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"Do you have a list of building automation abbreviations" is a common request we get here at Smart Buildings Academy.

This guide will continue to grow every week as we add more and more definitions to the guide. If you have a suggestion for an acronym please post it in the comments. Please be aware this list is a work in progress.

If you would like to contribute to this guide with blog content or definitions please email marketing@smartbuildingsacademy.com

[Last Updated 5-2-22] Please keep the great feedback coming, we have added even more definitions!


Access Control List (ACL)- 

Access control lists are filtering mechanisms set up within networking gear or software the control the flow of network traffic. Typically access controls lists are set up with an implicit deny which means that any traffic not explicitly permitted will be denied access. 

As you've probably already picked up, ACLs use Deny and Permit statements that regulate network traffic. The traffic can be regulated by subnet, IP address/range, Port, or protocol.


A control device that enables the building automation controller to change the state of dampers and valves by converting electrical energy into torque (usually measured in foot lbs). Actuators accept control signals from the building automation controller and power from transformers.


Air Handling Unit (AHU)

AHU's also known as air handling units are one of the main types of mechanical systems used for the distribution of conditioned air throughout a building. There are multiple types of AHU's but what really sets an AHU apart from make-up air units and rooftop units? 

The AHU is used to distribute large masses of conditioned air to a single space or multiple spaces. But wait makeup air units and rooftop units do that as well... That is because those are types of AHU's. I know mind blown right! So next time you hear someone use the term AHU (myself included) remember that could possibly mean RTU, Makeup Unit, ERV, etc...

Here are a couple of good articles on AHU and RTU control:

Airside Unit Control Fundamentals Part 1

Airside Unit Control Fundamentals Part 2

Airside Unit Control Fundamentals Part 3

Here is a good video on Air Handling Units


Airflow is the primary mechanism for controlling environmental conditions within the building. We primarily use fans to move air within the building and we use dampers and fan speed control devices (like variable frequency drives) to regulate airflow. 

Without airflow, we are unable to control pressure, temperature, CO2, and humidity levels. Airflow is the most important variable we can control in a building.


Amperage, also known as current, is the measurement of the flow electricity across a wire. Current is calculated by volts/resistance. Essentially as the resistance increases, you will get more current. Current produces heat (which on a side note is how electric heating works). Also, we use current for long-distance control signals because it is not as affected by distance and interference.

American Wire Gauge (AWG)-

American Wire Gauge or AWG is a measurement of the thickness of wire. As the number (known as the "gauge") gets larger the thickness or diameter of the conductors inside the wire sheath shrink in size. Therefore 14 gauge wire would be thicker than 22 gauge wire. 

The wire gauge is the first number in typical wiring descriptions with the second number being the number of conductors (aka wires). Therefore 18/2 would be as described in the table below.

Gauge Conductor Count
18 2


The most commonly used wires in building automation are 18/2 UTP, 22/3 STP, and 22/4 STP.

STP and UTP stand for unshielded and shielded twisted pair. We will discuss shielding in the "S" section of this guide.

Analog Input (AI)

Analog inputs are both physical and logical points. They represent an object which is analog in nature (meaning the value of the object can and most likely will change across a variable range). Common types of physical analog inputs are resistive, current, and voltage inputs. 

In terms of logical inputs, these objects commonly exist for integration purposes and represent read-only values due to the lack of a priority array.

Analog Output (AO)

Analog outputs are both physical and logical points. They represent an object which is analog in nature (meaning the value of the object can and most likely will change across a variable range). Common types of physical analog outputs are current and voltage outputs. 

In terms of logical inputs, these objects commonly exist for integration purposes. Unlike analog inputs, these objects represent writable values due to the presence of a priority array.

Depending on the manufacturer some "Output" objects will only exist for physical objects whereas other manufacturers will allow logical "outputs" to be created.

Analog Value (AV)

Analog outputs are ONLY logical points. They represent an object which is analog in nature (meaning the value of the object can and most likely will change across a variable range). These objects are used to represent setpoints and other "logical" data points.

Unlike analog inputs, these objects represent writable values due to the presence of a priority array.

Automated System Optimization (ASO)

Automatic Transfer Switch (ATS)



BACnet (Building Automation Control Network) is the primary communications protocol used in the building automation space. This protocol comes in multiple physical forms the primary ones being BACnet MS/TP and BACnet/IP.  BACnet is an object-oriented protocol that uses objects for its data type structures and services for its communication methods.

BACnet Overview


BACnet MS/TP Overview


BACnet Broadcast Management Device (BBMD)

BACnet Broadcast Management Devices or BBMD's are an integral part of the BACnet/IP protocol. BBMD's are required because BACnet/IP uses broadcasts for device discovery. The BBMD exists on every BACnet/IP subnet and contains a BDT. The BBMD can be contained in a control device or a BACnet networking device (like a router). The BBMD manages the broadcast routing process in order to build a list of BACnet nodes. 

The BBMD will send messages to all BACnet subnets listed in the BDT. Once the list of BACnet nodes has been constructed BACnet will utilize unicast and multicast directed messages for the other BACnet services.

Binary Input (BI)

Binary inputs are both physical and logical points. They represent an object which is binary in nature (meaning the value of the object can only be in two states true or false). Common types of physical binary inputs are dry contacts that monitor status. 

In terms of logical inputs, these objects commonly exist for integration purposes and represent read-only values due to the lack of a priority array.

Binary Output (BO)

Binary outputs are both physical and logical points. They represent an object which is binary in nature (meaning the value of the object can only be in two states true or false). Common types of physical binary outputs are internally and externally sourced voltage through relays, TRIACS, and floating outputs. 

In terms of logical inputs, these objects commonly exist for integration purposes. Unlike binary inputs, these objects represent writable values due to the presence of a priority array.

Depending on the manufacturer some "Output" objects will only exist for physical objects whereas other manufacturers will allow logical "outputs" to be created.

Binary Value (BV)

Binary outputs are ONLY logical points. They represent an object which is binary in nature (meaning the value of the object can only be in two states true or false). These objects are used to represent alarm states, enable modes, and other "logical" data points.

Unlike binary inputs, these objects represent writable values due to the presence of a priority array.

Broadcast Definition Table (BDT)

The broadcast definition table or BDT is a BACnet concept that enables BBMD's to route its broadcast messages to other BACnet subnets. Because broadcasts are not routable BACnet relies on BBMD's to manage the broadcast of discovery messages for the protocol.

The BBMD contains a registry of BDT's that list the address of the BBMD's on other BACnet subnets. On a side note, one of the biggest issues to routing in BACnet is not keeping your BBMD up to date.


Boilers are mechanical devices that provide heat to both hot water and steam in order to transfer heat into the building. Typically we utilize combustion or electricity to generate heat. This heat is then transferred throughout the building using piping and pumps and then that heat is transferred to the airstream via coils or radiators. 

Here is an article on how to control hot water systems.


British Thermal Unit (BTU)

A British Thermal Unit or BTU is a measurement of heat energy. Essentially BTUs are the amount of heat required to raise the temperature of 1lb of water by 1 degree. 

But that's not all we use BTUs for. BTUs are a very important data point for us in building automation. BTU's tell us how much heat addition AND removal capacity a piece of equipment has. For example, a chiller is rated in tons (one ton =12000 BTU) there for at 100% efficiency (no device is 100% efficient) a 100 TON chiller can remove 1,200,000 BTU of heat energy from the building.

The rate of exchange of BTUs varies. For example, the BTU capacity of different mediums is below.

Air 0.24 per lb per degree
Water 1.00 per lb per degree
Steam 1,194 per lb per degree


As you can see steam has a substantially higher capacity for BTUs. This is why we use steam on very large central utility plants. 

We can also see that air has a pretty dismal absorption rate for heat energy. This is why we primarily use chilled water and hot water for heat transfer/absorption. 


Building Automation System (BAS)

Building automation systems enable the control and visualization of control systems. Prior to building automation systems operators did not have the ability to control multiple control systems from a single interface.

Learn more with our Complete Guide to Building Automation Systems.

Building Management System (BMS)

Building Management Systems are similar to building automation systems but they typically are focused on the server and supervisory layers. Building management systems in their purest form consolidate multiple building systems into a single user interface (single pane of glass) to enable operators to manage multiple building systems (access control, lighting, conveyance, building automation, etc).


Carbon Dioxide (CO2)

Carbon Monoxide (CO)


Certificate Authority (CA)

A certificate authority or CA is something that didn't matter much in the past but is critical now for most modern building automation systems. At the supervisory level, most building automation systems use a protocol called HTTP to transfer webpages from the BAS web server to the BAS user's web browser.

HTTP by itself is a clear text protocol meaning that if you can capture the message as it travels across the network you will have access to all of the message's data including login credentials, etc. This data can not only be read but it can also be captured edited and resent. 

HTTPS (a secure version of HTTP) largely solves this issue. It does so through certificates (see certificate definition). By using certificates HTTPS can ensure that the messages maintain confidentiality and integrity. But how do you know the certificates are legitimate? 

Certificate Authorities ensure that the certificate and its keys are legitimate. As we will cover in certificates there are keys that are used to encrypt and decrypt data. These keys ensure that the data has not been tampered with.

You can self-sign certificates but it will become very difficult to validate the security and integrity of the certificate.

Current Transducer (CT)


Cubic Feet Per Minute (CFM) is a measurement of airflow used in HVAC. This is a value that is typically monitored and controlled in order to ensure proper ventilation. CFM can also be controlled using strategies like volumetric matching and offset in order to regulate pressure (typically space pressure is the main control variable). The term is called "cubic" feet per minute because it is the measurement of the cubic mass of air traveling per minute through a measured area.

Characterized Control Valves (CCV)

Characterized Control Valves (CCV) have a "characterized disc" inside the valve that enable the valve to have equal percentage flow across the full opening of the valve. Because of this CCV valves are able to maintain equal flow percentage during light loads, unlike traditional ball valves which have unequal flow percentage based on the position of the ball valve.

For this reason, most control valves are not actually "ball valves" but are CCV. It is common practice in the BAS industry for people to refer to CCV valves as ball valves even though they are different. Therefore it is important to ensure that the specification accurately reflects the correct valve assembly.

Traditional ball valves are typically used for manual isolation valves.


Chillers are used to remove heat from buildings. Chillers utilize the refrigeration process to transfer heat out of the building. There are two primary types of chiller's air-cooled and water-cooled (yes there are centrifugal, scroll, etc). Chilled water will flow through coils in the HVAC air device's airstream and will absorb BTUs into the "return chilled water". 

These BTUs will then be transferred from the evaporative to the condenser side of the chiller and then transferred to the atmosphere (depending on the chiller type). 

Here is a guide to chilled water system sequencing.


Classless Inter-domain Routing (CIDR)

CIDR is the method that is utilized to allocate IP Addresses for networks and ultimately routing. Often indicated by a "/" and then a "number". CIDR dictates how many of the 32 bits allocated to an IP address belong to the network and how many can be allocated to the host.

Often times you will see something like "/24". This means that 24 bits of the 32 bit IP address are allocated to the network and 8 bits are allocated to the Hosts. 

Since a bit can exist in two states "1" or "0" this means that you have 28 IP addresses or 256 addresses available to Hosts. In reality, you only have 253 as:

  • The first address of the range gets allocated to the subnet
  • 1 address (any except 1st and last of range) gets allocated to the default gateway
  • The last address of the range gets allocated to the broadcast address

Client-Server Architecture

Client-server architecture in the case of building automation is the architecture (structure) that defines how BAS servers and graphical user interfaces communicate. 

Prior to Client-server architectures all BAS user interfaces were known as thick clients this meant that the user interface was usually hard wired directly to a supervisory device. 

With the advent and adoption of the client-server architectures, BAS now use thin clients. A thin client is an interface (typically a web browser) that does not require additional software to interface between the server and the client. This enables users to interface with the building automation system directly from common devices like laptops, desktops, and mobile devices.

Cloud Computing

Coefficient of Performance (CoP)



Condensate is moisture that is produced through the act of condensation. In building automation, we are primarily concerned with two forms of condensate. 

Condensate from steam and condensate from chilled water coils.

In steam as we transfer heat (usually via coils or heat exchanges) we reduce the amount of BTUs in steam this causes steam to revert back from a gas into a liquid. This liquid is called condensate and typically is captured and reintroduced to the boiler (or used as domestic hot water) via a condensate return.

In regards to chilled water coils, we often will cool the air below the dewpoint. When this happens the moisture in the airstream will condense and form into a liquid (condensate) this condensate will often drip into the condensate pan to be recovered or disposed of.


Control Modes

Control modes are the methods used to implement a control process. 

Control Process

This is the internal process that is used to eliminate the error (difference between control variable and setpoint). This is typically used in PID, Floating, Step, and other control modes.

Control System

A control system is a physical system that processes inputs in order to control outputs. 

Common control systems are pneumatic, analog, electromechanical, and direct digital control.

Control Variable

The control variable (sometimes known as the process variable) is the value that is used for "control processes" in a BAS application. This is often the value that the setpoint is trying to drive to.



Data is information that is captured in physical or electronic form that provides context. Therefore data can be your trend logs from a temperature sensor, data can be your physical O&M manuals, data can be a live feed from a security camera. 

In order for data to be processed by a computational device (computer, phone, server, etc) it needs to be processed. Some data sources are structured and are easy to process like a weather station API. Other forms of data must be manually processed or scanned using specialized software (using optical character recognition OCR, to scan mechanical plans). 

Once this data is processed it can be acted upon through your control system, analytics, and other tools.

Here is a podcast episode recording on data.


Data Center Information Management (DCIM)

Data Schema

Data Tagging



Domain Name System (DNS)

Dry bulb Temperature

Dry bulb temperature is a measurement of temperature in absence of moisture. The majority of the time that you are measuring temperature you are measuring a dry bulb temperature. This term comes from the concept that the temperature sensing element is contained in a bulb isolating it from the effects of moisture. Because of this, the temperature reading is "dry".

Dynamic Host Configuration Protocol (DHCP)

Dedicated Outside Air System (DOAS)

Delta T

Delta T is the difference between two temperature readings. Usually used to measure the difference between the supply and return side of water flows or the leaving and entering airflow streams. Delta T is represented by the symbol Δ T.


Differential Pressure (DP)

Direct Digital Controls (DDC)

Direct Digital Controls (DDC) systems are systems that convert analog input signals to digital signals using an analog to digital converter. These systems contain a processor that is able to process digital signals (1's and 0's) in order to programmatically control outputs. 

Most direct digital control systems have the ability to intercommunicate via field buses to other DDC systems and to supervisory devices for graphical visualization.

Discharge Air Temperature (DAT)



Energy Conservation measure (ECM)

Energy Efficiency Ratio (EER)

Energy Savings Company (ESCO)

Energy Services Company (also ESCO)


Enthalpy in regards to air is the heat energy contained in the air.

Enthalpy is rated in BTU/lb of moist air or joule/kg. 

Remember that moisture (liquid water) contains much more BTUs than dry air. Because of this we often will compare return vs outside air enthalpy when making economizer decisions.

Equivalent Kilo-watt Hours (eKWh)


Exhaust Air

Exhaust Fan

Exhaust fans are fans that are used to take the air out of a space (in contrast to supply fans that introduce air to a space). Exhaust fans can be driven off of several control variables. The most common control variables are:

  • Temperature- Used to exhaust air when a space gets too hot.
  • Pressure/CFM- Used to exhaust air in order to control to a specific pressure or airflow setpoint
  • Interlock- The fan is interlocked to run any time the associated system (e.g. AHU, RTU, etc) is enabled.


Fan Coil Unit (FCU)

Fan Wall

Fault Detection & Diagnostics (FDD)


Filters are devices that are used to capture pollutants and other micro-particles from the airstream. There are several types of filters (which is beyond the scope of this guide) suffice to say we as building automation professionals are primarily concerned with:

Where is the filter located?

Does the filter exist before or after coils and devices that could be potentially impeded? If so then you may need to account for this in the design.

What is the pressure drop from filters?

Filters restrict airflow. Because of this, they induce what is known as a pressure drop. The pressure drop from coils needs to be accounted for. 

Floating Control


Functional Performance Testing (FPT)


Graphical Unit Interface (GUI)



Project Haystack is a semantic model for data (meaning that it gives context to data). Haystack and other standards like BRICK Schema, provide recommended approaches and structures for organizing metadata (data about data). 

Haystack (and other semantic models) enable context to be added to point objects. This makes the objects easier to query and work with. 

Here is a podcast interview I did with one of the board members at Project Haystack

Listen Now

High Availability (HA)

Hot Water System- 

Hot water systems (HWS) exist to introduce heat into the building or to provide hot water to occupants. There are two main HWS in the building, we have the hot water boilers that supply heated water to HVAC equipment. This water will typically vary in temperature from 140 to 180 degrees based on load. 

We also have domestic hot water, this water is at a significantly lower temperature and is used as a hot water source for occupant's sanitary needs. 

You can learn more about how hot water systems work and are sequenced in this blog post.

Hypertext Markup Language (HTML)

Hypertext Transmission Protocol (HTTP)

Humidity -

Humidity is the moisture content in the air stream. Human's primarily cool themselves down through the release of moisture (sweat) which then evaporates removing heat from the body. When there is a lot of moisture (humidity) in the air then the evaporative effect is lessened reducing the human's ability to cool as well as the efficiency of heat transfer from cooling systems to the outside atmosphere. 

The amount of moisture in the air changes based on the temperature. As the temperature of airdrops the capacity of air (measured in grains of moisture per lb of air) is reduced. This every changing capacity results in the term relative humidity, meaning that the amount of moisture in the air is relative to the temperature of the air.


HVAC (Heating, Ventilation, and Air Conditioning) is used to control the indoor environment within a built environment. HVAC uses equipment (like air handlers, boilers, etc.) and processes (like heat transfer, ventilation, dehumidification, etc.) to control the indoor environment.

You can learn more about these processes with our blog articles on:



Indoor Air Quality (IAQ)


Internet Protocol (IP)



Kilowatt (KW)

Kilowatt Hour (KWH)

Kilovolt (KV)

kilovolt-ampere (KVA


Linear Regression

Local Area Network (LAN)


LON which stands for (Logical Operating Network) is a protocol that is used in building automation systems. The primary difference between LON and BACnet is that LON implemented the objects and services within a predevelop Neuron Chip (this holds all of the core protocol firmware and code) whereas BACnet depends on the manufacturers of the BACnet device to write their own "software stack". 

You can learn more about LON by listening to our podcast episode right here


Main Distribution Board (MDB)

Media Access Control (MAC)

Mixed Air Temperature (MAT)


Monitoring-Based Commissioning (MBCx)


National Electric Code (NEC)

National Electrical Manufacturers Association (NEMA)

Network Interface Card (NIC)

Network Time Protocol (NTP)


Operation and Maintenance (O&M)

Outside Air Temperature (OAT)


Parts Per Million (PPM)

Particulate Matter 2.5 Micrometers (PM 2.5)

Particulate Matter 10 Micrometers (PM 10)

Personal Area Network (PAN)

PID Loop

Point to Point Checkout

Point to point checkout is an important part of the building automation installation and checkout process.  Basically, the technician validates that the inputs and outputs are properly installed and working and then calibrates the devices to make sure that the readings the controller has match up with the readings on the technician's meters.

Here is a video walking through the process.

Power over Ethernet (PoE)

Power Over Ethernet is a technology where power is sent to devices over ethernet wire. Direct Current (DC) voltage is sent across two unused wires from the switch port to the NIC on the device. The voltage range is typically 44 to 57 VDC and can support anywhere from 13 to 71 Watts depending on the version of PoE being used.

Power Supply Unit (PSU)

Pressure Independent Control Valves (PICV)


A protocol is a set of rules for communications. But it's also a set of rules for data structure and much more. That's what's confusing about protocols! In the BAS world, we primarily deal with BACnet, LON, and Modbus. However, as our devices become more dependent on IT networks we are finding ourselves having to understand HTTP, SNMP, SMTP, and many other protocols. 

The key to understanding protocols is:

  1. Understand what the protocol should do (and what it shouldn't)
  2. Understand how the protocol should be setup (including software and hardware settings) 
  3. Understand how the protocol structures data for communication

If you understand these three things you will be ahead of the curve when it comes to protocols!


Psychrometrics is the study of gas-vapor mixtures. Put simply Psychrometrics is the study of how air temperature, humidity, and moisture interact. In my opinion understanding, Psychrometrics and how to read a Psychrometric chart is a critical skill that should be required by ANYONE working within the BAS industry. 

In my experience, you can resolve so many design and troubleshooting issues simply by analyzing the current ambient and design conditions on a Psychrometric chart.

Here is a video talking through Psychrometrics





Redundant Array of Inexpensive Disks (RAID)





Return Air Temperature (RAT)

Relief Fan


Roof Top Unit (RTU)




Single Pole Double Throw (SPDT)

Service Set IDentifier (SSID)

Silicon Controlled Rectifier (SCR)


Structured Query Language (SQL)

Static Pressure

Switchgear (SWGR)

System Verification Check (SVC)


Supervisory Control and Data Acquisition (SCADA)

Supply Air Temperature (SAT)

Supply Fan


Transmission Control Protocol (TCP)


Temperature is a measurement typically measured in degrees celsius or farenheit. This reading is commonly used in building automation to define the temperature of air, liquid, and gas. We typically measure temperature with temperature sensors. 

Air temperature is often defined as dry-bulb or wet-bulb temperature and liquid/gas temperature is usually just called temperature.

Test and Balance



Transformer (XFMR)

Triode for Alternating Current (TRIAC)


Underwriter Laboratories (UL)

Universal Input (UI)

A universal input is an input that can be used for multiple different signal types on BAS controllers. Most commonly universal inputs are configured by removing the controller case and changing a dip switch or jumper on the circuit board of the controller (this is much easier than it sounds). This then enables you to use resistive, voltage, or amperage (milliamps folks let's not get crazy!) input signals.

Uninterrupted Power Supply (UPS)


Valve Flow Coefficient (Cv)

Variable Frequency Drive (VFD)

Variable Refrigerant Flow (VRF)

Variable Speed Drive (VSD)

Velocity Pressure

Virtual LAN (VLAN)

VLAN Tagging


Virtual Machine

Virtual Machines are just like regular compute devices (servers, desktops, etc) but they exist as a software image. This means that you can run a full "server" on another server. But why would you do this? 

Virtual machines enable you to use only the portion of resources (CPU, memory, and storage) that your device's operating system requires. This enables you to run multiple "devices" on a single piece of hardware. It also enables you to use the concept of Elasticity. Elasticity is where you are able to increase or decrease the memory, storage, and CPU available to your virtual machines on the fly. This enables you to scale your machine's resources based on how much the machine is being used.

Additionally, virtualization also enables you to take "snapshots" of your machine. This way if the physical device hosting your virtual machine were to fail or your virtual machine got corrupted you could "roll back" to an early "image" of your machine. You can also easily "deploy" your machines to virtual servers because you have precreated images.

Volt Alternating Current (VAC)

Volt Direct Current (VDC)


Wetbulb Temperature

Wide Area Network (WAN)

Wireless Access Point (WAP)


eXtensible Markup Language (XML)




Phil Zito

Written by Phil Zito

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