ran into this today,

gerry gill

and thought it was interesting, (not the chart but the thermo pictures)..i never took physics but if someone can explain how this works, i'm all ears..i have some customers who are physics professors and they tried to explain this to me but they couldn't get it down to gerry language..

Brad White

Emissivity, My Dear Watson

Emissivity is the ability of a surface to emit radiated energy, specifically infrared to our concerns.



The ideal is 1.0 or 100% which is based on the proverbial perfect black body. (Yes, Halle Berry is a 10 which is why we use logarithms   The black body concept was conceived by William Herschel, but he was just not that good looking.



So a material with an emissivity of 0.90 has 90 percent of the potential of Herschel's ideal black body. Most building materials are figured or defaulted to this number, but shiny metallic objects, bare bright copper pipe for example,  is in the 0.05 range, pretty low.



This is why your infrared thermometer does not show the "felt to the hand" temperature and may read very close to room temperature. THEN you grab the pipe. We all do.



Here is a table of various materials to give you an idea.



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



The IR camera "reads" emissivity and translates that into temperature and then temperature into color palettes. It does not "read" temperature specifically. But this is why the emissivity (e) factor is important to set to the material you are reading.  I hope that makes sense!

crash2009

The thermo pics support the old chart.

 Is that white over aluminum/grey?  NBC is great at explaining that molecular mumbo jumbo. 

gerry gill

holy crap Brad..

what did that mean in chicago public school english??

gerry gill

i don't know

what that is next to the white..but it looks much older.

Mark Eatherton

What Brad said was....

Halley Berry is HOT,



William Hershell is NOT, even though they both sport the same body temperature.



He went on to say, that metallic paint doesn't vomit energy the same way that duller flat paint colors do.



He also said NOT to trust your hand to an IR thermometer, unless it is made out of raw hide leather or is completely covered in asbestos....



Okay, maybe I took a little editorial freedom on the last part.



HTH :-)



ME

gerry gill

youz guys are killin me...lol

so i gerry english your saying that the energy gets thru the flatter paint easier and that the rest is an optical illusion to the thermal camera because they are actually two different materials?? is that what your saying?

Brad White

Sorta

The flatness of the finish is another issue and that has more to do with how that surface reflects radiation (be it light, infrared, UV, whatever you throw at it). Not the same thing.



Emissivity has to do with how that surface temperature, backed by the energy behind it, can send off energy. Now, that energy, (heat at whatever intensity or temperature), is transmitted by convection, conduction and radiation. Emissivity only has to do with the radiation portion.



So take your copper pipe, which your IR camera shows to be nearly room temperature. That will not emit much radiation, but convection (marked by rising air currents across it) and conduction (marked by a scream and several choice Anglo-Saxonisms), show that there is still energy transmitted. Just not across space as much.



Optical illusion? Mmmm. I would say that what the camera "sees" is a proxy, a stand-in for temperature. A very good one, but it is dependent on knowing the emissivity of the material in order to get the highest accuracy.

gerry gill

sooo

the emissivity of the base cast iron would be the same, but the emissivity is changed depending on what paint is on the cast iron..my brain hurts...

nicholas bonham-carter

thanks for the complement!

i have always wanted an i.r. camera. maybe if i had had some experience with one, i would be able to explain, after some study, whats going on here with brad white's emissions!--nbc

Brad White

Yes!

The last coat of paint is the launching pad for radiated energy.



A really poor analogy but the best I can do is to think of the surface as the tips of a baseball pitcher's fingers. The last touch determines the flight.



When you look at the table (engineers tool box site), you will see how the metallic materials, aluminum, copper, depleted uranium (kidding!), have low emissivity and thus aluminum and bronze paints reduce that "last touch" from what starts as conductive heat to the surface.



It was surprising how cast iron, bare and clean, is or approaches a 1.0 e factor. (Some charts have CI at 0.95 to 0.99, may depend on the amount of graphite and other lower emitting particles, just a guess on my part.)



My guess is that Goths, Emos and Hipsters with flat black cast iron radiators are reaping the thermal benefits, but I would never tell them. Especially the Emos. It might cheer them up and that would be just so wrong.

Brad White

I think that I will

leave that one alone, NBC!

Gordan

You're a riot.

Keep it up and we'll need to send in the water cannon. Emissivity: check!

Mark Eatherton

Cast iron emissivity varies....

I have seen bare cast iron fittings and steel pipes that would show a low surface temperature on an IR thermometer. Pump castings too. This is why I always use teflon (Blue Monster) pipe dope to dull the emissivity of the materials I am checking, so I get an accurate read of the true potential surface temperatures.



Keeps the blister count low, and allows me to go through the IR photo (Fluke) with the software and put a point on the dulled surface so I can read things like delta T.



Duct tape and 3M blue masking tape do the same thing as well.



The bad thing about IR thermography is that people have a tendency to pay attention to the color schemes, and get so tied up on those, that they miss actually seeing what is really going on with surface temperatures. The colors are simply a guide to show differential. Using the software to evaluate the picture pixel by pixel is where the real statistical analysis comes from...



Makes for some really interesting photography, but doesn't tell (obviously) the whole story.



But a fantastic WOW tool to the consumer. My camera has already paid for itself, and I've only had it for a little over a year. I used it the other day to show a homeowner GC why it is that insulation BELOW their radiant floor is critical. She and her husband were standing behind me as I scanned their basement ceiling (75 degrees MRT down stairs with T stats turned off) and you could see every foot of pipe on the floor above.



The basement ceiling was insulated the next day, and suddenly, the living space on the main floor actually hit set point and became comfortable! I then proceeded to walk through the house showing them gaps in their insulation that were also contributing to discomfort, and some HUGE areas of infiltration (it was -15 Degrees F outside) that were also contributing to their discomfort.



A tool well worth the while to own, and you CAN (and SHOULD) charge extra for its use, and the camera costs have come down significantly recently. I hear tell the FLIR folks have a basic model out for under $2K.



Use with caution...and knowledge.



ME

nicholas bonham-carter

choice of ir camera

i wonder how satisfied everyone is who has bought an ir camera with the choice of model in that initial purchase.

in our real estate management activities, i can see that the possibility of detecting roof leaks, bad electrical connections, and solving heat loss problems, would justify the purchase of one. what is daunting is the different models available, at ever increasing prices, and the learning curve of being able to use one to its full potential.

so would all who have one, please recount experiences, and wishes for more features [a separate thread may be required].

Brad White

I own a

FLIR b50, which is the mid-range of their hand-held line. The b40 was about $1k less and the b60 about $2k more but the b50 can be upgraded to a b60 for the cost difference if I ever wanted to. 

Mine was about $6k by the way, not including the cost of chocolate, flowers and slow dances to sway my lovely CFO to my way of thinking.



The pros who do building science for a living use what I call the "press camera" types, essentially two-handed cameras with higher resolution. But for my purposes (direct surveys with or without blower door testing and local spot checks), it works fine.



The only issue I have had is, if I leave the battery in the camera and it runs down, it takes the volatile memory with it. When I turn on the camera, the date/time calendar thinks it is year 2005 so has to be re-set. No one explained why but it is just annoying, not a show stopper. Removing the battery seems to solve that but it is strange...



I also use the camera during my day job and have found abundant leaks, gaps, things otherwise unseen which had a drag on our system design and in some cases, reputation.



My electrical engineers have used these more for circuit load mapping and trouble than I have for building evaluations.



As for training, Snell Infrared comes highly recommended.

An essential thing to keep in mind is, "do not freak out when you see blue on an inside wall". The palette spectrum re-scales automatically and what is "blue" when the spread is 30 to 70 degrees will also be blue when the spread is 65 to 70 degrees. Blue  showing up in room corners in that latter range are framing where there is no way to insulate so you admit defeat and move on.  A blue spot between studs otherwise insulated could be a gap, or a wet spot requiring further investigation.



From the outside, a warm spot could be an insulation gap or, in one case I found, a speaker was installed in the wall and was emitting more heat behind it. Heat loss but no net loss to the space. 



How to interpret is more important than net values. It is a tool to get you to ask yourself more questions.



For analyzing moisture issues a good hygrometer is key and you can adjust the higher grade cameras (or later, the images with the software) to find the dewpoint line. It is hard to explain the full range of things, which is why training is so important.



As for costs increasing, I disagree. My camera had a price drop just before I bought it and it has held since. But I used to have the use of an IR camera from MIT. Weight 80 lbs., had a back pack for the battery (40 pounds right there) and was only in black and white.



$80 grand would take it away, $1,000 per lb. I asked, what is it made of, Beluga caviar?

nicholas bonham-carter

infra red reflections

thanks for the observations. by the comment of increasing cost, i was referring to the prices of the different models, and what added features would be more useful as a result of the increase in price.

i should probably take the training course, before making my choice.--nbc

Brad White

Ah, I see, NBC!

That makes sense, price escalation model to model. I stand corrected.



I jumped right in sans formal training, just what I received when fiddling with the MIT unit about 10-12 years ago. No, I was not a student there, but I had connections and a whole lot of fun...

nicholas bonham-carter

fun at MIT

well even "click and clack" the tappet bros have a degree from MIT, so perhaps you are next!

after all, you are the "clack" of heatinghelp.com!--nbc

David Nadle

For the record

Brad, I'm pretty sure the blackbody was developed by Gustav Kirchoff and Max Planck. Herschel was the one who discovered infrared light.



I think (hope) that someday (maybe when a patent expires?) many digital cameras will have an IR mode and thermal imaging will be affordable to the "enthusiast" (nut).

gerry gill

i'm gonna try

that masking tape idea...do you think that if i had put masking tape on both sides of that two tonw radiator they would have read the same on the ir software?

crash2009

Here is a curve ball for ya Gerry

 Assumably, the emissivity of this paint changes with the temperature.  I was thinking about painting the Gortons so I could see when they are hot or cold.  I have not found the correct mix yet, but am still looking.  Here is what I have found so far.



http://www.colour-therm.co.uk/images/1500_colourc.jpg

gerry gill

wouldn't it be great

to see the look on a customers face when a radiator is painted a certain color and then changes when its heated...would be funny..they probably would hand me another paint brush..

Mark Eatherton

Within a degree or 2...

You have to get a good bond in order to see the true surface temperature. If there are a lot of minute details in the casting, it may be impossible to get a good flat bond, and subsequent poor surface reading.



It works great on smooth pipe surfaces.



ME

Brad White

David, thanks

I stand corrected! You are correct, Kirchoff first used/coined the term "black body".  I had thought it was Herschel. And yes, Planck quantified it. Did he ever.

Herschel indeed discovered IR radiation based on the temperature of the colors, first noting that black was the warmest color when exposed to refracted and primary sunlight. 



Herschel also bent over backwards and found Uranus!

Thanks for setting me straight. I almost bent over backwards myself