In early 2010, Fläkt Woods was contracted to upgrade 23 Variable Air Volume (VAV) fans ranging from 30 kW to 60 kW and four 30 kW cooling tower fans at the European Bank for Reconstruction and Development (EBRD), at Exchange Square in London.
This project included monitoring the overall effect of installing variable speed drives fitted to AHU's with axial fans inside them.

By fixing the fan blade pitch of a 30 kW fan unit and varying the fan speed, the energy usage was monitored and calculated to have been reduced by around 68 per cent, conclusively demonstrating the value of the works. The expected projected annual savings on electricity costs are £4,266 per fan with an environmental benefit in terms of CO₂ emission reduction of 30 tonnes per fan.

Fläkt Woods' brief was to upgrade each of the existing variable pitch in motion axial fans, which were originally supplied to the company as part of the first Broadgate build in 1990. The existing fans were not performing to their original specified design points for several reasons including age and higher process cooling.

Fläkt Woods identified an economic upgrade option that eliminated the need to introduce more expensive replacement options, by fixing the pitch of the existing fans, and controlling duty by using frequency inverter drives. In this case the company opted to use the ABB HVAC range of drives as the best match for the fans and the existing control systems.


'EBRD rightly needed a one-stop-shop for the supply of frequency inverter drives, electrical packages and a full team of project managers, fan engineers and electricians, who could work hand in hand with the on site control engineers to ensure that after each weekend working on site, 100 per cent of the plant was operational on the Monday morning,' explains Andrew Knight, service business manager for Fläkt Woods.

The planning and implementation on the project was as important as the end result. The building's tenants had to be able to leave the office on Friday and return on Monday and effectively not realise the extent of work that had taken place each weekend. All comfort cooling was re-instated with no down time for building occupants.

A variable speed drive often uses less energy than an alternative fixed speed mode of operation. Fans are the most common energy saving applications. When a fan is driven by a fixed speed motor, the airflow may sometimes be higher than it needs to be. Airflow can be regulated by using a damper to restrict the flow but it is more efficient to regulate the airflow by regulating the speed of the motor. It follows from the affinity laws that reducing fan speed to 50 per cent results in a power consumption drop to 12.5 per cent.

The project had to include integration with the existing Trend BMS system. Fläkt Woods worked carefully with the on-site Trend engineers to ensure the change-over from variable pitch to 0-10 v automatic control via the BMS system was seamless. Of course, the greater degree of control that can be integrated has a direct effect on the eventual savings.


The project was completed during four months and has already seen big energy savings. Before the works commenced Fläkt Woods commissioned an energy audit, taking a real day-in-the-life-of particular plant.

In order to collect accurate data, an energy profiler was installed to the fans electrical supply, sited inside the LV panel remote from the fan. To minimise disruption and interference with work at the fan location, the unit was left running for 24 hours a day for some seven weeks collecting data.

The profiler was capable of monitoring and recording energy consumption on each of the three phases and included data for kilowatts consumed, phase voltages and current, power factor and kVAr.

The same exercise was repeated after the upgrade works were completed, with the fan operating on the new VSD drives under the same auto control signal, achieving the same internal building conditions. 'This gives our clients real information on their own installed fans. We always prefer to give accurate data under real operating conditions rather than estimated data whenever possible,' adds Knight.

The 30 kW fan, which was previously averaging a 22 kW consumption, was now averaging a 7 kW consumption, a 68 per cent decrease, or 56,370 kW/h per annum based on 252 working days. For the project as a whole, the annual savings are estimated 1.3 million kWh or 690 tonnes of carbon. The reduction in running costs for the plant was of course proportionally significant.

Once the fans were completed engineers undertook a full set-up and setting to work of the new system. This included dynamic balancing where required. 'Projects of this kind offer a positive impact on the energy consumption of the HVAC plant at the same time as reducing our clients operating costs,' concludes Knight.