CHILLED BEAMS & FAN COILS
Coming up for air E
xposed ceilings, also referred to as open plenums or open ceilings, leave structural and HVAC systems exposed and visible to the occupants of the space.
Tim Tanner
The result is an industrial, stripped-back eff ect, which can convey a modern aesthetic, whilst also suggesting a commitment to minimisation of building materials for reduced environmental impact. The space can be made to feel more open plan and airy, enhancing the experience of the room occupant. A traditional suspended ceiling often makes a room seem smaller than it actually is, so an exposed ceiling can give the eff ect of extra space even in a crowded room. Depending on the position of the room within the building as a whole, it may be possible to increase the amount of natural lighting in the space by including skylights. An exposed ceiling can also off er the architect or interior designer increased creative opportunities, through the installation of custom lighting and piping fi xtures. Mechanical and electrical installations can become decorative elements, and not only distribution systems. Having exposed ceilings can also provide extra space for hot air to rise, making rooms cooler, reducing cooling requirement, particularly in warm climates. The cool industrial vibe of an exposed ceiling can prove decidedly uncomfortable for room occupants however. The absence of a suspended ceiling surface creates inevitable challenges in relation to air movement and acoustics, which can lead to unwelcome noise levels, uneven temperatures, and draughts.
Tim Tanner, product technical manager – ventilation technology, Trox UK, discusses eff ective approaches to air management for exposed ceilings.
So how do you overcome the air distribution challenges? Firstly, the system design needs to achieve the correct
comfort conditions for room occupants. In spaces with suspended ceilings, Coanda eff ect prevents ‘dumping’ of cold air into the room.
A typical air distribution approach would see the supply
air ‘attach’ to the ceiling due to the low-pressure diff erential between the jet and the ceiling. This keeps the cooler and denser supply air, higher for longer. As it travels the jet of air expands and mixes with the warmer room air, reducing the temperature diff erential and the velocity. When it hits the wall (Figure 1) or a jet travelling from the opposite direction (Figure 2) and descends into the occupied zone it is more comfortable for the room occupant. Standard ceiling diff users are only designed to work with an adjacent ceiling surface. If the ceiling system is removed, for an exposed ceiling, almost all standard diff users will be unable to function correctly. The loss of Coanda eff ect/ceiling attachment will result in near vertical discharge of cooler air into the space, resulting in insuffi cient time for air to mix. Even with a high discharge velocity and pressure,
diff users may still dump without a ceiling to provide Coanda eff ect. If the distance from the air discharge to the occupant is not suffi cient, the air will not mix, resulting in excessive velocity (high air speed), excessive temperature diff erential (large diff erence between room and supply air) and a high risk of draughts. This would make it diffi cult to
Figure 1 22 February 2024 •
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