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EXIN CDCE practice questions

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Question 1Data centre design

In data centre design, what does the term 'white space' refer to?

  1. The ceiling void used for cable trays and fire suppression piping
  2. The raised-floor area where IT equipment is installed and operated Correct answer.
  3. The electrical switchgear room adjacent to the main data hall
  4. The outdoor generator yard and fuel storage area

Explanation

White space is the industry term for the conditioned technical space in which IT racks are housed and operated, including the aisles around them. It is distinct from support spaces such as electrical rooms, plant areas and outdoor yards, which serve the white space but are not part of it.

Question 2Data centre design

Which metric expresses the total facility power divided by the IT equipment power?

  1. Power usage effectiveness (PUE) Correct answer.
  2. Rack power density
  3. Data centre infrastructure efficiency (DCiE)
  4. Energy reuse factor (ERF)

Explanation

PUE is defined as total facility energy divided by IT equipment energy, so a value closer to 1.0 indicates less overhead consumption. DCiE is its reciprocal expressed as a percentage, and rack power density describes load per rack rather than efficiency.

Question 3Data centre design

A design team must choose a topology that tolerates the failure of any single power path without interrupting the IT load. Which configuration meets this requirement?

  1. Two independent UPS systems, each feeding one cord of dual-corded servers Correct answer.
  2. One UPS with a maintenance bypass feeding a single power strip
  3. Two UPS modules sharing a common output distribution board
  4. A single UPS feeding dual-corded servers through one PDU chain

Explanation

Concurrent maintainability of the power path requires two independent distribution paths, each capable of carrying the load, with equipment connected to both. Sharing any common output element (a single board or strip) reintroduces a single point of failure.

Question 4Data centre design

In hot-aisle/cold-aisle layout, what is the primary purpose of fitting blanking panels in unused rack U positions?

  1. To prevent hot exhaust air from recirculating into the cold aisle Correct answer.
  2. To improve the earthing continuity of the rack
  3. To simplify cable management between adjacent cabinets
  4. To reduce the weight carried by the rack frame

Explanation

Open U positions let exhaust air from the hot aisle pass back through the rack into the cold aisle, raising inlet temperatures. Blanking panels seal those openings so supply air reaches equipment intakes as intended.

Question 5Data centre design

A data hall is designed for 8 kW per rack using air cooling with a 12 kW per rack future target. Which design decision best preserves the option to reach the higher density later?

  1. Install additional CRAC units only after the higher-density equipment arrives
  2. Design for higher airflow and chilled-water capacity than the initial load requires Correct answer.
  3. Specify racks with greater usable U height to spread the load
  4. Reduce the number of racks in the hall to lower total heat output

Explanation

Future density growth is limited by the capacity of the cooling and airflow infrastructure, so designing air distribution and chilled-water capacity with headroom preserves the upgrade path. Adding plant later is far more disruptive than provisioning capacity at build stage.

Question 6Data centre design

Which statement correctly describes the role of a maintenance bypass in a UPS system?

  1. It converts the UPS from double-conversion to line-interactive operation
  2. It transfers the IT load to the utility supply so the UPS can be serviced without dropping load Correct answer.
  3. It disconnects the battery string during a mains failure
  4. It limits fault current flowing into the UPS output distribution

Explanation

A maintenance bypass provides an alternative feed to the load, allowing the UPS module to be isolated and serviced while IT equipment stays energised. It is a switching arrangement, not a conversion mode or a protective device.

Question 7Data centre design

A raised floor is being designed to supply cold air through perforated tiles. Which factor most directly determines the achievable airflow per tile?

  1. The rack earthing arrangement
  2. The colour of the floor tiles
  3. The open area of the tile and the static pressure in the plenum Correct answer.
  4. The number of cable trays under the floor

Explanation

Tile airflow depends on the free open area of the perforations and the pressure differential between the plenum and the room. Designers balance open-area percentage and plenum pressure to deliver the required flow without excessive fan energy.

Question 8Data centre design

Why is a data centre often zoned into halls of limited size rather than one very large open hall?

  1. Zoning is required to obtain an energy performance certificate
  2. Larger halls cannot be cooled by any mechanical system
  3. Building codes prohibit data halls larger than 500 square metres
  4. Smaller halls limit the blast radius of a failure and allow staged deployment Correct answer.

Explanation

Compartmentation limits the impact of fire, water or cooling failures to a defined area and supports phased build-out matched to demand. There is no universal code limit on hall size, and large halls are routinely cooled.

Question 9Data centre design

Which fire suppression approach is generally preferred for an occupied data hall because it avoids leaving residue on IT equipment?

  1. Foam suppression
  2. Clean-agent gaseous suppression Correct answer.
  3. Wet-pipe sprinkler protection
  4. Deluge water spray

Explanation

Clean-agent systems extinguish fire without leaving conductive or corrosive residue on servers, which is why they are widely used in white space. Water-based and foam systems can damage electronics even when the fire is controlled.

Question 10Data centre design

A design specifies N+1 redundancy for the chiller plant. What does this mean?

  1. The plant can run at full load with one unit out of service Correct answer.
  2. The plant runs at one unit above the IT load at all times
  3. One chiller is always kept switched off as a spare
  4. Every unit is duplicated, giving 2N capacity

Explanation

N+1 means the installed capacity equals the required capacity plus one additional unit, so the system still meets design load with any single unit unavailable. It is not full duplication (2N) and does not require a permanently idle unit.

Question 11Data centre design

Which cabling practice best supports a structured cabling design in the white space?

  1. Using a hierarchical layout of main distribution, horizontal distribution and equipment areas Correct answer.
  2. Running copper and fibre in the same tray without separation
  3. Terminating each server directly to the core switch
  4. Using only patch cords between racks with no fixed cabling

Explanation

Structured cabling organises the network into a hierarchy of distribution areas with fixed backbone and horizontal cabling plus patch fields, which supports moves, adds and changes. Direct server-to-core links and patch-cord-only layouts are inflexible and hard to manage.

Question 12Data centre design

What is the main design consequence of specifying high rack power density in an air-cooled hall?

  1. The fire suppression system can be omitted
  2. Lower airflow is required per rack
  3. Higher airflow volumes and tighter aisle containment are needed Correct answer.
  4. The UPS capacity can be reduced

Explanation

Higher power per rack means more heat must be removed from a smaller footprint, which demands greater airflow and effective containment to prevent mixing. Air cooling becomes progressively less efficient as density rises.

Question 13Data centre design

Which of the following best describes the purpose of an economiser in data centre cooling design?

  1. To raise the supply air temperature to save energy
  2. To reduce compressor or chiller operation by using outside air or free cooling Correct answer.
  3. To store cold water for use during a power failure
  4. To increase the redundancy level of the cooling plant

Explanation

An economiser exploits favourable outdoor conditions, through direct air or a fluid economiser, to provide cooling with reduced or no mechanical refrigeration. This lowers energy consumption but does not change redundancy or provide backup storage.

Question 14Data centre design

A client requires that maintenance on any single power component can be performed without affecting the IT load. Which combination of features is essential?

  1. A single UPS with a larger battery and a generator
  2. Redundant servers with a single power supply each
  3. Dual-corded IT equipment, two independent power paths and maintenance bypasses Correct answer.
  4. Two generators sharing a single automatic transfer switch

Explanation

Concurrent maintainability requires that each IT load has two independent feeds and that each path can be bypassed for servicing. If any element is shared, working on it interrupts the load.

Question 15Data centre design

Which statement about hot-aisle containment is correct?

  1. It requires the removal of all perforated floor tiles
  2. It encloses the hot aisle so exhaust air returns to the cooling units without mixing Correct answer.
  3. It removes the need for any airflow management
  4. It encloses the cold aisle and exhausts hot air into the room

Explanation

Hot-aisle containment captures exhaust air within an enclosure and ducts it back to the cooling units, preventing it from mixing with cold supply air. Cold-aisle containment is the alternative approach, and neither eliminates airflow management entirely.

Question 16Data centre design

What is the primary reason for installing a raised floor in a data centre?

  1. To allow equipment to be cooled by natural convection only
  2. To increase the structural load capacity of the building
  3. To provide a plenum for air distribution and a route for cabling Correct answer.
  4. To improve the acoustic performance of the hall

Explanation

The raised floor creates a void used to distribute conditioned air and to route power and data cabling beneath the equipment. Structural capacity and acoustics are separate considerations.

Question 17Data centre design

In a Tier III classification, which characteristic distinguishes it from Tier II?

  1. No requirement for redundant components
  2. Fully fault-tolerant infrastructure
  3. A single non-redundant distribution path
  4. Concurrently maintainable site infrastructure Correct answer.

Explanation

Tier III provides redundant capacity components and multiple distribution paths that allow concurrent maintenance of any component. Fault tolerance across all paths is the defining feature of Tier IV.

Question 18Data centre design

A design must control the risk of water from a chilled-water pipe entering the white space. Which measure best addresses this?

  1. Routing pipework away from the white space or providing containment and leak detection Correct answer.
  2. Installing the pipework above the ceiling tiles
  3. Painting the pipework with a protective coating
  4. Increasing the pipe diameter to reduce pressure

Explanation

Water risk is managed by keeping pipework out of the IT space where possible, or by containing it and detecting leaks early. Larger pipes or coatings do not prevent leakage into the hall.

Question 19Data centre design

What is the purpose of a cold-aisle pressure differential measurement in a contained data hall?

  1. To verify that the containment envelope is maintaining the intended separation between cold and hot air Correct answer.
  2. To determine the fire suppression discharge pressure
  3. To measure the electrical load on the racks
  4. To calculate the UPS runtime available

Explanation

A pressure differential across the containment indicates whether the envelope is sealing correctly and whether supply air is being delivered as designed. It is an airflow diagnostic, not an electrical or fire measurement.

Question 20Data centre design

Which of the following best describes the role of a building management system in a data centre?

  1. To monitor and control mechanical and electrical plant such as cooling and power distribution Correct answer.
  2. To store backup copies of application data
  3. To control access to the white space
  4. To manage the network traffic between servers

Explanation

The BMS supervises and controls the facility's mechanical and electrical infrastructure, providing monitoring, alarms and setpoint control. Network traffic, data backup and access control are handled by separate systems.

Question 21Data centre design

A design team is evaluating a direct free-cooling system for a site with high humidity and airborne particulates. What is the main concern?

  1. The requirement to increase UPS capacity
  2. The need for filtration and humidity control to protect IT equipment Correct answer.
  3. The inability of the system to provide any cooling
  4. The need to remove all containment

Explanation

Direct free cooling introduces outside air into the hall, so contaminants and humidity must be controlled to avoid corrosion and condensation risks. It does not eliminate cooling capability or affect UPS sizing.

Question 22Data centre design

What does the term 'concurrent maintainability' mean in data centre design?

  1. The ability to perform maintenance only during scheduled outages
  2. The ability to run the facility at reduced load during maintenance
  3. The ability to service any component without shutting down the IT load Correct answer.
  4. The ability to maintain equipment using only external contractors

Explanation

Concurrent maintainability means every component can be maintained or replaced while the IT load continues to operate normally. It requires redundancy and multiple distribution paths rather than planned outages.

Question 23Data centre design

Which design choice best reduces the risk of a single cable tray failure affecting both power and data distribution?

  1. Using a single large tray for all services
  2. Placing all trays directly above the racks
  3. Bundling all cables with cable ties on one tray
  4. Routing power and data on physically separate tray systems Correct answer.

Explanation

Physical separation of power and data routes limits the impact of a single tray failure and reduces electromagnetic interference. A shared tray creates a common point of failure and interference risk.

Question 24Data centre design

Why might a data centre design specify a higher supply air temperature than traditional practice?

  1. To lower the fire risk in the hall
  2. To reduce the need for containment
  3. To increase the cooling capacity of the CRAC units
  4. To allow wider use of free cooling and reduce chiller energy Correct answer.

Explanation

Raising the supply air temperature within equipment limits widens the range of conditions in which economisers can operate, reducing mechanical cooling energy. It does not increase cooling capacity or remove the need for containment.

Question 25Data centre design

Which of the following is a typical function of a physical security layer in a data centre design?

  1. Removing heat from the equipment
  2. Controlling and logging access to the white space through layered zones Correct answer.
  3. Distributing network traffic between racks
  4. Providing backup power to the IT load

Explanation

Physical security uses layered zones, authentication and logging to control who reaches the IT space. Power, cooling and network distribution are separate infrastructure functions.

Question 26Data centre design

In data centre design, what is the primary purpose of a hot-aisle/cold-aisle layout?

  1. To allow a single CRAC unit to serve both aisles
  2. To separate exhaust air from supply air so that mixing is minimised Correct answer.
  3. To increase the total floor area available for racks
  4. To shorten cable runs between racks and the network core

Explanation

The aisle layout arranges racks front-to-front and back-to-back so that cold supply air is drawn in at the front and heated exhaust is released at the rear. Keeping these two air streams apart prevents recirculation and mixing, which otherwise raises the temperature of air reaching IT equipment.

Question 27Data centre design

Which metric expresses how much of the total facility power is delivered to IT equipment?

  1. Cooling load factor
  2. Power usage effectiveness Correct answer.
  3. Rack power density
  4. Energy reuse factor

Explanation

Power usage effectiveness (PUE) is the ratio of total facility energy to IT equipment energy, so a value close to 1.0 indicates that little energy is consumed by cooling, losses and ancillary systems. It is the standard efficiency indicator in data centre design.

Question 28Data centre design

What does a Tier IV topology provide that a Tier III topology does not?

  1. A raised floor with a documented air distribution design
  2. Fault tolerance against any single failure of the distribution path Correct answer.
  3. Concurrent maintainability of all power and cooling components
  4. Redundant capacity components in the cooling plant

Explanation

Tier IV adds fault tolerance: the site can sustain at least one worst-case unplanned failure of any infrastructure component without affecting the IT load. Tier III already provides concurrent maintainability, which is why that characteristic alone does not distinguish Tier IV.

Question 29Data centre design

Which statement best describes the function of an automatic transfer switch in a data centre power train?

  1. It limits fault current so that downstream breakers can be rated lower
  2. It balances the load evenly across the phases of the UPS output
  3. It converts alternating current from the utility into direct current for the IT load
  4. It switches the load between two sources when the preferred source fails or is taken out of service Correct answer.

Explanation

An automatic transfer switch monitors the preferred source and transfers the downstream load to an alternate source when the preferred one is lost or isolated. It is a switching device, not a converter, current limiter or phase balancer.

Question 30Data centre design

Why is a two-zone dry-pipe or pre-action arrangement often chosen for sprinkler protection in a data hall?

  1. It removes the requirement for portable extinguishers on site
  2. It keeps water out of the pipework above the hall until a detection signal confirms a fire Correct answer.
  3. It eliminates the need for any detection system in the white space
  4. It allows the sprinkler heads to be omitted from the ceiling grid

Explanation

In a pre-action system the pipes above the protected space are normally dry, and water is admitted only after a detection signal operates a valve. This reduces the risk of an accidental discharge caused by a damaged head or pipe.

Question 31Data centre design

What is the purpose of a cross-connect in a structured cabling design for the white space?

  1. To terminate the incoming utility medium-voltage feed
  2. To convert optical signals to electrical signals at the rack
  3. To bond the rack frames to the earthing grid
  4. To provide a flexible patching point between distribution and equipment cabling Correct answer.

Explanation

A cross-connect is an administration point where patching allows equipment to be reconnected without recabling the backbone. It brings flexibility and manageability to moves, adds and changes in the hall.

Question 32Data centre design

Which physical security measure is typically applied at the boundary between the loading area and the data hall?

  1. A hot-aisle containment canopy
  2. An uninterruptible power supply in parallel configuration
  3. A raised floor with perforated tiles
  4. A mantrap or interlocking lobby with access control Correct answer.

Explanation

A mantrap or interlocking door arrangement allows only one door to be open at a time and requires credential verification before entry, preventing tailgating into the secure zone. It is a standard layered physical security control.

Question 33Data centre design

What does the term 'white space' refer to in a data centre?

  1. The area housing switchgear and generators
  2. The roof plant area for chillers and dry coolers
  3. The area where IT equipment is installed and operated Correct answer.
  4. The loading dock and storage area

Explanation

White space is the conditioned floor area dedicated to IT equipment, as distinct from the grey space occupied by electrical and mechanical plant. The term is used in design to separate the IT environment from supporting infrastructure.

Question 34Data centre design

A hall is designed with an overhead supply plenum feeding rows of racks, and the design team wants to avoid recirculation at the top of the racks. Which measure addresses this most directly?

  1. Lowering the set point of the room temperature sensor
  2. Increasing the chilled-water flow rate through the air handlers
  3. Adding more perforated tiles in the cold aisle
  4. Fitting blanking panels in unused rack units and sealing cable openings Correct answer.

Explanation

Recirculation at the rack face occurs when hot exhaust can flow back through empty rack units or cable cut-outs. Blanking panels and sealed openings close these bypass paths so that supply air reaches the equipment intakes.

Question 35Data centre design

A client wants a power topology in which the failure of one UPS module cannot interrupt the IT load, and each module can be maintained while the load runs. Which arrangement satisfies both requirements?

  1. A single UPS with a maintenance bypass cabinet and one distribution path
  2. A single modular UPS with internal bypass and one distribution path
  3. Two independent UPS systems feeding dual-corded equipment via separate distribution paths Correct answer.
  4. One UPS feeding a static transfer switch with a single output path

Explanation

Dual-corded IT equipment fed from two independent UPS systems and separate distribution paths allows either side to fail or be maintained without affecting the load. A single system, even with bypass, leaves a common path through the output distribution.

Question 36Data centre design

A design team is siting a new hall in a region with a temperate climate and good air quality. Which cooling approach is likely to deliver the lowest annual energy use while maintaining the required conditions?

  1. Evaporative cooling using site water with no water treatment
  2. Air-side economiser with filtered outside air and humidification control Correct answer.
  3. Chilled-water plant with constant-speed chillers and no free cooling
  4. Mechanical DX cooling with fixed compressor staging

Explanation

In a temperate climate with clean air, an air-side economiser can use outside air for a large part of the year, cutting compressor energy. Filtration and humidification control are needed to protect the IT equipment when outside air is admitted.

Question 37Data centre design

During commissioning, cold-aisle pressure differential readings in a contained hall are near zero while rack inlet temperatures are above target. What is the most likely design explanation?

  1. Excessive leakage from the containment is allowing bypass air to escape before reaching the racks Correct answer.
  2. The containment is too airtight and is starving the air handlers of return air
  3. The racks are drawing more air than the air handlers can physically produce regardless of leakage
  4. The differential sensor is installed upside down

Explanation

A contained cold aisle should hold a small positive pressure relative to the hot aisle; a near-zero reading with hot inlets points to leakage paths through the containment. The supply air is bypassing the rack intakes rather than being delivered to them.

Question 38Data centre design

A chilled-water pipe route crosses the white space above the racks. Which design measure most effectively limits the consequence of a pipe or joint failure?

  1. Coating the pipe with anti-corrosion paint and inspecting it annually
  2. Routing the pipe outside the hall where practicable and installing drip shields and leak detection on any in-hall section Correct answer.
  3. Installing the pipe above the hot aisle rather than the cold aisle
  4. Increasing the pipe diameter to reduce working pressure

Explanation

The most reliable control is to keep water out of the IT space by rerouting; where that is impossible, physical shielding and leak detection limit the spread and speed up response. Paint and inspection do not prevent a pressurised joint from failing.

Question 39Data centre design

Why might a design deliberately specify a supply air temperature of around 24 degrees Celsius rather than the traditional 12 to 14 degrees?

  1. Warmer supply air increases the cooling capacity of each air handler
  2. Warmer supply air eliminates the need for containment
  3. Warmer supply air allows more hours of free cooling and reduces chiller energy while remaining within equipment limits Correct answer.
  4. Warmer supply air removes the need for humidity control

Explanation

Current equipment standards permit much warmer inlet air than older practice assumed. Raising the supply temperature widens the range of outdoor conditions usable for free cooling and lets chillers run less, improving efficiency.

Question 40Data centre design

A design must ensure that maintenance of any single cable tray or pathway does not interrupt both power and data services to a rack. Which approach achieves this?

  1. Installing power and data in the same tray to simplify inspection
  2. Using a single large tray with fire-rated barriers between cables
  3. Labelling the tray clearly so maintenance can be scheduled
  4. Providing diverse, physically separated routes for power and data with no shared single point of failure Correct answer.

Explanation

Diversity requires that power and data follow independent routes so that work on one pathway leaves the other intact. Physical separation also reduces the risk that a single incident, such as a fire or a fallen object, affects both services.

Question 41Data centre design

What is the main purpose of an equipotential bonding network in a data hall?

  1. To provide a redundant path for the UPS output
  2. To keep metallic parts at a similar potential and limit potential differences that could damage equipment Correct answer.
  3. To earth the neutral of the medium-voltage supply
  4. To carry the full IT load current back to the transformer

Explanation

Bonding connects conductive parts such as rack frames, trays and raised-floor stringers so that they sit at a common potential. This limits potential differences and the associated currents that could disturb or damage sensitive IT equipment.

Question 42Data centre design

A hall needs to support racks of very high power density in an air-cooled design. Which consequence should the designer plan for?

  1. Higher air volumes and closer attention to airflow distribution at each rack Correct answer.
  2. Elimination of the need for redundancy in the cooling plant
  3. Reduced need for humidity control in the hall
  4. Lower overall cooling energy because fewer racks are installed

Explanation

Air-cooled halls have a practical heat-removal limit per rack, so higher density demands more airflow and tighter control of where that air goes. It also pushes designers toward alternative cooling methods once the air approach reaches its limit.

Question 43Data centre design

What distinguishes a building management system from a DCIM system in a data centre design?

  1. The BMS is used only for fire detection and the DCIM only for access control
  2. The BMS manages IT asset records and the DCIM controls chillers
  3. The BMS supervises mechanical and electrical plant, while DCIM manages IT assets and capacity Correct answer.
  4. The BMS and DCIM perform identical functions and are interchangeable

Explanation

The BMS focuses on plant control and monitoring, such as chillers, air handlers and switchgear. DCIM addresses IT-side concerns including asset tracking, capacity planning and connectivity management, with integration between the two where useful.

Question 44Data centre design

A site has high airborne particulate levels and wide humidity swings. What is the principal design implication for a direct fresh-air free-cooling system?

  1. It requires a larger chilled-water plant than a closed system
  2. It can be installed without filtration because the IT equipment is sealed
  3. It removes the need for any mechanical cooling
  4. It needs effective filtration and humidity control, which may reduce the net energy benefit Correct answer.

Explanation

Admitting outside air brings contaminants and moisture into the hall, so filtration and humidification or dehumidification must be added. Those systems consume energy and can erode the savings that made free cooling attractive.

Question 45Data centre design

What does a concurrent maintainability requirement mean for the cooling distribution design?

  1. Any cooling component can be serviced while the IT load continues to be cooled within limits Correct answer.
  2. Maintenance tasks can be performed by one person rather than a team
  3. The cooling plant can be shut down for maintenance only during agreed windows
  4. The cooling system can be expanded without adding plant

Explanation

Concurrent maintainability means planned work on any single component does not interrupt the IT environment. The design must provide alternate capacity and isolation so the remaining plant can hold conditions during the work.

Question 46Data centre design

A design team is asked to reduce the risk of a single failure in the fuel system taking down all generators. Which measure best achieves this?

  1. A single large bulk tank with one common supply line
  2. Independent fuel storage and supply paths per generator with isolation valves Correct answer.
  3. Weekly fuel polishing of the common supply
  4. A larger day tank shared by all generators

Explanation

A common fuel line or tank is a single point of failure that can disable every generator at once. Separate storage and supply paths with isolation allow one side to be maintained or lost while the other continues to run.

Question 47Data centre design

Why is a data centre often divided into smaller halls or modules rather than one large open space?

  1. Smaller halls allow a single air handler to serve the whole site
  2. Smaller halls remove the need for cooling redundancy
  3. Smaller halls eliminate the need for fire detection
  4. Smaller halls limit the spread of an incident and allow staged build-out matched to demand Correct answer.

Explanation

Compartmentation confines the effects of fire, water or smoke to a limited area and supports phased construction so capital is spent as demand arrives. It also makes cooling and power distribution easier to scale in steps.

Question 48Data centre design

A rack contains equipment from two different vendors with different airflow directions. What is the most appropriate design response?

  1. Place all equipment in the hot aisle to simplify cabling
  2. Increase the chilled-water supply temperature to compensate
  3. Install the equipment as supplied and rely on the room air handlers to correct the flow
  4. Group equipment by airflow direction and arrange racks so that intakes face the cold aisle Correct answer.

Explanation

Equipment that exhausts toward its own intake or draws from the wrong side will short-circuit the aisle design. Grouping by airflow direction and orienting intakes to the cold aisle preserves the intended separation of supply and return air.

Question 49Data centre design

A client asks for the lowest PUE achievable but also requires Tier IV fault tolerance. How should the designer reconcile these goals?

  1. Recognise that fault-tolerance measures add parasitic load and optimise within that constraint rather than promising the absolute minimum PUE Correct answer.
  2. Guarantee the lowest PUE by using a single large UPS instead of parallel units
  3. Guarantee the lowest PUE by removing redundancy from the cooling plant
  4. Treat PUE and tier level as unrelated so no trade-off analysis is needed

Explanation

Fault tolerance requires redundant plant that may run lightly loaded, plus transfer and isolation equipment, all of which add overhead energy. The realistic approach is to optimise the design within the tier requirement and state the achievable PUE rather than the theoretical minimum.

Question 50Data centre design

During a failure-mode review, a design shows that a single busbar section feeds both the A and B power paths at the output of the UPS systems. What is the correct assessment?

  1. The arrangement improves efficiency and should be retained
  2. The arrangement defeats the intended redundancy because the shared section is a common point of failure Correct answer.
  3. The arrangement is acceptable provided the busbar is rated for twice the load
  4. The arrangement is acceptable because the UPS systems themselves remain independent

Explanation

Redundancy is only as strong as its weakest shared element; a common busbar section couples both paths so a fault or maintenance on it affects the whole load. The distribution must remain separate from source to rack to preserve the intended availability.