At CyrusOne our largest source of greenhouse gas emissions comes from the electricity we consume. One large consumer of electricity is the fans within our data halls that run 24/7 to circulate chilled air and cool critical electronics. To help create a more sustainable future, we have worked to reduce electricity consumption from these fans.
One way we’ve done this is to use sensors to determine how much air needs to be moved, and then control variable frequency drives on the fans to increase the speed to “just enough” to meet the needs of our customers, rather than running them at full speed 24/7. Why does this simple act of turning down the fans save so much energy? Well, the answer lies in the physics of air resistance.
The resistance of air on the fan blade (how hard it is for the fan blade to push through the air) is a function of its speed. This relationship can be felt with a simple hand fan as well: try fanning yourself at different speeds and you’ll notice how much harder you have to work when increasing the speed! Specifically, this relationship between speed and energy is cubic, meaning that doubling the speed (x2) increases the energy demand eight-fold (x23 or x2x2x2).
Applying this principle in our data halls, we can use variable frequency drives to operate fans at lower speeds rather than a binary maximum speed or off! For instance, we’re far better off operating three fans at 33% speed, rather than one fan at 100% speed, even though the same volume of air is moved. This enables us to reduce fan speeds to specific points and avoid consuming additional electricity for faster speeds. But if we have a short-term increase in server heat, the extra fan speed is available to throttle up, take care of the heat, then return to lower, more efficient speeds. It’s just one more way that we work to deliver the right cooling to the right place at the right time.
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