KileyroundKiley Sheehy

When it comes to the construction industry, there is a lot of jargon that gets used on a daily basis. Most project members will likely understand the more common ones, but the definition of “common” may vary from trade to trade. Each group has its own set of common lingo that other teams might not be familiar with, so with that in mind, I’d like to focus on ten control-specific terms you should add to your vocabulary.


Control systems have a wide range of regularly-used terms. Let’s start off with the basics, as defined by ASHRAE:

  • HVAC: The equipment, terminals, and distribution systems that provide, either collectively or individually, the processes of heating, ventilating, or air conditioning to a building or portion of a building.

  • Building Automation System (BAS): An energy management system, usually with additional capabilities, relating to the overall operation of the building in which it is installed; this includes equipment monitoring, protection of equipment against power failure, and building security.

When you boil it down, HVAC is the setup of machines that make a room or space warmer, cooler, or more conditioned in some regard. The BAS is the digital automation that takes operation of an HVAC design out of someone’s physical hands, and moves it onto a computer interface. This makes it a computer-based system:

With the advent of a BAS for HVAC, we can eliminate much of the opening/closing and turning off/on of equipment and devices behind hard-to-reach ceiling tiles, or up in lofty mezzanines. Often times you’ll hear BAS, BMS, DDC, and EMS used interchangeably across control installers and manufacturers. ASHRAE also defines them all near-identically:

  • Building Management System (BMS): An energy management system relating to the overall operation of the building in which it is installed. It often has additional capabilities, such as equipment monitoring, protection of equipment against power failure, and building security. It may also be a direct digital control (DDC) system, where the mode of control uses digital outputs to control processes or elements directly.

  • Direct Digital Control (DDC): A type of control where controlled and monitored analog or binary data (e.g., temperature, contact closures) are converted to digital format for manipulation and calculations by a digital computer or micro-processor, then converted back to analog or binary form to control physical devices.

  • Energy Management System (EMS): A system of computer applications used by building engineering staff to monitor, control, and optimize the building's operating performance (e.g., energy consumption, occupant comfort levels). EMS optimizes building operating performance through supervisory control programs that utilize core BMS functionality.

An EMS is a more refined definition of a BMS, focused exclusively on operating performance with things like IAQ (indoor air quality), occupant productivity and comfort, and energy output as key metrics.


But what do these things control?

A BMS is constructed to automate all of the HVAC equipment in a building - chillers, air handlers, fans, cooling towers, and much more. All things designed to move BTUs in and out of a building space via heating and cooling air and water to deliver a required temperature and humidity.

Anywhere you might hit a stat on the wall and call out a need for heating and cooling would be a HVAC zone:

  • HVAC Zone: A space or group of spaces, within a building with heating, cooling, and ventilating requirements, that are sufficiently similar so that desired conditions (e.g., temperature) can be maintained throughout using a single sensor (e.g., thermostat or temperature sensor).

Common items you might see wired up on a BMS would include:

  • Actuator: A device operated either electrically, pneumatically, or hydraulically, that acts as a motor to change the position of movable devices, such as valves or dampers.

These devices actuate the position of dampers allowing airflow into an air handler, through ductwork, and down to a space. Valves are also actuated to open and close to allow fluid flow through piping in a building. It’s a nightmare manually opening and closing all dampers and valves across a building or campus of buildings, which is one of the great advantages to implementing a BMS.

  • Sensor: A device or instrument designed to detect and measure a variable.

Whenever a measurement is taken in a building (such as temperature, humidity, CO detection), a sensor is the measuring tool. It’s also the tool that reports back to the BAS.

  • Variable-frequency drive (VFD): An electronic device that varies its output frequency to vary the rotating speed of a motor, given a fixed input frequency. Used with fans or pumps to vary the flow in the system as a function of a maintained pressure.

A VFD serves to automatically optimize speeds for anything that spins in a circle. Fans, motors, and pumps are the three main users of a VFD, and they’re huge in power consumption. The more we can automate the work of these items, the more savings a building owner will see.


So there you have it! These are ten commonly-used control terms you can now comfortably use on the job. Hopefully these definitions will help you better understand some of the lingo being used on your next project. After all, you can’t collaborate with others if you don’t understand what they’re talking about!

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