Grey Green has investigated the fans at numerous factories, including at several large grain mills. Often dampers are used to control flow rates and pressures. If so, removing the dampers or changing the fan speed produces good savings.
A mineral processing works has six identical, belt driven fans. All operate against dampers which are approximately half closed.
Grey Green calculated that a simple change to the belt drive ratio with fully open dampers would:
- Cost approximately R 7 500 to implement (equipment only – installation could be done by the factory’s own maintenance staff).
- Produce annual savings of R 173 400 (No typos here the payback period is really only 0.04 years – i.e. less than 1 month).
Another local grain mill has approximately 30 significant sized fans. None have damper control; whenever the mill is operating the fans run continuously at fixed speed.
Grey Green assessed 18 of the biggest fans. Our measurements and calculations showed that many of the fans were far from their optimum (maximum efficiency) operating points – i.e. when plotted on a fan curve like the typical one in the following diagram, their combination of flow rate and pressure rise was far from the best efficiency point.
Due to the age of the fans and their motors we recommended replacement of the worst performers.
- For five fans replacement gave payback periods less than 1 year and total annual electricity savings of >R 2 million.
- Six more fans could be replaced to produce payback periods between 1 and 2 years, with combined annual electricity savings of R 634 000.