R&M Data Center Handbook

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1.10. Energy Efficiency – Initiatives and Organizations
There are numerous measures for increasing energy efficiency in data centers. The chain of cause and effect
starts with applications, continues with IT hardware and ends with the power supply and cooling systems.
A very important point is that measures taken at the very beginning of this chain, namely for causes, are the most
effective ones. When an application is no longer needed and the server in question is turned off then less power is
consumed, losses in the uninterruptible power supply decrease and so does the cooling load.
Virtualization – a way out of the trap
Virtualization is one of the most effective tools for a cost-efficient green computing solution. By partitioning
physical servers into several virtual machines to process applications, companies can increase their server
productivity and downsize their extensive server farms.
This approach is so effective and energy-efficient that the Californian utility corporation PG & E offers incentive
rebates of 300 to 600 U.S. dollars for each server that is saved thanks to Sun or VMware virtualization products.
These rebate programs compare the energy consumption of existing systems with that of systems in operation
after virtualization. The refunds are paid once the qualified server consolidation project is implemented. They are
calculated on the basis of the resulting net reduction in kilowatt hours (at a rate of 8 Cents per kilowatt hour). The
maximum rebate is 4 million U.S. dollars or 50 percent of the project costs.
By implementing a virtual abstraction level to run different operating systems and applications, an individual server
can be cloned and thus used more productively. On the strength of virtualization, energy savings can be increased
in practice by a factor of three to five – and even more in combination with a consolidation to high-performance
multi-processor systems.
Cooling – great potential for savings
A rethinking process is also taking place in the area of cooling. The cooling system of a data
center is turning into a major design criterion. The continuous increase in processor performance
is leading to a growing demand for energy, which in turn leads to considerably higher
cooling loads. This means that it makes sense to cool partitioned sections in the data center
individually, in accordance with the specific way heat is generated in the area.
The challenge is to break the vicious circle of an increased need of energy leading to more heat, which in turn has
to be cooled, consuming a lot of energy. Only an integrated, overall design for a data center and its cooling
system allows performance requirements for productivity, availability and operational stability to be synchronized
with an energy-efficient use of hardware.
In some data centers, construction design focuses more on aesthetics than on efficiency, an example being the
hot aisle/cold aisle constructions. Water or liquid cooling can have an enormous impact on energy efficiency, and
is 3000 times more efficient than air cooling. Cooling is further discussed in section 3.5.2.
Key Efficiency Benchmarks
Different approaches are available for evaluating the efficient use of energy in a data center.
The approach chosen by the Green Grid organization works with two key benchmarks: Power
Usage Efficiency (PUE) and Data Center Infrastructure Efficiency (DCIE). While PUE
determines the efficiency of the energy used, the DCIE value rates the effectiveness of the
energy used in data centers. The two values are calculated using total facility power and IT
equipment power. The DCIE value is the quotient of IT equipment power and total facility
power, and is the reciprocal of the PUE value. The DCIE thus equals 1/PUE and is expressed
as a percentage.
A DCIE of 30 percent means that only 30 percent of the energy is
used to power the IT equipment. This would result in a PUE value of
3.3. The closer this ratio gets to the value of 1, the more efficiently the
data center uses its energy. Google can claim a PUE value of 1.21 for
6 of their largest facilities.
Total facility power includes the energy used to power distribution
switch board, the uninterruptible power supply (UPS), the cooling
system, climate control and all IT equipment, i.e. computers, servers,
and associated communication devices and peripherals.
PUE
DCiE
Level of
efficiency
3.0 33% very inefficient
2.5 40% inefficient
2.0 50% average
1.5 67% efficient
1.2 83% very efficient
Page 14 of 156 © 08/2011 Reichle & De-Massari AG R&M Data Center Handbook V2.0