Natural ventilation of the tree cavity
A natural change of air in the tree cavities only takes place to a limited extent. The flight hole is usually in the lower third of the tree cavity. 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 cavities that are naturally inhabited by bees in “The nest of the honeybee” (downloads).
Natural ventilation of magazine hives
Due to the construction, magazine hives sometimes have strong air changes. These air changes are intended by the constructors to reduce moisture:
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.
This basically working dehumidification takes place at a very high level. Condensation water can be largely prevented, but the relative humidity in the bee hive remains very high. The slight improvement in terms of condensation water accumulation is bought at a high price, via heavy energy losses. Large parts of the honeycomb construction and the hive construction lose their insulating effect for the bee grape due to the ventilation.
Ventilation of the beehive by fanning honeybees
Bees actively ventilate with the aim of exchanging gas, cooling or removing moisture. It is known that honey bees start fanning when air temperature, CO2 and relative humidity rise above the level for comfort. Not known – at least I haven’t found anything about it in literature – is wether and how they coordinate ventilation of the beehive. If each individual bee would start to fan in any direction when exceeding the respective limit value, then no effective flow pattern would develop within the honeycomb structure. There would rather be many diffuse air flows which partly work against each other.
Probably bees form ventilation lines within the hive. The opening of the Nasonov’s gland gives the air flow fragrances which signal the direction of the air flow to the following bees. Further bees start to fan in the direction of flow and keep the direction of flow. In this way they drive the air to the lower edge of the honeycomb structure.