"daylight" is interpretable, so you could possibly catch it in the late afternoon, say 1 or 2 hours before sunset.  At that point, the sun is low enough to minimize the direct radiation, while there is still plenty of absorbed and internal heat to show the differences you're looking for.

TTFN

Roy,

You've probably already done your roof scans, but in case you haven't I have a few comments:

1.) Marking roofs is a team effort. First and foremost is safety. You don't want to be alone on a roof where you suspect problems. And then there are the hazards of being that far off the ground and gravity and so forth. Also, it's nice to have someone else with a paint can to mark the suspect areas.

2.) I think you're right on with scanning at night. It's the whole idea of thermal inertia and looking for the contrast between the warm, water-soaked insulation panels and cooler, dry insulation. I'm just up the road from you so I know all about the 90° days and 80° nights. The roof needs time to cool slightly so you can more easily see the extent of the damage.

3.) Playing on the thermal inertia theme, and if no one wants you there at night (sounds like an OT issue), you could also take a look first thing in the morning when the dry insulation would warm first and the wet insulation will take longer to warm.

Just a couple of generic ideas. I haven't a clue as to what's under this roof or the insulation structure, etc.

Patrick

Just an expansion on Patrick's suggestion is that early morning thermal performance is not necessarily indicative of normal operational thermal performance.  

Our office building shuts down the A/C at 6pm, so by morning, the internal temperature as essentially zero correspondence with normal operation.  In fact, it takes until about 10am for office temperature to come down into the comfort zone.  

TTFN

Safety Note:  People have fallen through older industrial roofs, with no warning, and horrible results (death, paralysis, lawsuits).  Two causes have been: 1) corrosive atmospheres below the roof deck – slightly acidic vapors – that condense onto the cool roof deck during cold periods – causing steel deck panels to corrode, 2) wet insulation on top of the steel deck panel - causing corrosion from the top side.  Both weaken the deck.

Be safe – use planks to walk on, to spread the load to structural supports, and/or use a harness and safety ropes to minimize injury from falls over the edge, or through the roof.

To all,  Yes 1st and foremost is safety.  As a consultant and now program manager I never conduct IR roof surveys at night.

You are correct about the roff imaging being conducted at night.  The following is why.  I'm not sure about the thermal "inertia" comment but I do know that the following applies.  I think thermal capacitance is the term that would be used.  

During daylight hours the roof surface will heat to a uniform temperature.  Approx 1-2 hours after sunset the protions of the roofing insulation that are "dry" release thier thermal energy to the night sky thus allowing us to "see" the temperature differance between the "wet" and "dry" portions of the roof.

Things to watch out for.
Edges! (kinda goes without saying)
Water buildup on the roof surface of more than 1/4 inch
Aluminized roof surfaces (poor emissivity)
Blowing roof units or fans
Known weak areas
EPDM style roofs can be difficult to image

Hope this helps

Roy,
I have reviewed all the reply's and each one has at least one point that is correct.
1.Safety - Walk through the plant and view the underside of the deck and look for Rusted areas. Mark any areas on plan and stay clear of them while performing the scan.
2. Scans can be done during the day. Adjustment of your system is critical and understanding that the water trapped in the roof system acts as a heat sink and will become 5 to 15 degrees F higher than the surrounding areas so by recording the roof in a grid type syetem and then downloading the images onto your computer you should be able to recognize HVAC units and drains and plot the wet areas.
I could help you more if I knew what type of roof system you have. EPDM roofs are actually the easiest to perform scans on with ballasted EPDM being the most difficult.

This is what I have done for a living since 1984 with over 50 million square feet of roofs scanned. Let me know if you have any more questions.

Thanks and good luck

This post may be a bit late but daytime IR is a field that is comming around.  Please see the attached course that is offered by someone in the FLIR corporation.  I would suggest that you get a hold of him and pursue your question



Daytime Infrared Roof Inspections (You Can Get a Good Night's Sleep!) (HSW)

Infrared thermography is a proven technology that has been used for years to help roof consultants and building owners locate areas of wet insulation. This broad scanning technique has advantages over other methods; it is non-destructive, non-intrusive and it presents active visualization of wet areas. The most commonly used standard to conduct infrared inspections is ASTM-C1153, Standard Practice for Locating Wet Insulation Using Infrared Imaging. This standard addresses only night-time inspection of roofs. The presenter will discuss techniques to allow infrared inspections to be performed during the day - both from inside the building and on the rooftop. Case histories and a matrix of required roof material and environmental conditions will be presented. Daytime inspections offer equal sensitivity as night-time inspections but add increased levels of safety for the inspector. The potential for trips and falls is considerably reduced.

Ronald D. Lucier - FLIR Systems - North Billerica, MA
Lucier is a mechanical engineer with over 20 years of experience developing applications for infrared thermography. Each year, he conducts over thirty one-week training courses throughout North America. Lucier has offered lectures in Europe and China.

Performing an infrared scan during the day is very possible, even in the bright sunlight depending on the type of equipment you have. If you have a multi color display and it allows you to change temp gradiants, then you scan the roof area and record the data. Bring the information inside and plug it ito your computer and start your review. With moisture and water being the best heat sink there is you can pinpoint the wetest area and go from there. It does take a lot of practice and this comes with trial and error. There are capacitance meters for Tar & Gravel roof and also for rubber membranes from a company named Tramex. I don't know where to find them but a web search should get you what you need. I am also a source of free advice for anyone performing in house work. I am approaching over 100 million square feet scanned. Good luck and be safe up on the roof and always have someone with you.

But are you going to be seeing the same phenomenon?  

Will heat leaking from inside travel the same paths as heat penetration from the outside?

TTFN

IRstuff,
The heat escapeing from the inside may find the same path, but you have to consider temp differance and daytime sunlight can heat a roof surface to over 140 degrees. This will block any interior heat leakage that can be thermally viewed.

I understood that part.  

What I was wondering was whether IR survey at night, seeing heat leakage was exactly equivalent to a daytime IR scan showing heat penetration.  

The proposition was that you could avoid doing survey's at night, with the implied conclusion that a daytime survey would provide equivalent results.  That's not intuitively obvious, particularly in view of the solar load potentially obscuring escape paths.

TTFN

IRstuff
You are correct in that conclusion. Daytime is the way to go especially at this time of the year for your area.

Thanks to all for your valued replies. I just completed ITC's Level I course, aced the test and sent my project off today. This course has definitely broadened my understanding of thermography, and I look forward to putting this technology to work (correctly) here at our facility.

Roy Gariepy
Maintenance and Reliability Dept.
Bayer Corporation  Dorlastan Fibers Div.
Goose Creek, South Carolina  USA