Efficiency measures at the building envelope and the building services systems decrease the operational costs of buildings. But reduced costs can lead to changes in the behaviour of the building users. They consume more energy and parts of the originally planned energy savings are used-up. The so-called “rebound effect” describes the difference between the theoretically expected savings and the savings achieved in reality. The rebound effect can be indicated as percentage of the deviation from the expected savings.
Examples of the rebound effect in practice are higher room temperatures following the renovation measures as well as heating the whole house as opposed to heating selected rooms before the renovation. Some users perceive solar thermal energy for DHW as “cost free” energy and therefore use more hot water after the installation of solar thermal collectors. Furthermore, complex technologies and control strategies that are not completely understood or accepted by the user can lead to higher energy uses than predicted.