Liebert engineering lab technician Duane Hornsby checks equipment in the company’s XD Lab, a specially designed 840-square-foot facility for simulating areas of extreme heat that are common problems in data centers. The lab has a raised floor and four aisles of server simulation equipment to recreate hot spots that occur in computer rooms.
CHICAGO — Ductless cooling systems have been chosen by many building owners for maintaining data centers and computer rooms. The ductless units take up very little room and provide the necessary cooling for these small spaces.

But in the last few years, a new problem has surfaced with many computer rooms that is making ductless systems even more of a necessity. The primary reason some computer rooms are in need of special cooling is because of the amount of heat generated from the systems. New servers and communication switches are generating more power, which in turn creates more heat.

According to Liebert Corporation, some of these new computer servers are generating up to 10 times the heat per square foot as they did 10 years ago. In many cases, newer systems installed alongside previous generation systems are creating hot zones. Older data center cooling methods often have difficulty properly managing these new areas of heat.

Liebert is one manufacturer that has been actively investigating methods to solve this problem. In fact, the company has introduced its Liebert XD™ family of ductless cooling products. According to Liebert, the new products provide supplemental cooling to help rid computer rooms of these problematic hot spots.

The graphic illustrates how the Liebert XDO system supplements existing cooling systems by eliminating hot spots in the upper parts of a data center.

Packing Power

As technology advances, computer servers get smaller and smaller, and are packed with more and more power. But more power in a small system can create a huge amount of heat generation.

Fred Stack, vice president of marketing for Liebert’s environmental products division, has seen more hot spots popping up in computer rooms across the country due to the upgrades in servers.

He also explained that this problem is still fairly new. The occurrences of computer room hot spots have started to increase dramatically since 2000.

“The power densities of computer systems have risen to levels that exceed the capacity of traditional approaches to cooling,” Stack said. “And that is creating hot spots in the data center that can reduce the availability of business-critical computer systems.”

The technological advances in computer servers and data centers do have positive aspects. As servers get smaller, less space is required. It also means that companies do not have to expand the dimensions of their data centers. Smaller computers have made it possible to pack in more servers in the same space.

Although this is a benefit, the drawback is that smaller, more powerful processing systems consume larger amounts of power.

According to Liebert, traditional data centers were designed to handle densities of about 100 watts per square foot. This could be accomplished and handled through traditional computer room air distribution, which utilizes a raised floor to exhaust the air upwards to the ceiling through perforated tiles. But now heat densities are exceeding 100 watts per square foot, creating heat levels that cannot be completely alleviated through the traditional raised-floor methods of air distribution.

Finding Solutions

There are things that building owners can do to try and dissipate hot spots, but some of these solutions can have drawbacks. Space between computer equipment can be spread out in order to control high temperature hot spots. This may help with hot spots, but will take up needed room in the data center.

Computer room air conditioning units (CRACs) can be installed in order to accommodate the increase in heat, but Liebert believes that this too will take away valuable data center space. Also, the manufacturer said that CRACs, when installed next to older equipment, could actually contribute to the problem. When the new equipment is generating more heat than the equipment around it, hot spots occur.

Liebert said that a mix of old and new equipment can create large variations in temperature across the whole data center space.

Finally, Liebert said that building owners can try to increase airflow through the raised floor. This can require raising the floor even higher, in some cases to impractical heights. Liebert believes this can be a drawback because it could impact temperature distribution and could require moving existing equipment until the new floor is installed.

Liebert came up with its own solution when it created a test lab back in January. The lab is an 840-square-foot facility with a raised floor and four aisles of server simulation equipment that recreates the potential extreme density heat scenarios that currently occur in many data centers. By replicating these hot spots, Liebert was able to evaluate how it could eliminate the problem.

“Our test lab enables us to scientifically evaluate the performance of supplemental cooling systems in the same demanding conditions our customers are facing,” said Stack.

The Liebert XD Test Lab uses heating coils within computer enclosures to simulate the average densities of up to 500 watts per square foot and zone heat loads of more than 1,000 watts per square foot. Fluid dynamic modeling is used to analyze airflow and identify the efficiency of several different technologies and system configurations.

The test lab helped the company develop its Liebert XD ductless cooling products, which have been manufactured in rack-mounted and ceiling-mounted styles. The new product uses a coolant pumping method that is new to data center applications and is more environmentally friendly. The XD coolant is pumped as a liquid, converts to a gas within the heat exchangers, and is then returned to the pumping station, where it again condenses to a liquid.

Liebert reports that its lab testing reveals that the new coolant is 80 percent more efficient than water-based systems and eliminates the risk of fluid damage in the event of a leak.

Stack also suggests that the Liebert XD ductless systems are simple to install. He said that both the ceiling- and rack-mounted units only require two pipes for the flow of the coolant, three small fans, and a coil.

Building owners and contractors have their choice of the Liebert XDA Air Flow Enhancer, the XDV Vertical Rack-Mounted Fan Coil, and the XDO Overhead Fan Coil.

Both the rack-mounted and ceiling-mounted units aim to solve the problem of hot spots, but they have different ways of doing it. The XDA and XDV will draw hot air directly from the rack or from the hot aisles in the data center. Inside the XDV, air is cooled as it passes through the coil and cold air is exhausted into the cold aisle where the computer air intakes are located.

On the other hand, the XDO unit takes the hot air from the equipment in the room through the coils on the sides of the unit. Air is cooled in the coils and exhausted vertically down into the cold aisles where the equipment intake is located.

For more information, visit

Publication date: 06/16/2003