It’s a truism that almost nothing is 100 percent efficient; a measure of the inefficiency of most devices we deal with is how much heat they produce.
Heat is energy that has been lost for one reason or another and is not available to do the task at hand, whether that is moving our car along the road, moving a loudspeaker’s cone to produce sound, or moving large quantities of 1’s and 0’s around at very high speeds.
Heat not properly dealt in our AV or IT systems can cause problems.
Digital electronics — be they satellite receivers, DVD players, codecs, or computers — may “lock up” and become unresponsive when overheated. Analog components appear to be more heat-tolerant, but in reality electrolytic capacitors are drying out and thinner-than-hair wires inside integrated circuits and transistors are being subjected to repeated thermal cycles of excessive expansion and contraction, leading to premature failure.
Modern AV and IT systems consist of various electronic components frequently mounted in racks, which may themselves be freestanding or in closets or other enclosures. Each electronic component in the system will generate some heat, and the systems designer and end user can ignore this at their peril.
The trivial case, in which a few devices mounted in a skeletal rack frame, in the open, in conditioned space, and consuming very low amounts of power, can safely be ignored. But such systems are few and far between today. More typical is the rack containing many power-hungry devices, all mounted in a rack either shrouded by side and back panels or located in a closet, millwork — or both.
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In these cases, ignorance of likely damage from heat will be far from blissful. Overheated components will express their displeasure in any number of ways, from sub-par performance to catastrophic failure.
There are several ways to reduce the temperature within a rack. One is through passive thermal management; allowing natural convection currents to let heated air rise and exit at the top of the rack while cooler air enters through an opening at a low point.
Convection, while ‘free,’ is a very weak force. It is dependent on the small difference in density of hot and cold air, which is why a hot air balloon is huge, yet capable of lifting only light loads.
Convection currents are easily blocked or disrupted should a vent be even partially obscured. Heat loads today, given the increasing use of digital devices and the tendency to install more equipment in smaller racks and enclosures, are too often beyond the ability of convection to even approach the necessary level of heat removal.
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Another way to cool a rack is through air conditioning, or active refrigeration. Air conditioning systems, properly sized and installed, let us set rack temperatures as low as we want; the only caveats being that we don’t cool below the dew point and condense moisture on our equipment, or raise our energy bill to unacceptable levels.
While expensive to buy, install, and operate, air conditioning systems that are dedicated to electronic systems may be the only practical solution when heat loads are large.
Be aware when the air conditioning system is shared with people, as when the supply and/or return ducts are an extension of an HVAC system that also serves the building and its occupants. The danger is that the thermostat may turn the system off when the occupants are comfortable or keep it from running at all in the cooler parts of the year, while the electronics are still generating the same amount of heat.
