How Are Data Centers Cooled? Exploring the Types of Data Center Cooling

Cooling is one of the most critical aspects of data center design. Without effective heat dissipation, IT equipment will perform poorly and even fail.

Data center cooling strategies have evolved to address dramatic increases in power densities. According to the International Energy Agency, data center workloads increased 260 percent from 2015 to 2021. At the same time, rising energy costs and a focus on green initiatives are driving organizations to explore more efficient cooling options.

There are two primary elements to data center cooling: infrastructure design and cooling systems. Each has an important role to play in developing a cost-efficient cooling strategy.

Data Center Cooling Design

Data center cooling aims to ensure proper environmental conditions for IT equipment. Traditionally, that meant pumping enough chilled air into the environment to maintain a temperature of 72 degrees. This process is inefficient because the chilled air mixes with hot exhaust air. However, it was adequate for legacy data centers and is still used in some smaller, low-density facilities.

In most data centers, increasing power densities have made this approach obsolete. Modern data center designs and layouts need adequate airflow, effective heat dissipation, and chilled air focused on critical IT equipment.

Raised Floors

Many legacy data centers were designed with raised floors. Chilled air is pumped through the space between the raised floor and the slab and up through vents in front of the IT equipment. Raised floors are expensive to construct and do not provide adequate cooling for high-density data centers. However, data centers are still built with raised floor systems, often used with aisle containment. 

Aisle Containment

The layout of the data center and the infrastructure components significantly impact cooling efficiency. Best practices call for arranging racks and cabinets in rows, with alternating hot and cold aisles. Aisle containment systems maximize the value of that layout.

• Hot-aisle containment captures hot exhaust air and ducts it outside the data center or directly into the air conditioning return. It is primarily used to increase the efficiency of traditional computer room air conditioning (CRAC) units.
• Cold-aisle containment encapsulates and circulates chilled air to reach IT equipment effectively. It can be used with raised floor cooling or rooftop chillers with appropriate ductwork. 

In-Row Cooling

As the name implies, in-row cooling systems sit within a row of racks and cabinets to supply chilled air to nearby equipment. In conjunction with aisle containment systems or modular data center units, in-row cooling shortens the distance chilled air must travel and provides greater efficiency. 

In-Rack Cooling

In-rack cooling systems are mounted within a cabinet. Chilled air has no option but to flow into the intake of the IT equipment, and exhaust air is captured at its hottest point. Because capacity is matched to equipment needs, electricity usage is generally lower compared to other cooling systems.

Types of Data Center Cooling

CRAC units are still widely used in data centers around the world. However, data center managers have other options to consider when designing new spaces or retrofitting legacy environments.

Evaporative Cooling

Evaporative cooling systems work on the principle that water (and other liquids such as refrigerants) draws heat out of the air as it evaporates. Computer room air conditioning (CRAC) units work on evaporative cooling principles and are commonly deployed within data centers. 

What Is a Computer Room Air Conditioning (CRAC) Unit?

Computer room air conditioning (CRAC) units replaced traditional air conditioning units in data centers. They’re still self-contained air conditioners, but they offer more control and better performance for things such as air filtration, humidity control, and airflow. CRAC units employ a refrigeration cycle to keep IT equipment cool. Supply air is chilled by blowing over a cooling coil filled with refrigerant. 

It’s common for CRAC units to be deployed in raised floor environments. This configuration directs supply air through perforated floor tiles into the data center floor (cold aisles). It flows through the racks, picks up heat, exits through the rear of the cabinets (hot aisle), and is returned to CRAC intakes on the floor for the system to repeat. 

Chilled Water Cooling

Water has about four times the thermal capacity of air, so chilled water cooling systems tend to be more efficient than refrigerant-based systems. Computer room air handlers (CRAHs) use chilled water to cool the air used throughout the facility. 

What Is a Computer Room Air Handling (CRAH) Unit?

Computer room air handling (CRAH) units work in essentially the same way as CRAC units. The main differences are that instead of refrigerant and compressors, CRAH units use chilled water and control valves, and instead of being self-contained units, CRAH units are typically large systems requiring a network of chilled water pipes.

In CRAH systems, fans blow supply air over cooling coils filled with chilled water instead of refrigerant. The water is kept cool via a separate chiller or chilled water plant. The units draw in ambient air and cool it over chilled water coils, allowing the heat to transfer from the water to the air, and the return air is directed back into the chiller for the cycle to repeat. 

CRAC vs. CRAH Units

• CRAC units use refrigerant and compressors for cooling, while CRAH units use chilled water and control valves.
• CRAC units have more parts and often require more maintenance than CRAH units.
• CRAH units historically offer operators more control over cooling. They’re typically easier to adjust to match the variable cooling needs of the environment.
• CRAH units require retrofitting of plumbing systems, leading to higher upfront costs, but are easier to scale than CRAC units once installed.
• CRAH units are more expensive than CRAC units but offer more long-term efficiency because they rely on pre-chilled water, which is cheaper than refrigerant.
• CRAH systems do not use compressors and, therefore, use less energy than CRAC units.
• CRAC units are ideal for data centers with electrical loads of about 200kW or less, while CRAH units are ideal for data centers with electrical loads of 200kW or more.

Free Cooling

Data centers in colder climates can take advantage of free cooling — using outside air to chill water for liquid cooling systems. It is a very energy-efficient approach, especially in cold climates.

Air-Side Economizers

Although free cooling naturally works best in cold climates, it can also be effective in warmer climates via air-side economizers. With an air-side economizer, when the outside air is cooler than the return air, the return air is expelled and replaced with colder, filtered outside air. This lowers the reliance on traditional CRAC or CRAH and can lead to significant cost savings. Even in hot climates, such as south Florida, air-side economizers can offset cooling costs at night and in the winter months. With 24/7 cooling requirements, air-side economizers can significantly impact a data center’s bottom line no matter where it’s located.

Air-side economizers must be integrated into the central air handling system with ductwork for intake and exhaust. In cases where the outside air is too cold to use, economizers can mix exhaust air with supply air to bring the supply air to the correct temperature for cooling. An additional benefit of air-side economizers is redundancy. Should mechanical cooling systems fail, air-side economizers can still distribute outside air throughout the data center.

Water-Side Economizers

Like air-side economizers, water-side economizers leverage the natural environment for data center cooling. Think of them as chiller-less cooling systems. They enable data centers to use water from outside sources such as rivers or lakes, run it through a central on-premise processing plant, and use the naturally chilled water for cooling purposes within the data center. Facilities don’t even need a river or lake to source cold water in cold months. The outside air can keep the water in the processing plant cool enough to use within the data center. 

Water-side economizers require some retrofitting for deployment, but typically less so than air-side economizers. They offer significant cost-savings and can also serve as a redundancy measure should there be a failure in the mechanical cooling system. It’s a great way to extend the life of and offset costs from mechanical systems.

Measuring Data Center Cooling

It’s important to note that measuring the cooling system's effectiveness is almost as important as the hardware itself. After all, you can’t manage what you can’t measure. Data center operators typically use data center infrastructure management (DCIM) software to monitor performance and make necessary adjustments. DCIM software identifies environmental risks throughout the cooling system and data center at large, such as hot spots, humidity, changes in air pressure, and more. Modern DCIM software is often equipped with AI capabilities, enabling real-time adjustments such as matching the cooling load to the IT load. DCIM can unlock insights that significantly reduce cooling costs and power consumption and protect uptime.

The Future of Data Center Cooling

Escalating adoption of AI servers is driving new approaches to data center cooling. Liquid cooling technologies, including immersion and direct-to-chip cooling, extract heat from servers for maximum efficiency. With data center sustainability being an increasing focus across the industry, many larger data centers also use renewable energy sources to reduce cooling costs and meet ESG goals. The primary options include geothermal, solar, and wind.

Rely on Enconnex for Your Data Center Cooling Needs

The experts at Enconnex understand the importance of proper data center cooling. Our racks and cabinets, aisle containment systems, in-row and in-rack cooling, and cable management solutions are designed with the highest levels of quality and value. Our experts can help you choose the right solutions to maximize effectiveness and cost efficiency — no matter how you cool your data center. Just get in touch.