VAV Controls

Variable Air Volume System

Energy conservation is becoming an evermore important feature of any new laboratory environment and we can offer a number of cost effective solutions.

Typically fume cupboard installations operate on a constant air volume basis where there is either a small quantity of fume cupboards or where the fume cupboards operate periodically.

Where there are large quantities of fume cupboards or they run constantly, a variable air volume system should be strongly considered.

The basic principle of a VAV system is to reduce the amount of heated air being extracted through the open sash of a fume cupboard. The sash position is linked to a motorised damper on top of the fume cupboard.

When the sash is open at the standard 500mm safe working height, the fume cupboard VAV damper will be in an open position to achieve the required flow rate through the fume cupboard. The VAV controller measures the airflow rate through the open sash and as the sash is lowered, the motorised VAV damper takes a signal from the VAV controller and the damper blade closes to maintain a constant face velocity across the face of the sash, thus reducing the volume of heated air being extracted.

The extract fan however will be running at a constant speed with a constant discharge velocity at the discharge point to comply with the requirements of EN14175. To maintain a constant efflux velocity on the discharge stack, a fresh air bleed damper will modulate to allow outside unheated air to flow through the fan and discharge stack.

As the amount of extracted air from the laboratory will be variable the supply air to the room will also need to be variable to ensure a constant slightly negative pressure to the laboratory. Room pressure controllers can be provided to mean the difference in pressure between the laboratory and corridor and will supply signals to either supply air motorised dampers or AHU inverters to vary the airflows accordingly.

To obtain the maximum energy saving from the VAV system the users must close the fume cupboard sashes when operator access is not required.