Data Center Cooling
– Lars Strong, Senior Engineer, Upsite Technologies, says:
The rising cost of electricity, compounded by increasing densities, is driving companies to reduce operating expenses and maximize data center cooling capacity. The industry has recognized that airflow management (AFM) is essential to both of these goals. Initially, a lot of focus was placed on managing the openings in the raised-floor to help deliver conditioned air to IT equipment. Today, it’s common knowledge to seal openings in the raised floor, such as those resulting from cable cutouts.
Now, data center operators are turning their attention to aisle-level AFM strategies. Aisle containment, hot and cold, is becoming more common. However, with all the focus placed on these aisle-level solutions, significant unsealed openings at the rack level are often overlooked. Similar to the holes in the raised floor, sealing these “holes” in the rack are crucial to a comprehensive AFM program, with or without the implementation of containment solutions. Two of these overlooked “holes” are inside the rack and one exists under the rack.
Calculating the Openings
The three main overlooked openings, two inside and one under the rack, are a problem to be fixed and an opportunity for increased cooling efficiency in the data center space. The following open area assessment of these openings will provide perspective for the importance of sealing them.
Inside The Rack:
Even though it is a well-known best practice to install blanking panels in open spaces between IT equipment in racks, many data centers have yet to install them and most have not completed the job. Considering the distance between mounting rails in a rack is approximately 17.7” wide and a single U space is 1.75” high, this results in 31 sq. in. of open area per U space. Assuming a conservative average of 10 open U per rack, an average rack has 310 sq. in., or 2.1 sq. ft. of open space. For each 100 racks, there are 31,000 sq. in., or 215 sq. ft. of open space. This is equivalent to the open area of 215 standard 25% open area perforated tiles, or 107 50% open-area grates.
The open space between server mounting rails and the sides, top and bottom of the enclosure is particularly important to seal. As these spaces are so close to IT equipment intakes, server exhaust air often circulates through these spaces and is ingested by IT equipment. A typical 42 U rack has an open area of 74” x 2” on each side of the rails. This equates to 148 sq. in. per side and approximately 2 sq. ft. per rack. This translates to 200 sq. ft. of open space per 100 racks.
Under The Rack:
Lastly, the space under a rack is also important to seal. A typical cabinet is approximately 2” above the raised floor. At 24” wide, the open area under each rack is 48 sq. in. This equates to 4,800 sq. in. or 33 sq. ft. per 100 racks.
Combined, these often-overlooked openings represent 448 sq. ft. of area per 100 racks. Any site that seals 448 sq. ft. of open aisle are will see significant improvements in IT intake temperatures and cooling capacity at the aisle level. Also any site that seals, or has sealed, these areas will be able to make changes at the room level to the number of running cooling units and set points for the cooling units that will reduce operating costs and increase cooling capacity at the room level.
Closing the Openings
For this reason, data center operators should consider the best ways to improve the efficiency of the cooling infrastructure and right-size data center cooling capacity. Open spaces at the bottom of the cabinet and between the mounting rails and side of the cabinet allow hot exhaust air to re-circulate to the front of the cabinet, where it is ingested by IT equipment. Sealing these openings will help to ensure conditioned air is delivered properly to IT intakes.
Even in a fully contained cold aisle, low raised-floor static pressure and open spaces in cabinets cause variances in intake temperatures. Conditioned air that reaches the aisle is lost through the open spaces in the racks. Servers pull exhaust air from the back of the racks through open spaces. Sealing cable openings improves the amount of conditioned air delivered through perforated tiles and grates. This increases the load that can be cooled. Efficiency improvements only come from reducing the fan speeds of cooling units or raising the temperature set points of cooling units. Operational savings occur when efficiency improves or when cooling units are turned off.
Depending on each facility’s circumstances, innovative sealing solutions can be implemented to avoid server exhaust re-circulation and prevent the loss of valuable conditioned air from the cold aisle or the inflow of hot exhaust air. A variety of solutions are available to address these openings and improve the cooling capacity of a data center. Industry products, like those developed by Upsite Technologies and designed specifically for AFM best practices, are foundational to any airflow management strategy. With or without aisle containment, products like rack panels, blanking panels, and brushes help conditioned air reach its destination, improve cooling capacity and reduce operating expenses.
Author: Lars Strong, Senior Engineer, Upsite Technologies
Lars Strong, P.E., a thought leader and recognized expert on data center optimization, leads Upsite Technologies’ EnergyLok Cooling Science Services, which originated in 2001 to optimize data center operations. He is a certified U.S. Department of Energy Data Center Energy Practitioner (DCEP) HVAC Specialist. Lars has delivered and continues to deliver value-added services to domestic and international Fortune 100 companies through the identification and remediation of dilemmas associated with the fluid mechanics and thermodynamics of their data center cooling infrastructure. Lars brings his knowledge and ability to teach the fundamentals of cooling science to numerous U.S. and international private and public speaking events annually.
