January 30 2009

What is a Chilled Beam?

Above is a striking combination light active chilled beam by TROX

A Chilled Beam is a building conditioning system that uses convection and water to efficiently move energy throughout a building. Chilled beams come in both active and passive varieties but are in no way a part of the building?s structural system as the name might imply. The units are linear in form however, which might create the appearance of a ?beam? to untrained eyes. Chilled beams are known for energy efficient, comfortable, quiet operation in a robust system with few moving parts and low maintenance requirements.

Chilled beams function similarly, and are often associated with, radiant ceilings and floors. A fundamental functional difference, however, is that chilled beams use convection, in lieu of radiance, to transfer energy from the water loop (most commonly) to the space. Interestingly, radiant systems rely less on conditioning the air within the space and instead concentrate on delivering heat or coolth directly to the objects that need to be tempered. Many, including myself, consider radiant heat to be the most comfortable way to condition a space because the body, or objects within the room, receive the heat directly rather than being dowsed by conditioned air. Both strategies benefit from the higher density (higher than air), increased energy carrying capacity, of water and are therefore more energy efficient efficient than forced air systems which have to spend energy heating, moving and dehumidifying large volumes of low density air.

Passive Chilled Beams use no fans, have no moving parts and as a result make almost no sound. Passive systems use properties of buoyancy, air temperature and density to move air across a foil connected to the conditioned water. The system does not provide ventilation air and so requires a separate ventilation system. However, because the ventilation air is not conditioning the space, the system can deliver much lower volumes of air, reducing duct and fan sizes.


Placement of a passive chilled beams must be considered carefully because of their use of natural currents of hot and cool air. For instance, placing a passive chilled beam above a heat source, like a copy machine, may interrupt the flow of cool air down from the beam unit as it meets warm air rising from the copier. Passive chilled beams do not cause drafts and so are much more comfortable stand under, it is however recommended that passive units not be placed directly above a workstation as the occupant below will feel a constant stream of cool air flowing down.

Passive chilled beams do have limitations. The systems are not good at heating a space. Thermodynamics prevent the hot air from reaching the bottom of the room and leave the space stratified into hot and cold zones.

If heating is needed, the solution is to install an Active Chilled Beam system. Does that name make sense? Of course not. An Active Chilled Beam system can both heat and cool air by using high velocity ventilation air to disperse the conditioned air throughout the room, thereby forcing hot air to reach the bottom of the room. In the case of the Active Chilled Beam, active means that the water and fin unit from the passive system is connected directly to a ventilation supply air system. The ventilation air is blown through high velocity nozzles and forces convection of air over the water foil unit.

Active Chilled Beams, like Passive Chilled Beams, are are quiet, efficient and have low maintenance requirements because they have no moving parts within the individual units. The only maintenance is an occasional dusting of the radiant foils. The system does force air into the space which creates a minor draft, but this is insignificant compared to the amount of air being circulated in a traditional forced air system. All chilled beam technologies use the same hydronic water loop system to transfer energy, the only difference is that in the Active Chilled Beam, the water loop can be both heated and cooled.

The hydronic water system can be conditioned by any number of heat exchange devices including boilers, cooling towers, condenser units, geoexchange units, and any other system that can decrease entropy. The only constraints are that Passive Chilled Beams require the water temperature to be at least 2°F above the room?s dew point (typically 57-60°F) whereas an Active Chilled Beam allows for water up to 1.5°F below the room?s dew point.

Superficially, chilled beams units represent somewhat higher upfront costs when compared to a traditional forced air system, but several case studies point out, however, that overall costs are lower once reductions in fan, duct and heat exchanger or boiler elements are considered. Reduced upfront cost coupled with lower operating costs make the technology very attractive to building developers and owners alike. Higher efficiency and increased occupant comfort make them a sustainable choice.

a ceiling integrated Active Chilled Beam by TROX

I will be doing more research into Chilled Beams and hopefully electing to use some in our projects in the near future. I am encouraged to see such innovations in the air conditioning industry, especially a product that has benefits for the environment, the economy, and society; the true measure of sustainability.

For more information please visit Wikipedia or a great article in Architectural Record titled ?An Energy-Conserving Technology From Europe Makes Inroads in the U.S.?

For more information on building systems please visit other greenlineblog posts on Absorption Chillers, ETFE and Enthalpy Wheels.

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March 17th, 2009 at 3:57 PM

Michael Paige

Where does the condensation go? Unless this is a desert system only, when warm air meets the cool "beam", condensation usually results. As proposed, you would have a more or less constant rain on the space below, if you could not keep the dew point above the "beam" temperature.

June 19th, 2009 at 2:03 AM

Gabe Guzman

Having the chilled water temp. at two degrees above room dew point would avoid condensation, however, in very humid climates like the tropics, with normal infiltration and the fresh air needed by codes, the dew point temp. would be to high, consequently room temp. would also be above comfort temp. Relative humidity would probably be also way over 50%. Your comments please.

July 22nd, 2010 at 8:11 PM


These units have been installed in a number of subtropical and some tropical locations. To prevent condensation the supply air needs to be dry enough and in sufficient quantities to handle the expected latent load conditions. This is where DOAS with heat recovery is important, drive the dew point of the supply air much lower than with standard overhead systems (often around 48 deg F) and allow the heat recovery to raise the dry bulb of the supply air temperature. Because of the operation of the unit, a higher than normal supply air temperature is not a deal breaker (often temperatures are 55-65 deg F) because the sensible heat is removed primarily with the water side (secondary air) while the primary air provides ventilation and latent heat removal. It's also important to understand the efficiency of the unit. Under normal operating conditions it's possible to move 50-100 Btuh/cfm with a beam, while with a standard all air system a normal cooling capacity is about 21 Btuh/cfm (based on 55 deg SAT and 75 deg room temp). These types of conditions coupled with DOAS mean you can often supply 100% outside air instead of the standard 80% recirculated/ 20% fresh air that a standard overhead system is designed for.