Mechanical products and controls manufacturer Danfoss’s variable-speed drives (VSDs) have a back-channel cooling system that enables one to channel ambient air from outside a control room through the VSD and then vent it back into the atmosphere.
This process reduces cooling costs by reducing heat by 85%.
The cooling air only passes over the heat sink surfaces and is not in contact with the internal electronic components, preventing contamination of the con- trol electronics and extending life and reliability.
Dust build-up on the heat sink surfaces poses a challenge, as it could impair the heat transfer capabilities over a period.
Danfoss required a dust extraction system for a VSD destined for mining company Kumba Iron Ore’s Sishen mine, located near Kathu, in the Northern Cape, a semi-arid area that is renowned for its extreme ambient temperatures of up to 42 ºC. Kumba selected industrial solu- tions provider Rand Technical Services (RTS) to provide the solution.
RTS MD Ian Fraser says VSDs are, in principal, sophisticated pieces of engineered equipment that are able to electronically vary the speed of electric motors. He notes that challenges arise because VSDs rely on semiconductors for operation, which are renowned for generating heat.
“VSDs are placed inside containerised or brick motor control centre rooms on mine sites to protect them from the environment. Because the ambient temperatures on site are generally high, the inside of the container becomes a veritable hotbox. The addition of the VSDs own self- generated heat results in the need for oversized-specification air conditioners.
“These air conditioning units pump cool air into the area around the VSD panels and waste energy since all the energy absorbed by the unit is used to maintain a reasonable temperature within the container.
“Danfoss back-channel technology allows for smaller air conditioning units and a more energy efficient solution,” he says.
He adds that after the RTS team had consulted with the Danfoss team and the panel builder, it was determined that the back-channel air did not need to be cold, but rather that a continuous flow of fast-moving ambient air, which is cooler than the heat generated by the VSD, be directed into the VSD.
“The next challenge was the fact that the ambient air was dust-laden and, if pumped through the VSD, would quickly result in dust accumulation on the heat sink. This could possibly cause heat sink over-temperature tripping.
“Installing a new filter would not resolve this problem but rather exacerbate it, as the filters would quickly become clogged with dust and result in the incapacitation of the VSD,” he adds.
RTS’s self-cleaning internal spin filter technology solved this problem because, unlike conventional filter membranes that clog as a result of pressure build-up after a period of use, the pressure drop across the spin filter module never increases.
“The units are self-cleaning and do not block when installed correctly, offering consistent performance with consistent resistance,” says Fraser.
They are also energy efficient, as only the auxiliary purge fans that direct the dirty air out of the air stream require power.
“Our client required a maintenance-free system that would ensure low dust levels and a reliable flow of air at a rate specified by the Danfoss engineers.
“In addition, each of the eight con- tainerised units had different layouts, so we needed to design and engineer the spin filter to fit each specific application,” he says.
An example of this, says Fraser, is that the containers were mounted on stilts. The spin filters were fitted on the under- side of the containers, with different configurations to accommodate the various design requirements.