Design and sizing practices of ground source heat pump systems in Finnish multi-apartment building retrofits

Abstract

Ground source heat pumps (GSHPs) are increasingly used in cold-climate retrofits of multi-apartment buildings (MABs), yet empirical knowledge of their design and sizing remains limited. This study presents an exploratory analysis of a national survey of Finnish GSHP contractors, examining system design, sizing, configuration, and controllability in MAB retrofits. Respondents (n = 7) were categorised by experience level and together reported 605 projects, covering about 21% of the Finnish GSHP-equipped MAB stock, although the distribution was markedly uneven. Results show that GSHPs were typically sized to cover 75–85% of peak heating demand, with backup and top-up heating almost exclusively electric. The electrical grid connection was increased in 70% of these projects, although earlier studies based on historical consumption data suggest that the need for such enlargements is uncertain. Control functionalities based on electricity use or power demand appeared in fewer than 10% of systems. Despite broadly similar design outcomes, calculation tools, input data, and sizing rationales varied widely between contractors, reflecting the absence of shared standards and the predominance of investment-cost considerations. Findings highlight a gap between modelling-based optimisation and contractor practice and indicate directions for more consistent design guidance and assessment of grid-level impacts of GSHP retrofits in cold-climate MABs.