Integrating Temperature and Part-Load Dependent COP in Shallow Geothermal Borefield Design

In conventional shallow geothermal borefield design, both the building demand and a predefined seasonal coefficient of performance (SCOP) are used as inputs. The SCOP serves to convert building loads into ground loads. However, this method introduces two key inaccuracies: (1) both peak power and total energy demand are scaled equally, often leading to an overestimation of peak extraction power; and (2) the SCOP is typically based on standard conditions (B0/W35), whereas actual system temperatures are often higher, resulting in an underestimation of seasonal imbalance and an oversized borefield.Furthermore, because the SCOP is used as a fixed input, the borefield design process itself does not influence the efficiency of the ground source heat pump (GSHP), which is contrary to reality.This paper demonstrates the benefits of incorporating both temperature-dependent and part-load-dependent COP curves into the design process. Simulation results show that by accounting for the true operational behavior of the GSHP, seasonal efficiencies exceeding 7 can be achieved, significantly higher than the standard B0/W35 SCOP values, which are often below 5. On the other hand, including only the temperature dependency does not lead to a significant difference in SCOP. This results not only leads to more accurate and cost-effective borefield designs but also highlights the critical role of system design in the actual efficiency of GSHP installations.