Data Center Liquid Cooling vs. Air Cooling: Factors to Consider

As rack densities increase, data centers must reconsider their cooling strategies. High-density racks consume more power, which generates more heat and requires more cooling. Legacy cooling systems may not be up to the task.

Data centers have traditionally relied on air cooling for thermal management. However, air cooling can be inadequate for rack densities of 20 kW or more. Even if air cooling can support high-density racks, it is seldom the most efficient option.

That’s why more data centers are looking to implement liquid cooling, which is far more effective at transferring heat than air. However, there are several factors to consider when choosing between the different types of data center cooling systems. 

Liquid vs. Air Cooling: The Basics

We discussed data center liquid cooling in a previous post. Used to cool early mainframes, the technology is now being applied to today’s high-compute power servers. There are three primary types:

• Liquid immersion
• Direct-to-chip
• Rear-door heat exchangers

All three work on the same principles. Liquids have up to 3,000 times the cooling efficiency of air and can be directed to the heat source. Thus, data center liquid cooling requires less energy than filling the space with chilled air.

Data center air cooling involves blowing or circulating chilled air around the IT equipment and exhausting hot air to the outside or plenum. Again, there are three main types:

• Computer room air conditioning (CRAC)
• In-row cooling
• In-rack cooling

CRAC units cool designated data halls, while in-row cooling cools one or more rows of cabinets, and in-rack cooling cools a single cabinet.

Pros and Cons of Data Center Liquid Cooling

Because liquids are more efficient than air at conducting heat, liquid cooling addresses many problems associated with higher data center densities. Liquid cooling also consumes about 10 percent less energy, which results in 10 percent lower carbon emissions. As liquid cooling technology advances, the energy savings grow. For example, immersion cooling strategies can lower energy expenditures by 20% or greater depending on the scale of the deployment. Direct-to-chip liquid cooling systems enable operators to apply cooling directly to the heat source. This reduces the dependency on cooling fans and allows operators to increase the ambient temperature of their facilities, saving even more power.

Additionally, liquid cooling is quieter, uses less water than traditional air chillers, and often takes up less space in the data center (depending on the type of liquid cooling system).

However, liquid cooling typically requires significant upfront capital investments to realize its long-term efficiency benefits. Retrofitting complete liquid systems in existing data centers typically calls for significant plumbing infrastructure work and requires investments in training for data center staff. The management and maintenance processes are significantly different for liquid cooling systems than traditional air cooling systems. Additionally, IT teams are often reticent about adopting liquid cooling due to the risk of leaks, which could seriously damage equipment and cause downtime.

Pros and Cons of Data Center Air Cooling

CRAC systems have become more efficient over the years, and their effectiveness is increased by hot- and cold-aisle containment. In-row and in-rack cooling reduce the distance chilled air must travel to reach the IT equipment, further increasing efficiency.

Air cooling is well-understood due to its widespread use in data centers worldwide. Maintenance is straightforward, and data center personnel are familiar with the process.

However, air cooling is being challenged by rising energy costs and increasing data center densities. Some data centers are finding it increasingly difficult to justify the cost, which can account for more than half of operational expenses. Certain types of data centers, like hyperscale facilities with enormous power usage, are simply outgrowing air cooling strategies.

Water usage is also a growing problem. Evaporative cooling systems are energy-efficient but consume a lot of water, which can stress overtaxed water supplies. Large data centers use up to 5 million gallons of water daily, including direct and indirect sources. In addition to consuming vast amounts of water, evaporative cooling systems discharge contaminants in wastewater.

A separate but related (and equally important) topic is data center airflow management. Both overall and rack-level airflow must be managed effectively to maximize the efficiency of cooling systems.

How to Choose the Right Solution

Despite the drawbacks of air cooling, liquid cooling isn’t always the best choice. There are a number of factors to consider.

Cost

Power usage is among the most expensive line items on a data center’s balance sheet and cooling cost represents about 40 percent of that total, on average. Although liquid cooling generally comes with higher capital costs, it may be more cost-efficient over time due to lower operational costs. Still, coming up with a total cost of ownership (TCO) comparison can be difficult due to intangibles such as management complexity and vendor lock-in.

Maintenance

The cost and complexity of maintenance is a related factor. Immersion cooling systems, in particular, come with unique maintenance challenges, given that system components are submerged in dielectric liquid. Data centers might have to rely on vendors for most maintenance tasks.

Location

Liquid cooling is less attractive for data centers in colder climates, which can rely on free cooling by bringing in outside air. Data centers in warmer climates and areas with stressed water supplies are more likely to transition to liquid cooling.

Strategic Roadmap

The implementation of advanced applications such as AI and advanced processor chipsets could drive the transition to liquid data center cooling. Data center operators should consider whether these applications are on the strategic roadmap or whether there’s a need to consolidate workloads or grow within a small footprint.

Sustainability

Many data centers are facing mandates to increase sustainability. New developments are facing pushback from local communities as energy and water usage rises. As a result, resource usage is an important consideration when choosing cooling technology.

Data Center Infrastructure Solutions from Enconnex

Ultimately, one size doesn’t fit all when it comes to data center cooling. Many data centers will likely take a hybrid approach by adding liquid cooling to support certain use cases. Enconnex offers flexible data center infrastructure solutions that give you the agility to evolve your cooling technology as needs dictate. Get in touch to discuss the options.