A closed water loop buried roughly 1.5m deep (where ground temperature stabilizes near 12-15C) circulates through a salvaged car radiator and fan indoors via a small pump, a hydronic variant of ground-coupling, distinct from the air-duct earth tube and earth-sheltered form: it retrofits onto an existing structure with a radiator/fan-coil rather than requiring integrated ductwork. Source claims up to roughly 30kWh of cooling delivered per 1kWh of pump/fan electricity, i.e. a COP far above a compressor heat pump since it moves existing heat rather than creating a temperature difference from scratch, self-reported by a single builder, not independently measured.
Note: Cost, carbon and footprint are rated against the other options for this same need, not in absolute terms.
Ground area available for a buried pipe trench/loop at roughly 1.5m depth; workable (non-rocky) soil
No sizing or quantities: how much a technique yields, and how much a household needs, both depend on the build and the people, so the catalogue compares options rather than dimensioning them. It carries no bill of materials and no build sequence, and it is written for an oceanic, clay-soil climate (Normandy, France). Regulatory notes are indicative and need confirming locally.