Heating with a data centre: from available heat to useful heat

A data centre can supply heat to a building or network, provided a compatible need exists in the right place at the right time. Rejected heat, recoverable heat and heat actually delivered are not three names for the same quantity. A project must establish the transitions between these stages.

This guide proposes a technical and operational reading of a heat recovery announcement. It calculates neither national savings nor the profitability of a particular project. That would require site measurements, an identified heating need and documented economic conditions.

First, find a user for the heat

The DOE/NREL guide to data centres, section 7, recommends looking for a nearby consumer and a compatible temperature. It also notes the usual need for backup cooling when the heat consumer is unavailable. Recovery must remain compatible with IT operation.

The initial question is therefore not simply “how many megawatts?” You need to know who can use the heat, at what hours and during which months. A need located far away or absent for much of the year cannot be treated as a permanent outlet.

For an initial dossier, request two profiles covering the same period: available heat and heat demand. A maximum power figure on each side is insufficient to prove that they coincide. Two peaks reached at different times do not add up to useful energy.

Temperature is not a quantity of energy

Temperature indicates a thermal level. A quantity of heat is expressed in energy units, such as kilowatt-hours. Two flows can carry the same energy but be unsuitable for the same use if their temperatures differ.

The Scottish Government’s technical guide distinguishes temperature levels and ways of using heat. It describes heat exchangers, which transfer heat between fluids, and the use of heat pumps to raise a temperature when necessary. This technical explanation is not a French regulatory rule.

In a project analysis, document supply and return temperatures, the available flow rate and the consumer’s requirements. An announced connection without this information does not yet establish that the heating service can be delivered.

Track four quantities instead of a single total

Stage of the balance	What must be established
Heat present in the rejected stream	Measurement or estimate at the chosen system boundary
Recoverable share	Compatibility with equipment and site operation
Heat transported	Energy after circuit losses and constraints
Useful heat delivered	Energy actually received and used by the consumer

This breakdown is a framework proposed by Pnebbula. Boundaries should be drawn on the installation diagram. If a heat pump adds electrical energy to the system, its contribution must appear; all delivered heat cannot be attributed solely to the original rejected heat.

The distinction also helps interpret a recovery rate. “80%” is meaningful only when its denominator is known: total site heat, heat from a loop or heat available during certain hours. A percentage without a defined boundary does not support a comparison.

A seasonal example shows the difference

Consider an entirely fictional installation offering a constant 1 thermal megawatt of recoverable heat. For 4,000 hours, the consumer can absorb 0.8 megawatts. During the remaining 4,760 hours of an 8,760-hour year, it can absorb only 0.1 megawatts. We deliberately ignore losses, outages and any heat pump.

Usable energy in this simplified model is 0.8 × 4,000 + 0.1 × 4,760, or 3,676 megawatt-hours. Energy available over the year is 8,760 megawatt-hours. The ratio is about 42%, even though the source is assumed to be continuously available.

This result is not the efficiency of a real installation. It represents a limit arising from the match between supply and demand in the example. Adding a second use or storage would change the calculation, but would also require documenting capacity, losses, costs and availability. Storage should not appear as a free or unlimited solution.

Account for the heat pump and auxiliaries

For a heat pump, the coefficient of performance relates heat supplied to energy consumed within a defined boundary. The IEA explains this operating principle. With a fictional coefficient of 4, supplying 4 units of heat requires 1 unit of electricity and draws 3 units from the source in a simplified ideal balance. This does not mean that 4 units of rejected heat have been recovered.

In a real installation, specify whether the measurement includes circulation pumps, controls and other auxiliaries. Temperature and load conditions must be stated. A nominal value under a test condition does not prove performance over an entire year.

The Scottish guide details technical recovery options and their constraints. The approach proposed here is to keep a separate line for each additional consumption, so that the balance is not reduced to heat leaving the data centre alone.

Plan for periods when either site stops

The heat producer may experience an outage or change its equipment; the consumer may reduce demand. The project must plan for what happens in both directions. IT cooling must remain assured if the heat network stops taking energy, and the consumer must know its heating options when the source is unavailable.

The commercial considerations in the Scottish guide put the organisation and commitments of a recovery project into context. When reading a dossier, ask who operates each piece of equipment, where delivery is measured, who provides maintenance and which assumptions about duration underpin the investment.

These questions are not a legal analysis of a contract. They make visible the operational dependencies that can distinguish thermal potential from a sustainably available service.

Check what the heat actually replaces

Recovered energy does not automatically correspond to the same amount of primary energy or avoided emissions. Describe the heating system that would have provided the service without the project, then include additional consumption and the chosen boundaries.

The comparison can use several scenarios if the displaced system is uncertain. Each result must remain tied to its scenario. Also avoid attributing the same benefit twice in consolidated accounts covering the producer and user.

The guide to lifecycle assessment (in French) helps establish these boundaries. The guide to data centre infrastructure (in French) places recovery within the site’s overall operation.

The decisive deliverable is a measured balance of useful heat, paired with additional consumption, periods without an outlet and the service actually replaced. An announcement of recoverable capacity remains a project milestone; actual delivery requires separate evidence.

Sources and scope

Consulted on 22 October 2026: DOE/NREL, Best Practices Guide for Energy-Efficient Data Center Design, July 2024, section 7; Scottish Government, technical characteristics and commercial considerations, 25 July 2024. Both numerical examples are fictional; no performance of an existing heat network is claimed.