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4.6. Cooling Tower
discharged in point 47. The cooling tower is either a dry tower (dry
cooler) or a wet tower, as described in section 3.14 page 71.
The parameter configuration for these two towers are different and
will be described separately in the next two paragraphs.
4.6.1 Wet Tower
The ambient air has a temperature of 30 ◦ C when the wet tower is used.
Since the water and air is mixed this allows a much lower CATD than for
a tube heat exchanger and it is thus estimated to be ∆T min,TOW ER1,a,o,wet =
3 ◦ C. This way the temperature of the discharged air (T 47 ) is almost in the
middle of the water outlet temperature (T 39 ) and water inlet temperature
(T 37 ).
According to [14] the ”wet bulb” Tower efficiency is typically around
0,75, so this has been assumed also to be the case here giving a water
outlet temperature of 22 ◦ C when the inlet air is 30 ◦ C and the relative
humidity is 40%.
4.6.2 Dry Tower
Ideally the dry tower should use the same ambient temperature as the
wet tower (30 ◦ C), but this gives a condenser and absorber temperature
so high that the model can not run at all. So it has been necessary to use a
lower ambient temperature for the dry tower although it gives a slightly
unfair advantage when comparing it to the wet tower. A temperature of
18 ◦ C has been chosen, since this is just below where COP ABS,f uel starts
to decrease rapidly (at 20 ◦ C the system will barely run), so the unfair
temperature advantage is minimized as much as possible.
The Approach Temperature Difference between water inlet (T 37 ) and
air outlet (T 47 ) is estimated to be: ∆T min,TOW ER1,a,o,dr y = 8 ◦ C.
4.6.3 Hot Water
Most of the energy in the exhaust gas is utilized in the absorption cycle
and for air preheating (eventually additional air preheating is used in
GGHEX4). In point 23 temperature of the exhaust gas is rather low
95