High Density Cooling by PTS Data Center Solutions, Inc.
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The power consumed, and heat generated, by the equipment housed in a single server rack enclosure can vary dramatically. Modern servers may demand as much as 20 kW of cooling per rack, approximately 10 times the average rack power in existing data centers. With most data centers designed to cool an average of 2 kW per rack, innovative strategies must be used to guarantee proper high density cooling.
The simple answer to this problem would be to provision a data center so that it is capable of providing 20 kW of redundant power and high density cooling to every enclosure. Unfortunately, this is not easily achieved, nor economically practical in most cases. However, there are a variety of solutions that allow high density computing equipment to be effectively deployed in conventional environments.
PTS encourages our customers to focus on the purchase of IT equipment based on functionality provided per Watt and ignore the physical size of the IT equipment. While designing entire data centers for high density remains impractical, data centers can support the limited installation of such equipment by using supplemental high density cooling systems, using rules to allow the borrowing of neighboring underutilized capacity, and by spreading the load among multiple enclosures.
Making the wrong choices when specifying a data center for high density cooling operations can needlessly increase the lifetime cost of the physical infrastructure exponentially. High density servers present a significant cooling challenge, but the experts at PTS can easily design efficient, cost-effective cooling strategies that match your needs.
PTS approaches data center cooling designs using our proven
project process approach:
Design goals are established across the following categories:
- Adaptability
- Availability
- Maintainability
- Manageability
- Cost
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Once appropriate design goals are established there are a number
of additional steps recommended for data center cooling best
practices.
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Determine the Critical Load and Heat Load.
Determining the critical heat load starts with the
identification of the equipment to be deployed
within the space. However, this is only part of the
entire heat load of the environment. Additionally,
the lighting, people, and heat conducted from the
surrounding spaces will also contribute to the
overall heat load. As a very general rule-of-thumb,
consider no less than 1-ton (12,000 BTU/Hr / 3,516
watts) per 400 square-feet of IT equipment floor
space.
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Establish Power Requirements on a per RLU Basis.
Power density is best defined in terms of rack or
cabinet foot print area since all manufacturers
produce cabinets of generally the same size. A
definite Rack Location Unit (RLU) trend is that
average RLU power densities are increasing every
year. The reality is that a computer room usually
deploys a mix of varying RLU power densities
throughout its overall area. The trick is to provide
predictable cooling for these varying RLU densities
by using the average RLU density as a basis of the
design while at the same time providing adequate
room cooling for the peak RLU and non-RLU loads.
-
Determine the CFM Requirements for each RLU.
Effective cooling is accomplished by providing both
the proper temperature and an adequate quantity of
air to the load. As temperature goes, the American
Society of Heating, Refrigerating, and
Air-Conditioning Engineers (ASHRAE) standard is to
deliver air between the temperatures of 68 °F and 75
°F to the inlet of the IT infrastructure. Although
electronics performs better at colder temperatures
it is not wise to deliver lower air temperatures due
to the threat of reaching the condensate point on
equipment surfaces. Regarding air volume, a load
component requires 160 cubic feet per minute (CFM)
per 1 kW of electrical load. Therefore, a 5,000-watt
1U server cabinet requires 800 CFM.
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Perform Computational Fluid Dynamic (CFD)
Modeling. CFD modeling can be performed for the
under floor air area as well as the area above the
floor. CFD modeling the airflow in a computer room
provides information to make informed decisions
about where to place CRAC equipment, IT-equipment,
perforated tiles, high density RLUs, etc. Much of
the software available today also allows mapping of
both under floor and overhead airflow obstructions
to more accurately represent the environment.
-
Determine the Room Power Distribution Strategy.
The two (2) main decisions in developing a room
power distribution strategy are: (1) Where to place
the power distribution units (PDUs)?, (2) Whether to
run power cables overhead or under the floor?
-
Determine the Cabinet Power Distribution Strategy.
In deciding how power will be distributed
through the cabinet, use of dual power supplies, and
cabling approach, it is important to understand the
impact of power distribution on cooling,
particularly as it is related to air flow within the
cabinet.
-
Determine the Room & Cabinet Data Cabling
Distribution Impact. Typically, there are three
(3) choices in delivering network connectivity to an
RLU. They are: (1) Home run every data port from a
network core switch, (2) Provide matching
port-density patch panels at both the RLU and the
core switch with pre-cabled cross-connections
between them, such that server connections can be
made with only patch cables at both ends, (3)
Provide an edge switch at every rack, row, or pod
depending on bandwidth requirements. This approach
is referred to as zone switching.
 Establish a Cooling Zone Strategy.
Recall that
effective computer room cooling is as much about
removing heat as it is about adding cold. Generally
speaking, the three (3) equipment cooling methods
along with their typical cooling potential can be
determined from the following table:
| Room Cooling |
~2 kW per RLU |
| Row Cooling |
~8 kW per RLU |
| Cabinet Cooling |
~20 kW per RLU |
It is also critical to consider high-density cooling
and zone cooling requirements.
-
Determine the Cooling Methodology.
Upon
determining what cooling zone will be required, the
decision of what types of air conditioners will be
needed, must be made. There are four (4) air
conditioner types: (1) air cooled, (2) glycol
cooled, (3) condenser water cooled, (4) chilled
water.
In addition, it is also important to determine
how heat will be rejected within the system and what
type of cooling redundancy is required and available
for a particular methodology.
-
 Determine
the Cooling Delivery Methodology. Different
architectural attributes affect cooling performance
in different ways. For instance, designs should
consider the location of the computer room within
the facility (I.e. onside versus inside rooms),
height of the raised floor, height of suspended
ceiling, etc.
-
Determine the Floor Plan.
The ‘hot aisle / cold
aisle’ approach is the accepted layout standard for
RLUs for good reason. It works. It was developed by,
Dr. Robert Sullivan, while working for IBM and it
should be adapted for both new and retrofit
projects. After determining the hot/cold
aisles it is critical to place the CRAC units for
peak performance. This may include room, row, or
rack based cooling approaches. Each works well
depending upon the IT infrastructure, power
densities, CFM requirements, and other attributes
previously discussed.
-
Establish Cooling Performance Monitoring.
It is
vital to develop and deploy an environmental
monitoring system capable of monitoring each room,
row, and cabinet cooling zone. A given is that once
effective cooling performance is established for a
particular load profile, it will change rapidly. It
is important to compile trending data for all
environmental parameters for the site such that
moves, adds, and changes can be executed quickly.
To learn more about PTS consulting services to support Air Conditioning Equipment & Systems deployments and support,
contact us
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Systems,
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