Diffusion lid for the removal of moisture in magazine hives

Status quo

The usual bee hives have deficiencies from a building physics point of view. Due to the low wood mass, lack of thermal insulation and diffusion-resistant constructions/materials, the humidity in these hives is very high. The inadequate thermal insulation is highly noticeable, as the dew point is located far into the honeycomb construction. The accumulation of condensation in honeycombs means an increased risk of mold growth and and leads to a watering of the honey. Both of these factors mean presumably a burden on bee health.

Diffusion lid

In order to defuse the problem of condensation and mold formation, a lid for upgrading hives can be created in the style of Émile Warré.

This lid is not an optimal solution and is just a way to reduce the negative effects of inadequate thermal insulation. A proper external insulation on the sides and the top would make much more sense. Then the bottom could also be closed and a diffusion lid would not be necessary.

Due to the diffusion-open structure, the moisture that accumulates inside is removed by diffusion through the lid. The accumulation of condensed water and the danger of mold in the hive should be minimized in this way.

The lid basically consists of a single vapor-permeable layer with an overlying rain protection. We have chosen hemp wool. Reed, straw or sheep wool are also possible. Due to the temperature differences applied to the lid, the entire moisture accumulated in the winter diffuses through the lid outside. The hives can be build with a closed floor and a single flight hole, more ventilation should not be necessary.

diffusion lid
Diffusion lid to eliminate humidity and mould in bee hives

Currently, such lids are already in operation and equipped with sensors. The measurement data confirm the function.

Here a simple and inexpensive form of realization of this lid:

  • use of a honey chamber from the existing hive system
  • cover the underside with a fabric or grid so that the honey frame still closes flush and without gaps afterwards
  • fill the lid with permeable material, a layer thickness of 5-8cm should be chosen as a rough guideline
  • fit spacers on the corners of the honey chamber (2-4cm)
  • place a board or sheet which protrudes at least 10 cm on all sides

Fighting the parasites

In the months in which the bees maintain a large breeding nest and thus a high temperature is under the lid, and on the other side it still cools down significantly at night outside, it comes to the largest water vapour transports. Here, the air humidity below the lid is now below 30% in phases. With this high drought, many parasites can reproduce much more slowly or not at all. For example, it is known that the larvae of the small hive beetle tends to dry out at a relative humidity of less than 50% (source: University of Florida). A relative humidity below 34% inevitably leads to dehydration (source: Current Zoology).
Relative humidity below 34% also inevitably leads to dehydration of the wax moths larvae. Above this humidity, the survival of the larvae increases with increasing humidity. The wetter it is, the better and faster they develop. The life expectancy of the adult animals also increases with increasing relative humidity (source: Current biotica).
The humidity within the bee cluster remains unaffected by this dryness. This is where the moisture accumulates. It is now interesting to see how the humidity on the floor and on the side walls changes. Here, too, measurement series will start shortly.