Cooling frame on the hive roof

Notes and Tests Bumblebees PLUS

We tested the solution and are providing some notes on it

• If the frame has a large mass, some of the cooling block capacity will be used to cool it. Therefore, it is better to make the frame thin and insulate it well from the outside – the roof and the sides.
• Depending on the solution and the volume of “coolant”, the air and lining temperature can be reduced quite significantly, or even drastically, by 15C – 20C. This is already a large and sudden temperature change. Therefore, we recommend a smaller cooling volume, which does not allow such a temperature jump and will not overload the bumblebees.
• When testing the solution, in an extreme case, 15C was measured on the surface of the liner and 30C at the bottom.
• From a physics perspective, this solution has one disadvantage – during cooling, condensate forms on the ceiling of the hive (underside of the roof), which can then drip into the nest. If there's a lot of it, it can harm the comb. The moisture itself isn't harmful, provided the condensate doesn't flow into the nest.  
• Heat transfer from the hive space will increase if you place a wet cloth under the cooling block – there will be a significant increase in the contact area of the cooling medium with the roof; however, the cooling block will be „consumed“ a little faster.
• This solution does not address poorly made hives. If such a hive has poor insulation, it is heated by warm ambient air from several sides. However, this is a problem with the hive and not with this solution.
• On hot days, there's no point in letting the block heat up and then cooling it down rapidly. It's better to use a smaller number of blocks (12x max) before the temperature rises and replace the block during the day (if possible).
• Do not use this solution on days when the maximum temperature does not exceed 30-32°C. On such days, it is better to use gentler cooling with a damp cloth and its evaporation.
• The condition for using the thermometer has already been stated above.
• The placement of the thermometer is very important. There's no point in measuring the temperature in the lining, as it's different everywhere. Placing the thermometer (probe) in the air gap above the lining at least gives you some idea of the air temperature in the hive. When using a cooling frame, cool air flows onto the thermometer, and the measurement is not accurate. However, it gives you some idea of how things are in the hive.
  If you use the same type of thermometer in your armpits and place it in the same spot, you can compare the temperatures in your armpits. However, don't expect to measure exact values.
• Be interested in the accuracy of the thermometer used. The accuracy of cheap thermometers is generally poor, with a margin of error of a few degrees. Without calibration, thermometers will show different values at the same moment. However, they can be easily calibrated at home and you can account for this.

Conclusion

• Despite some disadvantages, dictated by the laws of physics, this solution will enable them to overcome critical temperatures on very hot days. Although this may represent a considerable temperature shock for bumblebees, it will allow them to survive critical moments.
• We therefore recommend using it only during the day when temperatures are expected to rise to 35C, and only during the day. 
• Once outdoor temperatures have dropped, it is advisable to remove condensation by ventilating the hive (using a larger extension or an absorbent cloth placed under the roof) and restore the humidity inside the hive to around 90% RH.