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Electronic conductivity of the metallic element is connected to the switching element of the hole
Thermoelectric cooling devices
   Using the Peltier effect can be to get cold.
   The main functions of the thermoelectric cooling device performs a battery of thermocouples composed of semiconductors with possible high thermoelectric properties. Thermocouple is called cross-connected with each other two elements - the electron and hole. Electronic conductivity of the metallic element is connected to the switching element of the hole, etc. (Fig. 1). Of these thermocouples can be a battery, although there are cooling devices, and one thermocouple.

                                                                    Fig. 1
   With the passage of electric current through the battery system of a junction is cooled, while the other heats. If you change the current direction in the respective junctions of heat will change the absorption and vice versa.
The effectiveness of the cooling device determines the ratio
K = Q / W
This is essentially efficiency.
   At a given temperature difference at the hot and cold junctions of K is completely determined by the value z = α ^ 2 σ / χ, where α - the coefficient of electromotive force, σ - electrical conductivity, χ - the coefficient of thermal conductivity.
In metals, K is very small so the cooling devices use semiconductors.
   The temperature of the cooled (junction) can be adjusted by changing the current flowing through the thermocouple. With the increase of the current amount of heat absorbed by the Peltier phenomenon is increasing. However, the current can not give too much, since increasing the current increases and the Joule heat is released.
   Peltier heat is proportional to the current Q = PIt, while the Joule current is proportional to A = I ^ 2 Rt.
   For maximum cooling is necessary to select the optimal value of the current at which the Peltier heat (absorbed) exceeds the maximum allocated Joule heat.