When designing the chilled beam systems, it all starts with the loads. Despite the name, active chilled beams can heat as well as cool (2 pipe or 4 pipe). The beams are sized to meet the zone sensible cooling and heating loads, while the other loads are managed by the primary air system.
Chilled beams come in two flavours: passive and active. Passive beams have only chilled water connections, are not connected to primary air, and can only cool air. Active beams are effectively “turbocharged” by primary air. The primary air passes through nozzles that induce room air to move through the water coil to be heated or cooled as required. Almost all projects use active beams because of their higher performance.
Active chilled beams require primary air from a dedicated outdoor air unit (DOAS) to operate. Sizing this unit takes a little work but is well covered in the ASHRAE design
guide. The actual airflow must be the greater of:
- ventilation rate
- zone latent load
- zone sensible load
- ventilation load
The ventilation rate maintains acceptable indoor air quality and is based on ASHRAE Standard 62. An office ventilation rate is around 0.11 to 0.15 cfm/ft² while a classroom’s will be closer to 0.45 cfm/ft².
Excerpt from the article “Chilled Beam Systems” by Hugh Crowther published in the Canadian Consulting Engineer Magazine, December 2015. Read the article here (link here).