Ancient Persian qanats: Cooling homes without electricity
31 May 2024 09:12
Summer this year is expected to be hot, so air conditioning in homes is becoming essential. However, both the cost of purchasing and operating this device can be high. Therefore, it's worth considering alternative cooling methods that do not require the use of electricity. Interestingly, such methods were used in ancient times.
Air conditioners are an ideal solution during oppressive heat, but their installation is expensive, and usage generates high costs. However, cooling rooms techniques were already developed in ancient times. For example, the Persians used the so-called qanats – underground channels through which cool water flowed.
About 2300 years ago, the Persians developed systems that could lower the temperature inside buildings by up to 16 degrees Celsius. Their engineering solutions were so advanced that they enabled the storage of ice throughout the year.
How were the qanats built?
To understand the functioning of the Persian air conditioning system, one must look at 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 at the place where water was taken. The next step was to lead the tunnel towards the hill to reach the alluvial cone – the place where sediments carried by water settled. Thanks to this, water-bearing layers were found 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, creating 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, from 30 to even 270 metres. The gentle slope of the channels, amounting to around 1 meter per kilometre in length, ensured a steady flow of water, minimizing the risk of bottom erosion.
How did the Persian "air conditioning" work?
Qanats were built at great depths, which meant that 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 and sucking 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.
