Little thermal mystery (anti-freeze laundry)

[elephant]

no pipes, the fan is in the window opening. The temperature drops significantly after 20 minutes.

There is of course no question in the context of extending the experience: I could not take the risk of seeing the temperature drop even further.

I will resume the experience when the risk of frost is over, on longer periods

[Former Oceano]

Have you thought about the movements of air that will cool on the walls?
It's like the trick of putting a glass of cold water and a glass of hot water in a freezer. The more intense convection movements cause the hot water to cool faster.
Without a fan, the air is less mobile (there must still be convection) and therefore there is less heat transfer on the walls.

[dedeleco]

no pipes, the fan is in the window opening. The temperature drops significantly after 20 minutes.

There is of course no question in the context of extending the experience: I could not take the risk of seeing the temperature drop even further.

I will resume the experience when the risk of frost is over, on longer periods

but then with much smaller differences in T, the whole spontaneous starting convection will be different and therefore the results different.

A simple way is to direct the warmer flow of the fan through a few boxes or packages lying around on the portions to be heated.

Otherwise the fan changes all the convection circulation and therefore everything is possible, just by changing the position or orientation of the fan, because it is very complex. Is the soil wet or a slab ???