Data Center

Rack-Level Cooling Strategies

Mike Peterson

As a data center infrastructure expert, we provide data center cooling tips to eliminate hotspots and reduce energy use, protect equipment and your bottom line. By controlling data center temperatures and airflow, you reduce power usageoften the highest monthly data center expense.

In this blog, we share two important rack-level cooling strategies.

  1. Basic, low-cost thermal improvements to close physical gaps to cut costs & gain easy energy-efficiency wins
  2. Improvements at the aisle level to contain & separate hot/cold air

This blog is the last of our three-part series, discussing data center cooling at the rack level. As technology continues to tax data centers through applications like virtualization and cloud computing, power rack density requirements are rising – which leads to thermal management challenges.


With hot racks, the hot air generated inside the rack may leak out and impact a different rack, slowing down the entire

cooling process. Chimney containment manages this problem by mounting a metal chimney on the top rear of a rack, efficiently capturing and redirecting heat exhausted from rack equipment to a CRAC unit via ductwork or an air return layer.


This containment method completely removes hot air from the occupied space inside your data center, allowing the entire room to feel cooler. This can also lower operating costs, so you’re not paying to over-cool the space to keep temperatures comfortable.


Chimney containment is also very versatile; you can install chimneys on a one-to-one basis (one chimney per rack) or as a system (one chimney per several racks). Chimneys can be removed, added or moved as data center density grows or shrinks.


The only decision you have to make: passive or active chimney containment


Option 1: Passive chimney containment

Using the natural convection of hot air rising, a passive chimney containment system allows CRAC return fans to draw exhausted hot air to cooling coils. This prevents hot air from mixing with cold air that enters the front of the cabinets, ensuring that the hottest air gets back to the CRAC unit and that the cold air remains cold.


Passive chimney containment works best in lower-density racks (between three and eight kilowatts). Make sure that you’ve implemented the suggestions for basic thermal management improvement before investing in passive chimney containment. For example, if you haven’t installed blanking panels to keep cold air from bypassing equipment and mixing with hot exhaust air, you won’t gain the maximum efficiency possible.


Option 2: Active chimney containment

Active chimney containment works similarly to passive chimney containment with the addition of components to actively move air from the hot aisle to the CRAC return.

Depending on the type of active chimney selected, different active components move the air. The Belden active  Adaptive Enclosure Heat Containment (AEHC) System uses variable frequency drive (VFD) fans and a control unit that adjusts fan speed based on rear-cabinet air pressure vs. temperature. This allows the controller to detect a change in pressure when new equipment is added to a rack, automatically increasing fan speed.

Why measure pressure over temperature? When individual servers increase output to keep cool during high demand, the rest of the rack may sit idle. Although the average temperature in the rack may not increase, there is an increase in air pressure. By responding to the demand created within the rack, heat rejection always matches the load.

Remember: No matter what the approach, a containment system won’t work without covering the basics to close gaps in your data center.

Through CFD modeling, Belden can show you how rack-level chimney containment will impact your data center environment. Belden also offers a variety of data center solutions for chimney containment that help reduce cost, improve uptime and minimize energy usage.