Monitoring Temperature and RH Levels

Because of the importance of both temperature and relative humidity in keeping the data center continually up and running, it is critical to keep a constant check on the temperature and RH levels. The data center system must provide constant feedback with a detailed profile of the room conditions.

Monitoring System

A comprehensive monitoring system is an added expense to the design and maintenance of the facility, but it provides an invaluable tool for diagnosing and correcting problems, collecting historical data for system evaluations, and for day-to-day verification of room conditions. The following should be considered in the design of the data center and monitoring system:

• The room condition feedback should not be based on one sensor in one part of the room. A single sensor might tell that conditions are perfect, but in truth, they are only perfect in that particular part of the room. Sensors should be placed in specific areas of the center and near critical configurations. These sensors usually sense both temperature and RH. You could have separate sensors for these, but they will also be connected to a data storage device, and simultaneous temperature and RH information read by a specific sensor is the information you want recorded.

• The monitoring system should have historical trend capabilities. The historical psychrometric data can be used to analyze seasonal changes and other outside influences.

• The monitoring system should have critical alarm capabilities. At the very least, the system should be set to notify when conditions move outside the set parameters. It might also be necessary to have a system that performs automatic functions such as switching to a backup chiller if a primary chiller fails.

• Ideally, the monitoring system should be integrated with a tracking system for all parts of the center. This would include not only the in-room air conditioners and humidifiers, but the cooling support systems, power backup, fire detection and suppression, water detection, security, and any other infrastructure and life-safety systems.

• The HVAC system configuration and monitoring data should be periodically examined and evaluated by trained personnel to ensure that temperature and RH profiles are appropriate for the current room demands.

• These monitoring systems can use SNMP protocol to integrate into overall data center management systems.

Air Conditioner and Humidifier Set-Points

The set-points of the environmental support equipment will vary between data center sites, and even between individual units in the same site. An advantage of multiple HVAC and humidifier units is the ability to modify set-points individually in localized areas. The heat load in a room will vary from an area with dense hardware configurations to an area with little or no hardware. Adjusting for this variance can be done by changing the tile configurations in the raised floor, but adjustments to the HVAC or humidifier set-points might also be necessary. Ideally, these settings would be monitored and adjusted from a single console.

Figure 8-4. HVAC Control Panel and Digital Display

Under most circumstances:

• Air conditioners should be set to 72 ° F (22 ° C) with a sensitivity range of +/- 2 ° F (-16 ° C)

• Humidifiers should be set to 48 percent RH with a sensitivity range of +/- 3% RH

The decision for set-point settings will be influenced by several factors, including heat load and vapor barrier integrity. If, for example, the room has inadequate vapor barriers, it might be necessary to adjust humidifier set-points to accommodate seasonal influences.

The set-points should be chosen to maintain the optimal recommended temperature and RH levels while allowing wide enough sensitivity ranges to avoid frequent cycling of the units.