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HVAC

HVAC (heating, ventilation, and air conditioning) controls keep the air at a reasonable temperature and humidity. They operate in a closed loop, recirculating treated air. This helps reduce dust and other airborne contaminants.

Positive Pressure and Drains

All HVAC units should employ positive pressure and drainage. This means air and water should be expelled from the building. Untreated air should never be “inhaled” into the building, and water should drain away from the building.

A common malfunction of HVAC units is condensation of water pooling into the building, often going under raised floors where it may not be detected. Positive drains are designed to avoid this problem. Location of all gas and water lines, as well as all drains, should be formally documented.

Heat and Humidity

Data center HVAC units are designed to maintain optimum heat and humidity levels for computers. Humidity levels of 40–55% are recommended. A commonly recommended “set point” temperature range for a data center is 68–77°F (20–25°C).

With sufficient data center airflow, somewhat higher temperatures can be used. This can result in energy savings; however, the data center may heat to dangerous levels more quickly in the event of HVAC failure.

Note Many sources cite 68–72°F (20–22°C) as the optimum data center temperature range; in 2004, the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) recommended up to 77°F/25°C.

There is a recent “green” push to save energy costs by allowing a wider range for both temperature and humidity levels. As a result, the 2011 ASHRAE recommendations allow a much wider range: temperature of 18°C (64.4°F) to 27°C (80.6°F) and humidity from 25% to 60%, depending on the dew point. Higher set points require adequate airflow. Details may be found at https://www.ashrae.org/file%20library/technical%20resources/publications%20errata%20and%20updates/2011-gaseous-and-particulate-guidelines.pdf.

Static and Corrosion

Ever touch metal and receive a small shock? That is caused by buildup of static electricity; low humidity may cause such buildup. Static will discharge to balance a positive and negative electrical imbalance: sudden static discharge can cause damage from system reboots to chip or disk damage.

Static is mitigated by maintaining proper humidity, grounding of all circuits in a proper manner, and using antistatic sprays, wrist straps, and work surfaces. All personnel working with sensitive computer equipment such as boards, modules, or memory chips should ground themselves before performing any work.

High humidity levels can allow the water in the air to condense onto (and into) equipment, which may lead to corrosion. Maintaining proper humidity levels mitigates both static and corrosion.