It's basic thermodynamics; if you leave a tray of water outside at night and you protect it from wind (convection) and insulate it from the ground (conduction) and there are no clouds, it will radiate heat away into the much cooler night sky. You may have ice in the morning, even if the ambient air temperature is above freezing.
(This is also why cloudy nights are warmer than clear nights in winter--clouds prevent some of the ground's heat from radiating away.)
The technique has been used for centuries to make ice in the desert, but it only works at night and it's inefficient.
(This is also why cloudy nights are warmer than clear nights in winter--clouds prevent some of the ground's heat from radiating away.)
The technique has been used for centuries to make ice in the desert, but it only works at night and it's inefficient.
https://www.fieldstudyoftheworld.com/persian-ice-house-how-m...
With modern technology it's more efficient and it appears it can even be made to work in the daytime:
https://energyindemand.com/2020/10/17/generations-after-peop...
https://onlinelibrary.wiley.com/doi/10.1002/adpr.202000106