fan sizing implications of system effect for centrifugal fans in an exhaust application

[immsk]

Hi,

I am trying to understand the losses due to system effect for not having the recommended straight section of duct in an exhaust fan application. The existing fan is shown installed in the image. There are two main system effect losses at play here from what I understand.

1) Losses at the inlet due to not having an elbow
2) Losses at the outlet due to not having sufficient length of straight duct work

My question relates to point two. Since the air pumped out of the fan is simply being discharged into the atmosphere. Does it matter what type of outlet I have? From my understanding of this system I should be considering the following resistances when sizing the fan:
1) Duct friction losses
2) Duct fitting losses
3) Fan Inlet elbow losses
4) Fan Inlet system effect

What do you guys think?

 

[miningman]

If theres room, ALWAYS install some kind of evase on the outlet. Your photo suggests this would be relatively easy