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.
National standards
In some countries the term relates
to a specific building standard. In particular, these seek to limit the energy
used for space heating, since in many climate
zones it represents the largest energy use. Other energy use may also be
regulated. The history of passive solar
building design gives an international look at one form of low-energy
building development and standards.
Europe
In Germany a
low-energy house (Niedrigenergiehaus) has a limit equivalent to 7 litres
of heating oil for each square metre of room for space heating annually
(50 kWh/m²a or 15,850 Btu/ft²/yr). In Switzerland,
the term is used in connection with the MINERGIE standard (42 kWh/m²a or
13,300 Btu/ft²/yr) or the Minergie-P (equivalent to the Passivhaus).
In comparison, the German Passivhaus
ultra-low-energy standard, currently undergoing adoption in some other European countries,
has a maximum space heating requirement of 15 kWh/m²a or 4,755 Btu/ft²/yr.
A "sub-10 passive house"
is under construction in Ireland that has an independently evaluated PHPP
(Passive House) rating of 9.5 kW/m2/year. Its form of
construction also tackles the issue of embodied energy, which can significantly
distort the lifecycle CO2 emissions associated with even low energy
use houses.
North America
In the United States, the ENERGY STAR
program is the largest program defining low-energy homes and consumer
products. Homes earning ENERGY STAR certification use at least 15% less
energy than standard new homes built to the International Residential Code,
although homes typically achieve 20%–30% savings.
In addition, the US Department of
Energy launched a program in 2008 with the goal of spreading zero-energy
housing over the US. Currently, participating builders commit to constructing
new homes that achieve 30% savings on a home energy rating scale.
Zero-energy and energy-plus
buildings
Beyond ultra-low-energy buildings
are those that use, on average over the course of a year, no imported energy - zero-energy buildings – or even those that
generate a surplus - energy-plus houses – both of which have been and
are being successfully built.
This can be achieved by a mixture
of energy conservation technologies and the use of
renewable
energy sources. However, in the absence of recognized standards, the mix between
these – and consequently the energy-use profile and environmental impact of the
building – can vary significantly.
At one end of the spectrum are
buildings with an ultra-low space heating requirement that therefore require
low levels of imported energy, even in winter, approaching the concept of an autonomous building.
At the opposite end of the spectrum
are buildings where few attempts are made to reduce the space heating
requirement and which therefore use high levels of imported energy in winter.
While this can be balanced by high levels of renewable energy generation
throughout the year, it imposes greater demands on the traditional national
energy infrastructure during the peak winter season.
Low-energy technology
Introduction
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
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. In climates
and regions needing to reduce excessive summer passive solar heat gain, whether
from the direct or reflected sources, can be done with a Brise
soleil, trees,
attached pergolas
with vines, vertical
gardens, green roofs, and other techniques.
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.
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