The history of heat pump, and refrigeration in general, goes back a long way and have been studied since the 1700’s. In 1748, Scottish professor William Cullen designed a small refrigerating machine that utilized a pump to create vacuum over diethyl ether, which caused ether to boil and absorb heat from the surrounding air. This was noted as the beginning of the scientific principle behind refrigeration, which was later on, in 1852, developed by Lord Kelvin, an Irish-Scottish physicist and engineer, who suggested using the same principle to keep a room warm.
In 1805, Oliver Evans, an American engineer and businessman born in Delaware, designed a closed-cycle refrigerator using compressed ether as coolant. In 1844, John Gorrie built a similar machine in Florida, this time, using compressed air as coolant– a refrigerator model that was, later on, introduced by Alexander Twinning in the American market in 1856. In 1855-1857, Peter von Rittinger developed and built the first heat pump system in Austria using the principle previously developed by Lord Kelvin. It was also around this time in 1859 when Ferdinand Carre introduced ammonia as coolant. This coolant was used by Carl von Linde to build the first fully-functional ammonia-refrigerating machine in Germany in 1876.
In the end, it was Robert C. Webber, an American inventor, who first came up with the idea of a ground source heat pump in 1948. He was improving his electric deep freezer when he burned his hand and realized that his freezer had been producing scalding hot water. Not wanting to waste this heat, he ran the hot water into a copper tube and used a small electric fan to blow the heat from the tube into the surroundings. Realizing that his idea worked, he finally built a fully functional heat pump for his entire house. By burying copper tubing, charged with Freon, in the ground, he was able to utilize geothermal energy to heat up his entire home by letting the Freon condense and release the heat in his cellar. This is how the first ground-source heat pump was born.
Decades later, heat pumps are found in HVAC units around the world, this time, with more advanced system configurations and using more environment-friendly refrigerants.