Questions for the CDCS were updated on : Nov 21 ,2025
Should aerosol cleaning solutions be used in the computer room?
B
Explanation:
Aerosol sprays release particulates and residues into the environment, which can contaminate
sensitive ICT equipment. Such contamination accelerates corrosion, interferes with airflow, and
increases particulate levels beyond ASHRAE recommended limits.
Proper cleaning should use HEPA-filtered vacuum systems or dry wipes, not aerosols. Even odor
control aerosols are disallowed in critical rooms.
Therefore, aerosol cleaning solutions must never be used.
Reference: ASHRAE TC 9.9 “Contamination Guidelines,” NFPA 75 §8.4.
Which class of UPS is ideal for data centers?
C
Explanation:
IEC 62040 defines UPS topologies:
VFD: Line-interactive; dependent on mains.
VI: Stabilizes voltage but not frequency.
VFI: Double-conversion online; fully isolates output from mains fluctuations.
Data centers require continuous, clean, and stable power. VFI is the only topology that protects
against both voltage and frequency disturbances, meeting ANSI/TIA-942 Rated-3/4 requirements.
Thus, VFI is the ideal UPS class.
Reference: IEC 62040-3, ANSI/TIA-942-B §6.2.
Where should perforated tiles be installed?
C
Explanation:
Perforated tiles should be located in front of equipment racks, aligned with cold aisles, to deliver
supply air directly to server intakes. Best practice is one perforated tile per rack, adjusted based on
airflow requirements and rack load.
Placing tiles at the back (A) disrupts airflow.
Spacing every 5th rack (B) provides insufficient cooling.
Placing near AC (D) causes uneven distribution and pressure loss.
Thus, option C is correct.
Reference: ASHRAE TC 9.9 “Airflow Management,” ANSI/TIA-942-B §6.5.
Does hot/cold aisle containment impact PUE?
B
Explanation:
Hot and cold aisle containment prevents mixing of supply and return air, which improves cooling
efficiency. By maintaining higher return-air temperatures, cooling units operate more efficiently,
often allowing higher chilled water setpoints. This reduces overall cooling power consumption,
directly improving PUE (Power Usage Effectiveness).
Containment is recognized by ASHRAE and Green Grid as one of the simplest and most cost-effective
methods for lowering PUE. Options A, C, and D are false because containment benefits apply
regardless of cooling source or IT virtualization.
Reference: ASHRAE TC 9.9 – Airflow Management, The Green Grid White Paper #42.
What is a disadvantage of hypoxic-based fire suppression?
A
Explanation:
Hypoxic systems continuously lower oxygen concentration (~15%) to prevent combustion. While safe
for short-term human exposure, standards like ISO 20338 recommend they are not suitable for
continuously occupied spaces, because reduced oxygen may cause fatigue, reduced cognition, and
health risks for staff.
B is irrelevant—air change rates affect dilution, not feasibility.
C is incorrect—tanks can be remote.
D is false—positive pressure is not required.
Thus, the main disadvantage is restriction to non-continuous occupancy.
Reference: ISO 20338 (Oxygen Reduction Systems), NFPA 770.
Two servers stacked with no gap (metal-to-metal). What heat transfer occurs?
B
Explanation:
Heat transfer occurs in three modes: conduction, convection, radiation. Conduction is transfer by
direct contact of solids. Since the servers are touching metal-to-metal, heat flows directly from the
warmer surface to the cooler one via conduction.
Radiation occurs without contact, across air or vacuum.
Convection requires a fluid medium like air, which is absent between surfaces.
“No heat transfer” is incorrect—there will always be transfer.
Therefore, the unwanted transfer here is conduction.
Reference: ASHRAE Fundamentals – Heat Transfer Basics, EXIN DCS Thermal Management Section.
A computer room with raised floor and hot/cold aisles is designed. What is the minimum required
distance between the air-conditioner outlet and the first rack?
C
Explanation:
To ensure uniform air distribution, there must be a buffer zone between CRAC/CRAH discharge and
the first row of racks. Industry best practice (ASHRAE & TIA-942) specifies at least 1.2 m (4 ft).
Less than 1.2 m risks air velocity hotspots and turbulence, disrupting cold aisle containment.
More than 1.8 m wastes valuable floor space without added benefit.
Thus, 120 cm is the recommended minimum.
Reference: ANSI/TIA-942-B §6.5.3 (CRAC placement), ASHRAE TC 9.9 Thermal Guidelines.
What is the advantage of OM5 multimode fiber cabling?
A
Explanation:
OM5 is optimized for Short Wavelength Division Multiplexing (SWDM) between 850–953 nm. This
allows transmission of multiple wavelengths over a single fiber pair, reducing the number of fibers
required for high-speed links.
OM4 already supports 100 GbE to 150 m, but OM5 with SWDM extends reach and reduces cabling
bulk.
Option B is false because OM5 offers distinct SWDM benefits.
Option C is incorrect—OM5 is laser-optimized, not LED-based.
Option D is misleading; OM5 doesn’t extend 100 GbE to 500 m (that requires single-mode OS2 fiber).
Thus, the key advantage is SWDM support.
Reference: ANSI/TIA-568.3-D, ISO/IEC 11801-1, IEEE 802.3cm (400G over MMF).
What is the first step in the design stage of the data center life cycle?
C
Explanation:
The life cycle begins with planning and design. The very first step is to clearly define the project
scope: business requirements, capacity, availability targets, compliance standards, and budget.
Without scope definition, design validation or vendor selection would be premature.
Vendor selection (A) happens much later during procurement.
Validation (B) occurs after conceptual and detailed designs are prepared.
Freezing design (D) is the final stage before implementation.
Therefore, defining the project scope is the correct initial step.
Reference: ANSI/TIA-942-B Annex F (Lifecycle), ISO/IEC 30182 (Smart City & DC Lifecycle), PMI
PMBOK (Scope Definition).
Management requests a 15-minute battery bank at full UPS load. UPS specs:
30 kVA, PF 0.8
Battery 384 V (192 cells), end discharge 308 V
Inverter PF 0.8, 400 V output
What information is missing to perform the calculation?
A
Explanation:
Battery sizing requires determining the real power demand of the UPS. With 30 kVA at 0.8 PF, the
real load is 24 kW. To calculate required ampere-hours for 15 minutes of runtime, we need:
Where P = load, t = runtime, V = battery voltage, and η = UPS efficiency.
Without UPS efficiency, we cannot know actual DC load on the batteries. A UPS with 90% efficiency
will require more battery capacity than one with 95%. None of the other listed parameters (PF,
imbalance, charging current) are critical for runtime capacity calculation.
Reference: IEEE Std 1188 (VRLA Batteries), IEC 62040-3 (UPS performance), ANSI/TIA-942-B §6.2.
What is the focus of the Open Compute Project (OCP)?
A
Explanation:
The Open Compute Project (OCP), initiated by Facebook in 2011, focuses on open designs for servers,
storage, racks, and power systems. The goals are:
Reduce energy consumption by using efficient hardware.
Save materials by eliminating unnecessary components.
Lower costs by standardizing and sharing open designs.
Option B is wrong—OCP hardware can be adopted by enterprises as well. Option C is unrelated (OCP
is hardware, not OS). Option D is broader cloud adoption, not OCP’s direct mission.
Thus, the primary focus is energy, material, and cost savings through open-source hardware.
Reference: OCP Foundation Mission Statement, ANSI/TIA-942-B Annex (Emerging Technologies).
Smoke sensors must be installed in the computer room. What is the minimum density?
C
Explanation:
NFPA 75 (Standard for IT Equipment Protection) and NFPA 72 (Fire Alarm Code) recommend installing
at least one smoke detector per 250 ft² (≈25 m²) in IT rooms. This ensures early detection in high-
value environments.
A and B are far too dense, exceeding NFPA minimums.
D is too sparse and would not meet early detection requirements.
Therefore, the correct standard density is 1 per 25 m².
Reference: NFPA 75 §5.4.3, NFPA 72 Table 17.6.3.5.1.
What is the redundancy setup shown in the diagram?
B
Explanation:
The diagram shows three UPS modules, each 100 kW, connected in parallel to support a 100 kW IT
load. That means:
One module (100 kW) can support the load (N).
Two additional modules are installed as redundancy.
This equals N+2 redundancy.
2+N+1 and 2(N+1) imply dual active paths not shown.
N+N+N is not an industry term.
Thus, the correct redundancy level is N+2.
Reference: ANSI/TIA-942-B §6.2 (UPS Redundancy Models), IEC 62040-3.
Racks with 1.0 m depth and cold aisle containment with 3 perforated tiles are used. What aisle pitch
is recommended?
B
Explanation:
The aisle pitch is the total width of a rack row plus cold aisle plus rack row. For 1.0 m racks on each
side with cold aisle containment, ASHRAE and TIA-942 recommend the 7-tile rule (each tile ~0.6 m).
This ensures enough width for equipment clearance, airflow distribution, and human access.
5-tile pitch is too narrow, restricting containment effectiveness.
8–10 tiles may be used in some hyperscale layouts but are not standard for 1 m racks.
Thus, the correct design recommendation is the 7 tiles pitch rule.
Reference: ANSI/TIA-942-B §6.3.6 (Aisle Spacing), ASHRAE TC 9.9 “Airflow Management Best
Practices.”
Which efficiency indicator accounts for all cooling costs (installation, operation, disposal)?
D
Explanation:
LCC (Life Cycle Cost) is the metric that accounts for capital cost, operational energy, maintenance,
and disposal/replacement. This holistic view is critical when evaluating cooling technologies like
CRACs, CRAHs, chilled water, or free cooling systems.
HER (Heat Exchange Ratio) and COP (Coefficient of Performance) measure operational efficiency but
not total lifecycle costs.
PUE measures overall data center efficiency but not specifically cooling CAPEX/OPEX.
Thus, LCC is the comprehensive metric that covers installation, operation, and disposal.
Reference: ISO 15686-5 (Life Cycle Costing), ASHRAE “Data Center Energy Efficiency Metrics,”
ANSI/TIA-942-B §7.