FLIR ThermaCAM BX320 User Manual page 61

part. At a certain height there is a neutral zone where the pressures on the inside and
outside are the same, see the figure on page 48. This differential pressure may be
described by the relationship:
Air pressure differential within the structure in Pa
Δp
9.81 m/s
g
ρ Air density in kg/m
u
T Thermodynamic air temperature outdoors in K
u
T Thermodynamic air temperature indoors in K
i
Distance from the neutral zone in meters
h
3
If ρ = 1.29 kg/m (density of air at a temperature of 273 K and ≈100 kPa), this pro-
u
duces:
With a difference of +25°C (+77°F) between the ambient internal and external tem-
peratures, the result is a differential pressure difference within the structure of about
1 Pa/m difference in height (= 3.28 Pa/ft.).
Publ. No. 1558440 Rev. a156 – ENGLISH (EN) – February 28, 2006
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7 – Introduction to building thermography
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