Retrotec USACE - Manual (Page 354)

G24 ENERGY & PROCESS ASSESSMENT PROTOCOL
depressions in insulation, gaps between the insulation plates and the defects
in the seam, and so forth, can be detected by applying IR thermography. In
older apartment buildings, the thermal performance, especially in the attics
and basements, can be examined with rather good results.
G.10 Thermal Calculations
There is lot of information about the heat fl ow through building materials, both
theoretically derived and climate chamber–tested. Several software packages
intended for solving heat transfer problems are available, thus allowing the
modeling of temperature distributions and air leaks. Air leaks into a building
can decrease or increase internal surface temperatures very quickly. In spite of
this data and information, we hardly know how the surface temperatures vary
in well-constructed, high-quality buildings.
With IR thermography, temperature measurements calculated by the
camera can provide clues as to the effectiveness of the insulation. The thermal
index, insulation level factor, or insulation alarm is one way to analyze the tem-
peratures provided by the IR camera. “Insulation level factor” is a term used to
compare the effectiveness of a buildings’ thermal barrier.
f = (Tsi – Te)/(Ti – Te)
where
f = the insulation factor. A common value used is 0.6 – 0.8
Tsi = internal surface temperature
Ti = internal air temperature
Te = external air temperature
The idea is that you enter a desired factor and outdoor and indoor tempera-
ture (T
out
< T
in
). A formula can be used in conjunction with the camera to
fi nd the surface temperature of the inside of a wall that corresponds to the
insulation factor, and an “isotherm below” is set at this temperature. Areas
where the surface temperature is lower than desired are highlighted by the
isotherm.
However, the solutions mentioned above are mainly qualitative, and their
interpretation is based on knowledge about the structures and their thermal
characteristics. If the temperature distribution differs from expectations, the
defects can be assumed. The problem is that in addition to simply detect-
ing defects, their quantitative evaluation should be done. In the ideal case,
this would mean evaluating a U-value or fi nding an approximate estimate of
moisture content. In theory, this would be possible under dynamic conditions,
when a structure with different thermal characteristics cools down or warms
up slower or faster than its surrounding.