I85PREP
⌘ K
CDCP study materials
CDCP study resources

CDCP: Data Centre Cooling and Environmental Control

CDCP · Work through your exam, one topic at a time.

All guide sections

Data Centre Cooling and Environmental Control

This domain tests heat removal and air management: sensible and latent loads, ASHRAE environmental envelopes, CRAC versus CRAH systems, containment, economisers, and PUE. Scenario questions often give a rack load and ask for unit count, airflow, or the likely cause of hot spots.

Heat, airflow, and environmental limits

  • Nearly all IT electrical energy becomes heat. Cooling capacity must be expressed as sensible capacity, not total capacity.
  • ASHRAE TC 9.9 recommended envelope for IT equipment is roughly 18–27°C with a dew point of 5.5–15°C and a maximum relative humidity cap; allowable envelopes are wider but carry reliability risk.
  • Airflow is front-to-back. Hot- and cold-aisle containment, blanking panels, brush seals, and correct perforated-tile placement reduce bypass and recirculation.
  • CRAC units use direct-expansion compressors; CRAH units use chilled water. Both need correct airflow, filtration, and condensate management.
  • Economisers (air-side or water-side) reduce compressor/chiller energy when outdoor conditions allow. PUE = total facility energy / IT energy; it is a measurement, not a design target.

Capacity checks

  • Cooling unit count: total IT load ÷ sensible capacity per unit, then add redundancy.
  • Airflow estimate: m³/s ≈ kW ÷ (1.2 × 1.005 × ΔT), where ΔT is the air temperature rise across the IT load.

Worked example - CRAC count and airflow. A hall has 60 racks at 5 kW each: 60 × 5 = 300 kW. Each CRAC provides 60 kW sensible cooling. N = 300 / 60 = 5 units; N+1 requires 6 units. If supply air is 20°C and return air is 30°C, ΔT = 10 K. Airflow ≈ 300 / (1.2 × 1.005 × 10) ≈ 24.9 m³/s. The selected units must deliver that airflow at the required external static pressure, and containment must keep cold air at the rack inlet. A unit count alone does not prove the design works.

Traps that cost marks

  • Using total cooling capacity instead of sensible capacity.
  • Ignoring humidity/dew point while focusing only on temperature.
  • Adding units without checking airflow, floor-tile placement, or containment.
  • Treating PUE as a fixed design target rather than a measured ratio.
  • Forgetting altitude, fouling, or condenser derating.