THE PELTIER EFFECT
The Peltier effect is a thermoelectric effect consisting of a physical phenomenon of heat movement in the presence of an electric current. The effect occurs in conductive materials of different natures linked by junctions (contacts). One of the junctions then cools slightly, while the other heats up. This effect was discovered in 1834 by the physicist Jean-Charles Peltier.
The Peltier effect is linked to the transport of entropy by charge carriers (electrons or holes) within the material. So when in the principle diagram above there is an absorption of heat in X and a release in W, this is due to the fact that the electrons or holes lose entropy when passing from material b to material a in W (there is therefore a release of heat), while reciprocally they regain entropy by passing from material a to material b in X (there is therefore an absorption of heat), because there is conservation of energy, it is the first law of thermodynamics.