Alow-energy house is characterized by an energy-efficient design and technical features which enable it to provide high living standards and comfort with low energy consumption and carbon emissions. Traditional heating and active cooling systems are absent, or their use is secondary.[1][2] Low-energy buildings may be viewed as examples ofsustainable architecture. Low-energy houses often haveactive andpassive solar building design and components, which reduce the house's energy consumption and minimally impact the resident's lifestyle. Throughout the world, companies and non-profit organizations provide guidelines and issue certifications to guarantee the energy performance of buildings and their processes and materials. Certifications include passive house, BBC—Bâtiment Basse Consommation—Effinergie (France), zero-carbon house (UK), andMinergie (Switzerland).[3]
Buildings alone were responsible for 38% of all humanGreenhouse gas emissions (GHG) as of 2008, with 20% attributed to residential buildings and 18% to commercial buildings.[4] According to theIntergovernmental Panel on Climate Change (IPCC), buildings is the sector which presents the most cost effective opportunities for GHG reductions.[5]
During the 1970s, research on low-energy buildings was done inDenmark,Sweden,Germany,Canada, and theUnited States. The implementation of standardized low-energy building concepts has developed differently in each country.[6]
In the late 1970s, the province ofSaskatchewan contracted theSaskatchewan Research Council to design and build a passive solar house suitable for the extreme climate of theCanadian prairies, where winter temperatures can drop to negative 40 degrees Celsius (-40°F).[7] The project resulted in the construction of theSaskatchewan Conservation House inRegina in 1977 by a team led by engineerHarold Orr.[8] The project developed a heat recovery air exchanger (HRV), hot water recovery, and a blower-door apparatus to measure building air-tightness, techniques that became common in low-energy building in other parts of the world.[9] Orr would go on to apply many of those techniques to retro-fitting existing buildings to improve energy efficiency.[10][11]
Triggered in the 1970s by the first energy crisis and growing environmental awareness, energy conservation became increasingly important in Germany.[12] In 1977, the country's first energy-related building standard was enacted. The GermanPassivhaus Institute introduced the first certified passive house in 1990. The annual heating requirement was introduced as an important parameter by the third German Thermal Insulation Ordinance (1995). In 2013, however, there was no clear legal requirement for a low-energy building standard in Germany. According to Maria Panagiotidou and Robert J. Fuller, definitions, policies and construction activity of zero-energy buildings must be clear.[13] TheEuropean Union's Energy Performance Directive requires that beginning in 2021, only low-energy buildings may be built.[14]
Changes to national policies have occurred since May 2015 in the UK. One of the most significant has been the withdrawal of theCode for Sustainable Homes (CfSH) as a system for assessing and encouraging improvements in the environmental design of dwellings.[15] This has abandoned the code's schematic which provided a framework of achievement levels and to which low-energy designers could aspire to meet or surpass. Although energy-conservation legislation still exists in thebuilding regulations,[16] there is a lack of suitable standards exceeding basic regulations. As a result, the Passive House Standard may expand its influence and impact on energy-efficient houses.[17]
Interest in low-energy buildings has increased in the United States, primarily due to rising energy prices, decreasing costs for onsite renewable-energy systems, and increasing concern about climate change.California requires all new residential construction to bezero net energy by 2020.[1]
Low-energy houses are broadly defined, but are generally known as houses with a lower energy demand than common buildings regulated by the national building code. The term "low-energy house" is used in some countries for a specific type of building.[18]
A low-energy house is a guideline rarely specified in actual values (heat load or space-heating minimum). A passive house is a standard, with specific recommendations to save heating energy.
At one end of the spectrum are buildings with an ultra-low space-heating requirement which require low levels of imported energy (even in winter), approaching anautonomous building. At the opposite end are buildings where few attempts are made to reduce their space-heating requirement and which use high levels of imported energy in winter. Although this may be balanced by high levels of renewable-energy generation throughout the year, it imposes greater demands on the national energy infrastructure during winter.
The term "low-energy houses" may refer to national building standards.[19] These standards sometimes seek to limit the energy used forspace heating, which is the largest energy consumer in manyclimate zones. Other energy uses may also be regulated. Thehistory of passive solar building design provides an international view of one form of low-energy-building development and standards.
Standards for low-energy buildings in Europe have proceeded differently in each country, and there is no common certification or legislation for low-energy buildings valid in all EU member states. As a movement towards reducing energy use and emissions, a common legislation concerning buildings’ energy performance, theEnergy Performance of Buildings Directive (EPBD) was published in 2002 and became effective in January 2003.[20]
In NS 3700, the draft official standard, low-energy buildings are defined. About the buildings' energy performance, two alternatives for rating their primary energy use are under discussion:
Low-energy houses are defined in the National Building Regulation Building Regulations 08, and are divided into two classes. They are regulated in the regulations' chapter 7.2.4: Low-energy.
Low-energy houses certified by RAL-GZ 965 have 30 percent less heat losses than regulated in the EnEV, a national building code. Other criteria affectinsulation,air tightness andventilation. Low-energy buildings may be certified by RAL-GZ 965 for planning or construction.[18]
Low-energy buildings may receive theMinergie certification, a "quality label for new and refurbished buildings". The Minergie standard requires that buildings do not exceed 75 percent of average building energy consumption and fossil-fuel consumption must not exceed 50 percent of the average.[21]
The European Union directive has clarified low-energy houses in Europe, and a large portion of the discussions on zero-energy building in North America derives from the U.S.National Renewable Energy Laboratory (NREL).[22]
TheEnergy Star program is the largest certifier of low-energy homes andconsumer products in the U.S. Although certified Energy Star homes use at least 15 percent less energy than standard new homes built in accordance with the International Residential Code, they typically achieve a 20- to 30-percent savings.[23] TheUnited States Department of Energy introduced a program in 2008 to distribute zero-energy housing across the country.[24]
Canadian builders may use a range of standards, labels, and certification programs to demonstrate a high level of energy performance in a given project. These include:
InBritish Columbia the above programs align with theBC Energy Step Code, a provincial regulation to incentivize (or require) a level ofenergy efficiency in new construction beyond the base building code. The code was designed as a technical road map to help the province reach its target of all new net-zero-energy-ready buildings by 2032.
Energy efficient housing affectsindoor air quality. Airtight houses will trap pollutants inside them, whether produced indoors or outdoors, and lead to an increase in human exposure and potential health issues.[29][30]
Energy-efficient design often relies on new technologies and techniques. These may create technical obstacles in addition to social, cultural, and economic non-technical obstacles.[17]
Buildings designed for good energy efficiency do not always live up to the design goals; various reasons lead to thisperformance gap.
Low-energy building design is considered important to encourageresource efficiency and reduce globalclimate change associated with the burning offossil fuels. Design involves two general strategies: minimizing the need for energy use in buildings (especially for heating and cooling) through energy-efficient measures (EEMs) and adoptingrenewable energy and other technologies (RETs) to meet remaining energy needs. EEMs includebuilding envelopes, internal conditions, and building-services systems; RETs includephotovoltaic or building-integrated photovoltaic,wind turbines, solar thermal (solar water heaters),heat pumps, anddistrict heating and cooling. Impacts include life-cycle costs, environmental impacts, and climate-change and social-policy issues.[31] The best low-energy designs offer occupants a better environment and more stable, controlled thermal comfort in addition to reduced energy costs.
GHG emissions associated with buildings construction are mainly coming from:
The construction, renovation, and deconstruction of a typical building is on average responsible for the emissions of 1,000–1,500 kg CO2e/m2 (around 500 kg CO2e/m2 for construction only).
Strategies adopted by low-carbon buildings to reduce GHG emissions during construction include:
Reduction of energy consumption is more environmentally and financially advantageous than increasing onsite production to reach a low-energy goal. The less a home consumes, the smaller renewable-energy system it requires to reach net zero. Energy efficiency should always be the primary design strategy of a low-energy house.[1]
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Passive solar building design andenergy-efficient landscaping support the low-energy house in conservation and can integrate it into a neighborhood and environment. Followingpassive solar building techniques, where buildings are compact in shape to reduce surface area and principal windows oriented towards theequator (south in theNorthern Hemisphere and north in theSouthern Hemisphere) maximizes passivesolar gain. However, solar gain (especially intemperate climates) is secondary to minimizing the overall house-energy requirements. In hot 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.[32] Other techniques to reduce excess solar heat includebrise-soleils,trees, attachedpergolas withvines,vertical gardens, andgreen roofs.
Although low-energy houses can be constructed from dense or lightweight materials, internalthermal mass is normally incorporated to reduce summer peak temperatures, maintain stable winter temperatures, and prevent possible overheating in spring or autumn before the highersun angle "shades" midday wall exposure and window penetration. Exterior wall color (when the surface allows choice) reflection or absorption depends on the predominant year-round outdoor temperature. The use ofdeciduous trees and walltrellised (or self-attaching) vines can assist in temperate climates.
To minimize total primary energy consumption,passive andactive daylighting are the first daytime solutions to employ. For low-light days, non-daylight spaces and nighttime, sustainable lighting design with low-energy sources (such as standard-voltagecompact fluorescent lamps andsolid-state lighting withLED lamps,OLEDs andpolymer light-emitting diodes and low-voltageincandescent light bulbs,compact metal halide,xenon andhalogen lamps) can be used.
Solar-powered exterior security andlandscape lighting, withsolar cells on each fixture or connecting to a centralsolar panel, are available for gardens and outdoor needs. Low-voltage systems can be used for more controlled (or independent) illumination, using less electricity than conventional fixtures and lamps. Timers,motion detection and daylighting operation sensors further reduce energy consumption andlight pollution.
Home appliances meeting independent energy-efficiency testing and receivingEcolabelcertification marks for reduced electrical and natural-gas consumption and product-manufacturingcarbon emission labels are preferred for low-energy houses. Energy Star andEKOenergy are other certification marks.
Buildings
Air and temperature
Solar
Sustainability
Energy rating standards
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