The Peltier effect is the presence of heating or cooling at an electrified junction of two different conductors. A small Peltier device can usually be found in a hot & cold water dispenser. Peltier device works by transferring heat from one side to another, in which the action is reversible. The effect is one of the thermoelectric effect, when a current is flow through a junction between conductor A and conductor B, heat may be generated, or removed at the junction. The heat generated at junction per unit time is equal to:

Where   () is the Peltier coefficient of both conductors, and I is the current flowing through.

The effect may only has 2% efficiency in practice (up to 5% in theory), so at this stage cooling or heating objects from electricity is still sub-optimal and can waste a lot of energy. See references down below.

References:

http://www.eng.fsu.edu/~dommelen/quantum/style_a/nt_pelt.html

http://rimstar.org/science_electronics_projects/peltier_effect_module_cooling_efficiency_test.htm