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Lenze SMV AC vector drives save energy at US mail sorting centre

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article image Air curtains at the US mail sorting centre

Retrofit Lenze SMV AC vector drives are helping to reduce energy wastage at one of United States Postal Service’s largest mail sorting centres in New Jersey.  

The SMV drives are being used to provide cost effective yet precise variable speed control for the fans on air curtains used to keep out the cold at the 24/7 mail sorting centre. With energy usage improving by 60%, savings made over just one cold season are projected to cover the entire cost of retrofitting 50 separate loading bays.  

The United States Postal Service's New Jersey International & Bulk Mail Centre comprises of three main buildings spread over 1.8 million sq.ft. Heating efficiency of the building during the winter months is compromised by the 72 bay doors opening directly onto the outside.  

Each bay employs an air curtain that brings down a blast of high pressure heated air, effectively isolating the interior and exterior air volume while the bay door is open.  

Prior to the SMV AC vector drives being fitted, the air curtains operated at a fixed speed with the fans pushing at 1200rpm. At this speed and temperatures below freezing point, the blast of high velocity air was actually forcing cold air in at ground level, ten feet below the unit. In dry conditions, the high pressure blasts from the air curtains also pushed unwanted dust into the atmosphere.  

The air curtains were turned off as workers felt the unit was blowing cold air instead of warm air. The onsite maintenance team recommended variable speed operation as the best method of solving the problem.  

The local Lenze automation office supplied a simple AC drive that was protected against the elements for retrofitting without the cost of a complete new panel and external enclosure for each motor. The SMV AC drives offered IP65 protection and could be easily fitted and commissioned by the on-site electrical and maintenance teams.  

A test installation of the automation solution was made for a single bay door with the local crew receiving detailed technical support from Lenze to select EMC filters, the frequency ranges to pick to reduce total harmonic distortion, and DC injection braking kits to keep deceleration in-time with the automatic doors closing in addition to advice on the wiring and set-up procedure.  

The test bay was metered over a period of weeks and results showed that the SMV vector drives were very effective in improving surrounding temperature from 18ºC to a toasty 25ºC, especially when outdoor temperature was –5ºC.  

The ampere draw for three drives at 5.5kW each was on an average 4.81amps, the total harmonic varied from 20% to 70% while the power factor improvement was approximately 34%. Based on current US electricity tariff, the utility bills at the sortation centre are expected to reduce by $34,000 in one season when retrofitting work on all 50 remaining bays has been completed.  

Lenze SMV AC vector drives are distributed in Australia by FCR Motion Technology .

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