Chilled beam

rdf:langString Chilled beam

rdf:langString 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, reducing 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 that is 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.