An active chilled beam is an HVAC terminal unit that cools and ventilates occupied spaces by combining convective and radiant cooling with a primary air supply. Unlike passive chilled beams, active units incorporate nozzles that discharge conditioned primary air (ventilation air) into the beam housing, inducing room air across chilled water coils through the Venturi effect. This induction process significantly increases the unit’s cooling capacity while simultaneously delivering the required outdoor air for ventilation.
Technical Details and Performance Specifications
Active chilled beams operate by receiving conditioned primary air from a central air handling unit, typically paired with a dedicated outdoor air system (DOAS). This primary air is forced through a series of nozzles at moderate pressure, creating a low-pressure zone that draws warm room air upward through the chilled water coil. The cooled mixture of primary and induced secondary air is then discharged into the space, providing both sensible cooling and ventilation in a single device.
Key performance specifications include:
- Primary airflow rates typically ranging from 0.1 to 0.3 CFM per square foot of served floor area
- Chilled water supply temperatures between 54°F and 64°F (12°C to 18°C), often elevated compared to conventional systems to prevent condensation
- Cooling capacities of 200 to 600 BTU/hr per linear foot of beam length
- Induction ratios (secondary air to primary air) between 3:1 and 6:1
- Noise criteria (NC) ratings typically between 30 and 45, making them suitable for noise-sensitive environments
Because chilled water carries significantly more energy per unit volume than air, active chilled beams allow designers to reduce ductwork size and fan energy consumption by 30% to 50% compared to conventional all-air systems.
Common Applications
Active chilled beams are well suited for buildings with high sensible cooling loads and strict indoor air quality requirements. Typical installations include commercial office buildings, educational facilities, hospitals, and laboratories. They perform best in spaces with moderate to high occupancy densities and where ceiling heights allow proper installation, generally requiring a minimum ceiling plenum depth of 12 to 16 inches. Because they do not handle latent loads directly, active chilled beams are almost always paired with a DOAS that dehumidifies the primary air before delivery.
Related Standards and Design Guidance
Design and selection of active chilled beams are guided by several industry standards. ASHRAE Standard 62.1 governs ventilation requirements that determine minimum primary airflow rates. ASHRAE Standard 55 addresses thermal comfort criteria relevant to beam discharge patterns and room air distribution. Additionally, ASHRAE publishes chilled beam design guidance in its HVAC Systems and Equipment Handbook. Manufacturers typically test and rate beam performance in accordance with EUROVENT 6/3 certification procedures or AHRI guidelines.
Practical Significance
Active chilled beams provide a compelling balance of energy efficiency, acoustic performance, and occupant comfort. By shifting cooling duty from air to water, they reduce the size of air handling equipment and distribution ductwork, lowering both capital costs and long-term operating expenses. Their quiet operation and absence of moving parts at the terminal unit level result in minimal maintenance requirements. However, proper condensation management through dew point monitoring and chilled water temperature control is essential to reliable operation, particularly in humid climates.
Related Terms
- Passive Chilled Beam
- Radiant Cooling
- Induction Diffuser
- Dedicated Outdoor Air System (DOAS)
- Sensible Cooling