Chilled Beam: Cooling With Water Instead of Air

A chilled beam is a ceiling unit that cools a room by passing chilled water through a coil, with no fan of its own. Passive beams cool by natural convection; active beams use the building's fresh air supply to draw room air across the coil. Because the coil runs above the room's dew point, the beam handles sensible heat only, so humidity must be controlled separately.

By Dhruv Agarwal · · 2 min read

Why it matters on a project

Chilled beams are quiet, efficient and low-maintenance, which makes them attractive in premium offices. They are also unforgiving: a system that is well suited to a dry climate can drip on desks in a humid one if the moisture side of the design is treated as an afterthought.

Active versus passive

Passive beamActive beam
Air connectionNonePrimary fresh air through nozzles
How room air movesNatural convectionInduced by the primary air jets
Cooling capacityLowerHigher per metre
Provides ventilationNo, needs a separate systemYes
Testing and ratingEN 14518EN 15116

The one rule: stay above the dew point

The coil must run warmer than the dew point of the room air. That means:

  • Fresh air dehumidified centrally, usually by a dedicated outdoor air unit, so it carries the room's moisture load.
  • Chilled water supplied warmer than for fan coil units, with controls that track room dew point.
  • Condensation sensors on the pipework or beam, interlocked to close valves or raise water temperature.
  • An airtight building, because humid outside air leaking in brings moisture the beams cannot remove.

Ventilation rates are set under ASHRAE 62.1, within the air conditioning provisions of NBC 2016, Part 8.

Common mistakes

  • Treating beams as a straight swap for fan coils without redesigning the fresh air plant.
  • Leaving windows or doors open in a beam-cooled space during the humid season.
  • No dew point controls, or sensors installed but not commissioned.
  • Too little ceiling void for beams, water pipework and the primary air ductwork together.
  • Layouts that change often, where every move involves water connections.

Standards referenced

Active beams are tested and rated under EN 15116, passive beams under EN 14518; ventilation under ASHRAE 62.1; air conditioning provisions in NBC 2016, Part 8. Whether chilled beams suit a specific building, and their water temperatures and controls, must be established by the project's HVAC consultant.

Standards referenced

  • EN 15116 — Ventilation in buildings — chilled beams — testing and rating of active chilled beams (CEN-CENELEC)
  • EN 14518 — Ventilation for buildings — chilled beams — testing and rating of passive chilled beams (CEN-CENELEC)
  • ASHRAE 62.1 — Ventilation for acceptable indoor air quality (ASHRAE)
  • NBC 2016, Part 8 — Building services — air conditioning (Bureau of Indian Standards)

Frequently asked

A passive beam has only a coil: warm room air rises, is cooled by the coil and falls back into the room by natural convection. An active beam is connected to the fresh air ductwork; the primary air leaves through nozzles and induces room air across the coil, which gives more cooling per metre and delivers ventilation at the same time.

Because the beam has no drain tray in normal designs. If the chilled water is colder than the dew point of the room air, moisture condenses on the coil and drips into the space. The chilled water temperature is therefore kept above the room dew point, and room humidity has to be held down by dehumidifying the fresh air before it reaches the beams.

They can, but only with a dedicated outdoor air system that removes moisture from the fresh air, an airtight envelope, and controls that monitor dew point and raise the water temperature or shut valves if condensation risk rises. Without that humidity control, the risk of condensation is the deciding problem. The suitability for a specific building is a decision for the project's HVAC consultant.

In spaces with moderate, stable heat loads and controlled occupancy, a sealed facade and enough ceiling void for the beams and pipework. They suit less well in spaces with high latent loads, frequent door openings to humid outside air, or layouts that change often, because moving a beam means moving water pipework, not flexible duct.

No fans in the room, so low noise; water moves heat with far less transport energy than air; and there is little maintenance in the space itself, since there are no filters or fan motors at the beam. The trade-off is a dependence on careful humidity control and less flexibility for future layout changes.

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