Image by PhysicsCentral.com
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Thermal ImagingVisible light only accounts for only a small portion of the total light in the universe. Also known as thermography, thermal images use radiation in the long-infrared range of the electromagnetic spectrum to produce images. These are the waves that we can feel but cannot see with the human eye - the image below left shows the range of the electromagnetic spectrum - Infrared (IR) waves are just right of the visible spectrum. All objects (above absolute zero) emit infrared radiation with or without visible illumination (light). Thermal cameras are often used in medicine and surveillance, however we use it for building diagnostics to observe heat loss through building envelopes. As a note, it is difficult to get accurate temperatures with infrared photos so it is best used for comparison purposes only.
Each material has a different emissivity - the material's ability to emit thermal radiation. This may vary by temperature and infrared wavelength. The range is from 0-1. Silver, for example has a low emissivity of .02, meaning it will mostly reflect heat. Asphalt, on the other hand, has a high emissivity of .98 which will largely absorb heat. You may hear of low-emissivity (or low-e) windows - these windows use transparent coatings to emit less thermal radiation than ordinary windows (reduces heat loss through a window compared to uncoated glass) |
The students spent some time walking around the buildings they were most comfortable with to discover thermal leaks in building envelopes. We had two thermal cameras plus two additional infrared thermometers (otherwise known as "temperature guns")
University of North Carolina Charlotte, 2020
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Tulane University, 2018
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Here you can see visible heat loss through the seams in the pipes. |
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High emissivity materials will absorb heat and release it slowly over time. That's why you see a sharp line in shadow but a blurred line in the infrared photo. |
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Glass is infrared opaque. Instead of seeing the heat through the glass - we see a reflection instead. Here you can also see the significant thermal bridging through the header and sill (above and below the window) as well as the mullions. |
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Click to view the video |
Impact of thermal bridging on buildings...
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Heat comes from many places, including our bodies. We emit heat when we're still and we leave heat behind when we're on the move. That's why a room will heat up so much when there are many people in it. Maybe next year we'll play "thermal hide and seek"... |