A chilled beam is a type of radiation/convection HVAC system designed to heat and cool large buildings through the use of water. This method removes most of the zone sensible local heat gains and allows the flow rate of pre-conditioned air from the air handling unit to be reduced, lowering by 60% to 80% the ducted design airflow rate and the equipment capacity requirements. There are two types of chilled beams, a Passive Chilled Beam (PCB) and an Active Chilled Beam (ACB). They both consist of pipes of water (fin-and-tube) that pass through a heat exchanger contained in a case suspended from, or recessed in, the ceiling. As the beam cools 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 passive air movement called convection, to cool the room. The active beam consists of air duct connections, induction nozzles, hydronic heat transfer coils, supply outlets and induced air inlets. It contains an integral air supply that passes through nozzles, and induces air from the room to the cooling coil. For this reason, it has a better cooling capacity than the passive beam. Instead, the passive beam provides space cooling without the use of a fan and it is mainly done by convection. Passive beams can be either exposed or recessed. The passive approach can provide higher thermal comfort levels, while the active approach (also called an "induction diffuser") uses the momentum of ventilation air that enters at relatively high velocity to induce the circulation of room air through the unit (thus increasing its heating and cooling capacity). A chilled beam is similar in appearance to a VRF unit.
The chilled beam is distinguishable from the chilled ceiling. The chilled ceiling uses water flow through pipes like a chilled beam does; however, the pipes in a chilled ceiling lie behind metal ceiling plates, and the heated/cooled plates are the cause of the radiation/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 both because it is less efficient, and because it provides heating mainly by radiant means. Radiant heating capacity is proportional to surface area.
Installation
Active chilled beams are mounted in a suspended ceiling and then anchored to the overhead structure, because T-bar ceilings cannot support the typical operating weight of a chilled beam. The beams are generally wide, and require less than of overhead space. A typical wide chilled beam system generally weighs about per length of the beam while dry. Beams can be installed in a number of forms - fully exposed, recessed, or hidden within a suspended or perforated ceiling. When working within a suspended ceiling grid, the beams need to be installed before the grid - approximately 60 to 75mm above the finished ceiling, then lowered after the ceiling’s installation. The final mounting should allow for of movement in all directions. Chilled beams are generally installed so that the center of each beam is no more than from the center of the next beam. Some architects and end-users dislike the beams because they do not cover the entire ceiling so ducts, wiring, and other infrastructure can be seen. Beams are usually connected to the main supply and return water lines with flexible hoses. To minimize corrosion, oxygen diffusion resistant hoses can be installed. Higher system performance may be obtained by increasing the static pressure of the air in the building. The chilled beams are considered as easy to mount as light fixtures, but require suitable access for service and maintenance. The systems generally need little cleaning (vacuuming of dirt and dust from the fins every five years).
The active chilled beam system employs fins to help heat and cool. Active chilled beam systems are effective to the point where outdoor air can be mixed with the indoor air without any traditional air conditioning (such as heating, cooling, humidifying, or dehumidifying), thus enabling a building to meet its "minimum outdoor air" air quality requirement.