‘‘Zero Energy House is dimensioned to be self-sufficient in space heating and hot-water supply during normal climatic conditions...’’

With these targets and requirements started the idea of the first zero energy balance buildings, during the ‘70s. Since, the demands are growing, with the aim of full balancing the incoming to the outgoing energy. Both technology development and the recognition of the environmental problems have contrib- uted in this in significant way. The evolution of technology has contributed to two axis. The first one is the integration of computer application in the design, which predict the buildings’ energy performance during their life time. The second one, is related to the development and optimization of energy saving and energy productions systems, which are becoming more and more efficient, while the cost is reduced. On the other hand, the increasing environmental problems and the depletion of natural resources, which are no longer just a speculation but reality, have contributed in strict measures to minimize buildings’ energy consumption and reduce the dependence on fossil fuels. The built environment is of particular importance, because it is a sector that accounts for over 30% of global energy consumption.

The main target of this type of construction is to minimize their energy needs. However this is not suf- ficient, so it is necessary that the energy consumed comes from renewable sources. These can be pro- duced either on or off site, by an organized production unit. The evolution of the idea of energy balance, has created new approaches which depend on the construction’s targets. The energy balance can be based on energy consumption, primary energy consumption, the energy cost or carbon emissions. Nev- ertheless, whichever approach is selected it can be determined by additional parameters such as time period or the creation of specific internal conditions.
After this, all the elements that have the potential to affect the energy balance of a building, reduce en- ergy consumption and eliminate emissions of carbon dioxide will be studied. Achieving zero emissions is of high importance, because it explains better the environmental pollution. First of all, the achievement of zero emissions starts with the understanding of different balance approaches. It continues with the selection of the most appropriate design, through a variety of options, depending on the existing needs and circumstances. This is combined with the use and exploitation of renewable energy provided each time. The parameters and their combinations selected, with the use of a computer application lead to accurate calculation of the effect that they will have to the energy balance of the structure.

Of particular importance is to achieve zero carbon emissions in urban environment. This effort is difficult in comparison to rural areas, because the space and the potential are limited. The cities are expected to play a decisive role as they are inhabited by over the 50% of the global population. They also include the majority of built environment. At the same time, studies should not focus only on new construction but also on existing ones, which are the highest number and account for the consumption of large quantities of energy.

For this reason, the balance of energy consumption, primary energy consumption and carbon emissions of an existing 5-floor building with houses and shops in an urban environment are examined. With these changes implemented it is being understood which ones influence the most the building's energy bal­ ance. However, the findings obtained show that, besides the necessary measures and design changes made, its users are expected to play a significant role. Their habits, their awareness and their active par­ ticipation can contribute importantly to the balance of the construction. The impacts of their behavior on the energy efficiency of the construction are becoming more apparent when they have already adopted the measures for minimizing energy consumption.