CDCS CDCS Power & Cooling Systems 2 — Questions and Answers
Question 1: What is the ASHRAE A1 thermal envelope recommended inlet temperature range for most enterprise IT equipment?
- 41°F–77°F (5°C–25°C)
- 59°F–89.6°F (15°C–32°C) (Correct answer)
- 32°F–68°F (0°C–20°C)
- 68°F–95°F (20°C–35°C)
Correct answer: 59°F–89.6°F (15°C–32°C)
ASHRAE A1 class specifies an allowable inlet temperature range of 59°F to 89.6°F (15°C to 32°C) for standard enterprise servers and storage equipment.
Question 2: Which cooling technology uses water-chilled rear-door heat exchangers attached directly to server cabinets?
- In-row cooling
- Rear-door heat exchanger (RDHx) (Correct answer)
- Economizer free cooling
- Computer room air handler (CRAH)
Correct answer: Rear-door heat exchanger (RDHx)
Rear-door heat exchangers (RDHx) mount directly on the back of server racks, capturing hot exhaust air at the source and transferring heat to chilled water before it enters the room.
Question 3: What does N+1 redundancy mean in the context of data center UPS systems?
- One UPS module backs up the entire facility
- One additional UPS module beyond the minimum required for full load (Correct answer)
- All UPS modules run at 100% load
- N UPS modules share load while one is offline for maintenance
Correct answer: One additional UPS module beyond the minimum required for full load
N+1 redundancy means one extra capacity unit beyond the minimum (N) needed to support the full load, so the system tolerates one unit failure without losing capacity.
Question 4: What is the primary advantage of using a hot-aisle containment (HAC) system over cold-aisle containment (CAC)?
- HAC lowers server inlet temperatures more effectively
- HAC keeps the general room air cooler and safer for personnel (Correct answer)
- HAC requires fewer perforated floor tiles
- HAC eliminates the need for raised floor plenum
Correct answer: HAC keeps the general room air cooler and safer for personnel
Hot-aisle containment captures exhaust heat directly at the hot aisle and routes it to cooling units, so the ambient room temperature remains at a comfortable level for personnel working outside containment.
Question 5: Which metric describes the percentage of time a data center's power infrastructure is expected to be available per year?
- PUE
- DCiE
- Uptime percentage (nines) (Correct answer)
- DCIE
Correct answer: Uptime percentage (nines)
Availability is expressed as uptime percentage (e.g., 99.9999% = six nines), which correlates to Uptime Institute tier classifications for annual downtime tolerance.
Question 6: What is the function of a static VAR compensator (SVC) or active harmonic filter in a data center electrical system?
- Provide backup power during utility outages
- Mitigate harmonic distortion generated by non-linear IT loads (Correct answer)
- Step up voltage from utility feed to distribution level
- Synchronize generator frequency with utility frequency
Correct answer: Mitigate harmonic distortion generated by non-linear IT loads
Active harmonic filters inject corrective currents that cancel the harmonics produced by non-linear IT equipment loads, reducing total harmonic distortion (THD) and protecting electrical infrastructure.
CDCS CDCS Power & Cooling Systems 2
What is the ASHRAE A1 thermal envelope recommended inlet temperature range for most enterprise IT equipment?