In physics, “energy efficiency” refers to the ratio between the useful energy produced by a system and the total energy consumed for its operation.
This concept is often interpreted in a broader sense to refer to technologies and practices that reduce energy consumption while maintaining an equivalent level of final efficiency. We will use this second definition of energy efficiency, which aims to “do better with less”.
In the European Union, the construction sector is the largest consumer of energy. In 2008, it absorbed 40% of total final energy consumption(1) and emitted 36% of CO2 emissions. In France, it absorbs almost 44% of total final energy consumption in 2011 (2), i.e. 69 Mtoe. Its consumption has increased nationally by almost 25% in the last 20 years.
Improving energy efficiency in the building sector is, therefore, a priority area for progress. It relies in particular on public policies.
Among solutions to improve energy efficiency, it is common practice to distinguish between so-called “passive” solutions, which consist of reducing the energy consumption of equipment and materials through improved intrinsic performance, and so-called “active” solutions aimed at optimizing flows and resources.
They consist of increasing the intrinsic qualities of a building in order to optimize the use of the energies supplied to it.
For example, many parameters can be taken into account when constructing a building:
- their orientation and ability to harness light energy, to capture and protect themselves from solar energy (bioclimatic architecture (3), surface materials);
- reinforced thermal insulation, e.g. through false ceilings that prevent the use of thermal inertia, materials such as mineral wool or hemp, reinforced double glazing or pariethodynamic windows (4) (which allow outside air to be heated by moving between two glazings, one of which may be double). Thermal insulation from the outside (e.g. with expanded or extruded polystyrene bricks) reduces heat loss from the walls by up to 80% (5);
- better general water tightness of the frame (parasitic air due in particular to connections between facades and floors, especially between facades and carpentries or electrical equipment passages). The installation of watertight boxes and shutters can reduce air leaks by more than 90% (up to 15 kWh/m2/year savings) depending on the type of insulation of the building (6);
- more efficient ventilation systems. Double-flow controlled mechanical ventilation (7) reduces energy losses by up to 70% compared to conventional single-flow ventilation(8) (but installation is still much more expensive).
The heating system
The heating season absorbs approximately 2/3 of the total energy consumed in residential buildings in France for old buildings (9). More efficient systems are being developed:
- condensing boilers (energy recovery through the condensation of water vapor from fuels and reduction of pollutant emission rates) and low-temperature boilers (running on water varying between 30 and 75°C) consume between 12 and 20% less energy than conventional oil-fired installations (10);
- Heating systems based on renewable energies (heat pumps or solar systems) can also be installed. The different types of biomass heaters that use wood as fuel have high efficiencies (up to 95%);
- cogeneration boilers to produce electricity at the same time as thermal energy. They can generate primary energy savings of around 20%, but their electrical efficiency is low and does not meet needs.
In 2010, more than 40% of energy savings are achieved through the installation of energy-efficient heating systems and 13% through insulation work (mainly due to the lack of opaque wall insulation, but there is significant potential in this area) (11).
Lighting and household appliances absorb 15% of the energy consumed in the residential sector (12). Energy-saving lamps (fluorescent or LEDs) save more than 50% energy compared to incandescent lamps (on the other hand, they do not create heat like these incandescent lamps). The household appliances available in 2011 consume on average almost 40% less electricity than those marketed in 2000 (13). The electricity consumption of refrigerators and freezers was reduced by a factor of 3 between 1999 and 2009, thanks in particular to better cold circulation and more efficient compressors.
The “active” solutions
Its objective is to use the “only necessary” energy through the active management of the equipment.
Intelligent” technological systems
So-called intelligent systems make it possible to measure, control and regulate the electricity consumption of buildings (temperature sensors, presence sensors for lighting, CO2 emissions for ventilation, etc.) and thus avoid unnecessary consumption (14).
Intelligent electric heating systems include, for example, an electronic control system that detects the opening of windows (energy saving of 4% in this station) or the presence in the home (potential gain of 12% in this station). These intelligent solutions could reduce a building’s overall energy consumption by 10-20% (15).
At the European Union level, the 20-20-20-20-20 initiative sets the target of reducing the EU’s primary energy consumption by 20% between 2005 and 2020. Several directives are being implemented to improve the energy performance of buildings (e.g. the Energy Efficiency and Energy Labelling Directives of May 2010).
In France, the Grenelle Round Table on the Environment meets Community requirements and sets the objective of reducing the energy consumption of buildings by 38% by 2020. In particular, it foresees the renovation of 400,000 homes a year from 2013, whose consumption must not exceed 150 kWh/m2/year (16).
The French RT 2012 thermal regulation establishes a maximum primary energy consumption threshold for new buildings of 50kWh/m2/year on average (base weighted by geographical location and altitude)(17), which corresponds to the BBC (Low Consumption Building) standard. It is much more ambitious than the previous Regulation (RT 2005), which imposes (18) maximum average energy consumption of 120 to 220 kWh/m2/year for buildings constructed after 2005.
The State is also introducing incentives to encourage energy savings in buildings: subsidies, interest-free loans, tax advantages, creation of the “high energy efficiency” label, etc. The State is also introducing incentives to encourage energy savings in buildings: subsidies, interest-free loans, tax advantages, creation of the “high energy efficiency” label, etc. The State is also introducing incentives to encourage energy savings in buildings: subsidies, interest-free loans, tax advantages, creation of the “high energy efficiency” label, etc. The aim is to encourage people to do energy improvement work and to rent, buy or build energy-efficient housing.
For example, the “energy efficiency diagnosis” (EPD), which assesses the energy quality of a building by estimating its annual consumption (in kWh/m2/year), has been imposed since July 2007 in France, when selling or renting a building. It allows users to assess the level of their energy bills.
Individual and collective consciousness can influence the general way of thinking about habitat and its way of life. In 2010, only 47% of consumers knew the total amount of energy they consumed (19). Eco-citizen” behaviors and simple actions, such as turning off appliances while on standby, are promoted through communication actions. So-called standby consumption represents up to 18% of specific electricity consumption (excluding heating and hot water), i.e. almost 850 kWh per year and per household. Visualization of consumption on a screen and knowledge of the theoretical consumption foreseen in the design of the building allow individuals to better adapt their behavior.
Economic and industrial questions
The aging of the French housing stock and its low rate of renovation (1% per annum) are obstacles to improving energy efficiency. This depends to a large extent on the renovation of the 19 million homes built in the country before 1975. They account for 58% of housing in France and consume on average 2 to 3 times more energy than recent housing (20).
Improving the energy efficiency of buildings opens up important industrial opportunities (in particular for agents developing innovative and expensive technologies such as Bouygues, Schneider Electric, etc.). It requires the acquisition of new skills by the actors involved in the construction of the building. The European Union estimates that 1.4 million additional workers will need to acquire these skills by 2015 (21).
In France, the construction sector generates 25% of national greenhouse gas (GHG) emissions. Under the Kyoto Protocol, the European Union is committed to reducing its GHG emissions by 8% between 2008 and 2012 compared to 1990 levels. The agreement concluded at the Community level provides for different reduction efforts between the Member States and requires France to stabilize its GHG emissions over the period 2008-2012. Improved energy efficiency can help achieve this objective. Carbon markets are forcing industrialists and governments to limit their environmental footprint.
In France, average energy consumption per private dwelling was 196 kWh/m2/year in 2008 (of which 156 kWh/m2/year for heating and domestic hot water)(22) compared to 355 kWh/m2/year in 1973. The energy efficiency of the total housing stock improved by 24% between 1990 and 2008, mainly due to gains in heating (+27%) and in large electrical equipment (+23%)(23).
Area of presence or application
Many States have committed to improving the energy efficiency of their buildings in action plans such as that of the United Kingdom with the CRC Energy Efficiency Plan for Public Buildings (2008) or that of the United States.
Past and Present
In the 1970s, the oil shocks highlighted the need for energy efficiency measures to reduce dependence on fossil fuels. Thermal standards are successively established to limit the consumption of buildings in France: RT 1974, 1988, 2000, 2005 and 2012.
Global warming and rising energy prices are generating renewed interest in energy efficiency and the strengthening of public policies.
In France, the energy policy bill proposes to reduce French energy intensity (24) by 2% a year by 2030.
The TR 2012 limits the maximum energy consumption of buildings constructed after 2012 to an average of 50 kWh/m2/year. The Round Table of the Environment Round Table foresees that “positive energy buildings” will become the norm from 2020 for new residential buildings (to be considered at the district level)(25).
The European Union wants buildings constructed in the Member States after 2018 to be “zero energy” buildings, which produce as much energy as they consume (26). An intelligent European grid (electricity and heating sensors, etc.) must be deployed to enable consumers to use energy in a more controlled way (27).