rack power question, and a prediction about "direct heat removal" (DHR)

Patrick Giagnocavo patrick at zill.net
Fri Apr 4 05:58:31 UTC 2008

First, I would like to thank everyone who responded to my initial query.

It seems that power and how to remove the resulting heat, is certainly 
on a lot of people's minds.

Clearly the days of "including" power are past in all but sales and 
marketing materials.

There is a cost to each component and markup is applied (if internally 
and not broken out to the customer) on each rack, each power circuit, 
etc. with covering the overhead of UPS, diesel generator, chillers, etc. 
  being a big priority.

After some thought, I believe, to coin a term, that "DHR" or direct heat 
removal, in some fashion will be the "new" thing for the datacenter.

Somewhat counter-intuitively, the focus will be to remove the heat that 
comes out the back of the rack rather than worrying so much about the 
temperature of the air going in the front as long as it falls in a 
generally acceptable range of say, 68-75F.

My guess is that someone will come up with an inexpensive, reliable way 
to put a heat collector, which will basically look like a car radiator 
the size of a rear rack door, directly behind the hot air coming from 
the systems in the rack.

Hot air flows past the cooling fins and is quickly cooled back to 68F; 
the heated refrigerant is immediately piped away, out of the room and to 
the chiller, so that the evil BTUs do not spread out and contaminate 
other areas of the room.

It might involve a phase change material, or might involve a more 
traditional refrigerant.

My money would be on R744, also known as CO2, as it is not polluting and 
can serve double duty as fire suppression (provided you have enough on 
hand to flood the area/room).

Detectors for leaks are very inexpensive and the technology  for the 
closed-loop of the refrigerant cycle is already here.

It is not caustic the way any of the salts-based variants would be, is 
not explosive, and is heavier than regular air, meaning it will sink 
below the area that most people breathe at should there be a small leak.

With the heat being removed within a few inches of where it is 
generated, less CRAC units will be needed to keep the rest of the air 
cooled; and possibly, no separate unit would be needed if enough heat 
can be removed to drop the temperature below 68F.

For fire suppression, an alarm would sound and only when it can in some 
fashion be "proven" that no humans are inside the area, CO2 is flooded 
into the area and the fire goes out.  Some form of ducting which mixes 
the CO2 with regular air and exhausts it is needed after the fire is 
out.  Firemen go in with oxygen if they need to enter before this is 
done.  (obviously there would be an entire tested procedure for how this 
is done, probably including a small oxygen mask with ~4 minutes of O2 
placed beside each fire extinguisher and within easy reach).

(For racks with less than say 4KW of power use, network and power is fed 
from overhead with a few feet of slack in the cables, as well as a 
portion of the DHR piping being flexible tubing.  This allows them to be 
  placed more closely together than normal, almost front to back to 
front to back, with enough slack to pulled the wheeled racks "out" from 
the stack so it can be worked on (sort of like pulling a book out of a 
bookshelf). They use far less space and are sold a little cheaper by the 
colo facility.)

Surely there is a limit as to how much air can be moved around, even 
with the use of best practices, there are hot spots.

Simple physics dictates that this is a less energy intensive cooling 
method as a) moving a lot of air around requires a lot of energy b) air 
is a lousy way to transfer heat away from where you want it to be 
compared to other materials.


Patrick Giagnocavo
patrick at zill.net

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