SA = RA + OA = RA + EA + RFA
Where
• SA = Supply Air
• RA = Return Air
• OA = Outside Air
• EA = Exhaust Air
• RFA = Relief Air
If minimum OA (ventilation air) is greater than EA, then the space will be positive pressurized and
OA = EA + RFA
If EA is greater than minimum OA (ventilation air), then the space will be under negative pressure and
OA = EA; RFA = 0
For Economizer Cycle
OA = SA = EA + RFA; RA = 0
