Keeping electronics cool in an industrial application is essential to maximizing their lifecycle, reducing capital expenses and keeping operations running continuously without interruption. Heat can significantly damage and reduce the life of industrial electronics, which in turn not only impacts the performance of electronics but also affects manufacturer warranties.

Identifying Heat Sources in Industrial Enclosures

According to the Digital Equipment Corp., the life expectancy of most electronics is reduced by half with every 18°F (10°C) rise above room temperature (figure 1). Heat can be generated internally by electronic components and intensified by external sources. Uncooled components inside an enclosure can generate as much trapped heat as a home furnace.

There are a variety of sources of heat inside an enclosure, including:

• Variable-frequency drives (VFDs).
• Servo drives.
• Programmable logic  controllers (PLCs).
• Starter kits.
• Power supplies.
• Inverters.
• Indicator lights.
• Transformers.

In addition to heat sources inside an enclosure, heat is also generated from sources outside the enclosure. These can include:

• Solar heat gain.
• High ambient temperature.
• Welding processes.
• Paint oven.
• Blast furnace.
• Foundry equipment.

With the increasing deployment of smaller, more powerful and more portable mission-critical electronics into increasingly harsh environments and conditions, cooling and thermal management are primary engineering considerations. The density of modern electronics in smaller enclosures intensifies heat issues that can compromise component performance. In today’s market and for the foreseeable future, the trend, known as Moore’s Law, is moving toward increasing levels of heat in electronics — not less — because the desire for more information-processing capacity and speed continues to grow. There is no guarantee that an application that did not require much — if any — cooling in the past will not need cooling in the future. As many newer applications typically provide more functionality, it is more likely they will require some form of cooling as a result.

There are a variety of ways that the electronics trapped inside of an enclosure can be cooled; however, this article will cover the three primary methods:

• Conductive cooling.
• Open-loop cooling.
• Closed-loop cooling.

Conductive Enclosure Cooling Provides Passive Cooling to Electronics

Conductive enclosure cooling is a passive method to cool electronics. It simply allows the heat to be transmitted from the interior to the exterior through conduction, convection and radiation. Passive cooling works well with electronic systems that have small heat loads (less than 50 W) with cool air surrounding the enclosure. If heat is an issue, one option with this type of cooling is to increase the enclosure size to create more surface area to speed the transfer of heat. However, growing the enclosure size is not a practical solution because of space limitations and the greater heat loads associated with today’s high-powered electronics.

Open-Loop Cooling Manages Heat in Enclosure Cooling by Ventilation

An alternative to conductive enclosure cooling, open-loop cooling is an active method to manage heat in electronic applications. This type of cooling ventilates fresh air through the enclosure, exhausting heat away from the hot components. Open-loop cooling may be used when the electronics system is deployed in a relatively clean and cool environment such as an office building, data networking center or light-duty factory. Some open-loop cooling solutions such as filter fans utilize filters to protect the inside of an enclosure against dust, but because all open-loop solutions utilize ambient air to cool, they can potentially expose enclosed electronics to harmful elements such as dirt, water, metal filings and corrosive fumes. There are multiple options to cool electronic enclosures with fresh air, including filter fans, fan trays, motorized impellers, blowers and direct air cooling systems (DACS).

Filter Fans. Filter fans cool a range of heat loads in applications ranging from industrial drives to process equipment and controls. There are a variety of filter fans available to accommodate diverse applications, with airflows ranging from 16 to 571 cfm (28 to 970 m³/hr). Operators can also select from Type 12, Type 3R and Type 1 fans to satisfy diverse environmental requirements.

Filter fans are a flexible open-loop cooling solution with models available in multiple configurations, including side-mount, top-mount and shallow-depth options to fit tight spaces. Reverse airflow options also are available to push or pull air through higher static pressure environments.

DACS. Direct air cooling systems provide flexible, effective heat removal for outdoor enclosures in applications such as outdoor telecommunications equipment, industrial automation, outdoor kiosks and displays, and outside plant (OSP) applications. Featuring hydrophobic filters or standard MERV 12 filters, DACS protect against outdoor elements such as water, dust, bugs and rain. For specific applications, DACS are a cost-efficient alternative to closed-loop cooling solutions, utilizing quiet, fan-based technology to draw filtered ambient air into the enclosure to dissipate heat.

Closed-Loop Cooling Seals the Electronic Enclosure and Recirculates Cooling Media

Closed-loop cooling is another active method to cool electrical components. This type of thermal management maintains the seal of the enclosure — using an air conditioner or heat exchanger as examples — to remove heat from inside the electronics enclosure. Closed-loop solutions do not allow ambient air to enter the enclosure.

Closed-loop cooling is generally required when the electronics application includes one of the following:

• Operates in high temperatures, typically over 95°F (35°C).
• Deployed in a harsh environment such as an outdoor telecommunications base station, wastewater treatment plant, metal working operation, oil rig platform, paper mill or foundry.
• Generates a high heat load from its own components, usually more than 500 W.

There are multiple options for closed-loop enclosure cooling, including air conditioners, air-to-air heat exchangers, air-to-water heat exchangers, thermoelectric coolers and vortex coolers.

Air Conditioners. Air conditioners are suitable for applications when the temperature inside the enclosure must be maintained at or below ambient temperature; humidity must be removed; or a moderate-to-high heat load is being produced by the electronic system. The cooling capacity of an air conditioner should match or exceed the amount of total heat load generated by the electronic system.

It is important to select an air conditioner with an energy-efficient, reliable cooling design. To meet diverse indoor and outdoor applications ranging from low-profile cabinet cooling to large cabinet cooling, air conditioners are available in a variety of sizes and cooling capacities.

Air-to-Water Heat Exchangers. Air-to-water heat exchangers are an efficient, maintenance-free and low-noise solution for cooling indoor enclosures in industrial applications. Utilizing a customer-supplied water source, this cooling solution is unaffected by airborne contaminants because no moving parts are exposed to the environment. Air-to-water heat exchangers are suited for applications exposed to high-ambient temperatures or extremely dusty and dirty conditions that make traditional air conditioners susceptible to mechanical failures.

Air-to-Air Heat Exchangers. Air-to-air heat exchangers can be used to transfer heat from inside the enclosure to the outside atmosphere when the electronic components can operate at a temperature above the ambient air temperature; humidity is not a factor; or a low-to-moderate heat load is being produced by the electronic system. This type of closed-loop cooling is an efficient, maintenance-free and low-noise solution for cooling enclosures in industrial environments.

Thermoelectric Coolers. Suited for cooling small indoor and outdoor enclosures in demanding or low-maintenance environments, thermoelectric coolers have a compact design with no refrigerant, compressors or filters required for operation. Thermoelectric coolers use Peltier effect cooling capacities to efficiently remove heat around critical electronics within an enclosure.

In comparison to conventional refrigerant systems, thermoelectric coolers offer greater mechanical simplicity with no moving parts or liquids, a smaller footprint and less maintenance. Thermoelectric coolers are suitable for climate-controlled applications in compact spaces to maintain a consistent temperature.

Vortex Coolers. Powered by compressed air, vortex cooling systems generate chilled air to cool small enclosures without refrigerants or moving parts. These systems provide reliable, low-maintenance operation in harsh and dirty indoor or outdoor environments.

 In conclusion, heat damages and reduces the life of industrial electronics, making it critical to keep electronics cool in virtually any industrial application. While it is important to understand how to properly cool electronics within an enclosure, it is also valuable to take into account specific considerations when selecting an enclosure cooling solution. This topic will be covered in an upcoming  issue.