Site Preparation Guide, Third Edition - Server Expansion Unit

Appendix A

General Site Preparation Guidelines

Environmental Elements

Return air from an under floor 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 server 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 server 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 can 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

server cabinets. The supply air is then available near the cooling air intake vents of the server 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.

Air-Conditioning Ducts

Use separate computer room air-conditioning duct work. If it is not separate from the rest of the building, it

might be difficult to control cooling and air pressure levels. Duct work seals are important for maintaining a

balanced air-conditioning system and high static air pressure. Adequate cooling capacity means little if the

direction and rate of air flow cannot be controlled because of poor duct sealing. Also, the ducts should not be

exposed to warm air, or humidity levels might increase.

Humidity Level

Maintain proper humidity levels at 40 to 55% relative humidity (RH). High humidity causes galvanic actions

to occur between some dissimilar metals. This eventually causes a high resistance between connections,

leading to equipment failures. High humidity can also have an adverse affect on some magnetic tapes and

paper media.

CAUTION Low humidity contributes to undesirably high levels of electrostatic charges. This increases the

ESD voltage potential. ESD can cause component damage during servicing operations. Paper

feed problems on high-speed printers are usually encountered in low-humidity environments.

Low humidity levels are often the result of the facility heating system and occur during the cold season. Most

heating systems cause air to have a low humidity level, unless the system has a built-in humidifier.

Dust and Pollution Control

Computer equipment can be adversely affected by dust and microscopic particles in the site environment.