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Blog #049 – Your THERMOGRAPHY COMFORT LEVEL – Thermal capacitance and its use in thermography.

So I point my Fluke Ti32 IR camera down on a flat roof at 11pm on a clear night and there’s no wind.  I see warm areas and cool areas.  The moisture meter verifies the warm areas as moisture.  But I thought moisture signatures were cooler than dry areas due to evaporative cooling.  There are two principles that a thermographer works with when using a thermal imaging camera to investigate moisture issues.  One is “evaporative cooling” and the other is “thermal capacitance”.  If moisture is on the surface and the conditions are right, evaporative cooling will result in a temperature drop of around 4-5°F.  If you are inspecting a flat roof you would want to use the principle of “thermal capacitance”.  Thermal capacitance is the capacity or ability of a material to store or hold thermal energy.  The higher the thermal capacitance of a material is, the slower the material changes it temperature.  Water has a very high thermal capacity or specific heat.  It takes one BTU to raise the temperature of one pound of water 1°F.  So it will warm up slower and cool down slower than other materials.  Roofing material, for example, has a lower thermal capacitance than water.  So it warms up faster and cools off faster than water.  Let’s say you have a leak in a flat roof and the water goes through into the insulation material.  The sun cooks the roof material and the water in the insulation.  After the sun goes down everything starts to cool off, both the roof membrane and the water in the insulation.  But because the water has a higher thermal capacitance than the roof membrane it will take longer for it to cool down.  It will keep the roof membrane above it warmer than the dry areas.  Your thermal imaging camera will be able to locate the “warm” areas pinpointing the areas of investigation.  The moisture meter can then be used to verify moisture.  This is one of many uses of the principle of thermal capacitance.

Fluke IR Fusion camera locates moisture signature due to the high thermal capacitance of water

Fluke IR Fusion camera locates moisture signature due to the high thermal capacitance of water

Fluke IR Fusion camera locates moisture signature due to the principle of evaporation (evaporative cooling)

Fluke IR Fusion camera locates moisture signature due to the principle of evaporation (evaporative cooling)

 

These principles are invaluable to the thermographer who is involved with moisture investigations.  Learn them well.

How’s your comfort level in thermography?
(The above comments represent my opinion).

Rod Hoff / Restoration Consultants Inc
Thermography Instructor / IR camera sales
3284 Ramos Circle, Sacramento CA 95827
toll free 888-617-3266 ext 301
fax 916-736-1134
rhoff@restcon.com

Provider of Fluke TiS, TiR, TiR1, Ti, Ti25, TiR27, Ti27, TiR29, Ti29, TiR32, Ti32, TiR3, and TiR4 infrared cameras.

See DEMO www.moistureview.com/demo.html

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About infrarod

Rod Hoff is a Thermographer and instructor with Restoration Consultants, Inc. He teaches a two-day IR class in moisture and building envelope investigations. A graduate from Florida State University, with a degree in education, he received his formal training in Thermography from Snell Infrared and Restoration Consultants, Inc.
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