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