Retrotec USACE - Manual (Page 342)

G12 ENERGY & PROCESS ASSESSMENT PROTOCOL
Figure G10. IR thermogram of a
one-story building showing cooler
patterning in the upper area of
the wall due to shading of the
exterior of the building. (Image
from Building Science Institute.)
The presence of background radiation is especially important in outdoor ap-
plications of IR thermography and in indoor applications, where there are very
hot objects (hot pipelines or process units, furnaces, heat treatment units, sun)
or very cool objects (sky). For instance, the clear night sky cools down the
upper parts of buildings rather than lower ones surrounded by other buildings
or vegetation. During the day, solar insolation is dependant on the angle of the
sun and shading from overhangs or vegetation (see Figure G9). The interior
conditions may also be affected (see Figure G10).
Thermal scanning can be accomplished both from inside and outside the
building. There is always a chance of making mistakes in the data interpreta-
tion when analyzing results of thermal scanning. The apparent simplicity of
thermal scanning can lead to wrong conclusions if certain physical phenomena
are not well understood. The temperatures in the structures are never evenly
distributed, and not all irregularities found in the surface temperatures neces-
sarily mean that there are defects in the tested structure.
G.5 The Three Different Modes of Heat Transfer
When considering heat movement or transfer in a building, there are three
ways that heat is transferred: radiation, convection, and conduction (see Figure
G11). These modes, which affect the patterning observed when using IR ther-
mography in buildings, are very important when interpreting thermal images.
G.6 Infrared Thermography of Buildings
A simple defi nition of a building is a separator of the indoor and outdoor envi-
ronments. This separator usually protects the occupants or the indoor compo-
nents of the building from physical, chemical, and biological reactions that tend
to affect negatively the occupants and components. Any building is supposed to
separate its internal space from the uncontrolled environment to create comfort-
able conditions for living and to reduce costs of maintaining those conditions.