The first heat exchangers, such as Gialotto’s design, had no means to prevent ماء التخمير from getting too hot and no means to cool the water if it did overheat. But by the 1950s, inventors such as Giampietro Saccani turned this problem into an asset: They introduced a thermosyphon system that delivered water to the group whilst also using this water to keep the group head warm.
The concept of a thermosyphon is simple: Cool water is slightly denser than warm water. Therefore, in a closed system, water that is heated will rise and water that cools will sink. English inventor Thomas Fowler lodged the first known patent for a thermosyphon in 1828. His ideas formed the basis of the first central heating systems, in which water heated in the basement of a building rises and delivers heat to radiators in the rooms above. The loss of heat energy in the radiators to the airmakes the cooler water in the system become denser, so it sinks back to the basement to travel through the boiler once again.
Giampietro Saccani’s group head design from 1955 featuring a thermosyphon. This early design draws the water from the steam boiler (21). The water syphons around the group head, keeping it warm (15). The cooled water then travels downward, reentering the boiler.
Heat Exchangers and Thermosyphons Combine
Steam boilers for espresso machines tend to be very large so that they can offer baristas a reliable source of steam at any time. Baristas generally prefer not to use the water from the steam boiler for brewing, however, for a couple of reasons. First, the water inside the steam boiler is generally somewhere between 118–124°C (244–255°F) — unmanageably hot. Second, over time, the water in the steam boiler can become very concentrated with minerals. As steam is removed from the boiler, any dissolved minerals that were attached to those water molecules remain in the boiler as الترسبات الكلسية or other dissolved substances,