[ On Thursday, March 29, 2001 at 21:19:03 (-0500), Andy Ball wrote: ]
> Subject: Cooling
>
> That's curious, why fight the natural inclination of warm
> air to rise, when it could actually help?

You mean in the 9U 12-slot floor chassis and the like?

My only guess is that it's to avoid picking up too much dust and dirt.
They do anyway, but not as badly as if they were pulling it right off
the floor in some places!  (Especially those with cats! :-)  There are
no air filters of any kind on those systems -- only fanblade guards.

Most older rack cabinets intended for stand-alone environments pull air
in from the top.  One smaller cabinet I had which exausts air out the
top, and has a sealed floor, has an air filter on the bottom of the
front door for intake.

When I had my 3/280 running in a big old digital PDP11 rack I ducted
(with cardboard) the twin 10" fans at the top of the cabinet down onto
the 280 chassis (which was missing its fan tray) and let me tell you it
sure did keep the concrete floor warm!  :-)  Of course on a big cabinet
there's usually a holder slot over the fans where you're supposed to put
a foam filter (eg. like those for air conditioners), so that's how I
kept even the floating cat hair out of the system.  Living in the city
though, especially near any major roadways, you have to make sure you
change those thin foam filters fairly frequently lest the ozone turn
them into a horrible find powder that'll get forced into every crevasse
in a system....

-- 
							Greg A. Woods

+1 416 218-0098      VE3TCP      <gwoods@acm.org>      <robohack!woods>
Planix, Inc. <woods@planix.com>; Secrets of the Weird <woods@weird.com>