Chilled beam
A chilled beam is a type of convection HVAC system designed to heat or cool large buildings. Pipes of water are passed through a "beam" (a heat exchanger) either integrated into standard suspended ceiling systems or suspended a short distance from the ceiling of a room. As the beam chills the air around it, the air becomes denser and falls to the floor. It is replaced by warmer air moving up from below, causing a constant flow of convection and cooling the room. Heating works in much the same fashion, similar to a steam radiator. There are two types of chilled beams. Some passive types rely solely on convection, while there is a "radiant"/convective passive type that cools through a combination of radiant exchange (40%) and convection (60%). The passive approach can provide higher thermal comfort levels, while the active type (also called an "induction diffuser") uses the momentum of ventilation air entering at relatively high velocity to induce the circulation of room air through the unit (thus increasing its heating and cooling capacity).
The chilled beam is distinguishable from the chilled ceiling. The chilled ceiling uses water flowing through pipes like a chilled beam does; however, the pipes in a chilled ceiling lie behind metal ceiling plates, and the heated or cooled plates are the cause of convection and not the pipe unit itself. Chilled beams are about 85 percent more effective at convection than chilled ceilings. The chilled ceiling must cover a relatively large ceiling area because it provides heating and cooling mainly by radiant, rather than convective, heat transfer.
Water can carry significantly more energy than air. Although 1 cubic foot (0.028 m3) of air has a capacity to hold heat of 37 joules per kelvin (JK−1), the same volume of water has a heat capacity of 20,050 JK−1. A metal pipe of water just 1 inch (2.5 cm) in diameter can carry as much energy as an 18-by-18-inch (46 by 46 cm) metal duct of air. This means that chilled beam HVAC systems require much less energy to provide the same heating and cooling effect as a traditional air HVAC system.
Chilled beam cooling systems require water to be treated by heating and cooling systems. Generally, water in a passive chilled beam system is cooled to about 16 to 19 °C (61 to 66 °F). In active chilled beam heating systems, water temperature is usually 40 to 50 °C (104 to 122 °F). (Chilled beam heating systems usually cannot rely solely on convection, however, and often require a fan-driven primary air circulation system to force the warmer air to the ground where most people sit and work.) There are effectiveness and cost differences between the two systems. Passive chilled beam systems can supply about 5.6 to 6.5 watts per foot (60 to 70 watts per metre) of cooling capacity. Active chilled beam systems are about twice as effective. In both cases, convection is so efficient that the ratio of incoming air to heated/cooled air can be as high as 6:1. However, studies of the energy cost-savings of active versus passive chilled beam systems remained inconclusive as of 2007, and appear to be highly dependent on the specific building.
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