Data Center Field Guide

Every data-center system exists to do one of five jobs: deliver power, remove heat, move information, protect equipment, or keep the first four running.

Glossary

Acronym	Term	Category	Definition
AC	Air Compressor	Fire Protection	Fire protection equipment acronym listed for air compressor.
ACC	Air-Cooled Chiller	Mechanical	Refrigeration system that lowers fluid temperature and rejects heat outdoors using fans instead of cooling towers.
ACCU	Air-Cooled Condensing Unit	Mechanical	Packaged outdoor component that expels absorbed indoor heat to the outside atmosphere and houses the compressor, condenser coil, and fan.
ACU	Air Conditioning Unit	Mechanical	Generic term for an air conditioning unit, such as an AHU, FCU, or other unit that provides airflow and air conditioning to a room.
ADC	Adiabatic Dry Cooler Units	Mechanical	Closed-loop dry cooler units that use evaporation to pre-cool air flowing through the coil.
AFM	Air Flow Measuring Device	Mechanical	Instrument used to measure the rate of air movement in CFM, L/s, or m/s for HVAC, ventilation, fire protection, and environmental monitoring.
AHU	Air Handling Unit	Mechanical	Unit that conditions and distributes large volumes of air to support temperature control, humidity regulation, filtration, and air circulation.
AS	Air Separators	Mechanical	Devices that eliminate entrained air from closed-loop heating and cooling piping systems.
BD	Back Draft Damper	Mechanical	Mechanical damper installed in ducts to prevent reverse airflow while allowing air to move in the intended direction.
BMS	Building Management System Panel	Mechanical	System/panel associated with building systems such as HVAC maintenance, fire detection, security, access control, smoke control, indoor air quality, and energy management.
BP	Booster Water Pump	Plumbing	Pump system designed to increase and maintain water pressure in plumbing, cooling, or distribution networks.
BSU	Branch Selector Unit	Mechanical	Variable refrigerant flow branch selector unit listed for VRF systems.
BUS	IT Busway	Electrical	Prefabricated modular electrical distribution system that delivers power to IT equipment using enclosed busbars.
CD	Ceiling Diffuser	Mechanical	HVAC component used to distribute conditioned air evenly throughout a room.
CDWR	Condenser Water Return	Mechanical	Condenser-water return side shown in the chilled-water system diagram.
CDWS	Condenser Water Supply	Mechanical	Condenser-water supply side shown in the chilled-water system diagram.
CFM	Cubic Feet per Minute	Mechanical	Volume of air moved or supplied by equipment per minute; calculated as velocity multiplied by area.
CH	Chillers	Mechanical	Machine that removes heat from a liquid coolant using vapor-compression, adsorption, or absorption refrigeration cycles.
CHWP	Chilled Water Pumps	Mechanical	Pumps that circulate chilled water in a closed chilled-water system.
CHWR	Chilled Water Return	Mechanical	Water that returns to the chiller plant after absorbing heat from building cooling coils.
CHWS	Chilled Water Supply	Mechanical	Distribution of cold water to cooling applications within a building or system.
COND	Condenser	Mechanical	Condenser component shown in the chilled-water diagram as part of the chiller system.
CP	Condenser Pump	Mechanical	Pump that circulates cooling water through a condenser heat exchanger coil.
CPP	Chiller Power Panel	Electrical	Central electrical enclosure on a chiller that manages, distributes, and protects high-voltage power for compressors, pumps, fans, and controls.
CRAC	Computer Room Air Conditioner	Mechanical	Air conditioner designed for computer rooms with higher sensible cooling capacity and targeted cooling.
CRAH	Computer Room Air Handler	Mechanical	HVAC unit used in data centers to cool equipment by circulating air.
CT	Cooling Tower	Mechanical	Evaporative heat rejection device used in water-cooled HVAC systems to remove excess heat from building or process operations.
CU	Condensing Unit	Mechanical	Outdoor component of a split refrigeration or air-conditioning system that houses the compressor, condenser coil, fan, and controls.
CWP	Condenser Water Pumps	Mechanical	Pumps that circulate cooling water between a water-cooled chiller condenser and a heat rejection device, such as a cooling tower.
DOAS	Dedicated Outdoor Air System	Mechanical	Rooftop system that brings in, conditions, and delivers fresh outdoor air directly to indoor spaces.
ECS	Engineered Corrosion Solutions Nitrogen Generator	Fire Protection	Nitrogen generator system used to mitigate internal corrosion in fire sprinkler piping.
EF	Exhaust Fans	Mechanical	Fans that remove stale, warm, or humid air from indoor spaces and expel it outside.
EOP	Emergency Operating Procedure	Operations	Documented protocol for responding to critical or emergency situations to maintain operational continuity.
EPMS	Electrical Power Monitoring System	Electrical	Monitoring system used to track electrical load, breaker status, and power quality within the facility.
ERCS	Emergency Responder Radio Communication System Panel	Fire Protection	Panel acronym listed for emergency responder radio communication system.
ESEW	Emergency Shower / Eye / Face Wash Station	Plumbing / Safety	Station used to quickly flush hazardous chemicals, dust, or particles from skin, eyes, or face during exposure events.
ESS	Energy Storage System	Electrical	Technology that captures and stores energy for later use to balance supply and demand, support reliability, reduce cost, and improve sustainability.
ET	Expansion Tanks	Mechanical	Tanks that absorb expansion and contraction of water to manage pressure and protect closed-loop systems.
EWC	Electric Water Cooler	Plumbing	Plumbing equipment acronym listed for electric water cooler.
FAAP	Fire Alarm Annunciator Panel	Fire Protection	Central display and control interface that provides visual and audible notification of fire detection events by zone, device, or floor.
FACP	Fire Alarm Control Panel	Fire Protection	Centralized panel that monitors and manages fire detection systems, alarms, and suppression zones.
FCU	Fan Coil Unit	Mechanical	Compact HVAC device consisting of a fan and heat exchanger coil used for heating or cooling.
FCW	Fan Coil Wall	Mechanical	Configuration of high-capacity fan coil units designed for perimeter use in data centers.
FOST	Fuel Oil Storage Tank	Fire Protection	Fire protection equipment acronym listed for fuel oil storage tank.
FP	Fire Pumps	Fire Protection	Pumps that boost water pressure and flow rate to support fire suppression systems.
FPC	Fire Pump Controllers	Fire Protection	Electrical control panels that automatically start, monitor, and manage fire pump operation.
GEN	Generators	Electrical	Devices that convert mechanical energy into electrical energy through electromagnetic induction for backup, emergency, prime, or load-support power.
HCP	Humidifier Control Box / Panel	Mechanical	Control system that manages humidifier operation using sensors, relays, interfaces, and safety functions.
HMI	Human Machine Interface	Mechanical / Controls	User interface or dashboard that allows operators to monitor, control, and interact with machines, systems, or automation equipment.
HUM	Humidifiers	Mechanical	Devices that add moisture to air to maintain relative humidity levels for equipment protection and environmental control.
HWP	Hot Water Pump	Mechanical	Pump that circulates heated water through hydronic heating systems, boilers, radiators, underfloor heating, or heat exchangers.
HX	Heat Exchangers	Mechanical	Devices that transfer thermal energy between fluids without mixing them.
IDF	Intermediate Distribution Frame	IT / Telecom	Telecommunications wiring closet or rack located between the MDF and end-user devices.
IDU	Indoor Unit	Mechanical	Indoor component of a split-system or VRF air-conditioning setup that works with an outdoor unit to regulate indoor climate.
IT	Information Technology	IT / Telecom	Used in the page to describe data center technology loads, IT busways, IT equipment, IT POE, and IT rooms.
JP	Jockey Pumps	Fire Protection	Small low-capacity pump that maintains pressure in sprinkler or standpipe fire suppression systems.
JPC	Jockey Pump Controllers	Fire Protection	Fire protection equipment acronym listed for jockey pump controllers.
LBB	Load Bank Breaker	Electrical	Heavy-duty breaker or switchgear device used to isolate, connect, or disconnect a load bank during testing.
LP	Lighting Panels	Electrical	Electrical panels that distribute and protect power to lighting fixtures, receptacles, and small loads.
M	Mechanical or Plumbing Room / Closet	Locator Prefix	Mechanical or plumbing room/closet locator prefix.
MAU	Makeup Air Unit	Mechanical	Rooftop unit listed for makeup air systems.
MBB	Maintenance Bypass Breaker	Electrical	Heavy-duty breaker or switchgear assembly that allows isolation and bypassing of UPS equipment during service, testing, or repair.
MBP	Maintenance Bypass Panel	Electrical	Electrical distribution system designed to reroute power around a UPS during maintenance, repairs, or testing without interrupting critical loads.
MCP	Modular Central Plants	Mechanical	Mechanical equipment acronym listed for modular central plants.
MDB	Main Distribution Board	Electrical	Referenced as another name for a main switchboard or as an upstream source for panels.
MDF	Main Distribution Frame	IT / Telecom	Referenced as the upstream telecommunications distribution frame relative to an IDF.
MDP	Mechanical Distribution Panels	Electrical	Electrical panelboards designed to distribute and control power to mechanical systems such as HVAC equipment, pumps, fans, and chillers.
MOP	Method of Procedure	Operations	Structured step-by-step guide used to execute complex operational tasks safely and consistently.
MP	Mechanical Panels	Electrical	Electrical panels associated with mechanical systems; paired with MDP in the glossary.
MSB	Main Switchboard	Electrical	Primary electrical distribution panel that receives power from utility service or generators and distributes it to downstream equipment.
MV	Medium Voltage	Electrical	Electrical power systems operating between 1 kV and 35 kV.
MVS	Medium Voltage Switchgear	Electrical	Central electrical control and protection system that manages, distributes, monitors, and protects medium-voltage power flow.
MVTP	Medium Voltage Transfer Pair	Electrical	Redundant MV switching configuration that transfers between primary utility feeds and backup sources within an MUSB.
NG	Nitrogen Generators	Fire Protection	Fire protection equipment acronym listed for nitrogen generators.
NPWP	Non-Potable Water Pumps	Mechanical	Mechanical equipment acronym listed for non-potable water pumps.
NPWRP	Non-Potable Water Storage Recirculation Pumps	Mechanical	Mechanical equipment acronym listed for non-potable water storage recirculation pumps.
NPWT	Non-Potable Water Storage Tanks	Mechanical	Mechanical equipment acronym listed for non-potable water storage tanks.
NVCP	Nitrogen Purge Vent Control Panel	Fire Protection	Fire protection equipment acronym listed for nitrogen purge vent control panel.
ODU	Variable Refrigerant Flow Outdoor Condensing Units	Mechanical	Centralized heat rejection components in a VRF HVAC system; also known as VRF outdoor units.
PDU	Power Distribution Units	Electrical	Electrical panels that deliver, monitor, and control low-voltage power to IT equipment.
POE	Point of Entry	IT / Telecom	Central demarcation facility where IT cabling, power, and connectivity services first enter the data center.
PQM	Power Quality Meter	Electrical	Digital instrument that monitors, analyzes, and logs voltage, current, harmonics, and transients in MV and LV systems.
RH	Relative Humidity	Mechanical	Humidity level referenced for data center environmental control and humidifier operation.
RO	Reverse Osmosis Water System	Mechanical	Mechanical equipment acronym listed for reverse osmosis water system.
RP	Receptacle Panels	Electrical	Low-voltage distribution boards that provide branch circuit power to non-IT loads such as maintenance tools, lighting, office equipment, VRF controls, RO systems, and facility devices.
RSTSDP	Reverse Static Transfer Switch Distribution Panels	Electrical	LV distribution systems that automatically transfer critical IT loads from rack-level PDUs back to alternate power sources using SCRs.
RTU	Roof Top Unit	Mechanical	Self-contained packaged HVAC system mounted outdoors or on roofs to deliver conditioned air through ductwork.
SCR	Silicon-Controlled Rectifier	Electrical	Solid-state switching device referenced as the technology used in STS and reverse STS systems.
SGA	Supervisory Air Gas Analyzers	Fire Protection	Fire protection equipment acronym listed for supervisory air gas analyzers.
SOP	Standard Operating Procedure	Operations	Detailed written set of instructions for performing operational tasks safely and effectively.
SPD	Surge Protector Device	Electrical	Also called surge arrestors; fast-acting components that clamp transient overvoltages to safe levels.
SSHP	Split System Heat Pump	Mechanical	Mechanical equipment acronym listed for split system heat pumps.
STS	Static Transfer Switch	Electrical	High-speed solid-state device that switches critical IT loads between dual power sources.
TX	Transformer	Electrical	Static electrical device that steps voltage up or down using magnetic induction.
UDP	UPS Distribution Panels	Electrical	Electrical equipment acronym listed for UPS distribution panels.
UDS	UPS Distribution Switchgear	Electrical	Integrated LV power distribution system combining UPS, STS, reverse STS, intelligent breakers, and PDU-level metering.
UPS	Uninterruptible Power Supply	Electrical	Power conditioning and battery backup system that provides clean continuous AC power during power quality events or outages.
VESDA	Very Early Smoke Detection Apparatus	Fire Protection	Highly sensitive fire detection system used to detect smoke at the earliest stage, often in data center environments.
VFD	Variable Frequency Drive	Mechanical / Electrical	Solid-state power electronics that control AC motor speed by modulating voltage and frequency to match load demand.
VRF	Variable Refrigerant Flow	Mechanical	HVAC system type referenced for branch selector units, indoor fan coil units, and outdoor condensing units.
WH	Water Heater	Plumbing	System that provides hot water for humidification, reheat coils, domestic use, and waste heat recovery.
WSHP	Water Source Heat Pump	Mechanical	Closed-loop water-to-air heat pumps that transfer heat between a central water loop and indoor air using refrigerant compression.

1 - What Is a Data Center?

2 - How Does Electricity Get to a Server?

Utility Service

Acronym	Component	Resources
Utility	Utility Grid
TL	Transmission Line
SS	Utility Substation	Practical Engineering — How Do Substations Work?
RM	Revenue Meter
MVSG	Medium Voltage Switchgear	Eaton — Medium-Voltage Switchgear Fundamentals
MVTP	Medium Voltage Power Transformer	Eaton — Unit Substation Fundamentals

Backup Power

Acronym	Component	Resources
GEN	Diesel Generator
GCB	Generator Circuit Breaker	ABB — VD4G Vacuum Generator Circuit Breaker
GPS	Generator Paralleling Switchgear
ATS	Automatic Transfer Switch	Eaton — Automatic Transfer Switch Fundamentals
AST	Aboveground Storage Tank
Day Tank	Generator Day Tank

Low Voltage Distribution

Acronym	Component	Resources
LVSG	Low Voltage Switchgear	Eaton — Low-Voltage Switchgear Fundamentals
MSB	Main Switchboard	Eaton — Switchboard Basics
MDB	Main Distribution Board	Eaton — Switchboard Fundamentals
MDP	Main Distribution Panel	Eaton — Panelboard Fundamentals
UPS	Uninterruptible Power Supply
MBS	Maintenance Bypass Switch
STS	Static Transfer Switch	Vertiv — Static Transfer Switches in Data Centers

Distribution to IT Equipment

Acronym	Component	Resources
PDM	Power Distribution Module	Schneider Electric — Modular Power Distribution
PDU	Power Distribution Unit	Schneider Electric — Modular PDU and RPP Operation
RPP	Remote Power Panel	Schneider Electric — Galaxy Remote Power Panel
Busway	Busway / Bus Duct	Eaton — Busway Explained
BCMS	Branch Circuit Monitoring System
rPDU	Rack Power Distribution Unit	Vertiv — Guide to Power Distribution Units
PSU	Server Power Supply Unit
Server	Server

Monitoring &Protection

Acronym	Component	Resources
CT	Current Transformer
PT	Potential Transformer
EPMS	Electrical Power Monitoring System
SPD	Surge Protective Device
GFCI	Ground Fault Circuit Interrupter
EPO	Emergency Power Off

3 - How to Manage Heat?

Heat Transfer

The Engineering Mindset — Heat Transfer Explained

Refrigeration Cycle

The Engineering Mindset — Refrigeration Cycle Explained

Chillers

The Engineering Mindset — Chillers – What Are They?

Chiller Components

The Engineering Mindset — Chillers – Main Components

Chiller Types

The Engineering Mindset — Chiller Types and Application Guide

Air-Cooled Chillers

The Engineering Mindset — How Air-Cooled Chillers Work

Water-Cooled Chillers

The Engineering Mindset — Water-Cooled Chiller Design Data

Cooling Towers

The Engineering Mindset — How Cooling Towers Work

Chilled Water Systems

The Engineering Mindset — Chilled Water Schematics

Air Handling Units (AHUs)

The Engineering Mindset — Air Handling Units Explained

CRAHs, Chillers &Cooling Towers

The Engineering Mindset — How a Chiller, Cooling Tower and Air Handling Unit Work Together

HVAC Heat Exchangers

The Engineering Mindset — HVAC Heat Exchangers Explained

Refrigeration Tons

The Engineering Mindset — Refrigeration Ton Explained

Psychrometrics

The Engineering Mindset — Psychrometric Chart Explained

Data Center Cooling

The Engineering Mindset — Data Center HVAC Cooling Systems

4 - How Does the Building Know What to Do?

Building Automation Systems (BAS)

The Engineering Mindset — Building Management Systems (BMS) Explained

Programmable Logic Controllers (PLCs)

The Engineering Mindset — Programmable Logic Controllers (PLCs) Explained

SCADA

RealPars — SCADA Basics: From Fundamentals to Practical Applications

Human-Machine Interfaces (HMIs)

RealPars — What Is the Difference Between SCADA and HMI?

Distributed Control Systems (DCS)

RealPars — What Is the Difference Between DCS and SCADA?

PLC Inputs &Outputs

RealPars — PLC Hardware Fundamentals

Sensors

RealPars — Sensor Types and Working Principles Explained

Actuators

RealPars — Introduction to Industrial Sensors and Actuators

PID Control

RealPars — PID Controller Basics

Control Loops

The Engineering Mindset — Control Loops Explained

Alarms &Trending

The Engineering Mindset — Building Management Systems (BMS) Explained

5 - How Does the Building Stay On All the Time?

Redundancy

Topic	Definition
N Redundancy	Exactly the amount of equipment required to support the critical load. No backup capacity is available.
N+1 Redundancy	One additional component is installed beyond what is required so the system can continue operating if a single component fails or is removed for maintenance.
N+2 Redundancy	Two additional components are installed beyond what is required, allowing multiple simultaneous failures or maintenance events.
2N Redundancy	Two completely independent systems, each capable of carrying the entire critical load by itself.
2(N+1) Redundancy	Two independent systems, each with its own spare capacity. Either system can support the full load even after a component failure.
Block Redundancy	Spare capacity is shared among a group of systems rather than dedicated to each individual system.
Distributed Redundancy	Redundant capacity is spread across multiple operating units so the loss of one unit is absorbed by the remaining units.

Concurrent Maintenance

Topic	Definition
Concurrent Maintainability	Any component can be removed from service for maintenance without interrupting the critical load.
Fault Tolerance	The system continues operating despite the unexpected failure of a component or distribution path.
Single Point of Failure (SPOF)	A component whose failure would interrupt the critical load because no alternate path exists.
Maintenance Bypass	A temporary electrical path that allows equipment such as a UPS to be serviced while power continues to reach the load.
Isolation Procedures	Planned steps used to safely remove equipment from service without affecting the remaining system.

Electrical Reliability

Topic	Definition
Dual Utility Feeds	Two independent utility power sources supplying the facility to reduce dependence on a single electrical feed.
Dual-Corded Servers	Servers equipped with two power supplies connected to separate power sources for continuous operation.
A/B Power Distribution	Two completely independent electrical distribution paths serving critical equipment.
Automatic Transfer	Automatic switching from one power source to another when the primary source is lost.
Static Transfer	Solid-state switching between power sources with virtually no interruption to the load.
UPS Redundancy	Multiple UPS units arranged so critical loads remain powered if one UPS fails or is removed from service.
Generator Redundancy	Multiple generators arranged so standby power remains available after a generator failure or during maintenance.
Battery Redundancy	Additional battery capacity or independent battery strings that maintain UPS operation during battery failures or maintenance.

Mechanical Reliability

Topic	Definition
N+1 Cooling	One additional cooling unit beyond the required capacity to maintain cooling during failures or maintenance.
Pump Redundancy	Multiple pumps arranged so cooling water continues circulating if one pump becomes unavailable.
Chiller Redundancy	Multiple chillers providing reserve cooling capacity during equipment failures or maintenance.
Cooling Tower Redundancy	Multiple cooling towers ensuring continued heat rejection when a tower is unavailable.
CRAH / CRAC Redundancy	Additional computer room air handlers or air conditioners maintaining airflow and temperature despite equipment outages.
Automatic Lead/Lag Rotation	Control strategy that rotates equipment duty assignments to equalize operating hours and improve reliability.

Network Reliability

Topic	Definition
Dual Core Switches	Two independent core network switches providing redundant network connectivity.
Diverse Fiber Paths	Physically separated fiber routes that reduce the likelihood of a single event interrupting communications.
Network Failover	Automatic transfer of network traffic to a redundant path following a failure.
High Availability	System design focused on minimizing downtime through redundancy, monitoring, and rapid recovery.
Redundant Firewalls	Multiple firewalls operating together so network security continues if one device fails.

Operations

Topic	Definition
Change Management	Formal process for planning, reviewing, approving, implementing, and documenting changes to critical systems.
Method of Procedure (MOP)	Step-by-step instructions for performing planned work on critical infrastructure.
Standard Operating Procedure (SOP)	Approved instructions describing the normal operation of equipment and systems.
Emergency Operating Procedure (EOP)	Predefined actions taken during abnormal or emergency conditions to protect personnel and maintain operations.
Root Cause Analysis (RCA)	Structured investigation used to identify the underlying cause of an event rather than only its symptoms.
Incident Response	Coordinated actions used to identify, stabilize, communicate, and recover from operational incidents.

Reliability Metrics

Topic	Definition
Uptime Institute Tier I–IV	Classification system describing increasing levels of redundancy, maintainability, and fault tolerance in data center infrastructure.
Availability	The percentage of time a system is capable of performing its intended function.
Mean Time Between Failures (MTBF)	Average operating time between successive failures of repairable equipment.
Mean Time To Repair (MTTR)	Average time required to restore equipment to normal operation after a failure.
Service Level Agreement (SLA)	A contractual commitment defining expected service performance, such as uptime, response time, or recovery objectives.