Experimental study to assess the effect of coatings radiative properties on the temperature of a Dadant hive

The temperature in a beehive is the result of a thermal balance between the colony thermoregulation activity and daily weather variations. Beehives exchange energy via (1) outside air convection (2) solar radiation and (3) infrared radiation with surrounding objects. In summer, the sun radiation may be strong enough to alter the colony activities and could even soften the wax leading to a collapse of the honeycombs.

To help beekeepers to mitigate sun radiation, especially for beehives that are exposed to direct sunlight, this experimental study investigates the effect of coatings (paints) on the internal temperature of a Dadant hive. Two empty hives are instrumented using several temperature sensors and a local weather station monitors the immediate environment. The results show a significant reduction in temperature when the hive’s roof is painted white (-27∘^{\circ}C on peak for the roof and -2.5∘^{\circ}C on daily-average for the hive body) compared to the steel roof. Conversely, this steel roof (new or oxidized) is roughly equivalent to one painted black. The effect of coatings on the side walls is more marginal with a maximum temperature change of few degrees.

To better understand these results, spectral emissivity measurements of these coatings between 0.4 to 20μm wavelength are presented. They were carried out in CEMHTI laboratory using two integrating spheres. A closed-form equation is derived from steady state equation to provide the temperature change with respect to coating emissivities ε\varepsilonsun and ε\varepsilonir, respectively in the visible and infrared ranges. As predicted by the equation and confirmed by measurements, a black painted roof and a steel roof are very close in term of temperature.

This work is a collaboration between CEMHTI -UPR CNRS 3079 and CoActions-AltRD company whose research are funded by the European Better-B project (101081444-Better-B) in the frame of European Programme HORIZON-CL6-2022-BIODIV-02-two stage on resilient beekeeping (2023-2027).

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