Re: Airflow direction in rack-mount cases

John Larkin <jjlarkin@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote in
news:er826459ghl18nabn43ltdhurrglc7t7m3@xxxxxxx:

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.


The standards exist so that designers and users can have a better chance
of getting their equipment to play well with others.
I've seen a lot of rack mount equipment, and the back to front airflow is
quite rare. Brocade are doing something that is different.


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.

Bottom to top may be installed with 1 or 2U high angled panels between
the equipment to make the airflow in at the front/bottom and out and the
top/back. Bottom to top is quite commonly used with vertical "line
cards" in 4-6 U chassis.

The north American CO style with open backs will have farms of racks
organised so that "cold aisles" and "hot aisles" alternate, with the
equipment drawing air from the cold aisle, and blowing hot air into a hot
aisle.

The ETSI ones are designed to have closed backs (which allows two racks
to be placed back to back or against a wall). Typically, air will be
exit out the top, and enter at the bottom front of the rack.

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


Thanks for your input.


Regards,
Allan
.