University demonstrates massive energy savings still available by installing VSDs



University demonstrates massive energy savings still available by installing VSDs.


Despite being promoted for energy saving for over thirty years, huge opportunities still exist for retrofitting inverter drives in building services. In a recent example, installing ABB drives at the university of Leeds reduced carbon emissions by over 809 tonnes p.a. and saved £194,000 a year in energy costs. Payback of 1.2 years has been achieved on a capital outlay of £228,859.


Fan and pump duty

The project formed part of the university’s Carbon Management Plan, in which it identifies ways to save energy and cut its carbon emissions. This included installing 94 ABB variable speed drives (VSDs) ranging from 5.5 to 55 kW VSDs on existing motors powering fans in air handling units and fume extraction equipment and water pumps. Most of the assessed motors had no speed control, being connected direct-on-line.


Payback period less than 15 months

The Carbon Management Plan originally estimated the VSDs to deliver annual savings of £45,655 in energy and 364 tonnes of carbon at a capital cost of £251,600. Based on these figures, the university estimated a payback period of just under six years. However, the ABB drives substantially improved on the university’s estimates, producing savings of 1,800MWh a year in energy consumption, providing a payback of less than 15 months.


Robert Douglass, energy project officer for the university, says: “Initially we used ABB’s online DriveSize tool to identify which motors would be best for use with VSDs. This showed that any motor of 10 kW or above would produce the greatest savings.”


The drives are concentrated in 20 buildings across the campus used for teaching and research, are controlled by a building management system (BMS) using a 4-20 mA connection to provide speed references to the drive and monitor alarms. The BMS also maintains an operating schedule and signals when the drives should be switched on and off. ABB drives can monitor their own energy use and run hours, and this has been used to identify the kWh used at various times, thereby proving the savings.


Harmonic mitigation

Harmonic mitigation was another important factor for the university. The ACH550 has harmonic mitigation built-in as standard. Swinging choke technology ensures the drive delivers up to 25 percent fewer harmonics at partial loads compared to a conventional choke of equal size.


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