Why do datacenters continuously use more water instead of recycling the same water in a closed loop system?
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It all leads back to heat exchange and thermodynamics.
First, not a datacenter guy – so I’m not overly familiar with the details of their cooling water setups. But here’s my best attempt…
Something like a datacenter generates a lot of heat. Water is a great (and generally cheap) way of exchanging heat. Closed loops can effectively do this, but even with refrigerants heat doesn’t just go away. You need a way to cool that closed loop as well. Evaporation is a tried and true way to cool off something. Like other posts have eluded to, that’s how our bodies works. We sweat, the sweat evaporates, and the temp of our body decreases.
Cooling towers use this same principle. They spray water in an environment that has airflow (generally through the work of a fan, but hyperbolic cooling towers use some even “cooler” science to create the same effect, if you’re ever interested in researching those). By creating airflow and an increased surface area of the water you’re increasing the evaporation rate of the water.
However, the water leaves behind a lot in the process of evaporating. All those solids in the water stay in the the open water loop. Also, things like alkalinity and microbiological growth begin to change. This combo can lead to scale, biofilm, and corrosion which are detrimental to heat exchange. The solution to this is dilution. You send the concentrated water down the drain and make up water with the water source of choice. It’s generally most cost effective to use whatever water source the plant uses as a whole. You can soften the water, use reverse osmosis, deionize or distill the water to decrease water usage, but often times that costs significantly more than using a raw water source and then you’re still concerned about how corrosive the water is to the the metallurgy of the system. And something like reverse osmosis still dumps all the concentrated water down the drain, so you aren’t getting a huge payback on water usage.
All that being said, the main cause of water usage is evaporation. Which is again the most reliable way to cool water that then cools the closed loop. If there was a solution to the fundamental laws of thermodynamics where heat could disappear without the loss of something else (in this case water), then that problem solver would be generationally wealthy. But as it stands today you have to give up something in order to get rid of heat. So far, the best answer we’ve come up with is water. Now, that evaporated water does go back into the hydrologic cycle, but it’s still a drain on water sources like Lake Mead and other non renewable fresh water sources, so it’s far from perfect.
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