Environmental Engineering Reference
In-Depth Information
sprayed on a contact matrix give similar performance results, as the absorption heat
cannot be efficiently removed during the process. The best performance was achieved
for a cross-flow heat exchanger for simultaneous dehumidification and indirect evapo-
rative cooling (system 4) with nearly 6 g water kg 1
air dehumidification at no temperature
increase. Concentrated lithium chloride and calcium chloride solutions have been used
as liquid desiccants in the two absorber units. The lithium chloride solution gave 40-
50% higher dehumidification rates over a wide relative humidity range. The measured
dehumidification drops by about 1g water kg 1
air if the volume flow rates are tripled from
100 to 300m 3 h 1 .
For the summer design conditions of 32 C, 40% relative humidity, the integrated
system reaches supply air temperatures of 18.8 C, which corresponds to a cooling
power of 886W at the measured volume flow of 200 m 3 h 1 . This is 32% more
cooling power than reached by awater-sprayed cross-flowheat exchanger with directly
humidified return air (system 1).
The developed numerical models have been validated using the experimental data
and good agreement was found between experiments and simulations. The model of
the heat exchanger absorber unit was then used to study the optimization potential
of the system. If the surface wetting can be improved from currently only 35% to
60%, about 15% higher dehumidification rates can be achieved at significantly lower
solution volume flows. A further improvement to system 4 can be reached if the
efficiency of the water-sprayed cross-flow heat exchanger is increased from 70% to
about 76%, by the implementation of heat transfer ribs between the heat exchanger
walls. With these improvements to system 4, the supply air temperatures could be
reduced to 18 C.
The new system offers a high potential for low-cost solar thermal cooling applica-
tions in residential buildings using liquid desiccants in an air-based ventilation system.
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