A consultant has recommended FreeAxez for the raised floor in a new data
center. I checked it out and have concerns since it says it does NOT
create a plenum and cannot be used as an air handling space; it's a
low-profile flooring system.
How would cooling be done in this scenario? Open air (with intake/exhaust
mixing) seems like a step backwards in terms of efficiency.
Descriptions of any operation experience with this product will be
gratefully accepted.
~JasonG
What is the purpose of raised flooring if it *doesn't *create a plenum?
What is the purpose of raised flooring if it *doesn't *create a plenum?
...cabling? (though I think working under a floor to route cables vs overhead ladder is a pain..but mixing cabling AND air underfloor is much worse)
How would cooling be done in this scenario? Open air (with intake/exhaust
mixing) seems like a step backwards in terms of efficiency.
The usual methods of overhead (or possibly underfloor if you have enough height) distribution: Ductwork. 
Feed cold air into your cold aisle, and depending on your density and ceiling height use a general hot air return that pulls from the top of the ceiling (likely the same way you're used to seeing it done for most raised floor installs) OR drop additional hot air returns right over your hot aisles.
Further hot/cold seperation is entirely possible, too, to support higher densities...
Personally I'm not a fan of using raised floor for a cold air plenum for reasons I'm not inclined to go into right now.
What is the purpose of raised flooring if it *doesn't *create a plenum?
Cable management, low(er) install costs and high-load bearing capacity.
Frankly if you're gonna go with that, you're better off bolting the racks
directly to the concrete slab and use Snake Trays for cable management,
easier to access.
Alex
<
http://serverspecs.blogs.techtarget.com/2007/07/10/data-center-raised-floor-vs-solid-debate/>
is an excellent article on the matter.
ryan
Not sure about the purpose of a raised floor if it doesn't create a plenum, but, the
step forward from raised-floor plenum is hot-aisle/cold-aisle which requires a good
bit more discipline in your datacenter, but, is substantially more efficient.
Owen
Hi Owen,
Hot-aisle/cold-aisle is a separate issue from a raised floor plenum.
They're mutually supportive but not mutually dependent.
Raised floor has pros and cons which make it good or bad depending on
the environment. If you haven't yet started implementing hot
aisle/cold aisle, on the other hand, you're already the better part of
a decade out of date and your equipment is suffering for it.
For the original question: Non-plenum short raised floor can be useful
if you want to separate your power and data wiring. Other than that, I
can't see any advantage versus a solid floor and either snake tray or
other overhead wiring systems.
Regards,
Bill Herrin
Correction: short raised floor is also useful in a general office
environment. It allows you to quickly and cleanly reconfigure your
cube system.
Regards,
Bill Herrin
Yeah, it made it easier to feed power by running whips instead of
conduit and also got the power away from the data lines. The problem
with running any wiring under the floor is it always becomes a place
to hide the bodies. (Ever looked under a floor that's been there for
20 years?) If you also used it as a cold air plenum, bad wiring and so
on also interferes with airflow and people removing tiles or having to
cut tiles to get around this or that affects your static pressure and
throws your AC off. So these days, I personally favor nothing but air
under the floor and strict policies regarding movement of floor tiles.
-Wayne
I've never seen anyone do hot asile/cold aisle using raised floor.
Overhead cabling has become the norm in most modern installations
and once you go to hot aisle/cold aisle, you no longer need the lower
plenum, so, while they can be mutually supportive, neither requires
the other, and, in practical modern usage, hot-aisle/cold-aisle usually
precludes the need for the additional expense of raised floor.
Absent the need for the expense of the raised floor, it's rarely
installed in my experience, thus making them mutually exclusive
for most practical terms.
Owen
Not sure about the purpose of a raised floor if it doesn't create a plenum, but, the
step forward from raised-floor plenum is hot-aisle/cold-aisle which requires a good
bit more discipline in your datacenter, but, is substantially more efficient.Hi Owen,
Hot-aisle/cold-aisle is a separate issue from a raised floor plenum.
They're mutually supportive but not mutually dependent.I've never seen anyone do hot asile/cold aisle using raised floor.
Hi Owen,
Switch & Data in Vienna VA does it that way, as do parts of Equinix in
Ashburn VA. As often as not it's a retrofit where the raised floor was
already in place.
Even if you're not, though, the heat-density in the modern data center
is simply too high to prevent the warm air from the prior cabinet from
entering the top of the next cabinet unless you either generate a
minor hurricane through the floor or use a hot-aisle/cold-aisle design
so that nobody's breathing the other guy's warm air.
Overhead cabling has become the norm in most modern installations
and once you go to hot aisle/cold aisle, you no longer need the lower
plenum, so, while they can be mutually supportive, neither requires
the other, and, in practical modern usage, hot-aisle/cold-aisle usually
precludes the need for the additional expense of raised floor.
The ductwork for hot aisle cold air can get in the way of access to
your wiring, especially in a large room. A raised floor obviates the
need for ductwork.
In general, though, I agree with you: if you don't already have raised
floor it isn't worth the additional expense, at least not in the data
center.
Regards,
Bill Herrin
Actually, my experience has been that most of the newer installations
(last 5-7 years) that I have been able to see where raised floor is
employed are also doing hot/cold rows.
-Wayne
We have/are building new datacenters with a raised floor plenum. Air
is directed into the racks from below, and ducted out of the top. No
hot/cold aisle, just lots of cold air to cool the equipment. It's an
AFCO rack design. Seems to be efficient so far.
We have/are building new datacenters with a raised floor plenum. Air
is directed into the racks from below, and ducted out of the top. No
hot/cold aisle, just lots of cold air to cool the equipment. It's an
AFCO rack design. Seems to be efficient so far.How do you measure efficiency? How do you blow air on all the
computers in the rack and not just the bottom one?Hot/cold aisles are going to be way more efficient, or at least more
uniform. Your systems are probably like most rack mount gear and
designed to take air in the front, route it over the internals in an
ideal way (possibly using baffles) and spitting it out through the
back. Hot/cold aisles work with this system. Your way hits the bottom
box and then spits the air out of the rack missing the top systems.
Same way you cool the top of a rack in a cold/hot aisle system. Blow
cold air up the front of the rack. We measure temperature at select
points in the rack. Keep the hottest spot below set point, and
everything is fine. The physics aren't that much different.
We are cooling 20kw per rack with this setup. 4 hp c-class chassis per
rack. Works great.
Hi Tim,
I poked through AFCO's drawings at
http://www.afcosystems.com/pdf/AFCO_Drawings.pdf, How much of a size
hit is typical? Do you take the depth out to 52" to create enough
space in front of the equipment for air to flow and take the 6-inch
hit to the side for the cabling sidecar?
What's the impact with respect to sharing the facility with non-AFCO
cabinets? I would imagine that with a bunch of these things
dynamically changing their air flow it would be hard to maintain a
static pressure under the floor.
Regards,
Bill Herrin
I poked through AFCO's drawings at
http://www.afcosystems.com/pdf/AFCO_Drawings.pdf, How much of a size
hit is typical? Do you take the depth out to 52" to create enough
space in front of the equipment for air to flow and take the 6-inch
hit to the side for the cabling sidecar?
EHD racks with 6" sidecars, one on each side, as we have significant
cabling density to handle. Rack frame is 48" deep.
What's the impact with respect to sharing the facility with non-AFCO
cabinets? I would imagine that with a bunch of these things
dynamically changing their air flow it would be hard to maintain a
static pressure under the floor.
No impact - it's all the same racks
Airflow under the floor has not been an issue. It's not much different
than moving perf tiles around periodically.