Peltier modules are said to be less efficient than conventional air conditioners. Can a medium like moving cold water over the heat sink increase the efficiency of a peltier module? By how much? Another ideas is to bury the heat sink deep in the ground to cool the hot side through conduction instead of convection.
Be careful: "efficiency" usually means the ratio of energy applied to energy removed from the "cold side" object. Since a Peltier junction has a fixed delta-T , you won't get any colder by increasing the heat-sink capability. You will get to the cold limit faster, or even get to a lower temperature if you use cold water instead of room-temp air.
The only way to get a greater delta-T is to stack junctions.
BTW, there's a pretty good discussion of Peltier coolers here , where the practical limits of drive current are explained.