Environmental Engineering Reference
In-Depth Information
Table 6.4 Summary of boundary conditions for different simulation runs. Case 0 and Case 1 both
operate at constant generator temperature, but in Case 0 the solar thermal system operates at low-low
conditions
Cases
Cooling tower
Cold distribution
Generator inlet
type
6 C/
15 C/
85 C/
70-95 C
12 C
21 C
Const.
Variable
0
Wet
×
×
1
Wet
×
×
2
Wet
×
×
3
Wet
×
×
4
Dry
×
×
If a dry cooling tower is used, the heat removal at the absorber and condenser occurs
above ambient air temperature levels (Case 4). The setpoint for the absorber inlet
temperature is 27 C, which cannot always be reached for the dry cooling tower.This
leads to an increase of required collector surface area to 36m 2 , that is 2.4m 2 kW 1 .
The cases are summarized in Table 6.4.
For the improved control strategy, the collector energy delivered to the storage tank
reaches between 511 and 670 kWhm 2 a 1 depending on the cold and recooling water
temperature levels.
The thermal COP of the absorption chiller is highest (0.76) if the cold water temper-
ature level is high (21 C/15 C) and stays high, even if a dry recooler is used (0.73).
Low cold water temperatures give COPs of 0.67-0.7 (see Figure 6.14). The solar ther-
mal efficiency is calculated from the energy produced and delivered to the hot storage
tank divided by the solar irradiance.
Figure 6.14 Average annual COP and solar thermal collector efficiency for different operating modes
 
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