Building Services Engineering 5th Edition Handbook

248 Condensation in buildings
Temperature (°C)
t ai
t a
1
Q f (W)
R si
2
3
R so
4
Thermal conductivity
λ (W/mK)
5
I
Thickness I (m)
10.2 Temperature gradient through a solid construction.
and,
Q f = λ l
W
m 2 K × A m2 × (t 2 − t 4 ) K
and,
Q f = 1
R so
W
m 2 K × A m2 × (t 4 − t 5 ) K
The heat flow rate Q f can easily be evaluated from U, t ai and t ao . The only unknowns in the
other equations are the second temperatures t 2 and t 4 . An intermediate temperature t 3 can be
calculated at half the concrete thickness by using l/2:
Q f = 2λ
l
W
m 2 K × A m2 × (t 2 − t 3 ) K
If the wall area is taken as 1 m 2 , then:
and,
Q f = 1
R si
(t 1 − t 2 )
t 2 = t 1 − Q f R si
Similarly:
Q f = λ l (t 2 − t 4 )
and,
t 4 − t 2 − l λ Q f