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Humidity
Datacenter cooling systems must also be able to adapt to exterior temperature and
humidity. Because these factors will change depending on where on the globe the
datacenter is located—along with the time of year—datacenter air-conditioning systems
must be able to adapt to these sorts of changes.
Too much humidity can wreck your datacenter equipment. Too little humidity can wreck
your datacenter equipment. Use these tips to help keep your datacenter at the right level:

• Establish a humidity sensor calibration schedule Humidity sensors drift and
require frequent calibration—more so than temperature sensors. Also, incorrect
humidity sensors are less likely to be noticed than incorrect temperature sensors. As
such, establish a frequent test and calibration schedule for your humidity sensors.
• Allow for sensor redundancy Make sure you have enough sensors to keep an eye
on your datacenter’s humidity level. To ensure a tight control, multiple sensors
should be used. At the very least use two, but more are better.
• Manage humidity with a dedicated unit If ventilated air is used (maybe from an
air-side economizer), control humidity with a single ventilation air handler.
• Lock out economizers when necessary When using an air-side economizer,
minimize the amount of air that’s brought in when the dew point is low. This saves
money on having to humidify the dry air.
• Centralize humidity control Each datacenter should have its own centralized
humidity control system. Multiple systems wind up fighting each other, and the
system becomes less efficient.

Adding Cooling

If your datacenter is especially “equipment dense,” you’ll need to add some extra cooling
capacity. The best way to cool your equipment is to make sure the cooling gear is as close as
possible to the heat sources. When you decide how to supplement your cooling systems,
you should consider what type of system to use (air or fluid based) and what type of design
the system will use.

Fluid Considerations
As anyone with a car knows, fluid is a great way to move heat from equipment (in this case,
the engine) to keep it cool. As anyone who has ever left their cellular telephone in a pocket
as it went through the wash knows, electronics and water don’t mix. That’s not to say that
fluid-based cooling systems have no place in datacenter environments. It just means you’ve
got to use care.
Of course, water isn’t the only fluid used for cooling. Though water is normally used in
floor-mounted cooling, because of safety concerns, R134a refrigerant is typically used when
cooling is used closer to the equipment. This is because refrigerant turns into a gas when it
reaches the air, so leakage doesn’t pose a threat to your equipment. Table 4-3 lists the
advantages and disadvantages of both solutions.
However, it isn’t just safety and effectiveness that makes refrigerant a good match
for cooling needs. Fluid solutions employ microchannel coils for better efficiency, and a