Relief fan on ducted return system

[waterice]

Hello Everyone!

I was wondering if anyone here has used a relief fan on a ducted return system. We usually go with a return fan but due to budgetary and size constraints are contemplating on using a relief fan for the unit. I was wondering if anyone here has done this and could share their experiences?

Thank You!

 

[lukaiENG]

I do projects with (normally unducted) relief fans. Some thoughts to consider:
[ol 1]
[li]How are you going to control the relief fan? building pressure? airflow calculation based on airflow measuring stations?[/li]
[li]Do you not have an airside economizer? if you do, doesn't your relief fan need be be sized for 100% of the return air flow rate? this might negate any cost savings you are anticipating.[/li]
[/ol]

 

[waterice]

Hi lukaiENG, thank you for your inputs.

1. We're planning on using airflow measuring stations to control the relief fan.
2. We do have an airside economizer and yes, it looks like the unit was selected for 100% return air already.

Will having all that static on the supply fan be a problem? It could easily be about 4-5 in.wc.

 

[GT-EGR]

In theory they both are capable of accomplishing the same goals, mainly being space pressure control, but have a slightly different method of doing it. The big design differences would be that your supply fan now has to be sized to include all the static pressure on the return side, return fans are always on and relief usually aren't, some relief fan options don't have the static capabilities of return fans (but that's if you get an accessory/add-on relief fan), and there is a little more added complexity to controlling a return fan configuration (return fan speed control and relief damper modulation) than a relief fan (relief fan speed control, damper usually open/closed).

 

[chicopee]

Look into push pull ventilation systems. Such system is normally noted in restaurant kitchens where vapor laden exhaust air is removed from the surfaces of cooking appliances and air conditioning losses within the structure is minimized. It saves hard earned income on air conditioning.

 

[waterice]

Thank you everyone for your inputs!