Geothermal energy: https://en.wikipedia.org/wiki/Geothermal_energy

Geothermal heating > Extraction (GCHE, GHX) || Ground source heat pump (GSHP) https://en.wikipedia.org/wiki/Geothermal_heating

GSHP: Ground source heat pump: https://en.wikipedia.org/wiki/Ground_source_heat_pump

Heat pump: https://en.wikipedia.org/wiki/Heat_pump #Types :

> Air source heat pumps are the most common models, while other types include ground source heat pumps, water source heat pumps and exhaust air heat pumps.

Heat pump > Types:

- SAHP: Solar-assisted heat pump; w/ PV

- acronym for a heat pump with TPV thermophotovoltaic heat to electricity:

- acronym for a heat pump with thermoelectric heat to electricity:

- TAHP: Thermoacoustic heat pump

- ECHP: Electrocaloric heat pump

Electrocaloric effect > Electrocaloric cooling device studies: https://en.wikipedia.org/wiki/Electrocaloric_effect#Electroc...

GCHE, GHX: Ground-coupled heat exchanger: https://en.wikipedia.org/wiki/Ground-coupled_heat_exchanger

Acronyms! From https://www.google.com/search?q=Ground-coupled+heat+exchange... :

HGHE: Horizontal Ground Heat Exchanger: a GCHE installed horizontally e.g. in trenches

VGHE: Vertical Ground Heat Exchanger: GCHE installed vertically e.g. in boreholes or piles.

PGHE: Pile Ground Heat Exchanger: A specific type of GCHE that is integrated into the structural foundation piles of a building.

Solar chimney or Thermal chimney: https://en.wikipedia.org/wiki/Solar_chimney

OTEC: Ocean Thermal Energy Conversion: https://en.wikipedia.org/wiki/Ocean_thermal_energy_conversio... and the ecological salinity gradient:

FWIU archimedes spiral turbines power some irrigation pumps in Holland at least. Is there an advantage to double/helical archimedes spirals in heat pumps if/as there is in agricultural irrigation?

Screw turbine: https://en.wikipedia.org/wiki/Screw_turbine

Noiseless double-helical Achimedes spiral wind turbine on a pivot like a pinwheel: Liam F1 average output with 5m/s wind: 1500 kWh/yr (4.11 kWh/day); Weight: ~100 kg / ~220 lbs; Diameter: 1.5 m / 4.92 ft

What about CO2 and heat pumps? Would a CO2 heat pump make sense?

Absorption Heat pump (AHP) https://en.wikipedia.org/wiki/Absorption_heat_pump

Adsorption Heat pump (AHP)

CO2-Sorption Heat Pump: a Adsorption Heat pump (AHP) that uses CO2 as the adsorbate.

NISH: Nano-Ionic Sorption Heat Pump; with e.g. sustainable hydrogels

Is it better to just recover waste heat from other processes; in a different loop?

LDES heat pump

Supercritical CO2 heat pump

Aerogels don't require supercritical drying anymore,

There's also buoyancy. The pyramid builders may have used buoyancy in a column of heated bubbly water to avoid gravity, in constructing the pyramids as a solar thermohydrodynamic system with water pressure.