Chilled beams are now widely used for cooling offices and other commercial spaces and are generally seen as consuming less energy than systems such as fan coil units.

The principle of a chilled beam is that pipes carrying chilled water pass through a ‘beam’ at ceiling level. These then cool the surrounding air, which increases in density and falls downward. In doing so, it displaces warm air upwards.

There are two types of chilled beams, passive and active. Passive chilled beams rely solely on convection currents to distribute cooled air, whereas active chilled beams use ducts to direct air across the beam. Active chilled beams have a higher cooling capacity than passive chilled beams and are generally specified when internal heat loads are too high for the passive variety. Both systems may use pipe fins to increase the surface area for heat exchange.

As well as consuming less energy than a conventional fan coil system, chilled beams generally have a lower operating cost. There are several reasons for this. One is that the temperature of the chilled water is not so cold as that supplied to a fan coil system, so that chillers consume less energy. In addition, fewer circulation fans are required, thus reducing electrical energy consumption further. However, additional ductwork may be required to meet indoor air quality requirements, which to some degree would offset the savings in energy consumption.

There are also limitations on ceiling height, as passive chilled beam systems will not circulate cooled air effectively above a height of 2.7m. As chilled beams require less ceiling space than forced-air systems, they may enable lower ceiling heights in new build projects, which can reduce overall construction costs.

Chilled beams are not a universal panacea and while they have proved very effective in some projects they have been disappointing in others. As such, they should be viewed as one of the options available to the building services engineer, to be considered in the context of each specific project.

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