IEA Solar Heating and Cooling Programm - NachhaltigWirtschaften.at

IEA SHC Task 38 Solar Air Conditioning and Refrigeration Subtask C1 Report, 31 October 2010
Perhaps a more appropriate nomenclature would be to call such systems semi-open
absorption systems. Therefore, there would be a clear distinction between closed, semi-open
and open-absorption, where both absorption and desorption are in direct contact with air.
The fact that liquid-desiccant systems are usually used for dehumidification is not enough to
clarify the nomenclature in the literature. For example, Grossman [87] proposed a system
with an open regenerator and absorber, where the dehumidified air was directed to a cooling
tower. This way, the system generated chilled water, as in a traditional vapour compression
or closed absorption system. Bolzan and Lazzarin [88], Lazzarin et al. [89], and Johansson
and Westerlund [90] presented systems that were liquid-desiccant cycles with open
absorbers and regenerators, where the air running through the absorber was the air to be
conditioned. Although this is an arrangement that has been mostly referred to as a desiccant
system, the authors labelled the system as open-absorption.
One advantage of LDS over solid desiccant and closed absorption systems is the flexibility in
terms of heat sources for regeneration and heat sinks for the dehumidification process. Heat
can be supplied by any medium temperature source, usually above 60°C. Cooling can be
accomplished by the use of heat sinks providing moderately low temperatures, usually
between 5 and 25°C.
4.3 Applications
Liquid desiccant systems are growing in popularity because of their ability to independently
control humidity levels (latent loads) moisture without cooling the air to saturation, the supply
air relative humidity falls below 70%. This keeps supply ducts dry and helps avoid mold and
bacterial growth. In addition, the scavenging action of liquid desiccant systems could improve
indoor air quality by removing airborne contaminants. Heinzen et al. [91] presented a
comprehensive overview for the liquid desiccant applications.
Figure 20: Liquid desiccant air drying process, from source to application. Source: Heinzen et
al. [91].
Figure 20 shows a schematic of the liquid desiccant air drying process in the dashed area. It
presents possible driving heat sources (left), the coupling to different cooling technologies
(center right) and possible applications where LDS can be technically viable and
economically and ecologically useful (right).
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