Two things about using ‘cooling fans:’

First, and this may be obvious to some people, but in my experience this is not obvious to all people: fans do not cool the air, they only increase circulation. If a fan creates a flow of air which causes heated air to exit and/or cooler air to enter, then the space through which the air flows will become less warm. If a fan merely moves air more vigorously around in a closed environment, like an enclosed cabinet, cooler and warmer air will be mixed together, but the average air temperature inside the closed space will not decrease.

Why do I say this is not obvious to all people? In one instance I was installing equipment in a small equipment room the size of a large closet. With the door shut, there would be no circulation to the outside. Inside would be equipment dissipating approximately 3000 watts of electricity as heat. When I presented this problem to the facilities person, the response was basically, “There were problems providing venting and cooling. We’ll just put a fan inside.” I have found other installations where this was actually done and people wondered why equipment kept burning up. Can anyone imagine putting two 1500-watt space heaters in a closet, with or without a fan, turning them on and closing the door? How far away are the fire engines and emergency crews?

My second point: the increased circulation of air also means more airborne particles and dust are drawn through your equipment. Personal computers have fans to force circulation and provide cooling. Has anyone looked inside a personal computer after a year or two of heavy use? Yikes! In professional installation training, for installations involving closed racks that have cooling fans, there is the cheap way and the better way. The cheap way is to put an exhaust fan at the top of the rack. Because the air pressure inside the rack is has been lowered, general room air enters the rack wherever it can, through both intentional venting and unintended gaps, carrying dust and dirt with it. The better way is to place the fans in the lower part of the rack, drawing cooling air inward ONLY THROUGH A GOOD FILTER. Warm air leaves the rack via intended venting at the top and through unintended gaps. Filtered air leaving the enclosed space does not introduce dust. If the filtering is done well, and maintained, the equipment does not overheat and the equipment does not become a dust collector. Good filtering also provides some muffling of any sound the fan(s) may make.

But, Gunslingers, don't go to overboard. Electronics designed to dissipate electrical energy as heat can get uncomfortably hot to touch and still be OK, although my general preference for consumer gear is the closer to room temperature, the better.

[This message has been edited by bestbang4thebuck (edited May 01, 2003).]