Enclosure air conditioners remove the heat generated by electronic devices from the inside of cabinets or enclosures. Powerful electronic assemblies and components function within increasingly high temperatures. The heat generated is a hazard for production and functional machinery. Enclosure air conditioners are critical for the safety of production and personnel in the event of component failure. The devices typically use refrigerants and include thermostatic controls to maintain programmed environmental conditions.

 Enclosure air conditioner. Image credit: OK Solar

There are three ways to cool an enclosure: natural convection cooling, forced convection, and closed loop cooling. The first method does not require an active cooling section so we are only concerned with forced convection with an air conditioner and closed loop cooling. Natural convection is used if the ambient temperature outside the enclosure is cooler than the inside of the enclosure. The heat can be dissipated into the atmosphere by radiating it through the surface of the enclosure and through the use of grills with filters. Forced convection is best used if there is clean and cool ambient air outside of the enclosure. This may be as simple as a filter fan with the appropriate filter.

Sealed enclosure cooling is considered a closed-loop system because the seal of the housing is maintained. This prevents elements which can damage the electronics inside the enclosures. Sealed enclosures are best used in harsh conditions and when the ambient temperature is as high or higher than the desired internal temperature.

 Enclosure cooling. Image credit: Automation Notebook

Enclosure cooling is not the same type of "comfort"cooling as found in homes and buildings. Heat-producing power and control components are typically limited to maximum enclosure air temperatures of 100°F to 110°F. The actual component surface temperatures are higher. Maintaining low enclosure temperatures often becomes problematic. Condensation may form on live electrical surfaces if their temperature falls below the dew point of the air. Subsequent corrosion or electrical safety becomes a serious issue.

Some enclosure air conditioners automatically evaporate condensate, eliminating the need for draining. Others include an air flow sensor that monitors the temperature of the condenser and ensures that blockage or contamination does not compromise cooling efficiency.

Enclosure Air Conditioner Specifications

Enclosure air conditioners use either single-phase or three-phase power and vary in terms of cooling efficiency, which is often expressed in kilowatts, tons of refrigeration, or British thermal units (BTU) per hour. Cooling capacity is the capacity of the air conditioning unit to remove heat from the room or industrial space. Physical specifications for enclosure air conditioners include mounting style, NEMA rating, and IP rating.

Phase

• Single-phase - Single-phase power is used in light commercial and residential applications.
• Three-phase - Three-phase power is typically used industrial applications. Improved efficiency and smooth running is achieved with three-phase power.

Operating Voltage

• Direct current (DC) voltages operate at 12 or 24 VDC.
• Alternating current (AC) voltages operate at 115, 230, 380/400 or 460 VAC. For AC devices, frequencies include 50, 60, and 400 Hz. Typically, 400 Hz devices are used in aerospace applications.

Mounting

• Side wall mounting is used in a standard cabinet rack.
• Recessed pockets or cavities are used for mounting in tight spaces.
• Top-mount devices are used in enclosures that do not provide adequate clearance for side mounting.
• Bottom-mount devices fit the enclosure base or bottom and are usually rack-mounted.

NEMA & IP Rating

The National Electrical Manufacturers Association (NEMA), a non-profit trade organization, rates enclosures for electrical equipment. Enclosure air conditioners with NEMA 3R, NEMA 4, and NEMA 4X ratings are suitable for indoor or outdoor use and provide protection against dirt, rain, sleet, and snow. Ingress protection (IP) 34, a European standard, sets criteria for preventing the ingress of particles larger than 2.5 mm. IP 54 sets standards for protection against shock, vibration, dust, and rain. In terms of outdoor use, IP 54 is nominally equivalent to the NEMA 3 rating.

Features

Enclosure air conditioners are available with a variety of special features.

• Electrical or electronic filters - Filters on the incoming power line suppress noise caused by electromagnetic interference (EMI) or radio frequency interference (RFI).
• Interlocks, alarms, or signals - Alarms will alert users to faults or system failures.
• Short cycle detection is a feature that monitors compressor on/off cycles for length and efficiency.
• Refrigerants without chlorofluorocarbons (CFCs) - Chlorofluorocarbons are chemical compounds believed to be responsible for depleting the Earth’s ozone layer.
• Precision cooling - Designed to meet the needs of high-density computing while maintaining precise temperature levels.
• Weather resistant - The air conditioning unit is resistant to the outdoor environment and may be placed outside.
• Condensate evaporator - Products automatically evaporate condensate from the cooling operation to minimize or eliminate the necessity for draining.
• Explosion proof - Cases for explosion-proof devices are designed to prevent explosions within the air conditioner from the ignition of surrounding gases or vapors.
• Intrinsically safe - Intrinsically safe (IS) products minimize or eliminate sparking or other thermal effects that could cause ignition in the surrounding environment.
• Thermostatic control - Thermostatic control is feedback control of the cooling operation to maintain programmed environmental conditions.

Standards

Many safety agencies rate or certify enclosure air conditioners. For example, the International Engineering Consortium (IEC) publishes and maintains standards for electrical product conformity. In Europe, electrical and electronic equipment must bear the CE Mark to indicate compliance with product safety and electromagnetic compatibility directives. In North America, the Canadian Standards Association (CSA) Mark may appear alone or with indicators. Products that bear the CSA Mark alone are certified only for the Canadian market. Products that appear with the indicators "C and US" or "NRTL/C” are certified for both the U.S. and Canadian markets. Underwriters Laboratories (UL) approves both component parts and complete assemblies.

Resources

Electrical Enclosure Cooling With Special Purpose Air Conditioners