Liquid Desiccant Air Conditioning Systems and Performance

In this section, a review of liquid desiccant air conditioning systems is provided, with a particular focus on membrane contactors and waste heat driven designs. The application of liquid desiccant in a tri-generation system context is provided in Sect. 2.5.4.

In a liquid desiccant air conditioning system, the desiccant solution needs to be cooled prior to the dehumidification process. This is because it enhances performance through a greater dehumidification potential, removes the latent heat of condensation produced during the dehumidification process, and can provide sensible cooling to the supply air stream. Desiccant solution cooling can be achieved in a variety of ways, including; internal contactor evaporative cooling, use of an internal or external cooling fluid or external pre-cooling. The technique used is dependent on the system and its application. The contactors used in the regeneration process do not require the provision of cooling, but employ an external heating source. Because the cooling achieved in liquid desiccant systems is almost exclusively latent, an additional stage of sensible cooling can be used to lower the supply air temperature (Lowenstein 2008). Liquid desiccant dehumidifiers combined with a VCS or VAS is termed a ‘hybrid’ system. Another common technological pairing is with evaporative based cooling technology, to create ‘stand-alone’ systems. Evaporative based cooling compliments liquid desiccant due to its improved performance when operated with dry air and its low electrical requirement (Daou et al. 2006; Ouazia et al. 2009; Kozubal et al. 2011, 2012). Currently, it is reported that hybrid systems are most widely used. This is because of stand-alone system’s large geometrical size and system complexity (Jain and Bansal 2007). However, with continual technical improvements to component technology, stand-alone systems are expected to become a major competitor to the hybrid system due to a high COPth, low electrical use and thus environmental impact.

Next, Sects. 2.3.3.1 and 2.3.3.2 presents a review of hybrid and stand-alone liquid desiccant systems respectively. Particular reference to system performance and any operating considerations are made throughout. The summary aims to identify the type of design best suited to the development of a SOFC liquid desiccant trigeneration system.

 
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