Where the ceiling height is insufficient for the installation of a TTC and duct system, an under-ceiling VTD can be installed instead. VTD has the same functionality as TTC, and also has a unique active slot that allows extremely high pressure without generating noise.

Built-in sensors

VTD has built-in sensors for pressure, flow, duct temperature, room temperature and occupancy.

Inferior mixing and greater risk of draughts with rear diffusers

Air supplied from the rear has disadvantages too; mixing is inferior and the risk of draughts becomes greater. See our CFD report.

Adjustable grille

The adjustable grille can be used in order to direct the air towards any surface.

Cellular office with supply air via the VTD active wall diffuser that uses a built-in regulator and sensor to regulate temperature and air quantity in the room, by increasing or decreasing the slot size between the blades in the diffuser section. Pressure and flow sensors and encoders on the motor ensure extremely accurate flow regulation and make possible pressure optimization of the aggregate. The flow is set at three different levels: absence, occupancy and maximum flow. The built-in occupancy detector also controls economy and comfort modes after an adjustable time delay.

Extract air

Extract air via transmitted air to corridors with flow balance regulation through the flow that is communicated by digital bus. Adjustable offsets compensate for fast flows such as WC groups etc.


Via the CBX connection box, the supply air diffuser regulates the A4004 valve actuator on the radiator. Adjustable cold draught protection. The flow temperature and circulation pump on/off for heating can be optimized.

Extra heating/cooling steps

Further heating or cooling steps can be connected in the CBX box for extreme operating modes.

Extra sensors

CO2 or air quality sensors can be connected in the CBX box. This input can also be used for other sensors if required. The sensor signal is used to regulate an adjustable P band.


The CBR lighting control box is used to connect push buttons and 230 VAC to the lighting system. The lighting is turned on and off either via a signal from the occupancy sensor placed in the supply air diffuser or from connected push buttons. The time to automatic switch-on (one operating mode) can be set, as can the time to switch-off after the last recorded movement. The number of on and off operations and the number of hours with lighting illuminated are registered for measurement of the number of burning hours for the armature and thereby the optimal time for replacing fluorescent tubes.

The cable used throughout is a PVC-free shielded combined supply and communication cable. It is pre-terminated in the diffuser's diffuser section with ready-made contacts in the other end for rapid installation. For other products, it is connected in the same way throughout.

Cable lengths

The bus cable can be pulled for long distances in respect of communication, but the voltage drop must be taken into account for power supply. See electricity design guide. The limiting factor for cable length is that each CMA ("communication hub") can only have 100 nodes/products installed on it.

Power supply and transformers

In a normal situation, one transformer is installed per 12-15 diffusers/products but this is a rule of thumb that applies with short distances between products. See electricity design guide.

In some cases, you may wish to place a larger transformer in cable recesses instead of many smaller ones deployed throughout the installation. This can be done, but you must take note of the voltage drop in cables, and you will need separate thick 24 VAC cables on cable ladders.

Air supplied from the rear is not straightforward, and it becomes more difficult when you want to demand control the air flow with cold air. In the winter, mixing is poor and in the summer you risk draughts.

As the report shows, the convection resulting from the heat load creates a stream towards the diffuser that means that cold air is pressed down towards the floor during low flows (winter).

To resolve this situation, it is recommended to direct the grille towards a wall without a desk in order to create a rotation of air in the room. This procedure works well in rooms like cellular offices (such as hotels/hospital rooms), but not at all in open plan offices or conference rooms. In these cases we instead advise you to use the PBF flat duct (see Cellular office/Low ceiling height: Ceiling diffuser).