Free-cooling is a data centre cooling strategy that reduces or even eliminates the need for mechanical refrigeration. We achieve this by harnessing naturally cool air or water. By leveraging environmental conditions, free-cooling can dramatically cut energy use, lower operating costs and reduce environmental impact. All without compromising thermal performance or uptime.
How Free-Cooling Works
Free-cooling works by substituting compressor-driven cooling with ambient conditions when outdoor temperatures permit. Instead of relying solely on chillers or DX systems, facilities can tap into outdoor air or water. This ambient approach helps to maintain optimal server temperatures.
Using Ambient Air or Water to Offset Mechanical Cooling
Free-cooling typically falls into two categories:
- Air-side economisation which uses filtered outside air to cool the data hall directly.
- Water-side economisation which uses cooling towers and heat exchangers to cool chilled water without compressors.
This approach is most effective during cooler months or in climates with consistently low temperatures. But hybrid systems can switch between free-cooling and mechanical cooling year-round.
Free Cooling Technologies
Core components include:
- Economisers (air-side or water-side) to manage air intake and heat exchange
- Plate heat exchangers for indirect free-cooling via closed-loop water circuits
- Bypass systems that route water or air past chillers when free-cooling is viable
Free-Cooling in Data Centres
Supporting Uptime, Efficiency, and Sustainability Goals
For mission-critical facilities, free-cooling offers a unique blend of efficiency, reliability and environmental compliance. When integrated effectively, it supports:
- Lower PUE (Power Usage Effectiveness)
- Reduced strain on mechanical systems
- Enhanced system longevity
- Contribution towards sustainability certifications
Climate Considerations and Optimal Conditions
Free-cooling thrives in cooler climates, but it’s not limited to cold regions. With the right design it can be viable in temperate or even warm regions during certain hours.
To determine whether free cooling is suitable for your site, several environmental factors need to be assessed:
Wet-bulb and dry-bulb temperature profiles
These indicate how much cooling can be achieved using ambient conditions. The dry-bulb temperature reflects the air temperature. The wet-bulb temperature shows how cool the air can get through water evaporation. This is a key factor for systems like adiabatic or evaporative cooling.
Air quality and filtration requirements
In areas with dust, pollutants, or salt air, filtration systems may need upgrading. This is to protect internal components and maintain air quality.
Seasonal temperature variance and humidity control
Sites with predictable temperature swings and manageable humidity are better suited to take full advantage of free-cooling modes.
Types of Free-Cooling Systems
Integrated vs Standalone Systems
You can deploy free-cooling in different system configurations, depending on your facility’s design and operating requirements.
Integrated Systems
These systems have free-cooling capabilities built directly into primary cooling equipment, such as chillers or CRAC units. They use intelligent controls to switch automatically between free-cooling and mechanical modes based on external temperature conditions. Integrated designs are space-efficient and ideal for facilities looking to upgrade without significant infrastructure changes.
Standalone Systems
Standalone free-cooling systems, such as dry coolers or adiabatic units, operate separately from the main mechanical cooling system. Many large facilities install these systems where there’s space for dedicated equipment. Operators value standalone systems for their flexibility, with the ability to scale or retrofit them alongside existing infrastructure.
Each approach has its own advantages. Integrated systems offer seamless operation and easier control. While standalone options are modular and adaptable for more complex site conditions.
Examples: Chiller Bypass, Plate Heat Exchangers, Evaporative Cooling
Some common implementations include:
- Chiller bypass systems to divert flow when conditions allow
- Closed-circuit adiabatic coolers that enhance efficiency with minimal water usage
- Plate heat exchangers that enable indirect free-cooling while maintaining indoor air quality
Benefits of Free-Cooling
Energy and Cost Savings
Free-cooling can reduce cooling-related energy use significantly in suitable climates. This translates to major cost savings over time. Even partial use can significantly reduce compressor runtime and electricity bills.
Lower Carbon Footprint and Reduced Equipment Wear
Reduced reliance on chillers and compressors lowers greenhouse gas emissions. It also extends the lifespan of your infrastructure by reducing mechanical stress.
Challenges and Design Considerations
Geographic and Temperature Limitations
Not all sites are suitable. If outdoor air is hot, humid, or polluted, free-cooling can pose risks to hardware or result in high filtration costs. Hybrid designs can help mitigate this.
Filtration, Controls, and Maintenance Needs
Effective free-cooling requires:
- Advanced controls to switch modes smartly
- Filtration systems to protect sensitive equipment from particulates
- Regular maintenance to avoid fouling in heat exchangers or towers
Is Free-Cooling Right for Your Facility?
What to Consider Before Implementation
Before integrating free-cooling, evaluate:
- Climate data and temperature thresholds
- Existing cooling architecture (for example chillers, raised floors)
- Redundancy and uptime requirements
- Compliance targets and reporting needs
A thorough site assessment and simulation modelling can help determine whether free-cooling is feasible in your facility.
How STULZ Supports High-Efficiency System Design
At STULZ, we specialise in designing integrated solutions that balance efficiency, resilience and environmental impact. From chiller units and liquid cooling to rack-based cooling, we help clients implement free-cooling with confidence.
Free-Cooling as Part of a Resilient Infrastructure Strategy
Free-cooling offers a compelling path toward greener data centre operations. Its success depends on tailoring the system to your site and operating profile. It’s not a one-size-fits-all solution. But when implemented correctly, the rewards are significant.
Speak to STULZ About FreeCooling Solutions
Looking to cut energy costs while boosting sustainability? Contact the STULZ team today to explore how free- cooling could work for your facility.
FAQs: Free-Cooling in Data Centres
1. What is free-cooling in a data centre?
Free-cooling is a method of reducing or eliminating the need for mechanical refrigeration by using naturally cool air or water to regulate server temperatures. This strategy significantly lowers energy consumption and operating costs while maintaining performance.
2. How does free-cooling work?
Free-cooling uses ambient outdoor air (air-side economisation) or water (water-side economisation) to cool servers. When outdoor conditions are suitable, systems bypass traditional chillers, cutting down on compressor use and saving energy.
3. What types of free-cooling systems are available?
There are two main types:
Integrated systems, which combine free-cooling with existing chillers or CRAC units for seamless operation.
Standalone systems, such as dry coolers or adiabatic units, which work independently and offer modular flexibility.
4. What are the benefits of using free-cooling in data centres?
Free-cooling reduces energy costs, lowers your carbon footprint, extends the life of mechanical equipment, and supports sustainability targets. Even partial use of free-cooling modes can yield measurable savings and system efficiency.
5. Are there limitations to free-cooling?
Yes. It’s most effective in cooler climates or during certain times of the year. Factors like high outdoor temperatures, humidity, or poor air quality can limit its use. Proper filtration, advanced controls, and hybrid designs help overcome these challenges.
6. How do I know if free-cooling is suitable for my facility?
A site assessment is essential. You'll need to evaluate local climate data, your existing cooling setup, air quality, and your uptime and compliance requirements. A tailored design—like those provided by STULZ—can determine feasibility and ensure optimal performance.