Low-energy house

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 be zero net energy by 2020.[1]

Triggered in the 1970s by the first energy crisis and growing environmental awareness, energy conservation became increasingly important in Germany.[7] In 1977, the country's first energy-related building standard was enacted. 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.[8] The European Union's Energy Performance Directive requires that beginning in 2021, only low-energy buildings may be built.[9]

Changes to national policies have occurred since May 2015 in the UK. One of the most significant has been the withdrawal of the Code for Sustainable Homes (CfSH) as a system for assessing and encouraging improvements in the environmental design of dwellings.[10] 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 the building regulations,[11] 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.[12]

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, the Energy Performance of Buildings Directive (EPBD) was published in 2002 and became effective in January 2003.[14]

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:

• A limit on a building's annual CO₂ emissions, calculated by multiplying the annual supplied energy by a CO₂ factor
• A percentage of its heating demand must be met with renewable energy.

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 affect insulation, air tightness and ventilation. Low-energy buildings may be certified by RAL-GZ 965 for planning or construction.[15]

Low-energy buildings may receive the Minergie 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.[16]

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).[17]

The Energy Star program is the largest certifier of low-energy homes and consumer 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.[18] The United States Department of Energy introduced a program in 2008 to distribute zero-energy housing across thecountry.[19]

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:

• Net Zero Home and Net Zero Ready Home certifications, administered by the Canadian Home Builders' Association[20]
• Built Green labels, administered by Built Green Canada[21]
• Energy Star for Homes, administered by Natural Resources Canada[22]
• The Canadian Passive House standard, administered by the Canadian Passive House Institute[23]

In British Columbia the above programs align with the BC Energy Step Code, a provincial regulation to incentivize (or require) a level of energy 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.

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 near net zero. Energy efficiency should always be the primary design strategy of a low-energy house.[1]

Passive solar building design and energy-efficient landscaping support the low-energy house in conservation and can integrate it into a neighborhood and environment. Following passive solar building techniques, where buildings are compact in shape to reduce surface area and principal windows oriented towards the equator (south in the Northern Hemisphere and north in the Southern Hemisphere) maximizes passive solar gain. However, solar gain (especially in temperate 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.[25] Other techniques to reduce excess solar heat include brise-soleils, trees, attached pergolas with vines, vertical gardens, and green roofs.

Although low-energy houses can be constructed from dense or lightweight materials, 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" 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 of deciduous trees and wall trellised (or self-attaching) vines can assist in temperate climates.

To minimize total primary energy consumption, passive and active 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-voltage compact fluorescent lamps and solid-state lighting with LED lamps, OLEDs and polymer light-emitting diodes and low-voltage incandescent light bulbs, compact metal halide, xenon and halogen lamps) can be used.

Solar-powered exterior security and landscape lighting, with solar cells on each fixture or connecting to a central solar 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 and light pollution.

Home appliances meeting independent energy-efficiency testing and receiving Ecolabel certification marks for reduced electrical and natural-gas consumption and product-manufacturing carbon emission labels are preferred for low-energy houses. Energy Star and EKOenergy are other certification marks.

• World Map of international known Net Zero Energy Buildings
• Building of low energy houses with Insulating Concrete Forms