In December 2017 I took measurements on a beehive with a Diffusion-lid for 2 weeks to get an overview of the average temperature below the lid. For this purpose, 7 temperature sensors were installed as shown. The values given are the average temperature difference between the sensor and the outdoor temperature. The average temperature difference to the outside air is 5.5°C in the 2 weeks considered (the average outside temperature in the period was 0.4°C). The temperature difference is much smaller than expected, especially since the hive is provided with an additional external insulation, a closed floor and only 3 small entrances. But the bees do not heat the hive, but only their bee cluster :-).
Since December 23, only the two middle sensors were operated, since the others were needed in other projects. Up to 11.4., the following average values resulted:
|T left||rF left||T right||rF right||T outside||rF outside|
These measurement results confirm the effect of the lid: The moisture is removed through the lid by water vapour diffusion.
It becomes especially interesting when we take a closer look at the curve of the last weeks (March/April 2018): The humidity below the lid is subject to large daily fluctuations. It is very nice to see how dependent the relative humidity is on the differential temperatures on the lid. Whenever the temperature difference is greatest, there is maximum diffusion and relative humidity reaches its minimum under the lid. The relative humidity under the lid reacts immediately to a change in the temperature difference. For short periods of time, even relative humidities below 30% are achieved at low outside temperatures.
Due to the direct dependence of the diffusion on the temperature differences, the highest values for these diffusion should occur in spring and autumn when it is still/already cold at night and the bees inside keep up high temperatures. No increase in the available data is therefore to be expected for the summer.