Submittal

WW-CPWP-09, Rev.0, 09/2009
©2009 PANDUIT Corp. All rights reserved.
5
Deploying a Vertical Exhaust System
to Achieve Energy Efficiency and Support Sustainability Goals
The segregation of hot and cool air allows the data center to be operated at a higher temperature set point,
which in turn reduces energy consumption by the cooling system. Directing hot air into the return plenum also
reduces energy use by maximizing the difference in temperature between the return air and chilled water across
cooling coils, which enables CRAH units to run at higher capacity. The deployment of a VES-based air
containment system provides opportunities to lower CRAH fan speeds and observe fan power savings while
maintaining the cabinet inlet temperatures within the desired range (e.g., ASHRAE-recommended temperature
limit of 80.5ºF).
A VES enables significant energy savings in the data center by potentially reducing the number of CRAH units
required to obtain desired thermal performance and by optimizing the work performed by those units, resulting
in immediate and considerable energy and cost savings. For example, a 3,000 ft
2
raised floor data center with
68 server cabinets would require 6 CRAH units to manage 8 kW of heat per cabinet. As equipment is added,
data center stakeholders face the challenge of managing the additional thermal load.
This hypothetical data center would require additional CRAH units to reliably manage up to 10 kW per cabinet,
at a capital cost of $35,000 per unit. At an average electrical utility rate of $0.11 per kW-hr, the cost to operate a
CRAH unit at maximum capacity runs about $9,000/yr
2
, plus any other installation and maintenance costs to
service the unit. By contrast, for less than the cost of one CRAH unit, a passive VES can be deployed on all
heat-generating cabinets to manage thermal loads without additional ongoing operating costs (see Table 2).
All of these factors combine to reduce cooling system operating costs by at least 25%, with actual cost savings
potentially increasing with layout configuration, equipment density, and maintenance savings. For all these
reasons it is clear that VESs are the cost-effective (and green) choice to efficiently cool high heat-generating
cabinets.
Table 2. Cost Savings Achieved Using Passive VES for Thermal Management (3,000 ft
2
Data Center with
68 Server Cabinets)
Capital Costs* Utility Costs**
Thermal
Management
Option
CRAH
unit cost
# of
CRAH
VES
unit cost # of VES Total
Annual
per
CRAH Total
Option 1: Additional
CRAHs
$35,000 8 $700 0 $280,000 $9,023 $72,184
Option 2: VES
Cabinets
$35,000 6 $700 37 $235,900 $9,023 $54,138
Total Cost Savings Using VES $44,100 $18,046
% Cost Savings Using VES 16% 25%
Assumptions:
* Does not include cost to install.
**Electricity rate of $0.11 per kW-hr.
Return on Investment (ROI) For VES Deployment
Payback period: 0.3 years
10-year ROI: 266%
2
Value calculated with the Liebert Power and Cooling Energy Savings Estimator, using an electricity rate of $0.11 per
kW/hr at 90% motor efficiency.