How to protect electrical enclosures

A helpful tool to get a better understanding of enclosure cooling capacity needs is a heat load calculator.

To combat system failure, it’s crucial that cabinets are equipped with an enclosure cooling system. Many types of enclosure cooling devices are available: passive cooling types (fans, blowers, heat sinks, and heat exchangers) and active types (air conditioners, thermoelectric devices, and vortex coolers). There are pros and cons to each method, depending on what the specific application is. It’s key to consider the following factors when selecting an enclosure cooling product: heat load, enclosure location, and solution type.

Heat load

The most important thing to consider when selecting an electrical enclosure cooler is the unit’s total heat load, which is made up of two main components. First is the internal heat load; this is the heat that is generated by the electric components inside the enclosure. Second is the external heat load; this is the amount of heat that is either gained or lost through the walls of the enclosure.

The internal heat load can be determined in three different ways:

1. The user knows the amount of heat that the electronics create (in either watts or btu/h).
2. The user knows the total power that all the electric components consume, and then estimates that about 10 to 15% of this is generated as heat load (this is assuming electronic efficiency is between 85 to 90%).
3. The user measures the existing temperatures inside the enclosure at the top of the unit and the existing temperature outside of the enclosure. The difference between these temperatures, along with the total surface area of the enclosure that is subject to the temperature difference, allows for the calculation of the internal heat load.

If the desired temperature inside the enclosure is less than the temperature outside the enclosure, then there is a heat load gain in the enclosure. Heat load gain depends on the difference in temperature, the amount of surface area that is subject to the temperature difference, the thickness of the enclosure walls, whether the enclosure is insulated, and the enclosure material. In this calculation, the external heat load is then added to the internal heat load to determine the total heat load.

If the desired temperature inside the enclosure is greater than the temperature outside the enclosure, there is a heat load loss from the enclosure. This loss is then subtracted from the internal heat load to get the total heat load.

Enclosure location

When selecting an enclosure cooler, it’s important to consider what type of environment the unit will be placed in. The effects of the sun and heat were covered already in this article, and the outside elements and operation hazards need to be considered as well.

• Outside: If an enclosure is subject to the outdoors (think rain, wind, ice, and frost) it’s important that the enclosure cooling system has a NEMA 4 or 4X rating. This is important to ensure that the interior of the enclosure remains dry and clean.
• Inside general: When placed indoors, and not subjected to a washdown operation or hazardous environment, typically a NEMA 12 enclosure cooler is suitable.
• Washdown: In washdown operations, a NEMA 4X enclosure cooler is needed to maintain the sanitary conditions in the facility and to ensure that the washdown solution does not enter the enclosure.
• Hazardous locations: If the enclosure is situated in one of several hazardous locations, it’s vital to comply with IECEx, ATEX, and UL recommended system requirements.

Types of enclosure cooling solutions

The following are common types of enclosure cooling solutions:

• Fan systems: Fans are typically the most affordable option but can also be the least successful. Fans are constrained in their cooling capabilities; they allow little to no cooling adjustability and are reliant on the ambient air temperature. When factories have nearly invisible oil, aerosols, dust, and other contaminants in the air, a fan draws in the contaminated air and blows it onto the electronics and circuit boards. Although this will temporarily cool the components, it also deposits the contaminants onto the electronics, effectively insulating the electronic components. Eventually, this will cause the electronics to overheat, defeating the purpose of the fan in the first place.
• Thermoelectric systems: Thermoelectric coolers use the Peltier effect to create cooling by converting an electric current to create a cold junction and a hot junction. Fans blow air across the cold junction (a heat sink) to cool the air inside the enclosure. This cooling method has no moving parts and uses very little power. However, it is usually more expensive to purchase than other cooling types and therefore is primarily used in military and aerospace applications.
• Refrigerant (“Freon”) based systems: Refrigerant based cooling systems are more effective than fans, but they are limited in the environments in which they can operate. They typically do not function in ambient temperatures greater than 131°F (55°C). If contaminants in the ambient air are not adequately filtered out, the head pressures can rise in the condenser section, resulting in premature failure. Although an effective cooling option, refrigerants typically require an extensive physical footprint and higher upfront costs. Refrigerant-based systems also require periodic maintenance, which costs additional time and money.
• Vortex systems: Though compressed air can be costly, vortex cooling is an effective, safe, and low maintenance way to cool enclosures. Vortex tube technology converts compressed air into cold air without the use of electricity or coolants, and can reduce the temperature of the compressed air by 50°F (28°C) or more (see Figure 1). This means that enclosures are supplied with cold, slightly pressurized air, while oil and dust are also prevented from entering the cabinet. Vortex cooling systems have no moving parts, so they require very little maintenance, apart from occasionally changing a filter element, which ensures that clean, dry air enters the enclosure.

Note that most enclosure cooling methods use a thermostat to monitor the temperature inside the electrical enclosure and regulate the operation of the cooling device to keep the temperature within an acceptable range. On average, most operations want to keep the enclosure temperature between 80 to 104°F (27 to 40°C).

Most thermostats are electrical types and can be adjusted by the user to set the temperature as desired. Some cooling methods, however, such as vortex cooling, can also use a mechanical type of thermostat that requires no electricity to operate. This eliminates the need for electricity to operate the cooling device and is what makes vortex cooling ideal for use on enclosures in hazardous locations.

For enclosures not located in hazardous areas, vortex cooling can be regulated using either an electric or manual thermostat.

Application specific

Each cooling system has its pros and cons, but what we all can agree on is having one of them is better than none. Every application is different and has specific demands. It’s important to pick a cooling solution that is appropriate for your application, to prevent malfunctions and shutdowns.