A computer room air conditioning (CRAC) unit is a device within a data center that allows managers to control the temperature, air distribution, and humidity. CRACs cool a data center by blowing air over a cooling coil filled with refrigerant, and excess heat is then expelled by a glycol mixture, water, or air.
Although there are many ways CRAC units can be setup within a data center, optimal placement is at the end of the hot aisles. This ensures the return of hot air back to the CRAC unit and maximizes static pressure to the cold aisle.
To ensure that the CRAC units are working effectively, data center managers should frequently check the airflow both above and below the floor. They should also check the air temperature throughout the room to determine which areas are hot and cold.
Importance of CRAC Unit Sizing
Today, data center managers are aiming to reduce the physical footprint of equipment to allow for more computing equipment and power in a smaller area, and therefore require greater heat dissipation.
Ultimately, the higher the heat density, the greater amount of air flow needed for the CRAC unit. The plenum below the raised floor allows air to flow at a specific cubic feet per minute (CFM) which is based on the load on the rack, and the CRAC unit should be sized to handle that load. The general rule is that a CRAC system rating should be 1.3 times the anticipated IT load rating plus any capacity added for redundancy.
If a CRAC unit is too small for the data center, it can lead to over-temperature conditions that can damage equipment and cause downtime.
If a CRAC unit it too big for the data center, it can cause condensation or static discharges as CRAC units can control humidity, unlike air conditioners. If the CRAC unit increases humidity above 55% (the maximum relative humidity for most server vendors), condensation will begin to form, which can damage equipment. In contrast, if the CRAC unit lowers the humidity below 45% (the minimum relative humidity for most server vendors), it can result in a static discharge which is the potentially dangerous buildup of electric charges on objects.
DCIM Software and CRAC Units
Data Center Infrastructure Management (DCIM) software greatly improves the efficiency of CRAC units. DCIM collects, reports, trends, and alerts on data from environmental sensors such as humidity and temperature, making it easy for data center managers to monitor their environment and know when to increase or decrease temperature and humidity set points. Data center managers can also visualize the formation of hot spots or overcooling with thermal time-lapse video, which ultimately helps save energy, maintain uptime, keep cabinets within ASHRAE guidelines, and increase data center sustainability.
Want to see how Sunbird’s world-leading DCIM solution makes it easy for you to increase the efficiency of your CRAC units? Get your free test drive now!