Type of works: upgrade of VAV fans and cooling tower fans.

Fläkt Woods has recently completed upgrading twenty three Variable Air Volume (VAV) fans ranging from 30 to 60kw and four 30kw cooling tower fans at the European Bank for Reconstruction and Development (EBRD), at Exchange Square in London, once completed the energy usage has been calculated to have been reduced by around 70%.

This project was designed to monitor the overall effect of variable speed drives when fitted to an axial fanned AHU. By fixing the fan blade pitch of the 30kW fan unit and varying the fan speed, the energy usage was monitored and energy usage has been calculated, conclusively demonstrating the value of the works. The expected annual savings on electricity costs are £4,266 with an environmental benefit in terms of CO₂ emission reduction of 30 tonnes.

Fläkt Woods' brief was to upgrade each of the existing variable pitch in motion axial fans. The existing fans were not performing to their original specified design points due to several factors such as age and higher process cooling. Fläkt Woods identified a way get more out of what you have without the need for to introduce more expensive options, by fixing the pitch of the fans, and controlling duty by using frequency Inverter drives. In this case, by opting to use the ABB HVAC range of drives to best match the fans and the existing control systems.

As Andrew Knight, Service Business Manager for Fläkt Woods explains “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 all 100% of the plant was operational Monday.”

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

An adjustable 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% results in a power consumption drop to 12.5%.

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 form variable pitch to 0-10v 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 over four months and has already seen big energy savings. Before the works commence, Fläkt Woods commission an energy audit, taking a real “day in the life of” particular plant. In order to collect accurate data, an energy profiler to the electrical supply fan, 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 three phases and includes data for kilowatts consumed, phase voltages and current, Power factor and kVAr. The same exercise was repeated after the upgrade works were completed by Fläkt Woods' engineering teams 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 whoever possible”.

This 30Kw fan previously averaging a 22kw consumption was now averaging a 7Kw consumption, a 68% decrease, or 56,370Kwh per annum base don 252 working days. For the project as a whole, the annual savings are estimated 1.3Million 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.

Andrew Knight advises “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. Making a difference through our Technical Site Services is what aim to do.”