I figured an example is the easiest way to explain my question. A 500-sq.ft laboratory with 9-ft ceiling includes an HVAC system delivering enough air volume for an air change (AC) rate of 10 AC/hr. However, both the air intake and exhaust are located in the ceiling, 18-ft apart. In this closed room with no additional air circulation air monitoring indicates that the air change rate is less closer to the floor (0-2 ft). Is there a way to calculate the air change rate at different room heights that includes air supply and exhaust located in the ceiling? Assume the laboratory is empty with standard temp, pressure, etc.