Energy · c. 1856

Heat pump

Running a heat engine backwards moves several units of heat per unit of work.

Peter von Rittinger built a mechanical vapor-recompression system for salt evaporation in Austria around 1856. Modern electric heat pumps deliver 3 to 4 units of heat per unit of electricity, and global sales grew rapidly in the 2020s as a way to decarbonize buildings.

See it in the living tree Wikipedia

Arcs above join it to what it stood on, arcs below to what it led to. The bar places this stretch on the tree's whole timeline.

What it built on 2

Laws of thermodynamics 1850
Watt steam engine 1776

Related measurements

The dashed line marks when it first worked.

Energy used per dollar of GDP Latest: 1.21 kWh per $ (2022) Source: Our World in Data

World electricity generation Latest: 31.8k TWh (2025) Source: Our World in Data

Energy use per person Latest: 20.3k kWh (2025) Source: Our World in Data