ENERGY STAR
EBAY DATA CENTER RETROFITS: THE
COSTS AND BENEFITS OF ULTRASONIC
HUMIDIFICATION AND VARIABLE SPEED DRIVES

eBay, with more than 90 million active users globally, serves as the world's largest online marketplace, where
practically anyone can buy and sell almost anything. They are committed to continually improving the efficiency and
environmental sustaina bility of their business. Data centers are the core
engine of so much of what they do, and it's essential thatthey continue
to innovate to get the maximum amount of work out of them, while
consuming the minimum amount of resources.
A major portion of this commitment can be seen in eBay's effort to reduce
its data centers' energy use. The design and construction of eBay's new
flagship $287 million data center facility1 has incorporated a myriad of
energy-efficiency measures. In addition, eBay considers retrofitting
existing data center facilities a top priority. eBay's 139,000 square foot
data center (65,000 square feet of white space) in Phoenix houses2 all of
eBay's business units. This facility, built in 2004, has been the target of
numerous energy-efficiency upgrades.
"eBay is to be commended for
their efforts to save energy
through these data center retrofit
measures and sharing their data
with EPA so that others can learn
from their efforts"
—Steve Ryan of EPA
ENERGY STAR program
manager.
This case study describes the costs and benefits deriving from two
retrofit measures eBay employed in its Phoenix facility: ultrasonic humidification; and variable speed drives (VSDs).
If implemented effectively, both measures can yield
Table 1. Retrofit Measure Paybacks	cost-effective energy savings. Table 1 presents
these measures' simple paybacks (costs divided by
annual energy savings), with and without incentives
from Arizona Public Service (APS) Company.
Ultrasonic humidification pays for itself in half a year
with incentives, and in less than 2.0 years without
incentives. VSDs pay for themselves in 1.6 years with
incentives and 2.6 years without incentives.
Measure
Payback without APS
Incentive (years)
Payback with APS
Incentive (years)
Ultrasonic
Humidification
1.9
0.5
Variable Speed
Drives
2.6
1.6
ULTRASONIC HUMIDIFICATION
Computer room air handlers (CRAHs) and computer room air conditioners (CRACs) rely on humidification units
to maintain data center humidity at specific levels. When data center humidity becomes too low, it can result in
electrostatic discharge (ESD) failures. Where humidity becomes too high, water can condense inside servers,
causing electrical shorts that trip circuit breakers, damage equipment, or
harm electrical circuits within the data center.
Typically, isothermal humidification methods (infrared and steam canister)
are used to maintain humidity levels. Ultrasonic humidification works
by vibrating water molecules3 (rather than heating them), producing a
fine mist (1 to 2 microns) of discharge. They use 90% less energy than
isothermal methods.
1 eBay's flagship facility hosts the eBay.com and Paypal.com Websites. The facility came online May 4,
2010, and is 30% more efficient than the most efficient data center in the EBay portfolio, with a designed
power usage effectiveness (PUE) of 1.4. http://www.datacenterknowledge.com/archives/2010/05/23/ebay-
unveils-new-fiagship-data-center/
2This includes server applications for the eBay services, analytical databases and storage devices
for internal analysis, and routers/switches to direct traffic to the applicable system arrays. In addition,
telecom gear will be required to interconnect to a fiber optic backbone.
3ln ultrasonic humidification, a small disc (often metal) transducer is vibrated through piezoelectric
application of voltage under a thin layer of water. The vibration's frequency is high enough to prevent
water molecules from conforming to the waveform induced by the transducer. The water cavitates on
the negative portion of the wave cycle, forming a micro pocket of negative pressure. Water in this micro
region is released from the surface tension of the thin film of water. Thus, small water droplets are
released into a discharge device, often a tube or fan assembly, http://www.datacenterfix.com/expert-
article/ultrasonic-humidification-data-center
"These rooms house UPS equipment, electrical switchgear, and chiller equipment.
The amount of humidification
required with an ultrasonic system
differs from the steam generator
units replaced. Proper sizing
should be reviewed with equipment
suppliers and engineers. In general,
steam humidifiers are oversized,
as their use leads to a higher heat
load, resulting in more cooling
that reduces relative humidity.
On the other hand, ultrasonic
humidification reduces cooling
loads, leading to less cooling,
which increases relative humidity.
At eBay, steam humidifiers supplied
533 lbs/hour of water vapor, while
ultrasonic humidification supplied
141 lbs/hour.

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Ultrasonic humidification must use
mineral-free, deionized water or water
treated with reverse osmosis. A reverse
osmosis/deionized water system
was already in place at eBay. When
considering ultrasonic humidification,
project managers must consider the costs
of installing these systems.
Table 2. Ultrasonic Humidification Payback

Power Draw
(kW)
Hours of Use5
Number of
Units
Energy Use
(kWh)
Steam Humidifier
30.3
4380
6
796,284
Ultrasonic Humidifier
0.67
4380
8
23,477
Energy Savings (kWh)
772,807
Energy Savings ($)
$50,232
Costs (labor and ultrasonic humidifier purchases)
$ 94,270
Payback (years)
1.9
Potential incentive at 11 cents per kWh
$85,009
Actual incentive limited to 75% of costs
$70,703
Payback (years) with Incentive
0.5
At eBay, the electrical and mechanical
equipment rooms4 were served by six, ducted
Air Handling Units, equipped with steam-
generating humidifiers to maintain the proper
humidity in those spaces. The duct-mounted
steam generating units were removed, and
room-mounted ultrasonic humidifiers were installed. Eight ultrasonic humidifiers were required to serve all areas adequately. The
newly installed ultrasonic humidifiers maintain equipment rooms at a relative humidity between 30% to 40%.
Table 2 shows energy use, savings, costs, and paybacks for eBay's purchase and installation of the ultrasonic humidifiers, with and
without the APS incentive. At the time of the retrofit, the incentive offered was 11 cents per kWh, capped at 75% of costs. Payback for
the costs was less than 2.0 years without the incentive and half a year with the incentive.
VARIABLE SPEED DRIVES
In the eBay facility, white space raised floor areas were cooled by 83 chilled water
CRAHs, each equipped with constant velocity fans. Each CRAH's chilled water valve
was controlled by a return air sensor, installed in the unit's return plenum. For this
retrofit, new high-efficiency motors (95% efficient) and new VSDs for the fans were
installed at each CRAH. VSD retrofit kits were supplied by the CRAH manufacturer.
In addition to these new installations, control system changes enabled more precise
use of the CRAH. Control changes included relocating the chilled water valve control
feed back sensor from the return air plenum to the supply air plenum, leading to much
better room temperature controls, and more consistentsupply air temperatures,
maintained at 65 degrees Fahrenheit.
Table 3. VSD Payback

Power (HP)
Efficiency
Hours of Use
Number of
Units
Energy Use
(kWh)
Constant Speed
10
90%
8760
83
6,026,685
Variable Speed
10
95%
8760
83
1,663,675
Energy Savings (kWh)
4,363,010
Energy Savings ($) at 6.5 cents per kWh
$ 283,596
VSD Equipment Costs
$341,960
Harmonic Transformer Costs
$338,984
VSD Installation Costs
$69,056
Payback (years)
2.6
Potential incentive at 11 cents per kWh
$479,931
Actual incentive limited to 50% of costs or $300,000
$300,000
Payback (years) with Incentive
1.6
Due to the amount of harmonics created
with VSD operations, 16 225-KVA
harmonic mitigating transformers had to
be installed. This caused project costs
to increase, and, more importantly,
proved to be one of the greatest
challenges during installation, primarily
due to locations of existing units in
electrical rooms, and many installed
in the overhead, complicating their
replacement.
The fan speed is controlled through an array
of wireless sensors installed in the cold
aisles. The CRAHs are responsible for specific
zones of control. Within these zones, in-row
temperatures sensors control fan speeds
to ensure sufficient cold air to maintain an
average cold aisle temperature of 75 degrees
Fahrenheit.
Table 3 shows energy use, savings, costs, and
paybacks with and withoutthe APS incentive.
The incentive for VSDs was 11 cents per kWh,
capped at 50% of costs or $300,000. Fan flow
rates were estimated at 65% of current rates
with VSDs. Paybacks were less than
3.0 years without the incentive, and less than
2.0 years with the incentive.
5 Humidifiers were estimated to run one-half the time. Other data centers may see much less frequent hours of use and should adjust their savings estimate accordingly.
ENERGY STAR®, a program sponsored by the U.S. EPA and DOE, helps us all
save money and protect our environment through energy efficient products
and practices. Learn more. Visitwww.energystar.gov.
ENERGYSTAR
March 2,2012

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