7.2.2 Active Chilled Beams

An active chilled beam is a device that is located in or above the conditioned space to provide heating, cooling and ventilation. The system consists of a coil box that is recessed in or hung from the ceiling with chilled water flowing through the coil. Ventilation air is introduced by a remote air handler into the diffuser box through small air jets, which induces room air to flow through the coils. Because the active introduction of ventilation air magnifies the natural induction effect, active chilled beams are commonly referred to as induction diffusers.

Depending upon the modeling software, active chilled beams may be modeled directly in the software or by using the more commonly available induction unit selection. Since each zone in a building will typically have its own chilled beam system (multiple units) with thermostatic control, a decision will need to be made as to how to properly zone the building to account for the individual chilled beam units. In most cases, conventional zoning of the building will be sufficient, such that thermally similar zones would be combined together. In combining zones, however, the source of ventilation air will need to be taken into account. Thus, two thermally similar chilled beam zones that are supplied by different ventilation air handlers would need to be separated out for modeling purposes.
 
Once the thermal zoning has been determined, each zone will then be modeled with a chilled beam induction system; inputs would include the system cooling capacity and the induction ratio. In addition, the source of heat, whether electric or hot water, would need to be specified. Since one or more dedicated ventilation fan systems will provide the outside air to the chilled beams, this would be modeled in the same fashion as the dedicated outside air system described below, with each chilled beam system coupled to this dedicated outdoor air system.