Ground-Source Heat Pump: Earth's Stable Heat

Climate & Location

Climate zone Temperate

Month of year Jan

Borehole (ground loop)

Borehole depth 40 m

Deeper loops reach soil the surface seasons can't disturb — the annual heat wave decays exponentially with depth.

Building

Indoor target temp 21 °C

Heat load needed 8 kW

How the numbers work

Surface temperature swings diffuse into soil as a damped, delayed wave:

T(d,t) = T_mean + ΔT·e^(-d/D)·cos(ωt - d/D)

D is the damping depth (~2–3 m for this soil). By ~10–15 m the swing is nearly gone — the ground sits near its yearly mean.

Ideal (Carnot) heating COP from a source at T_cold to a home at T_hot:

COP = T_hot / (T_hot − T_cold)   [Kelvin]

Real machines reach ~45% of that ideal value — used here as the practical COP.

Outdoor air Soil (surface) Soil (at loop depth) Refrigerant — hot side

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