Banff and Buchan College, located at Fraserburgh, Aberdeenshire, required a system to provide controlled air extraction from their welding school.

The new state of the art welding facility was recently opened by Alex Salmond, the First Minister of Scotland:

The welding school system comprises of 30 welding bays each of which is provided with an air extraction hood and outlet damper to the air extract ducting. The plant is provided by A-Mac Environmental and consists of a single fan extract system.

Sector 8 Solutions designed and commissioned a PLC system to run the fan extract system at different speeds depending on how many of the welding bays are in use. A staggered start facility was incorporated into the design to ensure that should multiple bays be in use at the same time after a restart from an emergency stop, the fan will not suddenly operate at high speeds causing potential damage through increased wear and tear.

Prior to the commissioning of the system, the fan ran at high speeds regardless if there was 5 bays or 30 operating. Obviously this meant a large electricity bill as the system was inefficient.

The following images and calculations highlight the efficiency savings enjoyed by Banff and Buchan college after the installation of the system :

The current, kW and number of bays in use relationship to fan speed is illustrated below.

The energy saving feature of the system is clearly demonstrated when comparing the number of bays in use with the power consumed.

For example with 15 to 19 bays in use 8.0 kW are consumed per hour with the fan running at 70% of full speed (i.e. 35Hz), however in a conventional system the fan would be running at 100% (i.e. 50Hz) regardless which would consume 22.7 kW per hour. In this instance an energy efficiency saving of 64.75% will be realised.

The system operation has been commissioned to achieve the required air extraction flow rates at the maximum possible energy efficiency. The energy efficiency profile is illustrated as follows:

The setpoints above are the percentage of full extract fan speed as-commissioned settings as at 30th August 2013.

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