Data centers as heat plants: thermal storage as the new frontier of energy efficiency

Data centers are the beating heart of the digital economy — but also major producers of heat. Every server, every operation, every processed byte generates thermal energy that, in most cases today, is simply dissipated into the atmosphere. But what if that heat could become a resource instead of waste?

This is where thermal batteries — energy storage systems capable of storing and redistributing heat — come into play, turning data centers into active sources of local renewable energy.

From waste heat to useful energy: the principle

During operation, servers heat up large volumes of cooling air or water. Normally, this thermal energy is released through evaporative towers or chillers, consuming a significant amount of electricity.

By using a thermal battery, the extracted heat can instead be stored in a storage medium — specifically in phase change materials (PCMs). The energy can then be released and reused in nearby buildings, district heating networks, sports facilities, or industrial processes.

In practice, the data center becomes an integrated energy hub within its territory, providing immediate and constant-temperature heat while reducing the district’s overall emissions.

How a “hot” thermal battery works

The heat generated by servers is collected through the cooling circuit and transferred to a storage medium — typically water, salts, or PCM.

Unlike traditional stratified tanks, where energy is released gradually, PCM thermal batteries are designed with a high heat-exchange surface between the fluid and the material. This enables an instant, high-power energy release depending on the water flow required.

When heat demand spikes — for example, during multiple simultaneous showers in a gym, barracks, or sports complex — the battery can deliver large amounts of thermal energy within minutes, with no need for complex control systems.

In other words, thermal energy is not released “gradually,” but instantly on demand, thanks to the combination of the PCM’s energy density and its optimized exchange surface.

This makes PCM storage systems ideal for covering short, intense demand peaks, integrating perfectly with variable heat sources such as data centers.

PCM: materials that change phase to store energy

Phase Change Materials represent the most advanced technology for thermal energy storage. During the state transition (solid ↔ liquid), a PCM can absorb or release large amounts of heat at an almost constant temperature, ensuring stability and continuity in the energy supply.

In data centers, PCMs can:

• store heat for district heating or domestic hot water;
• or, with different formulations, store cold energy, absorbing cooling power during nighttime or free-cooling periods.

This means the same principles can be applied to both the hot and cold sides of a thermal system, maximizing overall flexibility and efficiency. To learn how to integrate a thermal battery into a customized efficiency plan, read: Energy consulting and thermal storage: the ideal partnership.

i-TES and the valorization of heat in data centers

At i-TES, we have already implemented projects for heat recovery and storage in data centers, developing custom PCM-based thermal batteries. Our approach combines energy analysis, simulation, and design support to turn wasted heat into a tangible efficiency opportunity — in both urban and industrial contexts.

An exchange ecosystem: from data center to city

Imagine a digital campus connected to a residential neighborhood or hospital. The heat generated by servers is stored in a thermal battery and distributed through a low-temperature network (30–60 °C). Surrounding buildings use this heat for space heating, domestic hot water, or pre-heating industrial fluids — contributing to a model of territorial energy sustainability.

In this circular model:

• the data center reduces cooling costs,
• end users cut gas consumption,
• and the local energy system becomes more resilient and sustainable.

The role of free cooling: a key element of overall efficiency

In many European regions — especially those with temperate or cold climates — outdoor air can be used to naturally cool servers. This is known as free cooling. Combining free cooling + thermal batteries allows operators to:

• use cold outdoor air to cool the water circuits at night;
• store the cold energy in PCMs or water tanks;
• and use that stored energy during hot or peak hours.

Similarly, the heat recovered from servers can be stored and released to external users, turning the data center into part of a two-way energy network: cold in, heat out.

From dissipation to energy symbiosis

The paradigm of the “data center as a heat plant” is already real: several projects in Northern Europe and Northern Italy are integrating thermal storage and district heating systems. Thermal batteries — especially PCM-based ones — allow for dynamic energy management and efficient valorization of waste heat.

In the near future, every data center could become a small digital cogeneration plant, where energy is not wasted but recycled, stored, and shared with the local area.

The future of data centers will not only be digital — it will also be thermal. Every processed byte generates heat, and every degree can become an energy opportunity. Thanks to thermal storage and free cooling, tomorrow’s data centers will no longer be just computing hubs, but intelligent renewable energy nodes capable of powering not only the internet, but also our cities.

Through thermal storage and PCM technology, a data center can be transformed into a truly intelligent, efficient, and locally integrated power hub. Want to learn how to apply this model to your operations? Contact us for a personalized consultation.