Calculate Power Usage Effectiveness as Part of Data Center Power Audit

By James McEnteggart  
OTHER PARTS OF THIS ARTICLEPt. 1: Data Center Power Audits Can Improve EfficiencyPt. 2: Measuring Steady, Variable Data Center Loads Critical for Power AuditsPt. 3: This Page

If the organization does not have the time or capabilities to perform the calculations and analysis in house, an energy consultant/engineer can analyze the data and calculate the PUE. (See "Calculating PUE," below.) Providing the data to the consultant can significantly reduce the time and cost of the analysis, or provide a second opinion of an in-house analysis. The energy consultant can analyze the data and recommend ways to improve the power usage efficiency and reduce the associated operating cost of the data center.

Ten percent is a conservative estimate of potential savings from optimizing existing HVAC equipment and gradually raising air-conditioner setpoints — and the older the facility, the greater the potential for savings. The consultant can also identify cost-effective upgrades for appropriate stages in the life cycle of components.

Step By Step

Performing a power audit that yields accurate, detailed data is the first crucial step in identifying opportunities for energy savings. Remember to leverage the BMS, which often has excellent trending capabilities that can simplify data collection. Work methodically along the power and heat-transfer paths, supplementing installed meters with data loggers if needed.

As the data analysis identifies energy uses that do not match expectations, investigate further. Knowledge is power, and it translates into savings.

James McEnteggart, PE, is vice president of Primary Integration Solutions LLC, a national mission critical commissioning firm headquartered in Charlotte, N.C. He has more than 20 years of experience in MEP design and commissioning for mission critical and health care facilities. Reach him at

Calculating PUE

An energy use index, which standardizes all measures of power use as kilowatt hours, is valuable in understanding the relative power consumed in the cooling load, IT load, and electrical losses. Developing a standardized energy use index is also necessary to calculate PUE, which can help a facility manager identify potential sources of inefficiency. However, PUE can also be misleading.

How to develop an energy use index:

  • Convert various units of measurement into a standard unit: kilowatt hours. BTUs (if used to measure chiller power use) must be convevrted to kilowatt hours.
  • Organize the data, assigning it to each of the major components and subcomponents of power use:
  • Cooling load: chilled water; air movement
  • IT load: computers
  • Electrical losses: transformers; UPS

Perform PUE calculation:

  • Divide total data center load over time by IT load in kW:

pue equation

— James McEnteggart

Continue Reading:

Data Center Power Audits Can Improve Efficiency

Measuring Steady, Variable Data Center Loads Critical for Power Audits

Calculate Power Usage Effectiveness as Part of Data Center Power Audit

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  posted on 11/9/2012   Article Use Policy

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