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LOAD PROFILE

To properly size and select equipment and systems, it is important to determine the Day 1 (first day of operation) and final load. To establish the load profile, the following should be considered:

• Schedule: hours of operation.

• Load: What is the load? How much does the load vary? How rapidly does the load vary and for what duration?

• Future load: In addition to operational variation in the load, will it change over time (e.g., technology upgrades or expansions)?

• Life cycle: What is the life cycle of the equipment being cooled, and is the cooling system expected to provide service to some other equipment or application after the first life cycle is reached (e.g., a computer life cycle of three years and cooling-equipment life cycle of 15 years)?

Because of rapid advances in technology and short life cycles, it is common for the decision on equipment to be deferred as long as possible. As a result, the HVAC design, equipment procurement, and contract award easily could occur prior to the time the equipment to be cooled is determined. These types of situations tend to produce designs that are oversized.

For IT loads, ASHRAE datacom books (see sidebar) provide help both directly and indirectly. For example, “Thermal Guidelines for Data Processing Environments” created a thermal report for IT manufacturers to use. It establishes actual, rather than nameplate, load and recognizes that load varies depending on how the equipment is configured. “Datacom Equipment Power Trends and Cooling Applications” projects future loads for computer servers, storage servers, and communication equipment.

The combination of load variation and oversizing attributed to the unknown can produce unfavorable results (e.g., cooling equipment unable to handle low load). A good accomplishment would be to identify:

• Minimum and maximum load for Day 1 operation.

• Minimum and maximum load for the end of the equipment (IT or procedure) useful life.

• Minimum and maximum load for the next generation of equipment (IT or procedure).

With this information, equipment sizing and system selection can better match the load and achieve optimum performance.

OPERATING CONDITIONS

TABLE 1. Equipment-environment specifications.

Historically, data centers have been kept particularly cold (e.g., 68°F). Predominantly, this was anecdotal. “Thermal Guidelines for Data Processing Environments” identifies a wide range of acceptable temperatures and humidities (Table 1). These thermal guidelines are critical because they create far more freedom for the designer, opportunity to consider economizers, and less-stringent humidification requirements.

PROVIDING FOR THE FUTURE

Challenges in providing for the future include:

• Avoiding premature obsolescence of cooling equipment.

• A sizing mismatch resulting in cooling equipment operating inefficiently or outside its performance capabilities.

• Initial overspending by specifying and installing more equipment than was needed on Day 1.