How can ground-source heat pump systems be designed to use less electricity while remaining reliable under changing operating conditions? This question was at the centre of research presented by Lone Meertens of KU Leuven at the German Geothermal Congress 2026, held in Potsdam, Germany.

On 21 October 2026, Lone presented the paper “Assessing Zoned Borefield Design and Individual Zone Control for Robust Ground-Source Heat Pump Systems.” Co-authored with Victor Braciszewski of SmithGroup and Lieve Helsen of KU Leuven and EnergyVille, the research explores how borefield layout, hydraulic behaviour and pump control interact, and how these factors can be evaluated during the design process.

Looking beyond conventional borefield design

Ground-source heat pumps can support building decarbonisation, but their performance depends on more than the number and depth of boreholes. Fluid flow, pressure losses, pumping electricity and heat transfer between the building and the ground are closely connected.

Conventional design approaches often represent the borefield as a single aggregated system, limiting the detail available when evaluating individual hydraulic circuits and operational control strategies.

The research addresses this challenge through a Modelica-based zoned borefield model, which represents thermal and hydraulic interactions between parallel zones. This allows engineers to explore different layouts and control strategies during the design phase, including how the system might respond if an individual circuit becomes unavailable.

Variable-speed pump control reduces electricity use

The methodology was evaluated using the Dr. Martin Luther King Jr. Community Center in Racine, Wisconsin, a net-zero-energy facility served by a geothermal system with 60 boreholes.

One of the key findings concerned the way circulation pumps are controlled. In the modelled case, variable-speed pumping controlled by the temperature difference between supply and return fluid reduced total annual electrical energy use from 179.9 MWh to 84.8 MWh compared with constant-speed pumping at full design flow.

This represents a reduction of more than half in the modelled system’s annual electricity use. Pump electricity use fell from 108 MWh to approximately 6 MWh per year, reducing the pump’s share of total electricity use from 60% to around 7%.

The results also showed that pump control can help limit unwanted heat gains from pumping and reduce their effect on the ground’s long-term thermal balance. These findings highlight why pump operation should be considered alongside borefield design, rather than treated as a separate engineering decision.

These figures relate to the specific modelled case study and operating assumptions described in the paper; they are not guaranteed savings for every ground-source heat pump installation.

Borefield layout can improve resilience

The study also examined how the arrangement of boreholes into hydraulic zones affects a system’s response to component failure.

In the simulated scenario, the researchers compared a configuration with four zones of 15 boreholes against one with 15 zones of four boreholes. If one zone had to be isolated during peak heating conditions, the smaller-zone arrangement maintained operation for longer before the modelled fluid temperature crossed the specified design limit.

The estimated response time was approximately 27 hours for the 15-zone configuration, compared with around 7 hours for the four-zone configuration. This additional time could help operators diagnose and address a hydraulic fault before the system reaches its operating limit.

However, the study also identifies a trade-off: more zones can improve resilience but require additional distribution piping and manifold connections. The model therefore helps engineers assess reliability alongside investment and operating costs.

Supporting better-informed geothermal system design

By bringing thermal behaviour, hydraulic losses and control strategies into one modelling framework, the research provides a way to assess important design decisions before construction. It also opens opportunities for further work on advanced zone control, ground regeneration strategies and virtual monitoring of local ground temperatures.

For SEEDS, this research contributes to the wider exploration of how modelling, monitoring and intelligent control can support more efficient and flexible building energy systems.

Learn more about the research:
Read the full paper presented at the German Geothermal Congress 2026, Assessing Zoned Borefield Design and Individual Zone Control for Robust Ground-Source Heat Pump Systems.

Congress information: https://www.der-geothermiekongress.de/kongress/der-geothermiekongress

Funding acknowledgement

This research received funding from the European Union through the SEEDS project (Grant Agreement No. 101138211) under the Horizon Europe programme. The views and opinions expressed are those of the author(s) only and do not necessarily reflect those of the European Union or CINEA. Neither the European Union nor the granting authority can be held responsible for them.