CDCP Data Center Cooling 4 — Questions and Answers
Question 1: What is immersion cooling in data centers, and what liquid is most commonly used?
- Cooling servers with misted water vapor; distilled water is most common
- Submerging server components in a thermally conductive but electrically non-conductive liquid such as dielectric fluid (Correct answer)
- Immersing entire racks in chilled air at near-freezing temperatures
- Cooling CPUs by injecting liquid nitrogen directly into server chassis
Correct answer: Submerging server components in a thermally conductive but electrically non-conductive liquid such as dielectric fluid
Immersion cooling submerges IT components in dielectric (non-conductive) fluids like mineral oil or engineered fluorocarbon fluids, achieving very high heat transfer rates.
Question 2: What is the role of a cooling tower in a data center chilled water plant?
- To store backup chilled water for use during compressor failures
- To reject heat from the condenser water loop to the atmosphere, completing the refrigeration cycle (Correct answer)
- To pre-cool incoming outside air before it enters CRAC units
- To distribute chilled water throughout the facility via gravity feed
Correct answer: To reject heat from the condenser water loop to the atmosphere, completing the refrigeration cycle
Cooling towers remove heat absorbed by the condenser water from the chiller's refrigeration cycle by evaporating water into the atmosphere.
Question 3: What is 'N+1 redundancy' in the context of data center cooling systems?
- Having one extra cooling unit beyond the minimum required to handle the full load (Correct answer)
- Running all cooling units at 100% capacity simultaneously
- Installing cooling units from N different manufacturers for diversity
- Providing cooling to N racks with one unit serving multiple rows
Correct answer: Having one extra cooling unit beyond the minimum required to handle the full load
N+1 redundancy means one additional cooling unit beyond the number needed (N) to handle full load, so if any single unit fails, the remaining units can still support the entire load.
Question 4: How does evaporative cooling improve data center cooling efficiency?
- By converting server heat into electrical energy through thermoelectric effects
- By using the latent heat of water evaporation to cool air or water, reducing mechanical refrigeration energy (Correct answer)
- By circulating evaporated water vapor through server chassis to absorb heat
- By preventing hot and cold air mixing through water vapor barriers
Correct answer: By using the latent heat of water evaporation to cool air or water, reducing mechanical refrigeration energy
Evaporative cooling exploits water's high latent heat of vaporization—as water evaporates, it absorbs significant heat energy, cooling the air or water stream with minimal electrical input.
Question 5: What is a 'thermal wheel' (or rotary heat exchanger) used for in data center cooling?
- A mechanical device that generates electricity from server waste heat
- A rotating heat transfer device that exchanges heat between exhaust and supply airstreams for economizer operation (Correct answer)
- A flywheel system that stores cooling energy for use during peak demand
- A spinning air distribution device that improves airflow uniformity in large data halls
Correct answer: A rotating heat transfer device that exchanges heat between exhaust and supply airstreams for economizer operation
A thermal wheel rotates between exhaust and supply airstreams, transferring heat (and sometimes humidity) between them, enabling economizer operation by pre-cooling supply air.
Question 6: Which ASHRAE thermal guideline document specifically addresses data center environmental guidelines for IT equipment?
- ASHRAE Standard 90.1
- ASHRAE TC 9.9 (Correct answer)
- ASHRAE Standard 55
- ASHRAE Standard 62.1
Correct answer: ASHRAE TC 9.9
ASHRAE TC 9.9 (Technical Committee 9.9) publishes the thermal guidelines for data processing environments, including the equipment class definitions and temperature/humidity ranges.
Question 7: What is 'Delta T' in the context of data center cooling system performance measurement?
- The time delay between a cooling demand signal and cooling unit response
- The temperature difference between supply air (or water) and return air (or water) across the cooling load (Correct answer)
- The difference in ambient temperature between summer and winter design conditions
- The temperature variance between the top and bottom of a server rack
Correct answer: The temperature difference between supply air (or water) and return air (or water) across the cooling load
Delta T (ΔT) measures the temperature rise across the IT load—a higher ΔT means the cooling system is transferring more heat per unit of airflow or water flow, indicating better efficiency.
CDCP Data Center Cooling 4
What is immersion cooling in data centers, and what liquid is most commonly used?