Integrating the interaction between renovation measures and system temperatures in design decisions for multi-family houses

Building and Environment, vol. 285, pp. 113497

Abstract

Heat pumps are a key technology for achieving a carbon-neutral building stock. However, their use in existing multi-family houses is limited by administrative and technical barriers — notably, the need for high heating system temperatures. These can be reduced through optimized operation, building envelope renovation, and radiator replacement. While existing studies mainly focus on evaluating these measures for single-family houses within low-temperature district heating, comprehensive analyses for multi-family houses remain scarce — particularly regarding the economic and environmental viability of such measures alongside heat pump adoption. This study introduces a novel methodology combining detailed room-level assessments of temperature reduction measures with a mixed-integer quadratic programming optimization model. It identifies cost- and emission-optimal combinations of energy systems and temperature measures within an integrated framework. The method is applied to six representative multi-family houses in Germany, covering two construction periods (1960s and 1980s) and three building sizes. Results show that hybrid heat pump and boiler systems are cost-optimal for older buildings, while monoenergetic heat pumps with electric heaters dominate in newer buildings. Temperature reduction measures are not selected in cost-optimal cases under the assumption of properly sized radiators but become relevant toward the emission optimum, with radiator replacement rates up to 83.3%. A sensitivity analysis reveals that moderate radiator oversizing or cost reductions can make individual radiator replacement more cost-effective and shift solutions toward monovalent HPs. Overall, the findings suggest rapid decarbonization of MFHs is feasible without major envelope renovations— though insulation remains important for reducing peak loads and supporting grid-friendly monoenergetic HP operation.

Authors 3

1. Larissa Kühn corresponding Aachen E.ON Energy Research Center Institute for Energy Efficient Buildings and Indoor Climate

   RWTH Aachen University

   Affiliation as printed

   RWTH Aachen University, E.ON Energy Research Center, Institute for Energy Efficient Buildings and Indoor Climate, Mathieustraße 10, Aachen, 52074, Northrhine-Westphalia, Germany

2. Laura Maier Aachen E.ON Energy Research Center Institute for Energy Efficient Buildings and Indoor Climate

   RWTH Aachen University

   Affiliation as printed

   RWTH Aachen University, E.ON Energy Research Center, Institute for Energy Efficient Buildings and Indoor Climate, Mathieustraße 10, Aachen, 52074, Northrhine-Westphalia, Germany

3. Dirk Müller Aachen E.ON Energy Research Center Institute for Energy Efficient Buildings and Indoor Climate

   RWTH Aachen University

   Affiliation as printed

   RWTH Aachen University, E.ON Energy Research Center, Institute for Energy Efficient Buildings and Indoor Climate, Mathieustraße 10, Aachen, 52074, Northrhine-Westphalia, Germany