thermoelectric temperature control systems are being used in an increasing number of applications. typical applications of these systems are in thermal regulation of electronic enclosures, recirculating chillers for laser cooling, semiconductor process control and management of patient hypo- and hyperthermia.

thermoelectric coolers (tecs) are essentially solid state devices that pump heat against a temperature differential utilizing electrical energy. based on the peltier effect, each cooler consists of a matrix of thermoelectric p-n thermocouples connected electrically in series (figure 1) and thermally in parallel. a cross section of a thermoelectric cooler is shown in figure 1.

figure 1: a cross section of a thermoelectric cooler.

when positive dc voltage is applied, holes pass from the p-type to the n-type thermoelement and the cold side temperature (t_c) decreases while heat is absorbed. reversing the direction of current results in heating instead of cooling and this is a significant advantage of thermoelectric coolers. several thermoelectric coolers can be configured with common hot and cold sides to make up a thermoelectric heat exchanger. efficient heat removals from the hot and cold sides is a must for good efficiency.

a significant disadvantage of using thermoelectric systems for cooling electronic enclosures has been the dismal level of efficiency. the best thermoelectric systems can only provide around a 35% efficiency rating. however, depending on the application, thermoelectric temperature control systems can be given preference, if size and reliability are the issue.

bellcore[1] specifies that in a 50°c environment, the enclosure temperature cannot exceed 65°c. a passive system would be too large to accommodate such heat removal with only a 15°c rise. a compressor system can handle this heat load but will not provide any cooling under an ac line loss scenario. however, a thermoelectric system can provide adequate heat removal with a 15°c rise or even a 10°c differential in a more effective manner with dc capabilities.

there are numerous advantages to using thermoelectric temperature control systems. tabulated below is a comparison chart between a tec system and compressor system.

roger devilbiss and sathya rajasubramanian
thermotek, inc., 1454 halsey way, carrollton, tx - 75007, usa.
tel: +1 (214) 242 3232 fax: +1 (214) 446 1195

references

1. marlow industries, inc., "reliability of thermoelectric coolers".
2. bell communications research; "generic requirements for electronic equipment cabinets", ta-nwt-000487; issue 2; june, 1993.