Free cooling approaches are emerging as one of the key efficiency-led initiatives to minimize data centers’ costs and environmental impact.
The importance of guaranteeing temperature control in data centers is an established fact, as inappropriately high temperatures and humidity levels damage IT equipment and compromise its performance. In fact, while ASHRAE Thermal Guidelines recommend temperatures of between 18 to 20°C, common temperature ranges are typically expanded up to 27 °C or more.
Designing the right data center cooling system is thus a fundamental question to be solved today, especially at a time when public concerns and regulations are increasingly targeting data centers’ environmental impact.
In this context, the free cooling data center stands out as a key strategy to decrease cooling energy demand by maximizing the use of natural cooling resources, when available. In this quest, innovative design and the addition of chillers with top-efficiencies are making free cooling available for a broader range of locations.
What is free cooling?
The term free cooling encompasses a number of cooling techniques that employ natural sources like outdoor air or water for cooling purposes.
The goal is to reduce the need for energy-intensive cooling techniques, such as artificial air conditioning (AC).
While there are different approaches to free cooling systems, the main working principle behind this model is to collect natural resources such as air and water from the environment and then circulate them into data centers via appropriate systems.
This represents a fundamental shift away from other cooling models such as mechanical cooling, which employs compressors or refrigerants to cool air or liquids.
In contrast, free cooling aims at maximizing simplicity, avoiding the need for mechanical components and complex refrigeration cycles.
The basic principles and conditions of free cooling
First and foremost, it’s important to understand that free cooling is not available for every location: it’s restricted to data center sites where natural cooling resources are available.
Secondly, free cooling models must be understood as passive cooling systems, because they rely on natural physical processes (such as air circulation) to absorb or move heat. In this paradigm, when a resource (air or water) is found that is cooler than indoor conditions, it can be brought in to naturally cool the center’s equipment.
However, free cooling models are rarely strictly passive. Instead, they are typically accompanied by backup refrigeration solutions, such as efficient chillers. Following this premise, chillers are in charge of providing cooler air intakes that facilitate a reduction in temperatures.
In hybrid models, both paradigms work together to ensure temperature conditions are optimal irrespective of environmental conditions, extending the system’s possibilities even across seasonal changes. This is important because it allows operators to make the most of a location that offers ideal free cooling conditions during a certain time of the day or the year, but that may require additional cooling intermittently.
In other words, free cooling is typically regarded as a complement to other cooling systems, where the latter come in to push the overall efficiency for the data center.
The key here, as explained below in this article, is the design of flexible systems that allow for the intermittent use of chillers depending on outside temperatures.
Types of free cooling
1. Direct fresh air cooling
This method relies on directly bringing in outside air to cool IT equipment when ambient temperatures are optimal. It requires systems for air filtration and humidity control.
2. Water-based free cooling
Here, cold water is employed to absorb heat via heat exchangers, along with electrical chillers. Available water sources can include natural water but also cold water from cooling towers.
3. Other models
The incorporation of additional equipment allows some projects to expand their capacities. Such is the case of indirect free cooling, which involves technologies such as a rotating heat wheel, in charge of transferring heat between indoor and outdoor air through separate currents.
Additionally, heat pipe integration can also be considered. These passive heat transfer tools are capable of moving heat away from server racks and thus improve results in heat dissipation.
The rise of free cooling
According to Uptime Institute’s Global Data Center Results in 2023, “IT or data center power consumption” is a top priority for 88% of data center operators. Such widespread concerns around data center energy use are becoming the main driver behind the rise of free cooling solutions.
As one of the key data center market players, movements made by Google towards free cooling can illustrate current preferences for this model. As part of their attempt to minimize data centers’ power demand, the company has claimed their most efficient data centers are currently operating under the following conditions: free cooling techniques, allowing temperatures of up to 27°C and the incorporation of ad-hoc equipment designed for energy efficiency. A combination that is yielding outstanding efficiencies in terms of energy use, according to Google.
At the same time, the surge of the free cooling data center is the catalyst of important moves in data center trends across the globe. In this context, access to natural cooling resources is increasingly becoming a key aspect for choosing new data center locations. This, coupled with the availability of green energy, is pointing towards the emergence of Nordic countries as top contenders for major data center investments, with the data center market in Denmark representing a key example.
Benefits of free cooling
- Allows great energy efficiencies by moving away from energy-intensive processes and into passive cooling structures, which require less power demand.
- Increased sustainability thanks to the achieved energy efficiencies. Cutting down electricity consumption accounts to less CO₂ emissions, and further environmental benefits arise from eliminating or minimizing the use of refrigerants.
- Reduces operational costs related to energy consumption.
- The reduction of components presents low installation costs and easy operation and maintenance. While conventional cooling systems include moving parts (in compressors, pumps…), free cooling tends to either eliminate their need, or at least reduce their workload, thus extending their lifespan. This leads to cutting expenses in the medium and long term.
- Can be incorporated into hybrid schemes, where chillers take over when natural resources are not optimal.
Two key considerations when designing a free cooling system
This article has already mentioned the importance of site choice when it comes to developing a free cooling system. Put briefly, local weather conditions and access to potential resources such as cooling water will greatly determine the possibility of developing this type of model.
But data center cooling design represents a complex process that must be guided by a wide range of considerations. When considering cooling (free or otherwise), the following aspects are fundamental:
- Expected thermal load
- Expected demand and demand fluctuations
- Energy efficiency goals
- Possibility of incorporating automated control systems, so that free cooling is prioritized when conditions are optimal
- Integrations to build a hybrid cooling system with full redundancy.
- Sustainability goals, in terms of resource savings and the use of low-impact, green technologies
- Cost and Return on Investment considerations when incorporating long-term savings enabled by free cooling
- Compliance with relevant regulations and codes
Aside from these general considerations, there are at least two key aspects that stand out as especially important when designing free cooling models:
Air flow management
Adequate airflow management has the potential to optimize free cooling efficiency and must be carefully accounted for.
A look at data center cooling’s main design parameters reveals the most common rack arrangement for adequate air flow management is the hot-aisle/cold-aisle model. This arrangement is designed to avoid the mixing of separate air-flows, ensuring that cool air reaches the necessary components while warm air is expelled in an efficient manner.
Within this paradigm, it’s possible to opt for different recommended air-flow patterns through the racks, with the overall aim being to direct cold and hot air efficiently through the racks and aisles.
All in all, the importance of proper airflow management is crucial: when well balanced and designed, it optimizes performance in free cooling and minimizes the need for alternative, more costly cooling models.
Hybrid mode
As seen above, free cooling systems often operate in tandem with conventional free cooling chillers. In this paradigm, it’s important to achieve a balance between optimal free cooling temperatures and the conditions where chillers must be activated.
The following are three possible scenarios that might allow to control temperature ranges in a water-based free cooling systems, all without compromising on efficiency or equipment safety:
- For ambient air temperatures above 30 ºC, chillers come in to aid the free cooling system in guaranteeing optimal thermal ranges in the times when natural resources are not in the best condition.
In this scenario, choosing the right chiller represents a vital step. It’s crucial to opt for reliable and reputable providers which, today, are capable of building extremely efficient industrial chillers at both partial and full loads.
Looking at chiller efficiency, values can be understood as a comparison of the cooling provided to the energy consumed. This, however, can take many forms:
- In chillers powered by electric motors, efficiency is measured in terms of kilowatts/ ton of cooling.
- For measuring absorption chiller efficiency, formulas compare heat source (fuel/gas/vapor) consumed/ton of cooling.
Ultimately, the right choice of chiller must be understood as responsible for enabling free cooling by taking over when this resource is not available. This configuration is successful in helping operators obtain outstanding yearly average efficiency levels, guaranteeing optimal conditions remain even when free cooling is not viable.
- The next scenario sees ambient temperature levels of between 21 and 30 ºC. In this case, free cooling can still be largely accounted for achieving a desirable temperature in water (30ºC), with only minimal support from the chiller.
While energy consumption increases because of the chiller addition, it’s still outstandingly low.
- For ambient temperatures below 20 ºC, the free cooling system can run independently and chillers remain inactive. 30 ºC water can be obtained just by activating dry coolers. In this scenario, energy consumption from fans accounts for only 10% of the energy that chillers would require.
This is a favourable scenario for maximum energy efficiency and cost reductions and is viable for a majority of the year across various locations around the world.
ARANER: your trusted allies for maximizing efficiency in free cooling and beyond
As seen across the article, designing a free cooling system represents a complex, multifactorial process.
On the one hand, the use of available natural resources as part of free cooling models must consider the overall data center needs and requirements, in terms of thermal load and required redundancy. At the same time, considerations around energy savings prove vital for operators, while making a responsible use of resources is fundamental to meet growing concerns about these facilities’ environmental footprint.
This is particularly important as data center demand continues rising and power-intensive infrastructure scales up.
With top efficiencies and sustainability as an end goal, there are numerous approaches to data center cooling today. As seen above, free cooling models can be complemented with efficient chillers, but also with AI data center models, where technologies are capable of increasing energy optimization via dynamic cooling adjustments, optimized resource allocation and automation.
In this context, the right thermal engineering partners can help navigate each project’s potential and requirements, incorporating state-of-the-art technologies that take efficiency to the next level.
This is where ARANER comes in. We are committed to developing data center cooling that puts efficiency and sustainability at the forefront. As such, we put our thermal engineering expertise to work to design and implement cutting-edge data center cooling that considers each project’s needs and potential, including the possibility of free cooling.
Want to learn more? Discover our data center cooling solutions and get in touch with us to speak to our team about how we can help you.
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