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What does an Air-Cooled system mean and what are some examples?

Any refrigeration-based cooling system that rejects heat to the outdoors via a dry condenser coil and condenser fan. Examples include air-cooled chillers, package units, split systems or VRF system


Air Handling Unit (AHU) components

Supply fan, cooling coil, filters, and possibly return fan, economizer section, heating coil, humidifier and integral sound traps.


Air Separator

A device in a closed loop hydronic system to remove unwanted air


Air Terminal

A grille, register or diffuser.


Blow Through Unit

An AHU or FCU with the supply fan located upstream (BEFORE) the coils.


Chemical Pot Feeder

A small tank, typically 5 gallons, used in closed loop hydronic systems to manually add water treatment chemicals on a periodic basis


What is a Chilled Water system

A cold water system that allows cooling energy to be distributed throughout a building.



A piece of equipment with an internal refrigeration cycle used to make cold water.


What is a Cooling Tower?

A piece of equipment that rejects heat to the outdoors, used in water-cooled systems.


Condenser Water

The water system that allows heat to be rejected from cooling equipment


Condensing Unit

The outdoor unit in a split system, which typically contains a condenser coil, condenser fan, and compressor.



A device for delivery of supply air to a space.


Displacement Ventilation

An air distribution concept where cool air is supplied into the occupied space at low level, thereby displacing warmer room air. Return air is removed from the space at a high level.


Examples of Displacement Ventilation

Underfloor air distribution, with low-level sidewall diffusers, or via integral seat or step diffusers in theaters or similar spaces with fixed seating.


Dual Duct System

An older type of system sometimes found in existing buildings whereby cold and warm air are distributed throughout the building separately in two ducts to each zone. More modern approach is VAV RH Systems


Draw Through Unit

An air handling unit or fan coil unit with the supply fan located downstream (AFTER) the coils.


Economizer (Air Side)

Provide free cooling to a building whenever the outdoor air temperature is cool enough.


Economizer (Waterside)

Provide free cooling in a water-cooled chiller system by using the cooling tower to generate cold water when outdoor conditions are cold enough skipping the chiller.


Expansion Tank

A device in a closed loop hydronic system to allow for the normal expansion and
contraction of water as it changes temperature.


Fan Coil Unit (FCU)

small HVAC unit to supply conditioned air consisting of a fan, coil and filter.
Various types include chilled water, DX, heating water, and four-pipe


Fan Powered Box

A terminal unit with a small integral fan. Used in cold climates to handle spaces with high heating loads. The fan allows plenum return air to be mixed with the primary air. Supply airflow is increased and allows heating load to be satisficed with a supply air temp that isn't too hot.


Fire Smoke Damper (FSD)

A damper that is open during normal operation and closes when needed to stop the spread of fire or smoke.



An HVAC system or unit with chilled water and heating hot water. There is no duct for supply air.