FLIR B6 series, User Manual

Page: 236 / 326

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 219. This differential pressure may be
described by the relationship:
Air pressure differential within the structure in Pa Δp
9.81 m/s
2
g
Air density in kg/m 3
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
If
ρ
u
= 1.29 kg/m
3
(density of air at a temperature of 273 K and ≈100 kPa), this pro-
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.).
28
218
Publ. No. 1558550 Rev. a557 – ENGLISH (EN) – October 7, 2011
28 – Introduction to building thermography