[BC] Fire suppression

[towers at mre.com]

There is a trend away from general "plenum" pressurization in a raised
floor in favor of targetted ducting.  I've seen something in a HVAC trade
recently on using medium pressure high velocity systems to move the same
amount of air in a smaller duct obviating the need for the general plenum
approach (and all the electrical conformance headaches associated with the
open plenum).  Same 12-18" floor.

"Taps" are then fed into pressure reduction dispersers feeding a couple
rack ducts at a time. In really sophisticated systems, several sub-ducts
feed into various levels of a rack and dampers are introduced to regulate
general rack temperatures or even temperatures at various locations in the
rack.

A new mode of failure being explored is thermal shock introduced by a rack
being too cold and causing problems at start-up OR where there is a
significant thermal delta on a piece of equipment. Lightily loaded racks
fed the same amount of cool air (CFM) as more heavily loaded racks have
seen a disproportionately higher number of failures than those in heavily
loaded racks. Devices such as HD's where they typically run hot inside,
but the case is cool creates mechanical disparities in areas where there
needs to be some consistency.

This type of air handling system requires exceedingly careful balancing as
well as fire detection and suppression. Most locations require HVAC system
to shut down upon detection of fire or smoke to curtail spreading of any
active flame and to permit identification of the ignition source and
burning components.  Thus, doing so places the entire data center at risk
no matter what type of power protection and management systems are in
place.

As others have aluded, one can go hog wild in creating back-up systems. 
But when it comes to detection and supression, hog wild is an
understatement given the requirements of a UL listed supression system
installed in a locally code conformant structure.

Major data processing facility serving many clients secure operations or a
network node providing content to 1000 affilatesis one thing. But the
average station or cluster doesn't justify the expense in most cases of a
major supression installation. There is a point of dimishinging returns
which only senior management and ownership can assign accpetable risk
level and resultant true value. And whether it's worth the exponentially
increasing cost (captial and maintenance) to add each layer in order to
sustain operation.

MM

> Chris Gebhardt wrote:
>
> I could possibly make the argument that only being able to remove a
> single floor tile at a time or having to have the building manager
> present is overkill or speaks to an underbuilt system, but each room is
> unique.   We're fortunate to have plenty of capacity to handle
> maintenance in our raised floor facility.  But it's certainly a lot
> easier and faster to work in our overhead rooms.  And truth be told, the
> raised floor room doesn't save us a nickel on cooling.  But some folks
> just need to see that raised floor.
>
> Chris Gebhardt
> VIRTBIZ Internet Services
> chris at virtbiz.com | (972) 485-4125
>
>