Sweden is an early adopter of ground source heat pumps (GSHP) with the first wave of installations during the 2000’s now reaching replacement age. The spike in electricity prices has motivated building owners to renovate their heat pumps to high efficiency models. The higher efficiency means greater thermal demands on the borehole it was not designed for, limiting electricity savings and continued reliance on backup heaters.

There are several technical solutions: drilling additional boreholes, solar regeneration of the ground, thermal storage, and/or battery storage. Our project will identify the ideal renovation strategy for aging GSHP under a range of technical, economic, environmental, and aesthetic constraints. We do not expect one optimal solution for everyone but will describe the tradeoffs between possible solutions to make our results as informative for buildings owners as possible.

Our work requires the development of a new energy systems model which can simultaneously simulate a building, heat pump, solar energy, storage, and heat transfer in the ground from boreholes installed at different times. For the first time we will also validate models of solar regeneration of the ground and a novel phase-change thermal storage. When the techno-economic simulations are complete, we will present the results to potential adopters to describe end-user preferences and better understand the non-technical tradeoffs during the decision-making process.

On completion, our project will offer homeowners a new understanding of GSHP renovation strategies using the latest energy technologies for buildings. This user-centric approach will be valuable to the heat pump and solar industries and will produce new models valuable to GSHP researchers.

KTH leads the project and is responsible for combining the inputs from our industry partners into the holistic energy systems models:

• Bengt Dahlgren Stockholm Geo leads borehole model development
• Samster provides empirical data from their solar hybrid systems regenerating degraded boreholes and their new phase-change thermal energy storage product
• DualSun Nordic provides product data and insights on solar hybrid system design in the field
• Beteendelabbet will conduct semi-structured interviews or workshops with end users

The research advisory committee consists of Dr. Signhild Gehlin, CEA of Svenskt Geoenergicentrum, and Dr. Jan-Erik Nowaci, who has researched GSHP for over 40 years