Economizer Methods: A Breath of Fresh Air for Data Centers

Conventional wisdom on data center cooling may be about to change. If this happens, centers could see substantial cost savings, positive environmental impact and simplification of cooling procedures.

For years, the standard in most data centers has been to keep these areas at a much cooler temperature than necessary by using compressor-based cooling systems. However, given the marked and rapid increase in energy consumption in data centers, this practice has come into question.

Changing standards for cooling
Until recently, the thinking was that server rooms needed to be kept at a constant cool temperature — typically averaging around 68 degrees. However, keeping data centers cool has resulted in significant energy use and steep costs. According to newer information, it might not be necessary to go to such great lengths. Newer information reveals that traditionally prescribed temperature ranges were based on older, less reliable equipment than we have today. Compared to equipment used in the 1980s and 1990s, today’s data center equipment is typically able to withstand higher temperatures.

In the past, an entire data center would be cooled, but current thinking is trending more toward only cooling key areas that tend to stay hotter. Newer data center designs designate some areas of the data centers as hotter areas and others as being cooler.

The fresh air method
A recently adopted practice in data center cooling, dubbed the fresh air method, involves using outdoor air to cool and increase air flow in data centers. The hotter air from the data center is flushed outside, and fresh air from outdoors is pulled inside. The fresh air can come from open windows or vents, and this method of cooling is especially useful when outdoor air temperatures are suitable for having windows open. This method is also known as air-side economization.

Water and air systems are the two types of economizer systems. A water system involves a dry internal heat exchanger or an evaporative cooling tower. An air system is a method of opening and closing windows, thus allowing fresh air to flow into and out of the data center. It also involves facility fans and external dampers.

A 10-month study by Intel revealed that not only can servers handle being cooled by outside air only, but when that method is used, the server failure rate is comparable to that in servers cooled in the conventional way. In the study, failure rate in an area cooled by air economizers was 4.46 percent, compared to 3.82 percent for areas cooled conventionally.

This happened even in an indoor environment with humidity fluctuating between 4 and 90 percent. Outside temperatures ranged from 64 to 92 degrees. Also, indoor conditions became dusty, and the only air filter used was a simple household filter. In other words, the fresh air cooling method was effective even under challenging conditions.

Benefits of fresh air cooling

Some of the most important benefits of fresh air cooling are energy and cost savings. In the Intel study, the fresh air method resulted in a 74 percent decrease in energy consumption, compared to the conventional method involving recirculated air. In a larger data center with high conventional energy expenditures, potential savings can translate into significant dollar amounts — in the six figures or higher.

Challenges and concerns

Although the fresh air method can be an option to seriously consider and one that results in significant benefits, some challenges do exist.

First, filtering particulates from air is a concern. It can be difficult to remove any contaminants when the windows are open and air flow is thus much less controlled than when indoor air is recirculated.

Another challenge involves monitoring temperature increases and humidity. Both of these factors can fluctuate widely and rapidly when outdoor air is flowing into the data center.

Finally, using outdoor air for data center cooling is most ideal in climates where temperatures are on the cool, moderate side so that windows can be open for more months of the year. The Intel study took place in a dry climate, and fresh-air cooling might be better suited to these conditions, rather than more humid climates.