Thermoelectric modules are solid-state devices (no moving parts) that convert electrical energy into a temperature gradient, known as the "Peltier effect" or convert thermal energy from a temperature gradient into electrical energy, the "Seebeck effect." By applying a low voltage DC power source to a TE module, heat will be moved through the module from one side to the other. The TE modules are ideally suited to a wide variety of applications where space limitations and reliability are paramount.
　　The thermocouples, which are made up by P type and N type elements, play the same role of the common compressor, both thermoelectric coolers and mechanical refrigerators are governed by the same fundamental laws of thermodynamics and both refrigeration systems, although considerably different in form, function in accordance with the same principles.

　　In a mechanical refrigeration unit, a compressor raises the pressure of a liquid and circulates the refrigerant through the system. In the evaporator or "freezer" area the refrigerant boils and, in the process of changing to a vapor, the refrigerant absorbs heat causing the freezer to become cold. The heat absorbed in the freezer area is moved to the condenser where it is transferred to the environment from the condensing refrigerant. In a thermoelectric cooling system, a doped semiconductor material essentially takes the place of the liquid refrigerant, the condenser is replaced by a finned heat sink, and the compressor is replaced by a DC power source. The application of DC power to the thermoelectric module causes electrons to move through the semiconductor material. At the cold end (or "freezer side") of the semiconductor material, heat is absorbed by the electron movement, moved through the material, and expelled at the hot end. Since the hot end of the material is physically attached to a heat sink, the heat is passed from the material to the heat sink and then, in turn, transferred to the environment.

Features and advantages of TE modules (compared with compressor):
　　1 No refrigerants required, environment friendly
　　2 Localized cooling: it can cool special element in a limited space, the dimension and cooling power can be made on the basis of clients' requirements
　　3 small sizes, light weight, save space
　　4 low noise, no abrasion, minimal vibration, operate safely, easy maintenance
　　5 heating or cooling depending on current direction
　　6 can be a power generator, reliable converter of heat into electricity
　　7 fast temperature response, accurate temperature control is possible.
　　8 Applying the common power supply: Batteries, linear and switched DC power supplies are all appropriate sources.