White Paper

7
It is also advantageous to locate sensors near
the end of the row where they can detect
any hot air entering the cold aisle from the
hot aisle.
There are advantages to connecting
the temperature sensors directly to the
cooling system, as with the Liebert CRV,
as well as to a central monitoring system.
When the sensors and cooling system are
working in concert, the cooling system
can automatically adapt its operation
to eliminate hot spots, respond to heat
load changes, detect obstructions and
coordinate its operation with other cooling
units working in the same zone.
ASHRAE provides more detailed guidelines
for sensor location in the paper Thermal
Guidelines for Data Processing Environments.
2. Monitoring power usage
With power densities and energy costs
both rising, the ability to monitor energy
consumption is essential for effective data
center management. Where one measures
power can have an effect on how efciency
is measured. See the discussion of PUE
monitoring in Step 8 for more information
on efciency monitoring.
To gain a comprehensive picture of data
center power consumption, power should
be monitored at the Uninterrumpible
Power Supply (UPS), the room Power
Distribution Unit (PDU) and within the
rack. Measurements taken at the UPS
provide a base measure of data center
energy consumption that can be used to
calculate Power Usage Effectiveness (PUE)
and identify energy consumption trends.
Monitoring the room PDU prevents overload
conditions at the PDU and helps ensure
power is distributed evenly across the
facility.
The best view of IT power consumption
comes from the power distribution
units inside racks. Rack PDUs now
feature integrated monitoring and
control capabilities to enable continuous
power monitoring. Because rack power
consumption varies based on the specic
equipment within the rack and its load,
each rack should be equipped with a PDU—
two for dual bus environments—capable
of monitoring power consumption to the
rack PDU, as well as overload-protected
receptacle groups and, where required, at
the receptacle level.
These systems can provide PDU, branch-
level and receptacle-level monitoring of
volts, kilowatts (kW), amps and kW per hour.
This provides the most direct measure of
power consumption available to data center
management and supports both higher data
center efciency and availability. In addition
to more effective power management, rack
PDUs are used to support more accurate
chargeback of IT services and identify
stranded capacity.
Some models also enable individual
receptacles to be turned on and off remotely
to prevent the addition of new devices that
could create an overload condition.
3. Monitoring rack conditions
With increasing densities, a single rack can
now support the same computing capacity
that used to require an entire room. Visibility
into conditions in the rack can help prevent
many of the most common threats to rack-
based equipment, including accidental or
malicious tampering, and the presence
of water, smoke and excess humidity or
temperature.