Environmental Elements

The following environmental elements can affect an hp server installation:

Computer room preparation
Cooling requirements
Humidity level
Air conditioning ducts
Dust and pollution control
Electrostatic discharge (ESD) prevention
Acoustics (noise reduction)

Computer Room Preparation

The following guidelines are recommended when preparing a computer room for an hp server:

Locate the computer room away from the exterior walls of the building to avoid the heat gain from windows and exterior wall surfaces.
When exterior windows are unavoidable, use windows that are double or triple glazed and shaded to prevent direct sunlight from entering the computer room.
Maintain the computer room at a positive pressure relative to surrounding spaces.
Use a vapor barrier installed around the entire computer room envelope to restrain moisture migration.
Caulk and vapor seal all pipes and cables that penetrate the envelope.
Use at least a 12-inch raised floor system for minimum favorable room air distribution system (underfloor distribution).
Ensure a minimum clearance of 12 inches between the top of the hp server cabinet and the ceiling to allow for return air flow and ensure that all ceiling tiles are in place.
Allow 18 inches (or local code minimum clearance) from the top of the hp server cabinet to the fire sprinkler heads.

Cooling Requirements

Air conditioning equipment requirements and recommendations are described in the following sections.

Basic Air Conditioning Equipment Requirements

The cooling capacity of the installed air conditioning equipment for the computer room should be sufficient to offset the computer equipment dissipation loads, as well as any space envelope heat gain. This equipment should include:

Air filtration
Cooling or dehumidification
Humidification
Reheating
Air distribution
System controls adequate to maintain the computer room within specified operating ranges.

Lighting and personnel must also be included. For example, a person dissipates about 450 BTUs per hour while performing a typical computer room task.

At altitudes above 10,000 feet (3048 m), the lower air density reduces the cooling capability of air conditioning systems. If your facility is located above this altitude, the recommended temperature ranges may need to be modified. For each 1000 feet (305 m) increase in altitude above 10,000 feet (up to a maximum of 15,000 feet), subtract 1.5° F (0.83° C) from the upper limit of the temperature range.

Air Conditioning System Guidelines

The following guidelines are recommended when designing an air conditioning system and selecting the necessary equipment:

The air conditioning system that serves the computer room should be capable of operating 24 hours a day, 365 days a year. It should also be independent of other systems in the building.
Consider the long-term value of hp server availability, redundant air conditioning equipment or capacity.
The system should be capable of handling any future hp server expansion.
Air conditioning equipment air filters should have a minimum rating of 45% (based on "ASHRAE Standard 52-76, Dust Spot Efficiency Test").
Introduce only enough outside air into the system to meet building code requirements (for human occupancy) and to maintain a positive air pressure in the computer room.

Air Conditioning System Types

The following three air conditioning system types are listed in order of preference:

Complete self-contained package unit(s) with remote condenser(s). These systems are available with up or down discharge and are usually located in the computer room.
Chilled water package unit with remote chilled water plant. These systems are available with up or down discharge and are usually located in the computer room.
Central station air handling units with remote refrigeration equipment. These systems are usually located outside the computer room.

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 hp server 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.
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 hp 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 hp 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).
Adjust the supply air diffuser system grilles to direct the cooling air downward around the front of the hp server cabinets. The supply air is then available near the cooling air intake vents of the hp 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 may increase.

Humidity Level

Maintain proper humidity levels at 40 to 60% 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 electrostatic discharge (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.

Specifically, disk drives, tape drives, and some other mechanical devices can have bearing failures resulting from airborne abrasive particles. Dust may also blanket electronic components like printed circuit boards causing premature failure due to excess heat and/or humidity build up on the boards. Other failures to power supplies and other electronic components can be caused by metallically conductive particles, including zinc whiskers. These metallic particles are conductive and can short circuit electronic components. Use every effort to ensure that the environment is as dust and particulate free as possible. See the following heading titled "Metallic Particulate Contamination" for additional details.

Smaller particles can pass though some filters and over a period of time, cause problems in mechanical parts. Small dust particles can be prevented from entering the computer room by maintaining the air conditioning system at a high static air pressure level.

Other sources of dust, metallic, conductive, abrasive, and/or microscopic particles can be present. Some sources of these particulates are:

Subfloor shedding
Raised floor shedding
Ceiling tile shedding

These particulates are not always visible to the naked eye. A good check to determine their possible presence is to check the underside of the tiles. The tile should be shiny, galvanized, and free from rust.

The computer room should be kept clean. The following guidelines are recommended:

Smoking—Establish a no-smoking policy. Cigarette smoke particles are eight times larger than the clearance between disk drive read/write heads and the disk surface.
Printer—Locate printers and paper products in a separate room to eliminate paper particulate problems.
Eating or drinking—Establish a no-eating or drinking policy. Spilled liquids can cause short circuits in equipment such as keyboards.
Tile floors—Use a dust-absorbent cloth mop rather than a dry mop to clean tile floors.

Special precautions are necessary if the computer room is near a source of air pollution. Some air pollutants, especially hydrogen sulfide (H2S), are not only unpleasant but corrosive as well. Hydrogen sulfide damages wiring and delicate sound equipment. The use of activated charcoal filters reduces this form of air pollution.

Metallic Particulate Contamination

Metallic particulates can be especially harmful around electronic equipment. This type of contamination may enter the data center environment from a variety of sources, including but not limited to raised floor tiles, worn air conditioning parts, heating ducts, rotor brushes in vacuum cleaners or printer component wear. Because metallic particulates conduct electricity, they have an increased potential for creating short circuits in electronic equipment. This problem is exaggerated by the increasingly dense circuitry of electronic equipment.

Over time, very fine whiskers of pure metal can form on electroplated zinc, cadmium, or tin surfaces. If these whiskers are disturbed, they may break off and become airborne, possibly causing failures or operational interruptions. For over 50 years, the electronics industry has been aware of the relatively rare but possible threat posed by metallic particulate contamination. During recent years, a growing concern has developed in computer rooms where these conductive contaminants are formed on the bottom of some raised floor tiles.

Although this problem is relatively rare, it may be an issue within your computer room. Since metallic contamination can cause permanent or intermittent failures on your electronic equipment, Hewlett-Packard strongly recommends that your site be evaluated for metallic particulate contamination before installation of electronic equipment.

Electrostatic Discharge (ESD) Prevention

Static charges (voltage levels) occur when objects are separated or rubbed together. The voltage level of a static charge is determined by the following factors:

Types of materials
Relative humidity
Rate of change or separation

Table C-1 Effect of Humidity on ESD Charge Levels

Personnel Activity^[1]	Humidity^[2]and Charge Levels (voltages)^[3]
	26%	32%	40%	50%
Person walking across a linoleum floor	6,150 V	5,750 V	4,625 V	3,700 V
Person walking across a carpeted floor	18,450 V	17,250 V	13,875 V	11,100 V
Person getting up from a plastic chair	24,600 V	23,000 V	18,500 V	14,800 V
^[1]Source: B.A. Unger, Electrostatic Discharge Failures of Semiconductor Devices (Bell Laboratories, 1981) ^[2]For the same relative humidity level, a high rate of airflow produces higher static charges than a low airflow rate. ^[3]Some data in this table has been extrapolated.

Static Protection Measures

Follow these precautions to minimize possible ESD-induced failures in the computer room:

Maintain recommended humidity level and airflow rates in the computer room.
Install conductive flooring (conductive adhesive must be used when laying tiles).
Use conductive wax if waxed floors are necessary.
Ensure that all equipment and flooring are properly grounded and are at the same ground potential.
Use conductive tables and chairs.
Use a grounded wrist strap (or other grounding method) when handling circuit boards.
Store spare electronic modules in antistatic containers.

Acoustics

Computer equipment and air conditioning blowers cause computer rooms to be noisy. Ambient noise level in a computer room can be reduced as follows:

Dropped ceiling—Cover with a commercial grade of fire-resistant, acoustic rated, fiberglass ceiling tile.
Sound deadening—Cover the walls with curtains or other sound deadening material.
Removable partitions—Use foam rubber models for most effectiveness.