Building model (GEMOD)

GEMOD is a model developed by ifeu to calculate energy consumption for space heating and domestic hot water in buildings. Based on the representation of the current situation, the future consumption trend can be developed under various boundary conditions. This allows it to map development paths in the building sector, the effects of user behaviour, technical developments and political instruments, and to identify areas where action is needed. The balance sheet framework can range from a single building component to building stocks of any size. The German building stock is represented by a quantity structure containing 234 building types, differentiated by building age, type of use (residential buildings, offices, schools, warehouses) and geometry.

Current renovation status and boiler stocks are reproduced on the basis of empirical data from the Institute for Housing and the Environment. The energy requirement for heating and hot water is calculated bottom-up for each individual component and calibrated to the statistical final energy requirement by means of a top-down comparison. User behaviour can be taken into account depending on the energy status of the building. The model shows the final energy consumption separately for the individual energy sources and then calculates the primary energy consumption, greenhouse gas emissions and fuel costs. Based on the service life of components and heating technologies, GEMOD calculates the replacement cycles and thus the timing for possible energy-efficient renovations.

Furthermore, insulation thicknesses and U-values of components (omission and modification) can be specified for three renovation options. Buildings or components that cannot be insulated or cannot be fully insulated due to monument protection or other restrictions are automatically taken into account in GEMOD. Investment decisions regarding the replacement of heating systems can be modelled endogenously on the basis of specific heat production costs. Potential limits (e.g. due to limited fuel availability or a shortage of skilled workers) can be specified. Building demolition and new construction rates as well as global warming can also be specified exogenously and varied. In addition to the development of energy consumption, GEMOD also calculates the investment costs and material flows induced by building renovation.

In addition to the German building stock, GEMOD also includes the building stock of Baden-Württemberg and Heidelberg.

GEMOD is primarily used to create scenarios for the decarbonisation of the German building stock and to compare their economic and business costs from the perspective of the actors involved. The model has also been used to extrapolate the potential and limitations of building insulation and heating technology and to determine the material flows required for building renovation, which serve as the basis for comprehensive life cycle assessments. GEMOD has been used several times in the evaluation of energy consulting programmes to quantify the savings achieved.

Landlords' perspective: Comparison of relevant cash flows before and after refurbishment under current conditions

Flow chart of calculations in the GEMOD building model