The solutions of lithium chloride that are most commonly used in liquid-desiccant systems do present a practical maintenance concern: as with all strong halide salt solutions, lithium chloride is corrosive to metals commonly used in HVAC installations. AILR's wicking-fin heat exchangers addresses possible maintenance concerns by (1) operating with very low flow rates of desiccant so that possible droplet formation is suppressed, and (2) insuring that all wetted surfaces will resist corrosion by the lithium chloride.
All innovative technologies evolve as they mature. For the LDAC, this evolution may include alternative desiccants that retain the performance of lithium chloride but allow less expensive metals to be used for heat transfer surfaces. Several researchers have already proposed alternative liquid desiccants. The following pending or issued U.S. patents describe the application of polymers, salts of organic acids and ionic liquids to LDACs: US5,191,771 (Meckler), US5,846,450 (Atkinson), US20110247494 (Dinnage).
A second possible evolution for liquid desiccant technology is the development of heat and mass exchangers that isolate the liquid desiccant behind a membrane. The membrane is designed to be highly permeable to water so it introduces only a small resistance to the transport of water between the liquid desiccant and the process air. The following pending or issued patents describe technologies that introduce a membrane between the liquid desiccant and the process air: US,528,905 (Scarlatti), WO2014029003 (Lepoudre), US6,684,649 (Thompson), WO200909094032 (Slayzak,Kozubal), and WO2011150081 (Vandermeulen, et al.).
In 2012, NREL successfully tested the membrane-based liquid-desiccant conditioner shown in the photograph on the left that was designed and fabricated by AILR (Kozubal, Woods, Judkoff, Apri l2012). AILR has also designed, fabricated and tested a 500-cfm membrane-based conditioner with water cooled plates (as opposed to the evaporatively cooled plates in the conditioner tested by NREL) that incorporates technology described in AILR's pending patent application (WO2012170887, Lowenstein). The photograph on the right shows a single plate from this water-cooled conditioner.
A word of caution must be introduced when applying membranes to the task of isolating a liquid desiccant from the process air. Membranes can be fouled or otherwise compromised by trace contaminants that may be present in the air or the desiccant. The last photograph on this page shows the "weeping" of lithium chloride through a membrane that was a hydrophobic, microporous, polypropylene film. Although the source of the problem has not yet been identified, the hydrophobicity of the membrane was compromised allowing liquid desiccant to pass through the membrane's pores.