Hydronic terminals: fan-coil units, chilled beams, and radiant systems compared

One-line orientation

Hydronic terminals deliver heating and cooling locally via water-carrying pipes rather than large duct runs — the exam tests which terminal type suits a given constraint (noise, humidity, floor-to-floor height, or dew-point risk).

Key points

• Fan-Coil Unit (FCU): a water coil plus a fan; circulates room air over the coil for local heating or cooling. No central ductwork needed. Common in hotels, apartments, and office perimeter zones.
  • Fan-coil systems generally use a separate source of ventilation air. Some systems bring outdoor air locally. A fan-coil can remove some moisture when its coil is below the dew point, but it does not closely control humidity.
  • Noise: the local fan is audible, so an FCU is generally noisier than a fanless chilled beam or radiant system.
• Active Chilled Beam (ACB): a ceiling-mounted unit fed by (a) chilled water and (b) a primary air supply. Primary air is induced through nozzles, drawing room air across the coil — achieves both ventilation and sensible cooling in one device.
  • High cooling efficiency; lower noise than FCU; integrates into shallow ceiling plenum.
  • Limitation: not suited to high-latent / high-humidity spaces because the beam handles sensible cooling only; dehumidification must come from the primary air side.
• Radiant Cooling (and Heating): chilled (or warm) water circulates through tubes embedded in the floor, ceiling, or panels. Heat exchange is by radiation and natural convection — no fans, completely silent.
  • Critical constraint: surface temperature must remain above the room dew point at all times; if the surface is colder than the dew-point temperature, condensation forms on the floor or ceiling.
  • Best in low-latent environments (dry climates or spaces with tight humidity control).
• Closed-Loop Heat Pump (water-source): a loop of condenser water circulates at a moderate temperature; individual heat pumps in each zone either reject heat to or extract heat from the loop. Allows simultaneous heating in one zone and cooling in another.

Confusions / comparison

Terminal	Medium	Fan?	Ventilation	Humidity control	Noise	Key constraint
Fan-coil unit (FCU)	water	yes	separate or local outdoor-air source	limited; coil can dehumidify	moderate	fan noise; ventilation source required
Active chilled beam	water + primary air	no (induced)	built-in via primary air	limited (sensible beam)	low	no high-latent-load spaces
Radiant cooling	water	no	separate system needed	none	silent	surface ≥ dew point
Closed-loop heat pump	water loop	yes	needs DOAS	moderate	moderate	loop temp management

Related

→ HVAC distribution systems (all-water family) · HVAC system selection (noise / space criteria) · Plumbing: hydronic piping configurations (1-pipe / 2-pipe / 4-pipe).