数据中心蒸发冷却是否仍具合理性？

Cooling tower for a data center

Evaporative cooling can use roughly 20,000 to 50,000 gallons of water per day for every 1 MW of IT load, making water consumption a growing concern in data center markets.Getty Images

Water use has surged to the top of the list of community concerns around new data center development. In many markets, it now rivals power demand as a flashpoint for residents and local officials evaluating new facilities. Stories about data centers consuming enormous volumes of water circulate widely in neighborhood forums and on social media and have become a common argument against new construction, especially in drought-prone regions.

The concern is not unfounded. According to a report by Media Analytics Ltd., a data center with a 1 MW IT load using evaporative cooling can consume roughly 20,000 to 50,000 gallons of water per day. At that rate, a 10 MW facility could use 200,000 to 500,000 gallons per day, a 100 MW site could consume 2 million to 5 million gallons per day, and a 1 GW facility could use 20 million to 50 million gallons per day, depending on design and operating conditions.

With numbers like that, the obvious question is: why would any operator still choose evaporative cooling?

The answer is that while evaporative systems are water-intensive, they still offer meaningful advantages in cost and energy performance under the right conditions.

Evaporative cooling remains widely used because it can reject large amounts of heat more efficiently than dry cooling alone. In a typical setup, heat from the data center is transferred to water circulating through a cooling tower or a similar heat-rejection system. As a portion of that water evaporates, it carries heat away, and the remaining water is collected and recirculated. It is the same basic principle the human body uses when sweat evaporates and cools the skin.

The tradeoff, of course, is water consumption.

The Tradeoff: Water Savings vs. Energy Efficiency

Matt Green, CEO of HVAC firm Brucker, said one reason open-loop evaporative systems remain in the market is simple: first cost.

“Now, there are some reasons why open-loop cooling still exists, and it’s really driven in many cases by upfront first cost, so an open cooling tower is going to be less expensive [than a closed-loop system],” he said.

Green estimates that an open-loop system can cost 60% to 70% less upfront than a closed-loop alternative with comparable heat-dissipation capacity. That difference is largely driven by the amount of copper, aluminum, and other materials required in a dry cooler used in a closed-loop design.

Over the life of the system, however, Green argues that the economics shift. In data centers with long operating hours, he said, closed-loop systems have a lower total lifecycle cost than evaporative cooling systems once water use and ongoing operating expenses are factored in.

Brendan Mark, CEO of Capture H2O, a cooling and heating water treatment provider, makes the case from the other side of the ledger. He argues that evaporative cooling retains an important advantage in energy efficiency.

“Water-cooled systems, as opposed to closed-loop air-cooled systems, are about 25% to 40% more efficient from an energy perspective,” he said. “So, there’s a tradeoff. Yes, you are using less water, but you are using more energy.”

That tension between water and power is central to the debate. A closed-loop system may sharply reduce evaporation, but it typically requires more fan power and can be less effective at rejecting heat during extreme conditions. Evaporative systems, by contrast, can deliver better thermal performance with lower energy use, particularly when ambient conditions favor evaporation.

Ashlesa Mohapatra, quality manager at ServerLIFT LLC, which makes equipment for moving data center hardware, said operators should evaluate the full design picture before choosing a cooling architecture. That includes the facility’s power profile, capital budget, climate, and long-term operational impacts.

“You should look at the amount of power that your data center is taking,” Mohapatra said. “You should look at how much money you’re willing to invest in worn-out hardware due to the evaporative systems that you’re installing.”

Mohapatra also noted that while the cooling water is not in direct contact with IT hardware, water-based systems still introduce maintenance considerations and mechanical wear that should be accounted for in total cost calculations.

Mohapatra estimates evaporative cooling can use 10% to 35% less electricity during peak summer conditions than closed-loop alternatives, though the exact savings depend on climate and system design. For that reason, she does not treat the choice as absolute. Closed-loop systems are strong on water conservation, but evaporative systems can still make sense when energy efficiency is the higher priority.

Green is more skeptical. In his opinion, if an operator has the space and can absorb the higher upfront cost, there is little reason not to move to closed-loop systems.

“If you’ve got the space and you’ve got the additional capital that you can spend upfront to get the return on investment over the life cycle of the product, [non-closed-loop] technology really should not be used in this application,” he said.

He also argues that many companies stick with evaporative technology because it is familiar.

“A lot of individuals stick with what they know because it’s worked in the past, and they don’t want to absorb a perceived risk of changing technologies on something that’s been proven to work for them,” Green said.

Mark, however, defends evaporative technology on performance grounds.

“In a closed-loop system, you’re literally blowing air over a set of tubes that has some sort of fluid running through it,” Mark said. “That tube is not going to be able to reject the heat as effectively as evaporative cooling.”

Climate and Geography Change the Equation

Mohapatra takes a more situational view. In regions with abundant water supply, evaporative cooling may remain a practical option, particularly if the facility is near a major lake or river and local water availability is not under stress. That does not eliminate political or environmental concerns, but it can make the tradeoff easier to justify from an operational standpoint.

Climate also plays a major role. Evaporative systems generally perform better in hot, dry environments than in humid ones. In places such as Arizona, evaporation happens more readily, making the system more effective. In a humid environment such as Orlando, Florida, the air already contains more moisture, so evaporation becomes less efficient and the system has to work harder to achieve the same cooling results.

“Evaporative works on the principle that the water actually evaporates,” Mohapatra said. “So, when it’s already humid out there, and there’s a lot of moisture in the air, it takes more energy to pull the water and evaporate it into the atmosphere.”

Where Cooling Strategy Goes Next

Green believes open-loop evaporative cooling’s days are numbered. As chipsets get hotter and cooling requirements become more demanding, he expects the market to shift increasingly toward closed-loop cooling systems, such as dry or adiabatic coolers.

“I think we will, with the new chipsets that we’re seeing, be fundamentally shifted to almost exclusively closed-loop cooling systems,” he said, adding that open-loop systems will gradually disappear.

Mark is less categorical. He believes water-cooled approaches will remain part of the conversation and may become more politically acceptable again as the debate matures and the industry becomes more precise about how, where, and why water is being used.

“I think it’ll be more politically acceptable to look at water-cooled systems in the next 12 to 24 months,” Mark said. “But as we know, this space moves really quickly.”

Mohapatra sees a hybrid future rather than a single winner. In that model, evaporative cooling could help facilities manage peak summer demand. In contrast, liquid cooling and other closed-loop systems handle most day-to-day thermal loads more efficiently and in a more compact form.

“We’re going to have some features of evaporative cooling that will allow us to use it in peak summertime, wherever the data center is,” Mohapatra said. “And then there will be liquid cooling … running through the racks most of the time, but it won’t be bulky. It’ll be really quick and something more compact.”