All liquid-desiccant air conditioners require a regenerator--the component that concentrates the dilute desiccant by removing excess water.  The simplest regenerator is a single-stage scavenging-air regenerator in which the desiccant is heated to evaporate water into a scavenging air stream.  When regenerating lithium chloride to a high concentration, this regenerator will have a thermal COP of between 0.6 and 0.8 (when it is used with an air-to-air heat exchanger that preheats the scavenging air).

Multiple-effect boilers are commonly used to increase the efficiency of separation processes such as the regeneration of desiccant.  Their application to removing water from the lithium-bromine brine in absorption chillers has increased the COP of these cooling systems from about 0.6 to 1.0.

Although a double-effect boiler can be used to regenerate desiccant, a simpler approach, which achieves almost the same COP, is the two-stage 1½-effect regenerator.  As shown in the preceding figure, heat is applied to a first-stage atmospheric-pressure boiler.  The steam that leaves this boiler has a saturation temperature of 212^oF.  It is used to heat a secondary hot-water loop, the heating occurring in the direct-contact condenser that is located between the boiler and the scavenging-air (S-A) regenerator.  This secondary hot-water loop is then the heat source for the second-stage Scavenging-Air Regenerator.

We are now integrating a 1½-effect regenerator into our LDAC.  When complete, an LDAC that supplies air at 20% rh is projected to have a gas-fired COP of 1.05.  Field tests of this advanced LDAC are scheduled for the summer of 2011.