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The Greening of IT
124 How Companies Can Make a Difference for the Environment

equipment only). Currently, no comprehensive data sets exist that show the
true spread of the PUE for data centers. Some preliminary work indicates
that many data centers might have a PUE of 3.0 or greater, but with proper
design, a PUE value of 1.6 should be achievable. This theory is supported by
measurements completed by Lawrence Berkeley National Labs that shows
that the 22 data centers measured had PUE values in the 1.3 to 3.0 range.
Other research indicates that PUE values of 2.0 are achievable with proper
design. However, currently no comprehensive industry data set exists that
shows accurate PUE statistics for data centers.
Furthermore, there is no general agreement on what constitutes an efficient
or inefficient data center. In the future, The Green Grid will offer values that
profile target PUE and DCiE metrics for a variety of typical data center con-
figurations. In the short term, The Green Grid suggests that data center own-
ers begin using either the PUE or DCiE metrics. Although the measurement
points might not yet be clearly defined, The Green Grid recommends measur-
ing data center efficiency, even if the method currently requires data manipu-
lation. In addition, The Green Grid also encourages data center owners to
share and compare their respective PUE and/or DCiE results. Such collabora-
ptg
tion can help each data center owner to better analyze individual measurement
methodology, as well as to understand how the results compare.

Long-Term Green Grid Direction

A mixed-use building can house any number of functions, such as data
centers, labs, offices, and such. For these mixed-use environments, separating
out the power usage of just the data center environment is difficult. This is
particularly true when the utility power grid enters the building through a
single entrance point (for example, through a utility room) and is then dis-
tributed to various building locations. These building configurations also
make it difficult to determine the power losses between the power entry into
the building and its delivery to the data center.
To further complicate the calculation of PUE and DCiE, the latest cooling
technologies integrate cooling elements such as pumps, refrigeration, blow-
ers, and heat exchangers within the IT equipment. These technologies blur
the lines between what has traditionally been a clear delineation between
facility equipment and IT equipment. However, equipment used to provide
power and cooling to the data center must be accounted for in the metrics
described in this chapter.