If mechanical designers ruled the world, all rack-mounted equipment would be passively cooled. Why? There are five primary reasons:

  1. Eliminate moving parts that fail
  2. Decrease the cost of the equipment
  3. Eliminate rack room noise
  4. Decrease system downtime for maintenance
  5. Ensure warranty and longer product life

These are the promises of passive cooling systems in rack-mounted equipment, and really, they lead to a win-win-win for manufacturers, integrators, and end users alike.

To quickly define passive cooling, we’ll turn to Wikipedia:

Passive cooling is a building design approach that focuses on heat gain control and heat dissipation in a building in order to improve the indoor thermal comfort with low or nil energy consumption. This approach works either by preventing heat from entering the interior (heat gain prevention) or by removing heat from the building (natural cooling). Natural cooling utilizes on-site energy, available from the natural environment, combined with the architectural design of building components, rather than mechanical systems to dissipate heat.

Passive, or natural, cooling as it pertains to what we do at Biamp, means that we would design the cooling systems of our products to remove heat from the inside of the chassis and/or cool the air outside the chassis, without using a fan.

The 3 Ways to Cool a Chassis

The way I see it, there are three levels at which a chassis can be cooled: board level, box level, and rack level. Let’s take a look at what cooling methods are currently available/possible in the near future to cool each.

1) Board Level Cooling

Heat sink dissipating heat from component underneath.

Heat sink dissipating heat from component underneath.

At the board level, this is where we can get creative with our passive cooling methods, specifically with heat sinks and heat pipes.
We currently use strategically-placed heat sinks that are affixed over hot components on the board. The metal heat sinks provide a larger surface area for the heat from the components to dissipate. That heat gathered in the heat sink is then transferred out through the vents via ambient air outside the chassis, naturally cooling the components inside without requiring forced air from a fan.

Or you could conduct the heat to the outside of the chassis by arranging a big heat sink on the wall of the chassis that connects to the smaller heat sinks on the board.

Heat pipes are for extremely hot components like integrated chips that run a computer. None of our current equipment has processors that get that hot, but it’s a great option for electro-mechanical heat-generating devices.

2) Box Level Cooling

Fan cooling insides of box.

Fan cooling insides of box.

We find that fans are one of the primary components on our gear that is most likely to fail. So far, this is the primary method for cooling equipment at the box level. At Biamp, we install fans in our DSPs even if they’ll never get hot enough to actually need them. We do this as a just-in-case measure and as an assurance to our end users that our products never get uncomfortably hot-to-touch (even though they will operate just fine).

Remember the five primary reasons why passive cooling is so great? It all revolves around the use of fans (pun intended). The installation of fans on any piece of equipment means there will be more little pieces for manufacturers to purchase, for integrators to keep track of and know what to do with, and end users to replace when they eventually fail.

Depending on the fan, the retail price can be about $25, not including the other required bits like screws and plenums. That manufacturing cost is added to the price of the equipment. Oh, and they’re loud. I’ve heard rack rooms that sound like jet engines because of all the frantically spinning fans in there.

When a fan fails (not if), the integrator or IT person can replace it, or, as with our equipment, the end user may have to send it back to our Repair team. That means system downtime. That means a potential loss in business productivity, i.e. money. No one wants that.

It’s great then, that companies have equipment warranties. Ours is five years, so if your fan fails within five years of your purchase, we can take care of it for you within a few days (no really, our Repair team is that efficient…and there’s just not that much for them to do).

3) Rack Level Cooling
What if a large, slow-moving fan existed that could cool a whole rack? You could put it on top of the rack and it would slowly revolve, drawing heat in, moving it around the room, and cooling everything in it–all the racks, all the products on the rack, the whole room.

I don’t know of such a device, but could a rack fan eliminate or minimize some of the current costs of AC and control systems required in rack closets and server facilities? It’s just an idea…

The World According to a Mechanical Designer

By using analysis systems such as the Computational Fluid Dynamic (CFD), that allow you to analyze and characterize your entire design before it’s finalized and released for engineering, implementing effective passive cooling methods is a lot easier.

In other words, with the use of CFD, we can analyze and confirm where the hot spots in a product will be before it’s ever created. With this information, we can experiment with different cooling methods and component placement for maximum efficiency and cost-effectiveness, and maybe not even design in a fan.

By reducing parts and complex assembly, manufacturers can simultaneously reduce the cost of equipment and make it last longer. If you can place a heat sink on the top of the board and cool the box effectively without a fan, then that’s a better solution.

Fun Tip: How to Extend the Life of Your Electro-Mechanical Devices

If you’re multi-tasking on your phone or laptop and the processing is really high, it gets hot. It starts to whir and work really hard. If you’re in the car, stick it in front of the AC vent and cool it off. If you’re at home, put it on a cool surface. Any component, on any board, in any sort of electro-mechanical heat-generating device will last longer if it doesn’t get hot.

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