How Are Chilled Beam HVAC Systems Properly Designed?

The beam type decision follows the load and the airside architecture. Active beams need a primary air connection from the DOAS, so they fit naturally where ventilation ductwork is already routed — each beam becomes a diffuser, a cooling coil, and sometimes a heating coil in one ceiling unit. Their induction ratios multiply the primary airflow's cooling effect, letting a small ventilation air quantity drive a large sensible capacity. I lay them out on the reflected ceiling plan with the architect early, because beam placement, lighting, and sprinkler coordination is a three-way negotiation. Passive beams suit spaces where the loads are light and even and the owner wants the simplest possible system — no ductwork to the beams at all, just piping. Their capacity per linear foot is lower, so they need more beam length for the same load, and they depend entirely on the room's air movement to work. I verify passive beam layouts against the actual load profile including solar gains through glazing, since a passive beam can't respond to a sudden afternoon sun patch the way an active beam with more induction can.

Condensation control is designed in layers, and I treat it as life safety for the finishes below. The first layer is the DOAS, sized and controlled to hold space dew point well below the beam water temperature under design conditions — this is the layer that does the everyday work. The second layer is the control sequence: space dew-point sensors in beam zones feed the BAS, which raises beam supply temperature, increases DOAS latent capacity, or stages zones off the beams in a rising-humidity event, in that order, with alarming at each threshold. The third layer is failure-mode design. Valves fail to the warm position, the BAS alarms on any dew-point sensor fault rather than assuming dry air, and the sequence sheds beam cooling before it ever allows water temperature below the measured dew point plus a safety margin. During commissioning I test the high-humidity response by driving the sensors and watching the system protect itself — the owner should see the protection work before trusting it. A chilled beam system without demonstrated condensation protection is a liability with nice acoustics.

The fit checklist is really a latent-load checklist. Ideal applications have stable, controlled humidity and moderate sensible loads: private and open offices, classrooms, libraries, patient rooms, and any space where quiet operation matters and the envelope is tight. These buildings get the full benefit — small airside infrastructure, low fan energy, excellent comfort, and in many cases smaller mechanical rooms and shafts than an all-air alternative. I steer owners away from beams where moisture can't be controlled: natatoriums, commercial kitchens, lobbies with heavy door traffic in humid climates, and any space with large uncontrolled infiltration. Retrofit fit depends on ceiling height and structure — beams need clear ceiling space and the piping distribution to reach them. The decision belongs in schematic design, alongside the DOAS decision, because the two systems are one design. • Pair every chilled beam project with a DOAS that owns ventilation and humidity • Keep beam water at 57 to 60°F — above space dew point — with dew-point-based controls • Layer condensation protection: DOAS dehumidification, control response, and fail-safe valve positions • Use active beams for higher or variable loads, passive beams for light even loads • Confirm fit against the latent load — skip beams where moisture can't be controlled