ATP Power Usage Effectiveness & Efficiency 2 — Questions and Answers
Question 1: A data center reports a PUE of 1.0. What does this indicate?
- All power is used exclusively by IT equipment with zero overhead (Correct answer)
- The facility is operating at maximum cooling capacity
- Half the power is consumed by cooling systems
- The data center is running at 100% server utilization
Correct answer: All power is used exclusively by IT equipment with zero overhead
A PUE of 1.0 is theoretically perfect, meaning 100% of power goes to IT equipment with no overhead losses.
Question 2: Which metric is the mathematical reciprocal of PUE?
- DCiE (Data Center Infrastructure Efficiency) (Correct answer)
- ERE (Energy Reuse Effectiveness)
- WUE (Water Usage Effectiveness)
- CUE (Carbon Usage Effectiveness)
Correct answer: DCiE (Data Center Infrastructure Efficiency)
DCiE equals 1/PUE and expresses infrastructure efficiency as a percentage, where higher values are better.
Question 3: A colocation facility has total power draw of 8 MW and IT load of 5 MW. What is the PUE?
- 1.6 (Correct answer)
- 0.625
- 1.4
- 3.0
Correct answer: 1.6
PUE = Total Facility Power / IT Equipment Power = 8 MW / 5 MW = 1.6.
Question 4: What does a PUE measurement taken only at peak summer load fail to capture?
- Seasonal variation in cooling efficiency across the full year (Correct answer)
- The ratio of servers to networking equipment
- Total carbon emissions from the facility
- The cost of power per kilowatt-hour
Correct answer: Seasonal variation in cooling efficiency across the full year
PUE varies with ambient temperature and load, so a single peak-load measurement misses the more efficient winter and shoulder-season periods.
Question 5: Which of the following is NOT included in the IT equipment power denominator when calculating PUE?
- Computer room air conditioning (CRAC) units (Correct answer)
- Servers
- Storage arrays
- Network switches
Correct answer: Computer room air conditioning (CRAC) units
CRAC units are facility infrastructure overhead, not IT equipment, so they belong in the total facility power numerator only.
Question 6: What PUE improvement technique involves using outside air directly for cooling without mechanical refrigeration?
- Economization or free cooling (Correct answer)
- Hot aisle containment
- Power distribution unit (PDU) upgrades
- Server virtualization
Correct answer: Economization or free cooling
Economization (free cooling) uses ambient outdoor air or adiabatic cooling to eliminate compressor energy when temperatures permit, significantly lowering PUE.
Question 7: The Green Grid recommends measuring PUE at which boundary?
- At the utility meter entering the facility (Correct answer)
- At each individual server power supply
- At the raised floor perforations
- At the building transformer secondary
Correct answer: At the utility meter entering the facility
The Green Grid's standard boundary for total facility power is the utility meter, capturing all power consumed by the data center.
ATP Power Usage Effectiveness & Efficiency 2
A data center reports a PUE of 1.0.
What does this indicate?