[time-nuts] 5070B once more.... (actually 5370A fans)

[christopher hoover]

Magnus wrote:
> Having 1-10 kW per rack is not uncommon these days, so 
> forced convection needs to be done

That and more.  A fully loaded 42U rack of HP C-class blades runs 8 kW idle and peaks at 24 kW.

This can be air cooled (easily) in a properly designed and commissioned run-of-the-mill raised floor data center.

> It is unfortunatly common to see racks where one box has an airflow 
> left-to-right while ontop of it is one with right-to-left and the rack 
> has very narrow space between the side of the boxes and the sides

Hot aisle/cold aisle arrangement is current best practice.  (Colleagues in my group at HP Labs were the first to do CFD analysis on data centers and established many of today's best practices.)

The key is to avoid mixing of cold and hot air as that destroys exergy.

IT equipment is mostly well-behaved as typically installed.   There is a one notable exception -- rack switches are often mounted from the rear and blow hot air out the front into the cold aisle.   (HP recently announced a switch where the flow can be reversed where need be.)    

The other problem, which you have alluded to, is gear intended for a telco environment.  Unfortunately that includes most data center core switches.   These, as you indicate, typically exhaust to the side.

-ch