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EPI Data Centre Associate study materials
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EPI Data Centre Associate practice questions

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Question 1Data Centre Design

In data centre design, what does the Uptime Institute Tier classification primarily describe?

  1. The network carrier neutrality of the facility
  2. The concurrent maintainability and fault tolerance of the site infrastructure Correct answer.
  3. The rack power density supported by the cooling system
  4. The physical security level of the building perimeter

Explanation

The Tier system rates topology and operational sustainability of site infrastructure, focusing on whether components can be maintained or fail without taking the IT load down. Tier I through IV progressively add redundancy and concurrent maintainability. It does not directly specify rack density, security level, or carrier neutrality.

Question 2Data Centre Design

Which redundancy configuration provides two complete power paths where either path can carry the full critical load?

  1. 2N+1 configuration
  2. N+1 configuration
  3. 2N configuration Correct answer.
  4. N configuration

Explanation

2N means two independent systems, each sized to carry the entire load, so a single path can be removed for maintenance or fail without impact. N is a single path with no spare capacity, and N+1 adds one spare module within a single system. 2N+1 adds a further spare module on top of two full systems.

Question 3Data Centre Design

A data hall is designed for 8 kW per rack across 40 racks. What is the approximate total IT design load?

  1. 80 kW
  2. 3.2 MW
  3. 320 kW Correct answer.
  4. 32 kW

Explanation

Total IT load equals rack density multiplied by rack count: 8 kW times 40 racks equals 320 kW. This figure then feeds into UPS, PDU, and cooling sizing with appropriate design margins. Confusing kW and MW is a common error in early load estimates.

Question 4Data Centre Design

Why is hot-aisle/cold-aisle layout used in data halls?

  1. To reduce the number of racks needed per row
  2. To allow higher structural floor loading
  3. To simplify cable tray routing above racks
  4. To separate supply air from exhaust air and limit mixing Correct answer.

Explanation

Front-to-front and back-to-back rack orientation creates distinct cold supply aisles and hot return aisles, which limits the mixing of supply and exhaust air. Reduced mixing raises return air temperature and improves cooling efficiency. The layout does not change rack counts, floor loading, or cable routing requirements.

Question 5Data Centre Design

What is the main purpose of containment in a data hall?

  1. To suppress fire within the aisle
  2. To reduce electromagnetic interference between racks
  3. To prevent physical access to racks
  4. To keep cold supply air and hot exhaust air from mixing Correct answer.

Explanation

Containment uses physical barriers to separate cold supply air from hot exhaust, either by enclosing the cold aisle or the hot aisle. This raises the usable temperature differential across the cooling coil and improves efficiency. Access control, fire suppression, and EMI are handled by other systems.

Question 6Data Centre Design

In a raised-floor data hall, what does the plenum primarily provide?

  1. A route for draining condensate from cooling units
  2. A path for distributing cool supply air to perforated tiles Correct answer.
  3. A structural cavity for seismic isolation
  4. A space for installing the main switchgear

Explanation

The space between the structural slab and the raised floor acts as a supply air plenum, delivering cooled air to perforated tiles or grilles in the cold aisle. Its depth and sealing affect static pressure and airflow distribution. Drainage, switchgear, and seismic isolation are handled elsewhere.

Question 7Data Centre Design

What is the primary reason for using a UPS in a data centre power chain?

  1. To bridge the gap between utility loss and generator pickup Correct answer.
  2. To provide long-term energy storage for the site
  3. To step down utility voltage to rack level
  4. To correct power factor on the utility feed

Explanation

A UPS supplies ride-through power during the interval between a utility outage and the point where generators are running and stable. It is sized for short-duration support, not long-term energy storage. Voltage transformation and power factor correction are separate functions.

Question 8Data Centre Design

Which cooling approach places the cooling coil close to or within the rack to handle high densities?

  1. Chilled water CRAH units
  2. Room-based CRAC units
  3. Direct expansion rooftop units
  4. In-row or rear-door heat exchangers Correct answer.

Explanation

In-row coolers and rear-door heat exchangers move the heat rejection point close to the IT load, which is effective at high rack densities where room-level air distribution struggles. Room-based CRAC and CRAH units serve broader spaces and may not reach very high density racks. Rooftop DX units are a general building cooling option.

Question 9Data Centre Design

Why are data centre floors often designed with high structural load ratings?

  1. To allow the building to be converted to office space
  2. To permit the use of thinner floor slabs
  3. To reduce the need for vibration isolation
  4. To support the weight of dense IT equipment, batteries, and cooling plant Correct answer.

Explanation

Dense racks, UPS battery banks, and heavy mechanical plant impose significant concentrated and distributed loads. Structural design must account for these, often expressed in kN per square metre or pounds per square foot. Conversion flexibility, vibration, and slab thickness are separate considerations.

Question 10Data Centre Design

What is the role of a PDU in a data centre power distribution chain?

  1. To distribute power from the UPS or utility to racks and equipment Correct answer.
  2. To provide backup power during a utility outage
  3. To convert AC to DC for IT equipment
  4. To monitor network traffic between racks

Explanation

A power distribution unit takes power from upstream sources such as the UPS output and distributes it to downstream circuits and racks. It may include transformers, breakers, and monitoring. AC-to-DC conversion is done by rectifiers, backup power is the UPS role, and network monitoring is unrelated.

Question 11Data Centre Design

Which fire suppression approach is commonly chosen for occupied data halls to avoid water damage to IT equipment?

  1. Clean agent or inert gas suppression Correct answer.
  2. Dry chemical powder systems
  3. Wet-pipe sprinkler systems
  4. Deluge foam systems

Explanation

Clean agent and inert gas systems suppress fire without leaving residue or causing water damage to electronics. Wet-pipe sprinklers and deluge foam introduce water or foam that can damage IT equipment. Dry chemical powder leaves corrosive residue and is not typical for data halls.

Question 12Data Centre Design

Why is sealing cable penetrations in a data hall important?

  1. To improve the aesthetic appearance of the room
  2. To increase the current-carrying capacity of cables
  3. To reduce the weight of cable trays
  4. To maintain containment and prevent air leakage and smoke spread Correct answer.

Explanation

Unsealed penetrations allow cold air to escape and hot air to migrate, undermining airflow management, and can let smoke spread between zones during a fire. Sealing restores the intended pressure boundaries. Cable ampacity, tray weight, and appearance are unrelated to sealing.

Question 13Data Centre Design

What does a PUE of 1.5 indicate about a data centre?

  1. The facility has a redundancy level of 1.5N
  2. The facility uses 1.5 times the IT load in total energy Correct answer.
  3. The facility runs at 150 percent of its rated capacity
  4. The facility achieves 50 percent renewable energy

Explanation

Power Usage Effectiveness is total facility power divided by IT power, so a PUE of 1.5 means the facility draws 1.5 units of energy for every unit delivered to IT. The excess covers cooling, losses, and other overhead. PUE says nothing about renewable share, redundancy, or utilisation.

Question 14Data Centre Design

Why are dual-corded IT devices connected to two separate power paths?

  1. To reduce the energy consumption of the device
  2. To enable remote power cycling of the device
  3. To double the current available to the device
  4. To allow the device to survive the loss of one power path Correct answer.

Explanation

Dual-corded servers with each cord on an independent path can continue operating if one path fails or is taken down for maintenance. This is a key element of concurrent maintainability. It does not double available current, reduce consumption, or enable remote cycling.

Question 15Data Centre Design

What is the purpose of a hot aisle return plenum in a data hall?

  1. To house the fire detection panel
  2. To supply cold air directly to the racks
  3. To store spare equipment out of sight
  4. To collect hot exhaust air and return it to the cooling units Correct answer.

Explanation

A hot aisle return plenum captures heated exhaust air and routes it back to the cooling coils, often at higher temperature for improved efficiency. Cold air supply is handled separately, typically through the cold aisle or underfloor plenum. Equipment storage and fire panels belong elsewhere.

Question 16Data Centre Design

A facility has N+1 UPS modules in a single system. What risk remains compared with a 2N design?

  1. A fault in the shared distribution path can still affect the load Correct answer.
  2. The generators cannot be tested
  3. The UPS cannot support the load at all
  4. The system cannot be maintained without a shutdown

Explanation

N+1 provides a spare module within one system, but a fault in shared components such as the output distribution or switchgear can still take down the load. 2N provides independent paths that avoid this single point of failure. N+1 systems can still support load and be maintained; generator testing is unrelated.

Question 17Data Centre Design

Why is airflow management often more impactful than lowering the supply air temperature in an existing data hall?

  1. Lowering supply temperature increases fan and chiller energy and may not fix hot spots Correct answer.
  2. Airflow management eliminates the need for cooling entirely
  3. Supply temperature has no effect on efficiency
  4. Warmer supply air always reduces equipment reliability

Explanation

Hot spots are usually caused by poor air distribution, so improving containment and sealing can resolve them without extra cooling. Lowering supply temperature raises chiller and fan energy and may simply increase mixing. Warmer supply within allowable limits does not inherently harm reliability, and cooling is still required.

Question 18Data Centre Design

What is the function of a static transfer switch in a data centre power design?

  1. To convert AC power to DC power
  2. To transfer load between two power sources quickly Correct answer.
  3. To step up voltage for transmission
  4. To provide short-term battery backup

Explanation

A static transfer switch uses solid-state devices to move load from one source to another within a fraction of a cycle, supporting source redundancy. It does not convert AC to DC, store energy, or transform voltage. These functions belong to rectifiers, UPS batteries, and transformers.

Question 19Data Centre Design

Which factor most directly drives the choice between air cooling and liquid cooling for a new data hall?

  1. The number of network switches per rack
  2. The number of staff employed on site
  3. Rack power density and the ability to remove heat with air Correct answer.
  4. The building's exterior colour scheme

Explanation

As rack density rises, air cooling becomes limited by the mass flow and temperature differential achievable. Liquid cooling, including direct-to-chip, becomes attractive when air cannot remove the heat effectively. Switch counts, aesthetics, and staffing do not determine the cooling medium.

Question 20Data Centre Design

What is a key design consideration when locating batteries for a UPS system?

  1. Access to daylight
  2. Battery room ventilation and thermal management Correct answer.
  3. Distance from the loading dock
  4. Proximity to the network core

Explanation

Batteries generate heat and, for some chemistries, hydrogen gas, so ventilation and temperature control are essential for safety and service life. Proximity to the network core, daylight, and dock distance are not primary battery design drivers.

Question 21Data Centre Design

Why is a separate electrical room often required for switchgear and transformers?

  1. To improve network latency
  2. To isolate electrical hazards and manage heat and access Correct answer.
  3. To provide space for IT racks
  4. To reduce the building's structural load

Explanation

High-voltage switchgear and transformers present electrical and fire hazards, generate heat, and require restricted access for qualified staff. Dedicated electrical rooms address these needs. They do not affect network latency, house IT racks, or reduce structural load.

Question 22Data Centre Design

A design specifies 2N power but only N cooling. What is the resulting overall availability characteristic?

  1. The facility achieves Tier IV overall
  2. The cooling system is automatically fault tolerant
  3. The cooling system becomes the limiting single point of failure Correct answer.
  4. The power redundancy is wasted

Explanation

Overall availability is limited by the weakest system, so N cooling introduces a single point of failure even though power is 2N. Tier IV requires fault tolerance across all critical systems. Power redundancy still adds value for its own systems, and N cooling is not fault tolerant.

Question 23Data Centre Design

What is the purpose of economiser modes in data centre cooling design?

  1. To increase the redundancy of chillers
  2. To raise the supply air temperature above equipment limits
  3. To use outside air or water-side free cooling to reduce mechanical cooling energy Correct answer.
  4. To provide backup power to cooling units

Explanation

Economiser modes exploit favourable outdoor conditions, using air-side or water-side free cooling to reduce compressor or chiller operation. This lowers energy consumption. They do not add redundancy, provide backup power, or exceed equipment temperature limits.

Question 24Data Centre Design

Why are cold aisle containment doors often designed with automatic closing and pressure relief?

  1. To improve the appearance of the aisle
  2. To increase the cooling capacity of the CRAC units
  3. To reduce the weight of the containment structure
  4. To maintain separation while allowing safe egress and pressure equalisation Correct answer.

Explanation

Containment doors must preserve the cold/hot air boundary, but they also need to allow personnel egress and relieve pressure differences that could otherwise stress panels or doors. These are safety and operational requirements. Weight, appearance, and cooling capacity are not the drivers.

Question 25Data Centre Design

What does a design PUE target of 1.2 typically require compared with a 1.8 design?

  1. More efficient cooling, such as containment and economisers Correct answer.
  2. Higher supply air temperatures beyond equipment limits
  3. More IT racks to spread the load
  4. Larger generators and more fuel storage

Explanation

Achieving a low PUE requires reducing overhead energy, typically through containment, economisers, and efficient cooling plant. Generators and fuel storage relate to resilience, not efficiency. Adding racks changes load but not the ratio, and exceeding equipment temperature limits is not acceptable.

Question 26Data Centre Design

A data hall is designed with a slab-to-slab height of 6 m and a finished ceiling at 4.2 m. Which zone is typically reserved for service distribution above the racks?

  1. The sub-floor earthing grid below the slab
  2. The raised-floor void beneath the tiles
  3. The hot aisle aisle-end return path
  4. The overhead cable tray and busway zone between rack tops and ceiling Correct answer.

Explanation

In modern data halls, overhead trays and busways carry power and data above the racks, so the vertical space between rack tops and the finished ceiling must be sized for cable, busway, and sprinkler clearance. The sub-floor void serves air distribution and underfloor cabling, not the primary overhead service zone.

Question 27Data Centre Design

A design team must place a new 2 MVA transformer for a data centre. Which location best limits electrical noise and fire exposure to the white space?

  1. On the loading dock adjacent to the generator yard
  2. In the ceiling plenum above the hot aisle
  3. Inside the data hall at the end of the cold aisle
  4. In a dedicated electrical room separated from the data hall by a fire-rated wall Correct answer.

Explanation

Transformers and switchgear are located in dedicated electrical rooms with fire separation so that a fault or fire does not directly threaten IT equipment. Keeping them out of the white space also avoids heat, noise, and arc-flash hazards near racks.

Question 28Data Centre Design

A data centre has a design PUE of 1.25. What does this figure represent?

  1. The percentage of cooling energy saved by free cooling
  2. The share of total facility power delivered to IT equipment
  3. The ratio of total facility power to IT equipment power Correct answer.
  4. The ratio of IT load to generator capacity

Explanation

PUE is total facility energy divided by IT equipment energy, so 1.25 means 1.25 units of facility power are used for each unit delivered to IT. Lower values indicate more efficient overhead, and the theoretical ideal approaches 1.0.

Question 29Data Centre Design

Which floor loading consideration is most important when specifying a data hall for high-density racks?

  1. The number of floor tiles per aisle
  2. The acoustic rating of the ceiling tiles
  3. The point-load capacity at rack feet and the uniform live load of the slab Correct answer.
  4. The colour of the floor finish

Explanation

High-density racks concentrate weight at their feet, so the slab must be checked for both concentrated point loads and the uniform live load across the hall. Structural engineers size beams and slabs against these loads, not against finishes or acoustics.

Question 30Data Centre Design

In a data hall with hot and cold aisle containment, which arrangement is standard for rack orientation?

  1. Racks arranged in rows with fronts facing a shared cold aisle Correct answer.
  2. Racks placed back-to-back with no aisle
  3. Racks arranged so fronts face the hot aisle
  4. All racks facing the same wall

Explanation

Racks are arranged in rows so that equipment fronts face a common cold aisle and exhausts face a common hot aisle, which containment then seals. This separation prevents hot exhaust from recirculating into equipment intakes.

Question 31Data Centre Design

What is the main purpose of a data centre's building management system in relation to the white space?

  1. To store production application data
  2. To monitor and control mechanical and electrical plant such as cooling, humidity, and power Correct answer.
  3. To provide physical access control to the site
  4. To route network traffic between racks

Explanation

The BMS supervises mechanical and electrical infrastructure, gathering sensor data and controlling cooling, humidity, and power equipment. It is distinct from IT systems and from dedicated security or network systems.

Question 32Data Centre Design

A data centre design must limit the spread of a fire from a battery room to the adjacent data hall. Which measure is most appropriate?

  1. Installing additional server racks in the battery room
  2. Removing the fire detection system to avoid false alarms
  3. Using fire-rated compartmentation between the rooms Correct answer.
  4. Increasing the humidity in the data hall

Explanation

Fire-rated compartmentation, such as rated walls and doors, contains a fire within its origin room and protects adjacent spaces. Battery rooms are treated as higher-risk areas and are separated accordingly.

Question 33Data Centre Design

Which document typically defines the required redundancy and availability target that shapes a data centre's design?

  1. The cable schedule
  2. The rack elevation drawing
  3. The floor tile layout plan
  4. The customer or business availability requirement and service level agreement Correct answer.

Explanation

Redundancy levels and availability targets derive from business requirements and SLAs, which then drive topology choices such as N+1 or 2N. Drawings and schedules are outputs of the design, not the source of the availability requirement.

Question 34Data Centre Design

A data hall's cooling design assumes a supply air temperature of 24°C at the rack intake. Which standard framework is commonly used to justify allowable temperature and humidity ranges for IT equipment?

  1. ASHRAE thermal guidelines for data processing environments Correct answer.
  2. The PCI DSS payment card standard
  3. The IEEE 802.3 Ethernet standard
  4. The ISO 9001 quality management standard

Explanation

ASHRAE publishes widely used thermal guidelines defining allowable and recommended temperature and humidity envelopes for IT equipment. Designers reference these envelopes when setting supply conditions and humidity control.

Question 35Data Centre Design

A facility must run maintenance on one of two independent utility feeds without interrupting IT load. Which design element supports this?

  1. A single utility feed with a manual changeover switch
  2. A single generator shared by both feeds
  3. Automatic transfer and distribution arranged so each feed can be isolated while the other carries load Correct answer.
  4. Manual rack-level power strips

Explanation

Dual utility feeds with transfer and distribution arranged for independent isolation let maintenance proceed on one path while the other supplies the load. This requires the downstream distribution to be split so no single point carries the whole load.

Question 36Data Centre Design

A new data hall will house racks averaging 12 kW each. Which design decision is most directly affected by this density?

  1. The colour scheme of the containment panels
  2. The choice of cooling distribution and whether air or liquid cooling is required Correct answer.
  3. The type of carpet in the reception
  4. The number of floor tiles in the office area

Explanation

High rack densities exceed what conventional air cooling can reliably deliver, so the cooling distribution method and the air-versus-liquid decision are driven by the heat load per rack. Finish and layout details are unaffected.

Question 37Data Centre Design

A design uses an N+1 UPS configuration with a single output distribution path to the racks. What is the key limitation of this arrangement?

  1. It removes the need for a generator
  2. It doubles the cooling capacity
  3. It protects against UPS module failure but not against a fault in the single distribution path Correct answer.
  4. It provides no redundancy at all

Explanation

N+1 redundancy covers failure of one UPS module, but if all load passes through one distribution path, a fault there can still drop the IT load. Full path redundancy requires independent distribution paths, such as in a 2N arrangement.

Question 38Data Centre Design

A data hall uses underfloor air distribution. Which design detail most affects whether cold air reaches the top of tall racks?

  1. The perforated tile open area and the static pressure in the plenum Correct answer.
  2. The thickness of the floor finish
  3. The number of cable ties used under the floor
  4. The colour of the perforated tiles

Explanation

Tile open area and plenum static pressure determine how much cold air is delivered at each location, which affects whether tall racks receive adequate supply at their intakes. Cabling and finishes do not control air volume.

Question 39Data Centre Design

A client wants the data centre to remain operational during a full utility outage of several hours. Which combination of systems is required?

  1. Redundant PDUs alone
  2. Surge suppressors alone
  3. UPS alone
  4. Generator plus UPS Correct answer.

Explanation

A UPS bridges the brief gap until generators start and stabilise, while the generator supplies sustained power for an extended outage. Neither system alone covers both the short ride-through and the long-duration requirement.

Question 40Data Centre Design

A data centre is sited in a region with high seismic activity. Which structural design measure is most relevant for the white space?

  1. Bracing of racks and restraint of overhead services Correct answer.
  2. Reducing the number of floor tiles
  3. Installing carpet in the data hall
  4. Increasing the ceiling tile count

Explanation

In seismic zones, racks and overhead services must be braced and restrained to prevent toppling and falling hazards during an event. These measures protect both personnel and IT equipment.

Question 41Data Centre Design

A design specifies hot aisle containment with a return plenum above the racks. What is the main benefit of this arrangement?

  1. It prevents hot exhaust from mixing with cold supply air Correct answer.
  2. It allows racks to be placed without aisles
  3. It eliminates the need for cooling equipment
  4. It removes the need for humidity control

Explanation

Containment with a return plenum captures hot exhaust and carries it back to the cooling units, preventing it from mixing with cold supply air. This improves the return air temperature and cooling efficiency.

Question 42Data Centre Design

A data hall must support both current racks and future higher-density racks without a full rebuild. Which design approach best supports this?

  1. Designing for the highest anticipated density from the outset with scalable cooling and power distribution Correct answer.
  2. Removing containment to simplify the design
  3. Installing fixed cooling capacity with no spare
  4. Designing only for current density and ignoring future requirements

Explanation

Designing for the highest anticipated density and using scalable cooling and power distribution allows capacity to be added as racks are upgraded. Designing only for current density risks early obsolescence and costly retrofits.

Question 43Data Centre Design

A data centre uses a raised floor for both air distribution and cabling. Which risk is most important to manage in this combined arrangement?

  1. Using too many perforated tiles
  2. Increasing the floor height unnecessarily
  3. Installing too few cable trays
  4. Blocking airflow with poorly routed cables and debris Correct answer.

Explanation

Cables and debris under the floor obstruct airflow and reduce the plenum's ability to deliver cold air evenly. Good design separates cabling routes from air paths and keeps the plenum clear.

Question 44Data Centre Design

A data centre design must limit acoustic noise from cooling plant near a neighbouring office. Which measure is most appropriate?

  1. Removing the cooling plant
  2. Installing acoustic attenuation on plant and ductwork Correct answer.
  3. Increasing the fan speed
  4. Reducing the fire rating of walls

Explanation

Acoustic attenuation on plant and ductwork reduces noise transmission to adjacent spaces. Increasing fan speed would raise noise, and removing cooling is not a viable option.

Question 45Data Centre Design

A data hall has a design PUE of 1.15. Which combination of features most likely supports this target?

  1. Oversized chillers and open aisles
  2. Economisers, containment, and efficient UPS operation Correct answer.
  3. Single-path power and no economisers
  4. High humidity setpoints and no containment

Explanation

Low PUE targets are achieved through free cooling or economisers, airflow containment, and efficient power conversion. These reduce overhead energy relative to IT load.

Question 46Data Centre Design

A data centre must meet a requirement that no single maintenance activity can interrupt IT load. Which design principle is central?

  1. Manual switching during business hours
  2. A single path with a maintenance window
  3. Removing redundancy to simplify operations
  4. Concurrent maintainability across power and cooling paths Correct answer.

Explanation

Concurrent maintainability means any component can be serviced while the load continues, which requires redundant and independently isolatable paths. A single path or manual switching would require downtime.

Question 47Data Centre Design

A data hall's cooling design uses a higher supply air temperature with containment. What is the expected effect on energy use compared with a lower supply temperature without containment?

  1. Higher energy use because containment increases fan power
  2. Lower energy use because the chiller lift is reduced and mixing is limited Correct answer.
  3. Higher energy use because the air is warmer
  4. No change because temperature does not affect energy

Explanation

Raising the supply temperature reduces the chiller's lift and energy use, while containment limits mixing so warmer supply still reaches equipment intakes effectively. The combined effect is typically lower energy use.

Question 48Data Centre Design

A data centre design must balance capital cost against resilience. Which approach best captures this trade-off?

  1. Always choosing the lowest-cost option
  2. Selecting redundancy levels based on business impact and cost of downtime Correct answer.
  3. Always choosing the highest redundancy available
  4. Ignoring downtime costs entirely

Explanation

Resilience should be matched to the business impact of downtime, so redundancy levels are chosen where the cost of an outage justifies the capital spend. Always maximising or minimising redundancy ignores this balance.

Question 49Data Centre Design

A data centre is designed with a single points of failure review. Which finding is most critical to address?

  1. A redundant component with automatic failover
  2. A shared component that can interrupt both power paths Correct answer.
  3. A component with spare parts in stock
  4. A component with a documented maintenance procedure

Explanation

A shared component that can interrupt both paths defeats redundancy and is a critical single point of failure. Redundant components with failover, documented procedures, and spares mitigate risk rather than create it.

Question 50Data Centre Design

A data hall must support phased growth from 500 kW to 2 MW while keeping PUE low at each phase. Which design strategy is most appropriate?

  1. Installing full-capacity plant immediately and running it at low load
  2. Ignoring efficiency until full build-out
  3. Using a single large chiller with no staging
  4. Modular plant sized in blocks that are added as load grows Correct answer.

Explanation

Modular plant added in blocks keeps equipment operating near efficient load points at each phase, avoiding the poor part-load efficiency of oversized plant. Installing full capacity early typically results in low-load inefficiency.