Low-energy house

A low-energy house is any type of house that from design, technologies and building products uses less energy, from any source, than a traditional or average contemporary house. In the practice of sustainable design, sustainable architecture, low-energy building, energy-efficient landscaping low-energy houses often use active solar and passive solar building design techniques and components to reduce their energy expenditure.

General usage
The meaning of the term ‘low-energy house’ has changed over time, but in Europe it generally refers to a house that uses around half of the German or Swiss low-energy standards referred to below for space heating, typically in the range from 30 kWh/m²a to 20 kWh/m²a (9,500 Btu/ft²/yr to 6,300 Btu/ft²/yr). Below this the term ‘Ultra-low-energy building’ is often used.

The term can also refer to any dwelling whose energy use is below the standards demanded by current building codes. Because national standards vary considerably around the world, ‘low-energy’ developments in one country may not meet ‘normal practice’ in another.

Zero-energy building

Low-energy technology

Low-energy buildings typically use high levels of insulation, energy efficient windows, low levels of air infiltration and heat recovery ventilation to lower heating and cooling energy. They may also use passive solar building design techniques or active solar technologies. These homes may use hot water heat recycling technologies to recover heat from showers and dishwashers. Lighting and miscellaneous energy use is allieviated with fluorescent lighting and efficient appliances. Weatherization provides more information on increasing building energy efficiency.

Passive Houses are required to achieve a whole building air change rate of no more than 0.6 ac/hr under forced pressurisation and depressurisation testing at 50Pa minimum. On site blower door testing by certified testers is used to prove compliance.

A significant feature of ultra-low-energy buildings is the increasing importance of heat loss through linear thermal bridging within the construction. Failure to eliminate thermal pathways from warm to cold surfaces (“bridges”) creates the conditions for interstitial condensation forming deep within the construction and lead to potentially serious issues of mould growth and rot. With near zero filtration losses through the fabric of the dwelling, air movement cannot be relied upon to dry out the construction and a comprehensive condensation risk analysis of every abutment detail is recommended.

Improvements to heating, cooling, ventilation and water heating
Absorption refrigerator
Annualized geothermal solar
Earth cooling tubes
Geothermal heat pump
Heat recovery ventilation
Hot water heat recycling
Passive cooling
Renewable heat
Seasonal thermal energy storage (STES)
Solar air conditioning
Solar hot water
Solar devices

Passive solar design and landscape
Passive solar building design and energy-efficient landscaping support the low-energy house in conservation and can integrate them into a neighborhood and environment. Following passive solar building techniques, where possible buildings are compact in shape to reduce their surface area, with principal windows oriented towards the equator – south in the northern hemisphere and north in the southern hemisphere – to maximize passive solar gain. However, the use of solar gain, especially in temperate climate regions, is secondary to minimizing the overall house energy requirements. On the other hand in hot climates temperatures excess heat can create uncomfortable indoor conditions. Passive alternatives to air conditioning systems such as temperature-dependent venting have been shown to be effective in regions with cooling needs. Other techniques to combat excessive solar heat gains include Brise soleils, trees, attached pergolas with vines, vertical gardens, green roofs among others.

Low-energy houses can be constructed from dense or lightweight materials, but some internal thermal mass is normally incorporated to reduce summer peak temperatures, maintain stable winter temperatures, and prevent possible overheating in spring or autumn before the higher sun angle “shades” mid-day wall exposure and window penetration. Exterior wall color, when the surface allows choice, for reflection or absorption insolation qualities depends on the predominant year-round ambient outdoor temperature. The use of deciduous trees and wall trellised or self attaching vines can assist in climates not at the temperature extremes.

Sustainable landscaping
Sustainable landscape architecture
Sustainable gardening
Rainwater harvesting
Water conservation

Lighting and electrical appliances
To minimize the total primary energy consumption, the many passive and active daylighting techniques are the first daytime solution to employ. For low light level days, non-daylighted spaces, and nighttime; the use of creative-sustainable lighting design using low-energy sources such as ‘standard voltage’ compact fluorescent lamps and solid-state lighting with Light-emitting diode-LED lamps, organic light-emitting diodes, and PLED – polymer light-emitting diodes; and ‘low voltage’ electrical filament-Incandescent light bulbs, and compact Metal halide, Xenon and Halogen lamps, can be used.

Solar powered exterior circulation, security, and landscape lighting – with photovoltaic cells on each fixture or connecting to a central Solar panel system, are available for gardens and outdoor needs. Low voltage systems can be used for more controlled or independent illumination, while still using less electricity than conventional fixtures and lamps. Timers, motion detection and natural light operation sensors reduce energy consumption, and light pollution even further for a Low-energy house setting.

Appliance consumer products meeting independent energy efficiency testing and receiving Ecolabel certification marks for reduced electrical-‘natural-gas’ consumption and product manufacturing carbon emission labels are preferred for use in Low-energy houses. The ecolabel certification marks of Energy Star and EKOenergy are examples.

Energy-saving lighting
Energy conservation
Alternative energy

Constraints and economic benefits


The extra cost of a single house complying with the 2012 Thermal Regulation is generally 10 to 15%. This is mainly due to the prices of the materials needed and essential to achieve the objectives set

Return on investment:

You should know that the annual bill of heating represents 900 euros on average per household, with great disparities (250 euros for a house “BBC” up to more than 1800 for a poorly insulated house)

Savings on energy consumption, which is three to four times lower than a conventional home, provides a good return on investment (around 4 years). The real economy is estimated at 15,000 euros over 20 years, for a single house.

Tax benefits and financial assistance:
Some of the benefits of building RT2012-compliant buildings include:

the Eco-Ready Zero Rate (Eco-PTZ) which facilitates homeownership for first-time buyers investing in a new housing with high energy performance, thanks to the elimination of interests, supported by the State.
Buildings holding the “BBC” label may also benefit from a reduction or even a property tax exemption on built properties
Duflot law, former Scellier scheme for rental investment guarantees to all French taxpayers acquiring a new housing and intended for rental a tax reduction spread over nine years and which corresponds to 18% of the initial cost price, for housing labeled BBC
the sustainable development tax credit, for existing buildings (capped at € 8,000, it concerns thermal insulation or replacement of equipment, which must meet energy requirements)

Characteristics of a low-energy house

A bioclimatic conception of the habitat

The orientation of the house
The goal is to recover maximum heat and sunlight in winter and reduce these contributions in summer. East-West exposure is not recommended. In the West, the building accumulates heat due to direct sun exposure in the afternoons and overheating in the summer.

The North exposure is the coldest part. Less used spaces will need to be developed in the North in order to reduce the impact of the cold, minimize building temperature decreases and contribute to the energy savings and comfort of the inhabitants. Garage, stairs, hallways, etc. are little used and low temperature parts: they are ideal buffer zones.

The southern exposure is often the most interesting to respect the summer comfort and to recover the free solar contributions during the winter. In winter, the very low sun warms the walls of the house which preserve heat, solar rays penetrate inside the windows, and thus provide a basic heating. It is in the south that we will have the living rooms. The southern orientation is also favorable for solar energy systems (solar thermal collectors for heating and hot water, photovoltaic panels for electricity production). In summer, the sun arrives vertically and will not enter the house, whose bays can be protected by an advance (balcony or brise-soleil for example) or blinds slats orientable.

The shape of the building
The architecture of a house has a very strong impact on energy consumption. The role of the architect is very important. The more compact a building is, the less energy it consumes. For this reason, for a good home, the ratio of the wall surfaces in contact with the outside to the living space must be low. The spherical shape is the shape that has the smallest surface-to-volume ratio. It is therefore perfect for reducing thermal losses of the building envelope. Nevertheless, for the sake of traditional architecture, we use the cube that comes closest to the sphere. A compact building will therefore consume less than an L-shaped or multi-storey building.

Strong thermal insulation
Thermal insulation refers to all the techniques used to limit heat transfer between a hot environment and a cold environment. The 2012 thermal resistance standards (in m².k / W) are as follows: R ≥ 8 for attics, to 4 for walls and floors.

Whether the construction system is wood framing, blocks or bricks, all walls must be insulated. The insulation will be thermal, but also acoustic.

Wall insulation:
From the inside: There are two different methods: glued doubling, which consists simply of gluing on the wall the insulation associated with a plasterboard or the metal frame that consists of sliding between a wall and a metal structure made of rails and amounts insulating it.
From the outside: The house is wrapped with an insulating material that is then covered with an external covering such as plaster, cladding, etc. to protect against bad weather.
Distributed insulation: This system is only possible with certain construction modes where the building structure also has thermal performance.

Insulation of attics and ceilings: Roof insulation is essential for good thermal insulation, because it is considered that it is through the roof that escapes 30% of the heat of building. It will be necessary to isolate the lost roofs (insulation in “bulk” in order to form a continuous and homogeneous mattress) and the done up roof spaces (there are two techniques of isolation: from the inside or the outside, thanks to the sarking, this technique consists of laying a vapor barrier horizontally and parallel to the gutter of the building and then laying an insulation over it).
Soil insulation: To insulate the floor we opt for expanded polystyrene, extruded, wood wool, projected insulation, etc. When the floor is on a crawl space, a composite insulation floor made of polystyrene interjoist and under-floor insulation is manufactured.

The characteristics of some insulators:

The insulating power of a material comes from the air it traps. There are a lot of insulating materials, here are some of them:

Material Composition λ (W / (mK))
Glass wool Fiberglass 0.030 – 0.040
Expanded polystyrene Styrofoam beads expanded by water vapor 0.030 – 0.038
Extruded polystyrene Beads of extruded styrene monomer with a blowing agent (gas) 0.029 – 0.035
Cellulose wadding Recycled paper made non-flammable and resistant to vermin 0.035 – 0.041
Wood fiber Wood residues 0.038 – 0.045

Thermal bridges

A thermal bridge is a point or linear zone which, in the envelope of a building, presents a variation of thermal resistance. This is a point in the construction where the insulation barrier is broken. A thermal bridge is created if:

there is a change in the geometry of the envelope,
there is a change of materials and / or thermal resistance.
Ten years ago a thermal bridge accounted for 10 to 20% of total building losses. Over time, the insulation has improved and the percentage of losses due to the walls has fallen sharply, and that of the thermal bridges has greatly increased. However today, with the implementation of the Thermal Regulation 2012, solutions are put in place to minimize thermal bridging using thermal breakers and insulation from the outside. A breaker is a device set up to stop thermal bridges, as an “insulation” at these bridges. Thermal bridges are therefore areas of high heat loss. It is important to limit them to improve the building.

Performing openings
Why worry about dividing windows according to the cardinal points?

Because windows and exterior joinery are 3 to 7 times less insulating thermally than a solid wall.
Because windows allow sunlight to enter the house, which is very favorable in winter but can lead to overheating in summer.
It is recommended to provide openings on all four sides of the house to be able to benefit from ventilation through the summer, and not to exceed 25% of the living space in glazed area.

The distribution of window areas can be considered as follows: 50% south, 20% east, 20% west and 10% north.

Sun protection (various occultations such as external blinds, shutters, caps…) should be planned from the design to avoid overheating in the summer season.

The materials used: The high performance thermal insulation keeps the heat in the winter, but also keeps the summer cool. Windows must have a minimum performance of Uw <1.6 W / (m².k). For example double glazing with reinforced insulation: windows of 4 mm, one side of which is covered with a low emissivity layer, separated by a layer of gas of 12 mm (sometimes triple glazing in the mountain areas and for the façades facing north ), as well as an insulating frame, also made of several layers (wood, aluminum, PVC) reinforced with foams or other insulators. Special attention will be paid to the joints between the frame and the frame during installation.

The same care will be given to the quality (manufacture, materials, installation) of the doors.

A perfect seal
One of the big changes between RT2005 and RT2012 is the introduction of limit values for air leaks.

What is airtightness?

These air leaks in a house account for a large part of the energy losses. In homes, air leakage can occur at the connections between the elements (the joining of a frame to a wall for example) or the frames of sliding glass windows, or to the sockets (the air can pass by the electrical sheaths). Insulation work must be supplemented by measures to improve the watertightness.

The blower door test (or blower door test) consists of measuring the infiltration of air. A machine equipped with a fan is placed on the front door of the house or building. This measures the amount of air entering the house. Using a smoke machine, it is easy to follow drafts and detect leaks. The RT 2012 sets a sealing threshold. When a building is built, it has become mandatory to measure the airtightness at the end of construction.

Double-flow ventilation with heat recovery on stale air
There are VMC single stream or double stream. If the installation is content to evacuate the stale air, it is a simple flow controlled mechanical ventilation. It comprises a single network of ducts. In the living rooms, the fresh air supply is provided by air inlets directly connected to the outside.

Having an efficient air exchange system ensures the quality of the indoor air by a sufficient intake of fresh air and evacuate air pollution as odor, moisture, Volatile Organic Components (VOC)… It also improves the energy performance of the building by controlling the amount of fresh air to increase thermal and acoustic comfort. In addition, it protects the building from damage caused by humidity.

A VMC (or mechanical ventilation controlled ) humidity adjustable simple flow adapts according to the need of renewal of the air. The flow of this air increases when the humidity increases in the house and is reduced when the premises are empty, to save energy. The openings and closures of the vents and the air intakes are fully automated.

To renew the air in all the rooms of a house, the most logical thing is to bring it into the dry living rooms, like the living room, the bedrooms or the office, and to get it out of the places where there is a concentration. humidity and bad odors, such as the kitchen, the bathroom or the toilet.

Double-flow ventilation, with recovery of stale air, will be more ecological, because the heat of the exhaust air is recovered by means of a heat exchanger before being reintroduced into the circuit (without loss of heat).

The use of renewable energy

Thermal energy
Presentation: solar thermal energy is often used to provide partially or totally hot sanitary water (DHW), more rarely to ensure the heating of the house. This practice effectively limits greenhouse gas emissions, which is why this system is strongly encouraged by many states and local authorities via taxation and bonuses (ecological bonuses, tax credits). A solar water heater covers between 40 and 80% of hot water needs of a family.

Example of how the solar water heater works: the sun’s rays, trapped by thermal sensors, transmit their energy to metal absorbers, which heat a network of copper pipes in which a heat-transfer fluid circulates. This heat exchanger in turn heats the water stored in a cumulus. There are three types of solar thermal panels.

unglazed flat collectors: water circulates in a generally black absorber open to the air
flat glass sensors (most common)
vacuum tube collectors, composed of solar collectors primed with a heat collector on which vacuum solar tubes are fixed.
The solar panels are installed in the garden, on the roof or on sunshades, where the sun is most present (that is to say preferably in the south), with an optimal inclination of 30 °. Depending on the model, the sensors must be superimposed or integrated into the roof. For domestic hot water production only, it takes from 0.7 to 1.5 m2 of sensors per inhabitant depending on the region, combined with a storage of 50 liters / m² of collectors.

Cost of the operation and return on investment It will take about a family of 4 people from 3,800 to 5,800 euros investment (sensors, balloons, regulations, connections), with a return on investment of about 10 years.

Photovoltaic solar energy

Presentation and operation

Solar energy is available everywhere on Earth and represents, theoretically, 900 times the world demand for energy. Photovoltaic solar energy is electricity produced by transforming part of the solar radiation by means of a photovoltaic cell. Schematically, a photon of incident light allows under certain circumstances to set in motion an electron, thus producing an electric current.

The production of photovoltaic electricity is therefore based on a process of direct conversion of light into electricity, thanks to so-called “semiconductor” materials. Two technologies are mainly used today:

First generation panels that use silicon. These panels represent 85% of the global photovoltaic market.
A second generation, known as thin layers, has developed on the market. They are more efficient but also more expensive because they use more rare minerals (indium and telluride). They represent 15% of the world market.
In 2008, Germany accumulates 40% and Japan 25% of solar PV installed worldwide.

25 m2 of modules can produce in one year the equivalent of the electricity consumption (excluding heating, cooking and hot water) of a family of 4 people, or about 2,500 kWh. It is better to orient the modules to the south, if possible with an inclination of 30° relative to the horizontal.

Solar panels have a lifespan of 20 to more than 30 years and are almost fully recyclable.

Limits and cost

The most widespread photovoltaic panels, made of crystalline silicon, are heavy, fragile and difficult to install.
The electrical energy is not “directly” storable, that is to say in its primary form.
Photovoltaic technology is still too expensive to be fully competitive with fossil fuels, its cost per kilowatt hour is about 4 times higher.

The installation of solar panels remains relatively expensive: depending on the type of material used, the price of installing a photovoltaic system covering an area of 10 m2 varies between 5000 and 9000 euros. In addition, for solar photovoltaic, the price of the connection to EDF (Electricity France) is about 18,000 euros for 20 m2 connected to EDF. The challenge of current research is to improve yields and reduce the costs of photovoltaic cells.

By 2020 (positive energy buildings, which will be the norm, see RT2020), the buildings will necessarily be equipped with photovoltaic panels.

Domestic wind energy
Micro-wind power (power less than 1 kW) and small wind turbines (power between 1 and 20 kW) can represent, in suitable regions (regular and frequent winds), an alternative to fossil energy. Depending on the strength and regularity of the wind, a wind turbine 5 kW which rotates 2000 hours per year at nominal power can produce the equivalent of the annual consumption of a household.

Operation: A wind turbine consists of a mast, a rotor or propeller with a vertical or horizontal axis, composed of several blades and a generator that converts mechanical energy into electrical energy. The energy produced can be used on site or connected to the grid and sold to EDF.

Constraints and cost: below 12m height, the installation is free of any constraints (except declaration of work and unless stipulated otherwise in the Local Urban Plan). For a generator of 50 kg and a rotor of 3 meters, which gives a power of 1 kW, it takes between 3000 and 5000 euros, with a return on investment of between 5 and 7 years. A tax credit is attributed to the owner who embarks on the construction of a wind turbine, as well as various local aid.

Geothermal energy and Canadian well
The Geothermal characterizes the science of internal thermal phenomena of the Earth, and the exploitation of these natural phenomena to produce heat or electricity. It is in the form of a steam tank, hot water or hot rock. It is a renewable energy used by more than 70 countries.

Geothermal energy in the building: the heat is drawn from the soil by sensors which can be buried vertically, horizontally or placed in water webs:

The horizontal sensors are distributed and buried at a shallow depth (from 0.60 m to 1.20 m), where brine or refrigerant flows in closed circuit from the inside.

Vertical geothermal probes: they are installed in a borehole and sealed with cement, where brine is circulated in closed circuit. The depth can reach several hundred meters, where the soil temperature is stable throughout the year.

Heat pumps on a water table: they draw the heat contained in groundwater (where the water temperature is constant between 7 and 12 ° C), river or lake, and require two boreholes each of which can reach several tens or hundreds of meters deep.

The Canadian well: also called a provincial well or an air-ground exchanger, the Canadian well uses geothermal energy. This is a natural ventilation system, which consists of passing some of the outside air before it enters the house, which will be replaced by pipes installed in the ground at a depth of one to two meters. The dimensions of the well vary according to the terrain.

In winter, the soil has a higher temperature than the outside, the air passing through the pipes heats up and makes the temperature of the house more constant. Conversely, the floor is colder than the outside in summer, and the air passing through the pipes then refreshes the house. The Canadian well will be used in natural heating and cooling.

The Canadian well is coupled with a heat pump (PAC): here used in the thermal setting of the building, it is a thermodynamic device that transfers a quantity of heat from a so-called “transmitter” (which provides), to a “receiving” medium (receiving). Depending on its function, the heat pump can be used as a radiator or a refrigerator. Here, the air serves as a coolant (a fluid responsible for transporting heat between several temperature sources), while the tube serves as a heat exchanger while channeling the air of the building.

Principle: The Canadian well operates on the following principle:
The fresh air enters through the mouth of entry.
This is conducted in a pipe or a fresh air intake, which must be buried at least 1.5 meters deep, to be frost-free, and that the average monthly temperature at this depth varies at seasons. The tube must withstand corrosion, being in contact with air and water, crushing, because there may be passage of a surface machine, and slight deformations, to accompany a movement field without breaking.
The air is then removed from the condensate, before landing in a heat exchanger, where the stale air of the house is led outside, while the fresh air fills it.
This system, perfectly ecological and economical in operation, is however rather expensive in terms of installation (to count around 20 000 euros), which prevents its diffusion with a wider public.

A smart home
Houses with low energy consumption often use Domotics (word derived from the contraction of the Latin word “domus”, home, and the word automatic) because it allows to optimize the consumption of energy.

What is home automation ?

It is the set of techniques of electronics, computing and communication that improve the comfort and security of the house (apartments, businesses…). It allows to manage a part of the systems of the house. We can automate energy management, security system, heating, lighting…

Home automation applications for the home

Energy management: heating (homogeneous temperature throughout the house), air conditioning, ventilation…
The management of shutters.
The management of household appliances.
Lighting management.
Security: alert in case of intrusion, fire, detection of gas leak, flood…
Communication: reception of information, remote control…
Programming of electrical appliances.

How it works ?
Home automation allows all devices to communicate with each other using Wi-Fi, radio waves or the power grid. We can centralize all electronic devices on the same support like a computer, a smartphone, a tablet or a touch panel attached to the wall to control.

The BEPOS or positive energy building is a building that produces more energy than it consumes, hence its name. It therefore uses renewable energies produced locally. By 2020, this building will be the habitat model and new building standards should specify construction modalities and constraints.

When we try to imagine how tomorrow’s home will be, and how it will consume less energy, we can mention some projects that are at the stage of research and experimentation, or even improvement:

the use of fuel cells for boilers. It is a clean and very profitable energy (of the order of 90%) which makes it possible to produce electricity through the production of water by oxidation of H2 and reduction of O2: 2H2 + O2 = 2H2O. It also produces heat, which is recovered to heat the water (sanitary and heating). Unfortunately it has disadvantages including the cost, the life and the danger due to the materials used, which are explosive. In Japan, nearly 40,000 systems have already been installed by individuals as part of the ENE Farm.

the Smart Grid also known as “smart grid”. It aims to adjust in real time the production and distribution of electricity according to consumption. It allows a house to manage the hours of “peak” where electricity costs the most expensive via a smart meter. It also makes it possible to optimize plant performance, avoid having to regularly build new lines, minimize losses online and be able to distribute electricity at the best possible price. It is also useful at the scale of a neighborhood, the energy overproduced by a particular can be used nearby by a neighbor.

the habitat coupling / Transport, experienced on the INES site in Le Bourget (collaboration between the CEA, INES and Toyota, with the support of ADEME) terminals powered by photovoltaic solar energy recharge the batteries vehicles in an optimized manner (taking into account needs).

the prefabrication is increasingly used in the construction field. It consists in preparing a set of materials (example: a whole wall, a floor), which makes it possible to reduce the number of people on a construction site, to reduce the duration of construction, and thus the costs. The low-energy buildings are directly affected by this development.

The inter-seasonal storage solar: the PROSSIS (storage method Solar Inter-Seasonal) was experienced between 2007 and 2012 by the CNRS Savoy universities, Lyon, Grenoble, CEA-INES and CIAT. It is in summer that solar panels provide the most energy and that we need it the least. The process therefore consists in storing the energy produced in the summer: the reagents are separated by an endothermic process in the summer, they are then stored at ambient temperature, and the reactants are then mixed in the winter by an exothermic process. It is a LiBr / H2O absorption process that has been tested.

Source from Wikipedia