Just Coolin’

On almost a daily basis, from many different sources, we are reminded about the importance of the environment. Whether on a global scale or within our own equipment rooms and offices, there’s no question that temperature and other environmental factors such as humidity have an effect on our lives. Heat is the environmental factor that is most important in what we do.

Nothing will kill hardware faster than excessive heat. As we move further and further into a converged market, where large amounts of video are stored on massive, heat-generating hard drive arrays, it is more and more imperative we understand how to provide the cooling this equipment so desperately needs.

Dealing With Killer Heat

When I was in high school, I took a bunch of auto shop classes. When we started studying the concept and function of the radiator, my teacher made what, at the time, sounded like a “duh” statement. He said, “The theory of cooling is the absence of heat.” Though I blew it off at the time, I realize the true relevance of that thought.

It’s important to understand the theory of the above statement. Adding cold to a device may not necessarily relieve the temperature problem. Electronic devices all generate their own heat as a result of the very functions their circuits are asked to do. Blowing cold air on a device will not relieve that device of the heat building up inside it. The hot air inside and around the equipment has to be removed at the same time, for the cooler air to do its job.

There are several formulas out there that people use to calculate how fast equipment will fail under certain temperatures. The one I am most familiar with says that for every 10º F rise above 85º F, the life of digital equipment is reduced by almost 40 percent. This is a pretty good reason to control the temperatures in your installations. 

Heat is not only measured in degrees, however. As we specify hardware and the racks to contain it, we need to also look at British Thermal Units (BTUs). A BTU, by strict definition, is the amount of heat necessary to raise 1 pound of water 1° F. For our purposes, a BTU is the amount of heat a particular device will expel during the course of 1 hour.

It’s only been in the past couple of years that security manufacturers have put BTU measurements on their spec sheets. Still, not all do. Generally, if the company is manufacturing datacenter-grade equipment such as NVRs, DVRs and disk arrays, it will be more likely to publish this information.

BTU calculations are critical for large installations of enterprise-class video system installations with hundreds, if not thousands, of cameras. When the main distribution frame (MDF) or equipment room is designed, the HVAC system has to be sized properly. This crucial step cannot happen without knowing how much heat will be dissipated from the equipment in the room. Too often, equipment rooms are designed with little or no regard to the systems housed within and, almost without exception, temperature problems arise.

How many times have you walked into a job and found one or more DVRs stacked up in a small closet? Or even several recording boxes racked in a phone room with insufficient thermal management? I’ll bet you didn’t need a thermometer to figure out the temperature in those spaces possibly approached 90° or more. How long did it take before those DVRs failed? Maybe that’s why you were there in the first place.

Datacenters Set Good Examples

Now think about walking into a high-tech datacenter or server farm. What do you see/feel? You see raised floors, lots of fans, and it generally feels very cool if not cold. Generally, those raised floors contain air ducting that directs cold air up into the bottom of the racks and ejects warm air out of the top.

The folks who design those server farms and collocation facilities understand how important it is to make sure their systems stay at or below the specified temperatures. We need to make sure we in the security industry follow the same procedures for our equipment because guess what? Our equipment is rapidly becoming the same as their equipment.

Even when the room is designed correctly, heat can still be a factor. I know one very large networked video system that suffered this very fate. Even though the HVAC was sized correctly and all equipment was racked to meet specifications, the cooling/ventilation system was inadvertently turned off. The ambient temperature in the room was measured at 142º F. Imagine what it was like inside the racks themselves. Unsurprisingly, they lost several hard drives in the overheated disk arrays.

Thermal Management Methods

What can we do to make sure our equipment won’t end up the same way? How do we know that we are getting the most efficient movement of hot and cold air over, under, and into our hardware?

Thermal management in security equipment racks takes on one of two methods — passive and active.

Passive cooling — Passive cooling basically means the rack itself has no mechanism to move air. There are no fans installed in the rack. Passive cooling relies on the ability of the equipment itself to provide the airflow.

Passive cooling is most appropriate when the equipment you are installing draws cool air in from front to back via chassis fans mounted at the front of each device. Cool air is drawn through the device, and warm air is pushed out the back, and into the interior of the rack. At that point, since hot air rises, it will flow out the back and top vents in the rack.

For many years we have worked under the assumption that we need to leave one empty rack space between each device. While that may still be true in some cases, if you are utilizing passive cooling you actually want to rack each device directly on top of each other, leaving no space in between. If we were to leave that one RU between items it would provide a pocket for warm air to collect with no way to push it up and out, defeating your cooling system.

While on the surface the placement of vented panels or perforated doors may seem like the right idea, it is very possible those holes may be causing improper airflow and inefficient cooling.

Active cooling — Active cooling utilizes fans installed in the rack itself to move warm air up and away from the equipment. This is probably the most common way security installers design their racks.

In some cases, if there is excessive heat being given off, or if the equipment isn’t designed with front-to-back ventilation, fans can be installed in the rack to assist with the air movement.

Even here, though, care must be taken to make sure the most efficient path is taken for the airflow. Improper placement of fans can create areas where warm air is trapped, again, defeating the purpose of thermal management in the first place.

Keep It Cool

Remember the basics: Hot air rises, BTU calculations need to be done and heat kills (equipment that is). Take the time to design thermal management into your installations. Proper control of excess heat will mean the difference between a happy customer and repeated service calls.

For more information on this subject, several white papers are available on the Internet. One of the best I have found is titled “Best Practices for Thermal Management of Security Installations” published by Riverdale, N.J.-based Middle Atlantic Products.

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