Active Chilled Beams: Saving Energy and Space

Passive chilled beams operate through simple convection: as warm room air rises, it passes through the water-cooled heat exchanger fins inside the chilled beam, where it cools and settles back into the room. This pattern of rising and settling air circulates the cooling energy. Passive beams can provide an energy-efficient HVAC solution, especially in retrofits or modular office layouts where duct space is a problem, but they require the use of added ventilation—usually underfloor—to provide fresh air and humidity control, and they do not provide heating.

Active chilled beams (ACBs) account for most chilled beam sales and are the focus of this article. They use the same heat-exchanger technology as passive beams but can supply both cooling and heating, as well as ventilation air. ACBs contain an added compartment (plenum) that is connected to the ventilation air supply (see diagram). This primary ventilation air (dehumidified and filtered outdoor air) enters the beam’s plenum under pressure where it is forced through nozzles that direct the flow of the air along the outside of a second chamber and into the room. This action pulls secondary air (room air) into the unit from underneath via induction past the heat exchanger coils. The now-cooled/heated secondary air mixes with the primary air in this second chamber and is blown back into the room. Unlike passive beams, active beams do not rely solely on convection for air circulation, so they can force warm air down into the room, supplying heating as well as cooling. (Multi-service beams are custom ACBs that include lighting, sprinklers, security, sensors, or other features). There are no electrical connections or moving parts in the beams, minimizing maintenance and creating a quiet HVAC system.