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.
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