Tang dynasty
The inventor Ding Huan (fl. 180 AD) of the Han dynasty invented a rotary fan for air conditioning, with seven wheels 3 m (10 ft) in diameter and manually powered. In 747, Emperor Xuanzong had a "Cool Hall" built in the imperial palace, which the "Tang Yulin" () describes as having water-powered fan wheels for air conditioning as well as rising jet streams of water from fountains. During the subsequent Song dynasty, written sources mentioned the air conditioning rotary fan as even more widely used.
Robert Stirling
Robert Stirling's best known invention is the heat engine now referred to as the Stirling Engine. In 1816 Robert Stirling and his younger brother, James Stirling, applied for a patent in both Scotland and England for a device they invented, a Heat Economiser. The function of this invention was to store and release heat as air circulated through its mechanisms. This differed from most heat engines which used steam as their method of storing and releasing energy.