Dear uditha

Whether the outlets of the 2 fans should be in parallel is not a real issue.

Whether the fans have their own outlet into the atmosphere or into a common chimney, the outlet pressure of the 2 parallel fans is equal.

If the intakes are extracting gas from different sources, that is a different case.

If the 2 supposed, extraction pipes have different resistance, the extraction lines must be kept separate.

It is all a matter of calculating the required gas flows and pressure drops in the pipelines and check those against the centrifugal fan curves (parallel or single)

The arrangement depends on what is required from the installation. ■

Dear uditha

In your drawing, the 2 fan outlets can discharge in a shared chimney.

The chimney diameter must have a diameter, which is designed for the combined flow.

If the intakes are extracting gas from different sources and have different pipe resistances. The extraction lines must be kept separate.

Calculate the required gas flows and pressure drops in the pipelines and branches and check those against the centrifugal fan curves.

Then you know, if the installation meets the requirements.

If all the gas sources are operating simultaneously, this might be not that easy. ■

Dear uditha

Actually, you have designed 2 separate systems with a centrifugal system for each system.

The only thing is that the 2 fans discharge into a common chimney.

For both fan outlets, the discharge pressure is determined by the chimney flow resistance.

The chimney design must be for both fans running, whereby only a minor, negligible pressure drop is generated.

The performance of the whole systems must be checked by calculation, using the pressure/flow curves of the 2 fans. A Variable Frequency Drive can help to create the required conditions and performance.

There is no MUST. ■