IEA Solar Heating and Cooling Programm - NachhaltigWirtschaften.at

IEA SHC Task 38 Solar Air Conditioning and Refrigeration Subtask C2-A, November 9, 2009
Storage Tank
Two different scenarios are considered for the validation of the storage tank model. In the
first only storage is considered (m 1 >0 and m 2 =0 in reference to Figure 5) while for the second
it concerns desiccant cooling application with storage in the morning and regeneration in the
afternoon (m 1 >0 and m 2 >0). The flow rates m 1 and m 2 are measured as well as the inlet
temperature of the storage tank. The predicted and measured temperatures at the top and
the bottom of the buffer are compared in the Figure 13 below.
Storage load
Typical desiccant load
90
90
80
80
70
70
Temperature [ C]
60
50
40
30
Temperature [ C]
60
50
40
30
20
10
0
Top experimental
Top model
Bottom experimental
Bottom model
0 100 200 300 400
Time [min]
20
10
0
Top experimental
Top model
Bottom experimental
Bottom model
0 100 200 300 400
Time [min]
Figure 13: Comparison of the predicted temperature with measured one for the top and the
bottom of the storage tank under a storage load (left) and a desiccant load (right)
In both scenarios the model can accurately predict the temperature at the top and the bottom
of the buffer. In the first case the stratification remains fairly constant but increases when the
storage and the regeneration are combined. This may at first, appear incoherent as more
mixing occurs in the latter case. The fact that stratification is greater with the regeneration is
that the regeneration load was applied by water loss and the return water was cold and
significantly below the tank temperature which amplified the stratification. Even with this
extreme case the model was capable to predict accurately the temperature at the top and the
bottom of the buffer.
Now if the model has shown an acceptable accuracy when considered solely, we have to be
sure that this accuracy will not be lost when coupling the components making the numerical
simulation useless. In the next section the error propagation will be analysed and the impact
on the supply temperature is examined.
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