Latent Moisture - Part Two

[pogletree]

Dave,

Thank you for your response.

Your tear duct will be that temperature almost all of the time. I did not state that this method was the only way to do a calibration. You can also calibrate using a blackbody which in turn is a very expensive option. The main point I was trying to get across is - if emissivity is incorrect, the temperature reading is false.

Some thermographers do not have much experience performing building science work and possibly may not even know how emissivity effects temperature. A delta T will be different at an emissivity setting at .40 vice one at .98. Guessing at defects based on temperature without knowing what could be on the other side of a wall is not a good practice.

Palettes- you can do this with any image you have in your camera or hard drive with a thermal variance. I suggest you use one that will give you the best resolution for what you're inspecting. Many palettes may not be suited for the type of inspection being performed. By the way, what is the image you posted in your last thread?

Thanks again.

Paul Ogletree, Instructor/Consultant
NACHI # 04052691
ASNT Level III Thermal/Infrared #125356
The Snell Group
P.O. Box 6
Montpelier, Vermont 05601-0006 USA
Tel. +1.802.229.9820 Fax +1.802.223.0460
pogletree@thesnellgroup.com
www.thesnellgroup.com

[David A. Andersen]

I just grabbed a scan from an open report I was working on and changed it to a rainbow hi res palette and tuned the span to make it look as colorful as I could, as an example.

I would post the digital, but it has personal property in it and I do not have permission to release this photo. Not much to see in an IR.

It is a wall/ceiling insulation deficiency.

A delta T will be different at an emissivity setting at .40 vice one at .98.

This is very true, however the vast majority of materials in building science have a high emissivity. The scan in this thread has nothing with low emissivity except the outlet plate screws.

[John Snell]

"This "calibration" test leaves a lot to be desired in my opinion!"

In fact I just got back from an International Standards Committee meeting with a team of medical folks (doctors and medical device experts) in which we wrote a draft standard for using thermography for screening people in a pandemic situation to see if they have a fever. The screening would be based on the temperature of the "inner canthus" (the tear duct area Paul mentioned). You may remember IR was widely used for this purpose a few years back in China during the SARS epidemic, but mostly it was used VERY poorly.

This simple "calibration check," or really a functionality check as much as anything, is something we devised years ago to catch mistakes before they became costly—like an improperly set emissivity or background or, in some cases, a camera that simply is out of cal. It takes just a minute or two and quickly became an important part of what we consider a good practice.

I was very pleased to have the doctors in this meeting confirm that the surface temperature of the inner canthus varies very little, except perhaps in the wind or direct sun or with water splashed on the face. I was also surprised to have them validate that the offset between this surface temperature and "core" temperature was only a fraction of a degree-C, less than I'd always believed.

Anyway, thanks all for the good discussion.

Thermally yours,

John Snell
ASNT NDT Thermal/Infrared Level III #48166
Snell Infrared
800-636-9820
802-229-9820
http://www.thesnellgroup.com
http://www.IRTalk.com
http://www.thermalsolutions.org

[David A. Andersen]

That is very interesting to know!

for using thermography for screening people in a pandemic situation to see if they have a fever.

This alone is too great a veriable for testing the operation of my equipment. How do we know the subject does not have something?

I don't know of ice getting a fever. It can have salt in it though!

I would be interested in reviewing this standard.
Charlie B. and I do stuff on horses and it may prove safer than sticking stuff up the back side, if it applies to horses.

[David A. Andersen]

I was also surprised to have them validate that the offset between this surface temperature and "core" temperature was only a fraction of a degree-C,

So is the temp reading 92-94 or body core temp (98.6f)?

The core body temperature of an individual also tends to vary during the day and with activity level, with the lowest value in the second half of the sleep cycle; this low point, called nadir, is one of the primary markers for circadian rhythms.

http://en.wikipedia.org/wiki/Image:1911_Animal_heat.png

The duct may be close to body core, but it looks like this can not be considered "stable" .

[pogletree]

Dave,

You obviously have a great knowledge of IR not only in building science but even in equine examinations. Impressive...

We love talking to people like yourself helping out however we can to give you data that may have never been discussed during your travels. Our staff has over 170 years IR experience and if you ever have any questions, please feel free to contact us to discuss any roadblocks you may discover.

Have a great weekend....


Paul Ogletree, Instructor/Consultant
NACHI # 04052691
ASNT Level III Thermal/Infrared #125356
The Snell Group
P.O. Box 6
Montpelier, Vermont 05601-0006 USA
Tel. +1.802.229.9820 Fax +1.802.223.0460
pogletree@thesnellgroup.com
www.thesnellgroup.com

[Peter W. Bennett]

John, what do you scan and what don't you scan?
And if you don't mind, what's your work procedure, i.e., HVAC first then interior surfaces, electrical, etc.
Thanks,
Peter

[John Snell]

Dave,

We use this simple "tear duct check" as a gross means of determining if the camera is set up and functioning correctly. Skin temperature can vary widely. Inner canthus temperature varies much less widely but is certainly less than the bodies core temperature (which can also vary, obviously, depending on such factors as activity or illness).

If this simple check suggests something is amiss, we would check all correction parameters. For instance, I once had a student who was reading the tear duct at 78F using an older cooled, mid-wave system. All correction parameters were set correctly but he had installed a glass 35mm UV filter to protect his lens. It was, of course, only partially transparent to IR radiation so temperatures read low. He'd been working like this for six months! In other instances I've seen emissivity or background set incorrectly or, once, the camera set to Kelvin rather than C or F!

If we need a more accurate evaluation of calibration, we turn to a black body reference (approx. $3000), usually at three set points or more. This degree of verification would typically be overkill for a HI, but, if you thought you might be involved in litigation, it may well be worth it. You can, of course, use the ice bath, but it is only a single point check and it is difficult to perform it accurately (there is an ASTM standard). Ditto with boiling water. A good moderate water bath, well stirred, and a laboratory thermometer could also make a good, reasonably priced, calibration check.

Anyway, thanks for your comments. I just wanted to clarify what we are trying to do and acknowledge what we are NOT trying to do with this obviously simple check.

Thermally yours,

John Snell
ASNT NDT Thermal/Infrared Level III #48166
Snell Infrared
800-636-9820
802-229-9820
http://www.thesnellgroup.com
http://www.IRTalk.com
http://www.thermalsolutions.org

[John Snell]

Originally Posted by pbennett1

John, what do you scan and what don't you scan?
And if you don't mind, what's your work procedure, i.e., HVAC first then interior surfaces, electrical, etc.
Thanks,
Peter

The exact work procedure would vary somewhat with the scope of work. I schedule 1-2 weeks in advance and confirm 3 days out and again the day before, both based on the weather. If weather is a "no go" or "iffy" I will reschedule at that point. I also am clear with the owner about what I need with regard to the building (I'll look everywhere, need windows closed, HVAC on or off, etc.)

Assuming conditions are conducive to the inspection, I first walk around the exterior using both my eyes and, quickly, the camera. With my eyes I look for obvious issues (staining, torn shingles, etc.) and for the overall way the place is put together and potential trouble spots (overhangs, dormers, kneewalls, etc.). I use the camera to see the "big picture" and spot any gross exfiltration (warm during heating season). I take photos of the exterior.

Inside, I make a second quick pass through the home, again using my eyes to see how things are put together and for potential problem areas. With the camera I'm just looking for overall issues and to ensure the conditions are good enough to get good data.

Next I go through the home as slowly as needed to look at all walls (outside and interior) as well as insulated ceilings and floors, mainly for insulation integrity but also, to some extent, moisture. At each doorway I am always turning in the same direction so that I cover ALL walls—I often find problems on interior walls, usually bypass issues. Usually a trip to the attic is needed at this point, not my favorite part of the job!

Again, depending on the scope of work, I will either document ALL sections or just the defects, with both IR and visual images. I add notes either via the camera, if it has voice annotation, or in a notebook. I'll also make other measurements as I go, such as humidity, air temperature, moisture readings, etc. When freezing or condensation are issues, I'll spend more time measuring surface temperatures.

At this point (30-60 minutes or so after beginning), I'll fire up the blower door (or otherwise depressurize the building) and look for air leakage, bypasses, and, if need be, insulation problems that were not obvious during the previous. If we are also quantifying the air leakage rates, that happens at this time.

If in the scope, I would also check that the HVAC is working or balanced. Typically I will not check the electrical system. As I've tried to say in previous posts, I don't think IR is the best method of checking single-phase residential systems. In fact, I think results can be misleading and the testing can leave me open to unreasonable risk. I do believe there are tests that can work and should be done as part of a home inspection. In some instances I'm also asked to locate or verify structural elements, such as historic changes.

If need be, and it often is, I'll try to pull together all details at this point. That may involve going back outside or do some probing, etc. This is the point where I also try to shed the homeowner so I can think quietly on my own. I make final notes and depart, typically writing the actual report back in the office.

This may be beyond the scope of many folks, but it is what I've done for years having come out of the "energy" side of the business and it seems to work well. Feel free to take from what I've done and make it work for your own situations.

Thermally yours,

John Snell
ASNT NDT Thermal/Infrared Level III #48166
Snell Infrared
800-636-9820
802-229-9820
http://www.thesnellgroup.com
http://www.IRTalk.com
http://www.thermalsolutions.org

[David A. Andersen]

Interesting scan.

Is that air leakage at the second floor right center and second floor right window shutter?

The upper window headers appear warmer than the lower ones. Stack effect?

[John Snell]

Originally Posted by dandersen

Interesting scan.

Is that air leakage at the second floor right center and second floor right window shutter?

The upper window headers appear warmer than the lower ones. Stack effect?

Yes it is air leakage on both counts. I would say the upper windows appear warmer due to convection between the primary window and the storm rather than stack effect in the building as a whole.

The missing insulation on the first floor (and possibly under the windows on the second but that is tough to call from this image) were also significant defects.

Thermally yours,

John Snell
ASNT NDT Thermal/Infrared Level III #48166
Snell Infrared
800-636-9820
802-229-9820
http://www.thesnellgroup.com
http://www.IRTalk.com
http://www.thermalsolutions.org