Designing infrastructure for energy efficiency means planning server rooms, data centres and cloud services so that every kilowatt-hour goes into useful computing rather than into losses. The most expensive mistakes are made at the design stage, because fixing them later means rebuilding the power supply, the cooling or the whole architecture.
Quick Overview
What you will learn:
- Why you cannot calculate PUE without metering
- How oversized capacity and cooling drive up energy use
- What EU law says about waste heat from data centres
- Which reporting duties apply to data centre operators
Who this article is for:
- Infrastructure architects and IT teams planning a server room or a migration
- Data centre managers and facilities teams
- People responsible for energy management and ESG reporting
Reading time: 7 minutes
A Note on the Title
The title promises the mistakes that cost companies the most, but the order below is not a cost ranking. We quote no figures for losses, because none of the sources cited here measures what individual companies lose. The consequences are described in qualitative terms instead: higher energy bills, expensive retrofits once the facility is running, and the risk of missing a statutory reporting deadline.
The stakes are high. The International Energy Agency (www.iea.org) estimates that data centres used around 415 TWh of electricity in 2024, about 1.5% of global consumption, and in its Base Case that figure roughly doubles to around 945 TWh by 2030.
Mistake: Designing Without Metering
Trouble often starts in a facility where nobody knows how much energy goes to the IT equipment and how much to everything else. Without that split you cannot calculate Power Usage Effectiveness (PUE). Commission Delegated Regulation (EU) 2024/1364 (eur-lex.europa.eu) defines it as the data centre’s total energy consumption divided by the energy consumed by its IT equipment. The closer the result is to 1, the less energy is lost to cooling, backup power and other supporting systems.
The same regulation (eur-lex.europa.eu) requires total consumption to be measured at the facility’s power input, using the method in the EN 50600-4-2 standard or an equivalent, and records of the measurement points and devices to be kept for at least 10 years. Meters therefore belong in the design, not in a retrofit after go-live.
Mistake: Oversized Capacity and Idle Servers
Infrastructure built with a large safety margin keeps drawing power even when it has no work to do. Servers sized for a rare peak, machines left running after a project ends and test environments that never shut down are the usual culprits. Microsoft’s sustainability guidance for Azure (learn.microsoft.com) names the same pattern: workloads designed for peak demand rather than actual utilisation leave idle virtual machines and unused resources behind, and right-sizing, autoscaling and removing idle capacity cut both cost and energy use. On-premises, consolidation and virtualisation do the same job by moving the load onto fewer, better-utilised machines so the rest can be switched off.
When you design a new server room, start from the measured load of today’s systems and a realistic growth plan, not from a capacity figure that will “surely be enough”. Modular expansion gives you far more control than buying years of capacity up front.
Mistake: Leaving Cooling Unmanaged
Cooling accounts for much of the energy a facility uses outside the IT equipment itself. According to the IEA (www.iea.org), the cooling share of a data centre’s consumption ranges from about 7% in efficient hyperscale facilities to over 30% in less efficient enterprise data centres.
Common sources of waste include set points that are colder than necessary, hot and cold air mixing in the room, and aisles left without containment. Annex VII of Directive (EU) 2023/1791 (eur-lex.europa.eu) lists temperature set points among the indicators that must be monitored and published, so cooling settings are no longer just a matter for the facilities team.
Mistake: Treating Waste Heat as a Problem, Not a Resource
Heat from a server room is usually vented to the atmosphere. Under Article 26(6) of Directive (EU) 2023/1791 (eur-lex.europa.eu), Member States must ensure that data centres with a total rated energy input above 1 MW use their waste heat or other waste heat recovery applications, unless they can show that this is not technically or economically feasible. Article 26(7)(d) requires a cost-benefit analysis of using that heat when a facility of this size is newly planned or substantially refurbished.
Heat recovery is therefore a design decision. Location, distance to a district heating network and the water temperature in the cooling loop determine whether recovery will be feasible at all.
Mistake: Discovering Legal Duties After the Fact
Article 12(1) of Directive (EU) 2023/1791 (eur-lex.europa.eu) requires Member States to have owners and operators of data centres whose installed IT equipment has a power demand of at least 500 kW publish the information listed in Annex VII, by 15 May 2024 and every year after that. The list covers, among other things, energy consumption, waste heat utilisation, water usage and the use of renewable energy. Regulation 2024/1364 sets out how this data is reported to the European database on data centres: first by 15 September 2024, then by 15 May each year.
Article 11 of the same directive (eur-lex.europa.eu) applies to whole companies and, like Article 12, takes effect through national transposing rules. Under it, an enterprise whose average annual energy consumption exceeds 85 TJ must have an energy management system in place by 11 October 2027; one above 10 TJ without such a system must undergo an energy audit, the first of which was due by 11 October 2026. A company’s actual obligations therefore come from national legislation, so check them with legal counsel while the project is still on paper.
Who Needs to Be Involved
- The infrastructure architect sizes capacity and owns consolidation and service architecture.
- The data centre manager brings knowledge of power, cooling and metering.
- The energy manager connects consumption data with the energy audit and the energy management system.
- The finance team assesses whole-life costs, not just the purchase price.
Read Also
- Sustainable IT: Practical Green IT Operations — day-to-day practices
- Measuring the Carbon Footprint of IT Infrastructure — measuring emissions
- GreenOps: Sustainable Practices for IT Teams — the team’s role
Build Your Skills
Two courses take the topic further: Green IT in Practice — Measuring and Reducing IT Infrastructure Carbon Footprint and Sustainable Cloud Architecture — Designing Energy-Efficient Workloads. The first covers energy audits of IT infrastructure, PUE and server room cooling; the second, designing energy-efficient cloud services. Get in touch and we will tailor the scope to your organisation.
Frequently Asked Questions (FAQ)
What is a data centre?
It is a facility that houses the servers, storage and network equipment delivering IT services, together with the power and cooling they need. Regulation 2024/1364 (eur-lex.europa.eu) distinguishes enterprise data centres, which serve only their own company’s IT needs, from colocation and co-hosting facilities, which provide space or equipment to customers.
How is a data centre cooled?
Cooling and environmental control systems keep temperature and humidity within the range in which IT equipment runs reliably. How much energy they use depends on the set points, on keeping hot and cold airflows apart and on the efficiency of the equipment. The IEA (www.iea.org) shows that cooling takes a much smaller share of energy in efficient facilities than in less efficient enterprise data centres.
What does PUE measure?
Power Usage Effectiveness is the ratio of a data centre’s total energy consumption to the energy used by its IT equipment. EU Regulation 2024/1364 (eur-lex.europa.eu) uses it as one of the sustainability indicators for data centres, alongside indicators for water usage, energy reuse and the share of renewable energy.
How should you manage data centre infrastructure to save energy?
Start by metering the consumption of the whole facility and of the IT equipment on its own, then track PUE and server utilisation over time. Check whether the facility falls under the reporting duty in Article 12 of Directive (EU) 2023/1791 (eur-lex.europa.eu) and whether the company must carry out an energy audit under Article 11. Turn the audit’s findings into an action plan with named owners and deadlines.