CRAH Variable Speed Drive Upgrade


Located in the Encanto Village neighborhood of downtown Phoenix, this industrial property was acquired by eBay in 2005.  The 139,000 square foot 4-story building has since been built out into a Tier IV data center with 65,000 square feet of whitespace, and a connected load of 7,300 kW.  Before implementing this project the data center had an annualized consumption of 64,000 MWh.


In the PHX01 data center, the whitespace raised floor areas are cooled by 83 chilled water Computer Room Air Handlers (CRAHs). Each CRAH is equipped with constant velocity fans and a chilled water valve is controlled by a return air sensor, installed in the unit’s return plenum.  The facility was originally designed for a Power Usage Effectiveness (PUE) of 1.8.  The total cost of this retrofit was $750,000 ($342,000 for VSD equipment; $69,000 for VSD installation; $339,000 for Harmonic Transformers).  The upgrades led to an annual energy savings of 4,363,000 kWh, and a reduction in the actual PUE of 1.71 to 1.59.  



Equipment Upgrades

For this retrofit, new high-efficiency motors (95% efficient) and new Variable Speed Drives (VSDs) for the fans were installed at each CRAH.  VSD retrofit kits were supplied by the CRAH manufacturer and aimed to reduce the fan load by allowing the motors to operate at slower speeds during periods of low demand.  


Operational Adjustments

In addition to these new installations to improve running performance and operational efficiencies, further control system changes enabled more precise use of the CRAHs.  Control changes included relocating the chilled water valve control feedback sensor from the return air plenum to the supply air plenum, leading to much better room temperature controls, and more consistent supply air temperatures, maintained at 65 degrees F.


As a result of these upgrades, the whole-building energy load was reduced by 7%, leading to $284,000 in annual energy cost savings.  The facility's ENERGY STAR® score has improved by 10 points after 12 months of operation, and efforts are underway to achieve a score of 75, the threshold for ENERGY STAR® Certification.



Throughout the retrofit process, the eBay energy team engaged with their local utility to understand available rebate programs, and opportunities to partner on larger projects. This relationship created a pathway for eBay which they plan to replicate in other locations, when implementing future efficiency projects. The eBay team also was able to focus on a single upgrade at a time by taking advantage of available rebates. Since it takes vigilant oversight to ensure savings are maintained, and ensure that impacts rebates could be significant if the baseline data is truncated or not representative of a year.  Operators made sure their BMS systems were monitored and trending key energy consumption values to enable baseline data collection, and ensure the team could make changes to systems as they encountered anomalies, and continually manage the energy performance.


Lessons Learned:

•    Ensure your BMS systems are monitoring and trending key energy consumption values in your system to enable baseline data collection.  Impacts to rebates could be significant if the baseline data is truncated or not representative of a year.
•    Even though significant annual savings are anticipated with these changes, it takes vigilant oversight to ensure these savings are maintained. Operators could make changes and systems could encounter anomalies, so a program must be continually managed to ensure success.



Annual Energy Use

Baseline (2010)
63,948,000 kWh
Actual (2011)
59,585,000 kWh

Energy Savings:

16.9% Reduction in PUE-1

Annual Energy Cost

Baseline Total Building Consumption (2010)
Actual Total Building Consumption (2011)

Cost Savings:

7% Reduction

Sector Type

Data Centers


Phoenix, Arizona

Project Size

139,000 square feet

Financial Overview

Project cost $750,000

PHX01 Data Center
PHX01 Data Center

CRAH harmonic mitigating transformers
CRAH harmonic mitigating transformers

CRAH VSD installation
CRAH VSD installation