Slightly OT: Calculating HVAC requirements for server rooms

William Herrin herrin-nanog at
Sat May 2 05:13:38 CDT 2009

On Sat, May 2, 2009 at 12:06 AM, Ricky Beam <jfbeam at> wrote:
> 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 shouldn't even *have* a drop ceiling in a modern computer room.
You want the room to be as tall as practical so that the air from the
hot aisles has somewhere to go on its way back to the HVAC, other than
back through and around the cabinets.

Personally, I've found that there's a pretty wide disparity between
HVAC professionals that are capable of hooking up a CRAC and turning
it on versus HVAC professionals that understand the holistic picture
including hot aisles, cold aisles, humidity control and flow. I
wouldn't want to call in a professional without first understanding
the problem well enough to assess whether I was getting a competent

Bill Herrin

William D. Herrin ................ herrin at  bill at
3005 Crane Dr. ...................... Web: <>
Falls Church, VA 22042-3004

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