Hot Aisle/Cold Aisle


Hot aisle/cold aisle is a data center cooling strategy that involves organizing server racks in a specific configuration to optimize airflow and temperature consistency. This layout arranges racks back-to-back, creating alternating hot and cold aisles that segregate the hot exhaust air produced by equipment from the cold intake air used for cooling. The objective is to improve energy efficiency and minimize cooling requirements in the data center.


Hot Aisle: /hɒt ˈaɪl/Cold Aisle: /koʊld ˈaɪl/

Key Takeaways

  1. Hot Aisle/Cold Aisle is a layout strategy in data centers that aims to maximize cooling efficiency, reduce energy consumption, and maintain optimal equipment temperatures.
  2. It segregates hot and cold air through proper positioning of server racks, CRAC units, and vented floor tiles, resulting in a more consistent and controlled environment for the equipment.
  3. Proper implementation of the Hot Aisle/Cold Aisle strategy includes regular monitoring, maintenance, and adjustments, as well as potential supplementary techniques like containment or in-row cooling to further optimize data center performance.


Hot Aisle/Cold Aisle is an important concept in data center design because it helps optimize energy efficiency and maintain a stable environment for the equipment to function properly.

This arrangement is formed by alternating rows of server racks so that the front of each row faces the cold aisle, allowing cool air to be pulled into the front of the servers, while the back of each row faces the hot aisle, expelling warm air away from the servers.

This enables a controlled and efficient airflow system, minimizing the mixing of hot and cold air, improving cooling efficiency, reducing energy costs, and prolonging the life expectancy of data center hardware.

Overall, Hot Aisle/Cold Aisle arrangement plays a vital role in maintaining optimal server performance and promoting sustainable practices within the technology industry.


Hot aisle/cold aisle is a strategy utilized in data centers for efficient airflow management and energy utilization. The main purpose of this arrangement is to reduce energy consumption and improve the performance of cooling systems, thereby maintaining the optimal temperature and humidity levels, ensuring equipment reliability, and extending the life of the IT infrastructure.

The effective organization of equipment in hot and cold aisles enables data center administrators to better manage the thermal load accumulated from high-density computing equipment, ultimately reducing operational costs and enhancing overall efficiency. In a hot aisle/cold aisle layout, server racks are placed in alternating aisles, facing opposite directions.

This creates a pattern where the fronts of the servers face the cold aisles, while their backs exhaust hot air into the hot aisles. Cold air from the cooling systems is supplied to the cold aisles, where it gets drawn in through the server fronts and is then exhausted as hot air into the hot aisles.

This arrangement keeps the hot and cold air streams separated from one another, preventing the mixture of hot and cold air. Consequently, this minimizes the energy required to maintain optimal environmental conditions and prevents the cooling systems from overworking, leading to cost-effectiveness and operational efficiency.

Examples of Hot Aisle/Cold Aisle

Hot Aisle/Cold Aisle is a data center cooling strategy that involves arranging server racks in an alternating pattern with cold air intakes facing one aisle, and hot air exhausts facing the other aisle. This helps in managing airflow and reducing the energy consumption for cooling the equipment. Here are three real-world examples of this technology:Facebook’s Prineville Data Center: In 2011, Facebook opened its first data center in Prineville, Oregon, which utilizes the hot aisle/cold aisle concept along with several other innovations for energy efficiency. By separating the cold supply air from the hot exhaust air, the data center achieved a power usage effectiveness (PUE) rating of

07, which is considered exceptional in the industry.Google’s data centers: Google is well known for implementing and promoting energy-efficient designs in their data centers. The company implements hot aisle/cold aisle configurations in combination with innovative cooling systems, such as using seawater for cooling in its facility in Finland. Google’s measures have resulted in an average PUE of

12 across its data centers.Microsoft’s Chicago Data Center: Microsoft’s Chicago Data Center, opened in 2009, employs the hot aisle/cold aisle strategy for its container-based data center modules. These modules are essentially large shipping containers filled with servers, which are placed in rows with cold air intakes facing each other and hot air exhausts pointing away. This configuration, along with other advanced cooling techniques, has helped the facility achieve an impressive PUE rating of

FAQ – Hot Aisle/Cold Aisle

What is Hot Aisle/Cold Aisle?

Hot Aisle/Cold Aisle is a layout approach used in data centers, where server racks are arranged to improve energy efficiency and prevent the mixing of cold air and hot air. The cold aisles face the intake of the equipment, while hot aisles face the exhaust of the equipment.

What are the benefits of implementing Hot Aisle/Cold Aisle?

Some benefits of implementing a hot aisle/cold aisle setup include better energy efficiency, improved cooling, reduced operating costs, and extended lifespan of the equipment.

How do hot and cold aisles improve data center cooling?

Hot and cold aisles improve data center cooling by isolating hot and cold air using physical barriers and arranging the server racks to create separate aisles. This reduces the risk of hot air recirculation and increases cooling efficiency.

What type of containment systems are used in Hot Aisle/Cold Aisle?

There are two main types of containment systems used in Hot Aisle/Cold Aisle: Full or Partial Hot Aisle Containment, which focuses on enclosing the hot exhaust air, and Full or Partial Cold Aisle Containment, which focuses on containing the cold supply air.

What are some challenges when implementing Hot Aisle/Cold Aisle?

Some challenges when implementing Hot Aisle/Cold Aisle include the costs and potential complexities of retrofitting an existing data center, the need for proper sealing to prevent air leakage, and ensuring that the cooling infrastructure can support the new configuration.

Related Technology Terms

  • Data Center Cooling
  • Airflow Management
  • Rack Cabinet Layout
  • Temperature Control
  • Energy Efficiency

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