Replace exhuast fan with ERV?

[pbmechtech]

I am upgrading a building’s HVAC equipment with new equipment. There is currently a 5000 cfm fan coil unit supplying conditioned air to the space and a 5000 cfm exhaust fan returning the air back to the fan coil and exhausting a certain amount of air to the outdoors. The return side of the fan coil is ducted to an outdoor air inlet and the outlet side of the Exhaust fan. It is all controlled with pneumatic dampers.

My question is can I remove and replace the exhaust fan with an ERV? My space requires 400 cfm of fresh air and my bathroom exhaust requirements are about 350cfm. Can I remove the 5000 cfm exhaust fan and connect the new fan coil unit’s return air duct to the old exhaust fan’s inlet ductwork and then have the ERV to draw exhaust from the bathroom and supply 400 cfm of outside air into the return duct of the fan coil unit?

The location is Northern, Ontario with a winter outdoor design temperature of -25

Thanks in advance for your responses.

 

[cdxx139]

If I follow correctly, your not replacing the 5000 CFM exhaust fan with an ERV, your really removing the exhuast fan and adding a 400 CFM ERV?

I dont see why not. Add the return duct static (or the ERV staic pressure (if no ERV fan); whichever is greater) to the new FCU ESP. Pay special attention to frost protection options for the ERV.

knowledge is power

 

[pbmechtech]

You are correct. I am removing the exhaust fan altogether. Also replacing the existing FCU and will connect the return side to the existing inlet duct of the current EF that is to be removed.

Then will add an ERV to for ventilation air instead of using the FCU O/A duct/ EF combo.

 

[Compositepro]

You do not have a 5000 cfm exhaust fan. You have a 5000 cfm return air fan. It was put there for a purpose; probably to keep the conditioned space from being over-pressured. So, no you cannot just remove it.

 

[cdxx139]

You have a recirculation system, basically a built up air handler. If the new FCU fan static can handle both supply and return static pressure, I cant think of a reason not to eliminate the return fan. The questions seems to refer that it serves one large space. I dont see how the space will be over pressurized. Eliminate the return fan, save on first cost, maintennace costs etc.

just because you found it like that, doesnt always mean it was done right the first time.

knowledge is power

 

[pbmechtech]

Thanks for your input. The building is a small local airport.

 

[317069]

Do you have a chance to check the original drawings

 

[dbill74]

At only 5000 CFM, I would bet the "exhaust" fan was installed to facilitate exhaust based on the description of the system in the OP. With that in mind, OP's intent sounds reasonable; I see only 1 thing that could be problematic, that being the capacity of the new FCU's fan to overcome supply and return duct losses. If such a FCU can be found, I say proceed with original plan.

However, if the new FCU's fan comes up short on the pressure requirements, keep the "exhaust" fan and slow it down to be just return, block off/remove the exhaust portion of the duct, add the ERV as originally planned.

My money is on doing as originally intended.

 

[cry22]

looks like the RF is used for air-side economizer.
without RF, you would need relief damper somewhere.
I'd look at the control sequence of operation first before changing for the sake of changing without first understanding the purpose of the original design.