Keeping a data center cool is no small task. In today’s world of rising rack densities, hyperscale infrastructure, and sustainability mandates, cooling decisions ripple far beyond the server room. They impact operating costs, uptime, energy consumption, and the long-term scalability of your facility.
Two technologies dominate the conversation: direct evaporative cooling (DEC) and liquid cooling (LC). They approach the same challenge—heat removal—from two very different directions. One cools the air. The other cools the equipment. And in many modern data centers, the smartest move is to use them together.
At their core, both systems exist to do one thing: remove heat efficiently. But the way they do it is fundamentally different.
Direct evaporative cooling is a straightforward, time-tested method that uses the evaporation of water to reduce air temperature. Outside air is drawn through wetted media—typically cellulose or glass fiber pads—and the heat in the air is used to evaporate the water. This process cools the air, which is then circulated through the data hall. It’s a remarkably efficient approach in dry or low-humidity climates, with fewer moving parts and a low energy footprint.
Liquid cooling, by contrast, skips the room entirely and goes straight to the source of the heat: the chips. In these systems, a liquid—often water, glycol, or dielectric fluid—is circulated through cold plates or immersion baths, drawing heat away from the electronics. That heat is then transferred through a heat exchanger and released. The loop is closed, precise, and incredibly effective in high-density environments.
The right choice depends on your workload, your geography, and your thermal density.
Direct evaporative cooling is ideal for bulk air cooling in data halls where compute densities are modest—typically in the 15–25 W/ft² range. It’s widely used in hyperscale facilities in dry climates and where simplicity, low cost, and energy efficiency matter. It also scales well, making it a smart choice for large-volume deployments where facility-level cooling is the priority.
Liquid cooling is designed for precision. It shines when rack densities rise above 50 W/ft², or when workloads like AI/ML and HPC push thermal loads into triple digits—sometimes exceeding 1,000 watts per server. In these cases, air just can’t move heat fast enough. LC systems deliver high-performance cooling directly at the point of need, with minimal airflow or external dependency. They’re especially valuable in sealed environments, high-humidity regions, or where facility space is limited.
When you evaluate cooling systems, it’s not just about whether they can keep the chips cool. It’s about how efficiently they do it—and what that means for your sustainability goals, energy budget, and long-term planning.
From a sustainability standpoint, both approaches have their merits. DEC systems consume very little power and can be extremely water-efficient in the right climate. Their carbon footprint is low, especially in regions where renewable energy and clean water are abundant.
Liquid cooling systems, while more energy-intensive, offer the potential for waste heat recovery—a growing priority in hyperscale and enterprise data centers. They’re also less impacted by climate conditions, making them a compelling option in locations where temperature or humidity render evaporative methods less effective.
When it comes to choosing between DEC and LC, resource usage is one metric to look at — but it’s not the only factor to consider. PUE, WUE, CUE, and ERE are important, too.
Power Usage Effectiveness (PUE) PUE measures energy efficiency. A lower PUE indicates high efficiency.
Water Usage Effectiveness (WUE) WUE measures water efficiency. A lower WUE indicates greater water efficiency; for example, a WUE of 0 indicates minimal to no water usage.
Although LC systems use less water in the data center, overall water impact for an LC system should take into account the water used to create the electricity needed to operate the liquid cooled system. In many cases, LC’s overall water usage can be similar to DEC systems’ water usage.
Carbon and Energy Reuse Metrics (CUE, ERE) Carbon Usage Effectiveness (CUE) measures how efficiently a system captures and re-utilizes carbon. Energy Reuse Effectiveness (ERE) measures how efficiently a data center reuses or repurposes energy within its facility. In both metrics, the lower the number, the better it is for the environment.
Sustainability, energy efficiency, and usage metrics can provide guidance on which cooling approach and systems will be most effective for a data center. Ultimately, the environmental impact and performative results of either solution depends on its environment and how it’s deployed, maintained, and integrated into the broader facility design.
Beyond performance, cost plays a factor when considering which approach is best for cooling a high-performance data center.
Capital Costs DEC systems are simpler to install and generally cost less upfront. Equipment is more straightforward, and installation doesn’t require complex fluid handling infrastructure.
LC systems demand more upfront investment. Pumps, manifolds, cold plates, monitoring systems—it adds up. But in high-density environments, the payoff comes in the form of smaller footprint, higher performance, and the ability to host workloads that would otherwise require massive air cooling infrastructure.
Operating Costs DEC uses minimal energy but consumes more water. It’s climate-dependent—great in dry areas, less so in humid zones. Routine maintenance includes water treatment and periodic media replacement every 3–5 years.
LC systems consume more electricity due to pumping and heat exchange, but they’re more consistent across climates. Maintenance involves managing coolant purity, testing for leaks, and maintaining system seals and sensors.
Complexity and Risk DEC is mechanically simple and highly reliable when maintained properly. Maintenance costs, materials, and the required labor is cheaper and more readily available.
LC is more complex and requires careful planning—but when designed correctly, it’s robust, scalable, and incredibly precise. Beyond the sophisticated, interrelated systems that are used in direct-to-chip and immersion cooling applications, there are hidden costs in maintaining these systems; for example, liquid cooling systems require complete water treatment approaches that can add ongoing costs to the overall facility operating budget.
Beyond costs, your facility’s geography matters a lot.
DEC performs best in dry climates with relative humidity below 60%. It struggles in coastal or humid environments, where the wet bulb depression is small and the system can’t deliver enough cooling. It also requires attention to water chemistry: scaling from hard water can reduce performance unless treated effectively.
LC is largely climate-agnostic. It performs just as well in humid Miami as it does in dry Phoenix. And because the fluid is recirculated and sealed, it avoids many of the issues that DEC faces with local water quality.
In general, perarid, arid, semiarid, dry subhumid, and dry humid climates are well suited for direct evaporative cooling. Liquid cooling is often a strong consideration in moist subhumid, moist humid, and perhumid climates.
It’s easy to see that answer to the ideal approach for data center cooling is: it depends. However, the right solution for a data center may not require a decision at all. Because here’s where things get interesting: the smartest operators aren’t choosing between DEC and LC. They’re using both strategically.
In a hybrid system, DEC can be used to pre-cool intake air, reducing the thermal load before it ever reaches the racks. This cooled air can chill the data hall and facility, and can be used in hybrid systems to chill the liquid that runs in the liquid cooling system. Inside the server, chips, and equipment racks themselves, LC takes over—targeting high-density gear or sensitive equipment with precision cooling.
This hybrid approach offers the best of both worlds: the operating efficiency of evaporative cooling, and the pinpoint control of liquid systems. It’s also highly adaptable—enabling operators to respond to future load increases, climate shifts, or sustainability targets with confidence.
So what is the best approach for data center cooling? Ultimately, there’s no one-size-fits-all solution. Direct evaporative cooling and liquid cooling each have their place, and in most modern facilities, the smartest approach is a hybrid one.
Not sure where to start? Work with your HVAC team and professional partners like Condair Evaporative Technologies to assess your thermal profile, your geography and climate, and your growth plans. Whether you’re designing from the ground up or retrofitting an existing site, a smart, balanced cooling strategy will help you meet performance goals, sustainability mandates, and the demands of whatever the future throws at you.
The world's largest data centers trust our expert team when they need to increase efficiency, drive sustainability, improve system uptime, and lower energy costs. If those are your goals, reach out today for a complimentary cooling system analysis from the pros at Condair Evaporative Technologies.
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