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[datacenter] raised floor cooling the sub-floor slab?
Hi folks,
Our account rep from our regional energy provider (PG&E) was out here
recently and they seem to feel we are wasting quite a bit of cooling
capacity keeping our building slab cool underneath our raised floor and
one of our parameters walls. We are in Central California (coastal)
where the climate is relatively mild (70F to 80F) year-around. We are
on the ground floor on a solid cement slab (unsure of depth off-hand).
The datacenter environment is a sealed "box" built within our space
with a 12" raised floor. All cooling is forced air. The underfloor
space is usedly solely as a plenum (i.e. all cabling is overhead).
He's claiming that the slab sub-floor is not only heated by the earth
and "soaking" in the cooling that we provide, it is also getting hit
on the back and side by the sun where it is exposed at the parameter
and creating heat which then has to be cooled (since the slab extends to
the edge of our building up to the parameter walls and is exposed
therefore at various points to the outside briefly).
The parameter wall that is of concern consists of 8-inch (some portions
are thicker up to 12-inches) masonry brick, which gets sun on it much of
the day. I don't believe he thinks the wall is as big a deal as the
slab though.
Our under-floor supply air temperature is 49F. Ambient target is 72F.
Return air supply averages 72F to 74F.
The figures PG&E estimated add up to 15% to 20% of our bill. While I
can't dispute that outright -- since their concerns DO sound intuitive
-- I don't entirely believe them either (at least not to the degree they
are implying).
A few thoughts we've had on this:
* Yes technically true but since we keep the temperature consistent
around the clock the slab does not re-heat up EVER and therefore never
has to be re-cooled. We don't live on top of a hot spring so I just
can't imagine there being all that much energy lost in _keeping_ the
slab cool. Maybe if we had a more office type environment where we
turned the HVAC off at night and therefore had to re-cool the slab
everyday when the HVAC came back on but that's just not the case
here. While I don't particularly recall the slab being warm before
we built out I really didn't make a habit of walking back there
barefoot much. :) Though, admittedly, it was likely warmer than
49F and therefore I'm sure has SOME impact.
* The wall that is of concern does have sun on it all day but even
before it was part of our datacenter it was never warm to the touch
during the day even with the sun beating down on it all day.
Indeed, that area of the space has always been the coolest...largely
because of the thick "insulation" afforded to it by the 8-inches of
brick.
* Whatever "waste" there is is fixed and will not grow in absolute $$$
cost as the datacenter is filled with more equipment (even so, if
the CapEx to insulate the slab is less than the estimated lifetime
cost of the waste we'd probably still want to invest in improving
things).
Then there's the question of, if they are correct, how to insulate the
slab sub-floor properly. I don't want to have a mess to clean up in a
few years after whatever insulation slowly disintegrates and is pushed
out with the air supply. I don't want to be cleaning tiny particles out
of loads of equipment (and dealing with whatever hardware failures it
might cause). I presume there are insulators designed for use _in_ a
plenum that is constantly in use, in particular for use in a datacenter
or clean room type environment. Any idea what some of them are?
Anyone have any thoughts on all this?
-jr
--
Josh Richards | Colocation Web Hosting Bandwidth
Digital West Networks | +1 805 781-9378 / www.digitalwest.net
San Luis Obispo, CA | AS14589 (Production) / AS29962 (R&D)
[email protected] | DWNI - Making Internet Business Better
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