The silica gel/water adsorption heat pump (AHP) with an adsorber consisted of fin-type silica gel tube (FST) modules was proposed for producing cold heat energy with temperature below 288 K. Considering the performance of such a silica gel/water AHP, the heat and mass transfer characteristics in the FST module were studied by the proposed model, and the optimal sizes (fin pitch and fin length) of the FST module for obtaining maximum cold heat output were decided. It is found that an AHP using the optimized FST module in the adsorber can produce 2 times cold heat output as much as the AHP using the previous FST module (Fujisawa et al., 2002).