Active Thermal Cooling Technologies - Low Energy Cooling for Sustainable Buildings - page 177

System 2 In the basic desiccant cooling system, a desiccant rotor available on the
market is used for return air dehumidification. After dehumidification the return air is
precooled by ambient air in a water-sprayed cross-flow heat exchanger to remove the
adsorption enthalpy and the heat transferred from the regeneration side of the desiccant
rotor. The precooled return air is then injected into a second water-sprayed cross-flow
heat exchanger, where the return air is humidified by the water and heated by the
supply air, which is thereby cooled in the channels of the cross-flow heat exchanger.

System 3 Here the desiccant rotor is replaced by a liquid desiccant sprayed onto a
contact matrix absorber unit. A regeneration unit for the liquid desiccant replaces the
air heater of system2; all other components stay the same as described for system2. The
concentrated liquid desiccant is sprayed onto the contact matrix absorber unit, where it
is brought into contact with the return air for dehumidification. During the absorption
process the concentration of the liquid desiccant decreases, while the temperature
increases. After passing the contact matrix absorber unit the weak liquid desiccant is
stored in a storage tank before it is sprayed onto a regeneration unit, where the solution
is heated and the absorbedwater is removed. After regeneration the humidified ambient
air (exhaust air) after the first water-sprayed heat exchanger can be used to cool the
hot and strong liquid desiccant in a liquid to air heat exchanger before it is stored in a
second storage tank.

System 4 In the most integrated system, the liquid desiccant is sprayed directly
into a cross-flow heat exchanger, which also integrates a spray humidifier on the
secondary side. The temperature reduction of the liquid sorption material through
secondary water evaporation during the absorption process improves the absorption
performance and lowers the supply air temperature even further. Together with the
second water-sprayed heat exchanger already used in systems 2 and 3, the number
of components is now reduced to three. The circuit of the salt solution is similar to
system 3.

Experimental Set-up for Performance Analysis of Integrated Components

An experimental set-up was built to condition air (temperature, humidity) for both
the outside and return air side. Experiments were carried out for return air from the
conditioned space at 26 ◦ C dry bulb air temperature and 50 to 70% relative humidity
and for ambient air at summer conditions at 32 ◦ C dry bulb air temperature and 40%
relative humidity.
To compare the performance of the four systems described in the previous sections,
the return air dehumidification of the desiccant wheel, the contact matrix absorber
unit and the heat exchanger absorber unit were measured for return air at 26 ◦ C and
55% relative humidity and constant air and liquid flow rates (200m 3 h − 1 return and

ambient air, 100 h − 1 liquid desiccant and water).