Combustion air fan hydraulic study

[Norvin]

I have an assignment to model an existing boiler combustion air system, in order to advise on fan upgrades that would be required to meet revised air flows that the end user requires

The system is quite complex with several fans and fresh and recirculated air being mixed at certain points

I am looking for suggestions as to a suitable software to model the existing system and also trial changes in fan / fan impeller size to achieve the revised air flows

My search so far has found software designed for HVAC which I don't think really fits this application

The more powerful software such as PlantFLOW and Hysys are expensive and I think overkill for this exercise.

I am experienced with using Pipe-FLO software for centrifugal pumps and ideally I am looking for a similar sofware which allows me to enter fan curves and then asses fan duty / performance at different operating scenarios

I could do the exercise via spreadsheet but if I can find suitable software it would make the whole exercise more efficient

Any suggestions as to suitable software that is not too expensive? (I have also posted this on the boiler / pressure vessel forum!)