By Norman Quesnel
Senior Member of Marketing Staff
Advanced Thermal Solutions, Inc. (ATS)
Thermoelectric assemblies (TEA) efficiently control temperature in many applications across a variety of industries. For example, TEA are used for cooling laser diode packages in optics, lasers in medical and industrial instrumentation, and bio-sample storage units for medical diagnostics. They are also used to cool analytical instruments and batteries in automotive and telecom applications.
Depending on the model, TEA provide cooling capacity from approximately 10-400 Watts and can cool by removing heat from control sources through convection, conduction, or liquid means. 
Thermoelectric assemblies work according to the Peltier effect, which was initially discovered by scientists in 1834. The Peltier effect describes the temperature differential that is created across two electrical junctions when an electrical current is applied. As the current flows, heat is removed from one junction and deposited on the other. This means that TEA could be used for cooling or heating depending on the particular needs of the application. 
TEA offer several advantages over other cooling technologies. TEA are capable of cooling to well below ambient, while protecting electronics inside enclosures from outside contaminants and moisture because they do not require an air exchange with the outside environment, unlike, for instance, conventional fan trays. TEA also offer precise temperature control; many can provide a temperature accuracy of within 0.01˚C under steady-state conditions.
Compared to conventional compressor-based cooling systems, TEA are compact in size and lighter in weight. Their solid-state operation allows mounting in any orientation, without noise or vibration. They do not use refrigerants or CFCs, are Restriction of Hazardous Substances (RoHS) compliant, and their simple design does not require field servicing. 
The basic configurations of TEA are:
Air-to-Air Thermoelectric Assemblies
Air-to-air TEA are compact devices that will cool a local environment through convection. Heat is absorbed and pumped from one side of the thermoelectric assembly (i.e. cold side) by thermoelectric modules and dissipated from the other side of the assembly (i.e. hot side) to the environment by heat sinks and highly-efficient DC fans. Air-to-air TEA are often used when it is better to circulate cooled air rather than use direct contact with a cold plate.
Typical applications include regulating temperature in small electronic cabinets or enclosures. They provide quiet and precisely-controllable cooling for smaller capacities typically from 20 up to around 200 W.
Many air-to-air TEA are designed with a modular approach so, if needed, multiple coolers can be employed to achieve the cooling requirement. Several OEM can also develop customized air-to-air TEA designed for a system’s specific boundary conditions. 
Air-to-Plate Thermoelectric Assemblies
Air-to-plate thermoelectric assemblies are heat exchangers for removing heat from a plate attached to its cold side. Also called direct-to-air devices, the objects to be cooled down are mounted on a metallic plate on the cold side of the assembly. Heat is pumped through TEC modules and dissipated to the environment through heat sinks and DC fans on the hot side of the assembly.
Typical applications for air-to-plate TEA include cooling laser diode modules and temperature controlling bioreagents. Laser diodes need precise temperature stabilization at room temperature and higher heat loads. Bioreagents and process fluids often need to be temperature controlled at different stages over a wide temperature range.
Air-to-Liquid Thermoelectric Assemblies
Air-to-liquid thermoelectric assemblies offer dependable, compact performance. Heat is absorbed through a liquid heat exchanger, pumped through a series of thermoelectric modules and dissipated to the air through high-density heat sinks with integral fans. The heat exchanger is designed to be part of a liquid recirculating system and requires a pump.
The liquid circuit typically uses a recirculator to remove the heat into the ambient air. An air-to-liquid TEA system allows for precise temperature control of the fluid and has been the solution for many devices including those used for cooling lasers and medical applications such as blood preservation, patient rehabilitation pads and blankets. To improve heat transfer, turbulators can be inserted into the liquid channels of the heat exchanger.
Common TEA Applications
Some of the most common areas where TEA provide cooling are in laser systems, biomedical devices, telecommunications, automotive, battery cooling, and the food and beverage industry.
In medical applications, thermoelectric assemblies provide immunoassay reagent cooling (to detect or measure specific substances in the reagents), temperature control for in vitro diagnostic specimens, and cooling of genome sequencing reagents. Some air-to-air TEA help maintain specimen receptacles and reagents at very specific temperatures to ensure diagnostic test reliability and accuracy. TEA keep temperatures cool in bio-units for storing and transporting insulin, tissue and human organs.
Some liquid-to-air TEA are also used for cooling tissues and other body areas during laser or microwave thermo therapy. 
In telecommunications applications, a common use of TEA is to help cool small form-factor (SFP) transceivers. These optical transceivers transmit data over long distances in outdoor applications. An SFP unit contains a temperature sensitive laser diode that can transmit data a kilometer away, but only if the diode is kept below 70°C. Many other kinds of lasers also feature TEA for cooling. TEA help prevent wavelength drift in laser transmission (DWDM), pumped laser (EDFA), avalanche photodiode (APD) and CATV laser systems. 
In the automotive industry, TEA and thermoelectric modules are used in the individual cooling and heating of car seats. The seats in the front and rear cabin can be heated or cooled per the passengers’ preferences. An emerging application in the automotive industry is the temperature-controlled cup holder. Based on a switch setting, thermoelectric devices will preserve the warmth or chill of a beverage by temperature regulation of the cup holder. 
New hybrid and electric vehicles rely on costly battery-operated systems that often require maintenance or repair when exposed to temperatures outside a narrow, stringent operating range. Recently developed devices utilize thermoelectric modules to stabilize the temperature of a vehicle battery to achieve maximum performance in all environments. This increases battery efficiency and extends battery life.
Perhaps the most well-known applications for TEA are small refrigerators, beer chillers and wine cellars. TEA adjust the temperature inside beverage dispensing and vending machines, helping ensure freshness and the desired taste. Other applications are in the food catering industry, keeping food temperatures under control in mobile and open-air conditions. These include service and transport carts, serving trays, temperature-controlled preparation surfaces and cold plates. 
A report released by Transparency Market Research in 2015 said that the market for thermoelectric modules, which are components of TEA, would grow to as much as $763.5 million by 2022 driven by growth in the Asia Pacific market and manufacturers focusing on quick and cost-effective modules to meet specific customer needs. It also indicated that while bulk thermoelectric modules had 71 percent of the market share in 2014, the expectation was for micro modules to grow at a faster rate during the analysis period. 
The report called telecommunications, medical, aerospace, and industrial applications the key market segment for bulk modules, but micro modules would target growing consumer electronics, medical and laboratories, automotive, detectors and sensors, and energy harvesting industries.
A 2012 IDTechex report added that the market for thermoelectric generators could be as high as $750 million by 2022 with wireless sensors and wireless networks, waste heat recovery systems in vehicles, consumer applications from mobile phones to cooking sensors to sensory apparel, and military and aerospace leading this growth. 
For more information about thermoelectric assemblies or modules from ATS, visit https://www.qats.com/Products/TEC.
10. Thermoelectric Solutions, http://www.supercool.se/, Sweden
For more information about Advanced Thermal Solutions, Inc. (ATS) thermal management consulting and design services, visit https://www.qats.com/Consulting/Custom-Cooling-Solutions or contact ATS at 781.769.2800 or firstname.lastname@example.org.