Feature Report: Using Heat More Efficiently

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Heat Sources and District Heating

Like electricity, fuel and hydrogen, heat is an essential energy carrier. The challenge is to recover it or produce it from renewables, then deliver it to connected user sites, either clustered nearby or farther away.

fr - Les sources et les réseaux de chaleur
The boiler installation of a modern district heating system. © THINKSTOCK

In France, 58.7 million ton of oil equivalent (toe)Unit of energy measurement corresponding to the energy produced by the combustion of a ton of oil... (Mtoe) of energy is used for heating and domestic hot water in residential buildings and offices. That works out to some 38% of final energy consumption. Of this, 34.6 million tons of oil equivalent comes from oil and gas, accounting for 50% of French imports of expensive, carbon-emitting fossil fuels.

Half of all French fossil fuel imports are used to produce heat and domestic hot water.

But the potential heatIn the field of statistical thermodynamics today, heat refers to the transfer of the thermal agitation of the particles making up matter... available in France — either through heat recovery or renewable production — can be reasonably estimated at 46 million tons of oil equivalent. Tapping this potential would eliminate the use of fossil fuels for heating. And burning preservation (hydrocarbons)The final phase in petroleum system formation, after a deposit has accumulated... at flame temperatures of over 1,000°C to heat rooms to a maximum of 70 to 80°C does not make sense anyway. Some €20 billion a year would be saved and an estimated 200,000 jobs created if oil and gas were no longer used for heating.

These figures are a clear indicator of just how much rides on efficient heat management.

Heat Sources

There are several major heat sources available:

District Heating Systems

Once recovered or produced, the heat has to be distributed to users, either homes or businesses. The most effective method is a heating system that connects the energy source to points of use. A feed pipe carries hot water or steam to the buildings to be heated. Each building recovers some of the energy via a heat exchanger installed in a substation. A return pipe carried the now-tepid water to the boiler. The latest systems incorporate “smart” components to adjust the supply and return temperatures in line with changes in weather conditions.

District heating systems do not produce carbon dioxide (CO2See Carbon Dioxid ) or smokestack emissions or dust. They also reduce safety-related risks. When efficiently managed, they cut users heating bills.

Using Heat

District heating networks are extensive and expensive. In new neighborhoods, regulations are required to ensure that they are included in the planning process from the outset. In older neighborhoods, they are difficult and costly to retrofit. Close cooperation between the public authorities and businesses is critical. Countries have achieved different levels of progress in this area (See Close-Up: "Popularity Varies Worldwide").

A number of challenges arise when trying to match potential heat and end-of-chain applications (See Close-Up: "Obstacles to Overcome").


“Cow Water” Commercial dairy plants “concentrate” milk, an operation that consists of removing some of the water it contains. To do this, they must boil the milk by injecting steam. Often, several tons of steam an hour are released to the atmosphere, because it is no longer hot enough to be used in the process. The plants have developed mechanical processes to recompress the steam, sometimes called “cow milk”, and then reuse it.