A day in the life of a kilowatt-hour

On World Energy Efficiency Day, celebrated annually on 5 March, we are reminded of a simple truth: The cleanest energy is the energy we never need to use.

In a digital world powered by data, that statement carries particular weight. Data centers are the backbone of modern life, supporting everything from financial transactions and healthcare systems to streaming services and AI — and all of it runs on electricity.

But what actually happens to a single kilowatt-hour once it enters a data center?

We’ll give ours a name: Meet Joule, one kilowatt-hour of energy reporting for work.

8am: Arrival

Joule arrives at the data center from the power grid as alternating current (AC). Before powering anything, Joule is measured. We use metering to understand how much energy — whether electric or from other energy sources — enters the building and how it is used. This allows us to work more efficiently: We track and monitor energy consumption and performance continuously so we can identify trends and streamline operations.

From the grid connection, Joule travels through transformers and cables. A small portion of the energy is naturally lost as heat along the way — an unavoidable part of moving electricity. The higher the efficiency of the equipment, the smaller those losses.

Joule then reaches the uninterruptible power supply (UPS). Here, Joule is converted from AC to direct current (DC). Some of the energy briefly sits in the UPS, ready to step in instantly if the power-grid supply falters.

When everything is stable, Joule doesn’t stay long. The energy is converted back into AC and continues the journey toward the IT equipment. This constant readiness protects digital operations from interruption, but every conversion step introduces small energy losses. It is why modern, high-efficiency UPS systems matter.

9am: Powering the digital world

The kilowatt-hour now reaches its primary purpose: powering IT equipment.

Servers, storage systems and network devices convert electricity into computing power. This is the core function of a data center and where the real value is created.

But energy doesn’t disappear. Remember the law of conservation of energy: “Energy can neither be created nor destroyed; rather, it can only be transformed or transferred from one form to another.”

As Joule flows through processors and memory chips, the electrical energy is transformed. A tiny fraction becomes sound or light, but almost all of it eventually becomes heat.

And that’s where the next challenge begins.

10am: Turning into heat

As the servers process data, heat builds up. Without cooling, server performance would degrade and systems would shut down.

So, Joule’s work also supplies another system: cooling infrastructure.

This is where Joule’s friend Keith — another kilowatt-hour — enters the story. Instead of powering servers, Keith powers movement. Fans spin, pumps circulate water and chillers remove heat, all driven by that energy.

Cooling is essential for data centers, but it is energy intensive. The more efficiently we cool, the less additional energy we consume. The goal is simple: Help each Keith remove more heat with less effort, so more Joules can focus on digital work instead of supporting overhead services.

This is where operational excellence and efficiency make a measurable difference.

11am: Small adjustments, big impact

At one of our UK sites, teams identified an opportunity to improve how cooling fans were regulated. Pressure sensors that controlled fan speeds were losing calibration over time. As a result, fans were often running faster than necessary and consuming more energy than required.

By upgrading sensor quality and relocating them for easier access and maintenance, the team achieved:

• A 15% average reduction in fan speed
• Annual savings of about 6GWh

Rather than a complete system redesign, the improvement required attention, performance analysis and pragmatic action.

Now, each Keith in the cooling system can support more Joules using less energy. Like any workforce, improving productivity creates lasting impact.

Efficiency gains are often hidden in the details.

• WATCH → Energy efficiency: Pressure sensor optimization at HH3 UK

1pm: Reducing invisible losses

Not all energy inefficiencies are visible. At a site in the US, older UPS systems were operating at around 88% efficiency. Modern systems can achieve roughly 97% efficiency for the same load.

The difference may seem small, but it becomes significant across a large data center.

By upgrading to higher-efficiency UPS units with a modern design, our team achieved:

• A 9% increase in efficiency
• An annual energy reduction of 0.3GWh
• Lower maintenance requirements
• Improved system reliability

In practical terms, this means Joule now spends around 97% of its energy performing useful work — powering IT. Far less is lost as heat inside electrical infrastructure. More of the energy reaches its intended destination.

Energy efficiency is not only about reducing consumption. It also improves resilience and long-term operational stability.

• WATCH → Energy efficiency: UPS replacement at CA1 USA

3pm: Restoring performance

Efficiency is not always about new equipment. Sometimes it’s about restoring systems to operate as originally intended.

At one of our facilities in the US, chilled water valves within computer room air handlers (CRAHs) had gradually become clogged. This reduced chilled water flow, created localized hot spots and increased strain on the entire cooling system.

A targeted cleaning initiative delivered:

• 66% performance improvement on a CRAH
• Higher overall cooling efficiency
• Less operational load on the cooling system
• Increased cooling system redundancy

The lesson is simple: Proactive maintenance is an energy-efficiency measure.

• WATCH → Energy efficiency: CRAH valve cleaning at VA1 USA

5pm: Why this matters

By the end of the day, Joule has powered digital services, changed form, paused briefly in a UPS and helped trigger multiple supporting systems designed to ensure reliability and stability.

If managed efficiently, Joule:

• Delivers maximum computing value
• Requires less additional energy for cooling
• Produces fewer associated carbon and greenhouse gas emissions
• Reduces pressure on infrastructure and backup systems

Energy efficiency in data centers matters for three key reasons:

1. Climate impact: Reducing energy consumption lowers associated carbon emissions and supports global decarbonization efforts.

2. Operational resilience: Efficient systems generate less strain, operate more predictably and reduce dependency on backup generation.

3. Operational performance: Lower energy consumption reduces operating costs and protects against energy price volatility.

It is therefore both an environmental objective and a business imperative.

No efficiency without continuous improvement

Energy efficiency is not a one-time project. It requires structured measurement, ongoing monitoring, regular review and collaboration across operations, engineering and sustainability teams.

From detailed monitoring to targeted optimization initiatives, continuous improvement is embedded into how our data centers operate. Our energy management system is certified to the ISO 50001 standard across all buildings in Europe, the Middle East, Africa and India, along with other key buildings in the Americas and the Asia Pacific region.

Each improvement, whether a sensor upgrade, equipment replacement or maintenance intervention, contributes to a larger goal: Delivering digital infrastructure with the highest possible efficiency.

• ALSO READ → AI in action: Saving energy, cutting costs and keeping data centers cool

Every kilowatt counts

As World Energy Efficiency Day reminds us, the most sustainable energy is the energy we avoid using in the first place.

In data centers, every kilowatt counts. When we reduce losses, optimize cooling, modernize infrastructure and maintain systems proactively, we ensure that each unit of energy delivers maximum value with minimal waste.

Efficiency is not about doing less. It is about doing more with what we already have. And in a world where digital demand is growing, this principle has never been more important.

• ALSO READ → Innovation needs power: Why sustainability is now an operational imperative