Ventilation of the tree cave
A natural change of air in the tree cave only takes place to a limited extent. The flight hole is usually in the lower third of the tree cave. With a diameter of a few centimeters and a tunnel length of approx. 10 cm, no significant air exchange rates are likely to occur. This is negligible for the decrease in moisture.
You find the average geometric data of tree caves that are naturally inhabited by bees in “The nest of the honeybee” (downloads).
Ventilation of modern bee hives
As already shown under water vapor diffusion, the moisture produced in modern hives is not removed by diffusion. The buffering effect does not affect the climate in the modern bee hive either, the mass of the wood is too small.
Due to the low thermal insulation condensation already occurs in honeycomb construction. A supposedly sensible solution to the problem is increased ventilation in the form of an open floor or even through the application of cross-ventilation. The ventilation rates required for this are far from being achieved. The slight improvement in mould growth is bought at high cost through additional energy losses.
An hourly air exchange rate of 300 would theoretically be necessary to remove all moisture and keep the relative humidity inside at 70%. Of course, this air exchange rate is not achieved. As a result, the relative humidity inside, or the absolute humidity of the air, rises. As a result, more moisture is removed with each air change than before. But even at a relative humidity of 100%, theoretically 45 air changes per hour would still be necessary to remove the resulting amount of water.
It is obvious that such air exchange rates cannot be achieved. The moisture produced by the bees’ metabolism is reflected in the form of condensation. This is also the same in tree caves and well insulated slim hives! There, however, the condensation water accumulates in the lowest areas and is unproblematic, perhaps even desirable for the bees. In case of poor thermal insulation of the beehives and/or a wide geometry, the water already condenses in the middle of the honeycomb construction. And here it is certainly a problem.