German Framework Optimizes Cost-Effective Heat Pump Retrofits for Municipal Buildings

A German study identifies a practical retrofit pathway for heating systems in a municipal building, reducing long-term costs for building owners.

German researchers developed a framework to optimize the sequencing and bundling of hybrid heat pump retrofits for buildings. The approach combines techno-economic analysis of retrofit measures with simulations of system operation across multiple stages. This method was tested on an 888 m² municipal sports hall in Reutlingen, Germany—built in 1975 and originally equipped with a 339 kW oil boiler installed in 2002. The framework evaluated five specific retrofit actions: air-to-water heat pump installation, roof insulation, wall insulation, window replacement, and ventilation with heat recovery. While theoretical combinations of these measures totaled 541, financing constraints reduced viable pathways to just 18. Three scenarios were then analyzed: one prioritizing heat pump and ventilation heat recovery in 2026, roof insulation in 2028, and wall insulation/window replacement in 2030; another focusing on heat pump and roof insulation by 2026; and a third emphasizing roof insulation and ventilation heat recovery in 2026. Scenario 3 achieved the highest net present value at €89.71 per m² ($102.90 per m²), compared to €80.25 per m² for Scenario 2 and €76.94 per m² for Scenario 1. All retrofit measures except wall insulation were economically viable under this framework.

The study reveals that levelized cost of saved energy and changing the heating system (LCSE/LCCH) is more sensitive to investment costs than energy price fluctuations. Heat pump sizing also significantly impacts retrofit economics. Crucially, the findings are specific to this single building case study in Reutlingen, and financing limitations constrained the practical retrofit pathways from theoretical possibilities. This work demonstrates how targeted sequencing can yield substantially higher returns for building owners, though scaling beyond one municipal building and overcoming financing barriers remain key challenges for wider adoption.

Source: pv magazine