FLIR Exx series User Manual page 117

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 106. This differential pressure may be
described by the relationship:
Air pressure differential within the structure in Pa
Δp
9.81 m/s
g
Air density in kg/m
ρ
u
Thermodynamic air temperature outdoors in K
T
u
Thermodynamic air temperature indoors in K
T
i
Distance from the neutral zone in meters
h
3
If ρ = 1.29 kg/m
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. T559597 Rev. a500 – ENGLISH (EN) – December 10, 2010
2
3
(density of air at a temperature of 273 K and ≈100 kPa), this pro-
24 – Introduction to building thermography
105