Chapter 2
General System and Facility Guidelines
Environmental Factors
41
Basic Air Distribution Systems
A basic air distribution system includes supply air and return air.
An air distribution system should be zoned to deliver an adequate amount of supply air to the cooling air
intake vents of the computer system equipment cabinets. Supply air temperature should be maintained
within the following parameters:
• Ceiling supply system—From 55 °F (12.8 °C) to 60 °F (15.6°C)
• Floor supply system—At least 60 °F (15.6 °C)
If a ceiling plenum return air system or a ducted ceiling return air system is used, the return air grill(s) in the
ceiling should be above the exhaust area or the exhaust row.
The following three types of air distribution system are listed in order of recommendation:
• Underfloor air distribution system—Downflow air conditioning equipment located on the raised floor of
the computer room uses the cavity beneath the raised floor as plenum for the supply air.
Return air from an underfloor air distribution system can be ducted return air (DRA) above the ceiling.
Perforated floor panels (available from the raised floor manufacturer) should be located around the front
of the system cabinets. Supply air emitted though the perforated floor panels is then available near the
cooling air intake vents of the computer system cabinets.
• Ceiling plenum air distribution system—Supply air is ducted into the ceiling plenum from upflow air
conditioning equipment located in the computer room or from an air-handling unit (remote).
The ceiling construction should resist air leakage. Place perforated ceiling panels (with down discharge
air flow characteristics) around the front of the system cabinets. The supply air emitted downward from
the perforated ceiling panels is then available near the cooling air intake vents of the computer system
cabinets.
Return air should be ducted back to the air-conditioning equipment though the return air duct above the
ceiling.
• Above ceiling ducted air distribution system—Supply air is ducted into a ceiling diffuser system from
upflow air conditioning equipment located in the computer room or from an air-handling unit (remote).
Return air from an above ceiling ducted air distribution system may be ducted return air (DRA) above the
ceiling, or ceiling plenum return air (CPRA).
Adjust the supply air diffuser system grilles to direct the cooling air downward around the front of the
computer system cabinets. The supply air is then available near the cooling air intake vents of the
computer system cabinets.
Air Conditioning System Installation
All air conditioning equipment, materials, and installation must comply with any applicable construction
codes. Installation of the various components of the air conditioning system must also conform to the air
conditioning equipment manufacturer’s recommendations.
