Lets get it on

[David A. Andersen]

Boy, it's hard to keep up with this thread!
We may have created a monster here!

Please do not take offense of any short replies made. We can expound a little more as interest dictates.

all

I was surprised my self when the low temp showed up

Charlie, this is what this section on the board is all about (being surprised by what we find) and trying to understand why.
We can all learn by sharing..

The emissivity setting on camera (as John McKenna picked up on) doesn't matter. In our application of the infrared camera, as home inspectors we do not need to know the exact temperature of anything. Comparisons or Delta temperature is what we're concerned about.

I suppose monitoring a container of water would help but seems a bit extreme

Mr. Warner, this application may be a bit extreme, however the "normal window" is governed by readings that you achieve.
As home inspectors it is unlikely that we will ever do this much evaluation, but those that want to expand beyond should understand that there are circumstances that will affect your thermal scan and that there is a way to determine the best possible time to take your readings. Just because the thermal window occurs in the morning and the afternoon under most circumstances, it does not mean it will occur under all weather conditions. Someone may need to know the way to evaluate what the exact temperature differences between the roof and moisture levels.

The advantages of this board is that there are people out there that do nothing but roof evaluations and may can teach us some good stuff.

I suspect part of it is indeed reflection from the sky and space but your image indicates a temp range from -12 to 28. There's some awfully cold objects up there on that roof. You don't indicate ambient temp or the lowest temp of the night before. The low temp is probably due to the thermal capacitance of water and also due to latent heat of fusion. Also understand that air movement at 10MPH a surface will lose 50% of its actual temp. The slightest breeze will reduce surface temps.

Mr. Warner, I think we are reading into this a little too deeply, though you are raising some excellent points to consider. The temperature readings of the reflected sky would be even lower than you see in this scan if the camera had the capability of reading lower temperatures. I can almost guarantee that the lowest temperature is due to the reflection of the temperature of space at the time he took the picture. There was nothing on that roof 12° below zero Fahrenheit when he snapped the picture.

Dave, is that a reflection from the termination strip used on the carpeting?

Mr. Russell, actually the door is an exterior door between the house and an unconditioned attic space. The carpet strip would do the same thing, however in this case it is a full aluminum threshold.

Electrical breakers and the buss bars will absolutely reflect images.

Mr. Valley, I almost always pay attention to the insulation on the electrical wiring because it is close to the blackbody we are looking for. Basically what I'm saying is not to put your crosshairs and a temperature reading on the scan because an aluminum terminal connection is showing hotter than wire insulation.

In our application of this technology we should probably avoid things like aluminum terminal connectors. If you look at the emissivity tables posted on the Internet, aluminum has one of the widest ranges possible due to its physical condition which cannot be readily evaluated during our application. The distance between wire insulation in the connection is not significant enough to attempt a conversion at the terminal fixture.

[William Warner]

Originally Posted by dandersen

Boy, it's hard to keep up with this thread!
We may have created a monster here!

Please do not take offense of any short replies made. We can expound a little more as interest dictates.


Mr. Warner, this application may be a bit extreme, however the "normal window" is governed by readings that you achieve.
As home inspectors it is unlikely that we will ever do this much evaluation, but those that want to expand beyond should understand that there are circumstances that will affect your thermal scan and that there is a way to determine the best possible time to take your readings. Just because the thermal window occurs in the morning and the afternoon under most circumstances, it does not mean it will occur under all weather conditions. Someone may need to know the way to evaluate what the exact temperature differences between the roof and moisture levels.

The advantages of this board is that there are people out there that do nothing but roof evaluations and may can teach us some good stuff.


Mr. Warner, I think we are reading into this a little too deeply, though you are raising some excellent points to consider. The temperature readings of the reflected sky would be even lower than you see in this scan if the camera had the capability of reading lower temperatures. I can almost guarantee that the lowest temperature is due to the reflection of the temperature of space at the time he took the picture. There was nothing on that roof 12° below zero Fahrenheit when he snapped the picture.

Pretty much what I was trying to say but you did it better!

Thanks!