Data centers generate enormous amounts of heat from thousands of servers running 24/7. Understanding how is heat removed from a data center is essential for maintaining equipment reliability, preventing downtime, and controlling energy costs.
What Are the Main Steps for Removing Heat From a Data Center?
Data center heat removal follows a systematic process that captures, transfers, and rejects heat through multiple stages. The five primary steps include: capturing heat at the server level through airflow management, transferring heat via air or liquid cooling systems, containing hot air using aisle isolation techniques, processing heat through cooling equipment like CRACs or CRAHs, and finally rejecting heat to the outside environment through chillers, dry coolers, or cooling towers.
This process requires careful coordination between multiple systems to maintain optimal temperatures while minimizing energy consumption.
The Heat Generation Challenge
Modern data centers face increasing thermal challenges as server densities climb. According to AFCOM’s 2024 State of the Data Center Report, average rack density jumped from 7 kW per rack in 2021 to 16 kW per rack in 2025. AI workloads are driving even higher demands, with Vertiv projecting AI rack-level power density to surge from 50 kW to 1 MW between 2024 and 2029.
How Does Air-Based Heat Removal Work in Data Centers?
Air-based cooling systems remove heat by circulating conditioned air through servers and back to cooling units for heat extraction. Cold air enters servers through intake fans, absorbs heat from processors and components, then exits as warm air that returns to Computer Room Air Conditioners (CRACs) or Computer Room Air Handlers (CRAHs) for cooling.
This traditional approach works effectively for standard enterprise workloads below 15-20 kW per rack. The cooling units use refrigeration cycles or chilled water to extract heat from the warm return air before redistributing it as cold air.
Air Cooling Infrastructure Components
CRAC units contain integral refrigeration systems with compressors, condensers, and evaporators. CRAH units connect to building chilled water systems for heat removal. Both types include fans, filters, and humidity controls to maintain proper environmental conditions.
Hot aisle and cold aisle containment systems optimize airflow by separating hot and cold air streams, preventing mixing that reduces cooling efficiency.
What Role Does Liquid Cooling Play in Data Center Heat Removal?
Liquid cooling systems remove heat by circulating coolant directly to server components or immersing equipment in dielectric fluids. Liquids can carry heat approximately four times more efficiently than air and have up to 3,000 times the cooling efficiency of air, making them essential for high-density applications.
The data center liquid cooling market is projected to reach $21.3 billion by 2030, growing at a Compound Annual Growth Rate (CAGR) of 27.6% (Source: Industry Research, 2024).
Types of Liquid Cooling Systems
Direct-to-Chip Cooling: Liquid lines connect directly to server processors through cold plates, capturing heat at the source before it enters the surrounding air.
Immersion Cooling: Servers operate fully submerged in non-conductive dielectric fluids that absorb heat directly from all components.
Rear-Door Heat Exchangers: Liquid cooling coils mount on server rack doors to capture hot air before it enters the room.
What is liquid cooling in a data center becomes increasingly important as traditional air systems reach their limits with modern high-performance computing workloads.
How Do Data Centers Manage Airflow for Effective Heat Removal?
Proper airflow management creates controlled pathways for cool air delivery and hot air return, preventing hot and cold air mixing that reduces cooling efficiency. Data centers implement hot aisle/cold aisle layouts where server fronts face cold aisles for air intake, and server backs face hot aisles for heat exhaust.
Containment systems physically separate these air streams using doors, panels, or curtains. Cold aisle containment encloses the cold aisle, while hot aisle containment captures hot exhaust air before it mixes with room air.
Airflow Design Considerations
Perforated floor tiles in raised floor systems deliver conditioned air precisely where needed. Ceiling return plenums capture hot air for return to cooling units. Proper tile placement and sizing ensures adequate airflow without creating pressure imbalances.
Air velocity monitoring helps maintain optimal flow rates. Too little airflow causes hot spots, while excessive airflow wastes energy without improving cooling.
What Equipment Handles Heat Rejection in Data Centers?
Heat rejection equipment removes the thermal energy captured by cooling systems and releases it to the outside environment. Data center cooling towers, dry coolers, and chillers form the backbone of heat rejection infrastructure, each serving different capacity and efficiency requirements.
Chillers use refrigeration cycles to produce chilled water for CRAH units and liquid cooling systems. Cooling towers use evaporative cooling to reject heat from chiller condensers. Dry coolers rely on ambient air for heat rejection without water consumption.
Heat Rejection Capacity Planning
Cooling infrastructure accounts for approximately 50% of total energy consumption in a typical data center (Source: Industry Analysis, 2024). This makes heat rejection equipment sizing critical for both performance and operating costs.
Redundant heat rejection systems ensure continued operation during equipment maintenance or failures. N+1 or 2N configurations provide backup capacity based on criticality requirements.
How Is Heat Removed From a Data Center Using Modular Systems?
Modular data centers, including data center in a box solutions, use integrated cooling systems designed for specific power densities and deployment scenarios. These prefabricated units combine servers, power distribution, and cooling infrastructure in standardized containers or modules.
What is a modular data center becomes relevant for edge computing deployments where traditional data center infrastructure isn’t practical. These systems often use direct expansion cooling, liquid cooling loops, or hybrid approaches optimized for the expected IT load.
Edge Data Center Cooling Challenges
Edge locations typically lack dedicated facilities staff, requiring cooling systems with minimal maintenance requirements. Outdoor-rated equipment must handle temperature extremes and weather exposure.
How to permit a container data center involves understanding local HVAC code requirements, which often specify minimum ventilation rates, emergency shutoffs, and refrigerant regulations under EPA Section 608.
How Do Data Centers Monitor and Control Heat Removal Systems?
Advanced monitoring systems track temperatures, humidity, airflow, and equipment performance throughout the cooling infrastructure. ASHRAE TC 9.9 recommends maintaining temperatures between 64°F to 81°F (18°C to 27°C) and relative humidity between 20% to 80% for optimal equipment operation.
Building management systems integrate cooling controls with power monitoring to optimize efficiency. Schneider EcoStruxure and similar platforms provide comprehensive monitoring and automation capabilities for large-scale deployments.
Performance Optimization
Power Usage Effectiveness (PUE) measures cooling system efficiency by comparing total facility power to IT equipment power. Industry average PUE levels have remained mostly flat for the fifth consecutive year, typically ranging from 1.3 to 3.0, though newer facilities achieve better performance.
Variable frequency drives on cooling system fans and pumps adjust capacity based on actual thermal loads rather than running at full speed continuously.
For comprehensive guidance on cooling system selection and design, refer to our complete guide to data center cooling systems and research on modular edge data center approaches.
Frequently Asked Questions
What temperature should a data center be kept at?
ASHRAE recommends maintaining data centers between 64°F to 81°F (18°C to 27°C). Modern servers operate safely at these temperatures, and over-cooling wastes energy without improving reliability.
How much power does a data center use for cooling?
Cooling infrastructure accounts for approximately 50% of total energy consumption in a typical data center. This percentage varies based on efficiency measures, climate, and cooling system design.
Can existing data centers be retrofitted for liquid cooling?
Yes, existing data centers with chilled water systems can be retrofitted for liquid cooling. This requires extending facility piping, adding pump capacity, and potentially upgrading chiller infrastructure.
What is the difference between CRACs and CRAHs?
CRACs contain integral refrigeration systems with compressors and condensers. CRAHs connect to building chilled water systems for cooling. CRAHs typically offer higher efficiency and capacity.
How does humidity affect data center cooling?
ASHRAE recommends 20% to 80% relative humidity. Low humidity increases static electricity risk, while high humidity can cause condensation problems. Most facilities target 40% to 60% relative humidity.
What happens if data center cooling fails?
Over 65% of data center operators experienced at least one temperature-related outage in the past year, with an average outage length of 7 hours. Redundant cooling systems and monitoring prevent most failures.
Is air cooling sufficient for AI workloads?
Air cooling becomes inadequate for high-density AI applications above 30 kW per rack. These workloads typically require liquid cooling solutions to manage heat effectively while maintaining reasonable energy costs.
What refrigerants are used in data center cooling?
Common refrigerants include R-410A (GWP of 2088) and newer low-GWP alternatives like R-454B (GWP of 466). The AIM Act mandates HFC phase-downs affecting refrigerant selection.