Data Center Efficiency Series: Cooling Solutions

Cooling Solutions for the Data Center

Data center technologies are quickly becoming more and more compact and powerful, resulting in higher density systems which generate higher amounts of heat. Data center management teams are constantly finding new methods to address the increase in power consumption and heat output in order to efficiently cool the data center. Current cooling solutions include:

Cooling Systems that Provide Efficiency:


A chiller produces chilled water via refrigeration process. Chilled water is then delivered via pumps to CRAH.


Computer Room Air Conditioner (CRAC)
A CRAC unit moves air via fan systems throughout the data center: delivers cool air to the servers, returns exhaust air from the room.

Computer Room Air Handler (CRAH)

A CRAH unit moves air via fan systems throughout the data center: delivers cool air to the servers, returns exhaust air from the room.


Free Cooling/Economizer
This particular unit uses the ambient environment, typically sources of cold air or water, to augment or replace mechanical air conditioning.


A humidifier is usually installed within a CRAC / CRAH unit and replaces water loss before the air exits the A/C units.

Liquid/Complementary Cooling
By delivering liquid, either chilled water or refrigerant, closer to the heat source this unit can be more efficient and effective when it comes to cooling. Unlike a CRAC unit, segregated to a corner of a room, these air conditioners are embedded in a row of server racks, suspended from the ceiling, or installed in a closed relationship with one or more racks.

There is no definite answer as to which cooling solution is the best or which is the most efficient, so the data center management team must conduct a detailed engineering analysis that closely looks at the potentials of different air cooling strategies and systems for each unique situation.

Data Center Cooling Strategies

Computer Room Air Conditioner & Raised Floor Plenum (

Airflow Segregation and Barriers

Hot aisle/cold aisle containment configuration is the practice of configuring racks so that the inlets of the racks are in a common cold aisle which is supplied by the cooling system and the exhausts will blow into a common hot-aisle return that goes back to the cooling system.

The key to airflow segregation is keeping the cool supply of air from mixing with the warm air that is returned. Then delivering the requisite volume of airflow. Placing barriers above and below the cabinets, isolating the hot aisles from the cold aisles is one of the best approaches to prevent cold air and hot air from mixing. This technique significantly reduces both types of air flow, the amount of hot air that infiltrates back into the cold aisle (re-entrainment) and the cold air that goes directly from the floor which diffuses the return through air grills (bypass). The figure below displays air flow and temperatures when barriers are not present.

Raised floors

Some data center designs use raised floors to distribute cool air through the raised floor to server racks. But there is only so much that can be done, so trying to push too much air under the floor can create negative pressures that can actually draw cool air back down through the perforated tiles, rather than forcing it up into the room. In addition, the floor tiles themselves have limits as to how much air can actually pass through the perforations. Consequently, increasing cooling capacity will not necessarily result in a corresponding increase in cooling across the room.

Proper Solutions to Cool the Data Center

Hot air re-entrainment and cold air bypass in a data center without barriers between the aisles (

Tune in next week for part 4 of the Data Center Efficiency Series on Server Efficiency…

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