Designing and building low-energy homes and buildings, including zero-energy buildings, passive houses and green buildings, incorporates any of a number of building techniques and systems to lower the energy used. The following are just some of the building techniques that can be used to achieve lower the energy usage in buildings.

These low-energy building techniques exclude energy generation.

Improvements to the building

• Barra system - Developed by Horazio Barra in Italy this a passive solar building technique uses a collector wall to capture solar radiation in the form of heat. It then distributes the warmed air through channels incorporated into the floors, warming the floors and the building. In hot weather, cool nighttime air can be drawn through the floors to chill them in a form of air conditioning.
• Brise soleil - refers to a variety of permanent sun-shading techniques, ranging from the simple patterned concrete walls to more elaborate devices.
• Cool roofs - a roofing system that is designed to reflect the visible, infrared and ultraviolet wavelengths of the sun, reducing heat transfer to the building and has the ability to release a large percentage of absorbed, or non-reflected, solar energy.
• Green roofs - is a roof that is partially or completely covered with plants and soil. This does not refer to roofs which are merely painted green or use green coloured roofing material.
• Daylighting - during the day natural light provides effective internal illumination through the strategic placement of windows, or other transparent media, and reflective surfaces.
• Earth sheltering - is an age old practice of using earth against building walls to reduce heat loss and to maintain a constant indoor air temperature.
• Fluorescent lighting - converts electrical power into useful light more efficiently than an incandescent lamps and the lower energy costs offsets the higher initial cost of the lamps.
• Compact fluorescent lamps - are designed to replace an incandescent lamp and can fit in the existing light fixtures formerly used for incandescents.
• Passive solar building design - aim to maintain interior thermal comfort throughout the sun's daily and annual cycles whilst reducing the requirement for active heating and cooling systems
• Passive solar techniques - use sunlight for useful energy without use of active mechanical systems. They convert sunlight into usable heat (water, air, thermal mass), cause air-movement for ventilating, or store heat for future use, with little use of other energy sources.
• Passive cooling techniques - slow heat transfer into a building or remove unwanted heat from a building through ventilating or solar air conditioning.
• Superinsulation - uses predominantly intrinsic heat sources (waste heat generated by appliances and the body heat of the occupants), without using passive solar building design techniques or large amounts of thermal mass, and with very small amounts of backup heat.
• Trombe walls - are sun-facing walls built from material that can absorb heat(such as stone, metal, concrete, adobe or water tanks) and are combined with an air space, insulated glazing and vents to form a large solar thermal collector.
• Windcatchers - A windcatcher is a traditional Persian device used for many centuries to create natural ventilation in buildings.

 Ebooks like Home Made Power Plant shows you how to install energy replacement devices at a relatively low cost and without any major remodeling while online bookstores like Amazon have a number of books on Green building, remodeling and energy savings available.

Source: Wikipedia