Cooling in facebook data center

One of the most exciting and talked about best practices for data center efficiency is often labeled “free cooling”-the use of Air-side Economizers to dramatically reduce energy consumption and costs. Air-Side economizers have become a talking point, it seems, in any current data center cooling discussion.

What are Air-Side Economizers?
Mechanical cooling, depending on the source, is estimated to consume anywhere from 33% to 40% of a facility’s incoming electricity. Designed to accompany or circumvent this process, Air-Side economizers can bring nature into the data center whenever the ambient conditions are favorable.

The outside air is brought into building and distributed via a series of dampers and fans. The servers ingest the cool air, transfer heat, and expel hot air to the room. Instead of being recirculated and cooled, the exhaust is simply directed outside. If the outside air is particularly cold, the economizer may mix the inlet and exhaust air, ensuring that the resulting air temperature falls within the desired range for the equipment.

The economizer design is typically integrated into a central air handling system with ducting for both intake and exhaust. The equipment includes filters to reduce the amount of particulate matter or contaminants that are brought into the data center space.

                                      Schematic Diagram Of Air Side Economizer. 

However, air side economization is possible when the data center is located at a cold place where cold air are easily available for most of the year. That's the reason Facebook constructed its data center in Prineville, Oregon where the company pioneered  a design that relies 100 percent on using outside air to cool its servers. However recently, Facebook constructed data center in North Carolina where the temperature is not as same as Prineville. But despite this Facebook has been able to cool its servers through the North Carolina summer using only fresh air and no mechanical refrigeration, even on days when the temperature reached 102 degrees.

But to how to achieve this was a major question for Facebook.The key to the cooling breakthrough was raising the temperature inside the Facebook data center, allowing servers to run at an inlet temperature of 85 degrees F. That’s about five degrees warmer than Facebook’s data center in Prineville, Oregon, where the company pioneered  a design that relies 100 percent on using outside air to cool its servers.

July 2012 was the second hottest month on record in North Carolina, with the temperature hitting 102 degrees on July 1. Surprisingly, the Power Usage Effectiveness (PUE) for Forest City clocked in at 1.07  versus 1.09 in Prineville during roughly the same period. Despite the record-breaking heat, they didn’t run the DX coils at all (in North Carolina) in summer. According to Facebook mechanical engineer Dan Lee, it shows that when the record hot days occurred, relative humidity was low, allowing the misting system to provide all the needed cooling.”