The MOBASY research project aimed to reduce the energy consumption of rental housing through efficiency measures, addressing two distinct scales and action spaces. Subproject A, “Realbilanzierung,” focused on developing and testing a calculation model for expected energy consumption. The model was designed to be applicable to large housing portfolios and to provide realistic estimates of heating and domestic hot water demand. To validate the model, data from 108 residential buildings—comprising 211 individual houses—were collected from three housing companies. The sample covered 2,405 apartments, 157,967 m² of heated floor area, and 173,762 m² of reference area used for energy balance calculations. For each building, detailed information on geometry, insulation, window type, and building envelope was recorded using the energy‑profile forms developed by the project. The measured energy consumption of these buildings was then compared with the model’s theoretical expectations in a “Soll/Ist” analysis. Statistical evaluation of the sample produced consumption benchmarks for houses with varying insulation levels, enabling the creation of a consumption‑controlling framework that can guide future modernization strategies within housing companies. The empirical comparison also quantified remaining uncertainties, thereby improving forecast quality and increasing transparency and credibility for stakeholders.

Subproject B, “PassivhausSozialPlus,” demonstrated the potential for cost reduction in social housing by applying Passivhaus standards to two multi‑family buildings in Darmstadt—a modernized existing building and a new construction. The project emphasized not only the minimization of heat losses through high‑efficiency insulation and heat‑recovery ventilation but also the reduction of ancillary costs such as water, household electricity, and other utilities. A key feature of the study was the integration of flat‑rate utility billing and tenant budget constraints for water and electricity, ensuring that the energy‑saving measures translated into tangible savings for residents. The project’s findings illustrate how climate‑neutral construction can be economically viable in the social housing sector, providing a replicable model for other municipalities.

In addition to the technical work, MOBASY incorporated a user‑behaviour survey to capture heating and ventilation practices. A questionnaire, available in six languages, was distributed to 2,941 households, yielding 567 responses (19.3 %). The survey data were combined with the building‑level consumption data to assess the impact of occupant behaviour on energy use, offering further insights for targeted interventions.

The project was carried out in close cooperation with several partners. The Institute for Housing and Environment (IWU) in Darmstadt led the research and coordinated data collection. Hochschule Darmstadt contributed methodological expertise and supported the development of the energy‑profile forms. Neue Wohnraumhilfe, Darmstadt, provided access to housing portfolios and facilitated the distribution of the survey. Associated partners—Nassauische Heimstätte | Wohnstadt in Frankfurt, Wohnbau Gießen GmbH, and bauverein AG in Darmstadt—offered additional data sets and practical experience in housing management. The collaboration spanned the full project duration, with each partner assuming specific roles: data provision, field support, and dissemination of results. The joint effort enabled a comprehensive assessment of energy consumption patterns across a diverse set of rental properties and produced actionable recommendations for both technical upgrades and behavioural change.