Finally, the layout of air deliver and return vents is critical. Air conditioning performance is maximized when the CRAC output air temperature is highest, according to Schneider Electric, and in an ideal-world data center with zero recirculation, the CRAC output temperature would be the same 68-77°F (20-25°C) desired for the computer equipment. But this doesn’t happen in the real-world data center. So Schneider Electric suggests that the CRAC set point should now be set lower than what is necessary to maintain desired equipment intake temperatures. Although the CRAC temperature set point is dictated by the design of the air distribution system, the vendor notes, the humidity may be set to any preferred value. Setting humidity to high can detract from the air cooling capacity of the CRAC unit – which will need to power up dehumidification functions that affect its air cooling abilities – and humidifiers will have to be added to replace the water removed from the air by the dehumidification (oh, and humidifiers are a significant source of heat which then needs to be cooled and further detracts from the capacity of the CRAC unit).
Schneider Electric offers a lot of other tips in the white paper, titled Power and Cooling Capacity Management for Data Centers, which can be viewed here.