Refresh your data center cooling lexicon

Computer room air-conditioning unit

This appliance maintains and monitors data center air distribution, temperature and humidity. Computer room air-conditioning units, or CRACs, usually replace legacy air-conditioning units to cool data center hardware. Admins have a couple setup options.

The most common approach is using a CRAC to cool intake air and dispense it through an elevated floor. This forms cold aisles that flow through the racks and pick up heat before exiting the back of the rack.

Liquid immersion cooling

Considered to be a more cutting-edge data center cooling technology, liquid immersion cooling submerges hardware in dielectric liquid. This liquid is thermally conductive and uses absorption and evaporative cooling to draw heat away from the processing infrastructure.

Liquid immersion cooling uses 99% less electricity than traditional data center cooling methods, but it can prove costly, because of the amount of fluid required. Most systems are a mix of pumps, external radiators and evaporative cooling techniques.

Open bath systems, which involve tubs that completely submerge hardware in dielectric coolant fluid, are the cheapest way to install liquid immersion cooling and provide benefits such as nearly silent operation, required airflow reduction and decreased dust in the data center.

Hot/cold aisle

This data center cooling setup is often implemented during the design phase. A hot/cold aisle layout sets the server racks in a configuration that's conducive to more efficient airflow and creates an air heating/cooling feedback loop.

The design concept faces the cold air intakes one direction and the hot air exhausts in the other direction. Most data centers have cold aisles in front of air-conditioning output ducts and feed hot aisles into the air-conditioning return ducts.

Containment systems are another component of hot/cold aisle designs. They prevent different air temperatures from mixing. Originally containment systems were just plexiglass or vinyl coverings; today's offerings include plenums and variable fan drives to further prevent hot and cold air mixing.

Free cooling

Another way to address air temperature is free cooling. It uses naturally cold air or water as opposed to mechanical refrigeration. These systems filter, humidify and pump in the cooling source; they are also known as economizers. Of course, this means that organizations must build the data center in a location or at an elevation where naturally cooled air or water is available.

Some data centers draw cold water from nearby lakes, rivers or oceans instead of using refrigeration and a chiller to cool water. Such facilities include Green Mountain's Stavanger data center in Rogaland, Norway, and Nautilus Data Technologies' floating data center in Vallejo, Calif.

In using these systems, organizations can extend the lifecycle of their other data center cooling systems, which ultimately reduces overall maintenance costs and energy consumption for the entire data center.

Adiabatic cooling

The adiabatic data center cooling method addresses air pressure in the data center. It uses evaporative coolers to push warm air through moist pads, which chill the air and vents it into the facility.

The technique is based on the laws of thermodynamics that hot air is less dense and will rise above areas of cold, denser air. Adiabatic cooling lets organizations effectively cool air and control temperature through airflow adjustment to save on electricity costs; these cooling units can save more than 40% in electricity usage.

Some facilities also implement adiabatic heating, which is an energy efficient way to incorporate humidity into the data center. Common types include evaporative, ultrasonic and atomizing, which each use different required equipment.