Active Chilled Beam Cross Section
An active chilled beam is basically a cabinet with a water coil. There are no moving parts such as a fan and motor (i.e. fancoil). To get air in the space to pass through the coil, the induction principle is applied using primary air from a main air handling unit. The room air is “induced” to pass through the coil by creating a low pressure zone above the coil. As air passes through the coil, it can be heated or cooled using hot or chilled water. The induced air and the primary air mixed and delivered to the room via diffusers that are designed into the chilled beam to optimize mixing and take advantage of the coanda effect.
The ratio of induced air to primary air is the Induction Ratio. For example, if 1 cfm of primary air induces 3 cfm or room air to pass through the coil, the induction ratio would be 3 to 1 and 4 cfm would be delivered through the diffuser to the space.
The reason the induction process works can be seen in Bernoulli’s principle.
Said in words, if you increase the kinetic energy (the speed) of a fluid then its pressure must go down. In a chilled beam, the primary air passes through a nozzle bank and its speed increases, thus its pressure goes down and low pressure area is created downstream of the nozzle bank (above the coil).
This principle is how perfume atomizers and carburetors work, why sail boats can sail into the wind and of course, why airplanes fly.
To get room air to pass through a coil, work is being done and energy used. In a fancoil, the energy is electricity that the fan motor consumes to operate the fan. In a chilled beam the energy source is the primary air handling unit. The primary air must be delivered to the chilled beam and overcome the pressure drop of the nozzle bank. The nozzle bank requires more external static pressure at the air handling unit. Typically the fans and motors in air handling units are much more efficiency that mall fans and motors used in terminal products.
One way to look at the energy usage in a chilled beam is to consider the air flow rate (cfm) as equal to electrical current and the pressure drop of the nozzle bank as equal to voltage. Some combination of airflow are and pressure drop (i.e. voltage and current) will provide the necessary energy to draw room air through the coil.
Modern chilled beam design has advanced to the point where the pressure drop across the nozzle bank is less than a 0.25 inches w.c. and typically around 0.5 inches w.c. for the whole chilled beam (which includes the diffuser components.)
Chilled beams not only provide heating, cooling and ventilation air, they are the air distribution component that delivers good thermal comfort. Being able to adjust the airflow pattern from the chilled beams is critical to delivering optimal occupant comfort. As the building use evolves (re-purposing) the space loads and layouts change often requiring air pattern adjustments to maintain thermal comfort.
To achieve air pattern control Swegon chilled beams can adjust the airflow pattern by means of Anti Draught Control (ADC). ADC consists of a number of sections with adjustable fins arranged in the outlet of the unit with a simple grip of the hand, the fins can be set to an appropriate angle in 10 degree increments to direct the discharge air and in this way create the desired air distribution pattern.