Case Study

Extraction Fan Control Saves Energy at BRE, Watford

Extraction Fan Control Saves Energy at BRE, Watford


The existing extract fans were working at full speed with airflow controlled by three iris valves that constrict airflow into the extraction units. This is a highly inefficient system, costing money in terms of energy use and maintenance costs.


Optidrive Eco HVAC variable frequency drives were installed on the fans to control their speed depending on the airflow required. The iris valves remain wide open, reducing costs on maintaining these.

BRE Group

BRE previously used three 185kW two-speed AC induction motors controlled by star-delta starters to drive large fans to extract fumes from the burn hall after product testing had been undertaken.

As the extract fans were being run at full speed the airflow was controlled by three iris valves. These valves constrict air flow from the fans as required without reducing the energy required to run the fan motors, a highly inefficient system that wasted significant energy.

BRE approached Invertek sales partner, Motor Control Warehouse, with a view to replacing their star-delta starter system with a variable frequency drive controlled system. Motor Control Warehouse in conjunction with BRE, have designed, built and installed a fully automated VFD control system using three Invertek Optidrive Eco HVAC, 160kW, IP55 drives. The drives are housed in purpose built glass fibre weather resistant enclosures.

The existing two-speed motors have been adapted for inverter control and have been fitted with specially designed output inductors between inverter and motor to reduce the dV/dt (fast rise and fall) of the switching edges seen by the motor. The new system was integrated in to BRE's existing automated extraction control system.

With the systems iris valves fully open the airflow can now be controlled more precisely by the speed of the extract fans. The speed of the fans has been significantly reduced. This greatly reduces energy usage and gives a short payback period for the upgrade.

Kes Beech, Technical Manager at Invertek Drives, said: "Full payback on installation of Optidrive Eco HVAC is usually achieved within 12 months based on current energy costs in this type of application. In addition, Optidrive Eco HVAC allows fans to run for less time and at lower speeds, greatly reducing maintenance costs and acoustic noise generated by the fans."

He added: "Automated control of fan airflow also eliminates the need for valve adjustments, again reducing maintenance costs. This all combines to provide an overwhelming argument in favour of using Optidrive Eco HVAC for energy efficient fan control."