The selective inverted sink or SIS is a device used by

farmer A farmer is a person engaged in agriculture, raising living organisms for food or raw materials. The term usually applies to people who do some combination of raising field crops, orchards, vineyards, poultry, or other livestock. A farmer ...

s to protect plants from

frost Frost is a thin layer of ice on a solid surface, which forms from water vapor that deposits onto a freezing surface. Frost forms when the air contains more water vapor than it can normally hold at a specific temperature. The process is simila ...

, developed by

Uruguay Uruguay, officially the Oriental Republic of Uruguay, is a country in South America. It shares borders with Argentina to its west and southwest and Brazil to its north and northeast, while bordering the Río de la Plata to the south and the A ...

an Rafael Guarga in the late 1990s. The sink is actually a large fan housed in a chimney-like structure, and works by defeating surface temperature inversion. Cold air is denser than warm air, and will pool at ground level during calm weather. This lowers the surface temperature, even if the

ambient temperature Room temperature, colloquially, denotes the range of air temperatures most people find comfortable indoors while dressed in typical clothing. Comfortable temperatures can be extended beyond this range depending on humidity, air circulation, and ...

is higher. Vents near the base of the chimney allow cold surface air to be pulled up through the chimney, creating a suction effect that draws warmer air down to surface level. The SIS is more efficient than typical ground-heaters, and is widely used to combat frost.

References

To blow up or down? Inverted sink fans offer alternative form of frost protection
by Paul Franson

US Patent 7654035 * ttps://web.archive.org/web/20111015231204/http://www.produccionnacional.com.uy/ciclos-tv/2011/frost-protection/ ''Su mercado es el mundo'' Uruguayan inventions Farming tools {{Tech-stub