Environmental Engineering Reference
In-Depth Information
With the ambient air temperature
ϑ
A
, the water temperature
ϑ
W
, the water
surface area
A
W
and the heat transfer coefficient given by:
(3.47)
the convection losses become:
(3.48)
The wind speed
v
wind
at a height of 0.3 m above the water surface can be
calculated from measurements at other heights using the equations in Chapter
5, section headed 'Influence of surroundings and height', p185.
Radiation exchange between the swimming pool surface and the sky causes
radiation losses
. With the Stefan-Boltzmann constant
= 5.67051
•
10
-8
σ
ε
W
~
0.9), water surface area
A
W
and
absolute temperatures
T
W
and
T
Sky
of the water and the sky, respectively, the
radiation losses become:
W/(m
2
K
4
), the emittance
ε
W
of water (
(3.49)
The
sky temperature
(3.50)
can be calculated using the absolute ambient air temperature
T
A
in K and the
dew-point temperature
ϑ
dew
(Smith et al, 1994).
The
dew-point temperature
(3.51)
can be estimated from the humidity
ϕ
and the
saturated vapour pressure p
:
(3.52)
The saturated vapour pressure
p
depends on the ambient air temperature
ϑ
A
and is measured in Pascals (1 Pa = 1 N/m
2
= 0.01 mbar). The mean relative
humidity
in moderate climates (e.g. Germany) is about 70 per cent during
the outdoor pool season.
ϕ
