There are important parallels between a liquid-desiccant air conditioner (LDAC) and the thermally driven technology now most commonly used for cooling: the lithium-bromide absorption chiller. For both technologies a strong halide salt solution absorbs water vapor to create an atmosphere with a low water vapor pressure. For the LDAC, this atmosphere is dry ambient air that can serve the latent load on a building. For the absorption chiller, this atmosphere is within a vacuum chamber where water evaporates to cool a circulating fluid loop.
For both the LDAC and the absorption chiller, the weakened salt solution is "regenerated" with heat. Since the absorption chiller is a "closed" system, the water released by the hot salt solution is condensed and returned to the vacuum chamber where it again evaporates to produce the cooling effect. The LDAC, being an "open" system, simply rejects the released water back to ambient (preferably at a location where this humid exhaust air does not mix with ventilation air that might be brought into the building). A more detailed description of the operation of an LDAC appears in the Liquid Desiccant Tutorial.
The first-generation LDACs manufactured by AILR and its commercialization partner were similar to the 6,000-cfm unit shown in the neighboring figure. These LDACs, which were first installed in 2009, used plastic-plate heat exchangers for both the conditioner and regenerator.
Since the 2009 design of the first-generation LDACs, AILR has advanced its wicking-fin technology to a point where this technology is a lower cost, more robust alternative to plastic-plate heat exchangers for the conditioner and regenerator of an LDAC. The first wicking-fin LDAC began operating in October 2014.
Gas-Fired Flat-Plate LDAC Specification
- 6,000 cfm outdoor air
- 300 lb/h water removal (26 tons latent)
- 435,000 Btu/h thermal (CHP)
- 530,000 Btu/h natural gas (one-stage regen)
- 300,000 Btu/h natural gas (two-stage regen)
- 5 kW pump and fan loads
- 84" (W) x 108" (L) x 72" (H)
- 4,100 lb
- 25 ton cooling tower mounted separately