When Is it Necessary to Select an Air Conditioner for Your Electrical Enclosure?

Electrical enclosures are generally designed to allow cooling by natural ventilation, supplemented sometimes by forced ventilation. This usually works well, but there are situations when overheating of electrical panels occurs due to internal heat load, environmental, ventilation, and air flow capacity constraints.

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In these situations, enclosure air conditioners solve high temperature problems inside electrical enclosures, increasing component life and reducing the risk of overheating leading to component failure.

Heat Load

The heat load of an electrical enclosure is the heat generated in that cabinet, usually expressed in Watts. Sources of heat generation include:

• Electrical equipment: The efficiency of power supplies, servo drives, motor drives, and transformers ranges from 85 to 95 percent. The 5 and 15 percent of energy lost is converted to heat.
• Solar load: Solar radiation significantly adds to the heat load in outdoor enclosures.
• Ambient heat: Enclosures located in a hot environment absorb heat from that environment.

Hot Industrial Environments

Electrical enclosures placed in hot industrial environments, for example, near ovens, kilns, and furnaces cannot depend on natural cooling because ambient air temperature is close to or above optimum electrical equipment temperatures and items such as electrical drives, which are susceptible to overheating, may malfunction or fail. Although the maximum operating temperature of some devices reaches 140 °F, many others cannot exceed 120 °F. In all cases, component life is extended and doubled for every 10 °F decrease in operating temperature. Electrical enclosure air conditioning is the only viable method of maintaining safe electrical equipment operating temperatures in a hot industrial environment.

Hot Outdoor Climates

The effect of solar radiation on metal equipment is such that in hot climates surface temperatures of metal objects can easily exceed 100 °F. In these conditions, natural ventilation may be insufficient to prevent internal temperatures of electrical enclosures from reaching unsafe levels. These situations are common in hot, dry, tropical, and sub-tropical areas. When enclosures must be outdoors an enclosure air conditioner may be required.

Dusty Environments

Electrical equipment in dusty environments needs to be properly enclosed and natural ventilation is not recommended as dirt and dust can affect operation of the moving parts of relays and contactors. Some dusts may be corrosive or conducting and need to be kept away from electrical components. The best method of equipment protection is the use of sealed electrical enclosures provided with suitably equipped enclosure air conditioners designed for use in dusty environments.

Poorly Ventilated Areas

Electrical enclosures in poorly ventilated areas may overheat if the heat load from the electrical equipment inside the enclosure is excessive. Electronic equipment used to control motors produce a lot of waste heat that needs to be dissipated, or the enclosure may overheat. Other heat sources are electronic power supplies and air cooled transformers. An enclosure air conditioner will remove the excess heat from electrical enclosures and keep them cool.

Space Constraints

In some situations, space available for electrical panels is constricted. Examples include electrically powered coal and ore reclaiming equipment, mining equipment, earth moving equipment, and ships. Often this equipment is supplied at medium voltage power using a trailing cable or overhead pantograph and makes extensive use of variable speed drives. Enclosure air conditioning can be used to keep these electrical enclosure temperatures within operating parameters.

High Electrical Enclosure Temperatures Can Be Dangerous

The risk arising from the overheating of electrical components in panels cannot be under estimated. Many devices cannot withstand temperatures above 140 °F (60 °C) and electrical enclosures may achieve these temperatures in harsh environments with high ambient heat loads and poor ventilation.

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Once a temperature of 140 °F is reached, conductor resistance increases, leading to severe localized overheating especially of components carrying large currents. Thermal runaway becomes a distinct possibility which may lead to components burning out and a subsequent risk of fire and explosion. Air conditioning of electrical enclosures can prevent component temperatures from exceeding safe levels and has the added benefit that cooler running extends the life of the electrical equipment.

When an Enclosure Air Conditioner is the Right Equipment Cooling Choice

Modern electrical enclosures are often not cooled by natural convection because of the extent of the heat produced by the equipment inside. While forced convection methods by cabinet fans and air-to-air heat exchangers are simple and economical, an enclosure air conditioner is the right equipment cooling choice for many scenarios. Here are some common cases when an enclosure air conditioner is the best choice.

High Heat Load

Moore&#;s prediction about the ever-increasing density of transistors on chips has increased the heat dissipation of Variable Frequency Drives. A 25 HP drive with an efficiency of 95% produces almost 1 kW of heat in the enclosure. Cabinet fans and air-to-air heat exchangers are ideally suited for low to moderate heat applications. Efficient cooling and temperature control in higher heat applications are provided only by enclosure air conditioners. Digital controllers in air conditioners are easily programmable and can be set at desired temperatures. Air conditioners with thermal expansion valves easily maintain the enclosure temperature at preset values regardless of the heat load variation in the enclosure.

Fluctuating Ambient Temperatures

Manufacturers design their electrical equipment for use over a certain temperature range. VFDs can operate at a maximum of 40 °C (104 °F) while most other electrical equipment such as switches and electrical batteries need to be operated at temperatures below 35 °C (95 °F). Above the maximum allowable temperature, the performance, reliability and lifespan of equipment gets halved for every 10 °C (18 °F) above 70 °F. In environments where the ambient temperature drifts to values above the maximum allowable temperature of the equipment, open loop cooling systems are not viable options. Enclosure air conditioners have closed loop cooling systems that cool the enclosure below ambient temperatures.

Outdoor Enclosures Subject to Solar Heat Gain

Outdoor enclosures may be exposed to direct incident radiation from the sun and high ambient temperature. The contribution to the overall heat load in the enclosure by solar heat gain and ambient temperature can be pretty dramatic. On an average day, the incident solar radiation can be as high as 10 to 18 W/ft2. Cabinet fans provide a constant convective heat transfer that is not responsive to solar time or external temperature. On the other hand, enclosure air conditioners with thermal expansion valves are capable of reacting immediately to heat load changes within the enclosure.

High Levels of Dust, Dirt and Pollutants in the Environment

In locations such as flour mills, cement processing plants, wood and paper mills where air pollution is a problem, it is prudent to isolate your valuable electrical equipment from the ambient air. Dust and dirt tend to settle on equipment surfaces and can cause their rapid deterioration and failure. For instance, electrical relays and switches have mechanical moving parts that are affected by dust and particulate matter. Not only do they inhibit their optimal performance but also they can cause short-circuits and fires. The ideal solution for cooling equipment in dusty locations is the use of a sealed enclosure with an enclosure air conditioner designed for use in dusty environments. Some manufacturers offer additional options such as extended filters and coated coils for use in highly polluted areas.

Enclosures in Humid Areas

Humidity and dispersed oils in the air can affect electrical equipment in a multitude of ways &#; pitting corrosion, moisture absorption by equipment, short-circuiting and premature aging. It is highly recommended that you use a sealed enclosure in humid areas to protect your equipment from moisture. Enclosure air conditioners are excellent solutions for enclosures located in humid environments. Equipped with efficient condensate management systems, they can not only dehumidify the air going inside the enclosure but also direct the condensate out of the enclosure by boiling it off.

Use in Hazardous Locations

Petrochemical plants and coal mines are notorious for their potentially hazardous environments. The presence of flammable substances in the ambient air increases the risk of fire and explosions. These applications require the use of a NEMA 4X sealed enclosure with enclosure air conditioners specially designed for hazardous duty.

Enclosure air conditioners find applications in many industries due to their efficient design, versatility, easy programmability, and remote monitoring. They can fulfill application requirements that cabinet fans and heat exchangers cannot.

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