Slightly OT: Calculating HVAC requirements for server rooms

Seth Mattinen sethm at
Fri May 1 23:22:24 CDT 2009

Ricky Beam wrote:
> On Fri, 01 May 2009 21:32:19 -0400, William Warren
> <hescominsoon at> wrote:
>>> Specifically, I am using the guide posted at:
> "Before you decide on an air conditioning unit you should commission an
> audit from a suitably qualified air conditioning equipment specialist or
> installer."
> Translation: Hire a f***ing professional.
> And that's exactly what you need to do.  Qualified HVAC installers (with
> specific data center experience) will know far more than us "network
> types" will ever want to know about cooling.  They do this for a living,
> and thus, know all the tiny details and odd edge cases to look for.
> (like looking above the drop ceiling -- that's what it's called, btw --
> and seeing what's up there long before pencil meets paper (not that
> anyone uses paper anymore.))
>> You also have to take into account the environment surrounding the
>> data room.  At my wife's work The ceiling above is only separated with
>> a false ceiling to the metal roof above but the rest of hte spaces
>> surrounding the room are climate controled.  They [had] to
>> significantly upsize to account for the heat load of that ceiling.
> Unless you are pulling air through the plenum (that space above the drop
> ceiling), the air up there shouldn't matter much -- there should be
> plenum returns up there to begin with venting the air to the surrounding
> plenum(s) (i.e. the rest of the office, hallway, neighboring office,
> etc.)  However, I've seen more than enough office setups where the
> "engineers" planning the space completely ignore the plenum.  In my
> current office building the static pressure pushes the bathroom doors
> open by almost 2".  And they placed our server room directly under the
> building air handlers -- meaning all the air on the 3rd floor eventually
> passes through the plenum above my servers. (also, the sprinkler system
> riser room is in there.)

The space above the drop ceiling is only a plenum if it's used as air
handling space opposed to ducting the returns everywhere. If it's not an
air handling space, it's not a plenum, it's just where spiders might be.
It's easier to throw grated panels in all over the place for returns in
large systems.

Now, back on topic, plus nifty graphics explaining the difference:

> Bottom line, again, ask a professional.  NANOG is a bunch of network
> geeks (in theory.)  I'd be surprised if there's even one licensed HVAC
> "geek" on the list. ('tho I'm sure many may *know* an HVAC engineer.)

But yes, please, don't learn how to make your own system from what we
say here. HVAC systems are their own world. You wouldn't want an HVAC
guy designing your network just because he's seen a lot of server rooms,
would you?


More information about the NANOG mailing list