[Beowulf] followup on 1000-node Caltech cluster

[David Kewley]

On Monday 20 June 2005 07:44, Mark Hahn wrote:
> > > The intakes for the HVAC units are ~3 feet from the backs of the
> > > racks.  We
> > > expect to have almost laminar air flow, but with good local &
> > > roomwide mixing due to an up&down airflow pattern from the supply
> > > ducts.
>
> obviously the hot air will want to rise, but I suppose enough
> velocity will make it go where you want.  my machineroom is
> "half-ducted" as well: downflow chillers, 16" raised floor acting as
> a cold air plenum, but open space above for hot/return air.  it's a
> bit of a risk - it would offer a lot more control to have a suspended
> ceiling close to the top of the racks, with the supra-ceiling space
> acting as a return plenum.

Just to be clear what we have: There are six large Liebert HVAC units, 
alternating between upflow & downflow.  The front of *each* rack has a 
~50% open metal floor tile *and* a celing duct blowing cold air onto 
it.  The flow is enough at the front of the racks that it e.g. blows 
your hair & your shirt-sleeves around.  At the back of the racks the 
flow is not as obvious, but I expect it's sufficient.

Given the design & my paranoid intuition, I'm not worried about airflow 
or hotspots, but of course we'll see what actually happens.

David