece of plywood and see to what extent that influences your readings. If it doesn't (or only minimally), you're probably good to go with the operational approach.....  If it does, you may be restricted to measuring at night only.

Success,

Henk


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## henkmeuzelaar (Feb 5, 2011)

szmaine said:
			
		

> The emissivity of my IR is set at 0.95
> *Glass, paper, paint and plastics all hover around this value.*
> 
> http://www.engineeringtoolbox.com/emissivity-coefficients-d_447.html



Sorry, but didn't see this message until after I posted my response.

Yes, that seems to be a very reasonable emissivity assumption for nearly all "grey body" emitters we deal with in our homes. Grey body emitters, however, are supposed to be optically opaque (just like black body emitters with an emissivity of 1.0).

In case the material is transparent over certain wavelength ranges (no material is transparent over ALL wavelengths) then it's grey body emission value can only be used at those wavelengths were the material is NOT transparent to some degree.

As I said in my response, not knowing the transmittance spectra of the window used in your detector, nor that of the plastic sheet and glass panes used, I would not dare to use these emissivity values. For instance, just working from memory, I believe that polyethylene foil has transmittance windows deep into the infrared. The glass itself might perhaps be sort of OK at the lower temperatures you are working at (though not for the higher temperatures at which tempered glass fireplaces work, when more radiation is emitted at shorter wavelengths).

Henk


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## szmaine (Feb 5, 2011)

PyMS said:
			
		

> With transparent materials such as plastics and glass (or various combinations thereof), however, the biggest problem really is to avoid measuring background radiation from outside the house. Not knowing what type of window (if any) the detector in your particular thermometer has, nor what the precise transmittances of your glass and plastic sheets are, you might simply try to temporarily block all outside radiation with a piece of plywood and see to what extent that influences your readings. If it doesn't (or only minimally), you're probably good to go with the operational approach.....  *If it does, you may be restricted to measuring at night only.*Success,
> 
> Henk




Right, thats what I did...as per my original post:



> Here are my IR results for temperature drop (rough average) on the window system relative to the wall beside it. All were done later in the evening so the the sun would not skew my numbers.


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## szmaine (Feb 5, 2011)

:cheese:  :cheese:  :cheese: 

Ha! We are cross posting - drooling, er, I mean dueling geeks.


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## henkmeuzelaar (Feb 5, 2011)

Ah, we keep crossing our replies. 

I apologize for overlooking that!  

It sounds like you might be OK then for measuring the glass on an operational basis (i.e. not fully calibrated and thus perhaps not getting numbers that can be compared with what others get).   

However, my reservations for the plastic sheet measurements remain because of their infrared transparency. In other words, you might still largely be measuring the temperature of the glass behind it, rather than the surface temp of the plastic sheet.

If you can give me the precise brand name of the plastic materials used (one was "3M Shrinky Plastic" ??), I promise to help find their IR transmittance spectra.

Henk


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## szmaine (Feb 5, 2011)

Well, no offense truly, but I think you are over thinking this...

But if it floats your boat...
this is the "3M shrinky" product and I have no idea what I put on the "old style" windows
http://solutions.3m.com/wps/portal/3M/en_US/WindowInsulatorKits/Products/

Edit: If I am measuring the glass BEHIND the plastic then shouldn't all the measurments be equal since all the windows that have plastic, regardless of type,  is in front of the exterior glass? "Old style" window have plastic between the interior and exterior glass, and 3M Shrinky windows have the plastic on the interior with two layers of glass on the exterior...


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## henkmeuzelaar (Feb 5, 2011)

szmaine said:
			
		

> Well, no offense truly, but I think you are over thinking this...
> 
> But if it floats your boat...
> this is the "3M shrinky" product and I have no idea what I put on the "old style" windows
> http://solutions.3m.com/wps/portal/3M/en_US/WindowInsulatorKits/Products/



Yeah you're right. After all, the experiment has already been done.... 

Hope you will post your final calculations/interpretations (in terms of what you learned from your measurements!)  


Henk

PS: for future reference I am attaching the IR transmittance spectra of polyethylene (highly IR transparent) and green window glass (low to medium transparent below 3 micron or so; unless specially coated).


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## szmaine (Feb 5, 2011)

PyMS said:
			
		

> szmaine said:
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Well. now that is interesting...

so from what I can see its all good for my purposes- my IR operates at 635-660 nm, so from your graphs for green glass and polyethylene the setting is perfectly reasonable for an emissivity setting of 0.95
Green glass is slightly depressed however all my windows have two layers so are comparable...

Have I read it right? % penetration/transmission = emissivity?

Edit again: don't like loooking at graphs with different axis labels so went fishing, don't know why you picked green glass (ie tinted glass reduces transmittance), most old windows are soda glass = no transsmittance issue via IR measurement in the 600 nm range.

http://en.wikipedia.org/wiki/File:Soda_Lime.jpg

ok, gotta lie down now...


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## henkmeuzelaar (Feb 6, 2011)

szmaine said:
			
		

> Well. now that is interesting...
> 
> so from what I can see its all good for my purposes- my IR operates at 635-660 nm, so from your graphs for green glass and polyethylene the setting is perfectly reasonable for an emissivity setting of 0.95
> Green glass is slightly depressed however all my windows have two layers so are comparable...
> ...



Hate to be the bearer of bad news but, no, it's alas just the other way around....
emissivity at a given wavelength is equal to absorptivity at that wavelength and absorbtivity (absorbance) is the log inverse of the transmittance shown in the IR spectra. In other words: A = log(1/T) = -logT.  So when transmittance is .90 (90%), emissivity is only .045 (4.5 %) or so. 

The other piece of bad news is that your IR measurement is being done at 600 nm; i.e. within the visible (400-800 nm wavelength range). So, if the eye can see through the material, so will the IR thermometer. It would be better (and help accuracy for ambient temperature measurements) if the detector were to measure somewhere in the infrared range, where ambient temperature objects emit their maximum radiation and where most glass and plastic windows will have higher emissivities.

Yes, I hate it too when they switch axis labels on me. In particular I hate the reciprocal centimeter axes used by most spectrometrists.  However, this was all I could find without going to the library. Same story for the "green glass". If you do have an IR spectrum of soda glass I would love to have it too!

Henk


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## henkmeuzelaar (Feb 6, 2011)

Just found an infrared transmittance spectrum for soda-lime glass (see below).  It's pretty much the same as the "green glass" IR spectrum shown before. 

Although I haven't found direct confirmation I am personally convinced that the term "green glass" as used by the glass industry (and shown in the IR spectrum in one of my earlier post) is equivalent to "sodium-lime glass".  If you look at window glass from the side (i.e. looking at a very thick layer of glass) the green color is quite obvious.

Henk


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## szmaine (Feb 6, 2011)

Ok, I understand the graphs and terms better now, especially after digging around a bit more on the internet...

but I think my measurements are ok for  night time readings that show a relative temperature drop between window systems if inside and outside sources are equal and the transmittance of plastics and glass are also fairly well matched.

someone already mentioned the solution early on, put something non-relective on the window like masking tape, allow the tape time to come to temperature and then you can get a true temperature reading, rather than just a comparitive one.

for anyone interested interested in doing these types of measurements, here is a good article on using them on houses
http://www.ag.ndsu.edu/pubs/ageng/structu/ae1373.pdf

and here's a good one on the use of IR thermometers in general.

http://www.coleparmer.com/techinfo/techinfo.asp?htmlfile=IR_FAQ.htm&ID=378


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