ACBs use water flowing through heat exchangers to cool warm room air (arrows in). Ventilation air (arrows out) supplied at low pressure (circular duct, top) mixes with the now-cooled room air above the heat exchanger and is blown into the room, inducing air circulation.
Chilled beams are ceiling-mounted fixtures that use chilled water flowing through finned heat-exchanger coils to supply cooling, and sometimes heating, in commercial buildings. They are available in a variety of styles, typically in one- or two-foot widths (0.3 or 0.6 m) and in lengths up to ten feet (3 m).
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.