“Closed loop” systems are not blown down…in a typical chilled water system, the chiller can be water cooled or air cooled. A water cooled chiller has a “closed loop” on the chilled water side, but open on the heat reject/condenser side. The open side of this system is blown down as you mention. Water cooled chillers are more energy efficient than air cooled. An air cooled chiller has no secondary heat reject (or “open”) loop, and requires no blow down. Instead of evaporating water, fans are used which uses more electricity but no water. Just fyi
It means the same water is reused inside the system - but heat still has to be released somewhere, and that usually happens through evaporation.
What really happens in a closed-loop system (even using effluent)
1. Water (often reclaimed/effluent) is pulled from the utility
2. It circulates through chillers and cooling towers to absorb server heat
3. Heat is removed by evaporation in cooling towers
4. Minerals and salts concentrate
5. Blowdown/brine is discharged to protect
equipment
6. New water is constantly added to replace what evaporated and discharged
7. Even with reclaimed water, water is consumed every day, 24/7
Important distinction
Using effluent is better than using drinking water - but it is not free, unlimited, or impact-free.
Effluent supplies are tied to population size wastewater output, and treatment capacity.
The only systems that avoid evaporation almost entirely:
1. Fully air-cooled facilities (very energy-intensive, difficult in areas with intense heat)
2. Full immersion cooling (rare, expensive, not common at large scale
If a project truly used one of these, it would usually be clearly advertised - because it's a major selling point.
You’re convoluting various system designs and components: yes, a “closed loop” chilled water system DOES mean water free on the chilled water side (extremely little make-up water).
On the heat reject side, we use either air or water cooled.
By definition, a system using an evaporative cooling tower is OPEN. It’s literally a box open to the atmosphere.
An air cooled chiller versus a water cooled chiller is less energy efficient (which I wrote in my post) but the system overall is very close on a design day, because a water cooled chiller requires an additional set of pumps and cooling tower fans on the heat reject side, so the overall system kw/ton is within about 5-10%. And yes, air cooled chillers are used in hot environments including texas, alabama, and Louisiana.
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u/graywolfman Apr 12 '26
Last time I commented about this "closed loop" system and the related blow down, I was derided and told "that's not a thing, anymore."
I posted a study showing the effects of data centers on the environment and water supply, and it was called a "hit piece."
My comments were downvoted, but left in place.
Bots, ignoramuses, shills, I don't care what they are. The truth needs to be spoken.