Towards the positive energy building

The design of buildings must evolve by taking into account the energy balance. It is necessary to avoid energy losses and to increase solar energy inputs through the best adapted orientation and design of the building (bioclimatic architecture), and by imagining innovative solutions; thus, a vegetation cover can limit energy losses while improving the integration of the building into the surrounding environment.

New concepts of climatic housing, which have been developed, are applicable not only to individual houses, but also to large buildings. A recent design makes it possible to modulate solar energy input by using a concrete lattice, which can either let in solar light or operate as a sun visor [40]. This structure can also support solar panels.

Air circulation is achieved through natural convection and greenhouses are used to create vegetation protection of the sides most exposed to the sun's radiation (Hypergreen tower).

It is necessary to boost the efforts aimed at the development of better performing materials and equipment. This includes thermal insulation technologies, which are still advancing through the use of better performing materials and more efficient implementation. Triple-glazed windows, ensuring excellent thermal and also phonic insulation, are now available.

The reduction of energy consumption can be also achieved by using better performing equipment.

An important area for improvement is lighting, as it consumes 20 % of the world's electricity production.

Today, a fluocompact lamp produces three to four times more light per watt than an incandescent lamp. Also, the lifetime of a fluocompact lamp is around 10 000 h, that is to say, more than ten times that of an incandescent lamp. In the future, electroluminescent diodes (ELDs) will represent new options in terms of energy efficiency, with a lifetime reaching 80 000 h and a layout enabling an optimal distribution of light in buildings [43].

Energy conservation can be ensured by using better performing heating devices such as high efficiency boilers (condensing boilers), heat pumps or cogeneration.

Cogeneration and heat pumps enable a better use of electricity. In a fossil fuel power plant, electricity is produced from a heat source with a yield which, in most cases, does not exceed 35-40 %. The remaining energy is released and transmitted to the refrigeration air or water. In the case of cogeneration, the heat released is used for heating residential buildings or industrial installations.

A heat pump operates according to a different principle. It operates in a way similar to a refrigeration device. By withdrawing heat from an external medium (water or air), it supplies a quantity of heat much larger than the electrical energy consumed. The ratio of the quantity of heat thus delivered over the consumed electrical energy (coefficient of performance or COP) is frequently around 3.

Cogeneration is mainly applied in industry and in the residential or tertiary sector, while heat pumps can be used for individual houses.

In the residential area, a huge growth has occurred in terms of energy consumption. In France, in the case of an old building, dating from a year before 1975 (date of enforcement of the first thermal regulation), average thermal losses are around 330 kWh/m2/year. The application of the recent regulation RT 2005 should lead to losses limited to 85 kWh/m2/year.

By further improving the design of the building, it is possible to lower the level of losses down to 15-20 kWh/m2/year, which corresponds to the 'passive' house concept. In such a case, it is possible to maintain the required temperature in the house through natural solar input and the heat produced as a result of human activities [44].

The next step (further reduction of losses and increase of external solar input) leads to the concept of the positive energy building, able to export energy. From the stage when heat losses do not exceed 50kWh/m2/year, energy provided by solar thermal or photovoltaic panels can comparatively easily exceed the heating needs of the building.

Further developments are needed to ensure a better integration in the structure of the building of thermal solar panels supplying hot water and heating and also photovoltaic panels producing electricity. The development of the equipment which is now available facilitates the integration of solar panels into the building. It becomes possible to install solar roofs or walls. Such concepts lead to the need to revise the architecture and even the structure of residential heating.

The most difficult situation occurs in the case of old buildings, which require complete restoration. For instance in France, two-thirds of dwellings were built before 1975, in the absence of any thermal regulation. The energy restoration of these buildings is presently often difficult as a result of the complexity of decision making (especially in the case of joint ownership), and the lack of the required expertise to carry out the work. It is therefore most important to deploy the incentives and regulatory measures which are needed to make the renovation of such buildings easier.

The introduction of energy quality labels and energy diagnosis represents a first step, leading to the implementation of the required transformations.

A well adapted regulation is clearly a prerequisite, even though in the long term such an investment should be profitable for the final user, due to the probable increase of the energy price.

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