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PRO-ACTIVE HEAT MANAGEMENT

by Frank Federman

The Art of Compromise

One of the first things a man learns when he marries is that while his collection of really wonderful audio and video electronics—with glowing LEDs and lots of controls—may impress his men friends, the distaff side of the household is usually less impressed. Rather than being thrilled at the sight of black box upon black box and exposed coils of wire, these unreasonable people insist on putting all these beautiful boxes and cables into a cabinet or closet.  In time, situations may emerge when protecting audio and video gear becomes necessary to prevent mis-adjustments (or worse) by resident 3 year olds.  And so, the wise man yields….

Few consumers give much thought to the ventilation needs of home audio/video or computer equipment when stowing it into a cabinet or closet to get it out of the way or out of sight.  Yet most modern electronic gear—whether analog or digital—is designed to operate at room temperature, in an open environment where heat generated by the component will dissipate passively and not accumulate.

Placing such equipment in a restricted environment, especially in the presence of other heat-generating components having similar ventilation needs, will cause the heat to accumulate and the temperature to rise to levels that are unsafe for normal equipment operation.  This is an invitation to premature equipment failure, and disappointment.  Simple active thermal management techniques and products are available to ventilate modern electronic equipment that must be concealed for practical or cosmetic reasons.

Amplifiers, receivers, and their digital cousins are designed to operate in a 70 degree environment with unrestricted ventilation.  Even a component with internal fans needs free ventilation so that the fans can move hot air away from the chassis and bring fresh air in.  Putting self-ventilation gear into an unventilated enclosure simple creates a convection oven, ensuring that all the equipment is evenly heated and cooked—not exactly the desired result.

Actively ventilating enclosed equipment is not just a matter of domestic compromise; similar situations are common in commercial applications.  While modern technology is a necessity in board rooms and executive offices, visual aesthetics must be respected, so the equipment that brings those benefits must be out of view.  Here we will confine our discussion to residential matters, while recognizing that a residential BTU is no different than a commercial one!

In residential situations, a good balance between ideal cooling strategies and practical constraints can be achieved by allowing the temperature in the equipment enclosure to rise no higher than 85 degrees.  Lower temperature is even better, but may require more airflow (and noise) than is practical in a home environment.

13_Active_heat_mangement-02Many Factors

Ventilating home electronic systems usually involve many variables: the type of enclosure (free-standing or built-in), the number of components, the total power draw of the equipment, and whether that equipment is rack-or-shelf mounted.  The temperature of the immediate surrounding environment is also important—San Francisco summers are almost always cooler than those in Phoenix, even with air conditioning.

Then there’s the matter of where to dump the heated air.  If it is to be moved to an area beyond the cabinet, is there an acceptable place (such as a hallway, laundry room, attic or basement) in which to ventilate it?  In every case, the goal is always the same – remove air that has been heated and replace it with cooler room air.  And please note: rarely is it necessary to exhaust hot air outside the home; discharging it into the room or an adjacent area is almost always effective.

An equally important goal is to accomplish this heat exchange with an absolute minimum of noise.  Trading a heat problem for a noise problem still leaves us with a problem!  Most people are distracted (or even irritated) by the whoosh of moving air or the drone of fan motors. Fortunately, moving air quietly is not difficult; effective systems are available to accomplish both goals.

Short Circuits

No matter how the equipment is mounted, or what type of enclosure it’s in, cooling it is most effective when fresh air enters the enclosure, passes over the equipment, and then exits.  This results in the maximum heat removal possible for a given airflow, usually expressed in cubic feet per minute, or CFM.  A common rookie mistake is the “pneumatic short-circuit”; that is, the air entry and exit points are located too close together inside a cabinet, so that air passes between them without washing over the equipment.  This results in minimal cooling, so it must be avoided.   A different kind of short circuit can occur if the intake and exhaust vents or hoses are terminated too close together.  In this case the input hose takes in air that has just been heated by the equipment and then exhausted—the convection oven problem, again!

Thermal Control

To ensure that fans don’t run any longer than necessary, thermal control is a necessary feature in a cooling system.  A remote temperature probe connected to a control unit will turn fans on and off as needed.  A more sophisticated system can adjust the speed of the fans as temperature rises and falls.  Limiting fan operation to those times (and only to the extend) that it is actually needed minimizes noise, maximizes fan life, and saves energy, too.

Filters

Before getting into details of ventilating enclosures of various types, a word or two about filters is in order.  While filtering the air entering an A/V enclosure would seem to be a “motherhood and apple pie” issue (to keep the equipment pristine), the devil—as usual—is in the details. Fortunately, there are only a few of them:

  1. Unless changed regularly, filters will clog, and when clogged, they restrict or completely stop airflow, causing overheating and early equipment failure.
  2. People forget to change filters.
  3. See #1.

This may seem flippant, but it’s based on hard-won experience. When my company developed a line of non-clogging filters (yes, there are such things), we discovered a fourth detail:

  1. People won’t buy filtering systems. (More accurately, very few people will buy them.)

Then there’s an additional complication: most filtering systems partially restrict airflow, thus requiring the use of more powerful fans to force air through the filter media, increasing both kinds of fan noise.

While we’d all like our electronics to be sparkling clean, in reality ordinary household dust or the occasional cat or dog hair do little harm, but clogged filters that stop airflow and cooling can do great harm.

Some Practical Examples

Let’s examine some typical installations that call for cooling.

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Small to medium size free-standing cabinet  represent the most common enclosure type the A/V systems integrator sees when designing home entertainment systems for clients. These can range from the small, one-component-wide units with a small rack or a single shelf, to the two-components-wide cabinet with a larger rack or 2 to 3 shelves.

Since this cabinet type is free-standing, the back is available for installing fans which will be hidden from view.  Whether smaller 3 inch (80mm) fans or larger 4-3/4 inch (120mm) units are employed, a successful approach (shown above) is to put one fan in a lower corner blowing room air into the cabinet, while the other is located in the diagonally-opposite upper corner, exhausting hot air out of the cabinet.  With a few openings made in the shelves and a properly-sized cooling system, this mounting technique moves air from front to back, left to right, and down to up, effectively changing the air in the cabinet every few minutes.

Built-in cabinets present a challenge to the designer and installer, as the rear cabinet panel isn’t available for fan mounting and hot air exhaust.  In this application, fans and hoses might need to be visible.  Ventilation systems are available that feature metal grilles, or unfinished wood (of various species) to blend in with most styles of decor.  These systems will typically be set up to bring room air in through the toe-kick panel, or through the cabinet floor.  After passing over the electronics, it is exhausted through grilles placed high on side panels.  Fans can be integrated into the intake or exhaust grilles; in extreme cases, fans may be needed at both locations.  If television panels are located on the tops of these cabinets, air can be exhausted aesthetically through the cabinet top behind the TV.

Minimizing visible openings.  Sometimes it’s necessary to minimize visible cabinet openings. To accomplish this, the experienced designer can make use of cavities behind zero-clearance fireplaces, voids behind adjacent bookcases, or hallways or laundry rooms that abut the cabinet.  These are all possible places to exhaust heated air.   Also, by adding flexible tubing, venting systems can channel heated air to attics, basements, crawl spaces, or utility rooms.  A little imagination will frequently solve even difficult problems.

Larger home theater systems enclosed in cabinets can be treated as in the cases described above.  Depending on total volume and heat load, they may require more than one set of fans.  If rack-mounted, these larger systems typically require specialized cooling techniques and systems, depending on the details.

For racks that are free-standing, many systems are available commercially that mount within the rack, usually at or near the top, pulling hot air up and out through the rack’s top or front panel.  If the rack is located in a closet or equipment room, the heated air must then be removed from the rack’s near environment, or the hot air will just be pulled back in (short circuit), overheating the equipment rather than cooling it.  To solve the latter problem, systems are available that can move heated air many feet away to a remote location through 4” or larger flexible tubing.

Video projectors are frequently enclosed, either for esthetic or security reasons, or to reduce the noise of their internal fans.  Lower-powered projectors can be cooled by simply installing intake and exhaust fans in the sides of the enclosure, as shown here.  Exhaust fans should be located as close as possible to the projector’s exhaust port, to capture as much of the heated air as possible.  Intake fans should be located close to the projector’s intake port.

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More powerful projectors may require the use of flex tubing to move heated exhaust air to a remote location.  This tubing can be attached to an opening in the enclosure, adjacent to the projector’s exhaust port, or can be brought into the enclosure and attached directly to the projector.

Whatever the ventilation need, straightforward cost-effective solutions are available to protect valuable equipment without introducing noise that will detract from the A/V experience.

Frank Federman is founder and CEO of Active Thermal Management, Inc., a company that pioneered the development of ultra-quiet cooling systems for A/V and computer installations. His background is in the design and manufacture of audio and video components, including the first large screen projection systems.