How to Size my Return Air Conditioning Grills Correctly?

Take 100%-12.5% to find a multiplier of 87.5%. 340 CFM of return air x 87.5% = 298 CFM. You may round this number off to 300 CFM. If the pressure zone requires a positive pressure, decrease the airflow into the return grille and duct by approximately 20% using a volume damper.

2015 ASHRAE Handbook—HVAC Applications (SI) CHAPTER 57

ROOM AIR DISTRIBUTION page 2

Table 1 Recommended Return Inlet Face Velocities Across Gross Area, m/s

Above occupied zone                                             >4

In occupied zone, not near seats                    3 to 4

In occupied zone, near seats                           2 to 3

Door or wall louvers                                       1 to 1.5

Through undercut area of doors                  1 to 1.5

you will find the same values at SMACNA HVAC Systems Duct Design • Fourth Edition

Table 3−9 Recommended Return Air Inlet Face Velocities

page 3-26

An air-cooled chiller has a condenser that is cooled by the environment air. The air-cooled chillers are preferred for small or medium installations but lately the quality improvement in their structure, allows the usage, in modular type, for large installations also. An air-cooled chiller is preferred especially in cases that there is not enough water or the water is very expensive. The water-cooled chillers have water cooled condenser connected with cooling tower and are usually preferred for medium and large installations where there is sufficiency of water. In addition, they are also preferred in cases that is demanded constant performance of the system, independently of the ambient temperature (industrial air conditioning, air conditioning of digital systems etc), because the capacity of the water-cooled chillers are not affected by the ambient temperature fluctuations