Energy is a conserved quantity – it is never just lost. However, it can leave the system in which the energy is used. This is commonly described as an energy loss. Strictly speaking, the energy still exists but is in another form and another place. Losses such as this can occur in a building, for example by heat flowing from the inside to the outside through ventilation and transmission. Energy losses therefore largely determine the energy demand. In this context, the energy demand is the quantity of energy used to keep the interior of the building at a comfortable temperature level (heating, cooling).
A building can also accumulate energy. For example, the interior may heat up due to the presence of people and the waste heat from the equipment. Solar radiation can enter through a window and carry heat energy into the room. In addition to these passive internal and solar gains, active technical components integrated into the building, such as photovoltaic panels forming part of the facade, can create energy.
The balance scope has the task of meaningfully differentiating the above-described complex systems of
energy transfers, losses, and gains for each of the uses. It circumscribes the extent of the assessment and prioritizes the individual needs. Buildings consume a great deal of energy and therefore the EnEV addresses their operation and assesses every use of energy required to create
production, maintenance, and demolition of a building. Because these processes have similar effects on our environment, they likewise provide figures for the energy balance evaluation. By specifying their units of measurement, these figures can be considered in the calculation and evaluated in terms of their energy (kWh) or efficiency (€/ amount of energy). Depending on the purpose of the evaluation and the comparison, useful energy, final energy, and primary energy, emissions such as CO2, material resources, energy costs, or operating costs as well as embedded energy may make valuable parameters. The focus of the content can always be directed by selecting the appropriate balance parameters.
Balancing methods, even those with the same balancing criteria, are usually only comparable with one another to a limited extent. As well as the balance criterion, all other balance parameters must also be identical, as must the calculation procedure. National preset parameters are a further influence on the outcome of the balance.
For example, the primary energy factors differ from one another, depending on the make-up of a country’s energy supply. A building with an electricity supply in Germany may have the same calculated final energy consumption as one in, for example, Switzerland or Norway, but will have a considerably higher primary energy demand due to the greater proportion of renewable energy carriers (e.g. hydroelectricity) used in those two countries.
A third expansion of the balance scope takes place when the building is considered over its whole life cycle. This adds additional sources of energy consumption that go beyond operation and connect with the production, maintenance, and demolition of a building. The development of some magnificent building operating concepts in recent years has caused the energy consumption for operating a building to shrink noticeably. The ratio of the embedded energy – the energy necessary for the manufacture of building materials and the building works – to the operating energy approaches unity.
In principle, the balance scope can cover three areas: building operation, life cycle and user-dependent energy expenditure. In order to avoid highly complex, error-prone balancing systems and be able to evaluate specific areas, the balance scope defines the balance framework very narrowly. The EnEV considers parts of the building operation for residential buildings and an expanded area for non-residential buildings. These areas are shown against a colored background in the diagram.