CDCP Energy Efficiency and Sustainability 5 — Questions and Answers
Question 1: A data centre uses a wet cooling tower for heat rejection. What environmental resource does this approach consume that a dry cooler does not?
- Electricity for compressors
- Refrigerant
- Water through evaporation (Correct answer)
- Natural gas for supplemental heating
Correct answer: Water through evaporation
Wet cooling towers reject heat through evaporative cooling, which consumes significant quantities of water—a concern captured by the Water Usage Effectiveness (WUE) metric.
Question 2: What is the recommended server inlet temperature range published by ASHRAE for Class A1 data centre environments?
- 10–25°C (50–77°F)
- 15–32°C (59–89.6°F)
- 18–27°C (64.4–80.6°F) (Correct answer)
- 5–20°C (41–68°F)
Correct answer: 18–27°C (64.4–80.6°F)
ASHRAE A1 class specifies an allowable inlet temperature range of 15–32°C, though the recommended range for optimal efficiency without risking equipment is 18–27°C.
Question 3: Which renewable energy procurement model allows a data centre operator to claim renewable energy credits without physically receiving green electricity at the facility?
- Behind-the-meter solar installation
- Power Purchase Agreement (PPA) with a remote wind farm
- Renewable Energy Certificate (REC) purchase (Correct answer)
- On-site diesel generator replacement
Correct answer: Renewable Energy Certificate (REC) purchase
RECs (Renewable Energy Certificates) represent the environmental attributes of one MWh of renewable generation and can be purchased separately from the physical electricity supply.
Question 4: What is 'IT equipment utilization' in the context of data centre energy efficiency, and why does it matter?
- The ratio of virtual machines to physical servers; higher ratios increase cooling load
- The percentage of provisioned IT capacity actively processing workloads; low utilization wastes energy on idle servers (Correct answer)
- The network bandwidth consumed by IT assets; unused bandwidth wastes switching energy
- The ratio of storage capacity used to total provisioned storage; unused storage draws no power
Correct answer: The percentage of provisioned IT capacity actively processing workloads; low utilization wastes energy on idle servers
Most servers consume 60–70% of peak power even when idle, so low utilization means significant energy is wasted on servers that are provisioned but not doing productive work.
Question 5: A facility-wide energy audit reveals that legacy UPS systems operate at 85% efficiency. What technology should the operator consider to improve this?
- Modular UPS with high-efficiency (eco) mode (Correct answer)
- Additional static bypass switches
- Larger lead-acid battery strings
- Higher-rated transfer switches
Correct answer: Modular UPS with high-efficiency (eco) mode
Modern modular UPS systems with eco (high-efficiency) mode can achieve efficiencies of 97–99%, dramatically reducing conversion losses compared to legacy double-conversion UPS at 85%.
Question 6: Which of the following best describes a 'carbon-neutral' data centre operation?
- A facility that generates all its own electricity on-site using solar panels
- A facility that offsets its net greenhouse gas emissions through renewable energy and carbon credits (Correct answer)
- A facility that consumes no electricity from fossil-fuel sources under any circumstances
- A facility that achieves a PUE of exactly 1.0
Correct answer: A facility that offsets its net greenhouse gas emissions through renewable energy and carbon credits
Carbon neutrality means that a data centre's net greenhouse gas emissions are balanced by equivalent reductions or offsets, such as renewable energy purchases and verified carbon credits.
Question 7: What is the significance of a 'partial PUE' (pPUE) measurement in large, multi-tenant or campus data centres?
- It measures PUE only during peak summer months to identify worst-case efficiency
- It calculates PUE for a specific zone or module rather than the entire facility, enabling granular efficiency analysis (Correct answer)
- It excludes lighting and security systems from the PUE denominator
- It adjusts PUE for outdoor ambient temperature variations
Correct answer: It calculates PUE for a specific zone or module rather than the entire facility, enabling granular efficiency analysis
Partial PUE (pPUE) isolates the efficiency of a specific data hall, pod, or module within a larger campus, allowing operators to pinpoint inefficiencies at a more granular level than facility-wide PUE.
CDCP Energy Efficiency and Sustainability 5
A data centre uses a wet cooling tower for heat rejection.
What environmental resource does this approach consume that a dry cooler does not?