Is This Room Negative?

[jeb6294]

Forgive me for the stupid question, but I'm not a mechanical guy.  Our infection control nazi has decided that the barber shop in our new addition has to be negative.  She was here when we reviewed the design.  She walked through the building during construction every Monday morning.  She waits until the contractor is finishing up their punchlist and turn the building over to tell us this?

Anyway, my question is whether you can tell from the mechanical drawing if the room is negative.  In the attached drawing, I'm hoping the "85" at the diffuser and the "100" at the return are for CFM so I can tell her there's more air leaving the room than entering.

 

[P-E]

I would say it's not, not negative. 

 

[lundy]

Looks like it's on a VAV box, typically the CFM at the grill is the max and the box would ramp down to a minimum CFM at part load. So you should be negative in that space. 

 

[JalapenoScott]

Per design balanced cfm, the space is negative.  However, the space could go positive.  

The supply diffuser is showing 85 cfm which will be the vav box max.  However the vav box will most likely be set up as constant volume because the vav box appears to be a 6 in inlet.  The lowest controllable airflow in a 6 in inlet is generally around there (depending on manufacturer).  So supply air will most likely be 85 cfm all the time.

The return grille on the other hand will be at 100 cfm at maximum.  If the return fan turns down (as it does in a vav system) the return will start to turn down at the furtest runs first.  The air will want to come from the path of least resistance.  The return grill will be 100 max, and possibly  (not probable) 0 cfm at min.

Even if the return air was constant,  practically, the airflow offset is too small to make much of an impact.