A recent social media post by author Pedro Torrijos has ignited discussion around the environmental impact of modern air conditioning, drawing a stark contrast with the ingenious 2,400-year-old Persian yakhchāls, ancient structures capable of producing and storing ice in the desert. Torrijos highlighted these architectural marvels as a testament to sustainable cooling, prompting reflection on contemporary energy consumption.
"Hay follón entre estadounidenses y europeos con que si usamos mucho o poco o nada el aire acondicionado. Pues mirad lo que os digo, hace 2400 años, en Persia, ya inventaron una manera de refrescarse: fabricaban hielo EN EL DESIERTO," Torrijos stated in his tweet, emphasizing the historical precedent.
Yakhchāls, meaning "ice pits" in Persian, were sophisticated structures primarily found in the arid regions of modern-day Iran, such as the Dasht-e Kavir and Dasht-e Lut deserts. These domed, mud-brick buildings featured subterranean storage spaces, shade walls, and shallow ice pools, allowing for year-round ice preservation. Records indicate their use dates back to at least 400 BCE, with many structures still standing today.
The core principle behind yakhchāls exploited the desert's extreme diurnal temperature swings and low humidity. Water was poured into shallow pools, protected by east-west oriented walls that provided shade during the day. At night, the clear, dry desert sky acted as a "sumidero" (sink), allowing heat from the water to escape into space through radiative cooling, causing the water to freeze even when ambient air temperatures were above zero.
Once formed, the ice was harvested before sunrise and transferred to a subterranean chamber beneath the dome. These chambers, often reaching thousands of cubic meters, were insulated by thick walls made of "sarooj," a unique mortar composed of sand, clay, egg whites, lime, ash, and goat hair, known for its heat-resistant and impermeable properties. The conical dome also facilitated passive cooling by allowing warm air to rise and escape, maintaining a consistently cold environment.
Torrijos critically observed the modern reliance on air conditioning: "Nosotros, que sí tenemos la termodinámica entera... respondemos a la canícula encendiendo aparatos que devuelven al aire más calor del que extraen de la habitación, exportando el problema al pasillo, a la calle, a la atmósfera, al año que viene, a nuestros hijos y a los hijos de nuestros hijos." This highlights the environmental cost of current cooling methods, which contribute to urban heat islands and increased energy demand, often powered by fossil fuels.
While yakhchāls have largely been replaced by modern refrigeration—the Persian word for refrigerator is still "yakhchāl"—they serve as a powerful historical example of sustainable engineering. Their design has inspired contemporary architects and engineers exploring low-energy housing and passive cooling solutions. The ancient Persians, through keen observation and understanding of natural physics, developed a system that combated heat without generating more of it, offering valuable insights for today's climate challenges.
