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July 9, 2004 • Vol.26 Issue 28
Page(s) 5 in print issue

Heat Of The Moment
Data Center Climate Conditions Can Be A Major Key In High Availability

The biggest problem facing data centers today has nothing to do with security, connectivity, or storage. In fact, it doesn't have anything to do with data at all. The target in question? Climate control.

"It's gotten to be the most important thing in the data center," says Robert McFarlane, a data center design expert and president of the Interport Division at Shen Milsom & Wilke, an international consulting and design firm. "I did a seminar recently, and they did a show of hands as to how many people had cooling problems in their data center; 60% to 70% of their hands went up."

The problem has come to the forefront in recent years as server densities increase exponentially. In addition to providing the necessary computer power to run a modern IT network, these systems are creating a pesky by-product: lots and lots of heat.

"Manufacturers have been repackaging the circuitry into smaller form factors, and one way or another they are packing all of the heat into tighter places," says McFarlane, who stresses that most administrators are not prepared to deal with the newfound problems generated by this extra heat.

"Right now, millions of dollars of equipment is going in and burning up," McFarlane says. "These boxes are being handed to people who are data pros. They have got no education in mechanical engineering, fluid dynamics, or thermodynamics. Nor would one expect them to: They are experts at managing a network."

Lessons On Temperature & Relative Humidity

When it comes to data center climate control, there are two important measurements that will affect performance: temperature and relative humidity. As a data center designer for many years, Mark Welsko has been studying how each can affect equipment in the data center. In order to truly protect equipment, he warns administrators to treat the two as a single concern rather than two separate elements to be controlled.

"You must always tie temp and relative humid together as one entity," says Welsko, who leads Mission Critical Design for WES Engineering. "You can't look at temperature and humidity independently because when you adjust temperature you are also affecting the relative humidity."

As temperature increases, relative humidity decreases and vice versa. Both will affect equipment in different ways, making the control of each critical to maintaining high-availability systems.

At a high temperature and low relative humidity, the danger comes in two forms. The most obvious is from overheating. The other problem is from electro-static discharge. At ideal relative humidity, water ions act as a buffer between the equipment and potential sources of electrostatic discharges. When the relative humidity gets too low, that buffer is gone.

Most administrators go to extraordinary lengths to avoid the problems posed by overheating. But contrary to popular belief, there is also such a thing as overcooling equipment. "You need to remember that you are not trying to refrigerate your equipment," Welsko says. "You are just trying to remove the heat."

At low temperatures and high relative humidity, the dangers posed are mostly a result of humidity. When overcooled, equipment is exposed to a high amount of moisture that can promote the growth of salt deposits on conductive filaments in the circuitry. The result can be dysfunction or even short circuits.

In addition to these isolated dangers at each extreme, fluctuation between the two can cause additional problems. Even if average conditions are maintained at optimum temperature and humidity levels, you could be doing your systems great harm if these measurements vary considerably throughout the day.

"What you are going for are steady state conditions," says Welsko. "You don't want temperature fluctuating."

Where Your Center Should Be

According to Welsko, the ideal temperature and relative humidity combination should stand between 69 degrees and 73 degrees Fahrenheit and 45% and 50% relative humidity. The idea is to avoid irregular spikes or drops in either reading. And most importantly, these states are meant for the equipment, which means the closer you monitor the intake and exhaust at the rack level, the closer you will get to achieving optimum environmental control. "It is not the average room temperature that you should be looking at," he says. "It is what is going into your hardware that matters."

McFarlane and Welsko both note that after a short drop in popularity, subfloor cooling is still the preferred method of controlling climate in the data center. Welsko says that in order to truly maintain perfect conditions, administrators must abstain from a more-is-better attitude when it comes to placing perforated tiles on the floor. Because the subfloor works as a balloon, pushing cool air through the holes in the perforation, too many perforated tiles can actually degrade cooling performance.

Other common mistakes include not putting blank panels in the back of enclosures, which prevents air from reaching equipment at the top, and placing cables behind the exhaust outlets, which prevents proper airflow.

But above all, says McFarlane, the biggest mistake is believing all of the manufacturer hype. Administrators should always take claims of extraordinary cooling capacity with extreme caution, he warns.

by David Garrett

Keep It Cool

There is a dizzying array of climate control products on the market. The following are a sampling of some of the popular air conditioning products available.

AirPac (
The AirPac COOLIT2000 Series portable air conditioner is a fully functional unit for spot or entire-room cooling. The unit offers a programmable thermostat and timer for operational control. An optional handheld remote can also be added for easy ad hoc temperature control. Starting price: $2,925.

APC is one of the most trusted names in data center power and cooling management. In addition to offering the all-inclusive InfrastruXure line, there are hundreds of single product solutions available from APC. For smaller data centers, the PA4000 offers small-scale air conditioning with a huge install. Starting price: $3,499.

Liebert (
Emerson Network Power is another well-known player with its Liebert brand of air conditioners. The company recently introduced the Liebert XDO16 unit, a smaller, ceiling-mountable version of its existing XD line. The new unit is smaller than the other XD conditioners, offering supplemental coverage for larger centers in addition to small center coverage. Starting price: $2,000.

KwiKool (
A player in the portable cooling industry, KwiKool has taken pains to design a number of units for IT use. The KwiKool SAC 12043 is one such unit. It features KwiKool's I/O Integral Condenser system, which takes in air from an outside source to cool its condenser and then returns the hot air to an outside source, totally isolating the condenser section from the conditioned space. Starting price: $14,450.

Data Center Do's

Sometimes it can be difficult for data professionals to target their data center climates while still taking care of the rest of their day-to-day responsibilities. Mark Welsko, manager for Mission Critical Design at WES Engineering, offers the following pointers to keep your equipment safe from temperature and humidity fluctuations.

1. Set up appropriate goals for the room.

Welsko says that you need to set goals for intake temperatures and relative humidity before you do anything. Ideal settings should hover at 69 degrees and 73 degrees Fahrenheit and 45% and 50% relative humidity.

2. Make sure that you are maintaining appropriate subfloor pressure.

Cool air is pushed up to your equipment by taking advantage of the pressure differential between the subfloor and the rest of the room. Without a differential between 0.035 inches and 0.05 inches water gauge, there will not be enough airflow to make a difference.

3. Ensure proper calibration of the thermostat and humidostat in the air conditioner at all times.

If your air conditioner doesn't know the true conditions near equipment, it will never be able to properly control climate conditions.

4. Strategize when placing perforated tiles.

Placing perforated tiles too close to an air conditioner can fool the sensor into thinking that there is enough cooling when there isn't. Putting them too close to equipment can cause too much relative humidity and a resulting condensation that can damage equipment.

5. Practice caution when introducing outdoor air.

The ideal data center controls the introduction of outside air to a bare minimum. It must be done occasionally for proper circulation. Be careful not to dump this air directly onto your air conditioners, or you risk fooling the conditioner into thinking

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