Ancient Persian cooling methods offer eco‑friendly solutions for summer

Summer this year is expected to be hot, making home air conditioning essential. However, the cost of purchasing and operating these devices can be high. Therefore, alternative cooling methods that do not require electricity are worth considering. Interestingly, such methods were already used in ancient times.

Air conditioners are an ideal solution during oppressive heat, but their installation is expensive, and usage generates high costs. However, techniques for cooling rooms were developed long ago. For example, the Persians used the so-called qanats – underground channels through which cool water flowed.

2,300 years ago, the Persians developed systems that could lower the temperature inside buildings by up to 29 degrees Fahrenheit. Their engineering solutions were so advanced that they enabled ice storage throughout the year.

To understand the functioning of the Persian air conditioning system, one must examine its construction. The system consisted of several elements: underground channels, underground cisterns, and wind catchers. Qanats transported cool water, cisterns stored it, and wind catchers directed airflow. The Persians possessed advanced knowledge of physics, which allowed them to create such efficient cooling systems.

From a bird' s-eye view, qanats look like a system of evenly spaced pits in the ground. The construction of the channels began where the water was sourced. The tunnel was then led towards the hill to reach the alluvial cone—the place where sediments carried by water settled. This process enabled the discovery of water-bearing layers underground, allowing the creation of wells supplying the system with clean water.

During the drilling of the tunnels, the builders periodically created openings around which they scattered the excavated material, forming protective cones. These openings later facilitated the maintenance of the tunnel and the supply of fresh air.

Due to the slope of the terrain, the qanats were located at various depths, ranging from 98 to even 886 feet. The gentle slope of the channels, around 1 yard per 1,094-1,640 yards in length, ensured a steady water flow, minimizing the risk of bottom erosion.

Qanats were built at great depths, meaning the water was cold. Underground cisterns stored it and, in combination with wind catchers, created an air conditioning system. This system employed the Bernoulli effect: wind catchers directed hot air into the shaft leading to the channel, creating a vacuum that sucked cold air into the channel. This cold air could then be moved to the rooms. Continuous air circulation allowed the cooling of buildings without the use of electricity.