How to Beat the Heat

“Close the door! We’re not paying to air condition the whole neighborhood!”

Turns out that the universal parent rant about energy conservation actually had practical applications for the modern data center industry. Over the past decade, the continued development of aisle containment techniques that prevent cold air from mixing with hot has contributed to significant reductions in data center energy consumption.

Ten years ago, data center power usage had reached nearly unsustainable levels. A report from the Natural Resources Defense Council (NRDC) estimated that U.S. data centers were consuming 91 billion kilowatt-hours (kWh) of electricity each year, enough to power more than 7 million homes. Additionally, the report projected that data center electricity usage would rise to 140 billion kWh by 2020 at a cost of about $13 billion annually.

That has not been the case, however. A recent analysis published by Statista shows data center energy usage trending downward. After reaching a high of about 97.6 billion kWh in 2015, data centers used only about 33 billion kWh in 2021.

Broad Acceptance

It’s no coincidence that those energy savings parallel the increased use of aisle containment strategies. The technique wasn’t an immediate hit when it first emerged in the 1990s, but it gained favor once energy costs began increasing. Today, it is estimated that more than 85 percent of global data centers have implemented either hot- or cold-aisle containment. 

While aisle containment isn’t always easy to implement, the basic concept is pretty simple. Alternating rows of server cabinets are arranged so that cabinet fronts face each other, which helps prevent hot exhaust air from being drawn into the equipment. Aisles between the rows are closed off at each end and across the top, keeping cool air in and hot air out.

This arrangement allows for both focusing the cooling provided to the IT equipment as well as concentrating the heat which needs to be ejected from the data center space.  By bringing exhaust (hot air) directly to the cooling unit returns, the cooling units operate more efficiently as the space they’re cooling isn’t “mixing” air.  

The technique has been instrumental in the development of high-density data centers that increase the computing power — and the electricity consumption — of each server cabinet. The high-density approach reduces real estate costs and simplifies management. More importantly, it allows more processing power in less cabinet space, which makes it possible to handle today’s high-performance computing applications.

Traditional data centers typically use about 4 kWh per cabinet, but high-density data centers push that to between 7 kWh and 15 kWh by loading multiple blade servers or microservers into a single chassis. Such density is largely possible due to the ability of containment systems to maximize cooling. Analysts say a properly designed containment system can actually reduce energy expenses in high-density environments by up to 40 percent by increasing cooling capacity.

Go With the Flow

However, even well-designed systems can fail to meet expectations without practices that support effective airflow management. For example, leaving cabinet space open for future growth can allow cool air to leak through or hot air to be recirculated. That can cause air supply temperatures to rise 10 degrees or more — an increase that could cause equipment to fail. Also, by not actively exhausting hot aisle exhaust to the cooling unit returns, over time hot-aisle pressure can build to the point where the hot air is fighting the cold air trying to enter the fronts of cabinets.  

The following suggestions can help ensure proper airflow, preserve hardware and keep containment systems working properly:

• Use horizontal blanking panels to cover all empty spaces between hardware for optimal cooling efficiency.
• Use vertical blanking panels on the sides of cabinet frames to cover spaces used for cable pass-throughs.
• Use a cable management solution to organize power and network cables to avoid blocking airflow.
• Use gasket material between cabinets to seal off hot and cold zones.
• Install cable collars or similar devices at all underfloor openings to keep power and network cables properly aligned.

Rahi is a leading provider of data center infrastructure solutions, including aisle containment and other cooling systems. Contact us to learn more about closing the door on rising energy costs.