University of Greenwich cuts AHU bill by £10 000

ABB, variable speed drive, AHU
ABB drives are substantially reducing the energy consumption of air-handling units at Greenwich University.

The University of Greenwich is set to save £10 000 a year on its air-handling costs across its three campuses following the installation of ABB variable-speed drives for a number of buildings. Additional savings from future projects could cut running costs by another £4000 a year. David Blackburn, building-services engineers in the university’s building-services department, said. ‘We were looking for payback times on the projects of about five years, yet most were much quicker than that.’

The university has a 5-year target to reduce its carbon emissions. David Blackman explains, ‘We worked on the premise that most of the air-conditioning plant is over-rated and that were could reduce the speed of the fans without affecting the airflow adversely.

ABB drives-alliance member Mid Kent Electrical (MKE) was called in to investigate the potential for using variable-speed drives on AHUs in buildings on the Medway, Greenwich and Avery Hill campuses.

A survey on the Medway site found that many fans had rated speeds and powers less than that of the motors. Fans were either being run too fast or their speed reduced using pulleys. When the original system was set up, airflow was adjusted by setting dampers on vents at room level.

Monitoring of one fan motor on the Medway campus on direct-online operation for two days showed the 4 kW motor consuming 3.353 kW for an annual running cost of £871. Running the motor for two days with an ABB drive consumed an average of 2.087 kW for an annual cost of £542.

Based on these results, it was estimated that installing variable-speed drives on motors with a total installed power of 127 kW would save £10 472 a year in running costs and reduce CO2 emissions by over 57 t a year.

Further investigation on the Greenwich campus revealed the potential for saving £2040 a year and reducing CO2 emissions by 5 t.

Avery Hill campus could save £2157 a year, with a cut in CO2 emissions of 19 t a year.

For more information on this story, click here: December 2012, 120
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