GeoCorner

Tekijä: Erik Lindfors

Valvoja: Jussi Leveinen

Ohjaaja(t): Lauri Uotinen

Tiivistelmä

Ground source heat pump (GSHP) systems have experienced significant growth in Finland, but

questions remain about their long-term thermal sustainability, particularly the risk of cumulative

ground cooling around boreholes. This thesis evaluates long term thermal behaviour in Finnish conditions and examines whether cooling poses a meaningful risk to system efficiency or operational robustness. The work combines a literature review, simulation-based evidence, and multi year field

measurements from real installations.

The empirical part analyses brine supply and return temperatures from six Finnish GSHP sites with

operating histories of roughly 3 to 15 years and includes seasonal coefficient of performance (COP)

data where available. To strengthen the comparison between modelling and observations, Chapter

9 adds Earth Energy Designer (EED) simulations for three representative cases using realized operating loads and includes one hypothetical stress test representing a dense 10 × 10 square borefield.

The simulations are used to evaluate whether simplified models reproduce temperature trends consistent with measured system performance, and to demonstrate the influence of borefield geometry on long term cooling. The results indicate that most measured systems show minimal to moderate cooling, and only one

site exhibits clear signs of thermal depletion, while still remaining operational within acceptable

temperature limits. The EED simulations based on realized specific extraction levels of approximately 67 to 88 kWh/m produce long term mean brine temperatures that remain above 0 °C and

do not approach the −2 °C winter average criterion, whereas a hypothetical dense 10 × 10 borehole

field configuration (100 boreholes arranged in a square grid) subjected to an extraction rate of 100

kWh/m reaches the −2 °C threshold around year 33 and declines further by year 50. Together, the

field data and simulations support the conclusion that well designed and appropriately spaced

GSHP systems can remain thermally stable for decades, and that long term sustainability depends

strongly on borefield layout and thermal interference, not only on the specific extraction rate.