While precision cooling units provided reliable control of room temperature, humidity, and airflow, they were not enough to address the rising heat density at this data center. A complete solution included row coolers, a chiller, and a utility rebate.


Founded in 1993, CDW Berbee is a provider of IT solutions, including unified communications, security, remote managed services, information worker solutions, and more. The company’s data centers support host applications, co-location, and managed services for clients nationwide.

With offices spread throughout the Midwest, the company currently operates two enterprise data centers built on a redundant infrastructure to provide 24/7/365 managed services to customers worldwide. The data centers - located in Madison, WI, and Minneapolis - together include more than 24,000 sq ft of space.

When CDW Berbee began delivering managed services in 2000, the demands on its data centers skyrocketed. Not only did the data centers have to support additional technology, but they were also integral to the solution CDW Berbee was offering its customers. Downtime wouldn’t just impact internal operations; it would impact customer support.




When Planning Was A Luxury

Growth in the managed services business came so quickly that adequately planning for growth was a luxury Wayne Rasmussen, CDW Berbee data center manager, didn’t have. His attention was focused on addressing the challenges caused by rising densities and growing customer needs, most notably regarding cooling.

“Five years ago, I stayed up nights worrying about how space constraints would hinder my business and data center growth. But with form factors shrinking, concerns about space were replaced by concerns about heat density,” said Rasmussen. “All of a sudden, I was laying awake at night worrying about rising heat density.”

“Hotspots were a major issue in my data center. It was a challenge just trying to maintain a consistent temperature throughout the room. There were days when I had some units at 63°F and others between 78° and 80°. It’s not equipment-threatening level yet, but it is worrisome - and not energy efficient.”

The 12,000-sq-ft data center was arranged in a hot aisle/cold aisle configuration and featured a 9-in. raised floor with approximately 600 racks and 30 blade center chassis, each averaging 10 blade servers. It was cooled by 10 30-ton Liebert Deluxe System/3 precision cooling systems in a downflow configuration and the power protection was provided by Liebert Series 610 UPS systems. It also utilized the Liebert SiteScan critical facility monitoring system and a Liebert FPC power conditioning and distribution cabinet. While the precision cooling units provided reliable control of room temperature, humidity, and airflow, they weren’t enough to address the rising heat density.

“We installed additional CRAC units along the wall, but that was only a partial solution, and there was a limit to how much air we could push through the floor,” said Rasmussen.

Rebate Plays A Key Role

Rasmussen realized that the only way he was going to solve his hotspot problem was moving the cooling closer to the heat source, and he looked at a variety of supplemental cooling solutions. But it wasn’t until he talked with Eric Ollerman and Andrea Janssen from Data Center Systems, Inc., a local representative for Liebert critical support systems and services, that he found a solution.

The team also explored an opportunity to receive a rebate from local utility company Xcel Energy for installing the Liebert XDH in the CDW Berbee data center. This would be the first time this utility offered such a rebate for utilizing the Liebert XD system for data center cooling.

In July 2007, eight 20 kW Liebert XDH horizontal row coolers and one 160 kW Liebert XDC coolant chiller were installed. The XDH draws in air from the hot aisle through the rear of the unit and discharges cool air into the cold aisle where the electronic equipment air inlets are located. Because the XDH draws directly from the hot aisle, it takes advantage of higher heat transfer efficiency.

The indoor XDC coolant chiller connects directly to the XDH and provides coolant circulation and control while maintaining the coolant at a temperature always above the actual dewpoint. The pumped refrigerant turns into a harmless gas in the unlikely event of a leak.



Reaching A Consistent Level

Rasmussen now maintains a consistent temperature throughout his data center. “For the most part, we are keeping them all at 72°. This is such an outstanding improvement that we have another Liebert XD system planned for next year.”

The initiative with Xcel Energy resulted in a rebate of $1,725 based on the documented energy savings and energy efficiencies of the Liebert XD system when used appropriately with traditional computer room cooling. By deploying the Liebert XD system, CDW Berbee was able to save 11 kWh in operating costs. ES