It is actually simple in principle. Porous adsorbents like zeolite and
activated carbon can adsorb gases evaporated from the adsorbate (water
or methanol, etc.) giving the cooling effect.  Upon being heated, the 
gas-saturated adsorbent bed will give off the gases which are then to be
condensed.  This forms the adsorption refrigeration cycle.  The only problem
is that the COP is very low (0.2 -0.6).  

Max
