Tag Archives: thermoelectric coolers

Industry Developments: Cabinet Cooling Solutions

Critical electronics are routinely housed inside metal cabinets of different dimensions. Although their applications vary, a common issue within these enclosures is excess heat, and the danger it poses to their electronics. This heat can be generated by internal sources and intensified by heat from outside environments.

Cabinet Cooling

The trends toward compact, multi-function electronic controls, variable speed drives, programmable logic controllers, and tightly-packed processors and server racks can also cause thermal problems. Excess heat can adversely affect digital displays, controls, breakers, ICs and PCBs. In most cases this heat can’t be prevented, so it must be removed to ensure the proper function and service life of components and boards.

Issues with excess cabinet heat have been around for decades, and many cooling approaches have been utilized. Among the most popular are air conditioners, vortex coolers and heat exchangers. Each method has benefits and shortcomings, and improvements are continually made by the engineers who design these cooling systems.

Air Conditioners

As cabinet designs adapt to new needs, air conditioners are being designed for tighter spaces, higher performance and lower costs. Today’s ACs include traditional vapor-compression-refrigeration technology, as well as new thermoelectric systems.

IceQube is providing the Qube Series of air conditioners, which the company described as the world’s smallest compressor-based air conditioner and an ideal cooling solution for compact enclosures with high heat loads. The compact air conditioners are available in power coated and stainless-steel housings. [1]

Figure 1. The Qube series of vertical mount air conditioners from IceQube come in widths as narrow as six inches. [1]

The Blade air conditioners series, also from IceQube, is specially-designed for door mount applications on electrical enclosure cabinets. They have a space-saving, ultra-thin designs for use in NEMA type 12, 3R, 4 and 4X cabinet designs. Cooling performance from the Blade ACs is up to 50,000 BTU/hr. [2]

Thermoelectric ACs, also called Peltier ACs, work without compressors or refrigerants. Some feature efficiently-designed fans as their only moving parts to provide effective internal cabinet cooling. These models typically provide lower cooling performance, but enough to meet cabinet cooling requirements.

TECA recently introduced internally mounted thermoelectric air conditioners for enclosure cooling where there can be no external protrusions from the enclosure. Available in five sizes, the new air conditioners can be horizontally or vertically mounted inside an enclosure. Performance ratings range from 155 BTU/hr – 390 BTU/hr. These air conditioners use no refrigerants or compressors and have no moving parts other than their fans. [3]

Figure 2. Internally mounted TECA air conditioners are suited for use where space requirements prohibit external protrusion. [3]

When high levels of temperature drop are needed inside a cabinet, EIC Solutions offers an alternative to compressor-based air conditioners. EIC’s new High Delta T thermoelectric air conditioners provide a maintenance-free, solid-state solution for applications that require a large ΔT in any environment. ΔT is the difference between return air temperature and supply air temperature.

The new ThermoTEC 142 and 146 series air conditioners feature high ΔT capabilities to achieve greater drops from ambient temperatures compared to standard models. [4]

Figure 3. New thermoelectric air conditioners have high ΔT capabilities for greater drops from ambient temperatures than other TEC models. [4]

The 142 series (500 BTU/hr) and the 146 series (1000 BTU/hr) feature rugged, type 304 stainless steel, and NEMA 4X construction.

Another compressor-based air conditioner is the SpectraCool from Hoffman. Its filter-free design reduces clogging that can cause system failures. SpectraCool units feature an energy-efficient compressor and earth-friendly refrigerant. Models are available for up to 20,000 BTU/hr cooling performance.

The Hoffman SpectraCool ACs can also be controlled remotely. Access comes via a unique IP address to each equipped unit. This allows monitoring and control of cooling, heating, alarms, the compressor and the ambient fan. [5]

The company’s Easy Swap adaptor plenums provide a quick and easy way to upgrade the SpectraCool systems and deliver up to 23 percent greater energy efficiency.

Vortex Cabinet Coolers

Vortex enclosure cooling systems work by maintaining a slight pressurization in the cabinet to keep electrical and electronic components clean and dry. Most vortex systems are thermostatically-controlled to keep cabinet temperatures within a specified temperature range.

The core of these coolers is composed of vortex tubes, mechanical devices that separate compressed gas into hot and cold streams. Air emerging from the cold end can reach -50°C, while air emerging from the hot end can reach 200°C. The tubes have no moving parts. [6]

EXAIR Cabinet Cooler systems use vortex tube technology to create a cold air outlet flow which is pumped into an electronic cabinet. As air is pushed into the cabinet the Cabinet Cooler system also provides its own built-in exhaust. There is no need to vent the cabinet. This creates a positive purge on the cabinet to keep out dirt, dust and debris.

Figure 4. The Exair dual cabinet cooler system minimizes compressed air use and produces 20°F air for cabinet cooling. [7]

EXAIR Cabinet Cooler systems are unaffected by vibration, which can cause refrigerant leaks and component failures in traditional air conditioners. They are UL listed for NEMA 12, 4 and 4X integrity and are marked CE for conforming to European Union safety standards.

ITW Vortec, a leader in vortex tube technology and enclosure cooling provides the UL-listed Electric Vortex A/C. The Electric Vortex A/C is an electric thermostat cabinet cooler with plug-and-play functionality. Unlike traditional electric thermostat enclosure coolers which require additional wiring and piping to properly install, the new Electric Vortex A/C comes pre-wired, requires no additional wiring and just needs an outlet within six feet of the unit.

This new solution eliminates the need for an external solenoid valve and the piping traditionally used to install other enclosure cooler solutions. An electric thermostat allows the user to set the desired temperature to be maintained in the enclosure. The cooler will only turn on when necessary, conserving energy from compressed air usage.

Figure 5. The Electric Vortex air conditioner from Vortec eliminates the need for an external solenoid valve. [8]

Heat Exchangers

Using heat exchangers as cabinet thermal solutions can provide an enhanced solution in terms of performance, cost-effectiveness and smaller size designs. There are both air-to-air, and liquid-to-air models.

Air-to-Air Exchangers

Air-to-air heat exchangers are a proven and dependable cooling method that relies on passive heat pipe or folded fin impingement cores to disperse the heat from within cabinet enclosures to the outside ambient air.

Figure 6. Air-to-air heat exchangers transfer heat without moving parts. [9]

The Stratus line of air-to-air heat exchangers from AutomationDirect includes 120 VAC and 24 VDC models. The series has a closed-loop cooling system, using the heat pipe principle to exchange heat from inside to outside the cabinet.

Each heat pipe has an evaporator section and a condenser section. These are separated by a permanent baffle to provide a closed loop. The coil systems use aluminum end plates and baffles, which improve conduction and reduce corrosion for longer life. The Stratus heat exchangers are available in models for NEMA 4 and 4X enclosures. Units come in three frame sizes (compact, deep, and tall) with up to 72 watts capacity. They are equipped with two circulating fans with sealed overload protectors. [9]

Liquid-to-Air Exchangers

Liquid-to-air heat exchangers provide cooling through a closed-loop system. They are designed for use where heat dissipation needs are too great for natural or forced air convection systems, or where remote heat dissipation is required. Much of their higher cooling performance comes from using fluids with much higher thermal conductivity than air. Typical applications include cabinets, MRI and process cooling.

Figure 7. The WL500 water-cooled, liquid-to-air heat exchanger has a high-pressure pump for fast flow rates. [10]

Conclusion

Cabinet-housed electronics are susceptible to excess heat generated from within along with heat from outside environments. Thus, keeping the electronics cool inside cabinets is essential to maximizing internal device life cycles. Numerous cooling methods are available, including air conditioning, vortex cooling, and heat exchangers.

Each of these methods has its own methodology, such as the choice of air or liquid cooling, to provide options for meeting cooling requirements. A thorough awareness of options, application requirements, and resources should lead to the best cabinet cooling solutions

References
1. IceQube, http://www.iceqube.com/air-conditioners/qube-series-mm/
2. IceQube, http://www.iceqube.com/blade-series-products/blade-series-air-conditioners/
3. TECA Corporation, http://www.thermoelectric.com/2010/ad/internal-mounted.htm
4. EIC Solutions, Inc., http://www.eicsolutions.com/
5. Hoffman, http://www.pentairprotect.com/hoffman/
6. Vortex Tube, https://en.wikipedia.org/wiki/Vortex_tube
7. EXAIR, http://www.exair.com/ https://www.youtube.com/watch?v=CoxzwJmbyxY
8. ITW Vortec, https://www.vortec.com/p-284-electric-vortex-ac.aspx
9. AutomationDirect, http://www.automationdirect.com
10. Laird, http://www.lairdtech.com/products/wl-500

Electronics Cooling with Thermoelectric Assemblies

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.

Thermoelectric Assemblies

Fig. 1. This Air-to-Air TEA has a max cooling power of 83 Watts and a temperature range of -10°C to 70°C. (Advanced Thermal Solutions, Inc.) [1]

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. [2]

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. [3]

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. [4]

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.

Fig. 2. Air-to-Air TEA can provide up to 200 W of cooling. (Kryotherm) [5]

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. [6]

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.

Fig. 3. The plate on Air-to-Plate TEA is a mounting surface for components, boards or test specimens. (Adcol Electronics) [7]

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.

Fig. 4. A Liquid-to-Air TEA where the heat is absorbed by a heat exchanger and is pumped by thermoelectric modules to cooling heat sinks and fans. (Advanced Thermal Solutions, Inc.) [8]

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.

Figure 5. This Medical Laser Uses Thermoelectric Assembly Cooling to keep Optics Stable and at Peak Performance. [9]

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. [10]

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. [11]

Figure 6. Thermoelectric cooling and heating is used in this automobile cup holder. [12]

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. [13]

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. [14]

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. [15]

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. [16]

For more information about thermoelectric assemblies or modules from ATS, visit https://www.qats.com/Products/TEC.

References
1. https://www.qats.com/Products/TEC/TEC-Assembly/ATS-WFF-150W-12-C
2. https://www.electronics-cooling.com/2016/10/thermoelectric-assembly-cooling-for-temperature-control-in-co2-incubators/#
3. https://www.marlow.com/how-do-thermoelectric-coolers-tecs-work
4. https://www.lairdtech.com/sites/default/files/public/solutions/Laird-ETS-Thermoelectric-Assemblies-Handbook.pdf
5. http://kryothermtec.com/catalog-of-thermoelectric-cooling-assemblies-of-air-to-air-type.html
6. http://www.amstechnologies.com/products/thermal-management/thermoelectric-technologies/thermoelectric-assemblies/air-to-air-thermoelectric-assemblies/
7. http://www.peltier-thermoelectriccooler.com/sale-9776416-thermoelectric-cooling-plate-peltier-cooling-assembly-direct-voltage.html
8. https://www.qats.com/Products/TEC/TEC-Assembly/ATS-FW-72W-12-C
9. https://www.medicaldesignandoutsourcing.com/lairds-thermoelectrics-offer-lower-cost-ownership-medical-laser-cooling-applications/
10. Thermoelectric Solutions, http://www.supercool.se/, Sweden
11. https://www.lairdtech.com/sites/default/files/public/solutions/Laird-ETS-Active-Cooling-of-Optical-Transceivers-Application-Note.pdf
12. http://www.amstechnologies.com/solutions/solution-single-news/article/energy-balance-of-automotive-thermoelectric-cup-holder/
13. https://www.marlow.com/industries/automotive
14. https://www.lairdtech.com/solutions/thermal-management/consumer/beverage-thermal-management-solutions
15. https://globenewswire.com/news-release/2015/07/28/755640/10143440/en/Thermoelectric-Modules-Market-Expected-to-Reach-US-763-5-Mn-by-2022-Globally-Transparency-Market-Research.html
16. https://www.idtechex.com/research/articles/thermoelectric-generators-a-750-million-market-by-2022-00004631.asp

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 ats-hq@qats.com.

The Monthly Qpedia is Out!

Qpedia_Aug13_coverThe monthly issue of Qpedia has just been released and can be downloaded at: http://www.qats.com/Qpedia-Thermal-eMagazine/Back-Issues.

This month’s featured articles include:

Application of TECs to Thermal Management of 3D ICs

From the thermal perspective, 3D stacked chips pose different challenges than what has been experienced in 2D packaging. For example, the heat dissipation of 3D ICs is highly non-uniform and multidirectional, due to the intrinsic chip architecture and the available real estate. When cooling at sub-ambient temperatures is necessary, the small footprint of a 3D chip becomes an impediment to deploying a cooling solution. Additionally, precision temperature control becomes difficult, since the surface to be controlled may be buried deep in the 3D stack. In response to cooling concerns about 3D ICs, this article presents a review of methods available for cooling 3D ICs to sub ambient temperatures using TECs.

Challenges in Testing Thermal Interface Materials

When choosing a thermal interface material (TIM), most of the time we look at the datasheet and find the thermal impedance if it is a solid material or the thermal conductivity if it is grease. Then, we calculate the thermal resistance and temperature rise with those numbers. But, how do we know that a TIM is performing as advertised? Can we really tell if one TIM will perform better than another, based on their specs? Additionally, the material presented in this article suggests that the data printed in TIM datasheets should be evaluated carefully to ensure that the testing procedures are similar to the actual application. Furthermore, even with the existing standards, many variables still exist.

Industry Developments: Portable Cooling Systems

Buildings and rooms constructed to house data centers are getting larger, more congested and warmer. Many of these structures have sophisticated thermal management systems featuring high-powered coolers or harnessing cold local water or air. For some needs, however, a portable cooling system can provide a much simpler and less costly solution. These systems can deliver direct cooling relief to equipment hot spots, and some can lower a room’s temperature when a central cooling system is inadequate or nonexistent.

Technology Review: Enhancing Heat Transfer on Surfaces

In this issue our spotlight is on enhancing heat transfer on surfaces. There is much discussion about its deployment in the electronics industry, and these patents show some of the salient features that are the focus of different inventors.

Cooling News featuring the latest product releases and buzz from around the electronics cooling industry.

Download the issue now and see why over 18,000 engineer’s subscribe to Qpedia. Click here to subscribe Subscribe to ATS

Don’t forget the Qpedia Book Series Promotion that coolingZONE is currently running! Save 25% off the hardcover books that are a must have in every engineer’s library!

ATS Labs Thermal Management White Paper: Using Thermoelectric Coolers in Electronics Cooling

Thermoelectric coolers (also known as thermoelectric device or thermoelectric module) are semiconductor modules which use the Peltier Effect to create a heat flux between the junctions of two different types of materials. Named after French physicist Athanase Peltier, the Effect shows that a temperature differential is created when DC current is applied across two dissimilar materials. (It is one of the three thermoelectric effects; the others are the Seebeck Effect and Thomson Effect)

A typical thermoelectric cooler is manufactured using two thin ceramic wafers with a series of N and P doped bismuth-telluride semiconductor material sandwiched between them. The ceramic material adds rigidity and the necessary electrical insulation. The N type material has excess electrons, while the P type material has a deficit of electrons. One N and one P make up a couple, as shown in Figure 1.

Thermoelectric Cooler for thermal managementWhen a DC current is applied to the circuit, the thermoelectric device can work as a cooler or heater depending on the currents direction. A thermoelectric cooler (TEC), or solid state heat pump transfers heat from one side of the device to the other side against the temperature gradient. Many products use thermoelectric coolers, including small refrigeration systems, CCD cameras, laser diodes and portable picnic coolers. They are also used in the thermal management of microprocessors, memory modules and other electronic devices.

ATS’s white paper covers much more on this topic, and you can get your own copy for free, by clicking to, “Using Thermoelectric Coolers in Electronics Cooling“.