Humidity & Dew Point; Relative & Absolute Humidity - FLIR InfraCAM User Manual

Deviations and irregularities in the appearance of the infrared image often indicate
insulation defects. There may obviously be considerable variations in the appearance
of infrared images of structures with insulation defects. Certain types of insulation
defects have a characteristic shape on the infrared image. Section 12.2 – Typical field
investigations beginning on page 71 shows examples of interpretations of infrared
images.
When taking infrared images of the same building, the infrared images from different
areas should be taken with the same settings on the infrared camera, as this makes
comparison of the various surface areas easier.
12.3.7 Humidity & dew point
12.3.7.1 Relative & absolute humidity
Humidity can be expressed in two different ways—either as relative humidity or as
absolute humidity. Relative humidity is expressed in percent of how much water a
certain volume of air can hold at a certain temperature, while absolute humidity is
expressed in percent water by weight of material. The latter way to express humidity
is common when measuring humidity in wood and other building materials.
The higher the temperature of air, the larger the amount of water this certain volume
of air can hold. The following table specifies the maximum amounts of water in air at
different temperatures.
Figure 12.6 A: Temperature in degrees Celsius; B: Maximum amount of water expressed in g/m
level)
A B
30.0 30.44
29.0 28.83
28.0 27.29
27.0 25.83
26.0 24.43
25.0 23.10
24.0 21.83
23.0 20.62
22.0 19.47
21.0 18.38
Publ. No. 1558299 Rev. a200 – ENGLISH (EN) – February 12, 2007
A B
20.0 17.33
19.0 16.34
18.0 15.40
17.0 14.51
16.0 13.66
15.0 12.86
14.0 12.09
13.0 11.37
12.0 10.69
11.0 10.04
12 – Introduction to building thermography
A B
10.0 9.42
9.0 8.84
8.0 8.29
7.0 7.77
6.0 7.28
5.0 6.81
4.0 6.38
3.0 5.96
2.0 5.57
1.0 5.21
3
(at sea
A B
0.0 4.86
-1.0 4.49
-2.0 4.15
-3.0 3.83
-4.0 3.53
-5.0 3.26
-6.0 3.00
-7.0 2.76
-8.0 2.54
-9.0 2.34
105
12