Noise reduced – and costs slashed!

Staff working for a manufacturer of heavy-duty machinery complained to their managers about the noise from a bank of large air handling unit fans.

Bennett Electrical were called in to investigate whether changing the motors would help reduce noise.

How we did it

A sample motor was changed but this did not fully address the noise issue. We investigated further, and after considering various solutions recommended 2 x 22kW for the air intake, and 2 x 5.5kW for extraction.

Variable drive & auto-adjustment achieve 50% saving in energy costs

Using a Danfoss VLT variable drive unit, we were able to drop the cycle down to 40Hz, and set the air vents to open automatically in response to prevailing conditions. The VLT variable drive and auto-adjustment achieved a 50% saving in energy costs. This reduction will cover the cost of the unit in less than two years.

The original energy cost was £8,257 on the 22kW drive. By trimming speed the client reduced noise and also saved on maintenance because there is a significant reduction in wear and tear:

Example of energy savings that can be achieved

Motor

kW	Voltage	Speed	Current 1 (estimated)	kW absorbed
22	415	1440	41	22

Duty Cycle (Total Running Hours 6750)

Hz	55	50	45	40	35	30	25
Speed	1584	1440	1296	1152	1008	864	720
kW	29.28	22.00	16.04	11.26	7.55	4.75	2.75
Hours	0	0	0	6750	0	0	0

Energy cost – without Converter Control

kWh	148500
Total	£8257*

Energy cost – with Converter Control

kWh	76032
Total	£4227*

Total energy cost including 2% Converter losses

kWh	77553
Total	£4312*

Cost & savings breakdown

Annual energy cost saving	£3945*
Converter cost	£2300
Payback period (excluding installation)	0.58 years

* Electricity cost calculated @ £0.06/kWh