The release of water from the desiccant occurs at a lower pressure than its absorption. Energy is consumed in maintaining that lower pressure by pumping away th

The release of water from the desiccant occurs at a lower pressure than its absorption. Energy is consumed in maintaining that lower pressure by pumping away the water vapor as it is released (presumably, it is vented outdoors.) From the patent: [The vacuum pump] is used to provide modest compression to raise the vapor pressure sufficiently to condense to liquid water. Because the compression work is only done on the water vapor, this minimizes the energy consumption. Lastly, the condensate is pumped up to atmospheric pressure for discharge to a storage vessel (this consumes a trivial amount of additional energy). Update: The patent also implies that the high efficiency of any given device of this type may only obtain over a limited range of operating conditions: Sorbents optimized for a 43.degree. C., 60% RH condition are likely to perform poorly and result in much higher power consumption at the more challenging 27.degree. C., 10% RH humidity condition and vice versa.