A liquid-desiccant system can have a higher regeneration COP than a comparable solid-desiccant system, the advantage being quite dramatic when the liquid-desiccant system uses a two-stage regenerator. As shown in the neighboring figure, weak desiccant enters the gas-fired heat exchanger of a boiler. The desiccant boils within the heat exchanger and a mixture of steam and strong desiccant leave the heat exchanger and enters a spin separator. Concentrated desiccant leaves at the bottom of the spin separator, and steam at the top. The steam becomes the thermal source for additional regeneration in a conventional scavenging-air regenerator. Thus, each unit of energy supplied to the regenerator does double duty: once to remove water from the desiccant in the boiler and once to remove water in the scavenging-air regenerator. Whereas a scavenging-air regenerator operating on 200 F hot water supplied by an 80% efficiency gas-fired water heater might have a gas-based COP of 0.59, the COP for the two-stage regenerator will be 1.08.
