Ventilation Duty Standby Seamless Changeover

[cjw32]

Hi,

I'm reviewing a specification for a vent control system upgrade and I'd be grateful for some advice.

The system has three fan sets operating duty/standby. The first is for a cell extract. The second for building extract. The third is the air handling unit to supply conditioned air. The system operates in a cascade such that if the cell extract has failed then the building and AHU will shutdown. Start-up follows the same logic.

My query is regard to seamless changeovers. At the moment, if the cell extract Fan A were to fail (2oo3 voting) then the specification states that the AHU and Building extract will shutdown and then the cell Fan B will start. Once the cell extract is re-established then the building extract will start and finally the AHU will kick in.

I'm a control engineer, but I'd like to think there would be a way to change-over the cell extract fans without shutting down the building and AHU fans. Has anyone any experience with these type of cascade systems and is this the normal way to handle change-over operation?

Thanks in advance.

 

[SAK9]

Run both duty and stand by fans at reduced speeds to achieve the design air flow.If one fails the other fan can take over ramping upto full speed.

 

[cjw32]

Thanks SAK9, I should've mentioned that the cell fans are configured for both dual fan operation and duty/standby. I was just wondering if it's industry practice to have a seamless changeover on duty/standby vent systems.