Now that the recession is over, most of
us find ourselves in the same boat … trying to survive the
recovery! In the enterprise, capital budget cuts have returned with a
vengeance, and operating cost reduction programs are taking the form
of corporate green initiatives. So, “reducing energy costs with no
money to do it” seems to be the order of the day.
As
a result, companies are looking for operating strategies that target
the highest cost items and that give the biggest bang for the buck.
In data centers, companies usually try to reduce the energy costs of
providing HVAC.
I’d like to suggest some
easy and low-cost strategies to help data center operators achieve
greater energy-efficiency in their HVAC systems, along with a
step-by-step discussion to help them consider as many opportunities
as possible. These strategies are most effectively implemented in
facilities operating with greater capacity than
demand.
1. Controlling
your environment allows you to turn equipment off.Simple but prudent
changes to equipment operations take little time and effort to
implement. For example, turning off CRAC re-heaters and humidifiers
can pay off with reductions in both energy and maintenance costs.
Some devices may need to be turned back on to remain within ASHRAE
recommended limits for data center operations, so it is important to
monitor local temperature and humidity readings after these changes
are made.
On a larger scale, almost all of
today’s legacy data centers can profit from the “miracle” of
airflow controls. Heat removal and airflow strategies have improved
dramatically over the last few years and are now recognized as the
most influential single factor in defining the demand for data center
air conditioning. In order to take advantage of the newest airflow
strategies, it is important to maintain good control of the IT space
and to implement as many of the following progressive improvements as
possible.
At a minimum, IT equipment should
be laid out in open-air racks with racks and servers in a hot
aisle/cold aisle configuration. In this configuration, controls to
minimize by-pass air such as plugs in floor penetrations and blanking
panels in server racks can be very effective. These controls deliver
cooler air to the IT equipment and reduce the volume of air required
to remove the heat load. This reduction in chilled air is a strategic
improvement that may allow you to turn off some CRAC units. Turning
off CRAC units is one of the most aggressive methods of reducing HVAC
energy. Not only can the energy needed to power the CRACs be saved,
but the chillers and cooling towers that feed the CRACs can be turned
down as well. This procedure should be implemented with some caution
to assure that the necessary air pressures and volumes are maintained
in all areas populated with IT equipment.
Next,
damming chilled air in the under-floor plenum spaces below the
unpopulated areas of a raised floor can reduce demand further. More
CRAC units can be turned off as a result, along with the chiller and
tower capacity that supports them. Paneling off vacant areas to
contain chilled airflow creates a similar effect in IT spaces with
overhead air delivery systems.
Finally,
enclosing aisles with strip curtains or panels separates the chilled
supply air from the hot server-exhaust air and prevents their mixing.
That assures the delivery of air with predictable and uniform
temperatures to all the cold aisles so the supply air temperature can
be raised to the desired server inlet temperature...often twenty
degrees higher than before. This is another significant and strategic
improvement as the demand for chilled air is again reduced
dramatically; this time allowing for higher air temperatures instead
of lower air volumes. As a result of this change, chillers and
cooling towers can be turned down even further.
Computational fluid dynamics modeling can be
a valuable tool in predicting the changes in airflow temperatures and
volumes that you are bound to experience when deploying these new
airflow strategies in existing facilities. Monitoring the operating
environment during change can confirm what the analytical models
predicted.
2. Slow
down the fans, control the pumps, and open up the windows.With
airflow temperatures and volumes closer to an ideal state, equipment
controls can be added to take advantage of the new environmental
conditions while providing for more efficient and reliable
operations. From the perspective of energy efficiency, variable
frequency drives (VF) and economizers are possibly the two best
investments that a data center owner can make. These controls systems
remove much of the uncertainty inherent in the operating changes
suggested above.
VFDs provide several benefits
to systems operations. First, they allow equipment to operate at
ideal speeds to more precisely meet the demand for cooling, instead
of operating some equipment at full speed while other equipment is
off. Operating more equipment at lower speeds to achieve the same
total flow rates can provide surprising energy savings. And, the
lower operating speeds reduce equipment maintenance costs as well as
energy consumed. CRAC VFDs also provide a more uniform distribution
of static pressure in the cold aisles.
VFDs
are simple improvements that offer excellent returns on investment.
Usually, they can be easily installed on most rotating equipment
including chilled water CRACs, chillers, chilled water pumps,
condenser water pumps, and cooling tower fans and recirculation
pumps. VFDs and compressor controls are now being retrofitted onto
air-cooled and water-cooled Dx CRAC units, as well. This is something
that manufacturers often frown upon because of Dx CRAC design
limitations, but appropriate safeguards can be taken to avoid
problems involving freezing of the refrigerant.
Economizers,
on the other hand, use outside air to remove the data center heat
load instead of using the re-circulated air cooled by chiller plants.
Economizers introduce cool outside air directly into the data center
or via a heat exchanger, to remove IT equipment heat loads. In either
case, economizer operations sometimes allow an operator to turn off
chillers and cooling towers completely, and those energy savings can
be huge. Economizers can be expensive propositions in an existing
facility. But, when aisles are enclosed and supply air temperatures
are elevated, economizers can provide a quick return on investment
because they can operate for so many additional hours at higher
temperatures with little or no support from a chiller
plant.
Two other factors contribute to
achieving good returns on investment with economizers. First is the
selection of a cost-effective distribution system. Air economizers,
for example, can be designed to deliver outside air directly into
plenums that are already connected to existing distribution systems
so that new metal ductwork is less needed. And last, but not least,
electrical utility energy-efficiency incentives can turn an
economizer project that might not otherwise considered into a very
reasonable investment.
CFRT is a non-profit
organization based in the Silicon Valley and dedicated to the sharing
of information and solutions amongst our members made up of critical
facilities owners and operators. Please visit our Web site atwww.cfroundtable.orgor contact us at 415-748-0515 for more
information.