Thermoelectric modules are semiconductor-based components that act as small heat pumps.
If a typical single-stage thermoelectric module was placed on a heat sink maintained at room temperature, and the module then was connected to a suitable battery or other DC power source, the "cold" side of the module would cool down to approximately -40oF (-40oC). At this point, the module would be pumping almost no heat and would have reached its maximum rated temperature differential (∆T). If heat was added gradually to the module's cold side, the cold-side temperature would increase progressively until it eventually equaled the heat sink temperature. At this point, the thermoelectric cooler would have attained its maximum rated heat pumping capacity.