In most cases, the cold surface temperature is usually given as part of the problem – that is to say that some object(s) is to be cooled to some temperature. Generally, if the object to be cooled is in direct intimate contact with the cold surface of the thermoelectric, the desired temperature of the object can be considered the temperature of the cold surface of the TEM (Tc). There are situations where the object to be cooled is not in intimate contact with the cold surface of the TEM, such as volume cooling where a heat exchanger is required on the cold surface of the TEM. When this type of system is employed, the cold surface of the TEM (Tc) may need to be several degrees colder than the ultimate desired object temperature. The Hot Surface Temperature is defined by two major parameters:
1) The temperature of the ambient environment to which the heat is being rejected.
2) The efficiency of the heat exchanger that is between the hot surface of the TEM and the ambient environment.

These two temperatures (Tc & Th) and the difference between them (∆T) are very important parameters and therefore must be accurately determined if the design is to operate as desired. Figure 3 represents a typical temperature profile across a thermoelectric system.

The third and often most difficult parameter to accurately quantify is the amount of heat to be removed or absorbed by the cold surface of the TEM, (Qc). All thermal loads to the TEM must be considered. These thermal loads include, but are not limited to, the active heat load (I2R) from the electronic device to be cooled and passive heat load where heat loss can occur through any object in contact with ambient environment (i.e. electrical leads, insulation, air or gas surrounding objects, mechanical fasteners, etc.). In some cases radiant heat effects must also be considered.