At a new IBM location, the company's data center takes up the entire middle floor of an
office tower. The elevators, staircase and other services occupy the building core with the data
center built around it.
The heart of the data center is an "L" shape area occupying a quarter of the floor space and
consisting of 8 pairs of facing rows of racks, plus a CRAC row for each pair. Since the data
center is in the middle of a regular office building, there is insufficient height for both a
raised floor and a suspended ceiling, so only a suspended ceiling was used. This structure
necessitates a design where the CRACs, instead of pumping cold air down under the floor, pumped
the cold air up above the ceiling. Vents were built into the ceiling between facing rack rows in
order to direct the cold air down. The descending cold air then is supposed to enter the racks
and exit into the room and back to the CRACs for cooling.
Such designs are often problematic, since the cold air could be readily "shorted" from the
racks and instead go back into the hot portion of the room and to the CRACs. To further
complicate matters, both the racks and CRACs were near outside windows and, hence, were subject
to large amounts of heat from the sun.
During the initial design phase, engineers suggested adding fans at the top of each vent to
directly control both the volume and flow rate of the cold air. This would minimize chances of
short circuiting, ensure uniform air distribution between racks and push the cold air down
closer to server inlets. Although this solution had a greater chance of success, it would add
infrastructure cost, mean more equipment to maintain and therefore, more chances of breakdowns
and increased energy expense.
IBM asked CAS, a leading thermal design consulting company, to analyze the design. With the
aid of CoolitDC from Daat Research, CAS modeled the data center in less than a day.
Various data center configurations were considered, including those with and without the
ceiling fans and those with additional doors and partitions to create sealed cold aisles. The
analyses proved that no ceiling fans, additional doors or partitions were required to maintain
The results were a great benefit to IBM; the company was able to use the significantly less
costly, but the more reliable and more energy efficient design.