Optimizing data center

In my previous post i had written about how data center are created. But once it is created, optimizing Data center has always been major challenge. Facebook recently has followed some innovative approach to make their data center efficient. With their new strategies they are saving upto 2.5 million kw hour annually and reducing energy demand by 276 kw from one of their Data Center. In economic terms, they are saving $ 230,000 annually and in terms of environmentally they have reduced the amount of green house gases produced by 967 metric tons annually which is equivalent to emission from 332 cars and 221 homes. 

By realizing following saving they addressed following issue : 

• Inefficient airflow distribution

• Excessive cooling

• Low rack inlet and chiller water temperatures

Improving Airflow Distribution

They conducted their own internal computational fluid dynamics analysis that resulted in instituting a number of improvements to make airflow distribution more efficient, most notably by rolling out cold aisle containment throughout the facility. By enclosing the cold aisles within each server room, they more efficiently direct the air flow and control the temperatures in the data center by eliminating the bypass of cold air and the infiltration of hot exhaust into the cold aisles. Other mechanical improvements include adding skirting around the power distribution units and blanking plates as well as sealing cut-outs for cables to minimize air leaks.

Reducing Cooling Levels

They discovered that the server fans were spinning faster than necessary, so they optimize their fan speed control algorithm while keeping temperatures within the recommended range. For each server, this saves up to 3 watts and requires less air (up to 8 cubic feet per minute), which quickly adds up in a 56,000 square foot facility.

By analyzing airflows in each server room, they discovered that they didn't need to use as many CRAH (computer room air handler) units than were available. So they shut down 15 CRAH units, reducing the installed demand by 114 kilowatts.

Raising Rack Inlet and Chiller Water Temperatures

They also reduced their cooling levels by raising the set point temperature of the CRAH units while maintaining near uniform temperatures in the cold aisles. In the end, they raised the temperature for each CRAH unit's return air to 81 degrees Fahrenheit from 72 degrees Fahrenheit.

Finally, they raised the chilled water temperature from 44 to 52 degrees Fahrenheit, reducing their chilled water system load by 171 tons per hour.

Reference : 
Facebook Notes