Diverting Fresh Air to Ceiling Space when FCU is OFF

[EnOm]

Hi,
I have a bedroom with an adjacent toilet.
The room has continuous exhaust (via the toilet) and continuous Make-up Air
The FCU is located in the toilet above the ceiling space.
The return air is ducted back to the FCU to avoid picking up any odors from the toilet.
The fresh air is injected directly into the return air duct.

I am thinking about adding Motorized Dampers that are interlocked with the FCU such that
FCU ON: Fresh Air is directed into the return air duct
FCU OFF: Fresh Air is directed to the room's ceiling space
My purpose from this is to maintain air balance even when the FCU is OFF.
The fresh air supply is to be held constant at 75°F

Is this a practical setup?

Best Regards

 

[willard3]

How does the fresh air get to the ceiling space?

 

[BronYrAur]

If your fresh air is tempered to 75 deg, then it must be delivered via some form of air handling unit, correct? If that's the case, the fresh air will leak through the fan coil even if it is off. Plus the negative of the toilet exhaust will help pull it through?

Are you experiencing any problems? If not, I would leave it alone. You will just be adding 2 more points of failure with those dampers. many buildings are set up for fresh air to be delivered just to the corridors, and the toilet exhausts pull it from there.

 

[urgross]

The toilet is above the ceiling space? Sounds like the mother-in-law quarters in the outhouse might need an elevator.

 

[EnOm]

willard3:
Thank you for the response. The incoming fresh air duct has a junction. One side leads to the FCU's return duct. The other is open to the ceiling space.

BronYrAur:
Thank you for the response. Yes that is correct, the fresh air is delivered via an air handling unit. I had in mind that the air would still leak through the fan coil, but I was thinking maybe the FCU would somehow obstruct it and thus the air would leak from somewhere else with less resistance. Is this incorrect?

urgross:
Thank you for the response. My bad
The FCU is located in the toilet, above the false ceiling.