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Air-side economizers
bring air in from the outside

Server Server Server

FIGURE 4-2 Air-side economizers draw in outside air to cool the datacenter.

The sensors measure air temperature both inside and outside the building. If it notices
that the outside air is suitably cold enough to cool the datacenter, it will adjust its dampers
to draw in the outside air, making it the main source of cooling.
This cuts or eliminates the need for the air conditioning system’s compressors, which
provides a big cost savings. This is illustrated in Figure 4-2.

NOTE Air-side economizers also have exhaust air dampers to prevent the building from becoming
overpressurized when outside air is pumped in.

Not everyone is in love with air-side economizers. Their main beef is over contamination
and humidity levels. Because the economizers are drawing air in from outside, pollution can
potentially enter the datacenter. A larger concern is the change of humidity in the datacenter.

NOTE It’s not recommended to use an air-side economizer in your datacenter unless an engineering
evaluation of the local climate and contamination conditions has been performed.
If air-side economizers are something your organization wishes to employ, you should
consider air filters and supplemental humidification. However, what you spend on filtration
and humidification might be more than if you just used your regular air-conditioning system.

Fluid
A water-side economizer utilizes evaporative cooling (usually provided by cooling towers) to
indirectly produce chilled water to cool a datacenter when outdoor conditions are cool
(often at night). This is best for environments with temperatures below 55 degrees
Fahrenheit for 3000 or more hours a year.
Using economizers, chilled-water-plant energy consumption can be cut by up to 75 percent.
You will also see reductions in maintenance costs, because the fluid-chilled cooling system
allows you to drastically reduce—maybe even completely eliminate—the need for chiller
operation.
Water-side economizers are especially beneficial, because not only do they save costs,
but they don’t allow contaminants or altered humidity levels into the datacenter.