Systems with chilled beams are suitable for use to meet high cooling demands and/or where there is a requirement for individual control of the temperature. At normal room heights in offices, for example, the max cooling effect is 80 - 90 W/m2 of floor area. The limit is set by the max permissible velocity in the occupied zone, and high room heights thus provide the opportunity to supply a greater cooling effect.
As in the case of all cooling demand calculation, it is necessary to take account of the building’s dynamic and accumulation capacity. Simply adding the ”gross effects” together gives a cooling demand which can be approximately 50 % too large.
The supply air flow is responsible for the air quality in the room and in addition provides basic cooling. The maximum recommended under temperature of the supply air is 10° C. In certain cases, the supply air temperature can be compensated for, i.e. increased by a few degrees, with a falling outdoor temperature. The chilled beam covers the rest of the cooling demand. The water flow is varied depending on the demand with the help of a room sensor.
Compared with a system in which the cooling is brought to the rooms entirely with the air, a chilled beam system reduces the space required for air treatment units and ducts.
Supply air/Room air
Supply air beams
Supply air beams with their long slot air diffuser offer the possibility of a maximum supplied cooling effect without the velocity in the occupied zone being uncomfortable. The reason is that the supply air from the beam achieves very good mixing with the room air because the contact surface with ambient air is extremely large. In the maximum case, the outflowing air covers a large part of the ceiling surface.
One-way beams are positioned on a wall, whereas two-way beams are positioned inside the room.
The supply air beam for installation in a false ceiling utilizes the Coanda effect (adhesion effect) in order to cause the air to adhere to the ceiling for a certain distance before it curves downwards.
The covered supply air beam for freely suspended installation also utilizes the Coanda effect to a great extent. As a rule of thumb, in the case of a horizontal outflow, and with a maximum distance of 300 mm between the under edge of the beam and the ceiling, the air jet will be drawn up towards the ceiling and will adhere to the surface.
The possibility for adhesion is strengthened by an upward-angled outflow. The Fläkt Woods WinDon product selection program gives the actual flow pattern with different distances between the beam and the ceiling.
A one-way blowing supply air beam is suitable for certain types of premises, such as hotel rooms. This is preferably installed in the angle of the ceiling with a wet room/corridor and blows the air towards the façade. This provides a simple and adaptable opportunity for connecting water and supply air
Adjustment of flow pattern in the room
Fläkt Woods IQ beams have separately adjustable hole lengths on both sides. This means that the left/right air flows can be adjusted with optional proportions. When beams are positioned close to a wall, for example, the flow towards the wall can be selected at 30 % and in the other direction at 70 %.
Partition walls are often repositioned when rebuilding an installation, and with the help of the adjustable hole lengths, the air flow from each beam can be easily redistributed so that draught problems are avoided. The flow can also be increased or reduced as required. The question of moving the beams seldom arises, therefore.
The adjustability of the hole lengths means that the beam has an integrated damper function. Moderate changes in the pressure/flow can be made without affecting the cooling effect to any great degree. Even though chilled beams have a short throw, a room with a large cooling demand and high air flows can present the risk of draught problems. In order to avoid this, a number of Fläkt Woods IQ beams have a so-called FPC (Flow Pattern Control) function. This consists of built-in fins in the outlet slots. In lengths of 300 mm, the fins can change the direction of the outgoing air in stages up to 45° by a simple operation.
The consequence of an angled outflow from the beam is that the throw is shortened, measured perpendicularly from the beam.
Shortening the throw by 20 % can be used as a rule of thumb. A beam with FPC can thus be positioned both closer to a wall and closer to other beams compared with a beam without FPC.
Increasing the supply air flow
To increase the maximum air flow of the IQ beams, they can be provided with double rows of holes on both sides. Compared with IQ beams with single rows of holes, the double holes give an increased air flow and cooling effect for a given pressure drop. The Fläkt Woods WinDon product selection program provides the possibility of dimensioning with double rows of holes.
Passive beams give an essentially downward air flow in the room. At a low room height, it is not acceptable, therefore, simply to position the beam above a work- station with sedentary work, for example, in order to avoid draughts.
In rooms with passive beams, the air is supplied with separate supply air terminal devices. Both remixing and displacement terminal devices provide good comfort in the room in combination with passive beams.
With displacement air handling, the temperature difference between the floor and ceiling will be reduced, although the displacement function will be retained. In rooms without a false ceiling, it is important for the air flows from remixing supply air terminal devices not to disturb the influx of air to the beam, which reduces the beam’s cooling effect.
For passive beams built into a false ceiling, Fläkt Woods recommends a free area in the false ceiling of min. 0.1 m2 per linear metre of the beam and a free distance of 100 mm between the ceiling and the top edge of the beam for wide beams, see Figure 4.1, and 75 mm for narrow beams, see Figure 4.2.
Fig 4.1 Wide passive beam in a false ceiling
Fig 4.2 Narrow passive beam in a false ceiling