When it comes to cooling small enclosures, it's time to think inside the box.
Filter fans are best for applications with relatively clean ambient air and ambient temperatures lower than the desired internal enclosure temperature. They are generally available in sizes from 12 to 680 cfm.
Air-to-air heat exchangers use the counterflow principle. High-powered fans force two separate air circuits through the heat-exchanger cassettes. Separate air circuits keep dust out of the enclosure. They are also used where the ambient temperature is lower than the enclosure temperature, and have performance capacities from 14.6 to 69 W/°C.
Vortex coolers are used where compressed air is available from another part of the factory. They are good for low to moderate cooling (from 400 to 5,000 Btu) and where EMI/RFI must be minimized.
Air/water heat exchangers cool the enclosure interior below the ambient air temperature. They are used in environments where ambient is 130°F or above and provide cooling capacities between 2,400 to 10,250 Btu.
Air conditioners are used in environments where ambient temperature is 130°F or lower, and are available in sizes from 920 to 16,000 Btu. Separate air cycles prevent dust from entering the enclosure.
Get the heat out
All of this adds up to one thing: the need to get the heat out. In principle, heat can be dissipated through conduction, convection, and radiation. In conduction, heat transfers from object to object through direct contact. Heat transfer by convection uses air or a liquid as a medium. It absorbs and releases energy in the form of heat. Natural convection transfers heat by relying on density changes to cause fluid motion, whereas forced convection requires a pump or fan to move the fluid. Finally, radiation transfer of heat takes place via electromagnetic waves, the best example being the sun heating the earth. Conduction and convection play an important role in enclosures and electronic cabinets. Radiation is not a big factor.
An important criterion for heat removal from enclosures is whether the enclosure is an open (air can move freely through) or closed (airtight) system. While heat naturally dissipates from the inside of an open enclosure through a flow of air, heat can only be dissipated from a closed system through the walls or roof.
Another important consideration is the total exposed surface of the enclosure. Together with the location of the enclosure, these two factors determine the amount of heat dissipated. So for instance, an enclosure in the middle of a room can dissipate or absorb more heat than one placed next to a wall or in a corner.