Re: Airflow direction in rack-mount cases

On Sat, 28 Jun 2008 12:24:27 -0700, John Larkin
<jjlarkin@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:

On Sat, 28 Jun 2008 12:18:48 -0700, StickThatInYourPipeAndSmokeIt
<Zarathustra@xxxxxxxxxxxxx> wrote:

On Sat, 28 Jun 2008 11:01:33 -0700, JosephKK <quiettechblue@xxxxxxxxx>
wrote:

On Tue, 24 Jun 2008 09:48:23 -0700, John Larkin
<jjlarkin@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:

On Tue, 24 Jun 2008 11:02:25 -0500, Allan Herriman
<allanherrmian@xxxxxxxxxxx> wrote:

Hi, I'm aware of some standards that dictate airflow direction in rack
mount cases (e.g. ETSI 300 119 and NEBS), and it's usually front to back,
bottom to top, or (least preferred) left to right.

But recently I noticed some equipment from Brocade in a 1U case that drew
air in at the back, and blew it out the front. This is actually mentioned
in the data***, so it was not an assembly error (with the fans in the
wrong way around).

It's called a "hand warmer."


Why would designers go against the standards and do this? Could there be
some benefit to the equipment?

Standards are for sheep. If a rack is internally plenum-fed with cool
(and sometimes super-temperature-controlled) air, it makes sense to
intake from inside the rack and dump the warm air into the room. We do
a bunch of electro-optical stuff that way, with the most temp-critical
stuff in the back of the box. The fan's in front, so its own heat
heads straight out.

Left-right will just spin hot air inside a rack. And probably restrict
flow badly. Ditto bottom-top.

Small benchtop instruments usually blow out the back, so as not to
annoy users with the air and noise. Whatever works best.

John


Thinking a bit, bottom to top is helped by convection flows. Front
panel versus back panel requires consideration of who and why some is
at the front panel or back panel. The front panel is usually for
meter readers and such who are very intolerant of warm air in their
faces, back panels are usually full of connectors and such and
represent a restricted flow. Sideways flows in racks are useful only
in carefully managed situations. In all cases consider various users
and maintainers and total heat transport.


The idea is to create a positive pressure inside the rack module being
designed. One draws air in directly through the fans, and creates said
positive pressure. The fans should never be driving the exiting air, they
should always drive the incoming air.

The big advantage of negative pressure is that it lets you locate and
size various inlet holes to blow just the right amount of air on
specific hot spots. You can't get that sort of tunability with a fan
blowing in.

Plus, the heat from the fan motor heads right out, not in.

John


I see your point.

.

Quantcast