Why data centres consume water
A server turns almost all the electricity it uses into heat. That heat has to leave the building. Many data centres do this by evaporation: cooling towers or adiabatic systems cool air or water by evaporating water, much as sweat cools the skin. It works well, but the evaporated water is lost to the area, and it has to be replaced continuously.
In a country where fresh water comes from desalination, that water first cost energy to produce. Cooling by evaporation then means consuming two scarce resources at once.
The closed loop: heat travels, water does not leave
In a closed loop, a fluid circulates continuously between the servers and the outdoors, without ever being exposed to the air. It picks up heat in the halls, carries it to exchangers placed outside, gives it up to the ambient air, then returns. The same fluid goes round indefinitely: nothing is drawn, nothing evaporates.
The outdoor exchangers are dry coolers: large finned coils through which fans push air. They work like a car radiator, at the scale of a building.
What desert heat changes
A dry cooler cannot cool a fluid below the temperature of the air passing through it. When the outside air is very hot, two answers combine. The first is to size the exchangers for the hottest days of the site, not for an average. The second is to use a refrigeration cycle, as in an air conditioner, to reject heat into air that is hotter than the fluid being cooled. That cycle uses electricity, but still no water.
Liquid cooling helps here in another way. Graphics processors tolerate a coolant far warmer than the air of a conventional hall. The warmer the liquid comes back, the easier it is to cool it with outside air, even in midsummer.
The price to pay, and why it is worth it
Cooling without water takes more exchange surface and, at the hottest hours, more electricity than an evaporative system. It is a deliberate trade-off: energy can be generated on site, whereas water, in an arid region, is always taken from someone. A campus that consumes no water does not depend on a water network to run either, which removes an operating risk.
How to verify it
The indicator is called WUE: the water consumed compared with the energy of the IT equipment. On a campus cooled in a closed loop, it is zero. Ask for it to be measured and reported over time, on the same footing as energy efficiency: a promise is checked against readings, not against a brochure.
Key points
- Evaporation cools well, but it consumes water continuously.
- A closed loop carries heat to the outside air without drawing or evaporating water.
- In a very hot climate, it takes exchangers sized for the peaks and a refrigeration cycle.
- WUE, measured over time, proves that no water is consumed.